Absolute Radiometric Calibration of the RapidEye Multispectral Imager Using the Reﬂectance-based Vicarious Calibration Method
RapidEye AG is a commercial provider of geospatial information products and customized solutions derived from Earth observation image data. The source of the data is the RapidEye constellation consisting of ﬁve low-earth-orbit imaging satellites. We describe the rationale, methods, and results of a reﬂectance-based vicarious calibration campaign that was conducted between April 2009 and May 2010 at Railroad Valley Playa and Ivanpah Playa to determine the on-orbit radiometric accuracy of the RapidEye sensor. In situ surface spectral reﬂectance measurements of known ground targets and an assessment of the atmospheric conditions above the sites were taken during spacecraft overpasses. The ground data are used as input to a radiative transfer code to compute a band-speciﬁc top-of-atmosphere spectral radiance. Acomparison of these predicted values based on absolute physical data to the measured at-sensor spectral radiance provide the absolute calibration of the sensor. Initial assessments show that the RapidEye sensor response is within 8% of the predicted values. Outcomes from this campaign are then used to update the calibration parameters in the ground segment processing system. Subsequent veriﬁcation events conﬁrmed that the measured RapidEye response improved to within 4% of the predictions based on the vicarious calibration method.
calibration; planetary reﬂectance; radiometric accuracy; spectral radiance RapidEye