Test of the Vector Slope Gauge at Duck, North Carolina, 1995.

We performed a successful experiment to verify performance of the revised Vector Slope Gauge (VSG) and Ku-band scatterometer. We made measurements of the two orthogonal components of the ocean surface slope at Duck Pier during the second week of December 1995 with the VSG. The radar backscatter measurements at Ka band (VSG) and Ku band were of the same area on the ocean surface. Using the VSG-measured slopes, we determine the primary wave direction, power-slope modulation, and an estimate of the wind speed. Our measurements show strong agreement to the US Army Field Research Facility's (FRF) comparable measurements of waveheight, wave period, wind speed, and wave direction. Our new Autoregressive (AR) technique examines individual cycles of the primary wave. The powerful AR method allows us to see the non-linearities associated with each wave cycle instead of the traditional frequency dissecting when using the modulation transfer function (MTF). The AR method does not have any restriction to the primary wave direction. We illustrate the usefulness of the VSG by applying the AR technique to the VSG slope measurement. The experiment at Duck Pier proved the slope measuring concept of the VSG. We believe the unique VSG surface slope measurement, in conjunction with the AR technique, will result in new insights into ocean modeling for better interpretation of SAR images. We also believe the VSG will be an important tool for oceanographers as a wave direction finder and tool for slope measurements. To reap the full scientific potential of the proven, fully operational VSG, we need to conduct a tower experiment in the open ocean with other participants. We are excited by the Duck Pier results and look forward to using the proven VSG in the full open ocean environment.