LI Jiayue, JIAO Ziti, ZHANG Hu, et al. Variance of bidirectional reflectance and its application using operational MODIS BRDF model[J]. Journal of Remote Sensing, 2015,19(5):750-760.
LI Jiayue, JIAO Ziti, ZHANG Hu, et al. Variance of bidirectional reflectance and its application using operational MODIS BRDF model[J]. Journal of Remote Sensing, 2015,19(5):750-760. DOI: 10.11834/jrs.20153297.
The Bidirectional Reflectance Distribution Function( BRDF) qualifies variations in reflectance patterns as a function of illumination and viewing geometry. Statistically
directional reflectance in a given direction is considered as the mean. The variation in that direction can then be characterized by its variance. The BRVF is a useful method for characterizing reflectance anisotropy.In this study
we first explored the variance in bidirectional reflectance through the use of not only a BRVF technique based on the MODIS BRDF model but also an error propagation method. Then
we performed a method validation by using the MODIS BRDF / Albedo product from selected EOS Land Validation Core sites( LVCS) with underlying typical IGBP land cover types and NDVI threshold. Finally
as an initial application of the BRVF
we applied the aforementioned theoretical results in the simulation result derived from the collected 69 field measurements.Major results demonstrate that the spatial distribution patterns of the BRVF are linear combinations of the first-degree term and the second-degree term of geometric optical kernels( i. e.
K geo) and volumetric scattering kernels( i. e.
K vol). Validation results based on the MODIS BRDF / Albedo product are consistent with the theoretical derivations. In general
the BRVF spatial distribution pattern reaches its peak value at the hotspot direction. Beyond the large viewing angle( VZA > 60°)
the BRVF tends to increase along with the increase in VZA. The BRVF value in the near-infrared band is greater than that in the red band
thereby indicating that for the MODIS sensor
the BRVF is a band-dependent variable. The initial application of the BRVF to the simulation result derived from the collected 69 field measurements shows that at a large VZA where observations are not available
the modelextrapolated BRVF value increases prominently
thereby affecting the accuracy of surface albedo retrievals. The maximum relative error for the white sky albedo retrieval in the red band is about 38. 26%.This study is very helpful in understanding the uncertainty of surface albedo retrieved by a narrow VZA sensor. The results are also necessary in understanding a priori knowledge applications for the retrieval of surface albedo and other biophysical parameters.
关键词
二向性反射方差函数BRVFBRDFMODIS地表类型EOS地面验证点误差传播反照率核驱动模型
Keywords
BRVFBRDFMODISland cover typesEOS land validation core siteserror propagationalbedokernel-driven BRDF model