Ship-Based Observations of Ocean Waves Using Multiple X-Band Radars Christa McKelvey, Shanka Wijesundara, Andrew O’Brien, Graeme Smith, Joel T. Johnson, David R. Lyzenga (1) Department of Electrical and Computer Engineering - ElectroScience Laboratory, Ohio State University, Columbus, Ohio (1) Department of Naval Architecture and Marine Engineering, University of Michigan, Ann Arbor, Michigan

2 Short term forecasting of sea waves is possible by combining radar measurements with methods for predicting sea surface evolution in time X-Band radar is particularly interesting for this application Already widely used in marine navigation Cost effective solution and simple system deployment Two primary options available to date are based on: Radar backscattered power measurements Measurement of the velocity (requires coherent radar or application of coherent-on-receive techniques) Introduction

3 Koden MDS-63R Marine Radar 25 kW peak output power (non-coherent) Operating Frequency 9.41 GHz ± 30 MHz Ethernet Interface for Control H-Pol Antenna Instrument Description

4 Modifications: V-Pol antenna for better sea wave scattering sensitivity Stable Local Oscillator (LO) for improved Doppler measurements IF signal conditioning Added data acquisition system: Dual channel 16-bit 160 MSPS Mean phase removal processing to achieve coherence Instrument Description

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6 Radars installed on RV Melville Preliminary test measurements were performed over the period Sept. 6 to Sept Experiment Setup Several in-situ sensors available for “ground truth” validation Small boat with a radar reflector was used for validation of Doppler velocity calculations Campaign includes a variety of wind and wave conditions

7 Successful measurements of modulations in both backscattered power and Doppler associated with waves can be observed Relative radial Doppler fields are calculated up to 1 km in range, using IF power measurements Results: Doppler Measurements To produce a relative Doppler velocity field, mean phase removal processing is used to remove pulse-to- pulse variations in magnetron phase, and velocities associated with host ship motion

8 Maximum range to which waves are observable is a function wind speed Low wind conditions (< 5 m/s) can present a performance challenge for radar wave measurements However, wave information is present to several hundred meters even in the lowest wind conditions Results: Wind Speed Effects

9 To validate Doppler velocity calculations, data from a small boat with a high RCS reflector is used Relative “truth” velocity of the small boat is calculated using its recorded velocity and position, plus the host ship’s velocity Results: Validation of Measurements Measured velocity is obtained from Doppler velocity fields derived using mean phase removal processing A close agreement can be seen between relative “truth” radial velocity, and the small boat velocity observed by the radar

10 Data from RV Melville campaign demonstrates the capability of observing sea waves using X-Band marine radars Small boat radial velocity comparison demonstrates the viability of estimating relative Doppler velocity fields using mean phase removal processing Conclusions

11 Further improvements include measuring IF backscattered power up to 5 km, allowing calculation of Doppler velocities over full range (0.1 – 5 km) Future Work

12 [1] Dankert, H. and W. Rosenthal, “Ocean Surface Determination from X-band Radar-Image Sequences,” Journal of Geophysical Research, vol. 109, C04016, [2] Nieto-Borge, J. C., G. R. Rodriguez, K. Hessner, and P. I. Gonzalez, “Inversion of marine radar images for surface wave analysis,” J. Atmos. Ocean. Tech., vol. 21, pp , [3] Plant, W. J., W. C. Keller, and K. Hayes, “Simultaneous measurement of ocean winds and waves with an airborne coherent real aperture radar,” J. Atmos. Ocean. Tech., vol. 22., pp , [4] Eshbaugh, J. V. and S. J. Frasier, “Measurement of sea surface displacement with interferometric radar,” J. Atmos. Ocean. Tech., vol. 19, pp , [5] Johnson, J. T., R. J. Burkholder, J. V. Toporkov, D. R. Lyzenga, and W. J. Plant, “A numerical study of the retrieval of sea surface height profiles from low grazing angle radar data,'' IEEE Trans. Geosc. Rem. Sens., vol. 47, pp , [6] Nwogu, O. G. and D. R. Lyzenga, “Surface-wavefield estimation from coherent marine radars,” IEEE Geosc. Rem. Sens. Letters, vol. 7, pp. 631—635, [7] Trizna, D. B., “Coherent marine radar measurements of ocean surface currents and directional wave spectra,” Ocean Sciences 2012 Conference, proceedings, [8] Dankert, H., Horstmann, J. and Rosenthal, W. “Ocean wind fields retrieved from radar-image sequences,” Journal of Geophysical Research, vol. 108, C113352, [9] Smith, G. E., Majurec, N., O’Brien, A., Pozderac, J., Baker, C. J., Johnson, J. T., Schueller, G. (2013). “High power coherent-on-receive radar for marine surveillance,” In Radar (Radar), 2013 International Conference on (pp ). doi: /RADAR References

13 This work was supported by the US Office of Naval Research ONR Contract Number : N D-0370 Acknowledgements