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. 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. Simulation results obtained from high-dynamic synthetic data demonstrate the effectiveness of the proposed technique. Additionally, real data from the UK-DMC reflectometry mission is used to validate the approach.