Corson, Michael R.

Davis, Curtiss O.

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Volume 92 number 1910 mAY 2011pAges 161–168EOS, TranSacTiOnS, amErican GEOphySical UniOnUnderstanding and quantifying the natu-ral processes that occur along coasts are critical components of managing environ-mental resources and planning and execut-ing coastal operations, from humanitarian relief to military actions. However, the coastal ocean is complicated, with dissolved and suspended matter that hinders water trans-parency, phytoplankton blooms that can be toxic, and bathymetry and bottom types that vary over spatial scales of tens of meters, all of which affect processes in an area that spans millions of square kilometers. A hyperspectral imager collects the spec-trum of the light received from each pixel in an image. For environmental characteriza-tion the wavelength range typically spans the visible and shortwave infrared wave-lengths, and the spectrum is collected in contiguous spectral intervals 1–10 nano-meters wide. This spectral information is exploited to provide significantly more infor-mation about vegetation, minerals, and other components in the scene than can be retrieved from panchromatic or even mul-tispectral imagery, which rely primarily on the shape of the object for detection [Goetz et al., 1985]. Such technology can also work over shallow seas. Over the past 2 decades, experiments with hyperspectral imagers on airborne platforms have demonstrated the ability to characterize the coastal environ-ment [Davis et al., 2002, 2006] and produce maps of coastal bathymetry, in-water constit-uents, and bottom type. The Hyperspectral Imager for the Coastal Ocean (HICO™), now operating on the International Space Station (ISS), extends this capability to the diversity of coastal environments worldwide. HICO was built and, along with the previously developed Remote Atmospheric and Ionospheric Detec-tion System ( RAIDS), was integrated into the HICO-RAIDS Experiment Payload ( HREP) module in 24 months, at a small fraction of the cost of a traditional space instrument. The data now being received are provid-ing an exciting new view of coastal environ-ments around the world.The HICO InstrumentData from HICO are beginning to flow to the Earth- observing community. HICO (Fig-ure 1a), designed and built by the Remote Sensing Division of the U.S. Naval Research Laboratory, is the first hyperspectral imager specifically made for environmental charac-terization of the coastal ocean from space. HICO images one scene per 90- minute orbit, with each scene spanning an area approxi-mately 42 kilometers wide and 190 kilome-ters long, large enough to capture the scale of coastal ocean dynamics. Each pixel is a 95- meter square, with 88 spectral channels covering the range from 400 to 900 nano-meters. This includes visible light (400–700 nanometers), which penetrates the water and provides information on water proper-ties and bottom reflectance, and shortwave infrared radiation (700–900 nano meters), which is used to correct for atmospheric aerosols and surface reflectance.The development and construction of HICO were sponsored by the U.S. Office of Naval Research (ONR) under its Innova-tive Naval Prototype (INP) program. A key goal of the INP program is to demonstrate methods to save costs and time in devel-oping instruments for space. HICO accom-plished these savings by using commercial components where available, including the spectrometer, a control and data storage computer, the camera, and a rotation mech-anism to point the imaging line of sight. Because of low levels of ionizing radiation in the space environment at ISS, the latter three Eos, Vol. 92, No. 19, 10 May 2011A New View of Coastal Oceans From the Space StationPAGES 161–162Fig. 1. (a) The Hyperspectral Imager for the Coastal Ocean (HICO™) fully assembled and ready for integration into the HICO and Remote Atmospheric and Ionospheric Detection System (RAIDS) Experimental Payload (HREP) module launched to the International Space Station. (b) Early HICO image of Hong Kong, taken on 2 October 2009. (c and d) Nearly coincident Moderate Resolution Imaging Spectroradiometer (MODIS) and HICO data products from images collected near the Yangtze River, China, 18 January 2010. Figure 1c is a MODIS image (taken at 0500 UT) of chlorophyll a concentration (milligrams per cubic meter). The white areas indicate no retrieval due to saturation of one or more channels of the MODIS sensor. The outlined area indicates the location of the HICO image relative to the MODIS image. Figure 1d is a HICO image (taken at 0440 UT) of chlorophyll a concentration (milligrams per cubic meter) from HICO data using a standard chlorophyll algorithm. Note that HICO does not saturate and provides data at much higher resolution over the entire scene. (e) Spectral radiances measured by HICO and MODIS at the location of the cross in Figure 1d. HICO captures a full spectrum over its wave-length range compared to the specific channels of MODIS.Eos, Vol. 92, No. 19, 10 May 2011commercial electronic components could be used without radiation shielding beyond that provided by the experiment structure, with only mechanical reinforcement of the circuit boards. Even with the compressed schedule, HICO underwent characterization and calibration [Lucke et al., 2011] as well as full vibrational and thermal vacuum testing, providing a model for taking an experiment rapidly from the laboratory to space. Although HICO was built on a tight sched-ule and with a limited budget, it was built to meet a specific set of performance require-ments. The primary HICO performance parameters were vetted by 2 decades of air-borne hyperspectral imagery [Corson et al., 2008]. In particular, HICO has a high signal-to-noise ratio when imaging dark coastal ocean scenes (greater than 200:1 over visible wave-lengths). Further, it has low polarization sensi-tivity and spatial resolution sufficient to dem-onstrate the retrieval of coastal environmen-tal products from space. Observation CapabilitiesHICO was launched on 10 September 2009 and installed on ISS on 17 Septem-ber. It began collecting imagery 8 days later (Figure 1b). To save costs, HICO does not have an onboard calibrator. Periodic con-firmation of the wavelength sampled by each HICO spectral channel is performed in orbit by imaging a bright scene such as clouds and comparing the spectral features in the HICO image with known solar spec-tral lines. Radiometric calibration, used to quantitatively convert the digital data from the camera to the brightness of the scene, is performed in orbit through well- characterized land sites and comparisons with NASA’s spaceborne Moderate Resolu-tion Imaging Spectroradiometer (MODIS; http:// modis .gsfc .nasa .gov/) data. HICO is designed for the coastal ocean and has several advantages for that environ-ment (Figures 1c–1e) compared to MODIS, which is optimized for imaging the vast open ocean. HICO has sufficient spatial resolution to image the complexity of coastal features. Fur-ther, it can image over a wide range of scene brightnesses, allowing it to image the dark, open ocean as well as bright features such as river plumes. The additional spectral channels (88 on HICO as compared to nine on MODIS for ocean imaging) can be used to differenti-ate sediments, colored dissolved organic mat-ter, phytoplankton, and other components in the coastal ocean [e.g., Lee et al., 2007].Future DirectionsHICO has been operating since 25 Sep-tember 2009 and has collected more than 2500 images of coastal sites worldwide. Work continues on processing and validat-ing products from this unique data set to further scientific understanding of coastal environments. HICO data are a pathfinder for future sen-sors. A similar imager with space-qualified components on a small satellite in a low-Earth Sun-synchronous orbit would collect far more data, be more responsive to unfold-ing natural events such as pollution plumes or severe coastal weather, and meet many specific naval and civilian needs. NASA has identified a need for a similar sensor in geo-synchronous orbit, called the Geostationary Coastal and Air Pollution Events (GEO-CAPE) instrument [Committee on Earth Science and Applications From Space, 2007] to provide fre-quent sampling of the coastal ocean. GEO-CAPE would provide hourly sampling of U.S. coastal waters with approximately 300- meter pixels and produce hyperspectral image data. HICO data can be used to simulate those data or data for other potential coastal ocean sensors to help establish science and perfor-mance requirements and optimize the design of those instruments.AcknowledgmentsHICO was developed under funding from the ONR INP program. HICO was integrated, launched, and flown with support from and under the direction of the U.S. Department of Defense Space Test Program. The Japan Aerospace Exploration Agency (JAXA) pro-vided transportation to ISS on an HII-B Transfer Vehicle, and NASA and JAXA have provided support for operations on ISS. We thank the entire HICO team for their dedi-cated work in building and making HICO a successful demonstration of the power of hyperspectral imagery for the characteriza-tion of coastal environments worldwide.ReferencesCommittee on Earth Science and Applications From Space (2007), Earth Science and Applica-tions From Space: National Imperatives for the Next Decade and Beyond, Natl. Acad. Press, Washington, D. C. (Available at http:// www .nap .edu/ catalog/ 11820.html.) Corson, M. R., D. R. Korwan, R. L. Lucke, W. A. Snyder, and C. O. Davis (2008), The Hyperspec-tral Imager for the Coastal Ocean (HICO) on the International Space Station, IEEE Proceedings of the International Geoscience and Remote Sensing Symposium, 978-1-4244 -2808-3/08.Davis, C. O., J. Bowles, R. A. Leathers, D. Korwan, T. V. Downes, W. A. Snyder, W. J. Rhea, W. Chen, J. Fisher, W. P. Bissett, and R. A. Reisse (2002), Ocean PHILLS hyperspectral imager: Design, characterization, and calibration, Opt. Express, 10(4), 210–221.Davis, C. O., K. L. Carder, B.-C. Gao, Z.-P. Lee, and W. P. Bissett (2006), The development of imaging spectrometry of the coastal ocean, in 2006 IEEE International Geoscience and Remote Sensing Sym-posium, vol. 4, pp. 1982–1985, IEEE Press, New York.Goetz, A. F. H., G. Vane, J. E. Solomon, and B. N. Rock (1985), Imaging spectrometry for Earth remote sensing, Science, 228(4704), 1147−1153, doi:10.1126/ science .228 .4704 .1147.Lee, Z.-P., B. Casey, R. Arnone, A. Weidemann, R. Parsons, M. J. Montes, B.-C. Gao, W. Goode, C. O. Davis, and J. Dye (2007), Water and bottom properties of a coastal environment derived from Hyperion data measured from the EO-1 space-craft platform, J. Appl. Remote Sens., 1, 011502, doi:10.1117/ 1.2822610.Lucke, R. L., M. Corson, N. R. McGlothlin, S. D. Butcher, D. L. Wood, D. R. Korwan, R. R. Li, W. A. Snyder, C. O. Davis, and D. T. Chen (2011), The Hyperspectral Imager for the Coastal Ocean: Instrument description and first images, Appl. Opt., 50(11), 1501–1516, doi:10.1364/ AO .50 .001501.—Michael R. coRson, Remote Sensing Division, Naval Research Laboratory, Washington, D. C.; E-mail: corson@ nrl .navy .mil; and cuRtiss o. Davis, College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis

A New View of Coastal Oceans From the Space Station

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A New View of Coastal Oceans From the Space Station

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