Design and Performance of a GPS Constellation Power Monitor System for Improved CYGNSS L1B Calibration

The Cyclone Global Navigation Satellite System (CYGNSS) uses a bistatic radar configuration with the Global Positioning System (GPS) constellation as the active sources and the CYGNSS satellites as the passive receivers. The GPS effective isotropic radiated power (EIRP), defined as the product of transmit power and antenna gain pattern, is of great importance to the accurate Level 1B calibration of the CYGNSS mission. To address the uncertainties in EIRP, a ground-based GPS constellation power monitor (GCPM) system has been built to accurately and precisely measure the direct GPS signals. A PID thermal controller successfully stabilizes the system temperature over the long term. Radiometric calibration is performed to determine the system dynamic range and to calibrate GCPM gain. Single PRN calibration using a GPS signal simulator is used to compute the scale factor to convert the received counts into power in watts. The GCPM received power is highly repeatable and has been verified with DLR/GSOC's independent measurements. The transmit power (L1 C/A) of the full GPS constellation is estimated using an optimal search algorithm. Updated values for transmit power have been successfully applied to CYGNSS L1B calibration and found to significantly reduce the PRN dependence of CYGNSS L1 and L2 data products.