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United States Department of Agriculture

Agricultural Research Service

Title: Estimation of Algal and Suspended Sediment Loads (Singly and Combined) Using Hyperspectral Sensors and Integrated Mesocosm Experiments

item Schalles, John - CREIGHTON UNIVERSITY
item Schiebe, Frank - SST DEVELOPMENT GROUP
item Starks, Patrick
item Troeger, William - USDA (RETIRED)

Submitted to: International Conference Remote Sensing for Marine and Costal Environments
Publication Type: Proceedings
Publication Acceptance Date: March 17, 1997
Publication Date: N/A

Technical Abstract: Sunlit, cylindrical, black mesocosm tanks (80 cubic meters, 3 m depth) and a hyperspectral radiometer were used to examine reflectances of algal blooms and suspended kaolin white clay. In three integrated experiments, algae and clay levels were carefully manipulated: (1) Algal bloom water in one tank was pumped to a second which began with clear water, and clear make-up water was pumped to the first to obtain a well graded series (Chl.a=0-62 micrograms per liter). (2) White, kaolin clay was added stepwise to clear water, resulting in an organic seston range of 0-40 mg/L. (3) Algal bloom water from a single source was divided between two tanks to establish Chl. a loads of 31 and 57 micrograms per liter. Then, identical additions of clay were made to both tanks to achieve a range of 0-72 mg/L inorganic matter while conserving the algal loads. The first experiment revealed a strong interplay between algal scattering and absorption. Pigment absorbance dominated below 510 nm, while increasing cell scatterin in regions of low pigment activity caused green and NIR peaks to form near 560 and 700 nm. In spite of strong chlorophyll absorbance near 675 nm, this region had small reflectance increases with increased algae. In the second experiment, white clay had high albedo. At seston levels above 40 mg/L, green reflectance exceeded 50 percent and NIR reflectance at 800 nm exceeded 9 percent. In the third experiment, algal pigments strongly attenuated clay reflectance in a dose dependent manner, even at green wavelengths. Clay particles greatly amplified but also preserved algal reflectance patterns. Our findings affirm the importance of high spectral resolution at diagnostic wavelengths in turbid Case 2 coastal and inland waters.

Last Modified: 4/18/2015
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