DTIC ADA432157: Wind Direction Estimates from Synthetic Aperture Radar Imagery of the Sea Surface

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by  Defense Technical Information Center

ion Hstimates from Synthetic Aperture Radar Imagery of the Sea Surface

George 8. Young
“The Pennsylvania State University
Department af Metcorloxy
University Park, PA 16802
phone: (B14) 86-4228 fax: (B14) 265.3663 email: young @ems psu.cdy

Grant Number: NUOOL44

1089? TRIBUTION STATEMENT A

‘Approved for Public Retease
LONG-TERM GOALS Distribution Unlimited

1, We wil investigate de range of toar-srface mean wind directions with respoct te the
tviertacion of common maze atmospheric boundary layer (MABL} quasi-wo dimensional
fphenamnena soon in syntactic aperture radar (SAR) imagery, An doing so, we will provide empirically:
derived guidelines on how to distinguish the SAR-signature of onc feature Jrom anche.

2. We will provide the impact of position errors in nummerical weather madel-analyzcd synoptic
‘walle storais and fronts on the wind dizection-dependentcetrieval of wind spocd from SAR. This val!
beaccommplished via a thorough error analysis of CMOD-4 with an emphasis on wind direction ercoes
at varying incidence angles, und vurying wind-elative look directions,

OBJECTIVES

1. We pill iventiyale the range of near-suiface mean wind directions with respect tothe
frientution of common MABL quasi-twa dimensional phenomiena seen in SAR imagery of the me
surface, ‘We will provide empirieully-evived guidelines on how ro dlstingnish the SAR-xignature af
‘onc foatore from anviher Gee Figure 1 for examples of quasi-twa dimensimal phenamena sccn in SAR
‘nrugery if tre sea sustace). We have outlined the scope ofthis portion ofthe rescareh in Sikora und
‘Young (21K2). The qnasi-wo dimensional MABE phenomena that we will stady wre ehmguted
cellolar convecticn, bubyancy-driven / shear-organized roll vortices, inflection point-indced roll,
vvortiven, shear-diven gravity saves, and topographicully-driven gravity waves.

2, We will provide the impact of position cmrrs in nomnsrical weather modi-analyzed syaoptic
alle sloroon and fronts an the wiud dcetion-dependent retrieval of sind speed from SAR via 8
thorough error analysis of CMOD-4 with an emphasis oa wind diccction errs at varying incidence
angles, and varying wind-realive lxk directions (see Figure 2 for an example of such sn emor). We
vill use the rewuly of this essa analysis to develop automated or semi-aulomated detection and.
corretion atsocichms for displaced cyclonic ara frontal wind shift lines. These algorichms will
Improve the aecuracy of SAR wind speed retieval a conjunction with model-analyzcd sind dtection
Field,

APPROACH

“The basis ofthe fexture-idonlification esearch will be SAR imagery provided (0 us by collaborators at

20050427 009
Figure 1. Radarsat-t SAR imuge (eff) depicting the signature of volt vartices. The 300 m pivet
image is approximately 270m by 270 km. The image was acquired at C-hand, horizoutad
polarization, off the marth east coast of the United States at 2242 UTC' on 6 March 1997. The top of
‘the image ts directed towards 348°. {Provided courtesy of IHUAPL, © CSA} ERS-1 SAR image

(right) depleting the signature atmospheric gravity waves associated highly ageostrephic flow near @
Fron. The 180 m pixel image tx opprocimately 90 ko by.90 kan, Tee image was acquired at C-band,
vertical polarization, aver the Caspian Sea at 0723 UTC on 12 May 1996, The top ofthe image iv
directed towards UL2’T. (Provided courtesy of Werner Alpers and ESA, © ESA)

Figure 2. SAR wind speed image for 10 February 2002 generated hy the Johias Hopkins
niversity Applied Phynirx Laboratory, The image on was generated using NOGAPS wind
directions, The image contain an example of an erroneous hourcglass signature (at approximately
SF" N, -145°) resulting from the mis-positioning of the eyclone center by NOGAPS. Arraws denote
‘the carresponding mode? wind speed and direction.

Johns Hopkins University Applied Physics Labararory QHUAPL). This SAR imagery will be cross-
referenced with corresponding in sit, remote sensing, and movleling dala. This supporting data will be
Used to nsxess both the type of phenomena depicled in a given SAR scene and the relationship between
its ovientating and the near-surface mewn wind direction. Given chat hundreds of SAR images af boch
the Nasthvvest Atlantic Ocean and the Nentheast Pacifie Ocean are availabe ln us, our study will
provide a rabnst assessment of hath feature orientation with respect lo near-surface mean wind
sGroction and of hon ts discern one feature from: another, Tsing this knowledge, wc will endeavor wo
develop image processing algorithms mimicking ovr ability to distinguish berwoen quasi-tws
<irvetsional phenorncna busca on their siructare im the SAR backscatcr field. With these algorithms,
it willbe possible to wulumaue The determination of the relative ample between near-surface wind
rcction und the alignment quasi-ewo cimousional features in Uke SAR inragery,

‘Convection af model wind dirostion ields for misplaced synoptic features follows three lp: Fics,
erection and location of the SAR error signature. Second, eposition Ihe cyclone center oF frontal
wind shift Lin to climinate this erur, Third, mamph the surrounding madel sind dincetion ficld so that
the far field is unaffected by lhe position correction,

For the eytlone misplacemene prablom, che frst stop involves locating the madel-eralyzed vortex and
then quantifying the degree to which tho SAR derived wind speed field around the cyclone center
‘matches the position-ceror signature, TI the signature patcern explains at least 80% (a tunable
parameter) of the vuriame, the voles is classed as misplacod and the maaxirmumt range for which Unis
‘condition ix mel in used as a measure of zhe erar-signsture size, Because the weak and strong sec“ars
ff the error signature are ovicnted primarily with respect tothe tax dinection its slignmenc provides
lite dircot guicknce as to the direction of eyclome position enti. Tastead, feamures ofthe raw
backscatter fild such vorex~center-culmy and -spirals are analyzed to suggest likely vortex positions
Selection botworn curds positions 6nd tuning of the tual selection will be automated vie
‘minimization of fhe emor signature excerion given above, ‘Ihe center ix ehen displaced wily frus
location while points af greater radii from the center ae displaced less, is. a single control point
smcaphing. The diameter of dhe region alfocted should be proportiona? wo the displacement distance
‘with the constant of proportionality being a sccund tunable parameter

Frontal position carrectin wil follow the sare three stops selection betwoen enlliple eundidates will
not be tequited for computing displacement of a linear fexture, Depeneling on our success in
developing an automatic detection algorithm fer the more aublle rontal position eror signatures,
tbuman analysis of frontal position and displacement may he requited,

WORK COMPLETED

1. Weave documented the SAR-signatures of synoptic-scale cold fronss, warm fronts, occluded
fronts, and soclooa! frams, including their mesoscale and eicrosea'e sub-structntes, The basis for
those findings iy the analysis af some 6000 RADARSAL 1 SAR images from the Gull of Alaska and
from off the east coast of North America, ‘This analysis yielded 158 cases of well fined froncal
signanures: 22 warm fronts, 37 colé fronts, 3 stationary [ronbs, 32 vccluded fronts, and 64 seceded
fronts.

‘Most xynuplic- scale almaspherie frants share two genctie SAR-observsble Teafures. The fist isa near
‘eso osder change in the mcan backscattor while the second iy u near zero-cnder change in the character
‘of the micro oto meso--scale cddly SAR signatures.

‘Cold frome specific SAR signatures inclnde meso-y-soalo lobe und cleft instability, meso-y.scale
vortices, meso-y-scale Kelvin-Helmhelt: instability, and convective signatures to the immediate 10
the cold fron, Warm and cucluiled front-specilic SAR signarues include pre-frontal jets, mes0-P-
scale vortices, and mesiy of micro-a-scale handing aligned nesely perpendicular to tho fren!
sursccited sth gravity waves,

of

For more details on the above Findings, refer to the following publicacions:

Young, GS... D. Sikora, and N, S, Winstead, 2005; Uke of synthetic uperture radar in fine-scale
surface analysis af synoptic-acsle ment ul ea. Weather une Forecasting, i press.

Sikora, T.D.,G.8. Young, and I. 8, Winstex, 2004; Uke of synthetic upeture rar in te fine.
scale analysis of synoptie-scle fronts al sea. Preprinis, Thineenth Conferonce on
Interactions of the Sea and Atmosphere, 8MS, Portland, MR, 9-13 August 2004, CD
publication,

“The studies will primarily aid our second objective (morphing). Morcover, we ascertsinod that the
‘wind ditectioa information rovealod by the SAR signatures of mesoscale and microscale eddie is af
great importance in locating and typing evnopcic scale fronts. Thus, there is a direct two-wny
‘connection betworn these studies and sur rst objective.

2, We have completed a climatology of the err signatures asa function of frontal orientation,
‘wind ditection, and posicion vor diretire im fants und yclones. These results were eaplamed using
‘quanstative madclmg with CMOD-4. Muilab code was developed to recognize those siymatures and to
‘execute single-contrsl-poinl morphing af cyclone positions and mult-control-point morphing of
fv positions.

RESETS

1. Wehave documented the SAR-signatutes of synopric-soale ead nants, warm fronts, occluded
fonts, and secluded Fronts, including their wind dlzcclien-relaied mesoscele and ticroscale sub-
siruwcures, The basis for these findings isthe analysis of some 6000 RADARSAT] SAR images from
the Gulf oi Aliska and from off he cast const of North America. This analysis iclded 138 eases of
well defined frontal signatures; 22 wurm fronts, 37 cold thonts 2 stationary fronts, 2 oveluded fronts,
and 64 sceludet fronts. An example of our frontal identification Grange can he seen in Figuie 3

2. Wehave developed mannal morphing rules for hourglass, weak band ang strong-band SAR.
Signatures, including cause ind vure 1 aid usin our second objective. ‘the ease af the hourglass
signature isthe misphacernent oa wind dicetion siagulatity, The cure is to monph the point at the
cenler af the hourglass signature to the truc position ef the singularity. The cause ofthe weak und
stmnng-band signatures is an improperly placed wind direction shit across a front, The cure is 9
morph the wind direction Field sous W achieve a discontinuity in wind direction along the front and
more neurly uniform wind directions on each side of th front, We have used our morphing software
dermunsirate that aubstantial improvements im the SAR-derved wind speed field can be obtained by
‘wneetly morphing the numctical-model-wnnlysir-derived wind direction fields before application af
the CMOD-4 wind speed dingnosis algoricum

IMPACT/APPLICATIONS,

rhe research deseribed herein fulfills ONR abjectives by working towards the integraliam of standard
meteorological iheary amd xywhetic apertuce radar data with the goal of providing high-resolution
rerpotely sensed estimates of near-surface wind ficld and encteorstowy in in sina data-sparse regions
‘aver the ocean, including the coastal zone, Far exarnpl, the frontal ideacification work we've
complete tis fur will help isin fonecastera to use SAR to is full potential in marine synept
Tmll analysis. The morphing saftware we've developed will allow users to obtain accurate SAI
derived wind speods oven whzn numerical model analyses tsed for the wind direction ek! have:
postion errors for key synapGe features,
Figure 3. Radarsut-} SAR imane depicting the the intersection of a cold front, warm feons, and
‘ncluded front. The 600 m pixel image is appravimately 801 kun By 450 hn, The tage wes
seequired at C-band, horizontal polarization, over the Bering Sea at 0500 UTC on 31 Ostaber 1999.
‘Tis top of the SAR image is directed towards 348°T, (Provided courtesy of JIUAPL, © CSA)

RELATED PROJECTS

Project Co-P1 George Young hax on NSF-funded SAR project that supports the development of
analysis tools cascnlial taut ONR-funded rescarch. Tho Mullah CMIOD- cude was developed
Jointly with NST-co-PT Nathaniel Winstead, An interactive SAR wind field analysis program with a
_gruphieul user interface was dovelopod by George Young as part ofthis project and will serve as che
ttost application forthe water ani ialeraccive wind-discetion field morphing routines developed
under ONR finding,

REFERENCES

Sikora, T. 1, and G. S. Young, 2002: Wind-direclion dependence of quasi-2D SAR signatures,
Proceedings, Inernational Geoscience and Remote Sensing Syrpostuns 2062, ILUT, Torna,
CA, 24-28 une 2000, 1887-5889.

PUBLICATIONS

Sikora, T.D..G. S, Young, B.C, Beal, F. M, Monaldo, and P, W, Vachon, Applications of synthetic

pert radar in marine meteorology. Advances in Plvid Mechumilex: Atmosphere Ocea
iseractions-Voltone 2, W. Peo, Bd. Wessex Instuic of Technology, in press.

‘Young, G. $.,T.D, Sikow, and N.S. Winswad, 2005: Use of synthetic uporiure rudar in fine-scale
‘sutTave analysis. of Synapde-scale fronts at sea, Weather and Forecasting, in press.

Sikora. 1. D..G. $, Young, amd N, 8. Winstead, 2004: Use of gymthotic aperwre radar ia te tine-soale
nslysis of xymoptic-seale fronts at sea, Preprints, Thirteenth Conference ou knreractions of the
‘Sea aut Atmosphere, AMS, Poniind, MIE, 9-13. August 2004, CD publication,
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