Differential Coherent Algorithm Based on Fast Navigation-Bit Correction for Airborne GNSS-R Software Receivers

Signals from the Global Navigation Satellite System （GNSS） scatter over the sea surface resulting in relatively low Signal-to-Noise Ratios （SNR）. A differential coherent algorithm is given here to improve the SNR and reduce the performance degradation due to the Squaring-Loss and the navigation-bit effect. The algorithm uses fast navigation-bit correction for Delay-Doppler Maps （DDM） in airborne Global Navigation Satellite Signal Reflectometry （GNSS-R） software receivers. The system model is introduced with an analysis of the statistical properties with simulations to support the theoretical analysis. Field experiments with real airborne receivers then demonstrate the effectiveness of this algorithm. Comparisons with test results show that this algorithm offers a significant SNR gain over conventional algorithms.

First spaceborne demonstration of BeiDou-3 signals for GNSS reflectometry from CYGNSS constellation

The full constellation of Chinese Global Navigation Satellite System(GNSS)Bei Dou-3 has been deployed completely and started fully operational service.In addition to providing global Positioning,Navigation and Timing(PNT)services,the Bei Dou-3 satellites transmissions can also be used as the sources of illumination for Earth Observation(EO)with a bistatic radar configuration.This innovative EO concept,known as GNSS reflectometry(GNSS-R),allows to measure the Earth surface characteristics at high resolution via the reflected L-band radar signals collected by a constellation of small,low cost and low Earth orbiting satellites.For the first time in orbit,earth reflected Bei Dou-3 signal has been detected from the limited sets of raw data collected by the NASA’s Cyclone GNSS(CYGNSS)constellation.The feasibility of spaceborne Bei Dou-3 reflections on two typical applications,including sea surface wind and flooding inundation detection,has been demonstrated.The methodology and results give new strength to the prospect of new spaceborne GNSS-R instruments and missions,which can make multi-GNSS reflectometry observations available to better capture rapidly changing weather systems at better spatio-temporal scales.

TDS-1 GNSS reflectometry wind geophysical model function response to GPS block types

This paper presents the TDS-1 GNSS reflectometry wind Geophysical Model Function(GMF)response to GPS block types.The observables were extracted from Delay Doppler Maps(DDMs)after taking the receiver antenna gains effects and GNSS-R geometry effects into account.Since the DDM is affected by GPS EffectiveIsotropic Radiated Power(EIRP),we first investigate the sensitivity of observables to the GPS block.Additionally,the observables at high SNRs are more sensitive to wind speed,but the spatial coverage at high signal to noise ratios(SNRs)is lower,while DDMs at low SNRs have the opposite characteristics.To balance the accuracy and spatial coverage,the DDM datasets are divided into two parts:high SNR(>0 dB)and low SNR(>−10 dB and≤0 dB)to develop wind GMF.Then,the influences of GPS block on wind speed retrieval both at high and low SNR is analyzed.Results show that the block types have impacts on wind GMF and the use of a prior GPS block can contribute to a better wind speed retrieval both at high and low SNR.Compared with ASCAT,the Root Mean Square Error(RMSE)value of wind speed retrieval at high and low SNR are 2.19 m/s and 3.13 m/s,respectively,when all TDS data are processed without distinguishing GPS block types.However,if the TDS data are separately processed and used to develop wind GMF through different blocks,both the accuracy and correlation coefficient can be improved to some extent.Finally,the influence of significant height of the swell(Hs)on SNR observables is analyzed,and it is demonstrated that there is no obvious linear or nonlinear relationship between them.