ESTIMATING CHLOROPHYLL CONTENT AND BATHYMETRY OF LAKE TAHOE USING AVIRIS DATA

An AVIRIS image was obtained at Lake Tahoe on 9 August 1990, along with in situ data. Profiles of percent transmission of monochromatic light, stimulated chlorophyll fluorescence, photosynthetically available radiation, and spectral upwelling and downwelling irradiance, and upwelling radiance were measured. Chlorophyll-a + phaeopigments, total particulate absorption, detritus absorption, and absorption due to colored dissolved organic matter were measured on discrete samples. Spectral reflectance at the surface was measured with a handheld spectroradiometer. Image preprocessing included increasing the instrument signal-to-noise ratio by filtering to reduce patterned noise and spatial resampling, and application Of LOWTRAN-7 as an atmospheric correction. Several analyses were then performed illustrating the utility of the AVIRIS over a dark water scene. The water-leaving radiance measured by the AVIRIS compares very well with the upwelling radiance measured in-water, everywhere but in the very short wavelength channels. After recalibrating one AVIRIS channel, the chlorophyll concentration derived from the image compares extremely well with that measured with bottle samples. Application Of the pigment algorithm to the rest of the lake was confounded by covarying absorption at 440 nm by colored dissolved organic matter (CDOM), underscoring the importance Of accurate calibration Of the instrument in the short-wavelength channels. Surface spectroradiometer measurements made along a transect Of varying depth were used to condition a multiple linear regression bathymetry model. By applying the model coefficients to a portion of the image, a bathymetry map of the shallow parts of the lake was constructed which compares favorably with published lake soundings, indicating the potential for a bottom-reflectance correction to coastal ocean color imagery.