REPORT DOCUMENTATION PAGE Form ApprovedR DOMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection ofinformation, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports 10704-0188),1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to anypenalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 13. DATES COVERED (From - To)

07-03-2008 Final Report I Oct 2004 to 30 Sep 20074. TITLE AND SUBTITLE 5a. CONTRACT NUMBER

Final report: Measurement of Non-Linear Internal Waves and TheirInteraction with Surface Waves using Coherent Real Aperture Radars 5b. GRANT NUMBER

N00014-05-1-0274

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBERWilliam J. Plant

59. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

Applied Physics Laboratory - University of Washington REPORT NUMBER

1013 NE 40th StreetSeattle, WA 98105-6698

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR*S ACRONYM(S)

Office of Naval Research (ONR 322) ONR875 North Randolph Street

Arlington, VA 22203-1995 11. SPONSORIMONITOR'S REPORTNUMBERIS)

12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release

13. SUPPLEMENTARY NOTES

None

14. ABSTRACT

The objectives of the grant were to use a coherent real aperture radar to 1) study the interaction of surface waves with internalwave, the process that is responsible for the synthetic aperture radar (SAR) imagery of internal waves; 2) Determine the extent towhich Doppler velocity modulations observed by coherent radars, including along-track interferometric SARs, are faithfulrepresentations of surface currents generated by internal waves; and 3) track the temporal and spatial development of internal wavesas they are generated, propagate and dissipate.

15. SUBJECT TERMS

Non-Linear Internal Waves, Coherent Real Aperture Radar

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE PERSONa. REPORT b. ABSTRACT c. THIS PAGE ABSTRACT OF Theresa Paluszkiewicz (ONR 322PO)

PAGESU U U UU 19b. TELEPHONE NUMBER (Include area code)8 703-696-4533

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

Final Report: Measurement of Non-Linear Internal Waves and TheirInteraction with Surface Waves using Coherent Real Aperture Radars

William J. Plant, Applied Physics Laboratory, University of Washington, Seattle, WA98105-6698, plant(&apl.washinton.edu

Funding period: 1 October 2004 - 30 September 2007Grant Number: N00014-05-1-0274

Objectives of the Project

The objectives of our measurements were:

1. To study the interactions of surface waves with internal waves, the process that isresponsible for synthetic aperture radar (SAR) imagery of internal waves.

2. To determine the extent to which Doppler velocity modulations observed by coherentradars, including along-track interferometric SARs, are faithful representations of surfacecurrents generated by internal waves.

3. To track the temporal and spatial development of internal waves as they are generatedpropagate, and dissipate.

Summary of Results

1. Because our cross section measurements were calibrated, we were able to show that ata variety of incidence angles, internal waves produce higher cross sections at HHpolarization than VV. This is an indicator of wave breaking and casts doubt on previoustheories of internal wave microwave signatures.

2. Cross sections and surface velocities produced by internal waves frequently, but notalways, depend on the direction of look of the microwave antenna. Thus Dopplervelocity modulations cannot always be faithful representations of the internal wavecurrent.

3. The location of the maximum cross section produced by an internal wave was directlyabove the maximum surface current, the internal wave crest, produced by the internalwave in deep water. On the shelf, however, the maximum cross section was located onthe forward face of the internal wave crest. This provides a potential means of studyinginternal wave transformations. In no case did our internal wave signatures occur faraway from the crest of the internal waves as has been previously reported.

4. Phase speeds of internal waves could be determined in our images. These varied from0.8 m/s to 3 m/s in our data.

20080311230

Experiments Conducted

During the Non-Linear Internal Waves Initiative (NLIWI), we deployed our coherent,X-band radar, RiverRad, with fixed antennas on the R/V Melville, and on a Taiwanesevessel, the Ocean Researcher 1, in the South China Sea. We also mounted RiverRad in ascanning mode on the R/V Endeavor off the coast of New Jersey. Finally, we flewanother coherent, X-band radar, CORAR, on a Cessna Skymaster aircraft off the coast ofNew Jersey. Figures 1 and 2 show these installations.

The data collected with these radars documented some very interestingcharacteristics of the radar surface signatures of non-linear internal waves. We found thatthese signatures behaved differently depending on the incidence angle of the radarantenna, on the polarization of the radar, and on the nature of the internal wavesthemselves.

Figure 1. RiverRad installed on the various ships. Left Column - The R/V Melville in2005 with RiverRad and the PI shown below it. Middle Column - The RV Endeavor in2006 with RiverRad shown below it. Right Column - The Taiwanese OR1 withRiverRad and Gene Chatham shown below it.

Figure 2. Left - The Cessna Skymaster and the two pilots, John Ambroult, and JohnWilliams. The white rectangle below the plane houses CORAR's two antennas, one HHand the other VV. Right - Internal waves on the New Jersey Shelf as seen from theSkymaster.

Characteristics of Cross Section and Velocity Modulations

Larger HH than VV Polarized Cross Sections

One feature of these internal wave signatures that has not previously been documentedis that internal waves always seem to modulate backscatter cross sections at HHpolarization more than at VV polarization. This was a very clear message from ourmeasurements at many incidence angles as illustrated in Figures 3, 4, and 5.

o,(HH)-<o,(HH)>, dB, Run # 478, Scans 300 - 400 a0(W)-<0 (VV)>, dB; Dist 0 is 11.97 km from Start

30 30

20 20700 700

E E10 E 10

55 0 55 0i-10 5 -10

400 4 45 -204 -2

300 3040 -30 40;-30

1000 2000 3000 4000 1000 2000 3000 4000Distance, m Distance, m

Figure 3. Images of internal waves on the New Jersey shelf obtained with the airborneCORAR. Left: HH polarization, Right: VV polarization.

kic Ang 45 dgHHkko=W lr Ang =55 deg. * HH. ko =VV

0,8~-~> 0.8 L4

O I O W 0.6 - - - - --- - - - - - - -----

E* 0 1 F : 0 " * *0

o 0 0

D 0.4 F 0 0 I O[

0 0' -- -------- --------- --- - -- 02 - O -- -- --- -- ----- 1

-150 -100 50 0 50 100 150 -150 -100 -50 0 50 100 150Look Angle. deg Look Angle. dog

Inc Ang 65 dog r= HH, ko VV All IncAng. r FHH, ko = VV

0.8 -

~- - - - -0.4 - 0- T C, C, 1% 0 ,f ,,,," "C::: ! +0 00 00 0 . * "

0.oIF ..- oF . ..

-150 -100 50 0 50 100 150 -150 -100 -50 0 50 100 150Loo* Angle. deg Look Angle. deg

Figure 4. Measures of the visibility of internal waves on the New Jersey shelf byairborne CORAR plotted against antenna look direction. Red asterisks are HHpolarization, black circles are VV.

u.(HH) (418) ffo(PM (do)

600 -20 OW -20

E100 -25 E50 -25

400 -30 n4 30

130-3 300 -35

-200 0 200 400 40 0 -200 0 200 400

DIhance Acron Track. m DIslance Across Track. m

V, (MH Pal) (ms). V; (" PoI) (MfM),

600 3 600 3

E100 2 E800 2

~400 1 400

100 -2 00 -2

-200 0 200 400 0 -200 0 200 400

Distance Across Track, m Distance Across Track m

Figure 5. Images of internal waves on the New Jersey shelf obtained with the shipboardRiverRad. Incidence angles were near 880. Left column: HH polarization, right column:VV; Top row: cross sections, bottom row: velocities.

In all these figures, the internal waves are more visible for HH polarization than forVV. Interestingly, Figure 5 shows that the internal waves are more visible at HH thanVV in the velocity images as well as in the cross section images. Note that the greatervisibility at HH than VV polarization is consistent across the range of incidence anglesfrom 450 to 880.

Because our HH and VV cross sections are collected simultaneously and areabsolutely calibrated, we were able to document that the maximum values of HH and VVcross sections occur at the same location and that HH cross sections are larger than VVcross sections. This is important because previous models of the surface signatures ofinternal waves have been based on scattering from freely propagating waves that aremodulated by the internal wave surface currents. These theories always predict that HHcross sections will be smaller than VV cross sections. We believe that this is becauseeffects of breaking waves have been ignored. Breaking waves are sometimes knownproduce larger HH than VV cross sections and we are investigating these possibilitiesnow.

Upwave/Downwave Assymetry

%(PH) (do) - {ff (do)600 20 O0 4

E500 -26 E500 -25

,400 -30 400 ,40

300 5 3SO0 -6

-200 0 200 40 40 0 -200 0 200 400Distance Across Track, m Ostnce Across Track, m

V, (HH Pal) (Mis), V, (VV Po) (Ms),600 3 ON3

E 00 2 500 2

p400 1 p400

1300 0o 3o 0p20 -1 p200 -1

1100 -2 10 -2

0-M0 0 2D0 400 .200 0 200 400 -Disterms Across TracK rn IsUmnc Across TracK m

Figure 6. The same internal wave as seen in Figure 5 but viewed from the oppositedirection 30 minutes later.

A feature of our data that does not appear to be consistent across a range of incidenceangles is the dependence of the visibility of internal waves on the direction from whichthey are viewed. Figure 4 shows that no dependence on azimuth angle exists forincidence angles between 450 and 650. Yet Figure 6 is a shipboard image of the sameinternal wave seen in Figure 5 but observed from the opposite direction. Clearly the

visibility of the internal wave is much less here. The two images were obtained 30minutes apart.

Figure 7 shows, however, that images obtained on ships do not always show internalwaves better when looking into their propagation direction. This figure showsnormalized radar cross section observed on several crossings of a train of internal wavestraveling west in the deep basin of the South China Sea. Concentrating particularly onwave #2, we see that the cross section looking in the wave propagation direction (secondcrossing) is as large as or larger than that obtained looking into the internal wavepropagation direction (first and third crossings). This is very different than Figures 3 and4.

Solid: (o0 Dashed = 100Uc-40. Wsp = 2.83 r/s, Wdir = 206.7 Dog, Files 21690 - 22219

2 ~2 3 - 2 3 4 _Q .2 - - - A -- -. .. -.-......- ....- ....-. . ..-. .. ...-. ...- .. ..-. .... . .... . .-S 2

-40 -1 -. - - - € -\ ... - -- -- - -. . ' -' -- '--'c .. .. -

cc 60 - - - - - -

06:00 09.00 12:00 15:00 18:00 21:00

Solid = X (Art Look-Wind Dir); Dashed = 10(Wnd Speed), Dash Dot = Ship Heading

I [0 I I100------------------ 1 ---------- _ __ __ __ __ _

R o - --------------------- ----------- -

-100 ___ -- > ~ - ~ - < -- ---- ---- ---- ~----- ---

S-0006:00 09.00 1Z.00 15:00 18:00 21:00

lime

Figure 7. Measurements made on the R/V Melville in 2005. Top: Subsurface velocities(blue) times 10, minus 40 and oo(VV) (black). Bottom: Antenna look direction - winddirection (solid blue), wind speed times 10 (dashed blue), and ship heading (red).

Location of Signature Maxima

Previous experiments have had difficulty determining the precise location of themaximum cross section relative to the internal wave crest. This is because themeasurement of both locations simultaneously is difficult from aircraft or from the shore.Three out of four of our experiments had the advantage of being carried out onboardships where other instruments (echo sounders, Doppler sonars) were simultaneouslymeasuring the characteristics of the internal waves. Therefore we were able to determinethe relative locations of the maximum surface signature and the crest of the internalwave. Our measurements show that this relative location depends on the type of internalwave. Figures 8 and 9 show space/time plots of the return to RiverRad. The blackcurves in the figures show the ship's path. The lower panels show the component ofsubsurface velocity along the ship heading, the ship heading, and the ship speed. Theyalso give wind speed and direction.

We may track the progress of any internal wave in the figures as shown by thesloping black lines in the figures. The slopes of these lines are a measure of the phase

speed of the internal wave if the ship travels perpendicular to its crest. The point wherethese lines cross the ship's path is the location of the internal wave signature at the timethat the velocity measurements in the bottom panel were made. Clearly on the shelf(Figure 8), the maximum cross section occurs on the front face of the internal wave asconventional wisdom dictates. However, in the deep basin (Figure 9), the maximumcross section occurs at the maximum of the subsurface velocity. This is unexpected andunexplained. Furthermore, the maximum of the scatterer velocity appears to follow thatof the cross section, which is again unexplained.

V,(HH)-V(ship)(ms), Fesu441to443 2007 - ShelfE4i3000 - - , 5

2000 - --- --- ... .... .. --- -- - -- - -o

07:00 07:10 07:2044 ':30 07:40 07:50 08:00 08:10 08:20 08:30ao(HH)d13 ) , 04 -2007 06:53:34 UTC, (2 .047S°N, 117.31980W)

E -30

Cne 2000 - - - - - --- - --- .--... .. - -40

VU1000 ------ ----.. . .. . .--- - - -4 5

0-07:00 07:10 07:20 0 F:30 07:40 07:50 08:00 08:10 08:20 08:30

Depth = 606 m, V Ind Speed 2.3 m/s, Wh d Dir (from) a 85 deg

0-

o-.....

"; -2;- htoDeaed. ms: b.=ShlDIninlt) d -:. Cri 5.m on H H( (+ int,n

07:00 07:10 07:20 07:30 07:40 07:50 08:00 08:10 08:20 08:30Time, UTC

Figure 8. Data taken by RiverRad on the shelf in the South China Sea in 2007 along withdata collected by other instruments on the ship, the OR. Top: space/time plot ofscatterer velocities observed by RiverRad; Middle: space/time plot of normalized radarcross sections from RiverRad; Bottom: component of subsurface velocity along the shipheading (black), the ship heading (blue), and the ship speed (red).

Surf Vol in rn/s (from shAtedfl), Statt: Lt =20.5, Long =119.06, L 10:48:44, 2005- Basin

--

7 ; -- 2

11:00 11:15 11:30 11:45 12:00 12:15 12:30 12:45 13:00 13:15 13:30FigurC9.amaFigr xct fdat t akn iB nW the dp bi o. te S h C

E... --- 20... .

Se.HrBtemd l plo Show tHeig GeSsurace eloity Drcoponen iterirctono

400 I I ! l t I 40

thBhphadnlpstiei oad th Ship'S bo=W). See

2 ' " " - - - - T r r r T

u) 11:00 11:15 11:30 11:45 12:00 12:15 12:30 12:45 13:00 13:15 13:30

Figure 9. Sameas Figure 6eCret foata akeWng (n th depbainoth)Suhhn

anal Has een ied plot Son tH ai td e n dSruacneg cthsen ya o dat cection.

Wet hoetoctinethdnayi in thiprjchae ear future Wefobieve abt the rdar inandeso

to understand better the microwave surface signatures of internal waves in the ocean.Eventually such understanding may lead to a determination of the internal wavecharacteristics from their surface signatures, thus advancing the modeling and predictionof these waves.