- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Incoherent Range Walk Compensation for Spaceborne GNSS-R Imaging
摘要： Global navigation satellite system reflectometry (GNSS-R) receivers produce delay-Doppler maps (DDMs) by incoherently integrating coherent integration results. Due to system dynamics, during incoherent integration, the receiver aligns each coherent result by tracking the delay and Doppler of the specular point. This is known to cause a blurring of the spatial footprint of the Woodward ambiguity function (WAF) on the reflecting surface. In this paper, we demonstrate that the blurring of the WAF varies over the glistening zone (GZ), and even if a fixed point on the ground is tracked, blurring still occurs. We derive the expressions for the delay and Doppler change rates over the GZ and then predict the error introduced by range walk for typical GNSS-R scatterometry configurations. We find that ≈6 dB of loss is expected for a point scatterer near the edge of the GZ when a fixed point on the surface is tracked. The incoherent range walk compensation (IRWC) method is then presented for GNSS-R receivers to mitigate this loss. The IRWC method focuses the power in the DDM to the isodelay and iso-Doppler configuration occurring at the midpoint of the integration time. DDMs produced by tracking a fixed point with and without IRWC are simulated, and errors are found to be in agreement with those predicted. Spatial domain GNSS-R products will be improved with IRWC. Target detection will benefit from a larger usable swath, allowing longer tracking and detection times as a result of the increased target to clutter and noise ratio. At the same time, imaging applications will no longer suffer from a spatially variant blurring of the WAF, which limits the resolution of the estimated products. IRWC is shown to mitigate the range migration losses and improve the SNR of an imaging GNSS-R receiver by ≈6 dB near the edge of the GZ.
关键词： integration,global navigation satellite system reflectometry (GNSS-R),reflectometry,imaging,target detection,receiver,incoherent range walk compensation (IRWC),Dynamic corrections
更新于2025-09-23 15:23:52
-
Geometric Distortion Correction of Spaceborne GNSS-R Delay-Doppler Map Using Reconstruction
摘要： For spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R), the delay difference of direct and reflected GNSS signals among successive snapshots changes rapidly because of the high dynamics of low earth orbital and GNSS satellites. This change has to be compensated to avoid the distortion of incoherently averaged delay-Doppler map (DDM). The method to refresh the correlation window on each coherent integration time period may require too many instrument resources or too much data to be uploaded from the ground station. This letter proposes a new postprocessing approach based on the motion degradation model of DDM and the reconstruction to replace real-time compensation. Raw sampled data from UK TechDemoSat-1 are used to verify the availability of proposed approach. The results show that after reconstruction for the distorted DDM, the DDM accuracies relative to that compensated in real time are significantly improved.
关键词： Global Navigation Satellite System-Reflectometry (GNSS-R),reconstruction,Distorted delay-Doppler map (DDM)
更新于2025-09-23 15:22:29
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Relationship Between Bistatic Radar Scattering Cross Sections and GPS Reflectometry Delay-Doppler Maps Over Vegetated Land in Support of Soil Moisture Retrieval
摘要： This paper presents the application of a coherent bistatic radar scattering model from vegetated terrains and the extension of the model to circularly polarized incident wave cases for GNSS signals. It will then present an analysis relating the bistatic scattering Radar Cross Sections (RCS) of vegetated land cover to the customary Delay Doppler Maps (DDMs) resulting, e.g., from GNSS reflectometry (GNSS-R) observations. This step is key in being able to use GNSS-R data in soil moisture retrieval algorithms. While some analyses exist for this purpose for scattering from sea surface, such analysis has not been carried out specifically for vegetated land surface. The proposed model and methods are envisioned to be applied to the airborne GNSS Reflectometer Instrument for Bistatic SAR (GRIBSAR) project currently under development, as well as to the CYGNSS mission.
关键词： GRIBSAR,Coherent bistatic radar scattering model,GNSS-R,RCS,Delay Doppler Map
更新于2025-09-23 15:22:29
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Optimizing Waveform Maximum Determination for Specular Point Tracking in Airborne GNSS-R
摘要： In this study we present techniques that have been developed to optimize the processing of airborne GNSS-R data, with the goal of improving its accuracy and robustness under non-optimal conditions. This approach is based on the detailed analysis of data produced by the instrument GLORI, which was recorded during an airborne campaign in the south west of France in June 2015. Our technique relies on the improved determination of reflected waveform peaks in the delay dimension, which is related to the loci of the signals contributed by the zone surrounding the specular point. It is shown that when developing techniques for the correct localization of waveform maxima under conditions of surfaces of low reflectivity, and/or contamination from the direct signal, it is possible to correct and extract values corresponding to the real reflectivity of the zone in the neighborhood of the specular point.
关键词： GNSS-R,Land,Airborne,Processing
更新于2025-09-23 15:21:21
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Satellite Pitch Estimation Using Delay Doppler Maps
摘要： On TechDemoSat-1, the attitude uncertainty can be significant during eclipse, leading to large errors in the estimated antenna gain towards the specular point and the geophysical parameter inversion methods that rely on this knowledge. DDMs produced by spaceborne GNSS-R receivers are typically asymmetrical due to the projection of the receiver's antenna pattern over the glistening zone. Thus, an asymmetric DDM contains information about the satellite attitude. In this paper, we investigate the potential use of asymmetric DDMs in attitude determination.
关键词： GNSS-R,Satellite Attitude,Asymmetric DDMs,Reflectometry
更新于2025-09-23 15:21:21
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - 3Cat-4: Combined GNSS-R, L-Band Radiometer with RFI Mitigation, and AIS Receiver for a I-Unit Cubesat Based on Software Defined Radio
摘要： The 3Cat-4 mission aims to demonstrate the capabilities of nano-satellites plus the versatility of a Software Defined Radio for passive Earth Observation. Three different microwave payloads are integrated into a single unit CubeSat platform: a multi-constellation (GPS and Galileo) and a dual-band (L1 and L2) Global Navigation Satellite System-Reflectometer receiver, a total power radiometer including a novel Radio Frequency Interference (RFI) detection and mitigation technique, and an Automatic Identification System receiver for vessels tracking. Being able to validate these technologies in a CubeSat enables their fast adoption as hosted payloads or in more performing dedicated platforms in the future. This paper shows a novel approach for embedding multiple passive microwave payloads in a single platform.
关键词： GNSS-R,RFI,AIS,Nano-satellite,Radiometry,CubeSat
更新于2025-09-23 15:21:21
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Impact of the Elevation Angle on Cygnss GNSS-R Reflectivity over Different Scattering Media over Land and Ocean
摘要： Earth’s surface bistatic reflectivity LHCP,CyGNSS? profiles are obtained using Global Navigation Satellite Systems Reflectometry (GNSS-R) products from NASA’s Cyclone Global Navigation Satellite Systems (CyGNSS). The focus of this study is to evaluate the influence of the GNSS satellites’ elevation angle e? on LHCP,CyGNSS?. Specific target areas with differentiated scattering media are selected to characterize these profiles as a function of the land-cover type and the wind-speed regimes for ocean-surfaces. In the former case, the main interest is to further understand the function eLHCP,CyGNSS(,...)f??? in preparation of the potential application of the so-called Tau-Omega model to GNSS-R. In the latter case, the objective is to analyze the impact of the coherent scattering component in GNSS-R observables. Preliminary results show LHCP,CyGNSS? increases ~ 3.7 dB over land and ~ 5.3 dB ocean, as e? moves from ~ [70,90]o to ~ [20,40]o.
关键词： CyGNSS,GNSS-R,coherent and incoherent scattering,elevation angle,bistatic reflectivity
更新于2025-09-23 15:21:21
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Geophysical Relationship between Cygnss GNSS-R Bistatic Reflectivity and Smap Microwave Radiometry Brightness Temperature Over Land Surfaces
摘要： This work presents an assessment on the correlation between CyGNSS-derived Global Navigation Satellite Systems Reflectometry (GNSS-R) bistatic reflectivity rl? and SMAP-derived brightness temperature BT, over land surfaces. This parametric-study is performed as a function of Soil Moisture Content (SMC), and vegetation opacity τ. Several target areas are selected to evaluate potential differentiated geophysical effects on “active” (as many transmitters as navigation satellites are in view), and passive approaches. Although microwave radiometry has potentially a better sensitivity to SMC, the spatial resolution is poor ~ 40 km. On the other hand, GNSS-R bistatic coherent radar footprint is limited by half of the first Fresnel zone which provides about ~ 150 m of spatial resolution (depending on the geometry). The synergetic combination of both techniques could provide advantages with respect to active monostatic Synthetic Aperture Radar (SAR).
关键词： vegetation opacity,CyGNSS,GNSS-R,land,microwave radiometry,SMAP,multi-static radar,Soil Moisture Content (SMC)
更新于2025-09-10 09:29:36
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Two-Scale Model for the Evaluation of Sea-Surface Scattering in GNSS-R Ship-Detection Applications
摘要： Ocean GNSS-R is successfully being employed to retrieve wind speed from GNSS signals scattered by the sea surface. To obtain a sufficient scattered field intensity from the ocean surface, the receiver acquires data when it is located along the specular reflection direction. However, new applications of GNSS-R are being explored, among which ship-detection. In this case, scattering from the ocean represents the clutter to be suppressed, so that a different geometry, where the GNSS signals are received in backscattering configuration, is preferable to the forward scattering one. In this new geometry, the Geometric Optics, usually employed in the GNSS-R scientific community, is often no more appropriate to model scattering from the sea surface, and different scattering models must be used. To this aim, we here introduce the Polarimetric Two-Scale Model to evaluate the intensity of the GNSS backscattered signal.
关键词： ship detection,two-scale model,GNSS-R,sea surface scattering
更新于2025-09-10 09:29:36
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Considerations on Gnss-R Carrier Phase Altimetry
摘要： The European Space Agency has recently studied, assessed or approved GNSS Reflectometry mission concepts based partly or fully on carrier phase observables for altimetry applications. Examples of these are, respectively, the GEROS-ISS experiment on board the International Space Station, the G-TERN Earth Explorer proposal or the PRETTY cubesat mission, currently in Phase B. This paper touches upon a few topics which are specific to carrier phase GNSS-R altimetry, namely, the involved geometry, the observables, the link budget (related to the aperture of the receiving antenna) and the carrier phase ambiguity resolution.
关键词： GNSS-R Carrier Phase Altimetry,GNSS Reflectometry
更新于2025-09-09 09:28:46