During 1997-1998 NASA's Ames Research Center performed a remote sensing demonstration project in the Chesapeake Bay in collaboration with the Chesapeake Bay Program (CBP). The CBP was formed in 1983 as a cooperative effort between the U.S. Environmental Protection Agency and various state and local governments of the Bay watershed. Primary mission is restoration of living resources, including fish, shellfish, Bay grasses, and other aquatic wildlife of the nation's largest and one of the world's most productive estuaries. The CBP routinely conducts an ongoing ship-based Monitoring Program to collect in situ measurements of physical, chemical and biological indicators of the Bay's health. The CBP is evaluating the use of remote sensing as an adjunct to the Monitoring Program, with the idea that highly accurate point measurements may used in conjunction with appropriately processed imagery to generate a spatially contiguous dataset of the water quality variable(s) of interest. As an example, previous work by the University of Maryland has extensively explored the use of airborne multispectral remote sensing as a tool for generating chlorophyll concentration maps of the Bay.

NASA's Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) was flown over a study area in the southern mainstem of the Bay on 17-Aug-97 and 03 July-98. The data were atmospherically corrected to reflectance using public-domain ATREM code from the University of Colorado, and georegistered with land tiepoints matched to USGS 7.5 minute mapsheets. Previously published equations were applied to the imagery to derive estimates of chlorophyll, suspended sediment concentrations and Secchi disk transparency. Image values are compared with a limited set of CBP shipboard measurements.

The 1998 flight was optimized for identification of submerged aquatic vegetation (SAV), with respect to season and time of day. Two approaches were used for SAV identification: spectral unmixing and band ratio. The images are compared with aerial photography and a derived map product (both courtesy Virginia Institute Marine Science).

Study Area
AVIRIS true color image, acquired 17-Aug-97
AVIRIS true color image, acquired 03-Jul-98
Chlorophyll-a 1997
Chlorophyll-a 1998
Suspended sediment 1997
Suspended sediment 1998
Secchi depth 1997
Secchi depth 1998
End-members for abundance analysis 1998 (note error: yaxis should read *100 not *1000)
Comparison of AVIRIS with in-situ measurements
SAV Abundance image 1998
SAV by band ratio 1998
SAV map 1997 (courtesy VIMS)
Aerial photograph of study area, 18-Jun-98 (courtesy VIMS)

Lee F. Johnson
Sr. Research Scientist
Institute Earth Systems Science & Policy
California State University Monterey Bay

office:
NASA Ames Research Center 242-4
Moffett Field CA 94035-1000
Ljohnson@mail.arc.nasa.gov
tel: (650) 604-3331

Sponsor: NASA/Office of Earth Science

last update: 06 January 1999

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