Abstract
This study introduced a data screening method for comparing the reflectances in middle latitude forest regions collected by a Geostationary Earth Observing (GEO) satellite and a Low Earth Orbit (LEO) satellite. This method attempts to reduce the differences between the relative azimuth angles of the GEO and LEO observations. The method, called relative azimuthal-angle matching (RAM), takes advantage of the high temporal resolution of the GEO satellites, which enables collection of a wide range of relative azimuth angles within a day. The performance of the RAM method was evaluated using data in the visible and near-infrared bands collected by the Himawari-8/Advanced Himawari Imager (AHI) and the Terra/Moderate Resolution Imaging Spectroradiometer (MODIS). The consistency of the reflectance pairs of MODIS and AHI selected by the RAM method was compared with the consistency of the reflectance pairs acquired simultaneously by the two sensors. The data were matched pixel-by-pixel after applying atmospheric corrections and cloud screening. The results show that RAM improved the reflectance ratio by approximately 10% for the red and NIR bands on average relative to the simultaneous observations. Significant improvements in the two bands were observed (20%), especially among data collected in the fall and winter. Performance of RAM depends largely on season. Especially in summer, the reflectance pair chosen by RAM showed less consistency than solar zenith-angle matching (SZM). The results also indicated the relatively large influence of the spectral response functions on the green and red bands of the two sensors.
Highlights
Geostationary earth observing (GEO) satellites have played a major role in various fields of study for decades
This study proposed a data screening method, the Relative Azimuthal-angle Matching (RAM) method
The relative azimuthal-angle matching (RAM) method is a straightforward but unique technique for comparing GEO-Low Earth Orbit (LEO) reflectances over forest targets located in middle latitude regions
Summary
Geostationary earth observing (GEO) satellites have played a major role in various fields of study for decades. Much attention has been paid to the applications of GEO satellite to land observation [1,2,3,4,5] because of the enhanced band configuration and calibration strategy [4,6,7] These “new generation” GEO satellites, such as the Himawari-8 (2014–) [6], FY-4A [4], and GOES-16 (2016–) [7], have land monitoring capabilities with high radiometric and temporal resolutions, in addition to their primary atmosphere and ocean sciences monitoring capabilities. The geometric differences induce bidirectional effects on the observed land surface, causing fluctuations in the observed reflectances These fundamental issues must be addressed to improve our understanding of the data collected from GEO satellites
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