The Naval Research Laboratory
needed to analyze the structure of capillary and small gravity waves over a 10 cm x 10 cm area for air/ocean
energy transfer model development and to help determine reflectance characteristics of the ocean surface.
Solution
QUEST developed two sensors (scanning laser slope sensor and wave gauge array) and the associated data acquisition
systems that are mounted on a buoy for ocean deployment.The buoy is deployed
for up to 4 hours, after which the system is retrieved, and the data downloaded and analyzed. The scanning laser
slope sensor measures a 50 x 50 grid of wave slopes over a 10 cm x 10 cm square area.The 50 x 50 grid is measured at a 50 Hz rate and is used to analyze the structure capillary and small gravity waves.The high data rate allows the wave structure of the 10 cm x 10 cm area to be frozen
in time and analyzed every 20 milliseconds.The laser scanner uses a polygon
mirror to generate a laser beam that forms a raster scan pattern emanating from under the ocean surface.As the laser beam passes through the ocean surface, the beam refracts by an amount set by the wave slope.The refracted beam strikes a scatter screen above the surface and the position of
the refracted beam is measured.The steeper the wave slope the more the beam
is offset on the scatter screen.The data is post-processed to derive wave height
from slope to generate a 3D map of the ocean surface.The wave gauge array is
used to measure waves up to a meter in length.Forty vertical wires in two orthogonal
linear arrays of 20 are used to sense the wave height.The system measures the
capacitance between the wire and the surrounding water using a thin wire coating as the dielectric.The capacitance between the wire and the water increase linearly as the wire submerges.The capacitance of each of the 40 wires are measured at a 25 Hz rate and stored for retrieval after the
buoy deployment.
