Wind Direction Estimation by Deconvolution of GNSS Delay–Doppler Maps: A Simulation Analysis

Signatures of directional wind waves are discovered after deconvolution of delay–Doppler maps in Global Navigation Satellite System reflectometry from space. The simulation study and the proposed algorithm demonstrate that wind direction can be, in principle, retrieved in the presence of thermal noise and speckle. The method is based on a least squares approach where an overdetermined system of equations is solved with respect to wind direction assuming that sea surface mean square slopes have been previously estimated. Performance is assessed on simulated data, where the system geometry is defined according to a realistic ocean scattering scenario. The algorithm accuracy is investigated with respect to different sizes of the observable and with respect to speckle and thermal noise

A location scale based CFAR detection framework for FOPEN SAR images

The problem of target detection in a complex clutter environment, with Constant False Alarm Ratio (CFAR), is addressed in this paper. In particular an algorithm for CFAR target detection is applied to the context of FOliage PENetrating (FOPEN) Synthetic Aperture Radar (SAR) imaging. The extreme value distributions family is used to model the data and exploiting the location-scale property of this family of distributions, a multi-model CFAR algorithm is derived. Performance analysis on real data confirms the capability of the developed framework to control the false alarm probability

Simulation-Based Feasibility Analysis of Ship Detection Using GNSS-R Delay-Doppler Maps

In this article, we carry out a simulation analysis of ship detection via Global Navigation Satellite System-Reflectometry (GNSS-R) delay-Doppler map (DDM). The GNSS-R DDM simulator used here is a modified version of an algorithm conceived for the generation of GNSS-R DDMs of the sea surface. The new algorithm is based on an analytical model for the radar cross section of ships and is able to properly account for the presence of ship targets within the scene. The proposed GNSS-R DDM simulator is, then, exploited for assessing the viability of GNSS-R in ship detection applications at low incidence angles, where the adopted scattering models provide accurate results. The aim of the implemented simulation setup is to analyze what are the preferable conditions for ship detection using standard GNSS-R signal processing chain receiver and compare typical forward left-hand circularly polarized GNSS-R systems with nonstandard backward right-hand circularly polarized (RHCP) GNSS-R. The simulation study is two fold: First, detection performance is evaluated at spaceborne and airborne altitudes for both polarization channels under favorable detection conditions. Then, visibility of ship targets is assessed in terms of their location within the DDM. Simulation results show that ship detection is problematic when using satellite data, whereas interesting results are achieved at airborne altitudes, provided that the aircraft is approximately between the GNSS satellite and the target, and that appropriate RHCP polarization is probed. In such configurations, signal-to-noise-ratios larger than 10 dB are obtained with airborne receivers collecting the RHCP signal

IEEE 4003-2021

27 páginasThe scope of this effort is to develop a standard for data and metadata content arising from spaceborne global navigation satellite system-reflectometry (GNSS-R) missions, which uses GNSS signals as signals of opportunity, as described in “The IEEE SA Working Group on Spaceborne GNSS-R: Scene Study.” In particular, this standard would provide a means for describing: a) The terminology assigned to GNSS-R data and products, such as the product levels. b) The structure and content of the data. This includes, but is not limited to, units of measure, data organization, data description, data encoding, and data storage format. c) The metadata. This includes and is not limited to metadata, methods and algorithms applied to the data, parameters related to the algorithms, citation information, instrument calibration and characterization, and description of the input signals. The purpose of this standard is to provide a set of specifications and recommended practices that can be used to describe any known and future spaceborne GNSS-R data set, allowing users to work with different GNSS-R data sets at the same time. The definition of such standard would also allow any software that uses these data to fully operate and ingest any spaceborne GNSS-R input data as they will conform to the same standard

Simulation of L-Band Bistatic Returns From the Ocean Surface: A Facet Approach With Application to Ocean GNSS Reflectometry

We present the implementation of a facet-based simulatorto investigate the forward scattering of L-band signalsfrom realistic sea surfaces and its application to spaceborne ocean Global Navigation Satellite System (GNSS) Reflectometry. This approach provides a new flexible tool to assess the influence of the ocean surface roughness on scattered GNSS signals. The motivation stems from the study by Clarizia et al., which revealed significant differences between delay–Doppler maps (DDMs) obtained from UK-DMC satellite data and DDMs simulated with the Zavorotny–Voronovich (Z-V) model. Here, the scattered power and polarization ratio (PR) are computed for explicit 3-D oceanwave fields, using a novel implementation of the Kirchhoff approximation (KA), which we call the Facet Approach (FA). We find that the FA is consistent with the full KA and the Geometrical Optics (GO) used in the Z-V model, while being less computationally expensive than the KA and able to represent polarization effects not captured by the GO. Instantaneous maps of the bistatic normalized radar cross section computed with the FA show clear patterns associated with the underlying waves. The wave field is particularly visible in the PR, indicating that the scattering is generally dominated by the HH component, particularly fromocean wave troughs. Polarization effects show, for the first time, a strong correlation to the explicit sea surface from which the scattering originated. DDMs of the scattered power computed with the FA reveal patchy patterns and power distributions that differ from those obtained with Z-V and show closer similarities with observed DDMs from UK-DMC

GNSS-R altimeter based on Doppler multi-looking

Measuring ocean mesoscale variability is one of the main objectives of next generation satellite altimeters. Current radar altimeters make observations only at the nadir sub-satellite ground track, which is not sufficient to sample the ocean surface with the required spatial and temporal sampling. The GNSS-R concept has been proposed as an alternative observation system in order to overcome this limitation, since it allows performing altimetry along several points simultaneously over a very wide swath. Latest proposed GNSS-R altimeter configurations allow measuring sea height with an accuracy of few decimeters over spatial scales of 50-100 km, by means of a single-pass. This paper proposes an innovative processing and retracking concept for GNSS-R altimeters based on the acquisition of the full delay-Doppler map (DDM), which allows to acquire multiple waveforms at different Doppler frequencies, whose footprints are located outside the typical pulse-limited region. The proposed processing adapts the Synthetic Aperture Radar (SAR) delay-Doppler concept of spaceborne radar altimeters for use in a GNSS-R system. This processing yields additional multi-look with respect to conventional GNSS-R concepts and translates into an improvement of the altimetry performance estimated to be at least 25%-30%, and even higher, depending on the wanted along-track spatial resolution. The proposed processing can also provide measurements with high spatial resolution at best possible performance, and more generally, offers various possibilities for optimal trade-off between spatial-resolution and height estimation accuracy.Peer ReviewedPostprint (published version

GNSS-R altimeter based on Doppler multi-looking

Measuring ocean mesoscale variability is one of the main objectives of next generation satellite altimeters. Current radar altimeters make observations only at the nadir sub-satellite ground track, which is not sufficient to sample the ocean surface with the required spatial and temporal sampling. The GNSS-R concept has been proposed as an alternative observation system in order to overcome this limitation, since it allows performing altimetry along several points simultaneously over a very wide swath. Latest proposed GNSS-R altimeter configurations allow measuring sea height with an accuracy of few decimeters over spatial scales of 50-100 km, by means of a single-pass. This paper proposes an innovative processing and retracking concept for GNSS-R altimeters based on the acquisition of the full delay-Doppler map (DDM), which allows to acquire multiple waveforms at different Doppler frequencies, whose footprints are located outside the typical pulse-limited region. The proposed processing adapts the Synthetic Aperture Radar (SAR) delay-Doppler concept of spaceborne radar altimeters for use in a GNSS-R system. This processing yields additional multi-look with respect to conventional GNSS-R concepts and translates into an improvement of the altimetry performance estimated to be at least 25%-30%, and even higher, depending on the wanted along-track spatial resolution. The proposed processing can also provide measurements with high spatial resolution at best possible performance, and more generally, offers various possibilities for optimal trade-off between spatial-resolution and height estimation accuracy.Peer Reviewe