Vector analysis and satellite footprints

Projections of antenna pattern characteristics from a satellite in circular orbit onto the Earth´s surface, referred to as footprints, are derived using vector analyses. These vector analyses are described along with a winding number approach used to determine whether a given point on the Earth´s surface lies within the footprint contour. The utility of this program is illustrated using a Sun-synchronous satellite and a radiometric antenna that is mechanically scanned at a constant offset angle about the satellite nadir axis. The time sequence of the antenna pattern as the antenna scans and translates past a specified point on the Earth´s surface can be generated. This program has the generality to illustrate the effects of satellite attitude variations on the footprint contour. In addition, footprints for a nonspherical Earth are contrasted with those for a spherical Earth