Qudn ly Tdi nguyen rirng & Mdi tru-ons
DANH GIA KHA NANG KHAI THAC ANH VE TINH QUANG HOC MIEN PHI PHUC VU GIAM SAT L 6 P PHU MAT DAT TAI VIET NAM
Pham Van Duin\ Lg Sy Doanh\ Vu Thi Thin\ Nguyen Van Thj' Ho^ng Van Khien\ Pham Tien Dung^, Dinh Van Tuyen^
'Trucmg Dgi hgc Ldm nghiep
^Vien Khoa hgc Ldm nghiep
^Bg Nong nghiep vd Phdt trien nong thon TOM T A T
Viec ket hop cac loai Ur lieu ve tinh quang hoc khac nhau se lam tang co hoi cho viec co dugc anh khong may phuc vu thuong xuyen hem cho muc tieu giam sat be mat trai dat. Hien nay, cac ve tinh quang hpc nhu:
Landsat-8 OLI (tir 2013), Sentinel-2 MSI (Sentinel-2A - tir 2015; SentiDel-2B - tir 2017) hien dang cung c5p anh mien phi tren pham vi toan cau voi do phan giai khong gian tir 10 den 30 m tao ra co hpi rat ion de giam sat be mat trai dat. Su dung cac bp suoi tap anh Landsat 8 OLI va Sentinel 2 M S ! chup trong nam 2018 tren nen tang dien toan dam may ciia Google Earth Engine, nghien cmi da xac dmh kha nang khai thac timg loai tu heu anh neu tren va kel hpp chiing voi nhau tren toan lanh tho Viet Nam. Ket qua nghien cuu da chiing minh tien ich ciia viec ket hpp hai loai tu lieu anh Sentinel-2 va Landsat-8 de nang cao tan so va giam thoi gian lap lai anh cho tirng tinh ciia Viet Nam. Theo do, neu khong xet den anh huong ciia may va bong may thi trung binh tai mpt vi tri tai nuac ta, chu ky lap lai ciia anh: 15 ngay (Landsat 8), 4 ngay (Sentinel 2) va 3 ngay (ket hpp hai loai anh). Nhung neu loai bo anh huong ciia may va bong may thi, tinh trung binh cho moi vi tri tai Viet Nam, chu ky lap lai ciia anh: 30 ngay (Landsat 8), 10 ngay (Sentinel 2) va 7 ngay (ket hgp hai loai anh). Tuong iing vai ty le so anh Landsat 8 va Sentinel 2 co the sii dung cho muc tieu giam sat be mat so v6i tong so anh thu duoc tuong ling la 5 1 % va 39%. Voi chu ky lap lai ciia anh nhu vay, tu lieu anh Landsat 8 OLI phii hpp cho muc tieu giam sat bien dpng hang nam. Trong khi do, tu lieu anh Sentinel 2 MSI phii hgp cho muc tieu giam sat bien dpng hang quy. Su ket hpp ciia ca hai loai tu lieu anh co the dap iing dugc muc tieu giam sat bien dpng tren mat dat hang thang.
Tir khoa: Anh ve tinh quang hoc, GEE, Landsat 8 OLL Sentinel 2 MSL
1. DAT VAN DE
Ket hgp tu lieu anii quang ligc cua cac ve tinh khac nhau lam tang ca hpi lay dugc anh khong CO may phuc vu cho viec giam sat be mat trai dat (Roy et al, 2006; Brown et al, 2006; Fensholt et al, 2009; Kovalskyy va Roy, 2013). Gan day, cac loai tu lieu anh quang hgc CO do phan giai khong gian tmng binh nhu:
Landsat 8 OLI, Sentinel 2 MSI dugc cung cap mien phi da ma ra nhiing trien vgng va tiem nang ung dung rat Ion trong dieu kien cua cac nuac dang phat trien (Drusch et al, 2012; Roy et al, 2014) nhu Viet Nara.
Gan day, su ra dai va phat trien ciia nen tang dien toan dam may CLia Google Earth Engine (GEE) cho phep ket hgp mgt kho lim trii lan anh vien tham va cac dii lieu khac, dugc toi iru hoa cho xu ly cac dii lieu khong gian dia ly. Cac thuat toan dugc tich hgp trong GEE cho phep cung cap mgt each nhanh chong va true quan ve ket qua ciia cac phan tich khong gian phiic tap da thiic ddy manh me kha
nang va trien vgng iing dung cong nghe vien tham trong cong tac giam sat be mat trai dat a quy mo khu vuc va tung dia phuang. Dieu ma truoc day neu sii dung anh don le, tren cac phan mem thong dung, vai phuang phap xii ly truyen thong rat kho thuc hien hoac mat rat nhieu thai gian va cong siic.
Xet tren khia canh iing dung, khi cac ve tinh viin tham dugc thiet ke thuang quan tam den cac chi so; do phan giai khong gian, do phan giai pho, do phan giai xa, do phan giai thai gian (Carrasco et al, 2019). Trong do: (1) do phan giai khong gian la viing hoac doi tugng nho nhat tren mat dat co the phan biet dugc bai bg cam ciia ve tinh, hieu mgt each don gian thi do phan giai khong gian chinh la kich thuac cua diem anh; (2) do phan giai pho la vung buoc song ma biic xa tu'ong irng ciia no c6 the thu nhan dugc a bg cam ciia ve tinh, hieu dan gian ban thi do phan giai pho chinh la so kenh anh; (3) do phan giai xa la so bit ciia anh, do phan giai xa thap thi su phan biet cac doi tugng
TAP CHI KHOA HOC VA CONG NGHE LAM NGHIEP SO 3 - 2019 65
Qudn ly Tdi nguyen rung & Mdi tru-dns tren be mat se khong cao va ngugc Iai; (4) do phan giai thoi gian la khoang thai gian giiia hai lan thu nhan dii lieu lien ti^p tai mgt vi tri tren mat dat hay con ggi la chu ky bay chup, Bg phan giai thoi gian cang cao, nghla la khoang thai gian gian each giiia hai lan chup tai mgt vi tri cang ngan thi cang tang co hgi co dugc anh chat lugng tot trong di6u kien bi anh huong ciia may va cac tac nhan khac.
Do phan giai thai gian hay chu ky bay chup cua tieng loai tu lieu anh: Landsat 8 OLI, Sentinel 2 MSI (gom ca Sentinel 2A va Sentmel 2B) da dugc nha san xuat dua ra tuong ling la: 16 va 5 ngay. Nhu vay, tai mgt vi tri tren mat dat, neu bo qua su triim phii giiia cac canh anh ciia ciing mgt loai anh thi trong mgt nam se thu nhan dugc 22 - 23 eanh anh Landsat 8 OLI va 95 - 96 canh anh Sentinel 2 MSL Trong dieu kien nhu vay, khi ket hgp hai loai tu lieu nay vai nhau, tai mgt vj tri cit toi da 4 ngay se thu nhan dugc mgt canh anh. Tuy nhien, xet tai mgt vi tri cu the, trong so cac anh thu nhan dugc c6 bao nhieu anh dam bao chat lugng (khong co may va bong may) phue vu cho muc tieu giam sat tren mat dat lai chua dugc quan tam nghien ciiu thoa dang.
Muc tieu ciia bai bao nay la xac dinh so lan thu nhan anh Landsat-8, Sentinel-2 va su ket hgp ciia hai loai anh tai timg vi tri cu the tren ianh tho Viet Nam cho timg thang trong nam va ca nam 2018 trong dieu kien khong va co xem xet den anh huong ciia may. Tir do, xac dmh so lan thu nhan anh dam bao chat lugng:
trung binh, do phan giai thai gian toi thi§u, trung binh va toi da cho timg loai va ket hgp hai loai tu lieu anh Landsat-8, Sentmel-2 cho timg tinh va tren toan lanh tho Viet Nam.
2. PHUONG PHAP NGHIEN ClTU 2.1. Tir lieu sir dung
Tw lieu dnh
Ve tmh Landsat-8 dugc phdng ngay 11/02/2013 vao quy dao dong bg mat troi voi dp cao va do nghieng tuang img khoang 705 km va 98,22*^, thoi gian bay qua xich dao la 10:00 sang (Irons et al, 2012). Du lieu dugc thu nhan voi truang quan sat 15° cung cSp anh co kich thuac 185 km va chu ky bay chup la 16 ngay.
Sentinel-2 bao g6m 2 ve tinh: Sentinel-2A
dugc ph6ng vao ngay 23/6/2015 wi Sentmel- 2B dugc ph6ng vao ngay 07/3/20 1 vao quy dao dong bg mat troi vai do cao '^^6 km, . nghieng 98,62" va thoi gian bay qu^i '^ich dao la 10:30 sang va do tre pha giira liai ' ; tinh la 180" (ESA, 2015). Dir lieu dugc thu nh^n vai truang quan sat 20,6" cung cdp anh co kich thuoc 290 km va chu ky bay chup cua moi cam bien fa 10 ngay va 5 ngay khi k^t hgp hai cam bien voi nhau.
Tu heu anh: Landsat-8 OLI va Sentinel 2 MSI su dung trong nghien ciru nay dugc khai thac tii bg suu tap tren GEE. Cu the:
Anh Landsat 8 OLI dugc khai thac tir bg suu tap: USGS Landsat 8 Surface Reflectance Tier I, chup nam 2018, xii ly den mirc Tl da dugc dua vh gia tri phan xa be mat tren GEE.
Anh Sentinel 2 MSI dugc khai thac tit bg suu tap: Sentinel-2 MSI: MultiSpectral Instrument, Level-2A, chup nam 2018 tren GEE.
Tw lieu bdn do
Ban do ranh giai hanh chinh cac tinh Viet Nam dugc ke thira tir "He thong thong tin quan ly nganh Lam nghiep - FORMIS".
2.2. Phu'ong phap nghien cuu
Can cii vao cac bg suu tap anh tren GEE lua chgn trong nghien cuu, ranh gioi tmh Viet Nam, xac dinh tong so canh anh chup nam 2018 cua timg loai anh: Landsat 8 OLI, Sentinel 2 MSI va ket hgp 2 loai anh vai nhau.
Tap hgp cac canh anh thu dugc ggi la tap hgp anh 1. Moi canh anh trong tap hgp anh 1 dugc Igc may va bong may tu dpng bjng cac phin mem chuyen dung. Tap hgp cac canh anh thu dugc sau khi Igc may va b6ng may gpi la tap hgp anh 2. Nhu vay, tap hgp anh 1 chiia tdt ca cac anh chup lanh tho Viet Nam nam 2018 dugc nha san xuat chuyen len tren he th6ng cua GEE. Tap hgp anh 2 chinh la tap hop anh 1 da loai bo toan bg cac khu vuc anh c6 mav va bong may cho timg eanh anh.
Trong nghien cim nay, anh tai mpt khu vuc dam bao chdt lugng phuc vu muc tieu gJam sat tren mat dat dugc hieu la anh da <l\iac nha q' xudt dua vk gia tri phan xa be mh, khon may va b6ng may. Do d6, tai V. . h.jp ^j^u , ~ xac dinh duac so luong anh duu nha «i., a
, '"'* San xuat dua len he thong GEE cung cap d.^n n&r'
66 TAP CHI KHOA HQC VA CONG NGHE LAM NGHIEP SO 3-20 )
Qudn ly Tdi nguyen rimg & Mdi trwdna dung tai timg vi hi tren mat dit. Trong khi do,
tap hgp anh 2 cho phep xac dinh so lugng anh c6 thh su dung phuc vu muc tieu giam sat be mat tai timg vi tri tten mat dat.
Bh thuan Igi cho viec tinh toan va dan gian hoa viec kk hgp giira hai loai anh (Landsat 8 OLI, Sentmel 2 MSI), cac kenh tten timg canh anh ciia tap hgp anh 1 va 2 dugc dua ve cung do phan giai khong gian 30 m phu hgp vai do phan giai khong gian cua anh Landsat 8 OLI.
Voi m6i tap hgp anh (Tap hgp anh 1, tap hgp anh 2), iing vdi timg loai anh (Landsat 8 OLI, Sentinel 2 MSI) va su ket hgp cua hai loai anh voi nhau, tai timg vi tri cu the tten mat dat, nghien ciiu xac dinh tong so anh thu nhan dugc cho timg quy (tir quy I den quy IV) va cho ca nam 2018. Tit d6, ket hgp voi ranh giai hanh chinh de xac dinh: so anh tmng binh cho timg quy va cho ca nam 2018 ciia timg tinh. Cu the:
- Xet tai mgt vi tri tten mat dat, so lugng anh dugc xac dtnh la tong so anh tai vi tri d6 tir tap hgp anh 1 va tap hgp anh 2 tinh ea su triim Loc may va Bo anh
Landsat 8 OLI (L8), Sentinel 2 MSI (S2) Tren Google earth engine
phu giiia cac canh anh cua ciing mgt loai anh.
Tren pham vi mgt don vi hanh chinh (tinh), s6 lugng anh dugc xac dinh la trung binh so anh tai cac vi tri trong don vi hanh chinh do.
Qua trinh dem so lugng anh tai timg vi tti va tinh toan so lugng anh trung binh cho timg tinh dugc thuc hien tren cira so lap trinh Earth Engine Code Editor ciia GEE.
Tir ket qua tinh toan cac chi so neu tren cho timg tirih, tien hanh tong hgp theo 8 viing sinh thai Lam nghiep Viet Nam: Tay Bac, Dong Bac, Dong bang Bac Bg, Bac Trung Bg, Nam Trung Bg, Tay Nguyen, Dong Nam Bg, Tay Nam Bg. Trong moi vimg sinh thai xac dinh:
so anh trung binh, so anh Ion nhat, so anh nho nhat theo tinh ttong viing, cho timg quy va cho ca nam 2018.
Chu ky lap lai cua anh dugc tinh bang thdi gian chia cho so anh thu dugc theo vi tri.
Toan bg qua ttinh nghien cmi dugc the hien tai so do hinh I.
bong may Bp anh
L8,S2 Sau loc may va bong may
tren tJing canh anh
Chuyen anh v^ dp phan giai khong gian 30m
JL
, ^^±K±. gidi: hanh chiim>
^ - , _ v u n g sinh ftai^..
Xac djnh so anh (L8, S2, L8+S2) tai timg pixel
— i — r p ^
So anh L8, 82. L8+S2 Tnmg binh
Ldn nhat Nho nhat Theo dan vj hanh chinh tnrdc va sau loc may +b6ng
ll
^So ngay trong Quy I. n . m , IV
Nam 2018
Thdi gian lap Ipi anh L8. S2, L8+S2 tai rtrng pixel
Trung binh Ldn nhat Nho nhat Theo dan vi hanh chinli
Ty le anh co the sir dung cho muc tieu giam sat theo:
Thoi gian va Dtm vi h^nh chinh
De xuat hinh thuc giam sat c h o a n h : L 8 , S2,L8+S2 Hinh I. Sc do qua trinh nghien cmi
T A P C H I KHOA H O C VA C O N G N G H E L A M N G H I E P S 6 3 - 2019 67
Qudn ly Tai nguyen rimg & Moi trit&ng ^___^-=
3. K £ T Q U A VA T H A O LUAJN OLI, Sentinel 2 MSI, Landsat 8 OLI + Sentinel 3.1. So lirgng anh thu fltrffc trung binh tai 2 MSI tit tap hpp anh I tai mot vi tri theo cac m6t yi tri tren lanh th6 Viet Nam vung sinh thai dirge t6ng hgp tai bang 1 •
Ket qua xac dinh s6 lugng anh: Landsat 8
Bang 1. So Ijffng anh thu dirffc tai mot vj tri theo cac viJng sinh thai Tbtri gian/loai anh/So liryng anh thu difffc tai mot vi tri
Ving Gia tri ^HlJ 9Sjl 9 - ^ Q"y IV ' ^ ^ ^ ^ ' ^ L8 S2 ^^^ L8 S2 ^^ L8 S2 ^^ L8 S2 ^« LS S2 ^^
29 5 26 32 7 27 26 4 23 27 5 25 36 7 33 20 2 19
^ I 8 29^
39 14 37 24 4 21
^ 0 8 2 4 ^ 35 10 29 23 5 20 36 1 27 42 9 33 33 4 23 36 5 27 40 7 30 31 4 21 33 5 25 43 8 32 25 2 18 29 6 23 34 8 31 24 4 18
Do so lugng anh trong truong hgp nay - N6u tinh trung binh cho mgi vi tri tren dugc xac dinh khong tinh den anh huong cua toan qu6c, mgt nam co: 25 canh Landsat 8, 101 may (c6 may hay khong co may dSu dugc eanh Sentinel 2, 126 canh khi kk hgp hai loai thong ke), nen so lugng anh tuong doi on dinh anh vcri nhau. Tuong img voi chu ky lap lai va gan sat voi s6 anh theo chu ky lap lai do ciia anh la: 15 ngay voi anh Landsat 8, 4 ngay nha san xuat anh dua ra. Cu thi, tinh chung voi anh Sentinel 2 va 3 ngay khi sii dung ca hai cho ca nam: loai anh. Chu ky nay nho hon so voi chu ky - Cac vi tri trong vung Tay Bac c6 trung bay chup eiia mSi loai anh do trong trucmg hgp binh: 22 canh Landsat 8, 103 canh Sentinel 2 nay co tinh dfa do phii cua cac canh anh trong (22, 103). Cac viing khac tuong iing la: Dong ciing mgt loai anh rit co y nghia trong viec lua BSc (23, 95); D5ng bSng Bac Bg (31, 111); chgn anh tai mgt vi tri tren mat d4t.
BSc Trung Bg (28, 96); Nam Trung Bg (26, 3.2. S6 luong anh thu dirffc trung binh tai 109); Tay Nguyen (22, 108); Dong Nam Bg mgt vi tri co the sur dung phuc vu muc f""
(24, 100); Tay Nam Bg (25, 91). Khi kgt hgp giam sat bl mat tren lanh tho VietNaJ„
hai loai anh vai nhau, so lugng anh tai mgt vi Do anh hudng cua may va bong rj,s^ ., tri bing t6ng s6 lugng anh Landsat 8 va khong phai mgi anh thu dugc tbco i tn ,„ .x Sentinel 2 hlong iing. qua nghien ciiu thu nhit dfa co . ,6 ^tt dune
68 TAP CHI KHOA HOC VA CONG NGHf L A M NGHIEP SO 3 - 2-.; 9
Tay Bjc Dong Bic DB Bac 8 9 Bac Trung
B6 Nam Trung
Bg Tay Nguyen
Dong Nam
Bo Tay Nam Bo
Trune binli Lon nhat Nho nhat Trune binli Lan nhat Nho nhat Trurig_binh Lon nhat Nho nhat Trune binh Lon nhat Nho nhat Trune binh Lon nhat Nho nhat Tnine binh Lon nhat 1^6 nhat Trune binh
Lon nhat Nho nhiit Trune binh Lon nhiit Nlio nhat
6 7 5 5 7 4 6 10 3 7 9 5 7 8 6 8 8 7 7 10 5 7 9 5
7A 26 20 22 30 16 25 33 18 24 29 18 29 36 24 29 32 22 26 33 19 22 29 17
29 32 26 27 36 20 31 39 24 30 35 23 36 42 33 36 40 31 33 43 25 29 34 24
5 7 4 5 7 2 8 14 4 10
a
5 7 9 4 5 7 4 5 8 2 6 8 4
26 27 23 25 33 19 29 37 21 24 29 20 27 33 23 27 30 21 25 32 18 23 31 18
31 32 30 30 35 24 37 45 29 32 36 28 34 42 29 32 36 26 30 40 20 29 35 23
4 5 4 6 9 1 9 15 6 7 9 5 6 9 4 5 7 4 5 7 2 6 7 5
27 30 22 23 34 17 27 35 19 23 27 19 24 29 21 24 28 19 23 29 16 22 29 17
32 35 27 30 35 23 36 46 27 29 35 24 31 38 26 30 34 24 28 37 18 27 34 23
7 8 4 6 9 3 7 11 5 7 9 5 6 7 5 4 7 2 6 9 4 7 10 5
26 27 24 25 33 19 30 38 21 25 29 22 29 35 24 28 32 22 26 33 19 23 32 18
33 35 28 31 42 22 37 47 26 32 37 27 34 40 29 33 36 26 32 42 23 30 37 24
22 24 21 23 29 18 31 48 19 28 35 22 26 31 21 22 27 19 24 34 15 25 32 19
103 110
90 95 130 71 111 143 80 96 112 79 109 133 93 108 121 84 100 127
71 91 121 71
125 134 111
its
148 89 142 176 106 123 143 102 135 160 119 130 146 106 123 161 86 116 140 94
Qudn ly THi nguyen riing & Moi tnrirns cho muc tieu nghien cim, giam sat hh mat. De OLI, Sentinel 2 MSI, Landsat 8 OLI + Sentinel giam sat dugc hh mat, it nhat tren anh phai 2 MSI tir tap hgp anh 2 tai mgt vi tri theo cac khong CO may va bong may. viing sinh thai dugc tong hgp tai bang 2.
Kit qua xac dinh s6 lugng anh: Landsat 8
Bang 2. So luvng anh thu duoc tai mgt vi tri theo cac viing sinh thai sau khi da loai may va bong may
Thai gian/loai anh/So lirong anh thu dirffc tai mot vi tri Viing Gia tri t>"y ' Quy 11 Quy 111 Quy IV Ca nam
L8 S2 ^8 L8 S2 ^^ L8 S2 f^ L8 S2 ^^ ^8 S2 ^«
10 2 5 12 2 6 9 2 5 2 2 6 12 4 8 7 1 3 14 3 2 20 6 9 12 2 5
"15 3 6 ^ 19 4 9 12 2 4 18 4 9 22 5 12 15 2 7 I S 2 5 18 3 6 14 2 4 14 3 7 18 5 9 7 1 6 12 3 5 15 5 8 10 1 2
So sanh ket qua giira bang 2 va bang 1 cho may va bong may la: 30 ngay vai anh Landsat thay, sau khi loai may va bong may tren anh, 8, 10 ngay vai anh Sentinel 2 va 7 ngay khi sir so lugng anh thu dugc tai mgt vi tri giiim di dung ca hai loai iinh.
dang ke. Cu the: Bang 2 cung cho thay: trong cimg mgt viing - Cac vi tri trong viing Tay Bac chi thu dugc sinh thai, so lugng anh thu dugc co the sir dung trung binh: II canh Landsat 8, 36 canh cho muc tieu giam sat be mat rat khac nhau Sentmel 2 ( 1 1 , 36) khong co may va bong theo cac khoang thcri gian tuong tu nhau (theg may. Cac viing khac tugng img la: Dong Bac quy). Vay, a timg viing sinh thai nhat dinh nen (9, 27); Dong bang Biic Bg (12, 38); Bac khai thac anh vao thoi gian nag ia tot nhat la Trung Bg (12, 32); Nam Trung Bg (15, 44); cau hoi dat ra. De tra loi cau hoi nay can xac Tay Nguyen (13, 48); Dong Nam Bg (15, 50); dinh thcri gian nao cung cap nhifa anh co chat Tay Nam Bg (13, 38). luong nhit, 46 chinh la thai gian thu anh t6t
- Tinh trung binh cho mgi vi tri tren toan nhat. Bieu do hoa so anh thu dugc trung binh quoc, mgt nam thu dugc: 12 canh Landsat 8, cac vi tri theo quy trong mgt nam (thif tu tir 38 canh Sentinel 2, 50 canh khi ket hgp hai quy I den quy IV), theo viing sinh thai cho loai anh vai nhau khong co may va bong may. timg loai iinh va ket hgp hai loai anh dugc Tuong img vcri chu ky lap lai ciia anh khong co minh hga tai cac hinh tir hinh 2 dfa hinh 4.
TAP CHI KHOA HOC VA C 6 N G NGHE LAM NGHIEP SO 3 - 2019 69
Tay BSc
Dong Bac DB Bac
Bo Bac Trung Bp Nam Trung Bo Tay Nguyen
Dong N a m Bo Tay Nam Bo
Trune binh Lan nhat Nho nhat Trune binh Lan nhat Nho nhat Trune binh
Lon nhat Nho nhat Truna binh
Lan nhat Nho nhat Trung binh
Lan nhat Nho nhat Trune binh
Lan nhat Nho nhat Trune binh Lon nhat Nho nhat Trune binh
Lon nhat Nho nhat
3 4 2 2 3 1 2 2 1 2 3 1 4 7 2 5 6 4 5 8 3 4 6 3
10 11 8 6 8 3 6 9 5 6 11 4 13 18 10 18 20 14 19 25 14 13 18 9
13 15 10 7 10 5 8 10 6 9 13 6 17 25 13 23 26 20 24 30 18 18 23 12
2 2 2 2 3 1 3 6 2 4 5 3 4 5 3 3 3 3 3 4 2 3 4 2
8 10 6 7 9 5 11 13 9 11 15 9 14 17 11 13 14 11 11 14 6 9 11 8
10 12 9 9 12 7 14 20 12 15 19 12 18 22 15 16 18 14 14 18 7 12 15 10
2 2 2 2 4 1 3 6 2 3 4 2 4 5 2 2 3 2 3 5 1 3 5 1
5 6 5 6 8 3 7 9 5 6 9 4 9 12 7 5 6 4 7 9 6 5 8 2
7 8 7 8 11 6 10 13 8 9 10 7 13 17 10 7 9 6 9 14 7 7 12 4
3 4 2 3 6 1 4 6 2 3 4 2 3 4 3 3 5 1 4 6 2 4 6 3
12 14 11 9 12 6 14 16 11 9 11 6 9 11 6 12 15 9 14 17 9 10 14 6
16 18 13
u
16 7 IS 22 13 12 14 8 12 14 8 14 20 12 18 23 11 14 20 10
11 13 8 9 14 7 12 18 8 12 15 10 15 17 13 13 16 11 15 20 9 13 19 10
36 39 34 27 33 20 3S 48 32 37 45 25 44 55 35 48 54 37 50 65 34 38 51 27
47 50 43
M
44 29 50 64 41 44 57 35 59 70 48 61 69 51 65 85 44 52 70 40
Quin ly Tdi nguyen rimg & Moi tru-cmg
1
Tay Bac Dong BSc OB Bac B<f BJe Trung 86 Nam Trung B6 Tay Nguyen
Hinh 2. S6 anh Landsat 8 OLI thu dirffc trung binh tai cac vi tri theo
• lir^'ng anh
quy va theo viing sinh thai
I m if]
14 13 .,-,
4 '
5
\ \ )
Tay Bat; Dofig BSc OB Bac B6 BSc Tfung Bi/ Nnm T.ung B? Tay Nguyen Oong Nam Bp Tay Nam B9
Hinh 3. S6 anh Sentinel 2 MSI thu duqc trung binh tai cac vi tri theo quy va theo vung sinh thai
So lirij'ng anh
Ifl „ ••>
- I 12 ' if i
*.„ '1
1 1
16 14
L
ray BSc Bong B^c DB Bac Bo BSc Trung Bd Nam Ttung Bd Tay Nguyen Dong Nam B9 Tay Nr
Hinh 4. S6 anh thu du-ffc trung binh tai cac vi tri theo quy va theo ving sinh thai lihi ket hop Landsat 8 OLI va Sentinel 2 MSI
TIT bang 2 va cac hinh: 2, 3, 4, xac dinh thoi gian thu anh tot nhat theo cac vung sinh thai
the hien tai bang 3.
Bang 3. Thai gian thu anh tot nhat theo vung sinh thai TT
1 2 3 4 5 6 7 8
Viing sinh thai Tay Bac Dong Biic DB Bac Bo Bac Trung Bo Nam Trung Bo Tiiy Nguyen Dong Nam Bo Tay Nam Bo
Loai Landsat 8 OLI
Quy 1, IV Quy IV Quy IV Quy II Quy 1.11, III Quy I Quyl Quy 1, IV
aiih/Thiri gian thu anh tot nhat Sentinel 2 MSI
Quy IV Quy IV Quy IV Quy I!
Quy II Quyl Quyl Quyl
Kethorp 2 loai anh
Quyrv Quy IV QuvtV Quy II Quy II Quyl Quyl Quyl Ty le giua s6 anh co the sti dung phuc vu
muc tieu giam sat ba mat (anh lihong c6 may va bong may) vai tdng s6 anh thu duoc tning binh tai cac vi tri theo vung sinh thai lit chi so
quan trong cho biet ph4n tram kli.
t6t so vdi tong so anh thu dugc viing sinh thai do. Ket qua xac nay duoc the hien tai bang 4.
•^ng CO anh
° ^1 tri tai
•h * i tieu
70 T ^ P CHI KHOA HOC VA CONG NGHE LAIW NGHIEP SO 3 - 2l
Quiin ly Tdi nguyen rimg & Moi trirong Bang 4. Ty 16 so anh eo Ihl su- dung cho muc tieu giam sat be mat tai mot vi tri so vifi tong s6 anh
Thiri gian/loai anh/Ty le so anh CO the su- dung cho giam sat he mat (%)
Viing Quyl Quyl! Quy III Quy IV
L8 S2
L8 S2
L8 S2
L8 S2
L8 S2 Tay Bac
Dong Bac D B Bac Bo Bdc Trung Bo Nam Trung 86 Tay Nguyen Dong N a m Bo Tay Nam Bo
56 35 26 36 53 70 66 61
42 26 25 26 45 62 75 60
44 28 25 28 47 64 73 60
42 37 37 53 62 60 56 51
32 27 39 44 50 49 42 40
33 29 39 46 52 51 45 42
41 36 37 40 58 38 54 43
20 26 24 26 36 22 30 23
23 28 28 29 41 25 34 27
53 49 56 43 60 67 69 58
47 34 46 35 30 41 53 45
48 37 48 37 35 44 56 48
49 39 39 44 58 60 62 53
35 28 34 33 40 44 51 42
37 31 35 35 44 47 53 45
Tinh trung binh cho cac vi tri theo vung sinh thai, trong mpt nam ty le so anh Landsat 8 va Sentinel 2 tuong mig c6 the su dung cho muc tieu giam sat be mat so voi tong so anh thu dugc nhu sau: vimg Tay Bac (49%, 35%);
vung Dong Bac {39%, 28%); viing Dong b i n g BSc Bg {39%, 34%); vung BSc Trung Bp (44%, 33%); vung Nam Trung Bp (58%, 40%); viing Tay Nguyen (60%, 44%); viing Dong Nam Bp (62%, 51%); vung Tay Nam Bg (53%, 42%).
Neu tinh trung binh cho cac vi tri trong toan quoc, trong mpt nam ty le so anli Landsat 8 va Sentinel 2 tuang iing co the sir dung cho muc tieu giam sat be mat so voi tong so anh thu duac la 5 1 % so anh Landsat 8 va 39% so anh Sentinel 2.
Cac canh anh Landsat 8 OLI chup nam 2018 phu triim lanh tho Viet Nam (phan dat lien) truac va sau khi Ipc may va bong may de tinh toan s6 lupTig anh tai timg vi tri duoc minh hoa tai hinh 5.
(a) (b) Hinh 5. Cac canh anh Landsat 8 OLI chup nam 2018 phu triim ianh tho Viet Nam (phan dat lien)
truo'c (a) va sau khi loc may va bong may (b)
T A P C H I K H O A H O C VA C O N G N G H E L A M N G H I E P SO 3 - 2 0 1 9 71
Qudn ly Tai nguyen rCmg & Moi Iru&ne
Tit cac liet qua neu tren, tac gia xac dinh nhfa dS d j x u i t hinh thilc su dung anh de &••' thai gian trung binh lap lai anh tai mot vi tri sat be mat cho timg tinh, thanh ph^i tren ti'Jn tren mat dat va can cu vao thai gian lap lai lan quoc nhu bang 5.
Bang 5. ThM gian trung binh lap lai anh tai mot vi tri tren mat dat va hinh thirc sir d y sat be mat theo donn vj hanh chinh cap tinh
I, de giam
Vung Sinh thai
Tay Bac
Dong B5c
DB Bac Bo
g i Trung
Bo
Nam Trung Bo
Tay Nguyen
Tinh/Thanh pho
Dien Bien Lai Chiu Son La Hoa Binh Ha Giang Cao Bang Bac Kan Tuyen (Juang Lao Cai Yen Bai Thai Nguyen Lang Son ( ^ a n g Ninh B5c Giang Phil Tho Vinh Phuc TP Ha Noi Bac Ninh Hiii Ducfng TP Hai Phong Hung Yen Thai Binh Ha Nam Nam Dinh Ninh Bmh Thanh Hoa Nghe An HaTTnh Quang Binh (Juang Tri Thira Thien Hue TP Da Nang Quang Nam Quang Ngai Binh Dinh Phii Yen Khanh Hoa Ninh Thuan Binh Thuan Kon Tum Gia Lai D i k L a k Dak Nong Lam Dong
Thoi gian lap 1 ISho a h a t L8 24 21 23 37 31 39 39 42 19 35 47 28 16 22 34 40 31 15 17 18 14 29 24 23 31 28 27 20 28 17 21 20 22 18 20 23 19 17 13 16 16 20 16 15
S2 7 8 6 8 15 14 14 15 8 9 10 8 10 8 10 12 9 8 6 6 6 7 7 7 7 9 10 7 8 10 6 6 6 5 7 8 7 7 5 5 5 6 7 5
L8 S2 6 6 5 7 10 10 11 11 6 7 8 6 6 6 8 9 7 5 4 4 5 5 6 5 6 7 7 5 7 6 5 5 5 4 6 6 5 5 4 4 4 4 5 4
lai anh (ngay)/l Lon nhat L8 61 44 48 58 51 55 61 69 78 68 83 69 48 72 59 74 57 53 47 55 69 72 79 59 53 45 37 41 61 43 49 31 37 34 31 34 27 32 42 56 36 68 48 52
S2 17 19 18 14 18 18 17 20 14 18 15 14 32 17 15 19 15 14 13 18 11 18 15 17 16 16 15 19 23 19 11 9 11 9 13 16 13 11 13 20 14 18 23
L8 S2 13 14 13 11 12 13 12 14 11 14 13 11 19 14 12 15 11 11 10 11 9 15 12 13 12 12 10 13 15 13 9 7 8 7 9 11 8 8 10 15 10 13 16 12
loai anh T r u n g binh L8 39 31 36 48 40 47 45 52 50 50 59 41 33 41 46 54 41 27 31 37 31 50 39 40 38 39 33 27 41 28 33 24 29 26 25 28 22 24 28 30 29 40 31 34
S2 11 12 11 11 16 16 15 17 12 13 12 12 22 12 12 15 12 11 9 11 8 12 11 11 12 13 12 13 15 9 8 9 7 10 11 10 9 8 9 8 10 12 9
L8 S2 9 9 8 9 11 12 11 13 9 10 10 9 13 9 10 12 9 7 7 8 6 10 8 8 9 10 9 9 12 10 7 6 7 5 7 8 7 6 6 7 6 8 9 7
V'i •-
LS N Q N N N N N N N N N N N N N N N N N N N N N N N N Q Q N Q N Q Q Q Q Q Q 0
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^ T
72 T ^ CHI KHOA H O C \ - C O N G G H E L A M NGHIEP SO 3 - 2', Vl
Qudn ly Tdi nguyen rimg & Moi tru-cme
^=^^=
Viing Sinh t h i i
Dong Nam Bo
Tay Nam Bo
Tinh/Thanh ph6
Bmh Phuoc Tay Ninh Binh Duong Dong Nai Ba Ria VT TP Ho Chi Minh Long An Tien Giang Ben Tre Tra Vinh Vinh Long Dong Thap An Giang Kien Giang TP Can Tho Hau Giang Soc Trang Bac Lieu CaMau
T h ^ gian lap lai iinh (ngay)/]
Nho nhat L8 17 25 22 11 20 15 16 24 30 29 26 18 14 16 24 28 23 24 14
S2 4 6 4 5 7 4 5 6 5 5 6 6 7 8 9 10 8 9 7
L8 S2 3 5 4 4 5 3 4 5 5 4 5 5 5 5 7 7 6 6 5
L o u nhat L 8 51 49 42 30 74 26 28 43 41 53 40 29 31 39 50 51 62 46 47
S2 15 14 14 16 16 10 12 16 11 13 22 19 18 29 39 28 24 30 19
L 8 S2 12 11 10 10 13 6 8 10 8 10 14 11 11 17 22 18 17 18 13
oai a n h T r u n g binh L 8 27 36 30 21 50 19 21 31 34 38 34 23 24 28 37 36 33 31 28
S2 8 9 8 10 12 6 8 10 8 9 12 10 10 14 17 15 14 16 11
L8 S2 6 7 6 7 10 5 6 7 7 7 8 7 7 9 11 10 10 11 8
De \ u a t hinh giam sa L8
N N Q
0
N Q
0 0 0
N
0 0 0
Q N N N N N
S2 Q T T Q
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T T Q T T Q
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Q Q Q
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ithijc tL8 S2 T T T T T T T T T T T T T Q
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T
Tai bang 5, muc de xuat hinh thuc giam sat, ky hieu N la nam, Q la quy va T la thang.
Mac du, tinh tnmg binh cho mpi vi tri tren toan quoc, mpt nam chu ky lap lai cua anh khong CO may va bong may la: 30 ngay vcri anh Landsat 8, 10 ngay voi anh Sentinel 2 va 7 ngay khi su dung ca hai loai anh. Tuy nhien, chu ky nay lon nhat co the dat d6n: 83 ngay Vffi anh Landsat 8 (tinh Thai Nguyen), 39 ngay
" voi anh Sentinel 2 va 22 ngay khi ket hop ca hai loai anh {Thanh pho Can Tho). Vi vay, viec de xuat hinh thuc giam sat can can cu vao thai gian lap lai lon nhat cua anh. Gia su trong mot ky giam sat can it nhit 2 anh cho mpt vi tri, tir do xac dinh hinh thuc giam sat bien dpng tren mat dat phu hop cho tung loai anh nhu sau:
- Voi anh Landsat 8 OLI, so lieu tai bang 5 cho thay: co 40/63 tinh/thanh pho (chiem 63,5% so tinh) chi co the su dung anh Landsat 8 de giam sat hang nam hoac mpt nam toi da 2 lan giam sat va 23/63 tinh/thanh pho (chiem 36,5% so tinh) co the sii dung anh Landsat 8 de giam sat hang quy. Nhu vay, anh Landsat 8 phu hpfp cho muc tieu giam sat bien dpng tren mat dat hang nam.
- Voi anh Sentinel 2 MSI, so lieu tir bang 5 cho thiy, CO 40/63 tinh/thanh ph6 (chilm
63,5% so tinh) co the su dung anh Sentinel 2 de giam sat hang quy va 23/63 tinh/thanh pho (chiem 36,5% so tinh) co the sir dung anh nay de giam sat hang thang. Nhu vay, anh Sentinel 2 phu hpp cho muc tieu giam sat bien dpng tren mat dat hang quy.
- Khi ket hop ca hai loai anh, co 55/63 tinh/thanh pho (chiem 87,3% so tinh) co the su dung ket hop hai loai anh de giam sat hang thang; 8/63 tinh/Thanh ph6 (chilm 12,7%. s6 tinh) CO the sir dung hai loai anh de giam sat hang quy. Nhu viy, neu sir dung ket hop ca hai loai anh c6 the dap iing dupc muc tieu giam sat bien dpng tren mat dat hang thang.
3.3. Thao luan
Nghien cuu da xem xet so lupng anh Landsat-8 va Sentinel-2 thu dupc trung binh theo vi tri trong nam 2018 tren toan lanh tho Viet Nam va cho thay su ket hop giiia Landsat- 8 va Sentinel-2 lam tang so luong va giam thai gian lap lai cua anh theo vi tri. CJ mpt so vi tri nhat dinh, so luong anh thu duac lan hon va chu ky lap Iai cua anh nho hon so vai chu ky bay chup cua timg loai ve tinh do nha san xuat dua ra. Dieu nay la do phan tich c6 tinh den ca nhirng khu vuc trum phu giiia cac canh anh trong mpt loai anh.
TAP CHI KHOA HOC VA C 6 N G NGHE L A M NGHIEP SO 3 - 2019 73
Qudn ly Tdi nguyen rimg & Mdi trw&ns Ve ty le s6 anh phii hpp cho muc tieu giam sat be mat, Kovalskyy va Roy (2015) kit luan:
trung binh theo vi tri co 43%o s6 anh Landsat-8 a My bi anh huong bai may va bong may, nghia la tai My c6 57% s6 anh phu hgp cho muc tieu giam sat be mat so vai tong so anh thu dupc. Tren pham vi toan cau, cac dia diem thuong xuyen co may va bong may tren anh quang hpc da duac quan sat bao gom khu vuc can xich dao ciia Chau Phi, khu virc Amazonia ciia chau My, kliu vuc BSc va Dong Nam ciia Chau A (Roy et al, 2006; Kovalskyy va Roy, 2013; Ju va Roy, 2008). Tai Viet Nam, kit qua nghien cim cho thdy ty le so anh Landsat 8 phii hop cho muc tieu giam sat be mat tren toan lanh th6 la 51 % tuong d6i phii hgp voi cac ket qua da nghien cim.
Chu ky lap lai anh nho nhat va lon nhat cho timg tinh (Bang 5) rat dang quan tam vi chung xac dinh miic do co the khai thac dugc anh theo thai gian. Dac biet la thai gian lap lai anh lan nhat cho phep xac dinh kha nang giam sat mat dat cua timg loai tu lieu anh. Anh Landsat 8 phii hpp voi yeu cau giam sat hang nam, anh Sentmel 2 phii hpp vai yeu cau giam sat hang quy va sit ket hgp ciia hai loai anh voi nhau phii hgp vai yeu cau giam sat hang thang. Dieu nay se co Ipi cho mpt so luang lon cac iing dung vien tham nhu cac iing dung giam sat su thay d6i tren mat dat (Drusch et al, 2012; Roy et al, 2014; Zhu et al, 2017; Hansen va Loveland, 2012). Ngoai ra, cac irng dung cin giam sat su bien dpng theo thai gian gin voi thai gian thuc se tro nen kha thi han do su chac chan trong viec se thu dupc hinh anh mien phi va khong co may va bong may.
Ket qua ciia nghien ciiu nay !a tiln d l d l dinh hirong cac irng dung giam sat tren mat dit sir dung tu heu anh Landsat-8 va Sentinel- 2 da thai gian. Tuy nhien, nghien cii'u nay chua xem xet den su khac nhau ve dp phan giai khong gian va dp phan giai pho giii'a cac kenh anh cua hai loai tu lieu anh nay. Day se la van de can dupc xem xet khi su dung ket hgp hai loai tu lieu anh nay cho nhiing bai toan img dung cu thi.
4. KET LUAN
Nghien curu da chiing minh ticn icb cua . kit hgp hai loai tu lieu anh 5entinel--2 va Landsat-8 d l nang cao tin s6 va guHTi thoi gian lap lai anh. Nhung kit qua chinh la:
Tinh trung binh cho mpi vi tri tai Viet Nam, mpt nam tdng s6 anh thu dugc: 25 canh Landsat 8, 101 canh Sentinel 2, 126 canh khi kit hgp hai loai anh voi nhau, tuong ung voi chu ky lap lai cua anh la: Landsat 8 - 1 5 ngay, Sentinel 2 - 4 ngay va 3 ngay khi kit hgp hai loai anh
- Tinh trung binh cho mpi vi tri tai Viet Nam, mpt nam chi thu duoc: 12 canh Landsat 8, 38 canh Sentinel 2, 50 canh khi kit hap hai loai anh thoa man dilu kien khong c6 may va bong may, tu'ong img voi chu ky lap lai cita anh khong c6 may va bong may la: Landsat 8 - 30 ngay. Sentinel 2 - 1 0 ngay va 7 ngay khi ket hgp hai loai anh.
- Ty le so anh Landsat 8 va Sentinel 2 c6 the sir dung cho muc tieu giam sat be mat so vai tong so anh thu dugc la 51%) so anh Landsat 8 va 39%o so anh Sentinel 2.
- Tu lieu anh Landsat 8 OLI phu hpp cho muc tieu giam sat bien dpng tren mat dat hang nam. Trong khi do, tu lieu anh Sentinel 2 MSI tuong doi phii hcfp cho muc tieu giam sat bien dpng tren mat dat hang quy. Su ket hgp ciia ca hai loai tu lieu anh co the dap iing dupc muc tieu giam sat bien dpng tren mat dat hang thang.
TAI LIEU THAM KHAO
1. Brown M.E., Pinzon J.E., Didan K., Morisette J.T., Tucker C.J (2006). Evaluation of the consistency of long-term NDVl time series derived from AVHRR, SPOT-vegetation, SeaWiFS, MODIS, and Landsat ETM+ sensors IEEE Trans, Geosci Remote Sens 44 1787-1793.
2. Carrasco L, O'Neil A.W, Moium R D, Rowland CS (2019). Evaluating Corabmations of Temporally Aggregated Sentinel-!. Sentincl-2 and Landsat 8 for Land Cover Mapping with Google Eartli Ensine
Remote Sens, 11 (3). 288 ^ 3. Drusch M., Del Bello U., Cai hoi S p , „
•' Colin O Fernandez V , Gascon P., Hoersch B , l^ilg C r K • '•
P., Martimort P. (2012). Sentmel-2: LSA's opl,ca] h""h' resolution mission for GMES operaiional s -
Remote Sens. Environ, 120, 25-36. er\-ices.
74 TAP CHi KHOA HOC VA CONG NGHE LAM NGHIEP SO 3 - H:\^
Qudn ly Tdi nguyen rirng & Mdi trwdiis
4. Fensholt R., Rasmussen K., Nielsen T.T., Mbow C. (2009). Evaluation of earth observation based long term vegetation trends-Intercomparing NDVl time series trend analysis consistency of Sahel from AVHRR GIMMS, Terra MODIS and SPOT VGT data. Remote Sens. Environ, 113, 1886-1898,
5. Hansen M.C., Loveland T,R (2012) A review of large area monitoring of land cover change using Landsat data. Remote Sens. Environ, 122, 66-74.
6. Irons J.R., Dwyer J.L., Barsi J.A (2012). The next Landsat satellite; The Landsat data continuity mission.
Remote Sens. Environ, 122, 11-21.
7. Ju J., Roy D.P (2008) The availability of cloud- free Landsat ETM+ dala over the conterminous United States and globally. Remote Sens. Environ, 112, 1196- 1211.
8. Kovalskyy V , Roy D.P (2015). A one year Landsat 8 conterminous United Stales study of cirrus and non-cirrus clouds. Remote Sens, 7, 564—578
9. Kovalskyy V., Roy, D.P (2013). The global availability of Landsat 5 TM and Landsat 7 ETM+ land
surface observations and implications for global 30 r Landsat data product generation Remote Sens. Environ, 130,280-293.
10. Roy D.P., Wulder M., Loveland T., Woodcock C , Allen R., Anderson M., Helder D., Irons J., Johnson D„ Kennedy R., et al (2014) Landsat-8- Science and product vision for terrestrial global change research.
Remote Sens. Environ, 145, 154-172.
11 Roy D.P., Lewis P., Schaaf C , Devadiga S., Boschetti L. (2006). The global impact of cloud on the production of MODIS bi-directional reflectance model based composites for terrestrial monitoring. IEEE Geosci. Remote Sens. Lett, 3, 4 5 2 ^ 5 6 .
12. Zhu Z. (2017). Change detection using landsat time series: A review of frequencies, preprocessing, algorithms, and applications. ISPRS J. Photogramm.
Remote Sens, 130, 370-384.
13. European Space Agency (ESA) (2015). SentineJ- 2 User Handbook; Revision 2; ESA Standard Document;
ESA: Paris, France, 64p.
EVALUATE THE ABILITY TO EXPLOIT FREE OPTICAL SATELLITE IMAGES TO MONITOR GROUND COVER IN VIETNAM
Pham Van Duan', Le Sy Doanh^ Vu Thi Thin', Nguyen Van Thi' Hoang Van Khien', Pham Tien Dung^, Dinh Van Tuyen^
'Vietnam National University ofForestiy
Vietnamese Academy of Forest Sciences Ministry of Agriculture & Rural Development S U M M A R Y
The combination of different types of optical satellite imageries will increase the chances of obtaining cloudless images more frequently to monitor the surface of the earth. Currently, optical satellites such as Landsat-8 OLI (from 2013), Sentinel-2 MSI (Sentinel-2A - from 2015, Sentinel-2B - from 2017) has now offered free images on a global scale with a spatial resolution of 10 to 30 m, which facilitates terrestrial monitoring Using sets of Landsat 8 OLI and Sentinel 2 MSI images taken m 2018 on the cloud-based geospatial processing platform of Google Earth Engine, the study identified the potential use of these optical materials and how to combine them in whole territory of Vietnam. The results of the study demonstrated the utilities of combining two types of Sentinel-2 and Landsat-8 images to enhance the frequency and reduce image repetition time for each province m Vietnam, Accordingly, if the effect of clouds and shades is not considered, at one location in Vietnam, on average, the repeat cycle of the image is 15 days (Landsat 8), 4 days (Sentinel 2) and 3 days (two types of images are combined). However, if the effect of clouds and shades is neglected, at one location m Vietnam, on average, the repeat cycle of the image is 30 days (Landsat 8), 10 days (Sentinel 2) and 7 days (two types of images are combined). The ratio of Landsat 8 and Sentinel 2 images that can be used for surface monitoring purposes, compared to the total images collected, is of 5 1 % and 3 9 % respectively. With this repeat cycle, Landsat 8 OLI imageries are suitable for annual fluctuation monitoring Sentinel 2 MSI imagenes are suitable for quarteriy fluctuation monitoring The combination of both types of imageries can meet the goal of monthly fluctuation monitoring.
Keywords: GEE, Landsat 8 OLI, Optical Sattilte Image, Sentinel 2 MSI.
Ngay nhan bai Ngay phan bien Ngay quyet dinh dang
: 01/4/2019 : 20/5/2019 : 28/5/2019
TAP CHI KHOA HOC VA CONG NGHE LAM NGHIEP SO 3-2019