Ocean Engineering

Civil, Construction and Environmental

Engineering Department

Marine radar wave observations at the mouth of the Columbia RiverMerrick C. Haller, H. Tuba Merrick C. Haller, H. Tuba ÖÖzkan-Haller, Patricio Catalan,zkan-Haller, Patricio Catalan, J.D. Lentine, Justin Brodersen, Hai-Ying Jao, and Lisa Andes,J.D. Lentine, Justin Brodersen, Hai-Ying Jao, and Lisa Andes,

Civil and Construction Engineering, College of Oceanic & Atmospheric Sciences, Oregon State UniversityCivil and Construction Engineering, College of Oceanic & Atmospheric Sciences, Oregon State University

New Observing Technologies for the NANOOS-Pilot ProjectConventional marine radar technology is being adapted as a tool for wave observing in coastal areas. Recently, researchers within the Ocean Engineering Program at Oregon State University in cooperation with Imaging Science Research, Inc. have developed a high-resolution wave observation system using an X-band marine radar with a customized data acquisition system. These observation systems offer the potential for providing real-time wave information over large nearshore areas (~20 km2). We expect that remote sensing technology such as this can provide a considerable benefit at navigational entrances where wave conditions are often hazardous and highly variable and where traditional in-situ sensors are often ineffective or cannot be safely deployed.

Top left: Aerial photo of the north jetty; Top right: Temporary radar tower and support vehicles; Bottom left: View of waves at Benson Beach during the Jan. 16, 2006 storm. Bottom right: View of Benson Beach and north jetty from atop the radar tower.

Top: Portions of single radar images expanded to show the area near Benson Beach, WA. Waves were consistently breaking as far out as 1 km from shore leading to the bright radar returns as far out as the end of the north jetty.Bottom: Frequency spectra calculated from radar pixel time series located approximately 600 m offshore of Benson Beach. Estimated peak periods are compared with those measured by NDBC Buoy 46029 located approximately 37 km to the southwest.

North Head(USACE camera station)

south jetty

north jetty

Sampling capabilitiesImage frequency - 44 rotations per minute (1 image every 1.36 seconds)

Image resolution - 3 m in range, 1o in azimuth

Image footprint - 6 km radius (adjustable)

Duration - user specified, typical image sequences are 15 min long (640 images) and repeated every hour

Radar image time series provide a synoptic picture of the ocean surface over a large area. This is similar to having a wave buoy located every 10 meters! For wave analysis, image pixels from areas of interest are selected and processed with Fourier analysis routines and wave frequency and direction information can be determined at essentially the same resolution as the image pixels. This gives a detailed description of the spatial variability of wave conditions throughout the area. In addition, with calibration, radar systems can provide direct estimates of wave heights and signify the presence of breaking waves. Finally, large scale ocean density fronts can be identified in these images due to the changes in radar scattering they induce.

Radar images from the mouth of the Columbia River. Images span 6 km in range distance from the radar (located at center of each image). The left image covers 170 degrees in azimuth, the right covers 260 degrees. North Head is visible directly north from the radar, to the south are the Columbia River jetties.

Image rectificationRaw image

Rectified image

In order to geo-locate the wave data, each radar image needs to be rectified to the local real-world coordinate system. The figure at left shows a raw radar image and the image at left is after partial rectification. Full rectification requires GPS measurements of Ground Control Points visible in the images (such as the jetties) and interpolation onto a uniform grid.

Radar - Tp=10 secNDBC 46029 - Tp=10 sec

Radar - Tp=16.7 secNDBC 46029 - Tp=13 sec

Radar - Tp=16.0 secNDBC 46029 - Tp=14.3 sec

Radar - Tp=13.1 secNDBC 46029 - Tp=14.3 sec

Wave Analysis

Wave Modeling

Left: Wave heights predicted by the SWAN nearshore wave model, Jan. 17th 1pm.Center: Predicted wave directions, colors represent degrees from North.Right: Corresponding radar image from Jan. 17th 1pm.

The Future

North jetty

The flow out of the Columbia River varies depending on the stage of the tide and during periods of strong currents the wave field can be significantly modified. For example, during strong ebb flows waves over the Columbia River Bar are highly steepened and often break, which leads to dangerous navigational conditions.

Left: Radar image taken Jan 18th during a mid-tide condition when currents were not strong shows little breaking offshore.Right: Radar image taken on Jan 18th at 705PM during a strong ebb tide current shows a strong increase in wave breaking just offshore of the river mouth.

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azimuth

Wave heights (m) - SWAN Wave directions - SWANN

In the near term, we are assembling a mobile radar trailer and tower similar to the one depicted at right. The tower is retractable and will extend 30 ft high, which will allow the radar to see over dunes and jetties. We are also considering a renewable energy power system using a combination of solar and wind power technologies. When completed, the mobile system will allow for long-term radar deployments and radar wave observations can be made available in real-time to the NANOOS observatory.

Finally, model-data comparisons are ongoing in an effort to calibrate a high-resolution wave modeling system for the Columbia River mouth.