Artículo de publicación ISIThe application of Earth observation sensor data in quantitative approaches calls on the conversion of original digital numbers to radiometric quantities such as radiance or reflectance. This conversion depends on the sensor absolute calibration. One of the postlaunch methods adopted to calibrate orbital sensors is the reflectance-based approach. According to this method, a reference surface with specifics characteristics is required. The main objective of this work is to evaluate the suitability of a specific surface located at Atacama Desert in Chile to be used as a reference surface for calibration of Earth observation sensor purposes. A field campaign was carried out from August 19 to 22, 2014, when radiometric measurements were performed to spectrally characterize the reference surface and to evaluate the atmospheric characteristics of the study area. The average reference surface reflectance factor in the spectral region from 350 to 2500 nm ranged from 0.1 to 0.3, and its spatial uniformity was within 2%-4%. The amount of atmospheric aerosols was low, with an aerosol optical depth at 550 nm between 0.08 and 0.11 during the fieldwork period. The climate is hyperarid, and the water column abundance was lower than 0.43 g/cm(2). The results demonstrated that a reference surface at Atacama Desert could be effectively used for calibration of either airborne or orbital electrooptical sensors, providing an excellent surface in South America.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Coordena, ao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES), Fondecyt-Initial (CONICYT)
Abstract:The absolute radiometric calibration of a satellite sensor is the critical factor that ensures the usefulness of the acquired data for quantitative applications on remote sensing. This work presents the results of the first cross-calibration of the sensor on board the Sistema Satelital de Observación de la Tierra (SSOT) Chilean satellite or Air Force Satellite FASat-C. RapidEye-MSI was chosen as the reference sensor, and a simultaneous Nadir Overpass Approach (SNO) was applied. The biases caused by differences in the spectral responses of both instruments were compensated through an adjustment factor derived from EO-1 Hyperion data. Through this method, the variations affecting the radiometric response of New AstroSat Optical Modular Instrument (NAOMI-1), have been corrected based on collections over the Frenchman Flat calibration site. The results of a preliminary evaluation of the pre-flight and updated coefficients have shown a significant improvement in the accuracy of at-sensor radiances and TOA reflectances: an average agreement of 2.63% (RMSE) was achieved for the multispectral bands of both instruments. This research will provide a basis for the continuity of calibration and validation tasks of future Chilean space missions.
Ground reflectance was acquired at the Railroad Valley Playa calibration site in Nevada USA using different methods of collection. The data was collected near the time and date of Landsat 8 OLI and Sentinel-2 satellite overpasses so an inter-comparison could be made with the reflectance products to determine which method was more suitable for vicarious calibration. The field spectrometers and reference panels were characterized before the field campaign. A continuous acquisition method was compared to stop and measure collections. Both acquisition methods were collected along an 80 m east-west transect as well as for a series of north-south transects over an 80 x 320 m area, with the stop and measure method being performed at random sampling locations. The measurements were performed using two field spectrometers by three teams of two people to compare the repeatability. The aim of the field campaign was to determine the variability due to the operator and the method of collection.
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