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2023年4月1日发(作者:现在做什么行业比较赚钱)

Acta Oceanologica Sinica 2007,Vo1.26,No.1,P.48~54

http://www.oceanpress.com・cn

E—mail:hyxbe@263.net

phy detection of Shuangzi Reefs with SAR

images acquired in diferent time

YANG Jungang , ,

ZHANG Jie 一,MENG Junmin

Institute of Oceanology,Chinese Academy of Sciences,Qingdao 26607 1,China

Graduate School,Chinese Academy of Sciences,Beijing 100039,China

First Institute of Oceanography,State Oceanic Administration,Qingdao 266061,China

Key Laboratory of Marine Science and Numerical Modeling of State Oceanic Administration,First Institute of Oceanography,

State Oceanic Administration,Qingdao 266061,China

Received 17 April 2006;accepted 3 September 2006

Abstract

Ima ng mechanism of underwater topography by SAR and a underwater topography SAR detection model built on the theory of un‘

derwater topography detection with SAR image presented by Yuan Yeli are used to detect the underwater topography of Shuangzi

Reefs in the Nansha Islands with three scenes of SAR images acquired in diferent time.Detection results of three SAR images are

compared with the chart topography and the detection errors are analyzed.Underwater topography detection experiments of Shuan‘

gzi Reefs show that the detection model is practicable.The detection results indicate that SAR images acquired in different time

also Can be usedto detectthe underwatertopography,andthe detectionresults are affected bythe ocean conditionsinthe SAR ac・

quiring time.

Key words:Shuangzi Reefs.underwater topography,SAR image,topography detection

1 Introduction

Synthetic aperture radar(SAR)is one of the

advanced microwave remote sensors of environment

and resource.It can observe targets in all weathers

and all day and night in a multi—band,multi—polari—

zation and multi—look angle mode.SAR has been

used in many observations and researches of the

ocean,since American Seasat一1 equipped the SAR

was launched in 1978。such as internal waves。

ocean waves,ships and submarines,sea ices,oil

}Corresponding aHthor.E—mail:yangig@rio.org.ca

spill and underwater topography.Underwater topog—

raphy detection with SAR image is one of important

applications of SAR.Since De Loor found firstly

shallow underwater topography on X—band airborne

real aperture radar imagery,many scientists have

studied the SAR imaging mechanism and detection

model of shallow underwater topography.Alpers and

Hennings(1984)presented a simple theoretical

model(named AH—mode1)of the SAR imaging

mechanism of underwater bottom topography,in

which the topography—tidal current interaction was

described by a one—dimensional continuity equation

and the current—wave interaction was described by

1 2 3 4

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YANG Jungang et a1.Acta Oceanologic.q Sinica 2007,Vo1.26,No.1,P.48~54

weak hydrodynamic 一片孤城万仞山的仞是多长 interaction theory.But the AH—

model is one—dimensional and is too simple in many

conditions.Yuan(1997)presented an analytical

representation of the high frequency spectra of ocean

waves which were derived from the wave number

spectrum balance equation,and built the theoretical

basis of shallow underwater topography detection

tll SAR images.Ma and Zhang(2001)simulated

SAR image of underwater topography,and analyzed

the diferences of simulated SAR images in different

water depths and in different gradients of underwater

topography.In addition,Huang and Zhou(2000)

applied the AH・-model to study the underwater topog・-

raphy detection capability of SAR images.Jin Meib—

ins(1997a,b)and Jin et a1.(1998)utilized the

underwater topography detection model presented by

Yuan Yeli in practical application researches of an—

derwater topography detection with SAR images.

Zhou et a1.(1999)and Jin and Zhang(2000)also

studiod the underwater bottom topography detection

tll SAR images.

In this paper we detected the underwater topog—

raphy of Shuangzi Reefs in the Nansha Islands with

three scenes of SAR images which were acquired in

diferent time.In this process,we used underwater

topography simulation and detection models,which

aIe built on the SAR imaging mechanism of underwa—

ter topography,and the damped Newton—row action

method.Furthermore,we compared detection results

and analyzed errors as well as the reasons for these

errors.Detection results show that the detection

model and the algorithm of underwater topography

aIe feasible.Detection experiments realize the an—

derwater topography detection of the same area with

SAR images acquired in different time,and prepare

for practical detections of underwater topography of

Namha Islands with SAR images.

49

2 Detection mechanism of under春江花月夜原文朗诵视频 water

bottom topography with SAR images

2.1 SAR imaging mechanism

SAR can penetrate into seawater only to a depth

on the order of centimeter.so sAR can not observe

underwater topography directly.That underwater to—

pography can be observed by the SAR is because an—

derwater topography modulates radar backscattering

of sea surface,and the SAR measures radar back—

scattering of sea surface.It is well known that the

main SAR imaging mechanism of underwater topog—

raphy is hydrodynamic modulation of the short—scale

ocean waves by tidal current which flows over under-

water topography.This mechanism includes three

physical processes:Interaction of the tidal current

with underwater topography induces varieties of sea

surface currents;short—scale ocean waves are modi—

fled by the sea surface current;varieties of short—

scale ocean waves induce varieties of radar backscat—

tering.

According to the SAR imaging mechanism of

underwater topography,detection of underwater to—

pography with SAR images includes two parts:SAR

image simulation of underwater topography and de—

tection of underwater topography with SAR images.

2.2 Model and algorithm of simulation and detection

of underwater topography with SAR images

A model of simulation of underwater topography

with SAR images includes two parts:calculating the

tidal current field with the hydrodynamic model:and

calculating the gray value of simulating SAR images

with the tidal current field.The hydrodynamic model

used to calculate the tidal current is the Princeton o—

cean model(POM).Gray value expression of simu—

lation SAR images was introduced by Yuan(1997).

An algorithm of simulation of underwater topography

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VANG Jungang el a1.^f。£日Oceanoh ̄ica Sinica 2007.V0】.26. 0 I,P 48~54

with SAR images is to calculate the lidal curl'eut

field with the program of POM which introduces 一

coordinate and Arakawa—C gridding,then to calcu—

late the gray value of simulated SAR images with the

tidaI current field.

The model of detection o1"underwater topogra—

phy with SAR images is composed of the shallow wa—

ter hydrodynamic model and the function expression

of radar gray value(Jiu and Zhang,1998).The al—

gorithm of detection of undcn' ̄ater topography with

SAR images is the clamped Newton—ru'A,action meth—

od(Cut et al ,2(]03) This nnelhcd has been testi—

fled to be high1Y efficient,reliable and steady hy

simu1ated dala.

3 Underwater topography detection of

Shuangzi Reefs with SAR images ac-

quired in different time

3.1 Data of underwater topography detection exper—

iments

Three scenes of SAR images at(・used in u rlder—

water topography detection experiments with SAR

images.They are ERS一1 SAR image acquired oH 1 9

Novem1)er I993.RADARSAT SAR image acquired

0n 4 June 1998(shortecI for RADARSA.q’1998 SAR1

and RADARSAT SAR image acquired on i2 June

2003(shorle c】fi)r RADARSAT2003 SAR1.Original

SAR images of Shuangzi Reefs in these three SAR

images aFe showed in Fig.1

3 劲的拼音和组词 2 Preprocessing of SAR images

Three SAR images of Shuangzi Reefs should be

preprocessed before they'am used in the UFi(terwater

totmgraphy detection. 13ae preprocessor of SAR ima—

ges includes the following steps:

(1)Geometric cI)rrftelion of SAR images a —

cording to geographical coordinates of four corners of

SAR images girt n in the beader files I SAR data:

(2)Antenna pattern COt’rcction of SAR images

to eIiminale differel'lCeS of SAR images caused bv

side—lta)king of SAR;

(3)CaIculalion of backscattering cross.secti0n

of SAR images with corre]a棒的组词 tive parameters of SAR

an{I the satellite;

4 28。II4 32 I14 36 II44旷l II4 28’Il4 32’Il4 36 1I蝴组词2个字 4 as) I 圈

Fig・1-ERS一1(1eft),RADARSATI998(mid‘ue)and RAI)ARSA 12-003(fight)SARimagei㈣SFIJarI zi Reel ̄,

(4)33 pixels averaging processing of back—

scattering CROSS—section of SAR images;the ̄:solu 中华诗词论坛手机版

tion of SAR image is much larger than that ot。deice—

tion calculation’s dding,so we need to reduce the

resolution of SAR image;this process caH also fiher

the speckle noi .

3.3 Underwaler topo ̄q'aphy detection‘’f Shuangzi

reefs with SAR images

Geographical lot ati cm of the underwater topog—

raphy dete( lion of Shutngzi Reefs is 1 l。21 ~

1 1 30’N.1 14。16 ~1 I4。26 E.Gridding introduced

晰 m

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YANG Jung ng et a1.4cta OceanoJ ∞Siniea 2007.Vo1.26 No I.P・48 54

int(-the detection experiment is 0.02 0.02 (a—

bout 30 74 m30.74 m1 and the number of grid-

ding is 501451.

First.tide and tidal current were calculated nu—

merically by the POM and the tidal curreHt field ob—

tatned in this calculati0n was used to obtain the sire.

ulated SAR image of undec,vater topography.The

gridding of POM used in this calculation is 0.3 x

0.3 .Tidal ca九_etat conlponellIs£ and were input—

ted to Eq(I)(Yuma,1997)to calculatethe simu—

lated SAR image of underwater IopographY of Shuan・

gzi reefs:

G( ):( + f l ) ,

(1)

where 0l is the angle of sea surface wind directinn;

{l ,2 ;is the direction of sea sur ̄ce sh0n wave;

{ 一L I is the direction of sea surface nmin wave.

{ , I is the tidal current;ant] is the function of

{L—L I and:H, }(Yuan,I997).

After the sinmlated SAR image of Shuma ̄i

Reefs was ohtained,baekscatler CROSS—sections of

three SAR images which were used in the underwater

topography detection of Shuangzi Reefs were ob-

rained by Eq (2)

5l

(2)

where Or..is the lmekscatter coefficient of SAR im-

age;G is the gray value of the simulated SAR im—

age;S and S

are the standan:l deviation of G aml

orn;and G ,or0m are the average of G and or.

Second,the underwater IC,pography ol Shuangzi

Reefs was detected by three SAR images with the un-

derwater topography SAR image detection model

(Jin et a1.1998)and the damped Newton—mw ae—

tlon method(Cut et a1.,2003).The initial speed

of tidal current inputLed into the detection calculation

is the speed of tidM current in the SAR imaging

lime.which is obtaine(j by the calculation of PO、I.

The operl boundary condition is to input water level

in the SAR imaging time.An initim waier depth is

ot)lained by interpolation with the uoalse—gridding

actual wateF depth.The wind direetion of sea surface

in the SAR imaging time is obtaim ̄cI by the maximum

correlation coefficient of SAR image with simulated

SAR itriage.Underwaler topography deteclitm resuhs

of three scenes of the SAR images are shown in

Fig.2.

Fig 2 Contoum of water depth obtained by ERS一1/left).RADARSAT1998(middle)and I/AI)ARSAT2003

( )SAn im江上吟李白古诗 ages.

4 Analysis of detection results

Deteetion results of underwater tnpography by

three scenes 0f SAR images arc analyzed by eompari—

sims between the water depth obtained by the SAR

image detection and the real water depth.Average

absolute em)rs and average relative crmrs are caleu・

鳃 +

9 )1 m

_看 一

n (

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52 yANG jungang et al Aet, ̄Oc ̄ano/og/ca Sinico 2007,Vo1.26,No 1.P 48~54

laled.The range of wa[er depth detected by the SAR

images is about 2—60 m,so the detection results in

the gridding points where the water depth is in the

range of 2~60 in are analyzed.

4.1 Analysis of the detection result of ERS一1 SAR

image

Detection result of ERS一1 SAR image is shown

on the Jeft of Fig.2.Contours of the whole area of

islands and reefs are clear and four islands and roefs

are visible.Varieties of water depth i11 the middle

area of islands and reefs are smal1 and accord with

the teal status.All of these are consistent with ob.

servation results uf SAR images th eyes.and these

shot,that the detection results are g0od compare

the detecled water depth and the real water depth.

we can obtain that the average absolute error js 4.36

m and the average relative error is l7%.One small

section pm'alleling with the latitude line shown in

Fig.3 is selecte(I lU testify the reliability of roodel

Fig 3.Location of cross一 ̄ction.

and algofilhm of underwater tot ̄)graphy detection

with SAR images.The comparison of the detection

result with tile real water depth in this section is

shown in Fig.4.In order to testi flher the detec—

tion m‘・del an(I the algorithm are g00d,the detection

results in the range nf 2— 20 m are compared be—

cause the val ieties of water depth in the range 0f 2~

20 m are obvious.The comparison is shot'n_n F

6a.In this figure,one cao see that the detection l'e—

V ^ …hal1 wiiI ‘k…lI一

】 f , h J【

U 、 神 ^

0 10 20 ) 50 60 70 8U

Fig 4 Comparison of the re water depth and the

detection result of ERS—I SAR inmge

4.2 Ana1)'sis I)f the detection result of RADAR—SAT

I998 SAR image

Deteetion result of RADARSAT1998 SAR im.

age is shown in the middle nf Fig.2.Contours of

islands and ree are visible and the trend of variedes

of warer depths fn1m islands all(1 Feefs to the middle

area js also visible.But varieties of detection results

of v ̄aker depths relative“ iniIial ware[depths are e—

qual and Sillal】 The detection l_esults of RADAR—

SATI 998 SAR iantge are not ( relative to ERS一1

SAR inlage,and this is because ocean eondltions in

1he RADARSAT1998 SAR imaging time are not

good.It is known thai g(ml:l oceau conditions ol SAR

detecting water depth are that the tidal current is

changing from the minimum to the maximum or form

the maximum to the minimum and that the wind over

the ocean surface is about 3~10 m/s(Huang et

a1..2000).To compare the detecting water depth

and the real water depth.we can obtain that the av-

erage absolute eHor is 4.47 m and the average rela.

rive eH ̄Jr is 18%.The comparison nf some detecting

water depths with the rea】water depth is shown in

Fig.6b.

r . 0 帅

… :

维普资讯

YANG Jungang et a1.Acta Oceanologica Sinica 2007,Vo1.26,No.1,P.48~54

-J\ nitial water depth

…,L……..一J…●L

—。’ 一sea c ̄art water oeptn

・----・-一detection result

d L i

助 . ^t ・^ jk^fI

0 10 20 30 40 50 60 70 80

Grid point

nitial water deptb

● - ▲ I ▲●

—。’ 一sea ehart water depth

‘-。。。・。一detection result

。。

盈 I i

W,, V

0 10 20 30 40 50 60 70 80

Grid point

Fig.5. Comparison of the real water depth and the de..

teetion results of RADARSAT1 998(1eft)and RADAR.

SAT2003(fight)SAR images.

tection results of underwater topography with the

a ●

●●●

( j

: ’

O 5 lO l5 2O

Seachartwaterdepth/m

53

4.3 Analysis of the detection result of RADARSAT・

2003 SAR image

Detection result of RADARSA。l2U【)3 SAR im・

age is shown on the fight of Fig.2.Contours of

islands and reefs aye clear and visible and the trend

of varieties of water depth around islands and reefs is

also visible.Water depth in the middle of detection

area changes complicatedly and equally.All these

aye consistent with the results obtained from the SAR

image with eyes.To compare the detecting water

depth with the real water depth,we can obtain that

the average absolute error is 3.41 m and the average

relative error is 12%.Comparison of some detecting

water depths with the real water depth is shown in

Fig.6c.

Fluctuation of underwater topography is presen—

ted as bright・dark stripe in SAR images.From above

analyses,one can see that the detection results of

ERS一1 SAR image and RADARSAT2003 SAR im.

age are much better than the detection result of RA.

DARSAT1998 SAR image. is can be testified bv

the observation result with eyes.The main reason

why errors of detection result aye large is that the de.

June when summer monsoon is prevailing,the wind

●●

●●

^ .:

O 5 10 15 20

Sea chart water depth/m Sea chartwater depth/m

Fig・6・Comparison of real water depth with some detecting water depth of three scenes of SAR images

a・EllS_1 SAR image,b.RADARSAT1998 SAR image and c

.RADARSAT2003 SAR image.

SAR images rely much on the initial water depth

Otherwise,the ocean condition 在线免费观看完整版电影大全 in the SAR imaging

time also affects the detection result.The imaging

time of two scenes of RADARSAT SAR images is

speed of sea surface is large and changes frequently

and this weakens the information of underwater topog.

raphy in the SAR image.The imaging time of ERS.1

SAR images is November when winter monsoon is pre.

∞ 如 :。 m 0 ∞ :。 m .n O

量、Ll 4∞ 苗 量、壬 盎苗净

唇、{4 I)

量、苦4

目、壬da

维普资讯

YANG Jungang et a1.Acta Oceanologica Sinica 2007,Vo1.26,No.1,P.48~54

vailing,the wind speed of sea surface is small and

changes little and this makes the information of an—

derwater topography in the SAR images clears.

5 Conclusion

In this paper,three scenes of SAR images ac—

quired in diferent time were used in underwater to—

pography detection experiments of Shuangzi Reefs in

the Nansha Islands.These experiments testify the

practicability of model and algorithm of underwater

topography detection with the SAR images in the un—

derwater topography detection of Nansha Islands,and

analyze the feasibility ofSAR images ofthe salTle area

acquired in diferent time which can be used to detect

the underwater topography respectively.This prepares

for the practical detection of underwater topography in

the Nansha Islands with the SAR images.From this

paper we can draw the following conclusions:

(1)Model and algorithm of underwater topog-

raphy detection with the SAR images are feasible and

effective in the underwater topography detection of

reef region in the Nansha Islands;

(2)Detection result of underwater topography

with the SAR images is affected by the ocean condi—

tion in the SAR imaging time;

(3)Rationality of choice of the initial water

depth affects the final detection result in the detec.

tion calculation of underwater topography(Jin et

a1.,1998).

Work in this paper is the first an application of

the underwater topography detection with the SAR

images in the reef region,and it is helpful to practi—

cal detection of underwater topography with the SAR

images in the reef region in the future.

Acknowledgements

This study was supported by the National

“863”High Technology Projects of China under con—

tract Nos 2o02AA634O20 and 2o02AA135350.

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