Remote sensing

Remotely sensed surface velocity fields (approx. 200 by 200 m area) spanning the surf zone are calculated using video particle-image-velocimetry (PIV) by Tom Lippmann (Ohio State University, funded by ONR). Remote images are obtained by a motion compensated video camera mounted on a 3-point, tethered combined kite (approx. 2 x 4 m) and helium balloon, called a Helikite, at an elevation of approximately 150-m. The kite gives stable lift when the wind is blowing, and the helium balloon gives lift when the wind in not blowing. The images are acquired in real time using a RF telemetry link to the ground. Surface flow is mapped observing time series of foam, bubbles, biota and sediment visible on the water surface, and using PIV techniques to detect advection displacements. Surface flow patterns are quantified by interrogating pairs of images separated in time by a small amount. Video images are transformed into ortho-normal plan view using image-to-ground transformation geometry, and then convolved with a small (order 2 m wide) correlation kernel to determine feature displacements. The data are sampled at O(1 Hz) and then averaged to obtain estimates of the surface velocity field (Shore and Lippmann, 2000).

Figure1 Deployment of heli-kite by Tom Lippmann, Jennifer Shore and Ed Thornton


Most recent update of this page: 23 December 2002 
Comments? Contact Web Page Administrator
Material contained herein is made available for the purpose of peer review and discussion and does not necessarily reflect the views of the Department of the Navy or the Department of Defense.

Privacy and Security Notice
External Links Notice