Next Generation Bi-Static Radar Receiver for Possible CYGNSS Follow-On Mission

Global Navigation Satellite Signal Reflectometry (GNSS-R) instruments enable measurements of reflected GNSS signals using two methods. The conventional method (cGNSS-R) involves cross-correlating the received signals on the satellite with a locally-generated reference signal. In order to generate a local reference signal, the instrument designer relies on published codes from the various governments operating the transmitter satellites. In contrast, the interferometric method (iGNSS-R) does not use a locally generated reference signal. Instead, it cross-correlates a direct received signal with a reflected received signal. In this way, iGNSS-R is able to utilize both public civilian signals as well as non-civilian and restricted GNSS signals, resulting in a larger overall bandwidth. The current generation of spaceborne GNSS-R instruments, such as CYGNSS, utilize only narrowband GPS L1 C/A-coded signals at the L1 center frequency. A next-generation instrument is being developed at the University of Michigan and The Ohio State University which will also support Galileo E1bc signals as well as wideband GPS L5 and Galileo E5 signals. The additional bandwidth in the L5/E5 band should significantly improve the spatial resolution and range accuracy of measured reflections and the corresponding scientific products. In the proposed implementation, these reflection measurements will be made using a locally generated reference signal (i.e. conventional GNSS-R). However, the use of wideband, high-spatial-resolution, high-range-accuracy measurements are often cited as a benefit of the interferometric GNSS-R approach. A new rawIF processor has been specifically developed to compare the performance of the two approaches using simulated GNSS signals from both bands as well as recent CYGNSS and TDS-1 data. In this work we characterize the two methods in terms of measurement quality, implementation complexity, and potential scientific applications. This information will be utilized when planning for and performing environmental testing on the next-generation instrument in 2019. The subsequent analysis and additional characterization of this data may also be used to support a design for a possible CYGNSS follow-on mission.