Abstract
Brazil and China have a long-term joint space based sensor program called China-Brazil Earth Resources Satellite (CBERS). The most recent satellite of this program (CBERS-4) was successfully launched on 7 December 2014. This work describes a complete procedure, along with the associated uncertainties, used to calculate the in-flight absolute calibration coefficients for the sensors Multispectral Camera (MUX) and Wide-Field Imager (WFI) on-board CBERS-4. Two absolute radiometric calibration techniques were applied: (i) reflectance-based approach and (ii) cross-calibration method. A specific site at Algodones Dunes region located in the southwestern portion of the United States of America was used as a reference surface. Radiometric ground and atmospheric measurements were carried out on 9 March 2015, when CBERS-4 passed over the region. In addition, a cross-calibration between both MUX and WFI on-board CBERS-4 and the Operational Land Imager (OLI) on-board Landsat-8 was performed using the Libya-4 Pseudo Invariant Calibration Site. The gain coefficients are now available: 1.68, 1.62, 1.59 and 1.42 for MUX and 0.379, 0.498, 0.360 and 0.351 for WFI spectral bands blue, green, red and NIR, respectively, in units of (W/(m2·sr·μm))/DN. These coefficients were determined with uncertainties lower than 3.5%. As a validation of these radiometric coefficients, cross-calibration was also undertaken. An evaluation of radiometric consistency was performed between the two instruments (MUX and WFI) on-board CBERS-4 and with the well calibrated Landsat-7 ETM+. Results show that the reflectance values match in all the analogous spectral bands within the specified calibration uncertainties.
Highlights
The incorporation of Brazil into a long-term remote sensing program has begun with the establishment of the China Brazil Earth Resources Satellite (CBERS) program
Assuming that total optical depth remains constant over the range of air masses for which measurements are performed, a Langley plot will yield a set of data points distributed along a straight line with slope equal to the total optical depth and intercept equal the natural logarithm of the ASR calibration constant [26,27,28]
The data products derived from the ground measurements and geometries of the sensor/satellite and sun at the time the sensor measures the reference surface are used as input to a radiative transfer code to predict the top of atmosphere (TOA) radiance/reflectance
Summary
The incorporation of Brazil into a long-term remote sensing program has begun with the establishment of the China Brazil Earth Resources Satellite (CBERS) program. This work describes a complete procedure, along with the associated uncertainties, used to calculate the in-flight absolute calibration coefficients for MUX and WFI level 1 images. For this purpose two absolute radiometric calibration techniques were used: (i) reflectance-based approach and (ii) cross-calibration method. The MUX and WFI on-board CBERS-4 was cross calibrated with the newest Landsat series sensor OLI (Operational Land Imager). This calibrated was performed based on imaging of the Libya-4 Pseudo Invariant Calibration Site (PICS) [13,14,15,16].
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