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I T N G D U N G C O N G N G H E D I E N T O A N D A M M A Y G O O G L E E A R T H E N G I N E T R O N G N G H I E N C l T U L U L U T T A I D O N G T H A P ,
H A L l T U S O N G M E C O N G '
Vu Hull Long, Nguyen Vu Giang, Pham Viet Hoa, Vien Hdn Ldm Khoa hpc vd Cong nghi Viet Nam Nguyln Thanh Hung Vien Khoa hpc Thuy Im Viet Nam
Tom tat: Cdng nghe diin todn dam mdy dang la mpt xu hu&ng img dung cong nghe thong tin mai vd ddn tr& thdnh nen tdng de gidi quyet cdc bdi todn du: lieu l&n. Nghien cuu nciy ung dung khai thdc cdng ngh^ di^n todn ddm mdy Google Earth Engine (GEE) de xit ly chiit tdch thdng tin dien tich ngdp lut tie die lieu dnh v | tinh quang hpc Landsat (TM, ETM, OLI) giai dogn 1996- 2016 vd v | tinh radar Sentinel-1 giai dogn 2015-2017 cho khu vuc tinh Ddng Thdp, hg luu song Me Cong. Ket qud chudi cdc bdn do ngdp lut duac thdnh lap chi ra W & khu vuc Dong Thdp gdy ra diin ngdp l&n nhdt vdo th&i diem ndm 2000 chiem 77,68% diin tich todn tinh, vd gidm rd rit nhiing ndm gdn day, ngdp 27,76 % ndm 2015. Ngodi viec sii dung di hieu chinh mo hinh du bdo ngdp lut, kit qud ndy cung cdp them lugn cu khoa hpc vd thong tin tin cgy cho viec qudn ly khai thdc vd sic dung ngudn nu&c & dia phuang. Ben canh do, nghien cieu ciing cho thdy cong cu GEE CO tdc dp truy cap vd xie ly dnh ve tinh rdt nhanh v&i dp tin cdy cao. Ddy Id cdng cii rdt co tiem ndng trong viec khai thdc, xic ly, phdn tich dnh v^ tinh vd cdc die liiu khong gian khdc cho nhiiu muc tieu nghien cieu.
Keywords: Google Earth Engine, Bdn do nggp lut
Summary: Cloud computing is a trendy approach of information technology and gradually becoming a platform for addressing big data processing. This study explored the cloud-based platform - Google Earth Engine (GEE) to derive the flood information from optical satellite data Landsat (TM. ETM. OLI) from 1996 to 2017 and radar data Sentinel-1 in 2015-2017 in Dong Thap, lower Mekong river basin. The timeseries flooded maps indicated the most severe flood in Dong Thap in 2000. covered 77.68% province, andfloodings decreased recently, covered only 27.76% province area in 2015. This is a valuable information for water resource management, and validation offloading model in this region. This study also showed the potential application of GEE in accessing and processing multi-platform data for many geospatial researches.
1. DAT V A N D E edu rat biic thiet nhu xac dinh khu vyc bi anh Thanh lap ban d6 ngap lut tit tu li?u anh viln ' " ' ™ 8 ' "^ " ^ > " ? ' h , ! do lu I f t xac dinh v6t tham labai toan rjt ph6 bifa trong linh vvc ^\^^ "^^ <="•* '^° " • * <lw bio. Cimg vol sv c6ng nghl viln tham (MarionTanguy, 2017). " « " ' ' ' " ^ ^ ''>°"8 "^ ^'^ ^^ ' ^ S » * « • Ban d6 ngap M s5 giai quySt mpt s6 cac nhu '^'^ P ! " ' ™ ^ '^'^f' " ««" P^uc vu thanh lap
ban dd ngap lyt ciing cd nhOng thay ddi dd phu hap vdi xu the hidn nay.
Ngaynhanbai: 15/01/2018 -^ ^ Ngay thdng qua phan bi?n; 14/04/2018 Cae phuang phap thanh lap bandd ngap lyt da Ngay duy?t dang: 20/4/2018
TAP CHf KHOA HOC VA C O N G NGHt T H O Y LQI S(5 43 - 2018 19
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dugc nghien ciiu tren thd gidi rdt da dgng tuang ling vdi cac loai tu lieu anh viln thdm khdc nhau. Tgi Hoa Ky, Klemas (2015) da nghidn ciiu vung ngap lyt khu vuc sdng Mississippi bang cap dnh quang hpc Landsat TM truoc vd trong thdi dilm ngap lyt; Kucera (2014) da dimg dnh radar Sentinel-1 A d l thdnh ldp ban dd ngdp lyt khu vyc bdn dao Balkan dya trdn nguong gia tri tan xa ngugc ciia phan cue W trdn dnh. Trong nghien ciiu nang cao dp chfnh xac ban dd ngap lyt tit dnh Sentinel, ndm 2017 tgi Diic, Clement da sir dyng chuoi 15 anh Sentinel 1 phdn cue VV kit hgp vdi thong tin ngdp lyt ehilt tdch tir dir ligu viln tham quang hgc Landsat, cho phep chidt tach dugc ciia timg dilm nggp nhd vdi dg chuih xdc cao (M.A. Clement, 2017). T6 ehiic UN- SPIDER nam 2015 cung dua ra phuang phap thdnh lap ban dd ngdp lut bdng each sOr dung egp dnh Sentinel-IA trudc vd trong thdi diem ngap (UNSPIDER, 2015).
Ci Viet Nam, cdc nghidn ciiu thanh lgp ban do nggp lut da dugc tidn hanh khd nhidu vd ciing da xdy dung thanh cdc quy trinh, ed the ke tdi cac nghien ciiu tieu bilu nhu: nghien ciiu sii dung tu lieu anh radar ERS-2 SAR PRI trong thdnh lap ban dd ngdp lyt ciia Nguyln Thdnh Long vd Bui Doan Trgng (Long N.T., 2001);
nghidn ciiu sir dung du lieu dnh radar ENVISAT va RADARSAT-1 theo doi danh gid thdnh ldp bdn do ngdp lu tgi tinh Long An (QudnN.H.,2013).
Hdu hit vi|c thu thgp vd xii Iy anh vien tham trong cac nghien eiiu trdn dlu thyc hi?n theo each truydn thdng dd la tai dii lieu vl, sau dd xii ly timg cdnh anh sii dung cdc phdn mem hodc cdng cy tren may tinh cd nhan. Phuang thiic ndy vin cdn phd bien hidn nay, tuy nhidn nd cd nhidu nhuge didm dd la: tdc dg xii ly phy thudc vao do Ion ciia dii lieu ciing nhu cdu hinh may tinh. Nhung dii lieu midn phi hi?n nay, dung lugng cd thi len tdi vdi Gb trdn mgt cdnh anh, vi dy dnh landsat 8 khoang 1.8Gb, dnh Sentinel-2 Idn tdi trdn 6Gb, Sentinel-1 trdn
1 Gb, vide xd Iy doi hdi mdy tinh cd cdu hinh phai rat mgnh trdn cdc phdn mdm thuang mgi ddt tiln nhu ENVI, ERDAS. Bdn canh dd vi$c thu thap du lieu cung chilm nhilu thdi gian.
Didn toan dam may dang la m^t xu thd mdi trong xir ly, phdn tich va luu trii dQ lieu hidn nay. Xudt phat tir nhung yeu cdu khoa hpc vd cdng nghd trong ITnh vuc edng nghd khdng gian, Google Earth Engine (GEE) da dugc ng^hidn ciiu vd phat trien. Ddy Id cdng nghd duge phat triln trdn nIn tdng di$n todn ddm may, rdt manh d l xir 1;^ dnh v? tinh ciing nhu cac ngudn dii lidu quan trac khdc. Nhiing irng dyng dugc khai thae ban ddu trdn ndn tang GEE cd thi k l tdi nhu su dyng GEE de phat hidn suy thodi vd mat rimg trdn pham vi todn cdu nhd nguon du" lidu anh Landsat da thdi gian, hay sii dyng GEE d l phdn loai ldp phii, sii dyng GEE d l udc tinh sinh khdi vd trii lugng carbon rimg (M.C. Hansen, 2013; N.
Patel, 2015). Td chiic SERVIR-MEKONG cung dd su dyng cdng cy ndy nhdm ho trg kiem ke va qudn 1;^ ngudn nude mdt.
Xudt phat tir thyc tiln trdn, nghidn ciiu ndy hudng tdi myc tidu thit nghidm khd ndng phdn tfch, xir ly vd khai thdc hd thong co sd dii lieu dnh cua Google trong vide chidt tdch thdng tin dign ngdp lii. Cdng tdc thdnh lap bdn do ngdp lut dugc thyc hi$n trdn ndn tang edng ngh?
dien toan dam may Google Earth Engine. Mgi cdng dogn tir thu thap du lieu, xii Iy, phan tich dnh ddu tiln hdnh true tuyln trdn he thdng may chii cila Google. Tir d6, dl xuat cac phuong an sir dyng, khai thae cdng ey GEE ddy tidm nang nay.
2. KHU Vy'C NGHIEN CUtJ
Tinh Ddng Thap la tinh noi song Me Cdng chay vao Viet Nam tit Campuchia. Day la noi cd ddc didm lu ddc tnmg eho khu vyc Ddng bdng sdng Cim Long (DBSCL). La tinh ndm d viing ha luu sdng Md Cdng, Dong Thap c6 h^
thdng song rach ldn vdi hai sdng chinh la sdng Tidn vd song Hgu. Sdng Tidn chdy vao Vigt
20 TAP CHf KHOA HOC VA C O N G N G H $ T H O Y L(?I S O 43 - 2018
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Nam d khu vyc giap ranh giiia huydn Hdng Ngy tinh Ddng Thdp vd Tan Chau, tinh An Giang vd sdng Hdu chdy qua Ddng Thdp qua dia phan huydn Ldp Vd, Lai Vung.
Hinh 3. Sa do vi tri khu vuc nghien cuu Dgc didm lii tai tinh Ddng Thap chu yeu do mua trdn luu vuc sdng Me Cdng gay ra. Hdng nam, miia lii xdy ra ddng thdi vdi mua mua, keo ddi lien tyc khodng 4-5 thdng, thudng tir thdng 6 ddn thdng 11. Lii DBSCL thudng cd hai dinh, dinh dau thudng xay ra cudi thdng 7 din giiia thang 8, cdn ggi la lii ddu vy, lii thdng 8; dinh sau cudi thdng 9 den dau thang 10, thudng gpi la lii chinh vy. Tuy vay, lu chinh vu cd thi xdy ra mupn han, vf du nhu nam 2011, va mgt so ndm khdng cd lu hay lii rat nhd, chdng hgn nhu 1998, 2015. Lii ddng bdng ldn vd xudng cham, theo diing ban chat cua lii luu vyc ldn. Ndi chung, cudng sudt lii tir 2-3 cm ddn I0-15cm/ngay. Lii ddu vu eo cudng sudt ldn hon lii chinh vy. Trong thdi gian qua, lu d DBSCL dang ed nhOng biln ddi khac vdi traac day, lu ldn dudng nhu xudt hign ft hon trong khi dd lu vira va nhd nhidu hon. Lu trdn
sdng Me Cdng vdo nude ta theo hai hudng: (1) ddng chfnh Md Cdng; va (2) tran qua bidn gidi. Lii trdn quan bidn gidi cd tac dOng gay ngdp ldn trdn ddng bang. Hien nay, lii tran d Tii giac Long Xuydn da duge kidm soat khd tot, cdn d Ddng Thap Mudi gan nhu chua kilm sodt (SIWRR, 2013).
3. T A I L I | : U V A PHUOfNG P H A P
3.1. Cdng nghd dien toan dam mSy Google Earth Engme trong phdn tich xu- ly dnh v% tmh GEE la nen tdng fidn todn dam mdy de phan tich d& lieu vien thdm, thdng so mdi trudng, khi tugng cdp do tu khu vyc nhd tai quy md todn cdu. Tren GEE cd tfch hgp sdn mdt kho luu trii hang chuc petabyte dir lieu dnh viln thdm mien phi tu Co quan Hang khdng Vii try My (NASA), Cue Dja chdt lidn bang Hoa Ky (USGS), Co quan hdng khdng vii try Chdu Au (ESA) va cac dli ligu khdc. Ha tdng dien toan ddm mdy cila cua GEE duge tdi uu hod dl HLXL \^ dQ li^u khdng gian, kd cd ySx ly chudi du lieu vien thdm trong khodng didi gian dai vdi dung lugng rat ldn.
Dieu nay cho phep xii ly, chidt tdch dugc thdng tin nggp lii trong lich su mgt cdch ddng bg tren dign rOng. Nghidn ciiu nay sir dyng dnh vg tinh trong khoang thdi gian 20 nam, giai doan 1996- 2017. Ddy ciing Id giai doan xay ra cdc trdn lii ljch sii tgi Ddng Thdp.
GEE ra ddi xudt phdt tir nhiing y tudng kdt hgp tri thiic khoa hpc vdi nguon du: li^u khong lo va cdc ngu6n lue cdng ngh? mdi nhat cua Google. Sy kit hgp ndy dem den nhihig hi$u qud rdt ldn nhu tdc do xu ly va kha ndng tiiy biln phat triln irng dyng. Tdc dg tinh toan, ySi ly trdn GEE nhanh chua timg cd (NoelGorelick, 2017). Thdng thudng vi?c tdi va xii ly dnh vien tham nhieu thdi diem trong mgt khu vyc nghien ciiu r^ng nhu mgt tinh, mgt vimg hay toan qudc mdt thdi gian tai hdng tudn thgm chi tdi vai thdng cho dii sii dyng mOt may tinh dd ban vai cau hinh mgnh va cac phdn mlm thuang mai phd bien. Tuy nhidn vdi ndn tang di^n todn dam may ciia GEE, vige
TAP CHl KHOA HQC VA C O N G N G H E T H O Y LOI S(5 43 - 2018 21
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tinh toan nay chi mdt khoang thdi gian tinh bdng mgt vai phiit nhd vao vide phdn vimg dir lieu xir ly song song tren he thing may chil ciia Google.
Google Earrth Engine cho phep xdy dung chuong tinh tinh toan dua tren mdt giao dien lgp trinh iing dyng (API) sii dyng ngdn ngtt lap trinh rdt thdng dyng Id JavaScript vd Python.
Tir giao didn API nay, nhdm nghidn ciiu da xay dyng chuang trinh chiet tdch thdng tin dien nggp lii tir tgp d& lidu anh Landsat vd Sentinel-1.
3.2. DO- lieu su- dung
Nghien ciiu sit dung dii li^u dnh vg tinh quang hgc Landsat (cho giai dogn 1996 trd Igi day) va vd tinh radar Sentinel-1 (giai dogn 2015 trd lai day). Ddy Id 2 bd co sd dii lieu anh rat ldn cua MJ vd Chdu Au gdm NASA, USGS vd ESA dd dugc tfch hgp todn bd vao he thdng ea sd dii lieu cOa GEE.
Du- lidu anh Landsat duge sii dyng bao gdm anh Landsat-5 TM, Landsat-7 ETM+, Landsat- 8 OLI vdi cdc ddc tinh chung nhu do phan gidi khdng gian cdc kdnh da pho la 30 m, thdi gian chyp lap 16 ngay, sd kenh phd dii ldn de thuc hidn cdc nhiem vy quan sdt, theo doi nhieu loai ddi tugng, hidn tugng tren be mgt trai ddt, trong do cd lii lyt,
Du lieu dnh ve tinh radar Sentinel-IA, IB Id dii lieu v^ tinh thd he mdi eua co quan hdng khdng vG try chdu Au. Cac vd tinh nay dugc phdt trien de cung cap dii lieu anh vien thdm gidm sdt toan cdu thupc Chuang trinh Europe's Copernicus. Thdng qua vi$c cung cdp ngudn dG- lieu ehdt lugng cao va mien phi tren phgm vi toan cdu, Chuang trinh nay se tao budc thay doi trong cdch quan ly, gidm sdt mdi trudng, hilu va gidi quylt cae anh hudng cua bidn ddi khi hau. Vg tinh nay dugc thilt kl d l thyc hien cac nhiem vy nhu: gidm sat biln, bao gdm giam sat tran ddu vd quan ly an ninh hang hai; giam sat mat ddt ddi vdi rui ro sat Id ddt da, qudn ly tai nguyen riing, nude mat vd ddt dai, lap ban d6
ung phd vdi cae linh hudng khin cap, tfiidn tai phuc vy nhiem vy ciiu hp, nhan dao trong do ddc biet Id ldp bdn dd nggp lut.
Sentinel-IA dugc phdng vao q u j dgo ngay 3/4/2014 vd Sentinel-IB phdng ngdy 25/4/2016. Dli lidu Sentinel-IA va IB Wen nay da dugc cung cdp mien phf trdn he thdng di?n toan ddm mdy ciia GEE, sdn pham dugc dua vdo khai thdc su dyng sau khi da tien hdnh tiln xir 1^ theo quy trinh tieu chudn ciia cdng cy tiln xit ly Sentinel. Do vgy dii lieu Sentinel- 1 sit dyng phyc vy chidt tach thdng tin vimg ngdp lii tgi tinh Ddng Thap dugc bdt ddu tit nam 2015 tdi hidn nay. Trong ndm 2015 tdi cuoi nam 2016 chu ky chyp lap ciia vd tinh Id 12 ngay do mdi chi cd ve tinh l A dugc phdng len q u j dao. Tii khodng thdng 10 nam 2016 trd lai day, sau khi bd sung thdm vd tinh IB, chu k j chup lgp dugc day ban, khoang 6 ngdy mpt dnh. Ddy Id mgt Ipi the rdt ldn trong nghidn ciiu, theo ddi va danh gia dien bien lu lut.
3.3. Phuvng phap su- dyng
Quy trinh xd ly dnh Landsat vd dnh Sentinel-1 ehilt tach thdng tin viing ngap lu dugc m6 ta trong Hinh 2 va Hinh 3. Ve co bdn nhung quy trinh nay deu da dugc sic dung khd phd bien tren the gioi. Tuy nhien, trong nghien eiiu, ndy ngoai vide xu: ly anh ve tinh thdng qua GEE, cdn cd sy thay ddi trong quy trinh chiet tdch dd Id sir dyng ndn mat nuac thudng xuyen trong ndm dugc td hgp theo gia trj trung vi cua khoang thdi gian tmdc miia Iii. Nhd vao phuang phap td hgp nay, nh&ig phan dign tich m^t nude thudng xuydn nhu sdng, kenh, rach, ao nudi thiiy san dugc phan tach ridng. Do do, loai bd dugc phdn dign tich mgt nude khong phai do nguydn nhan ngap lii trdn dnh v^ tinh da thdi gian. Nguyen tdc nay dugc ap dung eho ea 2 loai tu lieu anh Landsat vd Sentmel-1.
Tu lieu dnh giai dogn 1996-2017 cung dd dugc sii dung truy vdn Igc kit qua dnh chup theo thdi dilm xay ra Iii, ddc bigt la dinh lu cde ndm. Lu d ddng bdng song Cuu Long ndi chung va d Dong
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Thdp ndi ridng cd dinh lu c6 the duy tri lidn tyc trong vdng 10 ngdy, sau dd cd the xudng, nhung xudng rat cham. Do vdy, xdc xudt chyp dugc anh vd tinh tai thdi diem lii la kha eao khi sii kdt hgp cdc ngudn tu lieu anh ve tinh hidn cd.
Vdi anh vd tinh quang hgc Landsat, quy trinh xir ly t|.p trung vao viec loai bd cac ydu td nhilu gay ra bdi may, tinh td hgp bu may, sau do tinh chi sd nude khac biet nude Normalized Difference Water Index (NDWI).
NDWI Id mgt phuang phap da dugc phat trien de nhan didn ddi tugng mat nude vd tdng cudng hidn thi ddi tugng mat nude trdn tu lieu viln thdm bdi McFeeters (1996). NDWI su dung kdnh phd phdn xa d ddi can hdng ngoai (NIR) va kenh phd phan xg d dai sdng xanh lyc (Green) de phdt hidn sy co hi|n didn cua nuac mat, ddng thdi loai bd su hien dien ciia cac doi tugng khac tren be mat nhu ddt vd thuc vat. Trong nghien ciiu ndy, NDWI cho phep xdc dinh didn tich phan bd nude mgt trdn dnh chyp thdi diem Iii vd didn tich nude mat thudng xuydn trdn dnh td hgp trudc lu (tii thdng 1 din thang 7). Cdng thiie tinh chi sd nude mat nhu sau:
Green-NIR
dnh sdm mdu, ddy Id co sd dd dd phdn tach didn tich nude vdi cdc ddi tugng be mat khdc.
NDWI= ^ Green+NIR
Trong dd Green tuang iing vdi kdnh 2 cila dnh Landsat TM, ETM va kenh 3 tren dnh Landsat 8 OLI. NIR tuong iing voi kenh 4 cua anh TM, ETM vd kdnh 5 cua anh OLI.
Ban dd vimg ngap lu la sdn phdm cudi cimg sau khi da logi bd cdc ddi tugng nhu mgt nude thudng xuyen trong ndm, cae ddi tugng khdng phai mat nude (ddt, thye vat).
Vdi anh radar Sentinel-1, nghidn ciiu sur dyng chuoi dnh phdn cue VV chyp trudc vd trong thdi didm lu. Ddc tinh sdng radar phan cyc W phan xg Igi tir bl mat nude tdi ddu thu tren ve tmh Id rdt nhd do tin hieu tan xg ngugc ciia cac sdng radar tir bl mat phdng cua nude ve dau thu rdt ylu. Vi vgy, cae dilm anh (pixel) trdn anh radar thudng CO gia trj rdt thdp, the hien bang cac diem
Anh v§ tinh Landsat (TM, ETM+, OLI) tren GEE
Lgc ^ h theo bi^n thdi gian v i khdng gian
Tien xir ly anh (Ipc b6 mSy)
Tinh chi s6 nude mat NDWI cho cdc anh trong nSm
Tinh chi s8 nuac mat NDWI tai
thfiri dilm lu
Tinh t6 hop chi so niiorc mat NDWI theo gii
tri trung vi tru<!fc thdi di^m
Chiet tach di^n tich vijng nggp lu
Lap ban do ng^p lu
Hinh 4. Sa dd quy trinh xie ly chiit tdch thong tin viing ngdp lu sii dung dnh Landsat tren GEE Anh ve tinh Sentinel-1 phdn cyc VV chyp trudc thdi didm lii cung dugc td hgp gia trj trung vj d l xac dinh cdc dien tich mdt nude thudng xuyen, tuang ty phuang phap da tiln hanh trdn dnh Landsat.
Anh Sentinel-1 phan cue VV chyp trong thdi didm Iii se cung cap thdng tin mat nude phan bd tgi thdi dilm chyp, tiic la bao gdm mdt nude thudng xuydn vd mat nude do ngap IG. De chidt
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tdch dugc dien nggp lii, phuong phdp ldy nguong hieu sd giiia dnh phan cyc chyp trong thdi didm ngdp Iii va trudc khi ngap lii. Qua phan tich thdng ke cae diem mau nude thyc td vd gid tri cac diem anh tren phan cyc W , nghien ciiu da Idy nguong gid tri higu 2 thdi didm vdi mat nude la nhd hon -3.5 Decibel.
T§p hpp anh Sentinel-1 tren GEE
LQC anh theo biln th&i gian vi khong gian
Lira chgn phan circ VV (don vj decibel)
Anh Sentmel-1 chyp trong th&i
di€m lu
T6 hgrp anh Sentinel -I chyp tmdc "thoi
diem lu
Liy higu gid trj dilm Anh t^i hai th&i dilm trudc vk trong lu
Chiet tach di?n tfch viing ngap Ifi
/ Lgp ban dd ngap lu /
Hinh 5. Sa dd quy trinh xie ly chiit tdch thdng tin vung nggp lii sie dung dnh radar
Sentinel-1 tren GEE
4. KET QUA VA T H A O IAJAN
Kdt qim cac budc xir ly dnh thyc hign cho mdt thai diem lu sii dyng dnh Landsat dugc minh hpa trong Hmh 4. Theo dd tap anh Landsat sau khi truy xudt tir co sd dQ Ueu cua Google se dugc lgc
bd may vd tinh anh td hgp cho thdi diem trudc va trong lu. Cae pixel dugc xdc dinh Id mdy dugc loai bd hdt, thay vao dd Id cac gjd trj dilm dnh dugc td hgp bii vao tir nhiing dnh khdng mdy c6 Ihdi gian, miia tuong ty trong ndm.
Anh Landsat td hgp trudc thdi didm lii trong ndm thd hien dugc gid tri tnmg vi cua timg pixel (Hinh 4b), nhiing phdn didn tfch nude thudng xuyen trong nam gan nhu dugc gift nguydn ddc tinh phd la nude do vay d l ddng dugc phat hien (Hinh 4d). Phuang phdp ndy cho phep ldy dugc mep nude dn dinh trong nam cua cac nhanh sdng, ciing nhu ao, hd ngi ddng. Kdt qud chidt tdch khdng chi ling dyng trong pham vi de tai nghien ciiu md cdn cd thd sir dyng dd nghidn ciiu thay ddi hinh thdi song, sgt Id vd bdi ty theo thdi gian.
Anh chyp thdi 4dm lu dugc tinh todn chi so nude mat NDWI, qua dd xac djnh dugc miic d0 phan bo nude mat tgi thdi dilm lii Bk ehilt tach ridng didn tich nggp lu thi phdi logi bd nhOng pkel khdng bi ngap vd nhiing pixel mdt nude thudng xuydn trong nam, do vay kdt hgp gifia anh truoc vd troi^ lu se thu dugc kit qua dien tich vung ngap lu (Hinh 4e). Vimg nggp lyt nay dugc sii dung ham thdng ke true tidp tren GEE cho phep trich xuat didng ke khdng gian cdc vung ngap lii.
Tiep can ndy dugc tiln hdnh tuong ty vdi anh Landsat cac ndm 1996, 2000, 2001, 2004, 2008, 2009, 2011, 2014. Day Id nhihig ndm diln hmh, cd dii lieu dnh vg tinh chyp tai thdi dilm lu. Dae bidt ndm 2000 la nam co tran lu Ijch sii ldn nhdt trong hon 80 nam qua tai ddng bdng sdng Cihi Long (Hdi T.N., 2009).
Kit qua xii l;y dir lifu anh radar Sentinel-1 tren Google Earth Engine, dugc md td vdi thdi dilm lii nam 2017 trdn Hinh 5. Trong dd Hinh 5a the hien dnh Sentinel td hpp nhiing thang trudc miia lu, tir thdng 1 din thang 7. Trong do, cac pixel sam mdu la dien tich mat nude thudng xuyen trong nam. Hinh 5b thd hien dnh chup tgi thdi dilm lii, vdi khodng di^n tfch mat nude la cdc pixel sam mdu phdn bd kha r^ng.
TAP CHI KHOA HOC VA C O N G N G H E T H O Y LOI S6 43 - 2018
Sau khi Idy hidu giiia hai anh chyp trudc vd trong lu thu dugc dnh nhu Hinh 5c. Tu: dnh bidu phan eye nay, ldy nguong d l ehilt tdch vimg ngdp lu (Hinh 5d), mOt t^p hgp cae dilm mdu chidt tdch da dugc thing kd de phan tich nguong chuan, gia tri chudn theo dan vi decibel bidu hai anh trudc vd trong lii dugc xdc dinh d ngudng -3.5. Phuong phdp nay ap dung cho dnh Sentinel-1 nam 2015, 2016 vd2017.
Thdng qua cdng cu GEE, nghidn ciiu da tien hdnh phan tich thong kd dien tich ngdp lii ndm cac nam. Kdt qud dugc t h i hidn trong Bang 1, bidu dd trong Hinh 6 vd Hinh 7.
Bdng thdng ke (Bang I) vd Bilu dd (Hmh 6) dd ehi ra, cdng vd nira dau nhung ndm 2000 trd ve truoc, dien tich ngdp lu cdng rpng, nhdt Id thdi didm ndm 2000, nam ghi nhdn cd dinh IQ cao thii hai trong lich sir, sau nam 1961. Dien tich ngdp lii Idn nhat vao nam 2000 vdi 77.68% dien tich tinh Dong Thdp. Didn tich nay cao hem rdt nhilu so vdi nhiing ndm cdn Igi, didu ndy phan ndo cho thay cudng dp eua trdn Iii ljch su ndy. Ngoai ra lii nam 1996, 2001, 2004 ciing cd dien tich ngdp lu khd ldn hi 68-70%, ttong dd lu nam 1996 vd 2001 ciing ndm vdo nhdm nhihig trdn lii Idn ljch su tgi ddng bdng sdng Cuu Long.
Vdi chudi sd lieu ket qua thu dugc, dien tich nggp lii khd tuong ddng tir sau ndm 2000, va hai giam nhiing ndm nita cudi thdp nidn, chilm khoang 62% giai doan 2008-2009. Ndm 2011 10 Igi tang trd lai vdi cudng do rdt mgnh, dinh lii dgt 4.87m vd didn tich ngdp lu thdng kd trdn dnh vao thdi 4dm thdng 10 (lii chfnh vy) ndm 2011 ldn tdi 67.84%. Sd lieu dinh lii ciing nhu thdng ke didn nggp lii trdn dnh tir sau ndm 2011 dd thdy cd sy gidm xudng nhanh chdng.
Sd lieu didn tich nggp lii thdng kd tren dnh radar SentineI-1 giai dogn 2015-2017 cho thdy thdi gian dinh lu chi ngap khoang 27.76 %, thdp nhdt trong giai dogn theo ddi. Cd nhieu nguyen nhan dan tdi su suy giam ndy, trong do phdi ke tdi hidn tugng El Nino (2014-2016), hogt ddng xay dyng de bao chdng lu dd san xuat liia vy 3,
tdc ddng tich nude vd didu tidt ddng chay eiia cdc dap thuy dien xdy dyng trdn thugng ngudn sdng Md Cdng. Day cung Id khdi ddu cho mgt ndm DBSCL ganh chiu mOt dgt ban man nghidm trpng nhdt vao miia khd 2015-2016.
e)
Hinh 6. Kit qud xii ly dnh Landsat tren GEE qua cdc bu&c, trong do: a) Anh th&i diem lii 27/9/2000; b) Anh td hap tru&c thai diim lU nam 2000; c) Anh chi sd nu&c mat th&i diem lu, d) Anh chl sd nu&c mat tru&c th&i diem lit;
e) Anh chief tdch vung nggp lU 9/2000.
TAP CHf KHOA HOC VA C O N G N G H E T H C I Y LOI S6 43 - 2018 25
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Hinh 7. Ket qua xu ly dnh Sentinel tren GEE qua cdc bu&c, trong do: a) Anh phdn cue W chup tru&c th&i diim ngdp lU to hgp thdng 1- thdng 7/2017; b) Anh phdn cyec Wchtfp trong
thai diim ngdp lu thdng 10/2017; c) Hieu s6 giua hai dnh trong vd tru&c lii, d) Diin tich vung ngdp lU duac chiit tach 10/2017
Bang 1. Thong ke dien ngap Ifi tirong irng vol dinh lu trong nam giai doan 1996-2017
S6 lieu quan tr4c dinh lu t^itr^mTan Cliau Dien tich ng^p lu tinh tir anh ve tinh Dien tich khong phai vung ngap Iii chiet tach ttr anh ve tinh
1996
4.86
68.93
31.07 2000
5.06
77.68
22.32 2001
4.78
69.65
30.35 2004
4.4
70.29
29.71 2008
3.73
62.84
37.16 2009
4.12
62.00
38.00 2011
4.87
67.07
32.03 2014
3.5
46.51
53.49 2015
2,55
27.76
72.24 2016
3,0
30.77
69.23 2017
3.5
42.70
57.30
S6 lieu thdng ke cho thjy lu nam 2016 rit nho, chi cao hon nam 2015 mot chiit voi 30.77%
ngap. Tuy nhien ikn nam 2017, tinh hinh lu tji khu vuc D6ng Thap da chuyjn biin, dinh lu dat 3.5m dien ngap lii la 42.7%. Lu 2017 duoc
danh gia la vira phai, khong ldn qua vk khong nhd qua da dem lai nhiSu Igi ich cho ngucfi dan sinh song va cac hoat dpng san xudt nong nghiep tai dia phucmg.
26 TAP CHl KHOA HQC VA CONG NGH$ T H O Y LOI SCi 43 - 201S
I KHOA HOC ^ E i ! g ? ! 3 ! a i
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^ ^ Sfi li#u quan trie dinh 10 t^i tr^m TSn Chiu
— Dijntich ng?p 10 ti'nh t(r j n h
Hinh 8. Sa do dien ngdp lii vd so lieu dinh lii theo cdc ndm giai dogn 1996-2017
N3m 2016
Nam ' 6 2015
N3m 2014
Nam 2017
>9.ay
E9 1996 100.00
Nam 80.00 2000
e o . o y ' ^ * * ^ - ^
^IJfL/ \ NSm
3 0 . > f «> ^ 4 ^ 0 . 3 5 \ 27.A0O I q 7 , 1
7 Y >••" ^^^
.4^132.93 JF-lfi / 2004
" A W-5o flf 84
2008 Nam N i m 2011 2009
—0\^n dch ng|p IG
^ D i ^ n ti'ch kh6ng ph j i vCing ng^p 10
Hinh 9. Biiu do so sdnh phdn trdm diin tich nggp la theo cdc ndm giai dogn 1996 - 2017
khu vuc tinh Dong Thdp Sd lieu nam 2011 eho thdy dinh lu rat cao, cao hon so vdi ndm 1996, 2001 va 2004, tuy
nhidn dign ngdp lii lai thdp hon tir 2-3%.
Nhin trdn dnh nggp lii cd thd thdy mgt sd khu vyc sdn xudt liia khdng bi ngdp nhd nhiing tuyen de bao ngdn lii mdi dugc xdy dyng tgi khu vuc ndy. Bidu do Hinh 7 md td didn ngdp lii so vdi phdn khdng bi nglp do lii gifta cae ndm. Nghien eiiu cho thdy sy dao chidu cua di^n ngdp lii giai dogn trudc ndm 20! 1 vdi giai doan sau ndm 2011. S6 lidu ndy ciing khdc hpa phdn ndo sy thay ddi didu kien nude mat ea vd ty nhidn (El Nino) lan tdc dOng cua con ngudi trong vi^c xdy mdi cdc dd bao ngdn lii vd vide tich tru, dieu tiet nude tir cac ho thiiy didn thugng ngudn sdng Md Cdng.
Vd ca ban phuang phdp chiet tach vimg ngdp lu su dyng edng nghe dien toan dam may da ddp ling dugc cdc yeu cau ky thuat vdi ehi phi vira phdi. Cdc quy trinh de xuat de giai quyet da cd nhihig cdi tien, hieu chinh ddp iing ydu cdu thye tidn. Vdn dd cdn thye hign trong thai gian tdi dd Id tich hgp vigc thu thgp va xir ly du: li^u vidn tham can thdi gian thuc. Ngodi thdng tin vd dign nggp lii cdn cd cdc thdng tin khi tugng va mdi trudng khdc cd thd hd trg la ddu vao cua md hinh du bdo lu sdm cho khu vyc nhu: dii ligu mua ve tinh, dg dm, do bde hoi vd cac dd lieu tram khi tugng m^t ddt dugc chia se tren GEE.
5. KET LU^J^ VA K H U Y £ N N G H | Kdt qud nghidn ciiu da xac lap duge quy trinh xii Iy, tinh toan chiet tach vimg ngdp lyt sd dyng tu li$u dnh vd tinh quang hpc va radar trdn ndn tdng didn todn dam mdy GEE. Nghien ciiu da thyc nghiem tic khau khai thdc, xu ly va phan tich dnh vg tinh tren hg thong GEE, qua dd chiet tdch dugc didn bidn ngdp lyt tai khu vyc tinh Dong Thdp.
Thdng tin di^n tich viing ng$p lu chiet tdch tir anh vg tinh qua cac nam giai doan 1996-2017
TAP CHf KHOA HQC VA C O N G N G H £ T H O Y Lpl SO 43 - 2018 27
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da phdn ndo eho thdy sy tinh chdt ddc diem lii tgi khu vyc tinh Ddng Thap va ddng bdng song Cim Long. Ket qud ndy ddng thdi cd thd dugc sii dung dd hidu chinh md hinh dy bdo lu sdm cho khu vyc nghidn ciiu. Vdi Igi the phdn tich dii lieu dnh ve tinh cho khu vyc cd phgm vi ldn cua GEE, khi md rpng khu vuc nghidn ciiu sang vimg Campuchia vd ha Ldo cd thd chidt tdch dugc thdng tin mep nude, vdt lii lich su dd cung cdp ddu vdo cho md hinh dy bdo lu tgi Ddng Bdng Sdng Ciiu Long.
Nghien ciiu nhan thdy viec sir dung ndn tang dign todn ddm mdy GEE cd rat nhieu tiem nang. Thyc td eho thdy tdc dg xd 1;^, phan tich dnh vd tinh nhanh hon rdt nhidu so vdi xd l^
tren mdy tinh ca nhan. Do vdy he thdng phii
hgp vdi cde nhiem vu cd quy md xd ly dii lieu d mgi cdp dQ td ldn tdi nhd. Cd thd phat tridn dd tich hgp xay dyng cdc h§ th6ng theo ddi giam sdt gdn thdi gian thyc.
L&i cdm an
Nghien ciiu nay da nhan dugc sy ho trg vd kinh phf vd dii ligu thuc hidn tir Dd tai Ho trg Nghien eiiu vien tre ma sd CNVT17.TR03 va Dd tdi "Xdy dyng co sd dtt ligu vd cdnh bao sdm lu lyt khu vuc H^ng Ngy, tinh Ddng Thdp" chu tri thyc hien bdi Vign Cdng nghe vii try, Vign Hdn ldm Khoa hpc vd Cdng nghe Vigt Nam. Dir li|u dnh vd tinh sir dyng tii USGS, ESA vd cdng cy xd ly dnh vd tmh mien phi GEE cua Google.
TAI LI^U THAM KHAO
[I] Camara. (2000). TerraLib: technology in support of GIS innovation. Proe. II Brazilian Symposium on Geolnformatics. Geolnfo, 1-8.
[2] Hdi, T. N. (2009). Mgt sd trdn lii didn hinh vd phdn vimg nggp lut d ddng bdng sdng Cihi Long. Tuyin tgp Khog hpc Cdng ngH 50 ndm xdy dung vd phdt trien. Vign Khoa hoc Thiiy Igi Vigt Nam.
[3] Klemas, V. (2015). Remote Sensing of Floods and Flood-Prone Areas: An Overview.
Journal of Coastal Research: VolumeSl, Issue 4:, 1005-1013.
[4] Kucera, J. (2014, May 28). Sentinel-1 aids Balkan flood relief. Retrieved from http://www.esa.int/Our_Activities/Observing^the_Earth/Copemicus/Sentinel-l/Sentinel- 1 _aids_Balkan_fIood_relief
[5] M.A. Clement. (2017). Multi-temporal synthetic aperture radar flood mappmg usmg change detection. Journal of Flood Risk Management.
[6] M.C. Hansen, P. P. (2013). High-resolution global maps of 21st-century forest cover change. Science, 342 (2013),, 850-853.
[7] MarionTanguy. (2017). River flood mapping in urban areas combinmg Radarsat-2 data and flood return period data. Remote Sensing of Environment, 442-459.
[8] McFeeters, S. K. (1996). The use of Normalized Difference Water Index (NDWI) in the delineation of open water features. International Journal of Remote Sensing, 17(7), 1425-1432.
[9] N. Patel, E. A. (2015). Multitemporal settlement and population mappmg from Landsat using google earth engine. Int. J Appl. Earth Obs. Geoinf. 35 (2015), 199-208.
28 TAP CH( KHOA HOC VA C O N G N G H C T H O Y LOl $6 43 - 2018
I KHOA HOC — A l J M ; M ! l d W [10] Long N.T., Trgng B.D. (2001). Flood monitoring of Mekong river delta, Vietnam using
ERS SAR data. Asian Conference on Remote Sensing. Singapore.
[ I I ] NoelGorelick, M. e. (2017). Google Earth Engine: Planetary-scale geospatial analysis for everyone. Remote Sensing of Environment, 18-27.
[12] Qudn, N. H. (2013). Mgt sd phuang phdp xdy dyng bdn db ngap lii tmh Long An trong dieu kien bien ddi khi hau, nude bidn ddng. Science & Technology Development, Vol 16, No, 32-39.
[13] SIWRR. (2013, 10). Retrieved from http://www.siwrr.org.vn/eng.asp7i d=news&cid=37I&nhom=94&page=
[14] UNSPIDER. (2015, 09 25). Step by Step: Recommended Practice Flood Mapping.
Retrieved from http://www.un-spider.org: http://www.un-spider.org/advisory- support/recommended-practices/recommended-practice-flood-mapping/step-by-step
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