![]() ![]() This letter analyzes the background signals and thermal noise received over ocean scenes in spaceborne global navigation satellite system (GNSS)-reflectometry (GNSS-R) remote sensing using observations from the cyclone GNSS (CYGNSS) constellation. The transmit power (L1 C/A) of the full GPS constellation is estimated using an optimal search algorithm. The GCPM received power is highly repeatable and has been verified with DLR/GSOC's independent measurements. Single PRN calibration using a GPS signal simulator is used to compute the scale factor to convert the received counts into power in watts. Radio-metric calibration is performed to determine the system dynamic range and to calibrate GCPM gain. A PID thermal controller successfully stabilizes the system temperature over the long term. 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. 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. 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.
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