Our long-term goal is to quantify ripple and ripple field properties in response to wave and current hydrodynamic forcing and grain size variability.
Spatial Surveys of Ripple Geometry:To obtain more detailed measurements of the large scale spatial variability of ripple morphology a REMUS AUV equipped with a sidescan and a small multibeam sonar will be used. The survey will cover the depth range of the fixed instrumentation, but will have a greater along shore spatial extent, which will be used to examine ripple variability that may be caused by gradients in wave energy or bottom characteristics. Using a REMUS AUV at SAX04 showed that the 900 kHz sidescan could measure the wavelength of large (50 cm+)and small ripples (15 - 20 cm minimum wavelength) when the vehicle was traveling parallel to the ripple crests, due to the geometry of the sidescan. A pencil beam sonar was also able to measure the height of large ripples (greater than 50 cmwavelength and greater than5 cmheight) when the vehicle was traveling perpendicular to the ripple crests. Thus height and wavelength measurements could not be conducted on the same ripples as the two measurements required different vehicle paths relative to the ripple crests.Since the SAX04 surveys low cost, lower power multibeam (sufficient to mount in a small REMUS AUV) have become available from Imagenex. This will allow simultaneous measurement of ripple wavelength over a relatively wide swath using the sidescan and ripple height using the multibeam while traveling parallel to ripple crests. It will also not require the use of a expensive and fragile inertial navigation system used with the narrow beam sonar in the SAX04 ripple height measurements.