An algorithm for the extraction of ocean wave spectra from narrow beam HF radar backscatteer

Howell, Randy Keith (1990) An algorithm for the extraction of ocean wave spectra from narrow beam HF radar backscatteer. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (42MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

An algorithm is developed and tested to interpret ocean wave spectra from the backscatter return of one or more narrow beam HF radars. The basis of this measurement is the inversion of the integral equation representing the second order radar cross section of the ocean surface (Barrick and Lipa, 1986; Srivastava, 1984; Walsh and Howell, 1990). This equation is numerically inverted by approximating it as a matrix equation and factorizing the resultant kernel matrix using a singular value decomposition to obtain its pseudo-inverse. -- Due to the limitations of the assumption used to linearize the integral equation, the proposed inversion algorithm is best suited for general use at high HF frequencies (≈ 20 to 30 MHz). However, this algorithm may still be applied for the crucial task of monitoring large sea state conditions at even very low HF frequencies (< 10 MHz). -- As a test of this algorithm, comparisons are made between wave spectrum estimates obtained from a WAVEC buoy and a set of two 25.4 MHz ground wave radars that were deployed during the 1986 Canadian Atlantic Storms Program (CASP). Overall, the results of this experiment have been positive and have demonstrated both the basic feasibility of the inversion algorithm and the wave sensing capability of HF radar. -- When using the data of a single radar, the principal information that can be obtained is the nondirectional or one-dimensional (1-D) wave spectrum. Although directional information may be obtained from a single radar it suffers from a left/right directional ambiguity. In general, the comparison of single radar estimates for the 1-D spectrum with those of the buoy at CASP have been good. This is demonstrated by the reasonable average difference from the buoy of ≈ 15% for significant waveheight estimates. This figure is roughly the same for all cross section models. -- When using the data of two radars, not only can more accurate estimates of the 1-D spectrum be obtained but full directional information as well. The comparison of dual-radar wave spectrum estimates with those of the buoy at CASP have been very good. For the Walsh and Howell (1990) cross section model, dual-radar significant waveheight estimates differed from the buoy by only 4.6% on average. For the Barrick and Lipa (1986) and Srivastava (1984) models this average difference is 9.1%. For all models, the average difference for dominant direction estimates is ≈ 10°. -- Although all cross section models produced estimates that correlated well with the buoy, it was the Walsh and Howell (1990) model which consistently provided the best agreement. This would seem to indicate that the Walsh and Howell theory provides a better model for the radar spectrum. Due to the somewhat small size of the CASP data set it is not yet possible to be statistically confident of this finding.

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