Abstract
A “nadir-only” framework of the radiometric intercomparison of multispectral sensors using simultaneous nadir overpasses (SNOs) is examined at the 1-km regimes and below using four polar-orbiting multispectral sensors: the twin MODerate-resolution Imaging Spectroradiometer (MODIS) in the Terra and Aqua satellites, the Visible Imaging Infrared Radiometer Suite (VIIRS) in the Suomi National Polar-orbiting Partnership (SNPP) satellite, and the Ocean and Land Colour Instrument (OLCI) in the Sentinel-3A satellite. The study is carried out in the context of isolating the on-orbit calibration of the reflective solar bands (RSBs) under the “nadir-only” restriction. With a homogeneity-ranked, sample size constrained procedure designed to minimize scene-based variability and noise, the overall approach successfully stabilizes the radiometric ratio and tightens the precision of each SNO-generated comparison event. Improvements to the multiyear comparison time series are demonstrated for different conditions of area size, sample size, and other refinements. The time series demonstrate the capability at 1% precision or better under general conditions but can attain as low as 0.2% in best cases. Solar zenith angle is examined not to be important in the “nadir-only” framework, but the spectral mismatch between two bands can give rise to significant yearly modulation in the comparison time series. A broad-scaled scene-based variability of ~2%, the “scaling phenomenon”, is shown to have pervasive presence in both northern and the southern polar regions to impact inter-RSB comparison. Finally, this paper highlights the multi-instrument cross-comparisons that are certain to take on a more important role in the coming era of high-performing multispectral instruments.
Highlights
Earth science and climate studies have made significant progress in the recent decades along with continual advances in remote sensing technologies
It can be argued that the two units of the MODerate-resolution Imaging Spectradiometer (MODIS) [1,2], in the Terra and Aqua satellites launched on 18 December 1999 and 4 May 2002, respectively, are the forerunners leading the era of the high-performance instruments and big data
The primarily important simultaneous nadir overpasses (SNOs) cases are those of marginal statistical quality with broad-scale error bar of few percent, approximately 2% to 4%, that can be improved to be below 2% to be added to the comparison time series
Summary
Earth science and climate studies have made significant progress in the recent decades along with continual advances in remote sensing technologies. Numerous radiometric intercomparisons of the reflective solar bands (RSBs) of Aqua MODIS and SNPP VIIRS ensued [5,6,7] utilizing the simultaneous nadir overpasses (SNOs) approach [8,9,10,11]. These studies demonstrated the capability of the radiometric intercomparison at the 1-km spatial resolution regime to be typically few percent. A main goal of this paper is to show that the capability, under an improved analysis procedure, is at the level of 1% precision or better
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