Title :
Measuring the Directional Variations of Land Surface Reflectance From MODIS
Author :
Breon, Francois-Marie ; Vermote, Eric ; Murphy, Emilie Fedele ; Franch, Belen
Author_Institution :
Lab. des Sci. du Climat et de l´Environ., IPSL, Gif-sur-Yvette, France
Abstract :
The directional variation of land surface reflectance generates an apparent noise in the time series acquired from satellites with variable observation geometries, which can be corrected through appropriate modeling of the bidirectional reflectance distribution function (BRDF). In a previous paper, we described and validated the VJB method that estimates a target BRDF shape and corrects for directional effects and yet retains the high temporal resolution of the measurement. Here, we analyze its potential to measure the BRDF of targets at the 0.5-km resolution of Moderate Resolution Imaging Spectroradiometer (MODIS). The description of the BRDF in the NASA MCD43A1 product shows very large temporal variations that are unrealistic. However, the reflectance time series, normalized to a standard observation geometry using this modeling, have a similar quality as those derived using VJB. Conversely, the MCD43A1 modeled reflectances for a nonstandard geometry are unrealistically variable. These results indicate that the standard BRDF model inversion used to derive the MCD43A1 product is underconstrained due to the limited directional sampling of the 16-day composite period. The apparent noise in the corrected reflectance time series is significantly larger than the one obtained at lower spatial resolution, and is very much a function of the spatial heterogeneity of the area surrounding the target. These results strongly indicate that the multitemporal MODIS measurement at high spatial resolution (0.5 km) is affected by a change in the effective resolution for off-nadir observation and by inaccurate registration. The resulting noise in the measurements precludes an accurate measurement of the BRDF at such a scale.
Keywords :
geophysical techniques; remote sensing; 16-day composite period; BRDF variable observation geometries; MCD43A1 modeled reflectances; Moderate Resolution Imaging Spectroradiometer; NASA MCD43A1 product; VJB method; bidirectional reflectance distribution function; corrected reflectance time series; directional variations; land surface reflectance; multitemporal MODIS measurement; nonstandard geometry; off-nadir observation; target BRDF shape; Geometry; MODIS; Pollution measurement; Shape; Spatial resolution; Time measurement; Time series analysis; Bidirectional reflectance distribution function (BRDF); Moderate Resolution Imaging Spectroradiometer (MODIS); surface reflectance;
Journal_Title :
Geoscience and Remote Sensing, IEEE Transactions on
DOI :
10.1109/TGRS.2015.2405344