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Maximizing GSMT Science Return with Scientific Figures of Merit. Maximizing value. Who are the interested parties? Scientist users Funding agencies What constitutes value to them? Scientific return Cost What gives greatest value? MAXIMUM SCIENTIFIC RETURN FOR COST. Quantifying value.

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Maximizing GSMT Science Return

with

Scientific Figures of Merit


Maximizing value
Maximizing value

  • Who are the interested parties?

    • Scientist users

    • Funding agencies

  • What constitutes value to them?

    • Scientific return

    • Cost

  • What gives greatest value?

    MAXIMUM SCIENTIFIC RETURN FOR COST


Quantifying value
Quantifying value

Components of value

  • Performance

    • Requirements

    • Goals

  • Cost

    • Build

    • Operations

  • Schedule

    • First light

    • Operating life

R

I

S

K

$$$

Science


Science merit function
Science merit function

Science merit function =  ( Wi x FOMi )

  • Figure of Merit (FOM)

    • For each capability, embodied as instrument + telescope

    • Quantitative, with analytical and numerical components

    • Function of instrument and telescope properties

  • Weight (W)

    • Scientific judgment call



Example 2 celt ir ao system emissivity
Example 2: CELT IR AO system emissivity

  • Cryogenic AO system at prime focus

    • Ultimate performance for emissivity

    • Negative impacts on telescope design, enclosure cost

  • Cryogenic AO system at Nasmyth focus

    • Quantifiably almost as good

    • Expect lower total observatory cost

  • Warm AO system at Nasmyth focus

    • Dramatically reduced performance

    • Low cost, maintains spatial resolution advantage

    • Trades against space platform sensitivity advantage


  • What is the science mission
    What is the science mission?

    Type of mission impacts FOM, weights

    • Design reference mission

      • Total science program specified

    • Timely science mission

      • Maximize science achieved in initial period

    • Scientific capability mission

      • Instrument capabilities for wide range of potential science


    Example ukirt wfcam program
    Example: UKIRT WFCAM program

    • WFCAM: widefield 1-2 m camera on 3.8 m telescope

    • Several large scale surveys over ~10 years (DRM)

    • Quick shallow surveys first (STM)

    • Selected deep fields done repeatedly (STM + DRM)

    • Instrument permits installation of custom filters (SCM)

      http://www.ukidss.org


    Gsmt sample imaging capabilities
    GSMT sample imaging capabilities

    • Enhanced seeing widefield imager

      • Gaussian profile

      • Tens of arcmin FOV

    • Narrow field coronagraph

      • Highest possible Strehl and dynamic range

      • FOV is arcseconds

    • Moderate field, diffraction limited imaging

      • Moderate Strehl over arcminute FOV


    Imaging fom inputs telescope
    Imaging FOM inputs: telescope

    • D, primary mirror diameter

    • TPtel (  ), throughput

    •  ( , , t ),delivered image quality

    • S ( , , t ) , Strehl ratio

    •  (  ) , emissivity

    • Etel , operating efficiency


    Imaging fom inputs instrument
    Imaging FOM inputs: instrument

    • TPinstrl (  ), throughput

    • DQE(  ), detector quantum efficiency

    •  ,pixel sampling

    • , , wavelength coverage and resolution

    • R, D, read noise and dark current

    • Sc, scattered light susceptibility

    • Etel , system efficiency


    Imaging fom inputs multiplex advantages
    Imaging FOM inputs: multiplex advantages

    • , total solid angle field of view

    • n, number of simultaneous spectral channels


    Imaging fom inputs other science value factors
    Imaging FOM inputs: other science value factors

    • Timeliness

      • First light

      • Other facilities

      • Competition

    • Access

      • To facility

      • To data


    Enhanced native seeing imager
    Enhanced native seeing imager

    • Science

      • Distribution of high redshift galaxies

      • Integrated properties of galaxies

    • Programmatic

      • Use at wavelengths where diffraction limit can’t be achieved

      • Use in less favorable conditions, e.g. thin cirrus

    • Implications for FOM

      • Slightly extended sources with some central concentration

      • Wavelength coverage is   1 m


    Enhanced native seeing imager1
    Enhanced native seeing imager

    Background limited, uncrowded field case

    Neglect

    • Emissivity

    • Strehl ratio

    • Read noise, dark current

    • Scattered light

    • Programmatic terms

      Gather terms into a Figure of Merit for (integration time)-1


    Enhanced native seeing imager2
    Enhanced native seeing imager

    Background limited, uncrowded field FOM

    1/time  [ (D2/2) • TPtel () • Etel] •

    [ • DQE • TPtinstr() • Etinstr • f(/) • f(n) • f(, ) ]

    • Track telescope, instrument separately

    • Some factors require simulations to determine appropriate formulations

    • Some factors may include weighting functions

    • Telescope

    • Instrument


    Formulation of image quality
    Formulation of image quality

    Poor conditions

    1.0

    arcsec

    Good conditions

    0.5

    0

    10

    20

    , arcminutes

    Delivered image quality vs field angle and conditions


    Optimizing
    Optimizing /

    photometry

    Time 

    detection

    1

    2

    3

    4

    /

    /


    Weighting function for
    Weighting function for

    1

    weight

    0

    0

    20

    , arcminutes

    Tel, atmos rolloffs

    MCAO regime


    Enhanced native seeing imager trades
    Enhanced native seeing imager trades

    Some performance (and cost) trades:

    • D, 

    • , 

    • TPtel () (coatings)

    • n (instrument complexity)

    •  (optics complexity, coatings choices)


    Narrow field coronagraphic imager
    Narrow field coronagraphic imager

    • Science

      • Discovery and characterization of planetary systems

    • Programmatic

      • Diffraction limited, very high Strehl at first light

      • Use in best seeing conditions

    • Implications for FOM

      • Wavelength coverage is 1    5 m

      • Treatment of systematic effects important

      • Independent of telescope design, AO implementation details


    Coronagraphic imager fom additional inputs
    Coronagraphic imager FOM additional inputs

    • d, subaperture size of primary

    • n, number of actuators on deformable mirror

    • , residual wavefront rms error

    • , speckle lifetime (site characteristic)

    • g, gain, ratio of peak intensity to halo level

    • R, amplitude reduction of primary core and halo by coronagraph


    Coronagraphic imager fom
    Coronagraphic imager FOM

    Comparison with enhanced seeing imager:

    • Neglect traditional seeing measure 

    • Include Strehl ratio S, emissivity 

    • Use additional terms to describe AO, coronagraph impacts


    Coronagraphic imager sensitivity fom
    Coronagraphic imager sensitivity FOM

    FOM for sensitivity (SNR):

    sensitivity  [ D2• TP• E •  • DQE• -1 •f(/) • f(n) • f(, ) ]½

    • [ S / (1-S) ] • [ D / d ]2 • [ 1/R ]

    • Includes “traditional” components, Strehl and gain advantages

    • Not yet in right units!

    • How to account for systematic effects?


    Coronagraphic imager systematics
    Coronagraphic imager systematics

    SNR limited by speckle structure in uncorrected halo

    • Pointlike

    • 100% amplitude modulation

    • Persist for time 

      Variety of solutions

    • Decorrelation (large n, kHz AO update rate)

    • Simultaneous differential imaging (NICI)

    • PSF engineering, e.g. speckle sweeping

    • Data taking and reduction methods


    Coronagraphic imager final fom
    Coronagraphic imager final FOM

    • Characterize time – SNR relation by parameter 

    •  = 2 for photon noise limited system, less if residual systematic errors are significant

      1/time  ( previous expression ) 


    Narrow field coronagraphic imager trades
    Narrow field coronagraphic imager trades

    • Mirror segment size d

    • Speckle lifetime  (site characteristics)

    • Emissivity  and Strehl ratio S

    •  error budget allocations

    •  /  with 

    • Suppression of systematic error



    Maximizing value redux
    Maximizing value, redux

    Return to performance, cost, schedule, risk mix:

    Is there a similar approach to maximizing value?

    Performance-cost index

    PCI = Science merit function / total cost (capital + ops)

    How to do optimization?


    Maximizing value redux1
    Maximizing value, redux

    • Evaluate a few plausible approaches

      • Telescope type

      • Instruments

    • Trade studies for key parameters

      • Effect on SMF

      • Effect on cost

    • Creative tension between Scientist, Engineer, and Manager


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