TRANSPARENCY OF WATER PASSO REAL RESERVOIR AND FACTOR REFLECTANCE IN IMAGES SENSOR MODERATE RESOLUTION IMAGING SPECTRORADIOMETER - MODIS

Abstract

This work has the goal of evaluating the use of MODIS images (band 1) to estimate the depth of the water transparence measured by the Secchi disc in the reservoir of Passo Real – RS. The transparence data were acquired by using the Secchi disc at 31 sample stations and in two different dates (July, 4th and October, 28th – both in the year of 2009). The MODIS (MOD09) images of dates close to the ones of the field works derive from the NASA image catalog. The values of band 1 reflectance – that have center of band in the wavelength of 648 nm – were correlated to the water transparence data. The reflectance showed an inverse relationship to the transparence of the water. The correlations were significant among the variables of the month of July, when the average transparence was 1,16 meters and it was not significant in October when the average transparence was 0,52 meter. The Modis images showed a good performance in specific conditions of the aquatic environment. When comparing satellite image estimated transparence data to the transparence evaluated in loco, one may conclude that Modis allows to estimate transparences greater to 0,5 meter.