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Maximizing GSMT Science Return with Scientific Figures of Merit

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

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  1. Maximizing GSMT Science Return with Scientific Figures of Merit

  2. 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

  3. Quantifying value Components of value • Performance • Requirements • Goals • Cost • Build • Operations • Schedule • First light • Operating life R I S K $$$ Science

  4. 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

  5. Example 1. GSMT spectroscopic capability

  6. 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

  7. 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

  8. 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

  9. 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

  10. Imaging FOM inputs: telescope • D, primary mirror diameter • TPtel (  ), throughput •  ( , , t ),delivered image quality • S ( , , t ) , Strehl ratio •  (  ) , emissivity • Etel , operating efficiency

  11. 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

  12. Imaging FOM inputs: multiplex advantages • , total solid angle field of view • n, number of simultaneous spectral channels

  13. Imaging FOM inputs: other science value factors • Timeliness • First light • Other facilities • Competition • Access • To facility • To data

  14. 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

  15. 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

  16. 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

  17. 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

  18. Optimizing / photometry Time  detection 1 2 3 4 / /

  19. Weighting function for  1 weight 0 0 20 , arcminutes Tel, atmos rolloffs MCAO regime

  20. Enhanced native seeing imager trades Some performance (and cost) trades: • D,  • ,  • TPtel () (coatings) • n (instrument complexity) •  (optics complexity, coatings choices)

  21. 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

  22. 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

  23. 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

  24. 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?

  25. 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

  26. 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 ) 

  27. 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

  28. Wide field – narrow field comparisons

  29. 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?

  30. 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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