Chuẩn hóa tư liệu ảnh SAR trong phân tích vết dầu trên biển

Hoi nghi Khoa hoc ky niim 35 ndm 1 'iin Khoa hoc vd Cong nghe Viet Nam - Hd Noi 10 2010<br /> <br /> <br /> <br /> CHU AN H O A Tir LIEU ANH SAR<br /> TRONG PHAN TICH VET D A U TREN BIEN<br /> <br /> Nguyen Dinh Duong , Le Minh Hang , Nguyen Mai Phuong'<br /> 'Vien Dia ly, Vien Khoa hgc va Cdng nghe Viet Nam<br /> 18 Hoang Qudc Viet, Cau Giay, Ha Ndi<br /> Email: duong.nguven2007(fl),gmail.com<br /> Hgc vien Ky thuat Quan su, 100 Hoang Qudc Viet, CSu Giiy, Ha Ndi<br /> <br /> <br /> Tom tat:<br /> Dif lieu dnh SAR diing trong phdt hiin d nhiim ddu trin biin mgc dit dd duac<br /> xu ly a mirc cao vdn edn cd bi dnh hudng bdi sir biin ddng tdn xg trong mdt cdt<br /> ngang ciia dnh. Hiin tiryng ndy tgg nin cdc dnh cd gid tri tdn xg chinh nhgu tren<br /> cdc rig dnh tgi vimg gdn vd xa ngudn birc xg siiu caa tdn. Hieu irng ndy gdy nen<br /> nhirng khd khdn nhdt dinh trang viec xu ly phdn tich vit ddu trin vitng biin.<br /> Trgng bdi bdo ndy cdc tdc gig sau khi phdn tieh bdn chdt ciia hien tuang dua trin<br /> mdt cdt ngang ciia dnh dd di xudt hai phuang phdp hiiu chinh; hdi quy tuyin tinh<br /> vd cira sd tnrat. Hai phuang phdp da duac triin khai vd su dung trong hiiu chinh<br /> dnh ALOS PALSAR xu ly a mirc 4.2. Kit qud cho thdy phuang phdp hdi quy tuyin<br /> tinh logi tru duac mdt phdn hiiu irng trong khi phuang phdp cita sd tnrat logi trir<br /> duac hodn lodn. Tuy nhiin tde dd tinh tgdn eug phuang phdp hdi quy tuyin tinh<br /> nhgnh han nhiiu sg vdi phuang phdp ciig sd tnrat. Trong bdi bdo cdc tdc gid dd<br /> trinh bdy sa dd thudt todn eug hgi phuang phdp vd niu kit qud budc ddu dp dung<br /> hgi phuang phdp ndy trong phdn tich vit ddu trin biin.<br /> Abstract:<br /> The SAR image data used in oil spill detection at sea is usually processed in<br /> high level; however there is still uneven brightness distribution in across image<br /> section. This phenomenon causes image pixels of the same sea surface feature<br /> having different backscattering coefficients in near and far range which<br /> complicates process of oil spill detection and analysis. In this paper, the authors<br /> after giving deep analysis of uneven brightness distribution in across image section<br /> using DN in image profile proposed two normglizadan methads; linegr regressign<br /> gnd mgving window. Both these two methods hove been implemented gnd used fgr<br /> correction of ALOS PALSAR level 4.2 products. The results pointed out that the<br /> linear regression method can only partly remove the uneven brightness distribution<br /> phenomenon while the moving -H'indow can eliminate almost perfectly this error.<br /> Algorithms of both methods are described in the paper together with resuhs of<br /> application in oil spill detection and analysis at Vietnam sea.<br /> <br /> <br /> 1. Mo dau<br /> Tu lieu vien tham SAR do kha nang quan sat trong mgi dilu kien thdi tilt, ngay cung nhu<br /> dem nen dugc sir dung trong nghien ciiu biln cho nhilu muc dich iing dung khac nhau. Tuy<br /> nhien tu lieu SAR dugc thu nhan dua tren nguyen ly quan sat tir ben sudn (side looking) nen<br /> Tieu ban: Cong nghi thong lin - Tir dong hod - Cong nghi I 'ii tru ISBN: 978-604-913-010-6<br /> <br /> <br /> <br /> cQng tilm in mdt sd hieu ung phu ma cho den nay van chua dugc giai quyet triet de. Trong<br /> qua trinh xir ly d miic cao nhat, cac gia tri da dugc chuyin ddi \h Sigma nought tuy nhien<br /> hien tugng phan bd khdng deu ciia gia tri anh van khdng dugc giai quyet triet de. Nhieu cdng<br /> trinh cdng bo trudc day va ngay trong quy trinh kiem dinh anh SAR van de nay ciing da dugc<br /> dl cap din nhilu. Theo Vachon et. al. 1997 gia tri sigma nought phu thugc khdng chi vao cac<br /> hieu ling bl mat ma cdn ca vao gdc quan sat. Viec ban cbl anh hudng ciia gdc quan sat den<br /> gia tri anh ciing dugc the hien qua viec tinh chuyen gia tri anh va hieu chinh thdng qua viec<br /> tinh toan beta nought, sigma nought va chuan hda trong mat cSt ngang NRCS. Trong mdt sd<br /> chuang trinh xir ly anh thuong mai, van de hieu chinh hieu ung nay ciing da dugc de cap va<br /> xay dung thanh modul xir ly. Vi du modul Brightness Adjustment trong ERDAS Imagine<br /> 2010 theo nhu gidi thieu trong tep trg giup cd kha nang hieu chinh dugc hieu ung gay bdi sir<br /> phan bd khdng diu eiia cac dilm anh den ngudn sdng sieu cao tan (ERDAS Imagine 2010,<br /> Brightness Adjustment Help). Tuy nhien qua sir dung va so sanh anh trudc va sau hieu chinh<br /> cac tac gia thSy ring vin dl van chua dugc giai quyet mdt each tbda dang. Tren hinh 1 la vi<br /> du ve hien tugng nay.<br /> <br /> <br /> <br /> <br /> Htnh I; Vi du vi su biin ddi gid tri dnh SAR trin biin trong mat cdt ngang<br /> Tu lieu sir dung tren hinh 1 la tu lieu ALOS PALSAR xir ly d mirc 4.2 do Trung tam phan<br /> tich dir lieu vien tham trai dat Nhat Ban cung cap. Chiing ta thay cac anh cd mdt ben sang va<br /> mdt ben tdi ban. Ben sang la viing near range va ben tdi la far range hay ndi each khac ben<br /> sang la viing gan vdi ngudn phat sdng sieu cao tan va ben tdi la viing xa hon. Hien tugng nay<br /> la phd bien ddi vdi cac bd cam quan sat tir ben sudn thay vi trong phuang thang dung. Theo<br /> quan diem ciia ERDAS thi hien tugng nay gay bdi sir khdng hoan hao trong thu phat tin hieu<br /> sieu cao tan ciia he thdng an ten va do tin hieu phan hdi tir doi tugng trong viing gin manh<br /> ban d cac viing xa ngudn sdng sieu cao tan (ERDAS Imagine 2010, Brightness Adjustment<br /> Help). Hien nay van chua cd cac cdng trinh phan tich ro ve ban chat va tir dd dl xuit cac<br /> phuong phap hieu chinh mdt each hgp ly. Trong bai bao nay cac tac gia gidi thieu mdt so kit<br /> qua nghien cihi ve su phan bd khdng diu do sang anh dua tren tu lieu ALOS PALSAR va dl<br /> xuat hai phuang phap hieu chinh su khdng diu vl do sang trong anh SAR trong mat cit<br /> ngang. Anh sau khi dugc hieu chinh cd thi dugc sir dung cho viec tao cac ban chip, nghien<br /> cim cac hieu img be mat va dac biet phan tich vlt dau tren be mat bien dua tren phuang phap<br /> phan ngudng toan cue don gian va thdng dung.<br /> <br /> <br /> <br /> 112<br />  Hoi nghi Khoa hoc ky niim 35 ndm I 'ten Khoa hoc vd Cong nghi Viet Nam - Hd Noi 10/2010<br /> <br /> <br /> Hien tuong phan bo khong diu gia tri anh SAR trong mat dt ngang<br /> <br /> Tren hinh 2 la md hinh hinh hgc cua viec thu nhan tin hieu anh SAR.<br /> <br /> <br /> Nguon song sieu cao tan tren ve tinh<br /> Trong do:<br /> tti: Goc tdi d viing gan ngudn song<br /> a.2., Goc tdi d vCing xa nguon song<br /> Ri: Viing gan nguon song<br /> R2: Viing xa nguon song<br /> RT: Ban kinh Ellipsoid<br /> H: Do cao quy dao ve tinh<br /> <br /> <br /> <br /> <br /> RT<br /> <br /> <br /> <br /> psoid<br /> <br /> <br /> <br /> <br /> Hinh 2; Md hinh hinh hoc dnh SAR<br /> Viec xii ly anh SAR thdng thudng dugc quy chuin theo cac budc nhit dinh. Gia sir khu vuc<br /> quan trac la phang thi tir cac gia tri DN (digital number) trong anh cd thi tfnh ra dugc gia tri<br /> P (Betanought). Sau do dua tren gia tri ciia gdc quan trie a cho mdi dilm anh c6 thi tinh<br /> dugc gia trj G^ (Sigma nought) theo cdng thirc sau:<br /> a = p .sin a<br /> Gdc a cd thi dugc tinh dua tren gia tri R, ciia dilm anh, Rj cua elipsoid va dd cao H ciia ve<br /> tinh.<br /> Dua tren hinh 2 dl dang chiing ta nhan thiy ring khoang each R, va R2 tuang irng cho viing<br /> gan va xa ngudn sdng la khac nhau. Trong trudng hgp quan sat tren dien rdng vi du tren biln<br /> thi sir chenh lech nay se cang Idn va dd cd thi la mdt trong cac nguyen nhan din din su biln<br /> ddi ciia a^trong mat cat ngang. Nhim lam sang td vin dl nay cac tac gia da sir dung ALOS<br /> PALSAR PASL4200706130316260911040000 thu ngay 13 thang 6 nam 2007 da duac xu ly<br /> d miic 4.2 do Trung tam ERSDAC cung cip. Do phan giai khdng gian ciia anh la 50 m va gia<br /> tri anh da dugc tmh d a . Gdc quan sat thay ddi tir 20.1° din 36.5°.<br /> <br /> <br /> 113<br /> Tieu ban: Cong nghi thong tin - Tir dong hod - Cong nghe Vit tru ISBN: 978-604-913-010-6<br /> <br /> <br /> <br /> Nhim danh gia diing sir bien ddng ciia gia tri anh trong mat cit ngang trudc tien anh dugc<br /> xoay lai sao cho true y ciia anh nam trong hudng bay ciia ve tinh. Tnen hinh 3a la anh da xoay<br /> va AB la mat cit ngang khdng di qua viing dat lien va khdng di qua nhiing viing cd di thudng<br /> tren bl mat biln. Sau khi xuit gia tri DN tir anh ta cd thi xay dung dugc dd thi mat cat nhu<br /> tren hinh 3b. Vi chiing ta da chgn mat bien trong mat cit la khdng chira dit lien cung nhu cac<br /> di thudng dac biet nen sir bien thien ciia gia tri anh trong mat cat cd the coi nhu the hien bien<br /> ddi ciia he sd tan xa theo gdc tdi va khoang each den vdi bd cam.<br /> Gia tri anh trong mat c^t |<br /> <br /> <br /> anh ,,l<br /> 1<br /> ,j,.i>yjii 1<br /> 1 iijj<br /> .IJUOU<br /> <br /> .J2Q0O - 1<br /> 11 , iM\ 1]^<br /> 0^mmt0m^w\'< "ff^<br /> MlMiiJH^^^^M<br /> iI<br /> 1 642 1233 1924 2565 3206 3847 4438 5129 5770 6411 7052 7693 8334 3975 9616<br /> <br /> So cot<br /> <br /> <br /> <br /> <br /> (a) , (b)<br /> Htnh 3; Anh dd xoay (a) vd dd thi mdt cdt nggng di qug vimg biin cho dnh SAR (b)<br /> Nhim thiy rd hon sir biln doi nay chiing ta so sanh 200 pixel dau tien va cudi ciing ciia mat<br /> cit va tiln hanh mdt sd phan tich. Tren hinh 4 la dd thi mat cat cua cac pixel da chgn. Ro rang<br /> nlu nhu dilu kien biln d 200 pixel diu tien va cudi ciing la nhu nhau thi cac gia tri tan xa<br /> ciing phai gin gidng nhau. d day chiing ta thay su phan bd ciia gia tri DN rat khac biet. Tren<br /> hinh 4 ciing neu cac gia tri trung binh, cue dai cue tieu va do lech chuan. Neu khdng cd sir suy<br /> giam ve tan xa thi chac chan cac gia tri nay se phai xap xi nhu nhau.<br /> 7000<br /> 200<br /> 6000 diem<br /> anh<br /> 5000<br /> dau<br /> 4000 tien<br /> trong<br /> 3000<br /> mit<br /> 2000 I cat<br /> 1000<br /> W^VWVAJ^?VV>^<br /> <br /> <br /> <br /> <br /> Gia tri truns binh 617 3309<br /> Cue tieu 304 1648<br /> Cue dai 1065 5878<br /> Do lech chuan 139.11 830.6<br /> <br /> <br /> Hinh 4; Dd thi mdt cdt cho 200 pixel ddu tiinvd cudi cirng eug mdt cdt AB tren dnh PALSAR<br /> Dua tren phan tich dd thi tren hinh 3b va hinh 4 chiing ta cd the thiy rang cac gia tri DN tren<br /> anh da bi bien ddi tang dan tir viing xa ve vimg gan ngudn sdng. Trong khi gia tri trung binh<br /> ciia 200 pixel diu tien chi la 617 thi lai la 3309 cho 200 pixel cudi. Gia tri min va max cung<br /> thay ddi nhilu. Su thay ddi gia tri min la tir 617 sang 1648 va cho gia tri max la tir 1066 sang<br /> 5878. Su biln ddi ciia bien do gia tri dugc thi hien qua gia tri do lech chuin. Ddi vdi 200<br /> <br /> 14<br />  Hoi nghi Khoa hoc ky niim 35 ndm I 'iin Khoa hgc vd Cong nghi Viet Nam - Hd Noi 10 2010<br /> <br /> <br /> <br /> pixel diu nd chi bing 139.11 trong khi ddi vdi 200 pixel cudi lai la 830.6. Nhu vay gia tri ciia<br /> cac pixel bj thay ddi khdng chi bing he sd cdng ma cdn ca nhan nira. Trong mdt khoang lan<br /> can nhd hai gia tri nay cd thi khdng doi nhung xet tren toan bg mat cat ngang nd bien thien<br /> theo tga do range. Cac tac gia dl xuat ham md ta quan he giira giiia gia tri DNl (chua hieu<br /> chinh) va DN'^ (sau hieu chinh) cho pixel cd tga do range i cd dang nhu sau:<br /> DN',=DN:f(i) + g{i) (1)<br /> <br /> <br /> Cac ham f(i) va g(i) la nhinig ham phi tuyen ma nhiem 'vu ciia chiing ta la tim ra each xac dinh<br /> nhu the nao. Trong trudng hgp cac ham nay la tuyen tinh thi bieu thuc (1) dugc viet dang<br /> quen thugc<br /> DN'^ =DN'„a{ci + d) + b (2)<br /> <br /> Trong bieu thiic (2) cac he sd a, b, c va d la chung cho toan mat cat, i la tga do cdt ciia pixel i<br /> trong mat cat ngang. Nham hieu rd hon ve bieu thiic (1) cac tac gia da tao mdt mat cat ciing<br /> tai vi tri AB nhu tren hinh 3 nhung cac gia tri hien thi dugc lay la gia tri trung binh cho cira sd<br /> cd do Idn 200 x 200 pixel. Cira sd nay trugt tuan tu tir trai sang phai va chiing ta cd dugc dd<br /> thi ve gia tri trung binh, min, max ciing do lech chuan dugc trinh bay tren hinh 5.<br /> <br /> <br /> <br /> <br /> no i«ch<br /> <br /> - C i j c ll^u<br /> <br /> - C i J c d»i<br /> <br /> <br /> <br /> <br /> .,_ . C 0 O r H m . ^ ' £ i r ^ m o f N m i / i ' ^ 0 0<br /> ^ i £ C O o m i n r . - d w r T i i p x a [ N r r - — CO<br /> ^ (N IN r^ n I — — — .^ .^ .^ rr r; \f\ \f, \f, \n \a 'Ii 'n 'SI •XI<br /> <br /> <br /> <br /> <br /> Hinh 5; Dd thi trinh bdy gid tri cue diu, cue dgi, trung binh vd do lich chudn cho cira sd kich<br /> thuac 200 X 200 dgc theg mdt cat AB<br /> Cac gia tri cue dai tren hinh 5 bi anh hudng nhieu bdi cac ddi tugng nhan tao vi du nhu tau<br /> biln, dan khoan, sdng biln v.v. Tai cac diem ma cac ddi tugng nay xuat hien gia tri tan xa<br /> tang dot biln. Day la di thudng khdng mong mudn tren hinh anh cua mat bien. Sir bien thien<br /> gia tri trung binh, do lech chuin va dd thi cac gia tri cue tieu phan anh rd net ban quy luat ciia<br /> ham (1). Tuy nhien dudng biln thien ciia gia tri trung binh van bi anh hudng nhieu bdi cac gia<br /> tri cue dai va cac hieu irng sdng be mat trong khi dudng bien thien ciia cac gia tri cue tieu the<br /> hien diing hon quy luat cua ham (1). Mdt dieu ngau nhien ta thay quy luat bien thien cua gia<br /> tn do lech chuan va gia tri cue tieu trong cac cira sd lai cd ve nhu triing nhau. Can phai cd<br /> nghien cim nhieu hon ve van de nay. Tren mat bien neu khdng cd nhirng hieu img dac biet<br /> nhu vlt diu, mua gidng, thi gia tri tan xa cue tieu la gia tri tan xa cua mat bien yen lang hoac<br /> <br /> 15<br /> Tieu ban: Cong nghi thong lin - Tir dong hod - Cong nghi ' ii tru ISBN: 978-604-913-010-6<br /> <br /> <br /> <br /> cd sdng it nhit. Neu nhu dieu kien khi tugng hai duong tai thdi diem quan trac la ddng nhat<br /> thi theo chiing tdi cd the sir dung dudng bien thien cac gia tri cue tieu trong cira sd cd kich<br /> tbudc hgp ly dl xay dung ham (1). Sir dung tap hgp cac gia tri cue dai hay cac gia tri trung<br /> binh dl xay dung ham nay cd ve khdng dugc hgp ly lam.<br /> 3. Chuin hoa gia trj anh trong mat cat ngang<br /> Khai niem mat cit ngang dugc hieu la mat cat vudng gdc vdi tuyen bay. Cac anh SAR xir ly d<br /> mirc cao thudng la cac anh da dugc dua ve he tga do mat dat (geocoded). Khi dd anh dugc<br /> xoay di va tuyin bay khdng cdn triing vdi true y cua anh. Do vay neu cd the duac nen tien<br /> hanh chuin hda ddi vdi cac anh mdi chi d miic quy chieu (georeferenced) va khi dd true y cua<br /> anh triing vdi tuyin bay va khdng cin phai xoay niia. Nhirng lap luan trinh bay tiep theo se<br /> lien quan din anh da dugc xoay va tuyin bay triing vdi true y ciia anh. Chiing tdi de xuat hai<br /> phuang phap chuin hda dd la chuin hda dua tren hdi quy tuyen tinh va dua tren cua sd trugt.<br /> 3.1 Chuan hda dim tren hoi quy tuyen tinh<br /> Muc tieu ciia chuin hda dua tren hoi quy tuyin tinh la xay dimg dugc ham hdi quy tuyen tinh<br /> ma dua theo dd cd thi hieu chinh gia tri anh tren cac viing bien. Cac budc xir ly chinh cd the<br /> liet ke nhu sau:<br /> - Che cac viing dat lien tren anh<br /> - Xoay anh sao cho true y triing vdi tuyen bay<br /> - Tim mdt hang anh trong mat cat ngang khdng di qua viing dat lien<br /> - Dgc cac gia tri sd tir anh va xay dung ham hdi quy tuyen tinh<br /> - Ap dung ham hdi quy tuyen tinh cho tat ca cac hang anh trong anh<br /> - Xoay anh trd lai vi tri ban dau<br /> Ham (2) cd thi dugc don gian hda thanh ham (3) trinh bay dudi day trong trudng hgp chiing<br /> ta khdng xac dinh dugc sir bien thien ciia bien do trong mat cat ngang phu thugc vao tga do<br /> range i.<br /> DN[.=DN'„a + b (3)<br /> <br /> Cac he sd a va b dugc tinh dua tren gia tri DN trong mat cat da chgn. Tren hinh 6 la mat cat<br /> ngang trudc va sau khi chuan hda.<br /> <br /> <br /> <br /> -Gia Iri<br /> chua<br /> chuan<br /> hoa<br /> <br /> -Gia In<br /> sau<br /> chuin<br /> hoa<br /> <br /> <br /> <br /> <br /> Hinh 6; Mat cdt ngang trudc vd sau khi chudn hda theo phuang phdp tuyin linh<br /> Chiing ta thi}' \h co ban dd thi gia tri khdng cdn xu the di len nira nhung su tang din ciia bien<br /> do van chua dugc khic phuc. So sanh anh trudc va sau khi chuan hda tuyen tinh chiing ta thiy<br /> <br /> <br /> 116<br />  Hoi nghi Khoa hoc ky' niim 35 ndm I 'iin Khoa hoc vd Cong nghe Viet Nam - Hd Noi 10/2010<br /> <br /> <br /> <br /> nhin chung su biln thien gia tri anh da dugc cai thien dugc it nhieu, mac dii chua phai la hoan<br /> hao nhung ciing da cd thi sir dung anh chuan hda bang phuang phap nay cho phan tich vet<br /> dau tren bien.<br /> 3.2 Chudn hda dira tren cua so trirfft<br /> Chiing ta hay gia thilt nlu khdng xet den vimg dat lien, be mat biln cd thi dugc coi gan nhu<br /> gidng nhau xet ve mat phan xa. Sir khac biet ve cudng do sang chi gay bdi hieu ung gan xa so<br /> vdi ngudn birc xa sieu cao tan. Do vay neu nhu chgn mdt cira sd mau nao do tieu bieu cho anh<br /> va hieu chinh cac viing cdn lai theo cira sd mau dd thi cd thi chuin hda dugc dugc anh. Vi tri<br /> cira sd mau dugc lira chgn dua tren su danh gia ciia ngudi phan tich. Vdi mdt kich tbudc cho<br /> trudc gdm N hang va M cdt, ddi vdi ciia sd mau ta tinh gia tri trung binh va do lech chuan<br /> /i„^ va a,.^f. Vdi phan cdn lai cua anh ta dung phuong phap cira sd trugt vdi kich thude gidng<br /> nhu cua sd mau trugt trong toan bd anh de chuan hda anh. Ddi vdi moi cira sd vdi pixel i,j la<br /> tam ta tinh gia tri //, ^ va cr,^ . Viec chuan hda pixel i,j dugc thuc hien theo cdng thiic sau:<br /> DN. A,<br /> DN =- 're/ + l^re,<br /> ref (4)<br /> <br /> Phuong phap chuan hda dua tren cira sd trugt do cac tac gia de xuat bao gdm cac budc xir ly<br /> nhu sau:<br /> - Tim cira sd anh mau cd kich thude N, M<br /> - Tinh cac gia tri p,.^j va cr^^^<br /> - Trugt trong anh theo trinh tu tir tren xudng va tir trai sang vdi cira sd cd kich tbudc N, M<br /> - Tinh cac gia tri //, ^ va cr, ^ va tinh gia tri Z)A'^„„„,<br /> - Vdng lap dugc thuc hien cho toan anh<br /> Tren hinh 7 la dd thi cac gia tri DN trong mat cat trudc va sau khi chuan hda.<br /> 7000<br /> <br /> 6000<br /> <br /> <br /> <br /> <br /> Hinh 7; Mat cdt ngang tnrdc vd sau chudn hda theo phuang phdp cira sd truat<br /> Nghien cim dd thi tren hinh 7 ta thay cac gia tri DN da dugc chuan hda tren ca hai mat xu the<br /> va bien do. Dudng xu the sau chuan hda da nam ngang va khdng cdn chenh lech ve gia tri<br /> tuyet ddi ciia bien do giira cac pixel dau va cudi hang anh.<br /> 4. Ket qua va trao doi<br /> Ap dung hai phuong phap chuin hda da dl xuit cho anh ALOS PALSAR<br /> PASL4200706130316260911040000 thu ngay 13 thang 6 nam 2007 ta dugc kit qua trinh bay<br /> tren hinh 8. Theo thir tu tir trai sang ta cd anh nguyen gdc, anh chuan hda theo phuang phap<br /> hdi quy tuyen tinh va anh chuan hda theo phuong phap cira sd trugt. cd the thiy rd sir khac<br /> <br /> 117<br /> Tieu ban: Cong nghi thong tin - Tir dong hod - Cong nghi ('it tru ISBN: 978-604-913-010-6<br /> <br /> <br /> <br /> biet giira anh chua chuan hda va anh da chuan hda theo phuang phap hdi quy tuyen tinh va<br /> cira sd truat.<br /> <br /> <br /> <br /> <br /> (a) ^ (b) ^ (c)<br /> Hinh 8; Anh nguyen gdc (a), dnh chudn hda theo phuang phdp hdi quy tuyen tinh (b), theo<br /> phucmg phdp cira sd truat (c)<br /> Nhirng viing den la \'iing dat lien hoac dao tren anh chuan hda da dugc che chan. Ve ca ban<br /> dp chenh lech giira hai ria anh khdng cdn Idn nhieu nhu trong anh gdc ddi vdi anh 8b va dugc<br /> loai bd hoan toan tren anh 8c. ap dung cho mdt anh khac viing bien mien Trung chiing ta cung<br /> dat dugc ket qua tuong tu.<br /> <br /> <br /> <br /> <br /> (a) (b) ^ (c)<br /> Htnh 9; Kit qud chudn hda dp dyng cho dnh (a) dnh gdc, (b) dnh chudn hda luyin tinh, (c)<br /> anh chudn hda theo phuo'ng phdp cira sd triral<br /> So sanh vdi ket qua xir ly bang modul Brightness Adjustment trong chuang trinh ERDAS<br /> Imagine 2010 ta thay chi rieng viec chuan hda bing phuong phap hdi quy tuyin tinh da cho<br /> ket qua tdt hon. Tren hinh 10 la so sanh anh anh dugc hieu chinh bing chuang trinh ERDAS<br /> Imagine 2010 va theo hai phuang phap da dl xuit.<br /> <br /> <br /> <br /> <br /> (a) (b) (c)<br /> Hinh 10; (a) Anh hiiu chinh bdng chirang trinh ERDAS Imagine 2010<br /> (b) vd (c) Anh hiiu chinh theo phuong phdp luyin tinh vd phuang phdp cua sd truat<br />  Hgi nghi Khoa hoc ky' niim 35 ndm Viin Khoa hoc vd Cong nghi Viet Nam - Hd Not 10 2010<br /> <br /> <br /> <br /> Tren hinh 11 la mat cat ciia anh sau hieu chinh bang chuang trinh ERDAS. Chiing ta thay gia<br /> tn anh khdng dugc hieu chinh nhieu ve xu the ciing nhu bien do.<br /> D(j thi m^t c i t ngang<br /> <br /> 7000<br /> 6000<br /> .= 5000<br /> ^ aOOO<br /> fi 3000<br /> 2 2000<br /> " 1000<br /> ii -Trutfc liiiQ chlcb<br /> . Sk-a bi