Enhanced Tropospheric Effects Compensation System

Propagation Research Associates (PRA) introduces an innovative system that willcorrect angle of arrival error for radars tracking long range, low elevation targets.The correction improvement will be an order of magnitude improvement over existingmodel based measurements and will extend time-lines for Ballistic Missile Defenseradars. The Enhanced Tropospheric Error Compensation (ETEC) System is proposed thatuses GPS Data Correction and a 3-D Refractivity Field to estimate angle-of-arrivalerror for low elevation radar signals due to tropospheric bending error. Phase Iwill demonstrate the feasibility of the GPS Data Correction technique to estimatebending error and establish a system error budget. The technique uses Dopplermeasurements from GPS signals compared with estimated true Doppler measurements basedon a priori knowledge of the position of occulting GPS satellites. A simulation willbe developed that will demonstrate the performance of the GPS Data Correctiontechnique in the presence of various error sources including errors due totropospheric inhomogeneities and GPS signal multipath. Antenna concepts will bedeveloped that mitigate multipath for low elevation GPS signals. PRA personnel havebeen working with the National Missile Defense (NMD) Project Office and RaytheonElectronic Systems to design the ETEC System to enhance the performance of the NMDradar for low elevation targets.A Phase I Option is proposed that will develop a prototype ETEC design that can beintegrated into either GBR-P or NMD XBR for real-time operation. The ETEC system willallow BMD radars to track long range, low elevation targets to extend operationaltimelines and coverage. PRA will pursue FasTrack support from Raytheon ElectronicSystems in Phase II to develop and test a prototype system that can be integratedinto GBR-P. In addition, PRA will pursue commercial opportunities with GPS vendorsto apply the ETEC technology to extend GPS coverage and improve GPS locationaccuracy. A primary source of GPS error is due to refraction, and the ETEC technologywill improve GPS performance by increasing the number of available satellites for aGPS solution and by compensating for troposheric refraction to improve signalsynchronization. PRA will also commercialize the antenna concept, designed in PhaseI, that will mitigate signal multipath for occulting GPS satellites. The multipathmitigation technology will have application in radar and communication systems.