SHOWEX

The SHOWEX (Shoaling Waves Experiment) took place from October to December 1999 at Duck and Corolla, North Carolina. We were funded by the US Office of Naval Research to provide wave measurements from the deployment of the University of Miami OSCR system.

The map below shows the area together with various instruments deployed there. The dotted area shows the radar coverage, "Master" and "Slave" sites show actual location of the two OSCR radars. Some results have been published in the Journal of Atmospheric and Oceanic Technology.

Below are some preliminary results.

Time series

As indicated in the chart below, the green and the red lines represent the significant waveheight as estimated by the buoy (X1 on the map above) and the radar. Gaps in radar curve occur either when there was no data due to some hardware problems or when the quality of data at the buoy location is poor. The large differences seen on 2 Dec are due to antenna sidelobes picking up large current signals away from the measurement position thus corrupting the wave measurements.

Hs maps

The next figures are two sample maps of the observed area with colour-coded significant waveheight and mean wave directions (arrows are pointing in the direction towards which the waves are travelling).

Wave spectra

One of the advantages of the radar technique of collecting information on the sea surface is that it provides the full directional wave-spectrum with a very good (approximately 1 sq. km) resolution. Presented below are two sample wave spectra for the same dates and times as the maps above at a location near the coast approximately in the middle between the two radars.

The black arrows are pointing in the direction in which the wind is blowing. The spectrum on the left shows a swell wave with a peak frequency of about 0.9Hz propagating towards the north-west and a wind wave contribution with a peak frequency of about 0.19Hz towards the north-east.

Mean directions measurements, as shown on the maps, average these contributions so the varying mean directions in the map above reflect a changing balance in the relative energy of these two components of the wave field across the measurement region.

On the right the spectrum is dominated by wind waves with a peak at about 0.15Hz towards the south-west. This persists across the whole region as is seen in the map above.

To request a copy of the HF radar CDs (availability subject to staff time constraints) please email: l.wyatt@sheffield.ac.uk.