the portable remote imaging spectrometer (prism) coastal
TRANSCRIPT
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The Portable Remote Imaging Spectrometer (PRISM) Coastal Ocean Sensor
P. Mouroulis, B. Van Gorp, R. O. Green, M. Eastwood, D. W. Wilson, B. Richardson, Heidi Dierssen*
Jet Propulsion Laboratory California InsLtute of Technology
*University of ConnecLcut
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The PRISM Team
Pantazis (Zakos) Mouroulis: PI, op'cs Byron Van Gorp: System engineer & mechanics Robert O. Green: Calibra'on, radia've transfer Daniel Wilson: Diffrac'on gra'ng
Heidi Dierssen (UConn): Science lead Bo-‐Cai Gao (NRL): Atmospheric correc'on algorithm Joe Boardman (AIG): Orthorec'fica'on, geoloca'on
K. Balasubramanian, David Cohen, Michael Eastwood, Brian Franklin, Linley Kroll, ScoX Leland, Frank Loya, Alan Mazer, Ian McCubbin, Doug Moore, ScoX Nolte, OXo Polanco, David Randall, Brandon Richardson, Jose Rodriguez, Chuck Sarture, Eugenio Urquiza, Rudy Vargas, Victor White, Karl Yee
Instrument team
Science team
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spectrometer
vacuum enclosure baseplate
telescope
2-‐channel SWIR radiometer
PRISM schema3c
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Spectral Range 350-‐1050 nm Sampling 2.85 nm ResoluLon (FWHM) 3.5 nm CalibraLon uncertainty < 0.1nm
SpaLal Field of view 31.7o Instantaneous FOV sampling 0.882 mrad IFOV resoluLon (FWHM) 0.97 mrad Cross-‐track spaLal pixels 608 Ground resoluLon 0.35 – 20 m
Radiometric Range 0 to max. beach R Sampling 14 bit Stability >99% CalibraLon uncertainty <2% SNR 2000 @450 nm* PolarizaLon variaLon: < 1%
Uniformity Spectral cross-‐track uniformity >95% Spectral IFOV mixing uniformity >95%
* At AVIRIS equivalent integraLon Lme and spectral sampling
Spectrometer parameters
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Parameter Channel 1 Channel 2
Channel center (nm) 1242 1608
Bandwidth FWHM (nm) 22 56
FOV (mrad, FWHM) 2.4 2.4
Boresight knowledge (mrad, relaLve to spectr.)
0.05 0.05
Radiometric stability 99% 99%
SNR @ 1.2mW/cm2 sr 325 390
SWIR channel parameters
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Performance metric System parameter Enabling technology
SNR Throughput (F/No=1.8)
Dyson spectrometer and two-‐mirror telescope design
Dynamic range Readout rate (176 Hz) Teledyne HyViSI detector and JPL readout electronics
PolarizaLon insensiLvity Angles of incidence, graLng response
OpLcal design, graLng groove design, coaLngs
Uniformity OpLcal prescripLon Dyson design, concave graLng, lithographic slit
Stray light suppression OpLcal surfaces, slit, graLng CoaLng and filter design, black Si slit, low scaXer graLng
CalibraLon stability OperaLng temperature (~22o C), vibraLon response
Optomechanical design, detector mount, athermalizaLon
PRISM integrates new technologies and design techniques to achieve performance
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PRISM spectral characteris3cs: spectral response func3ons
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SRF of Spectral pixels 57↔17, with Field pixels 321↔321 averaged. w/ λ = 345↔455 (nm). Filename: "srf 0p0deg 345to455nm 52mm"
350-‐450 nm
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SRF of Spectral pixels 162↔124, with Field pixels 321↔321 averaged. w/ λ = 645↔755 (nm). Filename: "srf 0p0deg 645to755nm 52mm"
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SRF of Spectral pixels 268↔228, with Field pixels 321↔321 averaged. w/ λ = 945↔1055 (nm). Filename: "srf 0p0deg 945to1055nm 52mm"
650-‐750 nm
950-‐1050 nm
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Spectrum of Er-‐doped spectralon panel received through PRISM (blue curve) and through reference ASD spectrometer (red curve).
Test spectrum extrac3on
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ScaXer plot of spectral channel centroids as a funcLon of spaLal locaLon for three isolated wavelengths (Hg lamp 437 nm and 547 nm, and laser at 639 nm).
Spectral uniformity
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PolarizaLon variaLon throughout the spectral range for five posiLons spanning the field of view. VariaLon = (Imax– Imin)/(Imax+ Imin)*100
Polariza3on characteris3cs
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Along-‐track spaLal response funcLons (without flight moLon blur) for all field posiLons.
Example along-‐track spaLal response funcLons (without flight moLon blur) for four wavelengths spanning the PRISM spectral range at a single field posiLon.
FWHM =~1.1 pixel
Spa3al characteris3cs: Along-‐track response
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Example cross-‐track spaLal response funcLons for four wavelengths spanning the PRISM spectral range at a single field posiLon. FWHM resoluLon =~1.05 pixel
Spa3al characteris3cs: Cross-‐track response
SpaLal/spectral IFOV mixing
Combined CRF non-‐uniformity with wavelength (containing both geometric “keystone” and FWHM variaLon) is <5% of a pixel
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Predicted in-‐flight PRISM SNR incorporaLng measured data from known radiance of NIST-‐traceable lamp illuminated spectralon panel.
IntegraLng sphere for spectral and radiometric field calibraLon
Predicted flight SNR based on lab calibra3on
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Image of several laser lines covering the enLre field of view. (image taken at room temperature, small residual imperfecLons disappear at operaLng temperature)
Stray light assessment
Order-‐sorLng filter seam locaLon
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CRF of Field pixels 322↔322, with 0 Spectral pixels averaged.Centered @ λ's=/949/751/629/451nm Filename: "arf 7mm scan 0p1mmpsec"
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CRF of Field pixels 321↔323, with 0 Spectral pixels averaged.Centered @ λ's=/949/751/629/451nm Filename: "crf 7mm scan 0p1mmpsec"
Boresight alignment of SWIR radiometer (blue) and spectrometer (red)
Cross-‐track, spectrometer channels 321-‐323 Along-‐track, without moLon blur
SWIR geometry and spa3al characteris3cs
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SWIR spectral bands measured at instrument level
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Aircras mounLng plate
VibraLon isolators
INS/GPS unit Connector plate
Detector electronics
Heater strips
22”
SENSOR HEAD AND AIRCRAFT MOUNTING PLATE
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Operator rack Control rack
Internal thermal control
Housekeepingdata logging
External heater PS
External heater control
Data recorder
Computer
Keyboard & monitor
ShuXer control
ELECTRONICS
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TEST FLIGHT SCHEDULE
CalibraLon/engineering flight May 2012: • Ivanpah Playa (spaLal properLes, radiometry high-‐R targets) • Lake Tahoe (low R water target)
First test/science flight July 2012: • Monterey Bay/Elkhorn Slough: seagrass coastal habitat
From les to right, Ivanpah Playa calibraLon site marked with tarps, dark Lle targets, portable solar radiometers.
Lake Tahoe buoy
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Slit curvature projected on ground (corrected in post-‐processing)
y = -‐0.0035x2 -‐ 0.0074x + 0.0009 R² = 1
-‐1
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-‐20 -‐15 -‐10 -‐5 0 5 10 15 20
Agrees well with theoreLcal predicLon of 0.82o
First recLfied PRISM image of JPL/Arroyo Seco area
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21
PRISM non-‐recLfied image from Ivanpah with blue tarp spectrum
Apparent radiance Reflectance aser radiometric correcLon and atmospheric removal
Retrieved spectrum is remarkably smooth at a single integraLon and without any applied spectral smoothing. Features above 900 nm are temporarily aXributed to database inaccuracies in water vapor line parameters. Improved atmospheric correcLon algorithm will aXempt beXer miLgaLon of these effects.
Preliminary atmospheric removal algorithm and radiometric calibraLon show good results (Bo-‐Cai Gao, R. Green)
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PRISM raw image from Lake Tahoe shows apparent elongaLon due to along-‐track oversampling.
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PRISM Tahoe Radiance before and after orthorectification
PRISM along track oversampling increases SNR
RGB image of Dollar Point (650, 550, 450 nm). Every spectrum is tagged with latitude, longitude, and elevation.
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Radiance spectra from Lake Tahoe (R. Green)
Data processing and algorithm refinement con3nuing.
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CalibraLon/validaLon PRISM to MODTRAN from Ivanpah data (against measured ground reflectance and atmospheric parameters)
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Conclusions • PRISM has demonstrated unique properLes and outstanding performance in terms of signal to noise raLo, response uniformity, accurate radiometry, and recovery of high quality spectra.
• PRISM is available to serve the needs of the coastal ocean science community.
This work has been performed at the Jet Propulsion Laboratory, California InsLtute of Technology, under a contract with the NaLonal AeronauLcs and Space AdministraLon. Funding has been provided by NASA’s Earth Science and Technology Office, and the Airborne Science and Ocean Biology and Biogeochemistry programs.