Redução do erro de estimativa da concentração de clorofila-a no reservatório de Bariri por meio do fator de proporcionalidade (ρ)

The remote sensing reflectance (Rrs) plays an important role in estimating the composition of an aquatic environment. It depends on the total radiance reaching the sensor (Lt), the downwelling spectral plane irradiance incident onto the water surface (Ed) and the radiance incident from the sky (Ls). The weather conditions, as wind speed, can be considered to correct the Ls value. The proportionality factor that relates these conditions is known as reflectance factor ρ. A set value was proposed for ρ to estimate Rrs, however it can also be calculated onwards the wind speed and the Ls geometry of measurement. An error on the Rrs estimate can affected the estimate of other radiometric quantities dependent on Rrs such as absorption (a) and scattering (b) coefficients. A correct Rrs estimate can ensure more accurate measurements of Ls and reduce the errors on the optically active compounds (OAC) estimates. The aim of this paper was to evaluate the influence of the ρ on the Rrs to estimate chlorophyll-a concentration in the Bariri reservoir. The results showed that an empirical model using a variable ρ to obtain Rrs values in order to calculate chlorophyll-a concentration had 6,5% less error when compared with ρ set value. Therefore we can conclude that the use of a set ρ value will improve the errors in estimating the Rrs and consequently in estimating the chlorophyll-a concentration.