Simulations Of Radar Backscatter Research Articles

Uncertainty Estimates for SeaSonde HF Radar Ocean Current Observations

Abstract HF radars typically produce maps of surface current velocities without estimates of the measurement uncertainties. Many users of HF radar data, including spill response and search and rescue operations, incorporate these observations into models and would thus benefit from quantified uncertainties. Using both simulations and coincident observations from the baseline between two operational SeaSonde HF radars, we demonstrate the utility of expressions for estimating the uncertainty in the direction obtained with the Multiple Signal Classification (MUSIC) algorithm. Simulations of radar backscatter using surface currents from the Regional Ocean Modeling System show a close correspondence between direction of arrival (DOA) errors and estimated uncertainties, with mean values of 15° at 10 dB, falling to less than 3° at 30 dB. Observations from two operational SeaSondes have average DOA uncertainties of 2.7° and 3.8°, with a fraction of the observations (10.5% and 7.1%, respectively) having uncertainties of >10°. Using DOA uncertainties for data quality control improves time series comparison statistics between the two radars, with r2=0.6 increasing to r2=0.75 and RMS difference decreasing from 15 to 12 cm s−1. The analysis illustrates the major sources of error in oceanographic HF radars and suggests that the DOA uncertainties are suitable for assimilation into numerical models.

Evaluation of Sub-Kilometric Numerical Simulations of C-Band Radar Backscatter over the French Alps against Sentinel-1 Observations

This study compares numerical simulations and observations of C-band radar backscatter in a wide region (2300 km 2 ) in the Northern French Alps. Numerical simulations were performed using a model chain composed of the SAFRAN meteorological reanalysis, the Crocus snowpack model and the radiative transfer model Microwave Emission Model for Layered Snowpacks (MEMLS3&a), operating at a spatial resolution of 250-m. The simulations, without any bias correction, were evaluated against 141 Sentinel-1 synthetic aperture radar observation scenes with a resolution of 20 m over three snow seasons from October 2014 to June 2017. Results show that there is good agreement between observations and simulations under snow-free or dry snow conditions, consistent with the fact that dry snow is almost transparent at C-band. Under wet snow conditions, although the changes in time and space are well correlated, there is a significant deviation, up to 5 dB, between observations and simulations. The reasons for these discrepancies were explored, including a sensitivity analysis on the impact of the liquid water percolation scheme in Crocus. This study demonstrates the feasibility of performing end-to-end simulations of radar backscatter over extended geographical region. This makes it possible to envision data assimilation of radar data into snowpack models in the future, pending that deviations are mitigated, either through bias corrections or improved physical modeling of both snow properties and corresponding radar backscatter.

The development of HJ SAR soil moisture retrieval algorithm

Four satellites with S-band synthetic aperture radar (SAR) onboard, along with four optical satellites, form the Huan Jing (HJ) constellation, which consists of the Chinese Environment and Disaster Monitoring Satellites that are designed for fast monitoring of the dynamics of soil moisture and other environmental variables. A 24-hour revisit time of the future four HJ SAR satellites enables an estimation of soil moisture change by using multi-temporal observations. The algorithm for estimating soil moisture change has been developed for HJ SAR in four steps: (a) theoretical simulation of radar backscattering from vegetated and bare soil with first-order scattering model and the Advanced Integral Equation Method (AIEM); (b) vegetation correction based on a simplified scattering model and ancillary optical observations of the HJ constellation; (c) simplification of a radar backscattering model for bare soil to separate the effects of surface roughness and soil moisture; and (d) estimation of soil moisture change from multi-temporal SAR observations. The comparison between field measurements and soil moisture retrieved by the proposed algorithm demonstrates good accuracy.

Study of Millimeter-Wave Radar for Helicopter Assisted-Landing System

Landing helicopters on rough unprepared terrain has always been considered hazardous, since the massive dust cloud generated by wind drafts from the helicopter's rotors completely obstructs the pilot's view of the landing area. This article presents a performance assessment of a proposed millimeter-wave (MMW) three-dimensional imaging radar system, specifically meant for helicopter assisted landing. The assessment includes simulation of radar backscattering from the underlying rough terrain, in addition to the signal attenuation and scattering from dust clouds generated by the helicopter's rotors. Terrain scattering is simulated in two steps: 1) generation of a two-scale random rough surface according to prescribed statistics of a large-scale undulation and a small-scale surface roughness; and 2) simulation of the returned signal, including the effects of the real-aperture radar parameters and the terrain-backscatter response. Details of the three-dimensional imaging algorithm are presented. Single-scattering theory is used to simulate the effects of a dust cloud - including signal attenuation and backscatter clutter generation - on the radar's performance. It is shown that operating in the upper millimeter-wave regime (70 GHz-220 GHz) is the most practical solution for a compact, high-resolution, three-dimensional imaging system for this problem.

Seasonal climatic forcing of alpine glaciers revealed with orbital synthetic aperture radar

AbstractThe evolution of four dynamic radar glacier zones at the surface of an alpine icefield in British Columbia is monitored using a time series of 35 First European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) images acquired from 1992 to 1994. These zones result from changing wetness and textural properties, and appear to represent: (1) cold snow with no liquid water present; (2) an initial melt front with an upper boundary near the elevation of the 0° isotherm; (3) metamorphosed, rapidly melting first-year snow with a rough or pitted surface; and (4) bare ice. This interpretation is aided by temperature and runoff data, air photographs and field measurements of snowpack properties acquired with two ERS-1 SAR scenes, ice-surface elevations derived from 1:50 000 topographic maps and simulations of radar backscatter from a geometric optics model of surface scattering. Meltwater production is affected by the development of zones (2), (3) and (4), which form, migrate up-elevation and disappear each year between April and September.

Seasonal climatic forcing of alpine glaciers revealed with orbital synthetic aperture radar

AbstractThe evolution of four dynamic radar glacier zones at the surface of an alpine icefield in British Columbia is monitored using a time series of 35 First European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) images acquired from 1992 to 1994. These zones result from changing wetness and textural properties, and appear to represent: (1) cold snow with no liquid water present; (2) an initial melt front with an upper boundary near the elevation of the 0° isotherm; (3) metamorphosed, rapidly melting first-year snow with a rough or pitted surface; and (4) bare ice. This interpretation is aided by temperature and runoff data, air photographs and field measurements of snowpack properties acquired with two ERS-1 SAR scenes, ice-surface elevations derived from 1:50 000 topographic maps and simulations of radar backscatter from a geometric optics model of surface scattering. Meltwater production is affected by the development of zones (2), (3) and (4), which form, migrate up-elevation and disappear each year between April and September.

Simulation of radar backscattering in a ripple tank

A ripple tank study of wave motion associated with the wave formation in the vicinity of a cone-sphere is discussed. The experimental test facility is described. Included in the interpretation of the ripple tank experiments are the wave formations in the shadow region of the cone-sphere showing traveling and creeping waves.