An Enhanced Tropospheric Effects Compensation System Combining Tomographic and GPS Correction Techniques

Propagation Research Associates (PRA) proposes an innovative system that will correct angle-of-arrival error for radars tracking long range, low elevation targets. The correction improvement will be an order of magnitude improvement over existing model based measurements and will extend time-lines for Ballistic Missile Defense radars. The proposed Enhanced Tropospheric Effects Compensation (ETEC) System uses GPS Doppler Correction and 3-D Refractivity Field to estimate angle-of-arrival error for low elevation radar signals due to tropospheric bending error. A 3-D Turbulence Field will be developed to determine the turbulence structure to mitigate the effects of turbulence and will significantly improve detection and target measurement characteristics for low elevation targets. In Phase I PRA demonstrated the feasibility of the GPS Data Correction technique to estimate bending error and establish a system error budget. The technique uses Doppler measurements from GPS signals compared with estimated true Doppler measurements based on a priori knowledge of the position of occulting GPS satellites. Also, PRA developed the Ray-Tracing Tomographic Refractivity and Turbulence Inversion Techniques that use GPS bending error estimates to create real-time refractivity and turbulence structure profiles. These profiles will be integrated into existing 3-dimensional mesoscale models of the troposphere to develop a real-time 3-D Refractivity and Turbulence Fields in Phase II.