A comparison of validation and vicarious calibration of high and medium resolution satellite-borne sensors using RadCalNet

摘要

The Radiometric Calibration Network (RadCalNet) routinely provides top-of-atmosphere (TOA) reflectance data from instrumented ground sites. The data represents the nadir view of the ground for different sites that cover areas ranging from 50 m × 50 m to 1 km × 1 km. The smaller sites can only be used with high resolution sensors (≤ 30 m), but the larger sites, such as Railroad Valley (RRV) in Nevada can also be used for the validation or vicarious calibration of medium resolution sensors (> 250 m spatial resolution). Prior to utilising RadCalNet data in this manner, this paper describes the application of a high and a medium resolution sensor to assess potential biases between the RadCalNet data and satellite data at two different spatial resolutions. Results are shown for initial comparisons over RRV for the high resolution Sentinel-2 MultiSpectral Instrument (S2-MSI) and the medium resolution Sentinel-3 Ocean and Land Colour Instrument (S3-OLCI), and indicate the potential for RadCalNet to validate and vicariously calibrate sensors with differing spatial resolutions. The comparison analysis includes taking into account the temporal differences between the Sentinel-2 and Sentinel-3 overpasses and the time of RadCalNet data collection, as well as the spectral response functions (SRF) of the bands for both instruments. The comparison against the RRV site has shown there are significant biases between the RadCalNet data and S2-MSI and S3-OLCI for non-nadir viewing geometries that may be due to directional viewing and illumination effects and the non-Lambertian character of the RadCalNet RRV site.