NGHIEN ClTU PHAT HIEN LU QUET TlT T l / LIEU ANH VIEN THAM RADAR PALSAR TAI KHU AOTC YEN BAI, SON LA
Nguyen Viet NghTa
Tdm tdt: Bdi bdo trinh bdy kit qud nghiin cieu sic dung tu lieu dnh radar Alos Palsar, chup ndm 2017 tgi hai tinh San La, Yen Bdi. de xdc dinh hien trgng lU quet, ngdp lut. Kit qud nghiin cuu cho thdy, bdng dnh Alos Palsar chup tgi thoi diim xdy ra lU quit vd sau khi xdy ra lU quit cho phep xde dinh duae diin tich ngdp lU vd hiin trgng, quy mo cua cdc Iran lU quel xdy ra trin dia bdn hai tinh mien nui Tdy Bac. Cdc bdn do Men trgng lU quit, ngdp lut trong khu vue nghien cieu dong gdp tich cue vdo viic hogch dinh vd kien todn ede hi thdng, edc gidi phdp eho lU quit, ngdp lut, sgt la,... nhdm ieng phd v&i bien doi khi hdu.
Til' khda: Alos Palsar; lU quet; mien nui Tdy Bdc; Yen Bdi; San La.
Mddau
Tren the gidi da cd nhieu nghien cdu iing dung tu lieu anh ve tinh sieu cao tan khau dp tdng hgp (SAR - Synthetic Aperime RADAR) trong phan loai ldp phii, theo ddi lira, lap ban do ngap lut, lii,... Cac ban do hien trang ve miic dp lu quet lay tir SAR la mdt ngudn thdng tin quan trgng giup quan ly thien tai, ciru frg nhan dao, giiip cac td cbuc va cac nha boach dinh chinh sach cd dugc nhirng thdng tin ban dau vl khdng gian Iii (de Moel, 2009). Han nua, cac ban do nhu vay cd the cung cap cac dii lieu de hieu chuan va hop thuc hda cac md hinh tuang tu, cac quy trinh luu vyc sdng (Garcia-Pintado, 2015; Giustarini, 2011;
Hoang Phi Phung, 2016; Schumann, 2009) va hd frg xay dyng, phat trien cac ban dd nguy co trong pham vi lii quet boat dpng, cac boat ddng phdng ngira, quan ly nii ro bao hiem va quy hoach khdng gian (de Moel, 2009). Nhd su dung budc sdng dai, anh radar dp md tdng hgp (SAR) cd thi thu dugc tin hieu phan xa tii' be mat frong mgi dieu kien thdi tiet nhu may, mu, bui khi quyen va ca nhirng tran mua nang hat.
Han niia, do dac diem hap tbu manh sdng
radar cua nude, ddi tugng nude thudng cd mau den khi bien thi tren anh SAR nen cd the nhan dang va tach biet dugc vimg ngap rd rang (Gan. 2012).
Anh ve tmh radar Palsar thu dugc tie ve tinb ALOS cua Nhat Ban la mdt loai tu lieu anh sieu cao tan nen cac tin bieu thu dugc khdng bi anb budng ciia may va thdi tiet, ddng thdi cd the quan trac trai dat ca ngay lan dem.
Tu lieu cd dd phan giai tu 5 den 100m. Day la loai tu lieu hien dang dugc sir dung nhieu vao ITnb vuc nghien ciiru tai nguyen mdi trudng, khi quyln, dia chat, khoang san va nhiing nghien cuu dy bao cac thien tai nhu lii lut, dgng ddt, trugt Id ddt, fran dau,... (Natsuaki, 2016; Nguydn Thanh Luan, 2017; Pham Xuan Hoan, 2018; Schldgel, 2015; Yin, 2020).
Tai Viet Nam, anh ve tinh Alos Palsar da dugc nghien ciiu phue vy mgt sd Imh vyc lien quan den xac dinb trir lugng, sinh khdi ning (Trdn Tudn Nggc, 2015), thanh lap ban do ngap lut (Nguydn Thanh Luan, 2017), nghien cuu rimg ngap man (Hoang Phi Phung, 2016), tbanb lap md hinh sd do cao (Pham Xuan Hoan, 2018). Tuy nhien, viec img dung anh
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Alos Palsar trong nghien cim phue vy phat bien lu quet chua dugc nghien cuu nhidu. Vi lii quet thudng xay ra trong thdi gian mua keo dai va ldp may phu lau ngay nen trong nhieu trudng hgp, viec sir dung hinh anb quang bgc tbirdng bi can trd. So vdi phuang phap lap ban dd so hda tbu cdng va ban ty ddng, cac be thdng SAR khdng gian thudng la cdng cu dugc lya chgn de quan sat lii quet tir khdng gian. Tuy nhien, trong hau bet cac tru'dng bgp, viec thu thap dir lieu chi dugc thyc bien khi cac c a quan quan ly thien tai yeu cau cac dan vi lap ban dd nbanb tien hanh. Do dd, viec thu thap dii lieu ve tinb de nam dugc dinh lii sau dd la qua mudn, lam giam gia tri cua thdng tin ban dau trong quan Iy khan cap.
Tai Viet Nam, lii quet thudng xay ra d thugng ngudn cac sdng sudi vung nui cd dia hinh phiic tap va mua nhieu, dac biet la cac tinh mien niii phia Bac. Lii quet thudng xay ra do anh hudng ciia mua ldn, xdi xa, hoac do mua trong cac can bao nhiet ddi, ket bgp vdi tinb chat dja binh nhu chenh cao ldn, dp ddc cao va cat xe sau, xay ra bat ngd, tdn tai trong khoang tbdi gian ngan, cd ddng chay xiet, cd ham lugng chat ran cao va sue tan pha ldn d cac khu vuc sudn niii va dgc theo thung liing.
Do vay, viec xay dyng lai hien trang lii quet tai thdi diem xay ra lii la rat can thiet, giiip xac dinh dugc miic do ciia lu quet va nhieu gia tri khac. Vdi nhiing \m diem dd, nghien cuu nay tap tnmg vao ky thuat chiet tach thdng tin ngap lut tir anb ve tinb SAR cho bai tinb Yen Bai va San La, phyc vu thanh lap ban dd hien trang lii quet tai kbu vyc nghien ciru.
1. P h a t hien lu quet tu' t u lieu anh vien t h a m r a d a r Alos Palsar
l.I. Xii'ly dnh
Alos Palsar la loai tu lieu ma hau bet cac phdn m i m thuong mai van chua hd trg md anh trye tilp. Sau khi anh dugc nhap vao pban mem, cac budc thyc bien tiep theo gdm tien xir
ly, xu ly va pban tich anb. Dudi day la mdt sd budc xir ly chinh da dugc tbuc bien:
(1) Dinh chudn dnh
Day la mdt cdng doan cdn thyc hien de chuyin cac gia tri do chdi 16 bit cua pixel thanh cac gia tri do bdng dB hoac do bang cac dai lugng vat ly nhu bien dp (amplitude) hay nang Iirgng (power) la cac dai lugng tuyln tinb, lien quan din cac dac trung vat ly nhu dp phan hdi, binh hoc anh va pha cua tin hieu.
Muc dich ciia viec hieu cbinh phan hdi la tao ra cac du lieu mang tinh dn dinh ve thdi gian va klidng gian ciing nhu loai bd cac anh hudng ben ngoai tdi cac dii Heu do d cac tbdi gian khac nhau. Do viec theo doi Idp phu bang anh radar la da thdi gian nen viec dinh chuan la hoan toan can thiet nham chiet xuat cac gia tn phan hdi ciia mat dat tir dii lieu anh va pbai tinh dugc cac gia tri thdng ke ciia gia trj phan bdi. Cdng viec nay rat quan trpng cho viec pban loai mpt each cd c a sd cac ddi tugng cd phan bdi tuang ty hoac gan nhau. Viec thdng ke theo ham logarit tinh theo dB cd kha nang phan di thdng tin cao hon ham tuyen tinb (tinh theo gia tri nang Iupng hoac bien dp), do dd se mang lai nhilu thdng tin ve sy bien ddi cua cac ddi tu'gng mat dat.
Mdi quan he giiia gia tri do xam ciia anh va he sd tan xa ngugc thdng thudng dugc thyc hien theo cdng thirc (M. Lavalle, 2009, p. 18):
Q O - K . D N ^ (1) Trong dd:
DN: Gia tri do xam cua anh radar K : Hdng sd dinh chudn tuyet ddi a" : Gia tri he sd tan xa ngugc
Mdi loai anh Radar khac nhau d i u cd gia trj K kliac nhau, dugc cung cdp bdi ca quan quan Iy ve tinh. Ddi vdi anb Alos Palsar thi hdng sd K dupe dua ra cho san phdm anh L l . l la-115 dB, cdn vdi san pham L 1.5 la-83 dB.
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Sau dd, he sd tan xa ngugc d l dang dugc chuyin sang gia tri dB theo cdng thuc sau (M.
Lavalle, 2009, p. 18):
0°[dB]-lO.logio(o'') (2) (2) Lgc nhiiu
Cac bd lpc thudng dugc sir dung de lgc anh radar la nhdm tuang tac (Adaptive). Nhdm bd lpc nay dugc thiet ke chuyen diing cho viec xir ly nhilu tren anh radar, trong qua trinh lgc khdng lam thay ddi gia tri trung binh cue bd (Local Mean) ma chi lam giam do lech chuan cue bd (Local Standard Deviation), cho anb min ban so vdi anb gde va van bao toan dugc cau tnic bd ranh gidi. Nhin chung, da sd cac bd Igc nay deu boat ddng tren nguyen tac dya vao tinh chat cue bd ciia vimg anb nam trong cira sd lgc tai mdi vi tri de xay dyng cac ma fran lpc thieh hgp sao cho tai nhii'ng vi tri dugc xac dinh la cd nhieu, Igc phai mang tinb chat ciia mdt phep lpc thdng tan thap (low passed filter) d l loai nhilu. Ngugc lai, tai nliiing vi tri phat hien dugc cac cbi tiet nhd hay cd chi tiet dang friyln chay qua, no phai bao tdn hoac tham chi boat ddng nhu mdt phep lpc thdng tdn cao (high passed filter) de lam noi rd cac chi tilt dd. Rieng lgc Lee lai dya vao md hinh nhilu thyc nghiem de tach rieng nhilu ra khdi tin bieu hiiu ich, qua do loai bd nhieu. Cac phep lgc hay dupe sii dung la: Frost; Lee; Lee- Sigma va Gamma-MAP.
Trong thyc t l , tiiy thudc vao tirng loai ung dung va dac diem cua timg loai anh khac nhau ma lya chgn loai phep lpc pbii hgp. Nhieu la dac tinh dac tnmg ciia anh radar nen khdng the bi Ioai bd hoan toan, my vay sir dung cac phep Ipc mdt each tbich bgp cd the lam giam nhieu di dang k l . Chi tilt v l cac thuat toan lpc cd the tham khao them tai phan thuat toan va trg giup frong cac phan mem.
(3) Hieu ehinh hinh hoc vd cdt dnh theo vung nghiin ciru
De dam bao cho viec ticb bgp giiia cac loai anh vdi nhau, viec hieu chinh hinh hgc phai dat dp chinh xac cao. Trong nghien ciiu nay, phucmg phap nan anh theo da thiic da dugc lua chgn. Tiiy vao timg trudng hgp ma cd the ap dyng da thiic bac 1 hoac bac 2, 3 hoac cao hon. Da thuc bac 1 cho phep xir ly cac sai sd do cac bien dang mang tinh chat tuyen tinh nhu ti le hoac xoay anh cdn de xu ly cac bien dang phiic tap ban thi can dimg cac da thiic bac cao bon, sii dung nhieu diem khdng che ban. Thyc t l cho thdy, ddi vdi nhiing khu vyc bdng phang, nhin chung phuang phap nan anh da thuc cho do chinh xac dat yeu cau cdn d cac khu vyc vimg niu, sai sd nan anh tbudng kha ldn va vugt ban sai cho phep do phuang phap nay khdng giai quyet dugc nhirng sai lech do chenh cao dia hinh gay ra, dac biet la ddi vdi anh radar.
1.2. Phdt hien lu tren dnh Alos Palsar Cac dii lieu anh SAR dugc lya chgn cd tinb din dac dilm phan cyc va kha nang phat hien viing ngap nude tdi da tir anh ve tinh Alos Palsar va anh radar vdi do phan giai cao phue vu chilt tach thdng tin lu quet. Tdt ca anb SAR diu dimg pban cyc HH (pbat phan cyc ngang, thu phan cyc ngang). Day la pban cyc dugc uu tien cho ban dd lii quet vi cd do nhay thdp ban so vdi nhiing sai khac theo cbieu diing tren be mat nude gay ra bdi sdng (Gan, 2012).
Bh xay dung ban dd ngap tir cac anh SAR, nghien ciiu nay su dung cac cdng cu hien dai d l xu ly anh: ENVI, SNAP, ArcGIS. Dua tren nguyen ly phan xa guang cua anh SAR chup b l mat Trai Ddt, khi tin hieu sdng radar truyen xudng b l mat nude (be mat phang, khdng cd sdng), nang lugng phan xa trd lai ve tinh rat thdp va hinb anh vimg ngap nude cd mau tdi xdm. Ngugc lai, cac doi mgng khac cd be mat
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gd ghd boac cd kha nang tan xa rat manh (nhu cac cau true kim loai, cau triic xay dyng, khu do thi, thyc vat cd mat dp day...), cac tia pban xa trd lai ve tinh cd nang lupng manh va hinh anb SAR thu nhan cd ldng mau sang. Trong phan Ioai anh SAR, nghien cuu da su dung phucmg phap dinh ngudng giii'a viing nirdc/
klidng nude de loai bd nhiing pixel viing khdng ngap nude. Anh phan loai vimg ngap nude (raster) d u g c chuyen khudn dang sang vector de xir ly thanh lap ban dd ngap lut tren cac phdn mem GIS thdng dung (nhu Arc/Gis, Map/info). Toan bd qua trinh xir ly anh den thanh lap ban do ngap lut qua 4 b u d c eg ban:
chpn kenh, tang cudng chat lugng anh, nan chinb hinb hpc, phan ngudng.
1.3. Quy trinh phdt hien lu tren dnh Alos Palsar
Quy trinh pbat hien lii quet tren anh Alos Palsar dugc thyc hien tbeo cac budc sau:
Bir&c 1. Chon kenh dnh Palsar, 6 nghien ciru nay kenh d u g c lya chpn la kenh HH.
Bic&c 2. Tdng cic&ng chdt lugng dnh:
Nhieu la mdt trong nhirng tbugc tinh cua anb radar gan lien vdi tinh "don sac" cua buc xa sir dung trong ky thuat radar. Ddi vdi ngudi su dung, day la mpt trd ngai ldn khi phan tich giai doan anh. Rat nhieu phuang phap Igc dugc dua ra nham khu nhieu tren anh radar, trong dd phai ke tdi cac phep lgc nhu Frost, Lee, Sigma, Gamma, Map. Phep Igc Gamma tao ra hinh anh da dugc loai bd ddm, nbieu vdi thdi gian tbuc hien tuong doi thap. Viec xu ly lam giam nhieu phai bao dam sao cho lugng mat mat thong tin la it nhat. Do dd, nghien ciru nay sir dung pbep Ipc Lee, cac hinb anh dugc thyc hien vdi khoang lpc Gamma d mirc 3 x 3 , cho ket qua tot phue vu cbict tach thong tin lu quet.
Bir&c 3. Ndn dnh: Cdng tac nan chinh hinh hgc nham muc dich xir ly nbtrng bien dang hinh bgc sinh ra trong qua trinh chup anh va
do anh huang cua dia hiri,,d6ng thai dBa anh ve he toa dp ban do. Viec nSn cUrii hinh hoc CO y nghia hSt stic quan trpng, Idiong nliihig '^
dam bao dp chinh xac v^ vj tri toa do cna cac doi tuong tren anh ma con ti dam bao sir chong kbit cua cac loai anh voi nhau phue vn cho viec xay dung cac t5 hpp anh ft buoc tigp theo. Do chup anh nghieng ttr mot phia nen anh radar giong nhu cac loai anh ve tinh quang hpc Idii chup nghieng ciing H anh huong lam sai lech vi tri ciia dia hinh. Sai lech tren anh radar la su dich lai gin ang ten thu hon so vol vi tri thuc cua no. MSi loai anh radar se duoc chup vcri goc nghieng khac nhau, tham chl cung mpt thiet bi cung co nhimg chj do chup vol goc nghieng khac nhau, cho nen anh huong ciia chenh cao dia hinh d6i vol mfti loai anh la khac nhau. Vi vay, viec hieu chinh sai so do chenh cao dia hinh gay ra khi n^n anh can sir dung mo hinh so dp cao (DEM). Tren ca sa do, cac phan mem xii ly anh da tich hgp san cac phuong phap nan, hieu chmh anh.
Nghien ciiu nay sir dung phuang phap nan anh
"Ranger ~ Doppler Terrain Correction" dugc tich hpp trong phin mSm SNAP 5.0. Day la phuang phap dupe khuyjn nghi sir dung "ong nghien ciiu thanh lap ban do lu quel tu anh SAR. Voi phuong phap nay, nghien ciiu sii dung ngu6n dir lieu mo hinh s6 dp cao SRTM (Shuttle Radar Topographic Mission) 30m loan ciu, tu dpng dupe tai ve coso dii lieu phin m i m voi phuong phap liy mau dia hinh:
npi suy song myen tinh.
Btmc4. Phdn nguong vd trich nit tkong tin hi: Cong tac phan nguong anh ve hnh SAR Alos Palsar la buoc quan trpng, nham phat hien nai xay ra lu mpt each tu dpng tren toan bo khu vuc nghien cuu. Viec phan nguong nay duoc tiin hanh liy mlu di tinh hung bmh oac thong s6 nguong max va min cua hmg anh, tu do trich xuit ra viing ngap K.
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2. Thirc nghiem phat hien lu quet tii du- iieu anh Alos Palsar tai khu vuc tmh Yen Bai va Son La
2.1. Khu vu-c nghien ctm
Yen Bai va Son La la bai tinb thudc khu vyc Tay Bac Viet Nam cd dia hinh nui cao va chia cat sau, cd nbieu khdi mii va day nui cao chay theo hudng Tay Bac-Ddng Nam. Day Hoang Lien San dai tdi 180 km, rdng 30 km, vdi mpt sd dinh niii cao tu tren 2800 den 3000 m. Day niii Sdng Ma dai 500 km, cd nhiing dinb cao tren 1800 m. Giiia hai day mii nay la viing ddi mii thap luu vyc sdng Da (cdn ggi la dia mang sdng Da). Ngoai sdng Da la sdng ldn, vimg Tay Bac chi cd sdng nhd va suoi gdm ca thuang luu sdng Ma. Trong dia mang sdng Da cdn cd mdt day cao nguyen da vdi chay sudt tu' Phong Thd den Thanh Hda, chia nhd thanh cac cao nguyen Ta Phinh, Mdc Chau, Na San. Khu vyc nay cung cd cac ldng chao nhu Dien Bien, NghTa Ld, Mudng Thanh.
Hai tinb San La, Yen Bai nam trong viing khi hau nhiet ddi gid miia, nhiet dp tmng binh la 21 - 23^C; (cao nhkt tir 37 - 39'^C, thkp nhat tir 2-4''C); lugng mua trung binb 1.500 - 2.200 mm/nam; do am trung binh 83 - 87%. Day ciing la hai tinh chiu nbieu anh hudng nang ne do bien mgng tai bien thien nbien ve lij quet.
Chi tinb tir thap ky 90 the ky XX den nay, hau nhu nam nao tai day ciing xay ra Iii quet vdi miic dp khac nhau.
2.2. Phtrffngphdp nghien ciru
Thdng thudng, biy thudc vao dieu kien thyc te cd the lya chgn phuang pbap giai doan bang mat hoac phuang phap phan loai anh sd.
De chiet tach thdng tin anh vien tbam, tru'dc het can phai tien hanh giai doan anh (hay cdn gpi la qua trinh suy giai anh). Dd la qua trinh tach cac tbong tin dinb tinh ciing nhu dinh iugng tu anh nhd cac dau hieu trye tiep (dau hieu anb) va dau bieu gian tiep (dau bieu phi
anh va cac chi thi). Cd the chia cac dau hieu giai doan anh thanh 8 nhdm chinh sau; kich thudc; hmh dang; hinli bdng; dp dam nhat;
mau sac; cau tnic; hinh mau; mdi lien quan.
Nhu vay, de xac dinh dugc cac trang thai ldp lii tren anh ve tinh can phai phat hien va phan tich cac dau hieu giai doan true tiep cung nhu gian tiep, sir dung ket hgp vdi nhieu ngudn tai lieu. Dac biet, ngudi giai doan phai cd kien thirc ve dia ly, cac dieu kien ty nhien, kinh td- xa hdi cua kliu vyc nghien cuu. Ben canh dd, ngudi giai doan cd the sir dung cac thuat toan cd san tren pban mem hoac xay dyng modul de phan loai va chiet xuat ddi tugng.
Nghien cim nay tien hanh viec phan ngudng tach nude va khdng nude, phan loai va tien hanh trich nit thdng tin dir lieu ngap lut de xay dyng ban dd lii quet va ngap lyt khu vyc nghien ciiu. Tai khu vuc nghien ciiu tinh San La, Yen Bai, ket qua xir ly anh Alos Palsar theo quy trinh tren da xac dinh dugc khu vyc xay ra lii, lu quet (khu vyc mau xanh) (Hmh 1, 2).
3. KSt qua va thao luan
Trong tbyc te, cac trudng bgp lu, lii quet thudng xay ra trong thdi gian mua keo dai va ldp may phii lau ngay nen viec sir dung hinh anh quang hgc thudng bi can trd hoac gan nhir khdng the xac dinh hien trang tai thdi diem xay ra lii quet. Tuy nbien, anh radar khau do tdng hgp (SAR) cho phep tin hieu phan xa tir be mat trong dieu kien thdi tiet cd may, mil, bui khi quyen va ca nhiing tran mua nang hat.
Do d budc sdng dai, anh SAR khdng bi anb hudng bdi tan xa khi quyen nhu anh quang hpc nen cbo phep xac djnb dugc nang lugng budc sdng trong mpi dieu kien thdi tiet va mdi trudng. Ben canh do, ca che tao anli ciia SAR sir dung ngudn nang lupng chii ddng, khdng phu thupc vao ngudn birc xa nang lugng mat trdi nen anli Radar cd the thu dugc ca ngay lan dem (Torres, 2012).
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Dii lieu dp phan cue HH co thi phan biet giUa thuc vat ngap lu va chua ngap lut. Trong khi do, dp phan circ HV c6 thS phan biet thuc vat lii lut va dat km. Anh Alos Palsar co phan cue giong nhau: HH (phat phan cue ngang, thu phan cue ngang), VV (phat phan cue diing, thu phan cue diing); va phan cue cheo: HV (phat phan cue ngang, thu phan cue diing), VH (phat phan cue dung, thu phan cue ngang). Vai cam nhan bang mat, co the thdy rSng phiin cue HH va VV CO doi chut khac nhau, hinh anh tren phan cue VV c6 phdn tdi han so vol HH.
Trong khi do, phan cue cheo HV va VH lai c6 phiin hoi kha giong nhau, cung cap dCr lieu phan cue kep. Do dii lieu HH co kha nang cung cap ket qua tot nen HH dupe chpn diing Hinh 1: HIEN TRANG LU QUET, NGAP LIJT
PALSAR (mdu xanh Id khu vuc xdy ra
ii phat hien lu trong nghien ciiu nay. Nuac dupe nhan biSt tuang doi d6 dang tren tat ca cac phan cue cua anh Alos Palsar do be mat bang phSng nen xay ra hien tupng phan xa guong, tin hieu phan hoi rat yeu va co mau toi.
Anh Alos Palsar tiSn hanh lay mSu de tinli trung binh cac thong so nguong max va min cua timg anh, tir do trich xuat ra viing ngap lut.
Kgt qua phan nguong tach nuac va khong nuoc khi tach thong tin, dupe phan loai va tiin hanh trich riit thong tin dii lieu lii de xay dung ban d6 lii, lu quet khu vuc nghien ciiu. Ket qua bl dii lieu anh Alos Palsar giilp xac dinh dirge hien trang lu quet, ngap lut trong eac ngay 10 -
12 thang 10 nam 2017 tai hai tinh Son La, Yen Bai (Hinh 1,2).
TAI TINH SON LA TlT DtT LIEU ANH ALOS lu quet xdc dinh duae tai tinh San La)
Ngudn. Tdc gid.
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Nguyen Vilt Nghia Nghien cd'u phat hien...
Hinh 2: HIEN TR^NG LU QUET, NGAP LUT TAI TINH YEN BAI TLT DU' LIEU ANH ALOS PALSAR (mdu xanh Id khu vuc xdy ra lu quit xdc dinh duae tgi tinh Yin Bdi)
• f.^f^i'.a;. ^:::$
Ngudn: Tdc gid.
Tren ca sd cae vet lu xac dinh dugc tii anh Alos Palsar, nhdm nghien ciiu tien hanh kiem
Yen Bai, Son La Ket qua khao sat thuc dia cbo tbay, cac vet lii tren thuc dia hoan toan trung khdp vdi hinh anh vet lu tbu dugc tir anh Alos Palsar.
tra xac xuat tren tbuc dia tai dia ban hai tinh
ffinh 3: MOT SO HINH ANH Dl KIEM TRA THUC DIA TAI TINH YEN BAI, SON LA
Ngudn: Be tdi "Nghien cuu xdy dung ban do phdn viing vd cdnh bdo Id quet dp phdn gidi cao eho mpl sd tinh viing Tdy Bdc nhdm tdng euang khd ndng ung phd v&i thiin tai cua edng ddng phue vu xdy dtmg ndng thdn m&i" thupc Chucmg trinh KH&CN phue vu xdy dung Ndng thdn mai giai dogn 2018-2020. Bd NN&PTNN.
PHATTRIEN BeNVO-NGVONGQUYeN 10 S6 1 (3/2020) 135
NGHIEN CO'U THLfC NGHIEM - KINHNRmn,
K6t luan
D6i vol anh radar, bi mat nuoc tai thoi dilm dien ra lu quet dupe su dung lam doi tupng ii xae dinh trirc tilp dien tich ngap hoac dien tich nuoc vi eac gia tri phan xa ciia nuoc rdt thdp. Vol anh Alos Palsar, viec chiet tach thong tin ngap lut tai thiri dilm lu quet ehii yen thu nhan dupe tir nhirng ddu vlt lu di qua de lai uen cac ddi Urong nhu cay coi. Do vay, bii-c anh dupe chup tai thoi dilm xay ra lu quet gay ngap tten bl mat hoan toan co the nhan biet bing mdt thuang. Tuy nhien, vol biic anh chup sau thai dilm xay ra lii thucmg co nhieu vet ngap nho xudt hien tren anh khi xu' ly, qua trinh xii ly anh cdn dupe hieu chinh qua thong tin lop dia hinh.
Lii quet la hien tupng tai biln diln hinh va khac biet so vai 10 thuong. Do tinh chdt diln tiln nhanh voi cuong dp manh, xay ra trong khoang thai gian ngjn, viec xac djnh dupe hien trang lu quet va ngap lut tai thai dilm xay ra lu quet tai 2 tinh Son La, Yen Bai cho phep xac dinh dupe quy mo va miic dp xiiy ra lii.
Tren ca so do, viec thu thap dO lieu anh SAR dp phan giai cao noi chung va anh Alos Palsar noi rieng tai nhieu thai diem xay ra lii quet khac nhau cho phep xay dung dupe biin dl hien trang ciia lu quet tren dia ban hai tinh. Kit qua ciia mo hinh gop phiin xac dinh sir thay doi dien tich ciia ngap lut do hien tupng lii quel gay ra. Cac ban do hien trang lu quet, ngap lut nay eiing co the dupe irng dung trong nhieu nghien cim tiep theo nhu du bao thien tai, lii lut, truot la.
LM cam ffn: D l hoan thanh eong trinh nay, tae gia nhan dupe su h6 trp ciia de tai "Nghien ciiu xay dung ban d l phan vung vii canh bao lii quet dp phan giai eao eho mot so tinh viing Tay Bac nhdm tang cucmg kha nang ling pho voi thien tai cua cpng d i n g phue "vu xay dung nong thon mdi"
thupc Chuong trinh Khoa hpc va Cong nghe phue vu xay dung Nong thon mdi giai doan 2018- 2020, Bp Nong nghiep va Phat triln nong thon (S6 03/HD-KHCN-NTM).
Tiii lieu tham khao
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Satellite-supported flood forecasting in river networks- A real case sX\iAy. Journal of Hydrolog}', 523, 706-724.
4. Giustarini, L., Matgen, P., Hostache, R., Montanari, M., Plaza Guingla, D. A., Pauwels, V &
Savenije, H. H. G. (2011). Assimilating SAR-denved water level data into a hydraulic model: a case stody. Hydrology and Earth System Sciences, 15(7), 2349-2365.
5. Hoang Phi Phung, Lara Dao Nguyen, Pham Bach Viet (2016). Sir dung dir lieu viln tham radar Uong xac dinh rimg ngap man. Tap chi Phdt tridn khoa hoc vd Cdng nghe, tap 19 s6 4, 2016, U 13-121 6. M. Lavalle and T. Wright, Absolute radiometric and polarimetric calibration of ALOS PALSAR
products generated within ADEN, ESA Technical Note, p. 18, 2009.
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(2010). Towards the sequential assimilation of SAR-derived water stages into hydraulic models using the Particle Filter: proof of concept. Hydrology and Earth System Sciences, 14(9), 1773-1785.
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Nguygn Viet Nghia Nghien ciiu phat Men...
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Thong tin tac gia:
^ ^ Ngay nhan bai: 07/2/2020 Nguyin Vigt Nghia, TS _ Ngay nhan ban sira: 28/2/2020 - Dffn vi cong tac: Khoa Trac dia Ban do va , , , . ' . , .- on^nnon Quan ly d4t dai - Tnrang Dai hpc Mo - Dia ^gay duyet dang: 20/3/2020 chat
- Dia chi email: [email protected]
PHAT TRIEN BEN VLJNG VUNG QUVeN 10 S6 1 (3/2020) 137
