Date of Award

1996

Degree Type

Thesis

Degree Name

Master of Science in Oceanography

Department

Oceanography

First Advisor

Tetsu Hara

Abstract

As part of the High-Resolution Remote Sensing Experiment, long-wave height is estimated from a moving catamaran using pitch-rate and roll-rate sensors, a three-axis accelerometer, and capacitive wave wires. The wave spectrum in the frequency band roughly from 0.08 Hz to 0.3 Hz is verified by independent buoy measurements. A scanning-laser slope gauge, located near the long-wave height sensors, is used to measure gravity-capillary wave slope. These measurements are then combined to study the modulation of the mean-square slope of gravity-capillary waves due to long gravity waves. This modulation is characterized with the hydrodynamic Modulation Transfer Function (MTF) and the coherence function. Coherence estimates are found to be generally less than 0.05, indicating that the modulation of short-wave slope by long waves is weak compared to the total short-wave mean-square slope. The hydrodynamic MTF estimates corresponding to coherence greater than 0.03 have reasonable statistical stability, and have magnitude 4 to 9 and phase 0° to 70°. These results are in rough agreement with previous measurements using X-band microwave radar.

The Data-Adaptive Spectral Estimator is extended to include the Doppler-shifting effects of a moving platform. The method is used to estimate the directional frequency spectrum of long waves for wave-wire measurements from the Risø Air-Sea Experiments. The propagation direction of the peak wind waves compares well with the measured wind direction. A numerical test is conducted which shows that the method is able to detect the presence of secondary waves propagating in a different direction, such as reflected waves, even if they contain significantly less energy than the dominant waves.

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