BRDF Applications in Semiarid Grassland Monitoring with the AVHRRs


Separability Afforded by 21 Orbits of AVHRR LAC/HRPT (acquired over a 17-day period),
BRDF-corrected to Nadir Viewing with Varying Solar Zenith Angles
(note model reciprocity).

Atmospherically-corrected AVHRR VIS and NIR reflectances from grassland field survey sites in Xilingol Aimag, Inner Mongolia P.R.C., corrected for the effects of surface BRDF.

Compare with the uncorrected data. More information on the sites (including codes, photos, maps) is given on this page.


The animated scatterplot above shows atmospherically-corrected and cloud-screened reflectances for eight point sites from 21 orbits from the period 3rd to 19th August 1996, adjusted for BRDF effects to represent the best estimate of what would be obtained with nadir viewing and different solar zenith angles in the principal plane (SZA=solar zenith angle, VZA=view zenith angle). The maxwod value is the maximum weight of determination, a quantity describing the noise incurred on modelling to each target geometry, given the angular sampling used in model inversion; this is based on theory originating with Gauss. As the solar zenith angle increases, the potential for discrimination between the classes (grassland types) also increases, although there is a penalty to pay in terms of increased noise, with the maximum weight of determination exceeding 1.00 when the solar zenith exceeds about 70 degrees. Nevertheless, the improvement over uncorrected data is massive.


Back | Index | Disclaimer
1