Abstract
ABSTRACTStandardized substrate, vegetation, and dark (S, V, & D) spectral endmembers (EMs) are presented for spectral mixture analysis (SMA) of MODIS version 6 daily nadir looking BRDF-adjusted reflectance (daily NBAR). EMs are derived from a diverse collection of over 43,000,000MODIS spectra spanning 6 continents and all non-polar biomes. EM spectra are similar to those from decametre studies. Sensitivity analysis using 351 pairs of 27 EM combinations shows mean differences in SVD fraction estimates of 4±3%, 3±2%, and 3±2%, respectively. An additional snow EM is identified, but deemed tentative pending further cryospheric analysis. Vicarious validation with Landsat shows under 0.5% bias in V fraction, −7% and +11% biases in S and D fractions, and comparable dispersion (standard deviation 6% to 7%) in all fractions. Model misfit is low (root-mean-square error under 5% for 99.9% pixels). When V is compared to Normalized Difference, Enhanced, and Soil Adjusted Vegetation Indices (NDVI, EVI, SAVI), NDVI shows over twice the dispersion (standard deviation 29% vs 13–14%) and over 4 times the bias (+18% vs 4%) of EVI and SAVI. Combined with previous studies, these results extend the scaling linearity and low misfit of the global SVD linear mixture model from 2m up to 500m.
Highlights
Spectral mixture analysis (SMA) is a robust, physically-based method of continuous land cover mapping from multispectral optical imagery [1,2,3]
nadir view BRDF-adjusted reflectance (NBAR) tiles were composited into a single image and the covariance-based principal component (PC) transform was applied
This study extends previous decameter-scale global analyses of spectral characterization and global EM identification to include hectometer-scale observations from the MODIS daily NBAR product
Summary
Spectral mixture analysis (SMA) is a robust, physically-based method of continuous land cover mapping from multispectral optical imagery [1,2,3]. Operationalization of the NBAR product facilitates the identification of MODIS-specific global EMs. Operationalization of the NBAR product facilitates the identification of MODIS-specific global EMs This extends the range of potential applications for multitemporal SMA to include larger synoptic areas with more frequent revisit than Landsat and a 15-year deeper historical archive than Sentinel 2. This analysis presents standardized global MODIS EMs determined from daily NBAR imagery of 9 cloud-free MODIS tiles spanning 6 continents and most non-polar terrestrial biomes. The EMs presented here will enable estimation of globally consistent EM fraction maps throughout the MODIS archive for retrospective analysis and prospective monitoring of changes in the Earth surface
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