A Bio-Optical Model to access the Trophic State of a Tropical Reservoir using the Sentinel-3 Spectral Bands
Alcantara, Enner1; Barbosa, Claudio2; Augusto-Silva, Pétala2
1Sao Paulo State University, BRAZIL; 2National Institute for Space Research, BRAZIL

Reservoirs, or man-made lakes, are usually built to store water for water supply, flood control, or power generation; but they are also used for agriculture, recreation, fisheries, wildlife and many others. Because of this uses there is an increasing concern that anthropogenic eutrophication threatens the usability of aquatic systems. In Brazil, there are approximately 159 hydroelectric reservoirs, responsible for 76% of Brazil's energy generation which is considered the largest hydroelectric park in the world. Traditionally the trophic state of water bodies have been assessed using limnological methods and laboratory analyses of field-sampled data. Determination of trophic state using field-collected data is time and cost consuming. Remote sensing can be considered a powerful tool to monitor aquatic systems and is particularly useful in remote large areas. Data collected using this technique can provide a synoptic overview of such large aquatic environments, which could otherwise not be observed at a glance. The aim of this work is to parameterize a bio-optical model using inherent and apparent optical properties and then simulate the spectral bands on Sentinel-3 satellite. The selected test area was Funil hydroelectric reservoir. Funil was constructed in 1969 and is the largest impoundment in the Rio the Janeiro state, southeastern Brazil. Samples of water quality were collected in two periods, in May and September 2012 and were analyzed in the laboratory. The remote sensing reflectance was obtained using the radiometers Trios RAMSES. The inherent optical properties, absorption and backscattering, were obtained with WET Labs AC-S underwater instrument and with a model, respectively. The parameterized model will be adapted to Sentinel-3 bands and the results will be compared with the measured chlorophyll-a in Funil reservoir. The chlorophyll-a concentration will be used as a proxy of the trophic state.