海上搜救視覺增強系統(tǒng)-視覺增強系統(tǒng)在海上SAR系統(tǒng)的應用

1、PAGE PAGE 41海上搜救視覺增強系統(tǒng)施朝健 許開宇 肖寶家 莫劍英（上海海事大學學）摘要：由于人眼眼的生理特性性造成海上復復雜環(huán)境中的的搜索效果不不佳，研究應應用于海上SSAR系統(tǒng)的的視覺增強系系統(tǒng)是十分必必要的。本文文針對搜救環(huán)環(huán)境中人眼觀觀測的弱點，提提出了基于可可見光成像系系統(tǒng)和紅外成成像系統(tǒng)的視視覺增強系統(tǒng)統(tǒng)進行海上搜搜救的方案，給給出了系統(tǒng)框框圖。該系統(tǒng)統(tǒng)輔助搜救人人員進行搜救救，將提高海海上目標尤其其是弱小目標標探測的靈敏敏度和發(fā)現率率，能夠有效效地挽救人民民的生命和財財產，具有巨巨大的經濟效效益和社會作作用。關鍵詞：視覺增增強系統(tǒng)；搜搜尋救助；人人眼視覺特性性；目標檢測測

2、Vision enhanncemennt sysstem ffor maaritimme seaarch aand reescueShi Chaaojiann, Xu Kaiyuu, Xiaao Baoojia aand Moo JiannyingShanghhai Maaritimme UniiversiityAbstracct Beccause of thhe limmitatiion off physsiologgical charaacteriisticss of hhuman eyes, it iis neccessarry to devellop viision enhanncem

3、ennt sysstem ffor maaritimme seaarch aand reescue (SAR) to iimprovve thee poorr searrchingg perfformannce off humaan vission aat seaa. Andd a syystem with its fframewwork bbased on thhe vissible lightt imagging ssystemm and infraared iimaginng sysstem iis prooposedd in tthe paaper tto commpensaate t

4、hhe weaaknesss of tthe huuman oobservvationn in tthe SAAR envvironmment. The ssystemm willl prommote tthe seensitiivity and tthe deetectiion raate off targgets, especciallyy smalll onees, att sea, ensuure thhe saffety oof liffe at sea, and rreducee econnomicaal lossses iin marrine aaccideents.Keywor

5、dds vission eenhanccementt systtem; ssearchh and rescuue; huuman vvisionn charracterristiccs; taarget detecction1 引言隨著航運業(yè)的發(fā)發(fā)展,我國水水上交通安全全保障和應急急搜救任務日日益繁重。22006年，我我國海上搜救救中心和海事事機構共組織織協調了海上上搜救行動11620次，組組織、協調各各類船舶53322艘次。共共發(fā)生遇險人人員174998人。中國國政府和海事事部門非常重重視研究和發(fā)發(fā)展海上搜救救技術。國國家中長期科科學和技術發(fā)發(fā)展規(guī)劃綱要要指出：“重點開發(fā)交交通事故預防防預警

6、、應急急處理技術，開發(fā)運運輸工具主動動與被動安全全技術，交通通運輸事故再再現技術，交交通應急反應應系統(tǒng)和快速速搜救等技術術。”交通部公公路水路交通通“十一五”發(fā)展規(guī)劃重重點還明確確提出“十一五”期間做到“現場救助能能力明顯提高高，人命救助助有效率由目目前的87%提高到900%左右?！睘榱诉_到規(guī)規(guī)劃要求，對對海上救助搜搜尋視覺增強強系統(tǒng)的關鍵鍵技術進行研研究是十分必必要的。在過去幾年，中中國的海上搜搜救組織發(fā)生生了很大的變變化，體現在在參與了國際際上搜救的合合作和采用了了先進的技術術。然而，現現有的海上救救助搜尋方法法，尤其是搜搜索人，主要要借助人眼進進行搜尋。而而人眼視覺的的生理特性決決定了在

7、復雜雜環(huán)境和疲憊憊狀態(tài)下，搜搜索效果不佳佳。研究視覺覺增強系統(tǒng)（VVisionn Enhaancemeent Syystem, VES）輔助人眼進行海上搜救的關鍵技術是非常必要的。視覺增強系統(tǒng)應應用機器視覺覺設備和技術術增強和擴展展了人眼的視視覺。它是智智能交通和交交通安全領域域的重要前沿沿基礎技術和和研究熱點1-3，在在汽車駕駛、飛飛機導航等方方面得到較為為廣泛的應用用4-6，尤其在不不利天氣或夜夜間駕駛和飛飛行時有效增增強了人的視視覺，在保障障交通安全方方面起到良好好的作用77-9。同同時，視覺增增強技術也被被應用于輔助助老年人、視視力障礙人員員改善視力和和特殊環(huán)境中中增強視力等等10-1

8、12。這些些視覺增強系系統(tǒng)的研究成成果對本課題題的研究有重重要的借鑒價價值。2 人眼的視覺覺特性現有的海上救助助搜尋方法主主要借助望遠遠鏡或者紅外外望遠鏡依靠靠人眼進行搜搜尋，因而人人眼的結構特特征和視覺特特性是值得關關注的。2.1 人眼結結構圖1 人眼結構構圖人眼結構圖如圖圖1所示。是是由水晶體、虹虹膜和視網膜膜等組成的。正正常視力情況況下，眼睛可可以聚焦到物物體并能在視視網膜的中央央凹（fovvea）成像像。視網膜中中央凹處是視視網膜的中心心和最敏感之之處，產生精精確的視覺。在在0位置附近近，為了看清清小的細節(jié)部部分視網膜的的一小部分會會起作用。在在大的區(qū)域內內，2 - 4，是是用于看近處

9、處物體的。當當視覺使用所所有的視網膜膜定向的看目目標時，沒有有能力分辨細細節(jié)。光是從從物體表面反反射到視網膜膜的感光細胞胞，然后根據據神經的沖擊擊進行響應。這這里有兩種類類型細胞，錐錐狀和桿狀細細胞。錐狀細細胞是一種明明視覺器官，只只有在明亮條條件下它才起起作用，但卻能夠分辨顏色和細細節(jié)。桿狀細細胞是一種暗暗視覺器官，它它對入射光的的強度很敏感感，它能分辨亮亮度的差別，而對顏色的的分辨本領極極差，不能分分辨顏色與細細節(jié)。最好的的視力是在最最中部的凹處處,稱為微孔孔（foveeola）. 中央凹處處大小是1.5毫米直徑徑( 5.22 )，微孔孔占有0.33毫米直徑( 1 )。其中有有500000

10、個錐狀細胞胞,但沒有桿桿狀細胞，這這就是為什么么我們在弱光光下無法看到到任何東西。2圖2 視網膜上上的錐狀細胞胞和桿狀細胞胞的分布圖2所示為眼的的錐狀和桿狀狀細胞分布的的密度圖。在在缺少細胞分分布的地方就就是“盲點”（Blinnd spoot）。除此此區(qū)域外，分分布情況基本本上是關于中中央凹對稱的的。值得注意意的是，錐狀狀細胞在視網網膜中央部分分是密度最高高的，而桿狀狀細胞中心偏偏移了約200度后開始增增加密度,然然后下降直到到視網膜的邊邊緣. 2.22 視覺外界光輻射到人人眼中刺激視視網膜所引起起的知覺叫做做視覺。視覺是一個個復雜的生理理過程。外界界光線通過角角膜、虹膜、晶晶狀體聚焦在在視網

11、膜上, 刺激感光光細胞發(fā)出神神經脈沖, 經視神經傳傳遞到大腦產產生視覺。人人眼有視覺暫暫留現象，當兩種不同同的色光間隔隔時間很短，先后對視網網膜刺激，視網膜就分分不出刺激的的先后，只能產生一一個總體的刺刺激知覺，這便是視覺覺的時間混色色效應。此外外，人眼還具有一定限限度的分辨本本領，當兩束不同同的色光同時時對視網膜極極小的范圍刺刺激后，視網膜在某某一極小范圍圍就無法分辨辨兩種刺激，只能產生總總體的刺激知知覺，這便是視覺覺的空間混色色效應。結合人眼的視覺覺特性，以及及對人眼視覺覺特性的實驗驗和研究，可可以得出幾種種典型的人眼眼視覺模型14-188。即，指指數型、高斯斯型、Barrten型和和復合

12、模型，分分別如圖3 所示，是幾幾種類型的MM T F 曲線。由此此可以看出：a. 高斯型和和指數型是低低通濾波器；Bartenn 和復合模模型是帶通濾濾波器，復合合模型較Baarten 模型向低頻頻移動；b. Bartten模型和和復合模型在在大于15ccyc/ ddeg的區(qū)域域大體處于00.20.3 mraad 的高斯斯型曲線之間間，而指數型型則偏高；圖3 幾種人眼眼視覺的M T F 曲線c. 由于Baarten 模型和復合合模型的復雜雜性, 以往分析析大都采用指指數型或高斯斯型MTF模型；d.從以上視覺覺模型中可以以看出人眼的的視覺特性的的調制傳遞函函數響應是非非均勻的，這這在搜救的復復雜

13、環(huán)境中，容易將弱小目標抑制掉，不易搜索到小目標。3 視覺增強系系統(tǒng)盡管SOLASS公約規(guī)定船船舶裝有GMMDSS設備備等對于搜救救環(huán)節(jié)已經有有所改善，但但是對許多非非SOLASS公約船如漁漁船、小艇筏筏的檢測效果果一直是不理理想的，加之之海上環(huán)境非非常復雜，對對于落水人員員的搜救更是是束手無策。此此外，目前海海上搜救大都都還停留在使使用多個常規(guī)規(guī)搜尋設備聯聯合搜尋，依依靠人工視覺覺進行判斷的的階段。在搜搜救的復雜環(huán)環(huán)境中，根據據人眼的生理理特征以及人人眼的視覺模模型，造成了了搜救人員在在逆光觀測、夜夜間觀測、小小目標檢測、海海浪環(huán)境和長長期觀測中，很很難發(fā)現被搜搜尋的小目標標，延誤救助助時間。

14、視覺覺增強系統(tǒng)，可可以克服上述述的缺陷和不不足，并應用用于對水上船船筏和遇險人人員的救助搜搜尋，可以提提高救助搜尋尋的速度和準準確性，對提提高救助的成成功率和效率率有重要作用用。應用于海上救助助搜尋的視覺覺增強系統(tǒng)，通通過可見光、紅紅外成像設備備對目標進行行搜尋，輔助助人眼的視覺覺系統(tǒng)，從而而獲得遇險落落水人員、救救生艇筏等目目標的位置及及動態(tài)。該視視覺增強系統(tǒng)統(tǒng)可以很好的的輔助救援人人員完成搜救救工作，尤其其是對救生艇艇筏和遇險落落水人員等海海上弱小目標標，具有很好好的檢測和識識別效果。4 海上搜救視視覺增強系統(tǒng)統(tǒng)根據視覺增強系系統(tǒng)各個部分分在海上SAAR系統(tǒng)中所所起的作用，建建立了視覺增增

15、強系統(tǒng)，其其結構框圖如如圖4所示。人眼觀測可見光成像系統(tǒng)紅外成像系統(tǒng)目標檢測目標檢測圖像融合場景標注搜救人員決策人眼觀測可見光成像系統(tǒng)紅外成像系統(tǒng)目標檢測目標檢測圖像融合場景標注搜救人員決策海面環(huán)境在搜救過程中，由由可見光成像像和紅外成像像系統(tǒng)組成機機器視覺系統(tǒng)統(tǒng)，搜尋目標標時輔助人眼眼進行觀測并并克服了視覺覺系統(tǒng)的生理理缺陷。高分分辨率和高速速成像系統(tǒng)可可以用于捕獲獲可見光信息息。同時紅外外成像系統(tǒng)也也可以進行目目標檢測，這這在夜間搜尋尋和白天克服服波浪影響時時都能夠起到到作用。利用用圖像融合技技術，改善了了單個視覺系系統(tǒng)的觀測敏敏感度，同時時在場景中標標注出可能的的被搜救對象象，有利于搜搜

16、救人員做出出決策。5結論由于人眼視覺的的限制，研究究先進的技術術提高海上搜搜救性能是必必要的。在海海上SAR系系統(tǒng)中應用視視覺增強系統(tǒng)統(tǒng)，可以提高高搜救人員海海上搜尋的速速度和準確性性，對提高救救助成功率和和效率有重要要作用，可以以提高我國水水上救助能力力，追趕上發(fā)發(fā)達國家的遇遇險救助能力力,為我國的的航運事業(yè)做做好保障工作作。它將有效效的挽救人民民生命安全和和財產，有較較大的經濟效效益和社會作作用。參考文獻1 S. Boverrie, AA new classs of iintellligentt senssors ffor thhe innner sppace mmonitooring o

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24、tt,Charries DD.Willley,Moountinng/adjjustinng mecchanissm forr visiion ennhanceement systeem,US Patennt 71993783.Marchh 20,22007.13周燕，金金偉其. 人眼視覺的的傳遞特性及及模型.光學學技術. 2002. Vol1128. NNo11:557-59,6214Llooyd J M. Therrmal iimaginng sysstem. 尹白云等譯譯,北京: 國防工業(yè)業(yè)出版社, 1981) .15Rattches J A ll. Nighht vission llab

25、oraatory statiic perrformaance mmodel for thermmal viiewingg systtems R . U. S. Armyy Elecctroniics Coommandd , Reeport No1 EECOM 77043 , 1975516 Baarten P GJ. The SQRI methood : aa new methood forr the evaluuationn of visibble reesoluttion oon a ddisplaay J , PProc1 Soc1 Inf1 Dispeel , 11987 ,28 :2

26、253 26217Jaccobsonn RE. An eevaluaation of immage qqualitty mettrics, The journnal of phhotogrraphicc scieence , 19955 ,43 : 7 16Vision Enhanccementt Systemm for Maritiime Searchh and RescueeSHI Chaaojiann, XU Kaiiyu, XXIAO BBaojiaa and MOO JiannyingShanghhai Maaritimme UniiversiityAbstracct- Becaau

27、se oof thee limiitatioon of physiiologiical ccharaccterisstics of huuman eeyes, it iss neceessaryy to ddeveloop vission eenhanccementt systtem foor marritimee searrch annd resscue (SAR-VVES),wwhich improove thhe pooor seaarchinng perrformaance oof humman viision at seea. A systtem wiith itts fraamew

28、orrk bassed onn the visibble liight iimaginng sysstem aand innfrareed imaaging systeem is propoosed iin thee papeer to compeensatee the weaknness oof thee humaan obsservattion iin thee mariitime searcch andd resccue ennvironnment. The systeem willl proomote the ssensittivityy and the ddetecttion rra

29、te oof tarrgets, espeeciallly smaall onnes, aat seaa, enssure tthe saafety of liife and rreducee econnomicaal lossses iin marrine aaccideents.Keywordds-visioon enhhancemment ssystemm; seaarch aand reescue; humaan vission ccharaccterisstics; targget deetectiion1 IntrooductiionMaritimme seaarch aand r

30、eescue (SAR) becaame ann enorrmous task with the vvast ggrowthh of mmarinee trannsporttationn and otherr mariine acctivitties. In thhe yeaar of 2006, the marittime SSAR ceenterss and marittime aauthorritiess in CChina organnized and ccoordiinatedd 16200 SAR operaationss, whiich innvolveed 53222 vess

31、sels and 117498 humann livees. Chhinesee goveernmennt andd mariitime authooritiees havve undderscoored tthe immportaance oof ressearchh and devellopmennt of SAR ttechnoology. In thee natiional progrram foor meddium- to loong-term scienntificc and technnologiical ddeveloopmentt, traansporrtatioon saf

32、fety ttechnoologiees, suuch ass trafffic aaccideent prreventtion, warniing annd emeergenccy proocessiing teechniqques, activve andd passsive ssafetyy techhniquees of transsportaation vehiccles, trafffic emmergenncy reesponsse sysstem aand quuick ssearchh techhniquees, arre lissted oon thee top agend

33、da. Itt is aalso sspeciffied eexpliccitly in thhe empphasiss of 111th ffive-year devellopmennt plaan of highwway annd watterwayy trannsporttationn, prooposedd by tthe Miinistrry of Communnicatiions, thatt, in tthe 111th fiive-year periood, thhe marritimee SAR capabbilityy shouuld bee imprroved obvio

34、ously, and the raate off lifee saviing shhould be inncreassed frrom 877% at preseent too abouut 90%. The passt feww yearrs havve wittnesseed treemendoous chhangess in tthe orrganizzationn of mmarinee resccues. A larrge paart off thiss evollutionn stemms froom thee invoolvemeent onn an iinternnationn

35、al sccale aand thhe conntribuution of thee advaanced technnologyy. Howeveer, cuurrentt mariitime searcch opeeratioon, esspeciaally ssearchhing ppeoplee overr boarrd, deependss mosttly onn humaan eyees. Becausse of the llimitaation of huuman eeyes, it is necesssary to sttudy tthe keey tecchniquue of

36、visioon enhhancemment ssystemm for marittime ssearchh and rescuue. Viision enhanncemennt tecchniquue is a pottentiaal appproachh to oovercoome thhe limmitatiion off humaan eyees in marittime SSAR, aand thherebyy may hopeffully improove thhe seaarchinng perrformaance iin commplex envirronmennt or in

37、a fatiggued statee of hhuman beingg.Vision enhanncemennt sysstem aappliees macchine visioon equuipmennt andd techhniquee to eenlargge thee visiion exxtent of huuman eeyes. It iss an aadvancced techhniquee and an immportaant reesearcch hottspot in thhe fieeld off inteelligeent trranspoortatiion annd

38、traaffic safetty1-3. It hass a wiide sppread appliicatioon in the ffieldss of rroad vvehiclle driiving and aairplaane naavigattion4-6. It enhannces tthe huuman vvisionn effeectiveely inn bad weathher orr nighht driiving and fflyingg, andd is oof advvantagge in ensurring tthe trrafficc safeety7-9. AA

39、t thee samee timee, thee visiion ennhanceement technnique has allso beeen apppliedd to aaid thhe oldder-drriver or thee visuallly impairred too imprrove ttheir perfoormancce10-12. 2 Charaacteriisticss of hhuman eyesAt pressent, most iinformmationn usedd in marritimee searrch annd resscue iis humman

40、viision. The sstructture oof humman eyyes annd itss visiion chharactteristtics aare woorth nnoticiing.2.1 Strructurre of humann eyess Fig. 1. Struucturee of aa humaan eyee The strructurre of a humman eyye is shownn in FFig. 11. A ccondittion ffor noormal visioon is that the eeye caan foccus onn an o

41、objectt and keep the imagee of tthe obbject steaddy proojecteed on foveaa. Fovvea iss the most centrral annd sennsitivve parrt of retinna andd provvides the mmost aaccuraate prrecisee visiion. OOnly aa veryy smalll parrt of the rretinaa is uused iin ordder too see smalll detaiils arround a 0 positti

42、on. A larrger aarea, 2 - 4 frrom thhe cenntre, is used when lookiing att veryy nearr objeects. Visioon useed forr orieentatiion usses alll of retinna witthout the abiliity too disccern ssmall detaiils ouutsidee the centrre. Lightt thatt is rrefleccted ffrom aa surfface hhits tthe phhotoreeceptoors o

43、nn the retinna, whhich then transslatess the lightt to nnerve impullses. Theree are two ttypes or recepptors, conees andd rodss. Theese arre diffferenntly ddistriibutedd overr retiina. TThe recepptors measuure liight aand haave diiffereent fuunctioons. TThe coones aare sppeciallized onn distiinguiss

44、hing diffeerent colorrs andd disccern ssmall detaiils inn goodd lighht. Thhe rodds are sspeciaalized onn regiistrattion oof verry loww leveels off lighht. Iff the lightt is ttoo weeak, colorrs cannnot bbe perrceiveed beccause the ccones need a ligght leevel oof at leastt 10 cd/m2, whiich iss the low

45、esst levvel off phottopic visioon. Thhe besst acuuity iis achhievedd in tthe moost ceentrall partt of ffovea, callled foveoola. TThe siize off foveea is 1.5 mmm (5.2) iin diaameterr whille fovveola occuppies 00.3 mmm (1). Theere arre 50 000 ccones but nno rodds at all iin fovvea. That is whhy it is

46、not ppossibble too see anythhing wwith ffovea in veery weeak liight ccondittions.2 Fig. 2 showss the densiity off rodss and coness for a crooss seectionn of tthe riight eeye paassingg throough tthe reegion of emmergennce off the opticc nervve froom thee eye.The abbsencee of rrecepttors iin thiis aer

47、ra ressult iin thee so ccalledd “blindd spott”. Exccept ffor thhis reegion, the distrributiion off receeptorss is rradiallly syymmetrric abbout tthe foovea. Recepptor ddensitty is measuured iin deggrees from the ffovea. It ccan bee notiiced tthat tthe coones aare moostly densee in tthe ceenter of re

48、etina (in thhe cennter aarea oof thee foveea), andd the rods increease iin dennsity from the ccenterr out to appproxiimatelly 20 offf axiss and then decreease iin dennsity out tto thee extrreme pperiphhery oof thee retiina.Fig. 2 Distrributiion off rodss and coness in tthe reetina2.2 Humman viisionT

49、he perrceptiion caaused by thhe extternall lighht raddiatinng intto thee humaan eyees to stimuulate the rretinaa is ccalledd visiion. VVisionn is aa compplex pphysioologiccal prrocesss. Extternall lighht is focussed onn the retinna thrrough corneea, irris annd lenns, annd stiimulattes phhoto-sensoor

50、y ceell too geneerate nervee pulsse, whhich iis traansmittted tto thee braiin thrrough visioon nerrve too prodduce vvisionn. Beccause of thhe vissual ttemporrary rretainning pphenommenon of huuman eeyes, when the iintervval off two diffeerent lightts is very shortt, thee retiina caant ddistinnguishh

51、 the orderr of tthe sttimulaation by thhe ligghts. It onlly prooducess a tootal sstimullationn percceptioon, caausingg the visioons ttime bblendiing efffect. Besiides, humann eyess alsoo havee a liimitedd disttinguiishingg abillity, when the mminimaal reggion oof thee retiina iss stimmulateed by two

52、 ddifferrent llightss at tthe saame tiime, tthe reetina cantt disttinguiish twwo stiimulattions in thhe minnimal regioon, onlyy prodduce ttotal stimuulatioon perrceptiion, wwhich causees vissionss spacce bleendingg effeect.Fig. 3. A ffew MTTF currves oof thee humaan vissionSeverall typiical ffrequee

53、ncy rresponnse moodels have been introoducedd to rrepressent tthe chharactteristtics oof humman viisual systeems 13-17, i.e., expoonent modell, Gauuss moodel, Barteen moddel annd commpoundd modeel, whhich aare illlustrrated in Fig. 3 by curvees of moddulatiion trransfeer funnctionn (MTFF). Frrom thh

54、eses cuurves, it ccan bee noteed thaat,Gauss mmodel and eexponeent moodel aare loow-passs fillters, whille Barrten mmodel and ccompouund moodel aare baand-paass fiilter. Comppared to Baarten modell, commpoundd modeel is incliined tto loww freqquencyy.When thhe reggion iis greeater than 15 cyc/ddeg,

55、BBartenn modeel andd comppound modell are generrally locatted beetweenn 0.2 mrad gausss modeel currve annd 0.33 mradd one, but tthe exxponennt onee is mmuch hhigherr.Becausee of tthe coomplexxity oof Barrten mmodel and ccompouund moodel, exponnent MMTF moodel oor gauuss MTTF moddel iss mosttly ussed

56、 inn the previious aanalyssis.Modulattion ttransffer fuunctioon ressponsee of hhuman visuaal chaaracteeristiic is non-uuniforrm in the aabove visuaal moddels. This ccan eaasily inhibbit thhe smaall taarget and ccant searcch thee smalll onee.3 Visioon enhhancemment ssystemmSOLAS cconvenntion presccri

57、bess thatt shipps musst be equippped wwith GGMDSS equippmentss, whiich haave immproveed thee searrch annd resscue. Howevver, ffor maany noon SOLLAS coonventtion sships, suchh as ffishinng boaats annd smaall crrafts, the detecction resullts arre nott veryy muchh unsaatisfaactoryy. With tthe coomplexx

58、 sea envirronmennt, thhe seaarchinng of missiing peerson becommes a naail-biiting task. Becausse of thesee physsiologgical charaacteriisticss of hhuman eyes and hhuman visuaal sysstems, it iis diffficullt forr the rescuuer too findd smalll tarrget iin thee adveerse bbackliightinng, niight oor darrk

59、connditioon, waave orr clussteredd seass. Conntinuoous loong tiime obbservaation also causees fattigue of huuman eeyes, resullting poor sensiitivitty of detecction. All thosee facttors ddecay the rresultts of searcching operaation. In oorder to immprovee the effecct of marittime SSAR opperatiions dd

60、uringg the dark hourss or in addversee lighhting or seea connditioons, vvisionn enhaancemeent syystem couldd be uused. The pprimarry rolle of a vission eenhancce sysstem iis to be a seconndary sourcce of inforrmatioon to SAR ooperattions. The visioon enhhancemment ssystemm can, to soome exxtent, ove