Compensating for propagation errors in electromagnetic measuring systems

The tion can compromise the accuracy of such equipment as tracking radars, photogrammetric cameras, and laser range finders. The refraction is caused by a lowering of the velocity of propagation of electromagnetic waves; this change in velocity has a direct effect on the measurement of distances using propagation time, whereas the deviation of the vertical angle is proportional to the rate of change of velocity with altitude. The errors can be reduced if the pertinent atmospheric parameters (such as temperature, atmospheric pressure, and water-vapor pressure) are known, or can be approximated, for the propagation path. This article derives straightforward techniques for the calculation of these errors and illustrates the procedures by exploring some typical optical refraction problems.