Considerations for Coherent Integration in Spaceborne GNSS-Reflectometry

The fundamental observable in Global Navigation Satellite System Reflectometry (GNSS-R) is the so-called delay-Doppler map (DDM), which is derived from the cross correlation of the reflected signal with either the direct signal or a locally generated replica of the transmitted signal as implemented in our algorithm. The efficient coherent integration is essential for enhancing the signal-to-noise ratio (SNR) and improving the quality of the retrieved data products. This work investigates the limitations of coherent integration in conventional GNSS-R (cGNSS-R) and proposes a novel blind compensation technique to extend integration time by mitigating phase differences caused by navigation bit changes and propagation effects. The maximum length of coherent integration depends on the application; however, achieving a higher SNR within the same integration time enhances the quality of DDMs. The simulation results obtained from high-dynamic synthetic data demonstrate the effectiveness of the proposed technique. Additionally, the real data from the U.K.-DMC reflectometry mission are used to validate the approach.