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M. R. Belmont and P. Ashwin

Abstract

Shallow-angle lidar offers an attractive approach to acquiring spatial profiles of sea waves, which are of value in both oceanographic research and practical engineering applications, such as in the control of wave energy capture devices and for a variety of vessel operations. However, the wave elevation values produced by shallow-angle lidar are inevitably nonuniformly distributed in space and, given that most processing algorithms require uniformly sampled data, an equivalent set of uniformly distributed data must be derived from the lidar measurements. A new class of algorithm is introduced to achieve this goal and applied to experimental shallow-angle lidar data. Compared to traditional methods the new approach has advantages in terms of both computational cost and the degree of nonuniformity that can be accommodated.

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M. R. Belmont, J. M. K. Horwood, R. W. F. Thurley, and J. Baker

Abstract

A lidar scanning system is described that is primarily designed to measure sea wave shape. The device is capable of measuring real-time spatial profiles over distances of hundreds of meters, and as the lidar must inevitably operate from modest elevations (e.g., from a vessel’s masthead), it is inherently a very shallow angle metrology device. This results in a highly nonuniform distribution of the wave elevation values. The vertical and horizontal resolution is primarily set by the characteristics of the optical system employed and range/data capacity is set by signal-to-noise ratio considerations. Illustrative data are presented as consecutive profiles taken 0.2 s apart for highly trochoidal waves under conditions where the height was recorded to ±0.03 m and horizontal sample separation to ±0.025 m. A comparison is presented with traditional wave staff measurements.

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M. Al-Ani, J. Christmas, M. R. Belmont, J. M. Duncan, J. Duncan, and B. Ferrier

Abstract

A number of maritime operations can benefit from a short-term deterministic sea wave prediction (DSWP). Conventional X-band radars have recently been shown to provide a low-cost convenient source of two-dimensional wave profile information for DSWP purposes. However, such rotating radars typically introduce temporal smearing into the data, which introduces errors when traditional Fourier transform–based wave prediction methods are used. The authors report on a new approach for DSWP that avoids such errors. Furthermore, it is not susceptible to the condition number problems that arise with any form of direct or indirect inversion-based approaches. Extensive numerical analyses are conducted to illustrate the effect of the mixed space–time nature of the data on DSWP and the efficiency of the proposed technique to handle it.

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M. R. Belmont, J. Christmas, J. Dannenberg, T. Hilmer, J. Duncan, J. M. Duncan, and B. Ferrier

Abstract

For a number of maritime tasks there is a short time period, typically only a few tens of seconds, where a critical event occurs that defines a limiting wave height for the whole operation. Examples are the recovery of fixed and rotary winged aircraft, cargo transfers, final pipe mating in fluid transfer operations, and launch/recovery of small craft. The recovery of a 30-t rescue submersible onto a mother ship in the North Atlantic Treaty Organization (NATO) Submarine Rescue System is a prime example. In such applications short-term deterministic sea wave prediction (DSWP) can play a vital role in extending the sea states under which the system can be safely deployed. DSWP also has great potential in conducting experimental sea wave research at full scale. This report explores the feasibility of using data from an experimental wave profiling radar in achieving DSWP. The report includes theory, simulation, and field testing. Two forms of DSWP are employed: a fixed point system based upon a restricted set of wave directions from which some success is obtained and the other a fully two-dimensional technique that requires further development. The main finding is that using wave profiling radar for DSWP offers promise but requires improvements both to the spatial reliability and the resolution of the wave profiling radar and to the temporal resolution of its sweep before the technique can be considered to be viable as a usable tool.

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