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OMB No. 0704-0188

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY) 13-07-2007

3. DATES COVERED (From - To)

2. REPORT TYPE Journal Article

1

4. TITLE AND SUBTITLE

5a. CONTRACT NUMBER

An experimental investigation of wave measurements using a dual-beam interferometer: Gulf Stream as a surface wave guide

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

0601153N 6. AUTHORIS)

Sd. PROJECT NUMBER

Paul A. Hwang, Jakov V. Toporkov, Mark A. Sletten, Douglas Lamb, Dragana Perkovic

5e. TASK NUMBER

5f. WORK UNIT NUMBER

73-6628-06-5 8. PERFORMING ORGANIZATION

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

REPORT NUMBER NRL/JA/7330-06-6082

Naval Research Laboratory Oceanography Division Stennis Space Center, MS 39529-5004

10. SPONSOR/MONITOR'S ACRONYM(S)

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

ONR

Office of Naval Research 800 N. Quincy St.

11. SPONSOR/MONITOR'S REPORT

Arlington, VA 22217-5660

NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release, distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT A dual-beam interferometric synthetic aperture radar measures remotely two radial components of the ocean surface current from a single fight pass. Combining two passes over the same area, all three orthogonal components of the surface velocity can be retrieved. An experiment is conducted near the Gulf Stream (GS) boundary. A sharp change of the surface velocity of about I m/s over a 500 m lateral distance is measured. The wind and wave condition is dominated by a 14-s swell system and low wind velocity. The wave variance inside GS is about twice the wave variance outside the GS in the present data set. The difference in the wave variance is considerably higher than that can be expected from wave-current interaction. An ocean current system with strong shears such as the GS is a wave guide and can trap waves with the right combinations of wavelengths and propagation directions. Numerical calculations suggest that the wave properties of the data set may satisfy the conditions of wave trapping by the GS. The standing wave pattern on the GS side of the sharp velocity front, indicative of the long swell bouncing offthe current front, also offers support for the wave guide hypothesis. In this respect, the Gulf Stream can be considered the nature's hydraulic breakwater that can attenuate about 50% ofthe incident wave energy generated by storms. Its role in protecting the U.S. coastlines in the Atlantic Ocean cannot be overstated.

15. SUBJECT TERMS

wave; measurement; mapping; interferometer; Gulf Stream

16. SECURITY CLASSIFICATION OF: a. REPORT b. ABSTRACT c. THIS PAGE

Unclassified

Unclassified

Unclassified

17. LIMITATION OF ABSTRACT

UL

18. NUMBER OF PAGES

U ss15

19a. NAME OF RESPONSIBLE PERSON

Paul Hwang 19b. TELEPHONE NUMBER (include area code)

202-767-0800

Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18

JOURNAL OF GEOPHYSICAL RESEARCII. VOL. 111, C09014, doi:I0.1029'2006JC003482. 2006

Full

Article

An experimental investigation of wave measurements using a dual-beam interferometer: Gulf Stream as a surface wave guide Paul A. Hwang.' Jakov V. Toporkov,' Mark A. Sletten,' Douglas Lamb.' 2 and Dragana Perkovic Reccived 9 January 2006I; rce ised "2 May 2006; accepted 9 June 2006; published 13 September 2006.

[I] A dual-beam interferometric synthetic aperture radar measures remotely two radial components of the ocean surface current from a single flight pass. Combining two passes over the same area, all three orthogonal components of the surface velocity can be retrieved. An experiment is conducted near the Gulf Stream (GS) boundary. A sharp

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change of the surface velocity of about 1 m/s over a 500 m lateral distance is measured. The wind and wave condition is dominated by a 14-s swell system and low wind velocity. The wave variance inside GS is about twice the wave variance outside the GS in the present data set. The difference in the wave variance is considerably higher than that can

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be expected from wave-current interaction. An ocean current system with strong shears

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such as the GS is a wave guide and can trap waves with the right combinations of wavelengths and propagation directions. Numerical calculations suggest that the wave

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properties of the data set may satisfy the conditions of wave trapping by the CS. The