Brightness gradients correction in airborne hyperspectral data by using empirical BRDF model

Abstract

In general, apparent reflectance data obtained by airborne hyperspectral sensor are affected by Bidirectional Reflectance Distribution Function (BRDF) of surface medium. A complete preprocessing of airborne hyperspectral sensor data should include the correction of a possible brightness gradient for measuring the feature of surface medium.
For a line scanner like airborne hyperspectral sensor, the brightness gradients mainly occur in across-track direction and depend on the sensor's view angle. However, when the observations are done with the small planes, hyperspectral sensor attitude changes in the 3 axes directions, such as a rolling, pitching, and yawing. Therefore, in order to correct brightness gradient with sufficient accuracy, it is necessary to take into consideration not only the across-track direction but the alongt-rack direction also. A Highly precise simulation of BRDF using hyperspectral sensor attitude information measured by GPS/IMU is indispensable.
This research examines the technique of conducting the simulation of the BRDF with the empirical approach using the lapped images of two or more hyperspectral data. The proposed technique enables the estimation of the nadir reflectance value without any additional field measurements and the estimated nadir reflectance value can be used for any subsequent qualitative and quantitative analysis.