Cross-calibration of the RapidEye Multispectral Imager payloads using near simultaneous acquisitions of pseudo-invariant test sites

Radiometric calibration of the RapidEye Multispectral Imager (MSI) and other remote sensing imaging systems is an essential task in the quantitative assessment of sensor image quality and the production of reliable data products for a wide range of geo-spatial applications. Spatially and temporally pseudo-invariant terrestrial targets have long been used to characterize Earth observation systems and provide a consistent record of their radiometric performance. This study focuses on the use of near-simultaneous acquisitions of calibration test sites by all of the RapidEye Multispectral Imagers (MSI) as a means to track the relative radiometric stability of the five sensors in the constellation. As the cameras acquired the sites with different image acquisition and solar illumination parameters, a compensation factor is derived to account for the site bidirectional-reflectance-function (BRDF) variations that occur with different sun-target-sensor acquisition conditions. The derived top-of-atmosphere reflectance is computed as a figure of merit to measure and track the constellation response to each of the test sites. The results show that the differences between the same bands on the different spacecraft are much smaller than what BlackBridge promises in the RapidEye product specifications.