Title :
Numerical Simulations and Analysis of Wide-Band Range-Resolved HF Backscatter From Evolving Ocean-Like Surfaces
Author :
Toporkov, Jakov V. ; Sletten, Mark A.
Author_Institution :
Remote Sensing Div., Naval Res. Lab., Washington, DC, USA
Abstract :
Low-grazing wide-band HF radar echoes from evolving ocean-like surfaces in 2-D space are simulated employing a first-principles boundary integral equation technique. The synthesized signals achieve range resolution of about 15 m and correspond to observations with a hypothetical narrow-beam system having a 10-MHz effective bandwidth. Range-time plots of backscatter magnitude appear to contain a pattern consistent with the long surface waves. The double Fourier transform of the signal magnitude or power in range and time reveals strong harmonics located along the dispersion curve of the propagating gravity waves. The effect is discernable due to the high range resolution employed and is not predicted by the first-order Small Perturbation Method (SPM) approximation. It is explained by considering the next, second order of the SPM under certain simplifying assumptions such as perfect surface conductivity (with the Norton attenuation factor set to 1). The derived analytical expression is then used to investigate the feasibility of the surface profile retrieval from such time-varying range-resolved HF backscatter (gathered in the course of the “numerical experiment” through the exact scattering simulations). For the case of perfectly conducting sea-like surface developed under 10-m/s wind conditions, the results are very encouraging. The approach is sensitive to the surface harmonics with wavelengths far exceeding the Bragg resonance scales of the HF band. Extending this type of analysis to cases with realistic finite conductivity and/or rougher surface (assuming that the second-order SPM is still valid) will require proper accounting for ground-wave propagation effects in perturbation expressions. The study offers a glimpse into ocean observation possibilities that the wide-band HF systems can provide if and when they become a reality.
Keywords :
Fourier transforms; ab initio calculations; backscatter; boundary integral equations; echo; gravity waves; numerical analysis; ocean waves; oceanographic techniques; perturbation theory; remote sensing by radar; underwater sound; wind; 2-D space region; Bragg resonance scales; Manuscript high range resolution; Norton attenuation factor; bandwidth 10 MHz; dispersion curve; double Fourier transform; first-order small perturbation method; first-principles boundary integral equation technique; gravity wave propagation; ground-wave propagation effects; hypothetical narrow-beam system; long surface waves; low-grazing wide-band HF radar echoes; numerical simulations; ocean-like surfaces; rough surface analysis; second-order small perturbation method; surface harmonics; surface profile retrieval; time-varying range-resolved HF backscatter; wide-band HF systems; wide-band range-resolved HF backscatter analysis; wind conditions; Backscatter; Hafnium; Radar; Sea surface; Surface impedance; Surface roughness; Surface waves; Boundary integral equations; high-frequency (HF) radar; perturbation methods; sea surface electromagnetic scattering;
Journal_Title :
Geoscience and Remote Sensing, IEEE Transactions on
DOI :
10.1109/TGRS.2011.2178032