Towards Nonlinear Wave Reconstruction and Prediction From Synthetic Radar Images

Abstract

The use of remotely wave sensing by a marine radar is increasingly needed to provide wave information for the sake of safety and operational effectiveness in many offshore activities. Reconstruction of radar images needs to be carried out since radar images are a poor representation of the sea surface elevation: effects like shadowing and tilt determine the backscattered intensity of the images. In [1], the sea state reconstruction and wave propagation to the radar has been tackled successfully for synthetic radar images of linear seas, except for a scaling in the vertical direction. The determination of the significant wave height from the shadowed images only has been described in [2]. This paper will summarize these methods, and provides the first results for the extension to nonlinear seas.

An improved algorithm for phase-resolved sea surface reconstruction from X-band marine radar images

“…The empirical parameter q = 0.5 is chosen in this study based on the optimization proposed by Wijaya (2016).…”

“…A simple geometric criterion is applied: a sea surface elevation at position r is visible by the radar if the radar ray, which scans the surface elevation at r, if it does not intersect any surface elevation at all distances less than r (e.g. Wijaya 2016). In obtaining synthetic radar image intensity ( , t) (Qi 2012;Qi et al 2016), we set the values of shadowing points equal to zero, change the range of not-shadowing points to a non-negative range and rescale the values into 256 Gy levels.…”

High waves in Draupner seas—Part 2: Observation and prediction from synthetic radar images

“…For the high Draupner seas, we will follow the same method, but now using the third-order nonlinear AB-code to evolve the updated sea states and to calculate a prediction. A preliminary result for reconstructing nonlinear long-crested seas has been discussed in Wijaya (2016). Some details of the procedure are now described.…”

Reconstruction and deterministic prediction of ocean waves from synthetic radar images

“…The lower visibility is due to the nonlinear effect which increases crest heights (and reduces trough depths). A preliminary result to derive the significant wave height from nonlinear long-crested waves was presented in Wijaya [2016]. The result gives us a confidence that the method can also deal with nonlinear short-crested seas.…”

“…Specifically, we will show the performance for a sea identified as number 13 from an ensemble of 40 seas (see van Groesen et al [2017]) for the area and time in which a freak-like wave train from north to south approaches the radar, for which a shift in coordinates is taken to have the origin in line with the direction of the train. A preliminary result for reconstructing nonlinear long-crested waves has been discussed in Wijaya [2016].…”