Patent ID: 7130449

Claim:
A method for determining the slope of a ground imaged area, the method comprising: generating a first and a second image of an area of ground from an aircraft, wherein the first and second images with pixels correlate to the area of the ground that are images taken at different times and wherein each pixel in the first and second images includes a viewing angle value; determining a material associated with a plurality of the pixels; retrieving a bi-directional characteristic information based on the determined material; determining a radiance change value for at least one pixel of the first and second images by subtracting a radiance value at a pixel location in the first image to a radiance value at the same pixel location in the second image; and determining a slope at a pixel location based on the associated viewing angle values, the determined radiance change value, one of radiance values of the first or second images, and the retrieved bi-directional characteristic information.