1. Change Record
  2. Model Documentation
  3. DMS Use Cases
    1. Actors
    2. Science Data Calibration and Quality Assessment
      1. Science Data Quality Assessment Pipeline
        1. Assess Data Quality
        2. Assess Data Quality for Calibration Products
        3. Assess Data Quality for Nightly Processing at Archive
        4. Assess Data Quality for Data Release
        5. Assess Data Quality for Nightly Processing
      2. Science Data Quality Analyst Toolkit
        1. Analyze SDQA Metrics
        2. Correlate SDQA metric with other data
        3. Correlate SDQA metrics
        4. Display SDQA Metrics
      3. Science Pipeline Toolkit
        1. Science Pipeline Toolkit
        2. Configure Pipeline Execution
        3. Execute Pipeline
        4. Incorporate User Code into Pipeline
        5. Monitor Pipeline Execution
        6. Select Data to be Processed
        7. Select Data to be Stored
        8. Upload User Codes
      4. Calibration Processing
        1. Periodic Calibration Products Production
          1. Produce Calibration Data Products
          2. Acquire Raw Calibration Exposures
          3. Calculate System Bandpasses
          4. Calculate Telescope Bandpasses
          5. Construct Defect Map
          6. Produce Crosstalk Correction Matrix
          7. Produce Master Bias Exposure
          8. Produce Master Dark Exposure
          9. Produce Master Fringe Exposures
          10. Produce Master Pupil Ghost Exposure
          11. Produce Optical Ghost Catalog
          12. Produce Synthetic Flat Exposures
        2. Nightly Calibration Products
          1. Calculate Atmospheric Models from Calibration Telescope Spectra
          2. Prepare Nightly Flat Exposures
          3. Reduce Spectrum Exposure
    3. Common Image Processing
      1. Low-level Image Operations
      2. Raw Exposure Processing
        1. Calibrate Exposure
        2. Combine Raw Exposures
        3. Process Raw Exposures to Calibrated Exposure
        4. Remove Instrument Signature
        5. Assemble CCD
        6. Detect Sources
        7. Determine Aperture Correction
        8. Determine Photometric Zeropoint
        9. Determine PSF
        10. Determine Sky Background Model
        11. Determine WCS
        12. Remove Exposure Artifacts
        13. Sum Exposures
    4. Nightly Processing
      1. Prepare for Observing
      2. Process Nightly Observing Run
      3. Association
        1. Perform DIA Source Association
        2. Perform DIA Object Association
        3. Create Instance Catalog for Visit
        4. Associate with Instance Catalog
      4. Alert Generation and Distribution
        1. Generate and Distribute Alerts
        2. Generate Alerts
        3. Distribute to Subscribed Brokers
        4. Distribute to Subscribed Users
      5. DIA Source Detection and Characterization
        1. Detect and Characterize DIA Sources
        2. Estimate Detection Efficiency
        3. Subtract Calibrated Exposure from Template Exposure
        4. Detect DIA Sources in Difference Exposure
        5. Measure DIA Sources
        6. Measure Snap Difference Flux
        7. Identify DIA Sources caused by Artifacts
        8. Perform Difference Image Forced Photometry
        9. Perform Precovery Forced Photometry
      6. DIA Object Characterization
        1. Update DIA Object Properties
        2. Calculate DIA Object Flux Variability Metrics
        3. Fit DIA Object Position and Motion
      7. Moving Objects Processing
        1. Process Moving Objects
        2. Find Tracklets
        3. Link Tracklets into Tracks
        4. Fit Orbit
        5. Prune Moving Object Catalog
        6. Perform Precovery
        7. Recalculate Solar System Object Properties
    5. Data Release Processing
      1. Perform Global Self-Calibration
      2. Produce a Data Release
      3. Cross-match Previous Release AstroObject IDs
      4. Global Photometric Calibration
        1. Perform Global Photometric Calibration
      5. Global Astrometric Calibration
        1. Perform Global Astrometric Calibration
      6. Single Visit Processing
        1. Perform Single Visit Processing
        2. Measure Single Visit Sources
      7. PSF Estimation
        1. Perform Full Focal Plane PSF Estimation
      8. Difference Image Characterization
        1. Detect and Characterize DIA Objects
      9. Deep Detection
        1. Detect and Characterize AstroObjects
        2. Detect Sources on Coadds
      10. Image Coaddition
        1. Create Template Exposures
        2. Create Coadd Exposures
        3. Coadd Calibrated Exposures
        4. Create Deep Coadd Exposures
        5. Create Short Period Coadd Exposures
        6. Create Best Seeing Coadd Exposures
        7. Create PSF-matched Coadd Exposures
      11. Object Characterization
        1. Characterize AstroObject Flux Variability
        2. Create Sky Coverage Maps
        3. Measure AstroObjects
        4. Perform Deblending and Association
        5. Perform Forced Photometry

   LSST Data Management Applications UML Use Case and Activity Model LDM-134    8/18/2011

 

 

 

 

 

 

Large Synoptic Survey Telescope (LSST)

Data Management Applications UML Use Case Model

 

Mario Juric, Robyn Allsman, Jeff Kantor

LDM-134

Latest Revision: October 10, 2013


 

 
 
 
 

This LSST document has been approved as a Content-Controlled Document by the LSST DM Technical Control Team. If this document is changed or superseded, the new document will retain the Handle designation shown above. The control is on the most recent digital document with this Handle in the LSST digital archive and not printed versions. Additional information may be found in the LSST DM TCT minutes.

Change Record
 

Version
Date
Description
Owner name
1 1/28/2011 Update Document to reflect Model based on Data Challenge 3 J. Kantor
2 7/12/2011 Update Document to reflect Model based on Data Challenge 3B PT1 R. Allsman
3 8/18/2011 General updates R. Allsman
4 9/11/2013 Final Design updates (revision 1.125) R.Allsman
5
9/26/2013 Formatting updates and WBS inclusion R. Allsman
6
10/10/2013 Returned SDQA to the Apps model (revision 1.144); TCT approved R. Allsman
       
       
       
       
       
       
       
       

 
 
 
 
 
 

 

 

Table of Contents


 

Change Record i
DMS Use Cases 1
Actors
2
Science Data Calibration and Quality Assessment 4
Science Data Quality Assessment Pipeline 4
Assess Data Quality 6
Assess Data Quality for Calibration Products 7
Assess Data Quality for Nightly Processing at Archive 7
Assess Data Quality for Data Release 8
Assess Data Quality for Nightly Processing 8
Science Data Quality Analyst Toolkit 8
Analyze SDQA Metrics 9
Correlate SDQA metric with other data 9
Correlate SDQA metrics 10
Display SDQA Metrics 10
Science Pipeline Toolkit 10
Science Pipeline Toolkit 11
Configure Pipeline Execution 12
Execute Pipeline 12
Incorporate User Code into Pipeline 12
Monitor Pipeline Execution 13
Select Data to be Processed 13
Select Data to be Stored 13
Upload User Codes 13
Calibration Processing 13
Periodic Calibration Products Production 14
Produce Calibration Data Products 14
Acquire Raw Calibration Exposures 15
Calculate System Bandpasses 15
Calculate Telescope Bandpasses 16
Construct Defect Map 16
Produce Crosstalk Correction Matrix 16
Produce Master Bias Exposure 17
Produce Master Dark Exposure 17
Produce Master Fringe Exposures 18
Produce Master Pupil Ghost Exposure 18
Produce Optical Ghost Catalog 18
Produce Synthetic Flat Exposures 19
Determine Illumination Correction 20
Produce Master Flat-Spectrum Flat Exposures 20
Correct Monochromatic Flats 21
Create Master Flat-Spectrum Flat 21
Create Master Illumination Correction 21
Determine CCOB-derived Illumination Correction 21
Determine Optical Model-derived Illumination Correction 22
Determine Self-calibration Correction-Derived Illumination Correction 22
Determine Star Raster Photometry-derived Illumination Correction 22
Nightly Calibration Products 23
Calculate Atmospheric Models from Calibration Telescope Spectra 23
Prepare Nightly Flat Exposures 24
Reduce Spectrum Exposure 24
Common Image Processing 24
Low-level Image Operations 25
Raw Exposure Processing 25
Calibrate Exposure 26
Combine Raw Exposures 27
Process Raw Exposures to Calibrated Exposure 27
Remove Instrument Signature 27
Assemble CCD 28
Detect Sources 28
Determine Aperture Correction 28
Determine Photometric Zeropoint 29
Determine PSF 29
Determine Sky Background Model 29
Determine WCS 29
Remove Exposure Artifacts 30
Sum Exposures 30
Nightly Processing 31
Prepare for Observing 33
Process Nightly Observing Run 34
Association 35
Perform DIA Source Association 36
Perform DIA Object Association 36
Create Instance Catalog for Visit 36
Associate with Instance Catalog 37
Alert Generation and Distribution 37
Generate and Distribute Alerts 38
Generate Alerts 38
Distribute to Subscribed Brokers 39
Distribute to Subscribed Users 39
DIA Source Detection and Characterization 39
Detect and Characterize DIA Sources 40
Estimate Detection Efficiency 40
Subtract Calibrated Exposure from Template Exposure 41
Detect DIA Sources in Difference Exposure 41
Measure DIA Sources 42
Measure Snap Difference Flux 42
Identify DIA Sources caused by Artifacts 43
Perform Difference Image Forced Photometry 43
Perform Precovery Forced Photometry 43
DIA Object Characterization 44
Update DIA Object Properties 44
Calculate DIA Object Flux Variability Metrics 45
Fit DIA Object Position and Motion 45
Moving Objects Processing 45
Process Moving Objects 46
Find Tracklets 46
Link Tracklets into Tracks 47
Fit Orbit 47
Prune Moving Object Catalog 47
Perform Precovery 48
Recalculate Solar System Object Properties 48
Data Release Processing 49
Perform Global Self-Calibration 50
Produce a Data Release 51
Cross-match Previous Release AstroObject IDs 51
Global Photometric Calibration 51
Perform Global Photometric Calibration 51
Global Astrometric Calibration 52
Perform Global Astrometric Calibration 52
Single Visit Processing 52
Perform Single Visit Processing 53
Measure Single Visit Sources 53
PSF Estimation 54
Perform Full Focal Plane PSF Estimation 54
Difference Image Characterization 54
Detect and Characterize DIA Objects 55
Deep Detection 55
Detect and Characterize AstroObjects 56
Detect Sources on Coadds 57
Image Coaddition 57
Create Template Exposures 58
Create Coadd Exposures 58
Coadd Calibrated Exposures 59
Create Deep Coadd Exposures 59
Create Short Period Coadd Exposures 60
Create Best Seeing Coadd Exposures 60
Create PSF-matched Coadd Exposures 60
Object Characterization 61
Characterize AstroObject Flux Variability 61
Create Sky Coverage Maps 61
Measure AstroObjects 61
Perform Deblending and Association 62
Perform Forced Photometry 62
  
 

Back to top

Model Documentation


 
 

Section: Section1

Back to top

DMS Use Cases
WBS:: 02C
The DMS Use Case Model captures the conceptual definition and relationships of the DMS processing elements. It is semantically very close in level to the OSS and DMSR.
The Use Case Model is described in the form of Unified Modeling Language (UML) 2.0. There are two types of diagrams included:
Package diagrams - Show the overall grouping of model elements into topical areas or modeling packages.
Use Case Diagrams - Show the interactions between human users and external systems (actors) that interact with the DMS. Also show the main processes (use cases) that occur within the DMS during operation of the system in response to these interactions.
The elements on the diagrams are each further defined in structured text. This text describes how the processing creates, updates, uses, and/or destroys Domain Classes. In certain cases, a Use Case may "invoke" (perform in-line) another Use Case. Sequencing of the structured text allows branching from and rejoining to the basic path based on specific criteria.

Figure 1 : DMS Use Cases Packages
This diagram depicts the packages contained in the DMS Use Case Model.


Actors
WBS:: 02C
This package contains the DMS Actors, which are human users of the DMS and external systems with which the DMS interacts.

Figure 2 : Actors

Actor Description
Public Interface User This actor represents all users/systems that access LSST public interfaces
Public Resource Locator This is an external system that contains locations and/or access information to public astronomical resources, such as surveys, tools, and services.
Pipeline Creator This actor is any user that has the access necessary to create a new component or pipeline type or a new instance of an existing component or pipeline type and to cause that instance to be available for execution.
Pipeline Operator This actor is any user with access to cause pipelines to execute, to terminate, or to be stopped and started.
Science User This actor is any user who has access to LSST Data Products, Pipelines, or both.
Simulator This actor represents any source of simlulated LSST science data, including images, meta-data, catalog data, alerts, etc.
Telescope This is the main LSST Observatory Telescope.
Observatory Operations This actor has authority to permit LSST Data Products to be released external to the project.
Camera This actor represents the Camera subsystem of the LSST, including the Science Data Subsystem (SDS) which is the primary Camera interface to the DMS.
Catalog Creator This actor is any user that has the access necessary to create a new catalog type or a new instance of an existing catalog type and to cause that instance to be populated with data.
Alert Category Author This is a user that sets up LSST Alert Categories, allowing for later Subscriptions to these Categories
Auxiliary Telescope This is the auxiliary telescope used for calibration.
Data Management System Administrator This actor is any user that has the access necessary to invoke system administration operations (e.g. configure security, equipment, system parameters, etc.) in the LSST Data Management Control System.
LSST Operations This actor is any user that performs an operational role in the LSST Observatory, including operators and administrators.
Observatory Control System This actor represents the overall master control system that coordinates the operation of all LSST subsystems.
DMS User This actor is any user that can access the DMS in any manner. It is the most general class of user, and therefore the least privileged.
DMS-External System This is any system not part of the DMS with which the DMS has an interface.  
 


Science Data Calibration and Quality Assessment
WBS:: 02C.01.02
Science Data Calibration and Quality Assessment includes
  - Science Data Quality Assessment pipelines and toolkits for use by data analysts and scientists to assess the quality of the DMS-generated data;
  - Science Data Pipeline Toolkit; and
  - Calibration Products Pipeline.


Science Data Quality Assessment Pipeline
WBS:: 02C.01.02.01
Science Data Quality Assessment Pipeline implements the SDQA Pipeline capabilities.

Figure 3 : Science Data Quality Assessment Pipeline

Figure 4 : Assess Data Quality


Assess Data Quality
WBS: 02C.01.02.01
Assess Data Quality allows the user to choose the data type to be examined and assessed.

Scenario Steps Summary Rejoins at
Basic Path
1.  When ( user selects Calibration Products ):(see AltPath: User Selects Data Release)(see AltPath: User selects Nightly Processing at Base)(see AltPath: User selects Nightly Processing at Archive)
2.  invoke: Assess Calibration Products
3.   fin:
 
AltPath: User Selects Data Release
1.   invoke: Assess Data Quality for Calibration Products
Basic Path step:3
AltPath: User selects Nightly Processing at Archive
1.   invoke: Assess Data Quality for Nightly Processing at Archive
Basic Path step:3
AltPath: User selects Nightly Processing at Base
1.   invoke: Assess Data Quality for Nightly Processing at Base
Basic Path step:3  


Assess Data Quality for Calibration Products
WBS: 02C.01.02.01
Assess Data Quality for Calibration Products

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Assess Data Quality for Nightly Processing at Archive
WBS: 02C.01.02.01
Assess Data Quality for Nightly Processing at Archive - On completion of a pre-defined number of observing nights or on command by Observatory Operations, the DMS does a complete assessment of the overall state of the LSST Data Products and produces Data Product Quality Reports. This assessment looks at the SRD-required observatory and mission satisfaction metrics, such as fields visited in each filter, % of raw images within photometric/astrometric specifications, etc.

Scenario Steps Summary Rejoins at
Basic Path
1.  Do Analyze Image Quality:
2.  ....Quality of calibration steps (flatfield, debias, defringe, etc); Flag Outliers
3.  ....Analyse artifacts: cosmic rays; ccd traps, bad columns, etc; satellite trails; stray light; Flag Outliers
4.  ....Analyze telescope optical performance: psf shape over the field and associated wavefront params; Flag Outliers
5.  ....Determine atmospheric seeing parameters - including spatial correlation; Flag Outliers
6.  done
7.  Do Analyze Photometric Qualtiy using several methods:
8.  ....Lightcurve analysis
9.  ....CMD analysis
10.  ....Global consistency of standards; Flag Outliers
11.  done:
12.  Do Analyze Astrometric Quality:
13.  ....Analyze astrometric solutions in the image WCS; Flag outliers
14.  ....Analyze proper motion/parallax solutions in the object database; Flag outliers
15.  done:
16.  Do Analyze Orbit Quality:
17.  ....Analyze quality of fit of orbits to observations; Flag Outliers
18.  done:
19.  Do Analyze Object Properties' Quality:
20.  ....Shape; Flag Outliers
21.  ....Type classification; Flag Outliers
22.  ....Deblending; Flag Outliers
23.  ....Photo Z; Flag Outliers
24.  done:
25.   Analyze Outliers
   


Assess Data Quality for Data Release
WBS: 02C.01.02.01
Assess Data Quality for Data Release

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Assess Data Quality for Nightly Processing
WBS: 02C.01.02.01
Assess Data Quality for Nightly Processing

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Science Data Quality Analyst Toolkit
WBS:: 02C.01.02.02

Figure 5 : Science Data Quality Analysis


Analyze SDQA Metrics
WBS: 02C.01.02.02
Analyze SDQA Metrics - when provided with selection and output criteria, the system acquires and formats the data according to the users' output preference.
GIVEN:
Analyst is using web-base tool to perform these tasks

Scenario Steps Summary Rejoins at
Basic Path
1.  System displays the Task Selection Page.
2.  SDQA Analyst selects the "Analyze SDQA Metrics".
3.  When (SDQA Metrcis selections exists):(see AltPath: SDQA Metric not populated yet)
4.  System displays the SDQA Metric Set Up Page.
5.  SDQA Analyst selects the SDQA Metrics, Sky Region, Focal Plane Region, Time Range, and output format.
6.  System queries the SDQA Data Archive,
7.  System generates SDQA Results,
8.  System formats them for output, and displays them on the SDQA Results Page.
9.   fin:
 
AltPath: SDQA Metric not populated yet
1.   System generates partial SDQA Results and displays warning that not all SDQA Results are available.
Basic Path step:1  


Correlate SDQA metric with other data
WBS: 02C.01.02.02
Correlate SDQA metric with other data - e.g. seeing from ancillary telescope, voltages from facilities database, number of sources extracted for a given exposure from DM database, etc.
GIVEN:
Analyst is using web-base tool to perform these tasks

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Correlate SDQA metrics
WBS: 02C.01.02.02
Correlate SDQA Metrics - with each other: e.g. noise level with number of poor extractions.
GIVEN:
Analyst is using web-base tool to perform these tasks

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Display SDQA Metrics
WBS: 02C.01.02.02
Display SDQA Metrics - when provided with the constraints of the data-of-interest and graphics style.
GIVEN:
Analyst is using web-base tool to perform these tasks

Scenario Steps Summary Rejoins at
Basic Path
1.  Select metric of interest (e.g. DC3 SDQA metric) .
2.  Select region of focal plane (e.g. segment, CCD, raft, or full focal plane).
3.  Select time range (e.g. full night, one exposure, etc.).
4.  Select display type (histogram, xy plot, image).
5.   Display chosen metric in chosen style.
   


Science Pipeline Toolkit
WBS:: 02C.01.02.03
Science Pipeline Toolkit provides capabilities that permit users of the DMS to perform processing of LSST data with LSST open software and user-supplied codes, for Level 3 Data Product production.

Figure 6 : Science Pipeline Toolkit


Science Pipeline Toolkit
WBS: 02C.01.02.03
Science Pipeline Toolkit provides capabilities that permit users of the DMS to perform processing of LSST data with LSST open software and user-supplied codes, for Level 3 Data Product production.
Given:
Science Pipeline Toolkit is a controller providing the following capabilities:

Scenario Steps Summary Rejoins at
Basic Path
1.  When ( upload requested ):(see AltPath: User Code Incorporation Requested)(see AltPath: Data is selected to be Stored)(see AltPath: Pipeline is selected to be Executed)(see AltPath: Pipeline Execution is selected to be Monitored)(see AltPath: Pipeline Execution is selected to be Configured)(see AltPath: Data to be Processed is selected)
2.   upload user codes
 
AltPath: Data is selected to be Processed
1.   invoke: Select Data to be Processsed
 
AltPath: Data is selected to be Stored
1.   invoke: Select Data to be Stored
Basic Path step:1
AltPath: Data to be Processed is selected
1.   invoke: Select Data to be Processed
Basic Path step:1
AltPath: Pipeline Execution is selected to be Configured
1.   invoke: Configure Pipeline Execution
Basic Path step:1
AltPath: Pipeline Execution is selected to be Monitored
1.   invoke: Monitor Pipeline Execution
Basic Path step:1
AltPath: Pipeline is selected to be Executed
1.   invoke: Execute Pipeline
Basic Path step:1
AltPath: User Code Incorporation Requested
1.   invoke: incorporate User Code into Pipeline
Basic Path step:1  


Configure Pipeline Execution
WBS: 02C.01.02.03
Configure Pipeline Execution

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Execute Pipeline
WBS: 02C.01.02.03
Execute Pipeline

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Incorporate User Code into Pipeline
WBS: 02C.01.02.03
Incorporate User Code into Pipeline

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Monitor Pipeline Execution
WBS: 02C.01.02.03
Monitor Pipeline Execution

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Select Data to be Processed
WBS: 02C.01.02.03
Select Data to Process

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Select Data to be Stored
WBS: 02C.01.02.03
Select Data to be Stored

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Upload User Codes
WBS: 02C.01.02.03
Upload User Code

Scenario Steps Summary Rejoins at
Basic Path
1.   TBD
   


Calibration Processing
WBS:: 02C.01.02.04
Calibration Products Processing :
- generates the   Calibration Products used to remove the instrument signature from Raw Exposures;
- generates the Calibration Data based on Engineering and Facility Database and Auxiliary Telescope.


Periodic Calibration Products Production
WBS:: 02C.01.02.04

Figure 7 : Produce Calibration Data Products


Produce Calibration Data Products
WBS: 02C.01.02.04
Generate the Calibration Products used to remove the instrument signature from Raw Exposures and photometrically calibrate flux measurements.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Produce Crosstalk Correction Matrix
2.  Invoke: Acquire Raw Calibration Exposures
3.  Invoke: Produce Master Bias Exposure
4.  Invoke: Produce Master Dark Exposure
5.  Invoke: Produce Master Flat-Spectrum Flat Exposures
6.  Invoke: Construct Defect Map
7.  Invoke: Produce Master Fringe Exposures
8.  Invoke: Prepare Nightly Flat Exposures
9.  Invoke: Produce Optical Ghost Catalog
10.  Invoke: Calculate Atmospheric Models from Calibration Telescope Spectra
11.   Invoke: Calculate Telescope Bandpasses
   

Acquire Raw Calibration Exposures
WBS: 02C.01.02.04
Acquire Spectrum Exposures, Arc Exposures, Monochromatic Dome Flat Exposures, Broadband Flat Exposures, Dark Exposures, Bias Exposures, Pupil Ghost Exposures, Star Raster Scan Exposures, for calibration.

Scenario Steps Summary Rejoins at
Basic Path
2.  Acquire Raw Calibration Exposure(s) on the LSST Telescope
3.  Acquire the appropriate subset of Raw Calibration Exposure(s) on the Auxilliary Telescope
4.  Absolutely calibrate relative intensities of Monochromatic Dome Flat Exposure(s) using the NIST-calibrated photodiode
5.   Store all Raw Calibration Exposure(s) into the Calibration Database.
   

Calculate System Bandpasses
WBS: 02C.01.02.04
Given the Atmospheric Model and the Telescope Bandpass Model, calculate instantaneous system bandpass for a given CCD in a Visit

Scenario Steps Summary Rejoins at
Basic Path
1.  Evaluate the Atmospheric Model at CCD and Visit coordinates
2.  Evaluate Telescope Bandpass Model at environmental values of the Visit
3.   Multiply the so-obtained contributions to derive the System Bandpass.
   

Calculate Telescope Bandpasses
WBS: 02C.01.02.04
From the Monochromatic Dome Flat Exposures and photo-diode response at each wavelength, determine the transmission of the Telescope   and   Camera system for each Observing Filter for each wavelength   and its dependence on focal plane temperature and Observing Filter position.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Observing Filter:
2.  .....For each Wavelength:
3.  ..........Fit the model of Telescope Bandpass Model and its dependence on environment given the available data
4.  .....done:
5.   done:
   

Construct Defect Map
WBS: 02C.01.02.04
Using the available Calibration Exposures, construct a Defect Map

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Calibration Exposure:
2.  .....Assess the response of each Pixel and classify as valid or as one of Hot, Dead, Trap, or Bad Column Pixel(s) in Defect Map.
3.  done:
4.   Store the resultant Defect Map into the Calibration Database.
   

Produce Crosstalk Correction Matrix
WBS: 02C.01.02.04
The  Crosstalk Correction Matrix describes the coupling of a signal being read out in one of the Camera's Segments into the signal read out in other Segments. The structure of this Crosstalk Correction Matrix will not be known until the Camera integration is well advanced. Although the Crosstalk Correction Matrix could in principle couple each Segment to every other Segment, it is expected to be much sparser, coupling only Segments within the CCDs in the same Raft, and maybe neighboring CCDs in adjacent Rafts.
The initial Crosstalk Correction Matrix will be produced from CCOB (Camera Calibration Optical Bench) data prior to installation of the Camera on the Telescope. The Crosstalk Correction Matrix will be periodically updated as the survey proceeds using the same Star Raster Scan Exposures utilized to validate the Illumination correction.

Scenario Steps Summary Rejoins at
Basic Path
1.  When (Data is Detector data):(see AltPath: Data from Survey data or Star Raster Scan Exposures)
2.  For each Detector Segment:
3.  .....Until the signal-to-noise is sufficient to reach OSS cross-talk requirements:
4.  ..........Set up the CCOB to focus a spot on the Focal Plane Array
5.  ..........Read out the entire Focal Plane Array into a Raw Exposure.
6.  .....done:
7.  done:
8.  After all Detector Segment(s) have been illuminated with the spot, analyze the collected Raw Exposure(s). The Crosstalk Correction Matrix element (i, j) can be directly determined as the ratio of the flux measured in Segment j to the flux measured in Segment i, at the corresponding Pixel Coordinates.
9.   fin:
 
AltPath: Data from Survey data or Star Raster Scan Exposures
1.  Identify Pixel(s) affected by bright point Source(s), whose cross-talk affected counterparts contain nothing more than the background
2.  Compute the ratio of fluxes of those Pixel(s), per amp-amp pair
3.   Average the measurement over all data collected in a period of time shorter than the timescale of cross-talk changes on the Camera
Basic Path step:9  

Produce Master Bias Exposure
WBS: 02C.01.02.04
Create Master Bias Exposure from individual Bias Exposures

Scenario Steps Summary Rejoins at
Basic Path
1.  Combine the Bias Exposure(s) to form the Master Bias Exposure
2.   Store the Master Bias Exposure into the Calibration Database
   

Produce Master Dark Exposure
WBS: 02C.01.02.04
Create Master Dark Exposure from individual Dark Exposures

Scenario Steps Summary Rejoins at
Basic Path
1.  Combine the Dark Exposure(s) to form the Master Dark Exposure
2.   Store the Master Dark Exposure into the Calibration Database
   

Produce Master Fringe Exposures
WBS: 02C.01.02.04
For each Observing Filter, the Monochromatic Dome Flat Exposures will be used to construct the Master Fringe Exposure. The formula for combining the individual wavelengths will be based on the average atmospheric line emission spectrum.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Observing Filter:
2.  .....Combine the Monochromatic Dome Flat Exposure(s) to form the Master Fringe Exposure for this time interval
3.  .....Subtract the mean level from the Master Fringe Exposure to give a zero mean resultant
4.  .....Store the Master Fringe Exposure in the Calibration Database
5.   done:
   

Produce Master Pupil Ghost Exposure
WBS: 02C.01.02.04
Produce the  Master Pupil Ghost Exposure using the  Optical Model

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Observing Filter:
2.  .....Configure and run the Optical Model
3.  .....Convert Optical Model outputs to Master Pupil Ghost Exposure
4.  .....Store the Master Pupil Ghost Exposure into the Calibration Database
5.   done:
   

Produce Optical Ghost Catalog
WBS: 02C.01.02.04
Using the Optical Model, produce a catalog of Optical Ghosts so their position can be predicted for each Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Configure the Optical Model to calculate positions of Optical Ghost(s)
2.  Detect and characterize the properties and positions of Optical Ghost images
3.   Store the results to Optical Ghost Catalog
   

Produce Synthetic Flat Exposures
WBS:: 02C.01.02.04

Figure 8 : Produce Synthetic Flat Exposures

Figure 9 : Determine Illumination Correction


Determine Illumination Correction
WBS: 02C.01.02.04
Using CCOB Data, Optical Model,  Star Raster Scan Exposures, and self-calibration derived Photometric Model, determine the  Illumination Correction

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Produce Master Pupil Ghost Exposure
2.  Invoke: Determine CCOB-derived Illumination Correction
3.  Invoke: Determine Optical Model-derived Illumination Correction
4.  Invoke: Determine Star Raster Photometry-derived Illumination Correction
5.  Invoke: Determine Self-calibration Correction-Derived Illumination Correction
6.   Invoke: Create Master Illumination Correction
   

Produce Master Flat-Spectrum Flat Exposures
WBS: 02C.01.02.04
Combine Monochromatic Dome Flat Exposures to construct a Master Flat-Spectrum Flat Exposure that would have been generated by a uniformly illuminated flat spectrum dome screen.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Determine Illumination Correction
2.  Invoke: Correct Monochromatic Flats
3.   Invoke: Create Master Flat-Spectrum Flat
   

Correct Monochromatic Flats
WBS: 02C.01.02.04
Apply Illumination Correction to   Monochromatic Dome Flat Exposures

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Monochromatic Dome Flat Exposure:
2.  .....Multiply the Monochromatic Dome Flat Exposure by the Master Illumination Correction for that wavelength
3.   done:
   

Create Master Flat-Spectrum Flat
WBS: 02C.01.02.04
Combine illumination-corrected Monochromatic Dome Flat Exposures to create a Master Flat-Spectrum Flat Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.   Make a single Master Flat-Spectrum Flat Exposure via linear combination of corrected Monochromatic Dome Flat Exposure(s) (AKA Synthetic Flat Exposure)
   

Create Master Illumination Correction
WBS: 02C.01.02.04
Given variously determined Illumination Correction models, create a consensus Master Illumination Correction by appropriately averaging or otherwise combining the inputs.

Scenario Steps Summary Rejoins at
Basic Path
1.   Optimal combination will be determined in Commissioning, based on the quality of data
   

Determine CCOB-derived Illumination Correction
WBS: 02C.01.02.04
Determine the Illumination Correction by treating CCOB data   as an Exposure with a single point Source.

Scenario Steps Summary Rejoins at
Basic Path
1.  Create Raw Exposure(s) from CCOB Data
2.  For each Raw Exposure:
3.  .....Invoke: Remove Instrument Signature
4.  .....Subtract Sky Background Model from Calibrated Exposure
5.  .....Measure intensity of point Source(s) on Calibrated Exposure
6.  .....Combine intensity measurements into Illumination Correction
7.   done:
   

Determine Optical Model-derived Illumination Correction
WBS: 02C.01.02.04
Using the Optical Model of the telescope-camera system (e.g., FRED), simulate the illumination of the focal plane by a uniform planar source. Use the simulated image to derive the Illumination correction.

Scenario Steps Summary Rejoins at
Basic Path
1.  Configure the Optical Model to simulate a flat field
2.   Use resulting Image(s) to derive the Illumination Correction
   

Determine Self-calibration Correction-Derived Illumination Correction
WBS: 02C.01.02.04
The self calibration Photometric Model contains the degrees of freedom related to Illumination correction. Use these to derive Illumination correction.

Scenario Steps Summary Rejoins at
Basic Path
1.   Construct the Illumination Correction using Illumination correction related fitted parameters of the Photometric Model.
   

Determine Star Raster Photometry-derived Illumination Correction
WBS: 02C.01.02.04
Calculate the Illumination Correction by processing an imaged dense field of stars.

Scenario Steps Summary Rejoins at
Basic Path
1.  For all Star Raster Scan Exposure(s):
2.  .....Invoke: Remove Instrument Signature
3.  .....Subtract Sky Background Model from Calibrated Exposure
4.  .....Measure instrumental PSF Flux of point Source(s) on Calibrated Exposure
5.  .....Combine PSF Flux measurements into Illumination Correction
6.   done:
   


Nightly Calibration Products
WBS:: 02C.01.02.04

Figure 10 : Produce Atmospheric Models from Calibration Telescope Spectra


Calculate Atmospheric Models from Calibration Telescope Spectra
WBS: 02C.01.02.04
Given calibration data for the night ( Spectrum Exposures, Microwave Radiometer Measurements, GPS PWV Measurements, Barometric Pressure Measurements), calculate the Atmospheric Model for the given night.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Spectrum Exposure:
2.  .....Invoke: Reduce Spectrum Exposure
3.  done:
4.  Fit an Atmospheric Numerical Model to the derived Auxiliary Telescope Spectrum, Microwave Radiometer Measurement(s), GPS PWV Measurement(s), Barometric Pressure Measurement(s)
5.   Save the Atmospheric Numerical Model into the Calibration Database
   

Prepare Nightly Flat Exposures
WBS: 02C.01.02.04
Using the Master Broadband Flat Exposure acquired at the time the Monochromatic Dome Flat Exposures were acquired, and a Broadband Flat Exposure acquired just before the start of observing, prepare the Nightly Broadband Flat Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Acquire Broadband Flat Exposure
2.  Compute the corrections to Master Flat-Spectrum Flat Exposure
3.  Generate the Nightly Flat Exposure
4.   QA the difference in spectrum of acquired Broadband Flat Exposure(s) and the Master Broadband Flat Exposure using the Calibration Spectrometer outputs.
   

Reduce Spectrum Exposure
WBS: 02C.01.02.04
Reduce a Spectrum Exposure to a set of Auxiliary Telescope Spectra.

Scenario Steps Summary Rejoins at
Basic Path
1.  Retrieve Monochromatic Dome Flat Exposure(s), Bias Exposure(s), and Arc Exposure(s) for the Auxilliary Telescope from the Engineering and Facility Database
2.  For each Spectrum Exposure:
3.  .....Reduce the Spectrum Exposure to a flux- and wavelength-calibrated spectra using the associated Auxiliary Telescope Calibration Exposure(s)
4.   done:
   


Common Image Processing
WBS:: 02C.03.01
This package covers common operations that can be performed on an Image. These operations are invoked in many use cases and do not naturally belong in any specific package.
Also, this package covers low level operations whose invocations are not explicitly called out in the other use cases due to their low level nature.

Figure 11 : Common Image Processing


Low-level Image Operations
WBS: 02C.03.01
Low-level Image Operations
A use case grouping low-level image operations, such as addition/multiplication, convolution, warping, subsetting, resampling, etc.
(none)


Raw Exposure Processing
WBS:: 02C.03.01
Raw Image Processing removes the instrument signature from the incoming Raw Exposures; assembles amplifier  Raw into CCD  Raw Exposures; handles Cosmic Ray and Streak removal; handles image characterization, including determination of PSF and WCS; and detects the sources present on the Raw Exposure (but does not characterize them in any great detail)

Figure 12 : Process Raw Exposures to Calibrated Exposure


Calibrate Exposure
WBS: 02C.03.01
Photometrically and astrometrically calibrate the Trimmed Exposure. Produce a Calibrated Exposure with a per-CCD PSF, Sky Background Model, Astrometric Model (simple per-CCD WCS), and Photometric Model (simple per-CCD Photometric Zero Point).

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Determine Sky Background Model
2.  Invoke: Determine PSF
3.  Invoke: Detect Sources
4.  Invoke: Determine Aperture Correction
5.  Invoke: Determine WCS
6.  Invoke: Determine Photometric Zeropoint
7.   fin:
   


Combine Raw Exposures
WBS: 02C.03.01
Combines the Trimmed Exposures belonging to the same Visit into a single Trimmed Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Remove Exposure Artifacts
2.   Invoke: Sum Exposures
   


Process Raw Exposures to Calibrated Exposure
WBS: 02C.03.01
Creates a Calibrated Exposure from the  Raw Exposures in a Visit.
The output of this step is a single Calibrated Exposure with a PSF, Sky Background Model, Photometric Model (simple per-CCD  Photometric Zero Point), Astrometric Model (simple per-CCD WCS), and a list of detected Sources.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Remove Instrument Signature
2.  Invoke: Assemble CCD
3.  Invoke: Combine Raw Exposures
4.   Invoke: Calibrate Exposure
   


Remove Instrument Signature
WBS: 02C.03.01
Remove bias, dark frame, flat field, fringing, and compensate for defects that can be optimally addressed at this point. For example, we will deal with non-square pixels in Measure and Characterize AstroObjects rather than here.

Scenario Steps Summary Rejoins at
Basic Path
1.  Interpolate saturated and bad Pixel(s).
2.  Compute current Raw Exposure bias adjustments from Overscan Columns and remove (trim) them, creating a Trimmed Exposure.
3.  Subtract adjusted Master Bias Exposure
4.  Subtract the scaled Master Dark Exposure
5.  Apply flat field correction using Nightly Flat Exposure
6.  When ( Atmospheric Model available):(see AltPath: No Atmospheric Model, skip defringing)
7.  Remove fringing using Master Fringe Exposure and the Atmospheric Model
8.   fin:
 
AltPath: No Atmospheric Model, skip defringing
1.   noop:
Basic Path step:8  


Assemble CCD
WBS: 02C.03.01
Assemble per-amplifier Trimmed Exposures into a per-CCD Trimmed Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Load all per-amplifier Trimmed Exposure(s)
2.   Write them into a single per-CCD Trimmed Exposure
   


Detect Sources
WBS: 02C.03.01
This process identifies the Sources that are present in the Raw.
The process outputs a list of Sources and the Pixels occupied by those Sources (i.e., a detection Mask). The detected and measured Sources need not necessarily be persisted.

Scenario Steps Summary Rejoins at
Basic Path
1.  Subtract Sky Background Model
2.  Correlate the Raw Exposure with its PSF, producing a detection likelihood Mask Plane.
3.  Find all Pixels above the specified S/N threshold in the detection likelihood Mask Plane.
4.   Decompose those Pixel(s) into spatially isolated groups --Footprint(s)-- and find peaks within the Footprint(s). The positions of the peaks will represent the nominal locations of detected Source(s), until a better Centroid is determined by later measurement.
   


Determine Aperture Correction
WBS: 02C.03.01
Determine Aperture Correction factors for the Raw

Scenario Steps Summary Rejoins at
Basic Path
1.  Select bright, isolated, point Source(s)
2.   Estimate Aperture Correction
   


Determine Photometric Zeropoint
WBS: 02C.03.01
Determine initial Photometric Model of the Raw Exposure, by using the detected Sources to determine the Photometric Zero Point. This model may further be refined by later processing steps, for example by taking into account the Exposures from adjacent CCDs.

Scenario Steps Summary Rejoins at
Basic Path
1.  Detect bright point-like Source(s)
2.  Measure instrumental PSF Flux
3.  Match the detected Source(s) to AstroObject(s) in the Level 2 AstroObject Catalog. Until Level 2 coverage of the entire sky is in place, External Catalog(s) will be used as a reference.
4.   Fit the constant Photometric Zero Point minimizing the difference between recalibrated instrumental and cataloged fluxes
   


Determine PSF
WBS: 02C.03.01
Determine the shape and variation of the Point Spread Function ( PSF) on the Exposure based on a sampling of high signal-to-noise stars.

Scenario Steps Summary Rejoins at
Basic Path
1.  Subtract Sky Background Model from Raw Exposure
2.  Detect point-like Source(s) using an approximate PSF model
3.   Model the PSF given detected high-S/N Source(s)
   


Determine Sky Background Model
WBS: 02C.03.01
Determine the Sky Background Model for the Calibrated Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Subdivide the Raw Exposure into 128 by 128 pixel bins (or similar)
2.  For each bin:
3.  .....Estimate the sky level by computing a robust statistic (e.g., median) of observed Pixel values:
4.  done:
5.   Fit a function to the resulting grid, resulting in a Sky Background Model.
   


Determine WCS
WBS: 02C.03.01
Determine the World Coordinate System transformation ( WCS) from Image Plane Coordinates to Sky Coordinates, creating an initial Astrometric Model. This model may be refined in subsequent steps by simultaneously solving for more than a single CCD, as well as in global astrometric calibration.

Scenario Steps Summary Rejoins at
Basic Path
1.  Select isolated, point-like, Sources
2.  Positionally match selected Sources to Astrometric Standards in the Astrometric Reference Catalog
3.   Derive the WCS using the match
   


Remove Exposure Artifacts
WBS: 02C.03.01
Identify and remove Cosmic Rays, Streaks.
Remove artifacts that can be easily identified given more than one back-to-back Exposures of what is assumed to be the same astronomical scene. Differences such as Cosmic Rays and Streaks can be identified and removed based on their appearance on only one of the two pairs in a Visit.
When implementing this step, care must be taken not to remove fast-moving asteroids as well. On the extreme end (of motion), these will be similar to Streaks. A trail-recognition algorithm may involve measuring the length and orientation of streaks in two snaps, and retaining only those that fit the same line. This does not require exact knowledge of the PSF.

Scenario Steps Summary Rejoins at
Basic Path
1.  For back-to-back visit pairs (i.e. when Visit consists of two or more FPAExposure(s)):
2.  .....Subtract per-CCD Raw Exposure #1 from Raw Exposure #2 producing a Difference Exposure
3.  .....Detect DIA Source(s)s on Difference Exposure
4.  .....Characterize DIA Source(s) (assess which ones are likely to be Cosmic Rays and satellite Streaks, vs. legitimate fast-moving astronomical phenomena)
5.  .....Flag Pixel(s) affected by artifacts
6.   done:
   


Sum Exposures
WBS: 02C.03.01
Sum the pixels of the Trimmed Exposures belonging to the Visit, potentially performing sigma clipping and taking flags into account.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Pixel:
2.  .....Get all values and flags for a given Pixel
3.  .....Perform clipping or flag-based rejection
4.  .....Add
5.   done:
   


Nightly Processing
WBS:: 02C.03
This package contains use cases describing the process flow associated with processing Raw Exposures for the purpose of generating Transient Alerts and Calibration Products.

Figure 13 : Nightly Processing Use Case Packages
This diagram depicts the use case packages associated with transient alert and calibration products processing.

Figure 14 : Prepare for Observing

Figure 15 : Process Nightly Observing Run


Prepare for Observing
WBS: 02C.03
Prior to the observing night, a sequence of preparation steps have been performed.

Scenario Steps Summary Rejoins at
Basic Path
1.  All Field of View(s) that are possible targets for tonight are obtained from the scheduler in the Observatory Control System
2.  For each Field Of View:
3.  .....When (Template is in the Template Exposure cache):(see AltPath: Fetch Template Exposure from Science Data Archive)
4.  .....Identify and prepare (e.g., cache) the current Template Exposure
5.  done:
6.   Invoke: Prepare Nightly Flat Exposures
 
AltPath: Fetch Template Exposure from Science Data Archive
1.   Fetch Template Exposure from the Science Data Archive
Basic Path step:4  


Process Nightly Observing Run
WBS: 02C.03
Receives and processes Raw Exposures from the Camera. The processing is driven by the need to assess the Raw Exposure data quality, reduce the data, and generate Transient Alerts within specified latency times.
At the end of the night of observing (in daytime), conducts processing of Solar System Objects and the fit of Atmospheric Model for the previous night.

Scenario Steps Summary Rejoins at
Basic Path
1.  When (not Data Release Level 1 Processing):(see AltPath: Data Release Level 1 Processing)
2.  Wait for receipt of signal from Observatory Control System:
3.  Invoke: Prepare for Observing
4.  For each received Raw Exposure:
5.  .....Invoke: Process Raw Exposures to Calibrated Exposure
6.  done:
7.  For each Visit:
8.  .....Invoke: Detect and Characterize DIA Sources
9.  .....Invoke: Perform DIA Source Association
10.  .....Invoke: Perform Difference Image Forced Photometry
11.  .....Invoke: Perform Precovery Forced Photometry
12.  .....Invoke: Update DIA Object Properties
13.  .....Invoke: Process Moving Objects
14.  .....Invoke: Generate and Distribute Alerts
15.  .....Invoke: Assess Data Quality for Nightly Processing
16.  done:
17.   fin:
 
AltPath: Data Release Level 1 Processing
1.  Invoke: Prepare for Data Release Processing
2.  Invoke: Process Raw Exposures to Calibrated Exposure
3.  Invoke: Detect and Characterize DIA Sources
4.  Invoke: Perform Source Association
5.  Invoke: Process Moving Objects
6.   Assess Data Quality of Data Release
Basic Path step:17  


Association
WBS:: 02C.03.02
Association matches DIA Sources, Visit Sources, and known AstroObjects (including Moving Objects).
The associations aid classifying DIA Sources as Moving Object, Artifact, Variable Object, or Transient Object categories. This categorization is needed to avoid issuing a Transient Alert for a  DIA Source matching a known Moving Object, Variable Object, or Transient Object, or to avoid sending Variable Objects to Moving Object Processing.
NOTE: This capability is also used in the Data Release Processing.

Figure 16 : Perform DIA Source Association

Figure 17 : Perform DIA Object Association


Perform DIA Source Association
WBS: 02C.03.02
Associate  DIA Sources to DIA and Solar System Objects via spatial match

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Create Instance Catalog for Visit
2.   Invoke: Associate with Instance Catalog
   


Perform DIA Object Association
WBS: 02C.03.02
For each DIA Object, find nearby AstroObjects most likely to be physically associated with the DIA Object. To do so, search the  Level 2 Catalog is searched for one or more AstroObjects positionally close to the DIA Object, out to some maximum radius. The IDs of these AstroObjects are recorded in the DIA Object.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Create Instance Catalog for Visit
2.  Invoke: Associate with Instance Catalog
3.   Update DIA Object catalog with associated AstroObject ID information
   


Create Instance Catalog for Visit
WBS: 02C.03.02
Calculate expected positions at the time of observing of AstroObjects from input Catalog, creating an Instance Catalog.
In the context of Level 1 processing, the earliest this can occur is when we know the shutter open time of the second  Raw Exposure in the Visit.

Scenario Steps Summary Rejoins at
Basic Path
1.  Calculate positions of AstroObject(s) in the Solar System Object Catalog that are expected to be in Field of View for the current Visit, add to Instance Catalog.
2.  When ( Using DIA Object Catalog):(see AltPath: Use AstroObject Catalog instead of DIA Object Catalog)
3.  Calculate positions (taking parallaxes and proper motions into account) of AstroObject(s) in the DIA Object Catalog that are expected to be in the Field of View for the current Visit, add to Instance Catalog.
4.   fin:
 
AltPath: Use AstroObject Catalog instead of DIA Object Catalog
1.   Calculate positions (taking parallaxes and proper motions into account) of AstroObject(s)s in the AstroObject Catalog that are expected to be in the Field of View for the current Visit, add to Instance Catalog.
Basic Path step:4  


Associate with Instance Catalog
WBS: 02C.03.02
Find cross matches between  DIA Sources (or DIA Objects; see alternate course) from a Difference Exposure and the predicted positions of AstroObjects, stored in the Instance Catalog.

Scenario Steps Summary Rejoins at
Basic Path
1.  When (using DIA Source):(see AltPath: Select all DIA Objects with a property change)
2.  The detected DIA Source(s) from the current Visit are cross matched with the entries in the Instance Catalog. The matching algorithm will take into account uncertainties in both measured and predicted positions (enabling, for example, matching of predicted positions of moving objects with poorly known Orbit(s) that have a substantial error ellipse).
3.  The ID of the matching Instance Catalog AstroObject (which may be NULL) is recorded for each DIA Source.
4.   fin:
 
AltPath: Select all DIA Objects with a property change
1.  All DIA Object(s) whose properties were changed by the current Visit are cross matched with the entries in the Instance Catalog. The matching algorithm will take into account uncertainties in both measured and predicted positions.
2.   The IDs of N best matching Instance Catalog AstroObject (which may be NULL) are recorded for each DIA Object.
Basic Path step:4  


Alert Generation and Distribution
WBS:: 02C.03.03
Alert Processing occurs on a nightly basis and produces Transient Alerts.

Figure 18 : Generate and Distribute Alerts


Generate and Distribute Alerts
WBS: 02C.03.03
Distribute Alerts to all subscribed Transient Alert Brokers, including the LSST  Transient Alert Brokers.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each alert:
2.  .....Load Transient Alert
3.  .....Forward to all subscribed Transient Alert Broker(s)
4.   done:
   


Generate Alerts
WBS: 02C.03.03
For each observed DIA Source, generate a Transient Alert in a community-accepted data format (such as VOEvent).

Scenario Steps Summary Rejoins at
Basic Path
1.  For each DIA Source detected:
2.  .....Load the associated DIA Object.
3.  .....Generate a Transient Alert with all relevant data, including a Postage Stamp containing the DIA Source.
4.   done:
   


Distribute to Subscribed Brokers
WBS: 02C.03.03
Distribute Alerts to all subscribed Transient Alert Brokers.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Transient Alert:
2.  .....Forward to all subscribed Transient Alert Broker(s)
3.   done:
   


Distribute to Subscribed Users
WBS: 02C.03.03
Distribute Alerts to all end-users subscribed to LSST's Transient Alert Broker. LSST's Transient Alert Broker will allow the end-users to receive a filtered subset of the Alert stream, based on user-defined Rules.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each subscribed user, for each Transient Alert:
2.  .....Execute the user's filter on the Transient Alert
3.  .....If the rule has been satisfied, forward the Transient Alert
4.   done:
   


DIA Source Detection and Characterization
WBS:: 02C.03.04
This package contains use cases to produces Difference Exposures by subtracting Template Exposures from Calibrated Exposures. It also detects, classifies, and measures  DIA Sources on the resulting Difference Exposures.
It also includes performing forced photometry on Difference Exposures to form Forced DIA Sources.

Figure 19 : Detect and Characterize DIA Sources


Detect and Characterize DIA Sources
WBS: 02C.03.04
This captures the overall process of finding the DIA Sources by subtracting a Calibrated Exposure from a Template Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Subtract Calibrated Exposure from Template Exposure
2.  Invoke: Detect DIA Sources in Difference Exposure
3.  Invoke: Measure DIA Sources
4.  When (less than 3 Exposures):(see AltPath: If more than 2 Exposures in a Visit)
5.  Invoke: Measure Snap Difference Flux
6.   Invoke: Identify DIA Sources caused by Artifacts
 
AltPath: If more than 2 Exposures in a Visit
1.   noop:
Basic Path step:6  


Estimate Detection Efficiency
WBS: 02C.03.04
Based on Measurements of a grid of inserted artificial Sources, estimate and store the point source detection efficiency at any point in the image.
Implementation note: the insertion, detection, and measurements of artificial sources will likely come in earlier stages, be optimized.

Scenario Steps Summary Rejoins at
Basic Path
1.  Insert artificial Source(s) into Template Exposure and Calibrated Exposure
2.  Invoke: Subtract Calibrated Exposure from Template Exposure
3.  Invoke: Detect DIA Sources in Difference Exposure
4.  Invoke: Measure DIA Sources
5.  Select only inserted Source(s)
6.  Compare characterized to truth values
7.   Derive a Detection Efficiency Map
   


Subtract Calibrated Exposure from Template Exposure
WBS: 02C.03.04
Register, warp, and subtract the Template Exposure from the Calibrated Exposure. The output of this step is a Difference Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  When (not Pre-Convolution Method):(see AltPath: Pre-Convolution Method)
2.  Load Template Exposure taken at similar airmass and seeing.
3.  Register the Template Exposure to Calibrated Exposure, by determining the Coordinate Transform between the two. This step may use the information from adjacent CCDs in the Focal Plane Array to derive a more accurate astrometric solution and aid the registration.
4.  Warp the Template Exposure to Calibrated Exposure Image Plane Coordinate(s)
5.   Subtract the warped Template Exposure from the Calibrated Exposure
 
AltPath: Pre-Convolution Method
1.   Correlate Calibrated Exposure with its PSF
Basic Path step:5  


Detect DIA Sources in Difference Exposure
WBS: 02C.03.04
Detect DIA Sources that are present in Difference Exposure where the signal-to-noise-ratio (SNR) is greater than threshold SNR specified.

Scenario Steps Summary Rejoins at
Basic Path
1.  When (not Pre-Convolution Method):(see AltPath: Pre-Convolution Method)
2.  Correlate the Difference Exposure with its PSF, producing a detection likelihood Mask Plane.
3.  Find all Pixels above the specified S/N threshold in the detection likelihood Image.
4.   Decompose those Pixel(s) into spatially isolated groups, aka Footprint(s), and find peaks within the Footprint(s). The positions of the peaks (Pixel Coordinates) will be the locations of detected Sources.
 
AltPath: Pre-Convolution Method
1.   Using the Difference Exposure, produce a detection likelihood Image
Basic Path step:2  


Measure DIA Sources
WBS: 02C.03.04
Measure PSF Flux, position, and shape of each detected DIA Source.
/* Note: See DPDD DIASource Table for measurement details */

Scenario Steps Summary Rejoins at
Basic Path
1.  For each DIA Source:
2.  .....Measure Centroid
3.  .....Measure PSF flux on Difference Exposure
4.  .....Measure PSF flux on Calibrated Exposure
5.  .....Measure Adaptive Moments
6.  .....Measure Trailed Source Model parameters
7.  .....Measure Dipole Source Model parameters
8.   done:
   


Measure Snap Difference Flux
WBS: 02C.03.04
Provide a measurement to detect variability on very short time scales.
Create a Difference Exposure out of two Raw comprising a Visit. Measure the PSF Flux at the positions of all detected DIA Sources.

Scenario Steps Summary Rejoins at
Basic Path
1.  Produce temporary Calibrated Exposure(s) for the pair of Raw Exposure(s) comprising the Visit. Difference them by simple subtraction.
2.  For each DIA Source:
3.  .....Measure PSF Flux on the difference at the position of the DIA Source
4.   done:
   


Identify DIA Sources caused by Artifacts
WBS: 02C.03.04
Identify DIA Sources that are caused by artifacts, e.g. dipoles not due to AstroObjects with high proper motions, Optical Ghosts (if any), or crosstalk ghosts (if any).

Scenario Steps Summary Rejoins at
Basic Path
1.  Compute predicted positions of cross talk ghosts and Optical Ghost(s) (if any), or crosstalk ghosts (if any).
2.  Cross-correlate the position of detected DIA Source(s) with expected positions of ghost artifacts.
3.  Flag any matched DIA Source(s) as ghosts.
4.  Detect DIA Source(s) with a positive and negative peak within a footprint, and flag them as dipoles.
5.   Identify and unflag dipoles due to true proper motion
   


Perform Difference Image Forced Photometry
WBS: 02C.03.04
Performs forced photometry on a  Difference Exposure to create Forced DIA Sources.

Scenario Steps Summary Rejoins at
Basic Path
1.  Load a list of positions of DIA Object(s) overlapping the Difference Exposure
2.  Remove DIA Object(s) already associated with DIA Source(s)
3.  At the coordinate position of each remaining DIA Object:
4.  .....Measure PSF Flux
5.  .....Store a Forced DIA Source to Forced DIA Source Catalog
6.   done:
   


Perform Precovery Forced Photometry
WBS: 02C.03.04
For all newly discovered objects, perform precovery forced photometry on Difference Exposures from Visits taken over a specified period (e.g. 30 days).
This processing is likely to occur in daytime.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each newly discovered DIA Object:
2.  .....Find all available Difference Exposure(s) overlapping the position of this DIA Object and taken over a specified period
3.  .....For every Difference Exposure:
4.  ..........Measure PSF flux at that position
5.  .....done:
6.   done:
   


DIA Object Characterization
WBS:: 02C.03.04

Figure 20 : Update DIA Object Properties


Update DIA Object Properties
WBS: 02C.03.04
Based on associated DIA Sources and Forced DIA Sources, update all dependent DIA Object properties (e.g. flux, position, shape, and variability).

Scenario Steps Summary Rejoins at
Basic Path
1.  Load all associated DIA Source(s) and Forced DIA Source(s)
2.  Invoke: Calculate DIA Object Flux Variability Metrics
3.  Invoke: Fit DIA Object Position and Motion
4.  When (not Release Processing):(see AltPath: If Release Processing:)
5.  Invoke: Perform DIA Object Association
6.  Calculate remaining dependent DIA Object properties
7.   Update the DIA Object Catalog, without over-writing the old version of the DIA Object
 
AltPath: If Release Processing:
1.   noop:
Basic Path step:6  


Calculate DIA Object Flux Variability Metrics
WBS: 02C.03.04
Given all associated DIA Sources and Forced DIA Sources, compute the necessary Flux Variability Model metrics for the DIA Object. These metrics will include estimates of the period, low-order light curve moments, and other statistics of interest.

Scenario Steps Summary Rejoins at
Basic Path
1.  Load the Time Series of PSF Flux from DIA Source(s) and Forced DIA Source(s) measurements of fluxes
2.   Calculate and store the Flux Variability Model
   


Fit DIA Object Position and Motion
WBS: 02C.03.04
Given measured positions of all associated DIA Sources fit for position, parallax and motion of the DIA Object.

Scenario Steps Summary Rejoins at
Basic Path
1.  Load all measured DIA Source positions
2.   Calculate and store best fit values of position, parallax, and proper motion
   


Moving Objects Processing
WBS:: 02C.03.06
Moving Object Processing predicts locations of known Moving Objects expected to appear in Difference Exposures. During the daytime it generates the predicted Ephemerides for Moving Objects that are expected to appear in the Sky Regions to be observed that night.
NOTE: This capability is also used in Data Release Processing.

Figure 21 : Process Moving Objects


Process Moving Objects
WBS: 02C.03.06
Fit Orbits to candidate Transient Sources, to discover new Moving Objects.
Note that this step is likely to occur in daytime, asynchronously with the rest of alert processing.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Find Tracklets
2.  Invoke: Link Tracklets into Tracks
3.  Invoke: Fit Orbit
4.  Invoke: Prune Moving Object Catalog
5.  Invoke: Perform Precovery
6.   Invoke: Recalculate Solar System Object Properties
   


Find Tracklets
WBS: 02C.03.06
Link candidate Transient  Sources into Tracklets.

Scenario Steps Summary Rejoins at
Basic Path
1.  Find pairs of candidate Transient Source(s), that satisfy conditions to form a Tracklet. These will be imaged on pairs of Visit(s) taken within the time interval that permits the detection of Moving Solar System Object(s)s, and within some plausible radius given expected sky motions of Moving Solar System Object(s).
2.   Add formed Tracklets to list of candidate Tracklets.
   


Link Tracklets into Tracks
WBS: 02C.03.06
Link candidate Tracklets into Tracks.

Scenario Steps Summary Rejoins at
Basic Path
1.  Find sets of Tracklets in list of candidate Tracklets that satisfy conditions to form a Track.
2.   Prune old Tracklets from list of candidate Tracklets.
   


Fit Orbit
WBS: 02C.03.06
Find sets of Tracks that are compatible with being on the same Orbit.

Scenario Steps Summary Rejoins at
Basic Path
1.  Find sets of Tracks that are compatible with being on the same Orbit.
2.  Fit orbital parameters.
3.  When (the associated goodness of fit is achieved):(see AltPath: Associated Goodness of Fit is not acheived)
4.  Accept the Orbit
5.  Associate the Transient Sources that constitute the Tracks with a new Moving Object.
6.   fin:
 
AltPath: Associated Goodness of Fit is not acheived
1.   Return the Tracks into the pool.
Basic Path step:6  


Prune Moving Object Catalog
WBS: 02C.03.06
Find sets of Orbits that are likely to belong to the same Moving Object.
As we observe, it is likely we will discover Moving Objects whose orbital fits will be imprecise to positively associate their later appearances (e.g., a year later) of the Orbit. Such Sources will be linked to new Orbits, and result in two entries in the Solar System Object Catalog for the same physical Moving Object. This step will scan the Solar System Object Catalog for sets of Orbits so close in phase space that it's likely they belong to the same Moving Objects. For such sets, it will attempt to re-fit the observation with a single Orbit.

Scenario Steps Summary Rejoins at
Basic Path
1.  Find sets of Orbit(s) that are likely to belong to the same Moving Object.
2.  Re-fit orbital parameters
3.  When (the required Goodness of Fit is achieved):(see AltPath: Required Goodness of Fit is not achieved)
4.  Accept the new Orbit, remove the old Orbit(s), and update the DIA Source and Source associations with this Moving Object.
5.  DIA Object(s) orphaned by delinking are deleted from the Level 1 Catalog.
6.   fin:
 
AltPath: Required Goodness of Fit is not achieved
1.   noop:
Basic Path step:6  


Perform Precovery
WBS: 02C.03.06
Given new and updated entries in the Solar System Object Catalog, look for additional DIA Sources in the DIA Source Catalog that are compatible with belonging to these Orbits.
These are most likely to be DIA Sources imaged before the Orbit in question has been fitted or updated (therefore the name "pre-covery").

Scenario Steps Summary Rejoins at
Basic Path
1.  Given an Orbit, find the Visit(s) in whichthe Moving Object may have been observed.
2.  Predict the position of the Moving Object in those Visit(s).
3.  Positionally associate DIA Source(s) with predicted Moving Object positions.
4.   Re-fit and update the Orbit given newly pre-covered DIA Source(s).
   


Recalculate Solar System Object Properties
WBS: 02C.03.06
Based on associated DIA Sources, update all dependent Solar System Object properties (e.g. orbital elements, absolute magnitudes).

Scenario Steps Summary Rejoins at
Basic Path
1.  Get all associated DIA Source(s)s
2.  Calculate dependent Solar System Object properties.
3.   Update the Solar System Object Catalog, without over-writing the old version of the Solar System Object.
   


Data Release Processing
WBS:: 02C.04
This package contains use cases describing the process flow associated with producing deep Template Exposures, Coadded Exposures, and Catalogs, which form the annual Data Release.

Figure 22 : Data Release Processing Use Case Packages

Figure 23 : Perform Global Self-Calibration

Figure 24 : Produce a Data Release


Perform Global Self-Calibration
WBS: 02C.04
Perform global photometric and astrometric self-calibration, using all observed Sources as inputs. The results are improved Photometric Models and Astrometric Models, for each Visit.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Perform Global Photometric Calibration
2.   Invoke: Perform Global Astrometric Calibration
   


Produce a Data Release
WBS: 02C.04
Annually reprocess the data in Science Data Archive to produce new versions of Catalogs with deeper and better detections and full AstroObject characterizations.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Perform Single Visit Processing
2.  Invoke: Perform Full Focal Plane PSF Estimation
3.  Invoke: Detect and Characterize DIA Sources
4.  Invoke: Detect and Characterize AstroObjects
5.  Invoke: Perform DIA Object Association
6.   Invoke: Cross-match Previous Release AstroObject IDs
   


Cross-match Previous Release AstroObject IDs
WBS: 02C.04
Since AstroObject IDs are unique across Data Releases, the same (as determined by positional cross-matching) AstroObject will have different IDs in each Data Release. This step creates a cross-reference of all IDs for all AstroObjects across Data Releases, primarily based on positional coincidence (possibly based on shape and flux as well).

Scenario Steps Summary Rejoins at
Basic Path
1.  For each AstroObject in current Data Release:
2.  .....Find most likely AstroObject match in each of the previous Data Release(s)
3.  .....Record the match
4.   done:
   


Global Photometric Calibration
WBS:: 02C.04.01


Perform Global Photometric Calibration
WBS: 02C.04.01
Perform global relative self-calibration of the survey, by fitting a Photometric Model that minimizes the scatter of internally calibrated magnitudes of repeatedly observed Sources. For each Observing Filter, take calibrated PSF Fluxes for bright, non-variable stars and find best-fit values for each stellar flux, patch gray zeropoint, and possibly Illumination Correction terms. Use Standard Stars to tie the system to a flux standard.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each filter:
2.  .....For each observed flux:
3.  ..........Assign observed flux to the nearest 4 HEALpixels
4.  ..........In parallel, across HealPixels:
5.  ...............Run self calibration algorithm on each HEALpixel
6.  ...............Return best-fit patch Photometric Zero Point, Stellar fluxes, and Illumination Corrections in each HEALpixel
7.  ..........done parallel:
8.  ..........Use common patch Zeropoints to tie the HEALpix solutions together
9.  ..........Use final patch Zeropoints to calculate weighted average Stellar fluxes
10.  .....done:
11.   done:
   


Global Astrometric Calibration
WBS:: 02C.04.02


Perform Global Astrometric Calibration
WBS: 02C.04.02
Perform global astrometric calibration of the survey, by fitting an Astrometric Model that minimizes the scatter of calibrated positions of repeatedly observed Sources. Find the best-fit proper motions, parallaxes, and differential atmospheric refractions for objects

Scenario Steps Summary Rejoins at
Basic Path
1.  For each patch of sky:
2.  .....Fetch all objects that overlap with patch
3.  .....Solve plate solutions for each exposure by matching to a reference catalog (from either GAIA or a single LSST exposure)
4.  .....For each object:
5.  ..........Calculate parallax and diffraction vectors (Requires astrometry package, e.g. PAL, SLAlib, SOFA, etc.)
6.  ..........Find the best fit position, proper motion, parallax, and diffraction
7.  .....done:
8.  .....Iterate to improve plate solutions
9.   done:
   


Single Visit Processing
WBS:: 02C.04.03

Figure 25 : Perform Single Visit Processing


Perform Single Visit Processing
WBS: 02C.04.03
Process all Raw Exposures to Calibrated Exposures, detect and characterize Sources, and compute global Astrometric Model and Photometric Model for the entire survey.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Visit:
2.  .....Invoke: Process Raw Exposures to Calibrated Exposure
3.  .....Invoke: Measure Single Visit Sources
4.  done:
5.   Invoke: Perform Global Self-Calibration
   


Measure Single Visit Sources
WBS: 02C.04.03
Sources detected on  Calibrated Exposure are measured on all Visits. Their Measurements are stored in the Source Catalog.
The description of the Source table in DPDD lists all Measurements to be performed, per Source.

Scenario Steps Summary Rejoins at
Basic Path
1.  For every Source in detected Source(s):
2.  .....Measure Centroid
3.  .....Measure PSF Flux
4.  .....Measure Adaptive Moments
5.  .....Measure Aperture Flux
6.   done:
   


PSF Estimation
WBS:: 02C.04


Perform Full Focal Plane PSF Estimation
WBS: 02C.04
Estimate PSF shape and variation across the focal plane using wavefront sensor CCD data, Camera metrology data, and simultaneously fitting the PSF to all available bright Sources detected in the Visit.
Camera metrology data will come both from the CCOB and Global Astrometric Self-calibration process

Scenario Steps Summary Rejoins at
Basic Path
1.  Estimate Telescope and Camera contribution to PSF variation using wavefront sensing data combined with Camera metrology
2.  Estimate the atmospheric contribution to the PSF by modeling detected bright Source(s), taking into account the Telescope and Camera contribution
3.   Produce a model of PSF variation for the entire Visit
   


Difference Image Characterization
WBS:: 02C.04

Figure 26 : Detect and Characterize DIA Objects


Detect and Characterize DIA Objects
WBS: 02C.04
Re-do parts of Level 1 Alert Processing to recreate Difference Exposures, detect DIA Sources, and associate them into DIA Objects.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Create Template Exposures
2.  Invoke: Detect and Characterize DIA Sources
3.  Invoke: Perform DIA Source Association
4.  Invoke: Process Moving Objects
5.   Invoke: Update DIA Object Properties
   


Deep Detection
WBS:: 02C.04.05

Figure 27 : Detect and Characterize AstroObjects


Detect and Characterize AstroObjects
WBS: 02C.04.05
Given all Visits in the survey, generate a set of Coadded Exposures of the entire observed sky to detect all AstroObjects to full coadded survey depth and fully characterize each AstroObject. Characterization can be performed by simultaneous fits to all available multi-epoch data (e.g. using MultiFit-type algorithms).

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Create Coadd Exposures
2.  Invoke: Detect Sources on Coadds
3.  Invoke: Perform Deblending and Association
4.  Invoke: Measure AstroObjects
5.  Invoke: Perform Forced Photometry
6.   Invoke: Characterize AstroObject Flux Variability
   


Detect Sources on Coadds
WBS: 02C.04.05
Coadd Sources will be detected on all Coadded Exposures. The source detection algorithm will detect regions of connected pixels, known as footprints, above the nominal S/N threshold in the PSF-likelihood image of the Visit.
Each footprint may have one or more peaks, and the collection of these peaks (and their membership in the footprints) are the output of this processing.
NOTE: Coadd Sources are intermediate products needed by subsequent processing steps; we do not plan to permanently store them.

Scenario Steps Summary Rejoins at
Basic Path
1.  Create PSF-likelihood image by correlating the Coadded Exposure with the PSF
2.  Detect peaks in the PSF-likelihood image (these are Coadd Source(s))
3.   Coarsely characterize Coadd Source to enable subsequent deblending
   


Image Coaddition
WBS:: 02C.04.04
Image Coaddition handles the co-addition of Exposures to form deep Template Exposures.

Figure 28 : Create Template Exposures

Figure 29 : Create Deep Coadded Exposures


Create Template Exposures
WBS: 02C.04.04
Coadd Calibrated Exposures to create Template Exposures for image differencing. There will be a number of different Template Exposures, each optimized for Visits taken at a different airmass.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Patch on the sky:
2.  .....Select an Exposure Stack overlapping the Patch
3.  .....Keep only those Calibrated Exposure(s) that meet the current Template Exposure selection criteria (e.g., airmass, image quality)
4.  .....Invoke: Coadd Calibrated Exposures
5.   done:
   


Create Coadd Exposures
WBS: 02C.04.04
Deep, seeing optimized, and short-period per-band coadds are created in ugrizy bands, as well as deeper, multi-color, coadds. Variable sources (including Solar System objects, explosive transients, etc), will be rejected from the Coadds.

Scenario Steps Summary Rejoins at
Basic Path
1.  Invoke: Create Deep Coadd Exposures
2.  Invoke: Create Short Period Coadd Exposures
3.  Invoke: Create Best Seeing Coadd Exposures
4.   Invoke: Create PSF-matched Coadd Exposures
   


Coadd Calibrated Exposures
WBS: 02C.04.04
Given an Exposure Stack of Calibrated Exposures, coadd them to create a Coadded Exposure or Template Exposure
Coadds are created by warping and adding together a stack of Calibrated Exposures. Transient sources (including Solar System Objects, explosive transients, etc), will generally be rejected from the Coadds.
Created coadds' Mask will include Mask Planes indicating potential problems with the Pixels.

Scenario Steps Summary Rejoins at
Basic Path
1.  When (skipping per-Pixel non-linearity correction):(see AltPath: Perform per-Pixel non-linearity correction)
2.  Warp the Calibrated Exposure(s) creating Warped Exposure(s)
3.   Add Warped Exposure(s) to create Coadded Exposure
 
AltPath: Perform per-Pixel non-linearity correction
1.   Perform per-Pixel non-linearity correction
Basic Path step:2  


Create Deep Coadd Exposures
WBS: 02C.04.04
Deep Coadded Exposures are designed to maximize coadd depth. They are created by warping and adding together a set of Calibrated Exposures. Transient sources (including Solar System Objects, explosive transients, etc), will generally be rejected from these Coadded Exposures.
One Deep Coadded Exposure will be created for each of the ugrizy bands, plus a seventh, deeper, multi-color Coadded Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Select set of Calibrated Exposure(s)s optimized for a reasonable combination of depth (i.e., employ no PSF matching) and resolution (i.e., Calibrated Exposure(s)s with significantly degraded seeing may be omitted).
2.   Invoke: Coadd Calibrated Exposures
   


Create Short Period Coadd Exposures
WBS: 02C.04.04
Short Period  Coadded Exposures are designed to enable detection of long-term variable or moving objects that would be “washed out” (or rejected) in full-depth Coadded Exposures. They are created by warping and adding together a set of Calibrated Exposures. Variable Sources (including Solar System Objects, explosive transients, etc), will generally be rejected from the Short Period  Coadded Exposures.
One Short Period  Coadded Exposure will be created for each of the ugrizy bands, plus a seventh, deeper, multi-color  Coadded Exposure.

Scenario Steps Summary Rejoins at
Basic Path
1.  Select set of Calibrated Exposure(s) spanning a period of time shorter than the elapsed survey time, optimized to enable detection of long-term variable or moving objects.
2.   Invoke: Coadd Calibrated Exposures
   


Create Best Seeing Coadd Exposures
WBS: 02C.04.04
Best Seeing  Coadded Exposures are designed to produce the highest possible resolution, thereby assisting the deblending process. They are created by warping and adding together a set of Calibrated Exposures. Transient sources (including Solar System Objects, explosive transients, etc), will generally be rejected from the Best Seeing  Coadded Exposures.
One Best Seeing  Coadded Exposure will be created for each of the ugrizy bands.

Scenario Steps Summary Rejoins at
Basic Path
1.  Select set of Calibrated Exposure(s) optimized for resolution (i.e., Calibrated Exposure(s) with degraded seeing may be omitted).
2.   Invoke: Coadd Calibrated Exposures
   


Create PSF-matched Coadd Exposures
WBS: 02C.04.04
PSF-matched  Coadded Exposures will be used to measure colors and shapes of objects at “standard” seeing. They are created by warping and adding together a set of PSF-matched Calibrated Exposures. Variable AstroObjects (including Solar System Objects, explosive transients, etc), will generally be rejected from the PSF-matched  Coadded Exposures.
One PSF-matched  Coadded Exposure will be created for each of the ugrizy bands.

Scenario Steps Summary Rejoins at
Basic Path
1.  Select set of Calibrated Exposure(s)s optimized for a reasonable combination of depth and resolution (i.e., Calibrated Exposure(s) with significantly degraded seeing may be omitted).
2.  PSF match the selected Calibrated Exposure(s)
3.   Invoke: Coadd Calibrated Exposures
   


Object Characterization
WBS:: 02C.04.06


Characterize AstroObject Flux Variability
WBS: 02C.04.06
Characterized periodic and non-periodic variability metrics of all AstroObjects.
Given all associated Forced Sources, compute the necessary Flux Variability Model metrics for the AstroObject. These metrics will include estimates of the period, low-order light curve moments, and other statistics of interest.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each AstroObject:
2.  .....Load the Time Series of associated PSF Flux(es) from the Forced Source Catalog
3.  .....Calculate the Flux Variability Model
4.  .....Store the Flux Variability Model metrics into the AstroObject Catalog
5.   done:
   


Create Sky Coverage Maps
WBS: 02C.04.06
Based on the Mask plane in Deep Coadded Exposures, and characterized AstroObjects, construct a map of the detection limit at each point on the sky covered by the survey.

Scenario Steps Summary Rejoins at
Basic Path
1.  Use Deep Coadded Exposure(s)' Mask Plane and Variance Image(s) in the co-adds to generate initial Sky Coverage Map
2.  Insert, detect, and measure artificial Source(s)s at a sample of positions in the sky to refine detection efficiency estimates.
3.  Construct a final Sky Coverage Map
4.   Store the Sky Coverage Map in the Science Data Archive so that it can be served in a community-accepted format (e.g., Mangle)
   


Measure AstroObjects
WBS: 02C.04.06
Perform a set of predefined Measurements on each of the identified AstroObjects, taking all available multi-epoch data into account.
Perform Measurements requiring model fits using MultiFit-type algorithms. Rather than coadding a set of Exposures and performing the Measurement on the coadd, MultiFit simultaneously fits PSF-convolved models to Postage Stamps of the AstroObject's multiple observations.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each AstroObject:
2.  .....Measure Centroid
3.  .....Fit Point Source Model (using Multifit)
4.  .....Fit Extended Source Model (using MultiFit)
5.  .....Measure Standard Color(s)
6.  .....Measure Adaptive Moments
7.  .....Measure Surface Brightness Profile (aperture, Petrosian, Kron)
8.  .....Compute derived values (extendedness, photo-z, etc.)
9.  done:
10.   Populate the AstroObject Catalog with the measurements
   


Perform Deblending and Association
WBS: 02C.04.06
Synthesize a list of unique AstroObjects. In doing so consider the Sources, Coadd Sources, DIA Sources, DIA Objects and Solar System Objects detected on Difference Exposures, and potentially AstroObjects from External Catalogs.

Scenario Steps Summary Rejoins at
Basic Path
1.  Identify sets of nearby Coadd Source(s)
2.  Create hypothesis on number and properties of AstroObject(s) consistent with the observed set of Coadd Source(s). Iterate until satisfactory solution is found
3.  For each AstroObject:
4.  .....Create and store a Deblend Template
5.   done:
   


Perform Forced Photometry
WBS: 02C.04.06
Performs forced photometry on a  Calibrated Exposure to create Forced Sources.
PSF Flux will be measured on every Visit, with the position, motion, shape, and the deblending parameters kept fixed. This process will result in the data necessary to characterize the Light-Curve for each AstroObject in the survey. The measured PSF Fluxes will be stored in the Forced Source Catalog.
Due to space constraints, only the PSF Flux will be measured.

Scenario Steps Summary Rejoins at
Basic Path
1.  For each Visit:
2.  .....Load a list of positions of AstroObject(s) overlapping the Calibrated Exposure
3.  .....For each AstroObject position:
4.  ..........Calculate Centroid at time of exposure
5.  ..........Measure PSF Flux at the predicted position, taking the deblend template into account
6.  .....done:
7.   done:
   

End
 
 
 

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The contents of this document are subject to configuration control by the LSST DM Technical Control Team.
 
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