# Presentation: 071714

## Dark Energy Survey                Survey Strategy

**James Annis**
**Experimental Astrophysics Group**
**Fermilab**

## Survey Strategy WBS 1.3

- Survey planning
- Science requirements and technical specifications
- Survey observing strategy
- Calibration
- Photometric calibration
- Astrometric calibration
- Photometric redshift calibration
- Survey data simulations
- Catalog level simulations
- Image level simulations
- Mock data challenge
- Mock analysis challenge
- Survey operations
*Defined as after commissioning*

- Dictionary

- DES Fermilab Director's Review

## Survey Planning (WBS 1.3.1)

- Science requirements and technical specifications
- Survey observing strategy

- DES Fermilab Director's Review

## Science Requirements (WBS 1.3.1)

- 10-sigma limiting magnitude
- g=24.6  500 sec
- r=24.1   500 sec
- i=24.0   900 sec
- z=23.6  1600 sec
- Calibration Accuarcy
- 10% single image
- 1% final coadd
- 2% spectrum convolution

- 5000 deg2 in the South Galactic cap
- overlap SPT
- redshift surveys
- Photometric redshifts
- To z=1.0 and 1⁄2 L* with δz <= 0.05
- all z <= 1 SPT clusters
- g,r,i,z
- PSF sufficient for weak lensing, FWHM <= 0.9”
- 40 deg2 supernova area
- Time domain, 1 hour every 2 days

- Science goals drive the science requirements,
- science requirements flow down to technical requirements.

- DES Technical Flowdown Document:
- 	v1: Dec 2003
- 	v3: May 2004

- DES Fermilab Director's Review

## Extinction Map, Centered SGP
Midnight on Nov 1 at CTIO
Black lines
Equatorial coords
Green lines
 Footprint
5000 sq-degrees total
In order of priority:
4000 sq-deg SPT
250 sq-deg SDSS stripe 82
Photo-z areas
700 sq-deg overhead
Alama, VLT, APEX, ACT

- Midnight on Nov 1 at CTIO
- Black lines
- Equatorial coords
- Green lines
-  Footprint
- 5000 sq-degrees total
- In order of priority:
- 4000 sq-deg SPT
- 250 sq-deg SDSS stripe 82
- Photo-z areas
- 700 sq-deg overhead
- Alama, VLT, APEX, ACT

- Science Requirements: Footprint

- DES Fermilab Director's Review

## Survey Strategy Design Goals

- Efficiently attain required depth
- Minimize photometric calibration errors
- Scientifically interesting data at natural points in the survey
- After year 1
- internal goal, we reserve the right to be affected by weather
- After year 3
- After end of survey

- DES Fermilab Director's Review

## Survey Strategy

- Decisions
- Area as function of time:
- Area more important than depth
- Entire survey area the first year
- Work during all phases of moon
- g,r during dark time
- i,z during bright time
- Moonlight has little effect

- Instrumental Factors
- Telescope slew time: 35 sec
- Instrument read time: < 20 sec
- Implies: 2 filters per position to minimize overhead
- Data Quality
- Airmass limit: <= 1.5
- Seeing limit: <= 1.1”

- DES Fermilab Director's Review

## Survey Strategies

- Baseline Strategy
- 2 filters per night
- 2 tilings of survey area per year, per filter
- 100 second exposures
- Calibration to 2% the first year
- 5 tilings is break point
- Calibration is ~1%
- g,r filters done
- i,z filters increase exposure time (years 4-5)
- Standard stars during night
- Alternate Strategy
- 1 tiling of survey are per year, per filter
- Divide total integration by 5 to find exposure time
- Calibration to <5% first year
- Standard stars during poor seeing nights

- We are exploring alternatives.

- DES Fermilab Director's Review

## Survey Strategy: Characteristic Magnitudes

- Note nonlinear behavior of limiting magnitude as function of time
- Knee at transition from       S/N  time to S/N ~ time
- Reach characteristic magnitude in O(100) seconds

- DES Fermilab Director's Review

## The Main Survey Strategy Table

- Catalog completeness

- Weak lensing depth maximal

- N=8 gal/sq-arcmin

- N=16 gal/sq-arcmin

- N=20 gal/sq-arcmin

- N=28 gal/sq-arcmin

- N=12 gal/sq-arcmin

- DES Fermilab Director's Review

## Survey Calibration (WBS 1.3.2)

- Photometric Calibration
- System response functions
- Relative calibration
- Absolute calibration
- Astrometric Calibration
- Photometric Redshift Calibration

- DES Fermilab Director's Review

## Large Area Survey Photometry 

- Unique properties of large surveys:
- Single stable instrument
- Huge homogeneous photometric data set
- System defined by 108 magnitudes of the survey
- Placing onto a standard system is unimportant
- Though transformations to standards is very useful.

- The aim of calibration in large surveys
- The magnitudes may be calculated by convolving a spectrum with good spectrophotometry with the system bandpasses, and
- The magnitudes vary only by 2.5log10(f1/f2), independent of position
- f1/f2  are the ratio of the photon fluxes
- The magnitudes have a well-defined absolute zeropoint.

- DES Fermilab Director's Review

## “The magnitudes may be calculated by convolving a spectrum with good spectrophotometry with the system bandpasses”

- Full system response measurement
- 1nm resolution
- Through all components of the instrument
- Focal plane array
- Filters
- Corrector
- Primary
- If without this, input beam has correct f/number
- Aimed at final system testing prior to ship

- DES Fermilab Director's Review

## “The magnitudes vary only by 2.5log10(), where are the ratio of the photon fluxes, independent of position”

- Relative photometry
- Use overlapping images of stars to place all images on same relative system.
- 1000’s of stars per overlap
- Precision very high, limited by systematics
- Overlapping tilings
- Allow reduction of systematics

- 1 tiling            3 tilings         3 more tilings

- DES Fermilab Director's Review

## Relative Photometry Simulation

- INSTRUMENT MODEL:
- A multiplicative flat field gradient of amplitude 3% from east to west
- A multiplicative flat field gradient of amplitude 3% from east to west
- An additive scattered light pattern with a amplitude from the optical axis, 3% at the edge of the camera
- An additive 3% rms scattered light per CCD
- Solution:
- Simutaneous least squares solution to the underlying relative photometry given the observations

- scaling bar is –0.20 mags to +0.20 mags

- DES Fermilab Director's Review

## “The magnitudes have a well-defined absolute zeropoint”

- Absolute photometry
- Transfer standard star magnitudes
- Need fainter standards (Tucker and Smith)
- Questions
- How many transfers to tilings?
- When are standards taken?
- What spatial pattern?

- Constant airmass tracks, std at end
- Standards on poor seeing night, on sparse hex grid

- DES Fermilab Director's Review

## Absolute Photometry Simulation

- INSTRUMENT MODEL:
- As before
- NIGHT MODEL:
- g band, 10% extinction
- Full photometry model of atmosphere
- Plus a linear gradient in k over night
- Induces RA gradients
- Constant airmass tracks, 4 standards night
- Assuming each standard calibrates track to 5%
- Solution:
- Simutaneous least squares solution to the underlying absolute photometry given the observations

- scaling bar is –0.20 mags to +0.20 mags

- DES Fermilab Director's Review

## Quality Assurance on Photometry

- Use principal axes of stellar locus to check colors
- Photometry calibrates mags, not colors
- sigma_o is 0.003 mags
- Check on CCD scales, and on smaller scales, looking for systematics

- DES Fermilab Director's Review

## Survey Simulations (WBS 1.3.3)

- Survey observation simulations
- Catalog level simulations
- Image level simulations

- Huan Lin will cover in detail in the next talk

- DES Fermilab Director's Review

## Mock Data Reduction Challenge (WBS 1.3.4)

- Task: reduce 1 year of imaging data
- Input: 1 Survey year of Image level simulations
- From Survey Simulation (WBS 1.3.3)
- Transfer to NCSA
- Run through Survey data pipelines
- Transfer to Fermilab
- Deliver to Mock Analysis Challenge (WBS 1.3.5)
- Results:
- Integration testing of pipelines
- Data throughput testing
- Plan:
- Staged: 1 night, 1 month, 1 year
- Aim at 1 year in starting in mid 2007

- DES Fermilab Director's Review

## Mock Data Analysis Challenge    (WBS 1.3.5)

- Task: analyze 1 year of data
- Input: 1 Survey year of pipeline processed simulations
- From Mock Data Reduction Challenge (WBS 1.3.4)
- Make available to Science Teams
- Coordinate science team efforts to
- Integrate science codes to catalogs
- Analyze 4 key project science goals
- Results:
- The season after the first year of observing will be spent on arguing the science, not developing science codes.
- Plan:
- Staged: start with catalog level simulations, then to MDRC data
- Aim at full test starting in 2008

- DES Fermilab Director's Review

## Survey Strategy WBS 1.3

- Year 1 (FY2005)
- Scientist: 1 FTE
- Year 2
- Scientist: 1 FTE
- CP: 0.5 FTE
- Year 3
- Scientist: 1 FTE
- CP: 1.5 FTE
- Year 4
- Scientist: 1 FTE
- CP: 1.0 FTE

- Year 1 (FY 2005)
- Year 2
- 10 TB
- Year 3
- 50 compute nodes
- 50 TB
- dCache front end
- 100 TB Enstore
- Year 4
- 100 compute nodes
- 100 TB
- dCache front end
- 300 TB Enstore

- Fermilab FTEs

- Fermilab Computing

- DES Fermilab Director's Review

## Summary

- Survey Planning
- Science requirements and technical specifications
- Survey observing strategy
- Calibration
- Photometric calibration
- Survey data simulations
- Catalog level simulations
- Image level simulations
- Mock data challenge
- Mock analysis challenge

- DES Fermilab Director's Review