Point position coordinates’ determination for synthetic-aperture radar antenna of spacecraft

Abstract

The article is concerned with a space vehicle that performs remote sensing of the Earth surface. The survey assignment contains the geodetic coordinates of the object: latitude, longitude and object height. The sighting point is determined as the intersection of antenna pattern (AP) axis of space vehicle with ellipsoid surface comprising the survey object. The task is to define error allowances in setting AP axis angles considering the input restrictions on error limit of the point position coordinates for antenna sighting. The synthesis coordinate system (SCS) is defined where the antenna angular positions are specified. There are calculated point position coordinates for antenna sighting  in Greenwich Coordinate System (GCS), as well as the center and corner points of RI (radar image) frame in SCS. This is required for the coordinate referencing of synthetic radar image. There was obtained a linear approximation dependence of sighting bias dispersions in the plane tangent to the ellipsoid surface on angle values’ dispersions of the antenna axis on the hypothesis that the angle estimates of AP orientation axis are uncorrelated variates. Calculation results are presented indicating, in particular, that if SV (space vehicle) orbital altitude is 600 km, AP elevation is 60 degrees, and error limit of the point position for antenna sighting of the aiming point is 20 m in azimuth and range, then it will be required to ensure standard deviations’ level of about 0.0001 degrees for antenna axis orientation angles.