FlexBRDF: A Flexible BRDF Correction for Grouped Processing of Airborne
Imaging Spectroscopy Flightlines
Abstract
Bidirectional reflectance distribution function (BRDF) effects are a
persistent issue for the analysis of vegetation in airborne imaging
spectroscopy data, especially when mosaicking results from adjacent
flightlines. With the advent of large airborne imaging efforts from NASA
and the US National Ecological Observatory Network (NEON), there is
increasing need for methods that are both flexible and automatable
across numerous images with diverse land cover. FlexBRDF corrects for
BRDF effects in groups of flightlines, with key user-selectable features
including kernel selection, land cover stratification (we employ NDVI),
and use of a reference solar zenith angle (SZA). We demonstrate FlexBRDF
using a series of nine long (150-400 km) AVIRIS-Classic flightlines
collected on 22 May 2013 over Southern California, where rough terrain,
diverse land cover, and a wide range of solar illumination yield
significant BRDF effects, and then test the approach on additional
AVIRIS-Classic data from California, AVIRIS-Next Generation data from
the Arctic and India, and NEON imagery from Wisconsin. Based on
comparisons of overlap areas between adjacent flightlines, correction
algorithms built from multiple flightlines concurrently performed better
than corrections built for single images (RMSE improved up to 2.3% and
mean absolute deviation 2.5%). Standardization to a common SZA among a
group of flightlines also improved performance. While BRDF corrections
tailored to individual sites may be preferred for local studies,
FlexBRDF is compatible with bulk processing of large datasets covering
diverse land cover needed for calibration/validation of forthcoming
spaceborne imaging spectroscopy missions.