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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
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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
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[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 - Bias Impact Analysis and Calibration of Uav-Based Mobile Lidar System
摘要： Over the past few years, developments in mobile mapping technology, specifically Unmanned Aerial Vehicles (UAVs), have made accurate 3D mapping more feasible, thus emerging as an economical and practical mobile mapping platform. LiDAR-based UAV mapping systems are gaining widespread recognition as an efficient and cost-effective technique for rapid collection of 3D geospatial data. To derive point clouds with high positional accuracy, estimation of mounting parameters relating the laser scanners to the onboard GNSS/INS unit is the foremost and necessary step. In this paper, we first devise an optimal flight and target configuration by conducting a rigorous theoretical analysis of the potential impact of bias in mounting parameters of a LiDAR unit on the resultant point cloud. Then, we propose a LiDAR system calibration strategy that can directly estimate the mounting parameters for spinning multi-beam laser scanners onboard a UAV through an outdoor calibration procedure.
关键词： multi-beam laser scanners,UAV,GNSS/INS,mounting parameters,LiDAR
更新于2025-09-23 15:22:29
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[IEEE 2018 14th IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT) - Qingdao, China (2018.10.31-2018.11.3)] 2018 14th IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT) - Design of a GNSS Signal Synchronization Chip
摘要： The 1PPS timing signal sent by GNSS has high precision and stability, so it can be used as a reference signal for a variety of purposes. This GNSS signal synchronization chip can synchronize the locally produced second cycle signal with 1PPS signal, which includes a hierarchical Time-to-Digital Converter (TDC) and a two-stage phase-shifting unit. The chip is implemented in 0.18μm 1P6M CMOS technology, and power voltage of core is 1.8V and normal operating temperature range is from -40°C to 125°C.Test results show the dynamic power current at work is about 4mA, while the static power current at low power consumption is about 32μA. The minimum time resolution is about 1ns.
关键词： TDC,GNSS signal synchronization,phase-shifting
更新于2025-09-23 15:22:29
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[IEEE 2018 OCEANS - MTS/IEEE Kobe Techno-Ocean (OTO) - Kobe, Japan (2018.5.28-2018.5.31)] 2018 OCEANS - MTS/IEEE Kobe Techno-Oceans (OTO) - Coastal Ocean Wind Speed Estimation Based GNSS-Reflectometry of BeiDou GEO Satellite
摘要： Global Navigation Satellite System-Reflectometry (GNSS-R) is useful for the ocean remote sensing. It has shown promising results as altimetry, Significant Wave Height, and wind speed measurement. To retrieve the information of the ocean surface, the GNSS-R technique receive the direct signal from GNSS satellites and capture the reflected signal by GNSS-R receivers. The difference delay of the reflected signal provided difference characteristics of the ocean including wind speed information. The aim of this paper is to estimate the ocean wind speed in the coastal area using the reflected signal information. This paper used the observed data sets from 3 to 12 January 2014 collected from the Geostationary Earth Orbit (GEO) of Chinese satellite (BeiDou G1) which consist of phase I and Q component and the in situ wind speed measurement collected from buoy station. A Method based on Artificial Neural Network (ANN) technique for wind speed estimation was presented. In addition, Particle Filter (PF) based autoregressive model was used to improve the efficacy of ANN. The performance of proposed technique has evaluated by using the Root Mean Square Error (RMSE) as shown in the experimental result section.
关键词： Particle Filter,GNSS-Reflectometry,Wind Speed Estimation,ANN,BeiDou GEO satellite
更新于2025-09-23 15:22:29
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[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
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[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
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[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
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[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 - Spaceborne GNSS-Reflectometry for Ship-Detection Applications: Impact of Acquisition Geometry and Polarization
摘要： In this paper, a comparative study of spaceborne Global Navigation Satellite System (GNSS)-Reflectometry for ship detection applications is provided. The analysis is conducted by evaluating the impact of 1) the acquisition geometry and 2) the received signal polarization on ship detectability in GNSS-R data. In particular, the backscattering acquisition geometry is demonstrated to be more suitable for ship detection applications, thus allowing for the detection of 20 m-length ships. Even very large ships are hardly detectable in the conventional forward-scattering geometry. Moreover, receiving right-hand circular polarization is demonstrated to provide significant improvements of the signal-to-noise-plus-clutter with respect to the conventional left-hand circular polarization channel, conventionally exploited in GNSS-R remote sensing. The study is based on a numerical tool for the bistatic radar cross section of the ship, which is presented in a companion paper.
关键词： backscattering geometry,GNSS-Reflectometry,bistatic radar,ship detection,maritime surveillance
更新于2025-09-23 15:21:21
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[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