Angle Effect on Typical Optical Remote Sensing Indices in Vegetation Monitoring

Optical remote sensing indices play an important role in vegetation information extraction and have been widely serving ecology, agriculture forestry, urban monitoring, other communities. Remote are constructed from individual bands depending on special characteristics to enhance the typical spectral features for identification or distinction of surface land covers. With development quantitative sensing, there is a rapid increasing requirement accurate data processing modeling. It well known that geometry-induced variation observed reflectance not ignorable, but situation uncertainty thereby introduced into these still needs further detailed understanding. We adopted ground multi-angle hyperspectrum, response function (SRF) Thematic Mapper (TM), Enhanced (ETM+), Operational Land Imager (OLI), Moderate-Resolution Imaging Spectroradiometer (MODIS), Multi-Spectral Instrument (MSI) optical sensors simulated their sensor-like reflectance; then, we investigated potential angle effect frequently involved monitoring examined forward/backward over both ground-based level actual Landsat TM/ETM+ overlapped region. Our results discussed show as following: (1) Identifiable effects exist with more elevated influence than by band difference among sensors; (2) The absolute between forward backward direction can reach up ?0.03 0.1 within region; (3) investigation at indicates different variations transmitted each index. Regarding cases crop canopy various growth phases, most 20% relative nadir value except Normalized Difference Vegetation Index (NDVI) Water (NDWI) magnitude lower 10%, less 16% Burn Ratio (NBR). For case wax maturity stage, (EVI), Soil-Adjusted (SAVI), (RVI), Char Soil (CSI), NBR, Moisture (NDMI), SWIR2/NIR exceeded 50%, while values NBR NDMI 115.8% 206.7%, respectively; (4) Various schemes index construction imply propagation uncertainty. “difference” partially suppress directional influence, “ratio” high amplify effect. This study reveals angle-induced greater induced spectrum mismatch sensors, especially under senescence. In addition, based this work, suppressed recommended retrieval avoid unexpected effects.