Modification of the ocean PHILLS hyperspectral imager

for the International Space Stationand 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. DorrisBoeing 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), 11,639-11,651, 2001.

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)

HyperSpecTM spectrograph (American Holographic, now Agilent Technologies)

1024 x 1024 CCD camera (Pixelvision)

PHILLS Radiometric Calibration

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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, 210--221.

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, 210--221.

PHILLS data for Great Bay Region (010731 Run15seq03)

• The image is 1000 pixels wide and 1024 pixels long. The spatial resolution is 1.8 meters.

• The data was processed to Rrs using laboratory

calibration data, and the Tafkaa atmospheric correction.

• “X” marks the location of spectra shown below.

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04 PHILLS-1

Ground Truth ASD

Physical Configuration of the WORF

The WORF enclosure

Speed of sub-Stationpoint ~ 7,250 m/s

• Window Transmission

The WORF windowAssembly, 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 30th 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 NoiseRatio is less than goalof 200 to 1

Required frame rateof 290 frames per secondis beyond capabilityof 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 NoiseRatio for nadir viewingis less than goalof 200 to 1

Frame rate for nadir viewingof 56 frames per secondis within capability of camera,but with significant spectralSmear

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 ModuleWindow

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 SensorSHUTTER

PHILLS POWER SUPPLY

HOSTCOMPUTER

WORF SSPCM(Solid-State PowerController Module)

WORF AAA(Avionics AirAssembly)

Power

Power

PowerPower

Air

Power

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Encoder Data

Data

Data

Data(TTL for shutter)

MOUNTINGASSEMBLY

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HyGEIA ProvidedISS Provided

H/WMOUNTING 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

Location 100 m GSDnadir

20 m GSDnadir

20 m GSD+- 30 deg

Bermuda 26 21 84

Camp Pendleton, CA 27 20 86

Chesapeake Bay, MD 22 27 106

English Channel 166 143 257

Key West, FL 11 7 67

Lake Okeechobee, FL 10 4 62

Melbourne Harbor, Australia 20 13 65

Monterrey Bay, CA 21 14 90

Straits of Gibraltar, Spain 19 9 85

Tampa Bay, FL 19 16 64Note: 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