Post-launch radiometric calibration of electro-optic sensors for Earth from space observation by differential method with the taking into account atmosphere transmittance coefficient

Abstract

The developed methodology of the post-launch radiometric calibration of the electro-optic sensors for Earth from space observation is considered. The novelty of this methodology consist in the implementation of the differential method for taking into account the spectral reflection coefficient of test objects from ground-based measurements, and in using of the atmospheric transmittance coefficient obtained from the world AERONET network data. The objective of the radiometric electro-optic sensor post-launch calibration consist in the evaluation of the linear regression dependence of the digital pixel number at sensor output from the spectral radiance at sensor aperture on Top of Atmosphere (TOA). The proposed differential method of the electro-optic sensor radiometric calibration is implemented in each spectral channel in the following stages: 1) determination of the coefficient of the sensor calibration characteristic inclination on the values of the spectral reflectance differences in all possible different pairs of ground measurement points on the surface of the test objects; 2) estimation of the coefficient of the calibration characteristic inclination as a mathematical expectation or as a median or a mod for a set of calculated its differential values; 3) determination on the basis of estimation of the coefficient of the calibration characteristic inclination the radiometric calibration coefficients: gain and offset; 4) recovery using the obtained radiometric calibration coefficients linear dependence of the spectral radiance at sensor aperture from the digital pixel numbers by the space imagery at the ground control points. The differential radiometric calibration method makes possible to avoid of unknown spectral radiance of the atmosphere caused by scattering. The atmospheric characteristics data were obtained from the international network AERONET observations. The nearest station to calibration test site in the area of the National Center for Space Facilities Control and Testing (Vitine, Crimea) (during the method testing procedure – summer 2012) was AERONET station in Sevastopol. The station provided the observational data of the atmosphere optical thickness, by whose values the atmosphere spectral transmittance were calculated based on the Bouguer law. The estimation of the calibration gain factor of the Landsat 5 TM and Landsat 7 ETM+ multispectral sensors on the developed methodology were obtained, which were provided the relative error from 1% to 22% and from –7% to 2% for the corresponding sensors, depending from the spectral channel of the sensor in comparison with etalon data of the calibration gain of these space systems sensors.