Accession Number : ADA115422

Title :   Tropospheric Refraction Corrections Using Exoatmospheric Sources.

Descriptive Note : Rept. for Apr-Nov 81,


Personal Author(s) : Altshuler,Edward E ; Mano,Koichi

PDF Url : ADA115422

Report Date : Jan 1982

Pagination or Media Count : 21

Abstract : The performance of radar and navigation systems that operate at low elevation angles is often limited by tropospheric refraction, which produces two main effects on radio waves, angular bending and range error. These errors increase with decreasing elevation angle and are of the order of 0.7 deg. and 100 m respectively near the horizon. For some locations, and for many applications, antenna pointing corrections based on surface refractivity are adequate for elevation angles above a few degrees. However, new systems which operate at elevation angles near the horizon require improved accuracies. A technique for obtaining angle error corrections by utilizing exo-atmospheric calibration sources, such as radio or satellites, has been reported. In this report, a sensitivity analysis of this technique established the accuracies possible for angle and range error corrections. Three types of errors limit the accuracy of these corrections: measurement errors, computational errors, and errors in estimating distances. The parameters to be measured are the apparent elevation angle of the calibration source and the surface index of refraction. One integral must be evaluated numerically to calculate the range error. Finally, the radius of the earth, the heights of the target and calibration source, and a residual range error that arises because the calibration source cannot be tracked to zenith must be estimated.

Descriptors :   *Radio waves, *Atmospheric refraction, Radar, Radio navigation, Radio transmission, Elevation, Low angles, Range(Distance), Errors, Corrections, Calibration, Sources, Exosphere, Artificial satellites, Sun, Extraterrestrial radio waves

Subject Categories : Active & Passive Radar Detection & Equipment
      Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE