Analytic construction of instantaneous field of view ellipsoids on an arbitrary earth projection

The instantaneous field of view (fov) of a nadir scanning satellite instrument can be described by the intersection of a cone with a sphere. The fov normally is circular at nadir and increases in size both along and cross track as the scan angle increases. The cross track distortion is due to the fact that the fov edge closer to nadir is also farther away from the horizon, which causes a stretching of the fov. The along track distortion is simply due to the fact that fov angular size is fixed, but the distance from the satellite to the viewing location on the earth increases as the scan moves away from nadir. This paper presents the mathematics necessary to draw the fov ellipses on an arbitrary earth projection.