Max Hammond Wavetank

The Max Hammond Wavetank at SRI is a state-of-the-art facility capable of hosting experiments over a wide range of nearshore research topics. The facility has been used extensively for studying the potential detectability of submerged tethered objects, and is currently being remodeled to study wideband shallow water wave evolution.

About the Wavetank

The wavetank is 20 m long, 1.3 m wide, and 1.5 m high. It is built with glass walls (for optimum optical access) carried on a steel frame. Waves in the tank are created by a sector-carrier designed shallow water wavemaker built by Edinburgh Designs. The wavemaker is capable of producing arbitrary wave profiles with a dominant wave frequency between 0.2 and 1.5Hz. Data can be obtained using several different measuring systems, including capacitative wave height gauges, particle image velocimetry (PIV), and Ku-band radar.
New linearly sloping beach

Current Research Results

Previous research has shown the presence of a number of different types of surface signatures due to hydrodynamic phenomena associated with the presence of shallowly submerged tethered objects. The present research attempts to set bounds on the potential detectability of these features using a simple microwave radar setup. In these experiments, a tethered sphere was placed at different submergences in an incident wave field in the SRI Max Hammond Wavetank. The water surface above the sphere was then illuminated by a quasi-monostatic radar operating at 18GHz. Two incident wave spectra were used: a monochromatic spectrum for repeatable experiments, and a JONSWAP spectrum for more realistic experiments. The radar return data were studied as a function of sphere submergence to determine: 1) the strength of the radar return of each signature mechanism for monochromatic incident wave spectra, and 2) the depth dependence of the radar return for JONSWAP incident wave spectra.

Our results show that for monochromatic incident wave spectra, the strength of radar returns falls off dramatically as the sphere submergence increases, which can be directly traced to the weakening of different surface signature mechanisms. For JONSWAP incident wave spectra, the strength of the radar return falls off gradually as the sphere submergence increases until a critical value is reached. This critical submergence value is shown to be the submergence at which the frequency of occurrence of broaching and near-broaching surface signature events drops to nearly zero. The radar return strength then falls off rapidly as the sphere submergence is further increased. These results show that mine detection by radar is certainly possible over a range of mine submergences.

Future Plans

• Shallow water wave and bore propagation studies

For further information:
The Max Hammond Wavetank is managed by Paul Piccirillo. Inquiries on collaboration and research on other applications are invited.

Paul Piccirillo
SRI International
333 Ravenswood Avenue, Menlo Park, CA 94025
Phone: (650) 859-2809