Modification of the ocean PHILLS hyperspectral imager for the International Space Station and the HyGEIA program Michael R. Corson, Jeffrey H. Bowles, Wei Chen, Curtiss O. Davis, Kiera H. Gallelli, Daniel R. Korwan Naval Research Laboratory, Washington, DC Clinton E. Dorris Boeing NASA Systems, Houston, TX August 27, 2003

The HyGEIA Program HyGEIA: Hyperspectral sensor for Global Environmental Imaging and Analysis Program objectives: –Adapt the NRL ocean PHILLS (Portable Hyperspectral Imager for Low Light Spectroscopy) for flight in the International Space Station –Produce hyperspectral images of the Earth at 25 m and 130 m Ground Sample Distance (GSD) –Achieve 200 to 1 Signal-to-Noise Ratio for water and forest scenes –Produce data products of value to the Navy and commercial community –Provide a further link between airborne and space hyperspectral imaging HyGEIA 25 m GSD comparable to 20 m AVIRIS

The HyGEIA Team Naval Research Laboratory –PHILLS hyperspectral imager under development since 1994 –Development of environmental data products of interest to Navy –Development of algorithms to remove the effects of the atmosphere and water reflection, produce ocean product and do data compression Boeing Space Utilization –Knowledge of requirements, interfaces, and procedures for Shuttle or International Space Station flights, liaison with NASA –Test and Qualification of hardware for flight on Shuttle Station –Development and test of software to interface with Station –Liaison with NASA managers and technical personnel NASA –Space Shuttle for delivery of PHILLS system to Station –Space Shuttle for return of data and PHILLS system –Station personnel for installation, changing lenses, changing data storage hard drives, troubleshooting –Control and communications links

HyGEIA Products and Sponsors Hyperspectral products –Water clarity and optical properties –Phytoplankton chlorophyll –Colored dissolved organic matter (CDOM) –Suspended sediments –Bathymetry –Bottom type –On-shore vegetation classification –Terrain classification Sponsors: –Office of Naval Research –Space Test Program –Navy TENCAP a) Bottom type and b) bathymetry derived from an AVIRIS image of Tampa Bay, FL using automated processing of the hyperspectral data. Lee, Z., et al., J. Geophys. Research, 106(C6), 11, ,651, Navigation channel Seagrass Beds

Overview of PHILLS PHILLS is a pushbroom hyperspectral imager, optimized for environmental characterization of the coastal zone –Designed for aircraft operation –400 to 1000 nm spectral range –Designed for 200 to 1 Signal to Noise Ratio –Meter-class GSD from aircraft altitudes –1.2 nm (minimum) spectral bins Normally binned by 4 or 8 for 4.5 nm or 9 nm spectral bins –Offner spectrometer with very low smile and keystone distortion Less than 0.1% –Backside-illuminated Si CCD, 12 micron square pixels for high quantum efficiency in the blue wavelengths PHILLS imager next to 18” ruler Primary COTS components: C-mount video lens designed for 400 to 1000 nm (Schneider) HyperSpec TM spectrograph (American Holographic, now Agilent Technologies) 1024 x 1024 CCD camera (Pixelvision)

PHILLS Radiometric Calibration Example of PHILLS Radiometric Calibration using the calibration sphere. a) Linear fits to Ocean PHILLS radiometric calibration data for four selected wavelengths. b)Typical values of the radiometric calibration gain for the left (sample # 488, top curve) and right (sample # 517, bottom curve) side of the 1024 sample CCD. The spectral channels that correspond to the response curves shown in a) are marked with their legend labels. C. O. Davis, et al. (2002), Optics Express 10:4,

PHILLS data for Great Bay Region ( Run15seq03) The image is 1000 pixels wide and 1024 pixels long. The spatial resolution is 1.8 meters. The data was processed to R rs using laboratory calibration data, and the Tafkaa atmospheric correction. “X” marks the location of spectra shown below. X

Physical Configuration of the WORF The WORF enclosure Speed of sub-Station point ~ 7,250 m/s

Window Transmission The WORF window Assembly, 20” diameter, ~6” thick Destiny Module Window K. Scott, S. Biggar, D. Eppler, E. Zalewski, L. Brownlow, and K. Lulla, “International Space Station Destiny Module Window Optical Characterization” submitted to the 30 th International Symposium on Remote Sensing of the Environment, Honolulu, HI, November 2003.

Modeled Signal to Noise Ratio at 25 m GSD The pushbroom operation of the PHILLS imager transfers naturally to use on the Space Station Model using spectral radiance above the atmosphere from Modtran, 5% surface albedo, 45 deg solar elevation, rural 5 km aerosols –5% albedo represents water and forest scenes Assume nadir viewing, 380 km altitude, 180 mm focal length collecting lens operating at f/4, 10 nm spectral bins Modeled Signal to Noise Ratio is less than goal of 200 to 1 Required frame rate of 290 frames per second is beyond capability of camera

Ground Motion Compensation Required for 25 m GSD Imaging Ground Motion Compensation (GMC) reduces the apparent speed of the scene past the line of sight

Modeled Station PHILLS S/N at 130 m GSD Spectral radiance above the atmosphere from Modtran, 5% surface albedo, 45 deg solar elevation, rural 5 km aerosols Assume 380 km altitude, 35 mm focal length collecting lens operating at f/4, 10 nm spectral bins Modeled Signal to Noise Ratio for nadir viewing is less than goal of 200 to 1 Frame rate for nadir viewing of 56 frames per second is within capability of camera, but with significant spectral Smear Anticipate using available GMC

Gimbaled Tip/Tilt Mount in WORF Tip / tilt mount provides ground motion compensation and cross track pointing Incident Light Cone Destiny Module Window HyGIEA Computer Mounting Surface

Additional Modifications required for HyGEIA Adding a mechanical shutter, controlled by the HyGEIA computer, to acquire dark frames Building a power converter to power camera and gimbal mount from 28 vdc WORF supply Writing interface and control software to receive imaging scripts from ground, power up and power down HyGEIA hardware, receive time and attitude information from Station, send health and welfare information to Station, execute scripts, process and store data Typical imaging sequence –Power hardware on for warmup –Receive time from Station and set computer clock –Receive attitude from Station and compute pointing offsets –Initialize pointing and acquire dark frame –Image ground swath –Acquire dark frame –Write image data to hard disk –Process and compress image data using NRL Optical Real time Adaptive Spectral Identification System (ORASIS)

PHILLS Implementation on Station Block diagram of PHILLS in the WORF WORF PEHB (Payload Ethernet Hub / Bridge) POINTING SYSTEM WORF STRUCTURE PHILLS Sensor SHUTTER PHILLS POWER SUPPLY HOST COMPUTER WORF SSPCM (Solid-State Power Controller Module) WORF AAA (Avionics Air Assembly) Power Air Power H/W Encoder Data Data (TTL for shutter) MOUNTING ASSEMBLY H/W HyGEIA Provided ISS Provided H/W MOUNTING ASSEMBLY H/W Power WORF RIC (Rack Interface Controller)

Modeled Access of Ground Scenes Modeled number of accesses for 20 m GSD nadir, 20 m GSD with +/- 30 deg off axis pointing, and 100 m GSD with +/- 30 deg off axis pointing –Time period June 1, 2002 through August 31, 2002 Location100 m GSD nadir 20 m GSD nadir 20 m GSD deg Bermuda Camp Pendleton, CA Chesapeake Bay, MD English Channel Key West, FL11767 Lake Okeechobee, FL10462 Melbourne Harbor, Australia Monterrey Bay, CA Straits of Gibraltar, Spain19985 Tampa Bay, FL Note: access valid when any part of ground swath intersects any part of scene

Status and Conclusions PHILLS Hardware and Software modifications are under way Modeled performance meets the goal of 200 to 1 Signal to Noise Ratio from 400 to 700 nm for water and forest scenes –Substantial effort required to provide gimbal platform Cross track pointing required for localized ground scenes 25 m GSD hyperspectral data from space can be compared to 20 m AVIRIS data –Hope to provide additional link between airborne and space hyperspectral imagery