The Need

Instantaneous and predictive information about sea waves is critical to forecast ship motion, which is needed for many applications, such as cargo transfer and helicopter landing at sea. Scientists use radar to obtain this information, but several challenges must be overcome to develop a robust wave measurement system. In particular, the “low grazing angle” geometry of ship-based or ground-based radar measurements at long ranges complicates the physics of the surface scattering process and inhibits inversion of radar measurements into sea wave information. To improve forecasting of ship movement, it is necessary to develop a robust method to measure sea wave properties that address issues created by a "low grazing angle."

The Technology

Researchers at The Ohio State University, led by Dr. Joel Johnson, have developed an X-band marine radar system for wave height and velocity measurements. This radar system is based on the coherent-on-receive approach with a traditional marine navigation radar having a 25 kW magnetron-based transmitter. In addition, the horizontally polarized antenna of the traditional radar was replaced with a vertically polarized antenna due to the increased sea backscatter returns expected in “VV” as opposed to “HH” polarization. The radar provides sea surface backscattered power and velocity measurements to ranges of approximately 4 km. A “wavefield processor” algorithm is applied to combine radar measurements at multiple azimuth angles into an improved measurement of sea waves and velocities. Thus, formed sensor data is fed into the ship motion prediction subsystem, which in turn provides the short term forecast of the relevant ship motion parameters.

Commercial Applications

• Cargo Transfer
• Radar Systems
• Ship Navigation and Control
• Offshore Platform Operations

Benefits/Advantages

• The radar used here measures sea wave information more precisely than existing systems
• Enables future prediction of ship motions based on current and past measurements of the wavefield surrounding the ship
• Improved measurement of sea waves and velocities