KHOA HOC C 6 N G N G H |
MGHIEIM CLUJ KET HOP AIXIH VE TIMH QUAMG HOC SEIXITIIXIEL - e VA RADAR SEIXITIIXIEL - 1 TROIMG PHAT
HIEM IVIAT RIJMG O T I M H GIA LAI
Nguyin Vdn ' n t i \ Trin Quang Bdo^ Lfi Sy DoanhS Ph?im v a n D u l n \ Nguyin Nam Hai^ Trin Xudn Hda^
T6MTAT
Nghien ciiu nay da kit hop chi sd NDVI ciia anh ve tmh quang hoc Sentinel - 2 vdi gia tri tan xa ngupc cua anh radar Sentinel -1 dl phat hifin mat rung tren dia ban linh Gia Lai giua 2 thdi ky khac nhau. Thdi k^ dau tinh tir ngay 01/01/2018 den ngay 30/6/2018 va tiidi ky sau tinh tii 01/01/2019 din 30/6/2019. Chi so NDVI duoc tinh tir tdp hgp cdc anh c6 ty le may che phii dudi 30% cho ky dau (136 canh) va ky sau (173 canh). Dli vdi anh Sentinel - 1 , m6t anh trung binh diroc tao ra tir tap hop 45 canh. Todn bp qua trinh tinh toan, phan tich du li^u dugc thuc hifin trfin Google Earth Engine. NghiSn cuu chi ra ring kha nang phat hien mdt rimg d Gia Lai blng du hfiu kit hgp (NBCI) cao ban so vdi su dung du heu quang hoc (NDVI) hay tan xa ngug^ radar (BKS) rifing re. Cu the dp chinh xac ciia phat hifin mat rimg bdng NBCI dat 91,7% trong khi NDVI chi dat 81,7% va BSK la 75%. Vdi mo hinh NBCI ket hgp vdi ban A6 hien trang rimg ndm 2017, nghifin cuu nay dd phat hien dugc p-fin dia ban tinh Gia Lai, tir 01/01/2018 den 30/6/2019, bi mat 3.415,79 ha rimg phan bd d 4.437 16, 2.022 khoanh, 657 diu khu, 130 xa va 16 huyen, trong do rimg tu nhifin la rpng thudng xanh Id 1.459,87 ha, rimg tu nhifin la rong rung la la 26,82 ha va rimg trong la 1.929,1 ha.
Tii khda: Gia Lai, Google Earth Engine, mdt rung, SenUnel -1, Sentinel - 2.
I.MffDAU
Gia Lai la mdt hong nhiing dia phuong cd dien tich rimg nhilu a Viet Nam. Vdi vi tri dia ly thudc khu vuc Tdy Nguyfin, dia hinh bi ehia eat phiic tap bdi cdc khe nui va he thdng sdng hd. Vi vdy, cdng tde tuan ha, giam sdt cua cdc Iuc lugng bao ve rimg d ddy gap nhilu khd khdn. Hien nay, khoa hpc cdng nghe hien dai da eung cap cho con ngudi nhilu edng cu hd h g hong edng tie quan ly bao ve rung. Trong dd, anh ve tinh Id mdt hong nhiing tu heu dugc iing diing pho biln hong nhieu linh vuc, ddc bilt la hong gidm sat tdi nguyin rimg.
Hifin nay, vific iing dung anh vifin tham d l gidm sdt tai nguyfin rung dd h d nfin pho biln. Ndm 2006, Huang va Siegert dd nghien ciiu giam sat biln ddng lop phu thuc vdt vdi quy md ldn d Bdc Trung Qudc blng anh ve tinh SPOT da thdi gian. Kit qua nay eiing phu hgp vdi nghiin ciiu ciia Cabral (2006) hong viec phdn loai lap phu d phia Nam chdu Phi.
Nhilu nghifin eiiu chi ra rdng, viec k i t hop dnh vfi
' Vi?n Sinh thdi rirng va Moi midng, Trudng D^i hgc Lam nghidp
^ Trudng Dai hgc Lam nghi?p
^ Sd Khoa hgc vd Cdng ngh^ tinh Gia Lai
tinh quang hgc va radar se cho k i t qud giam sat rimg tdt hon Id ehi sir dung rifing re cdc loai tu hfiu nay [3], [4], [5], [6], [7]. Kit qua nghifin ciiu cua Nguyin Thanh Hoan (2013) chi ra ring sir dung k i t hgp ALOS/PALSAR vdi ALOS/AVNIR - 2 cho k i t qua phan loai dat tdi 88% hong khi chi sii dung ALOS/AVNIR-2 Id 77%. Nghien cim vl phdn loai Idp phu sii dung dit khu vuc Amazone phia Ddng Braxin, Paulo Amador Tavares (2019) nhdn dinh nlu k i t hgp dii heu Sentinel - 1 vd Sentinel-2 thi kit qua phan loai dat din 91,07% so vdi 89,53% nlu chi su dung Sentinel - 2. Dir heu Sentinel - 1 ciing can duge ling dung nhilu hon hong dilu ha, gidm sdt rimg d khu vue nhiet ddi [5].
Cde nghifin ciiu hong va ngodi nude dd ehi ra kha ndng img dung dit hfiu viln tham hong giam sdt rimg se mang lai hifiu qua tot. Do vdy, ddi vdi nghifin ciiu tai tinh Gia Lai da su dung ky thudt kit hgp anh ve tinh quang hpe Sentinel - 2 vd anh vfi tinh radar Sentinel - 1 d l xdc dinh khu vuc rimg bi mit hoan todn (chat hdng) hfin quy md todn tinh. Kit qua nghifin ciiu sfi gdp phdn hodn thifin co sd khoa hge hong vifie iing dung edng nghfi cao vao quan ly tai nguyfin rimg eiia tinh nay, giup cho edng tdc gidm' sdt rimg dat hilu qua tdt hon.
NONG NGHIEP VA PHAT TRIEN NONG THON - KY 1 - THANG 3/2020 105
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2 . VAT UEU VA PHUDNG PHAP NGWBU CUU 2.LV§tli^u nghifin cmi
Nghifin ciiu nay su dung 2 loai dii Ufiu vfi hnh gom Sentmel-2 (cd ty lfi mdy ehe phu dudi 30%) vd Sentinel - 1 , ehia thdnh 2 thdi ky: ky dau (Kd toan bd dii Ufiu tiiu dugc tir 01/01/2018 din ngdy 30/6/2018 vd ky sau (IQ todn bd dii lieu tii 01/01/2019 din 30/6/2019.
- Sentinel - 1 : la mot vfi tinh Radar khau dd tong hgp bdng tin C dugc thilt k l de gidm sdt cdc vung bang biln, mdi trudng Bic cue vd nguy co ehuyin ddng mat dat cung nhu tao ra ban d6 rimg, nude va dat. Hifin tai. Sentinel - 1 gdm 2 vfi tinh (IA va IB) bay d do cao 693 km va each nhau 180° eung cap du lifiu phan cue VH va W (cd do phdn giai khdng gian 5 X 20 m vd dugc tai mdu 10 m) vdi chu ky lap lai cua ea 2 vfi tinh la 12 ngdy. Nguon dii Ufiu Sentinel - 1 su dung hong nghifin ciiu nay duge lly tir Google Earth Engine (ee.ImageCollection('COPERNICUS/Sl_
GRD')) vdi miic do xii ly IC (dii hfiu da dugc dinh chuan va chuyin gid tri tan xa ve decibel). Nghien ciiu nay sii dung phdn cue VH d l k i t hgp vdi gia tri NDVI cua anh Sentinel - 2.
- Sentinel - 2: G6m 2 ve tinh quang hgc vdi cam biln da quang pho chii ylu duoc iing dung hong ndng nghifip nhu gidm sdt va quan ly eay hong, gidm sdt thuc vdt vd rimg (vi du nhu chi sd difin tich la, ning do difip Iuc, ude tinh khoi lugng carbon), gidm sat str thay ddi dp che phu hong gidm sat mdi tnrdng, quan sat cdc viing ven biln (giam sdt mdi trudng biln, lap ban dd viing ven biln), gidm sdt nude ndi dia, gidm sat sdng bang, pham vi bdng vd Idp bdn do che phu tuyet (Christian Schiller, 2015).
Hai v§ tinh Sentinel - 2A va Sentinel - 2B bay d dp eao 786 km vd each nhau 180° cung cap anh gom 13 kfinh phd (eac kfinh nhin thdy va edn hdng ngoai cd do phdn giai 10 m, kenh red edge vd SWIR cd do phdn giai 20 m, cdc kfinh khi quyin cd dp phdn giai 60 m) vd ehu ky lap lai ciia ca 2 vfi hnh Id 5 ngdy. Dii Ufiu Sentinel-2 su dung hong nghifin ciiu nay duge lay tir Google Earth Engine (ee.hnageCoUection ('C0PERN1CUS/S2_SR')) vdi miic xu ly 2A (dd hifiu chinh khi quyen vd ndn chinh hmh hgc).
2.2. Phuong phdp xir ly dii U|u
2.2.1. Phuongphip loai bo miy tren inh quang hoc Sentinel-2
Cd nhilu phuong phdp de tao ra mgt buc a^ vfi hnh khdng ed mdy. Trong nghifin ciiu ndy da su dung anh da tiidi gian vdi phuang phdp bu trir, co nghia Id su dung nhimg ehd khdng cd mdy a anh nay de bii eho vimg cd mdy d anh khac hen cimg vi tri (Dial, G. etal., 2013). De tiiuc hifin dupe vific ndy can str dung dfin thudt todn tu ddng phdt hien ra mdy da dugc tich hgp sdn hen he thong Google Earth Engine (GEE) dua tren kenh anh "QA60". Phuong phap ehung ndy ddi khi cdn duge goi la Igc mdy (Gdmez-Chova etal., 2017). Sau khi loai bd may, tdt cd cdc kfinh eua todn bd cae dnh hong chuoi tiieo thdi gian da chgn dugc hgp nhit theo ham medianQ hen GEE di tao nen mdt anh khdng cd mdy.
2.2.2. Phuongphip tinh toan eac chisd - Chi so NDVI: Chi sd ndy dugc tinh todn hi 2 kfinh phd la NIR (can hong ngoai) vd RED (do) theo edng thiic:
NIR+RED
Ap dung cdng thiie (1) d l tinh todn NDVI cho anh Kl vd K, se duoc NDVIt va NDVI,. NDVI cua dnh ve tinh Sentmel - 2 dupc tinh todn hong GEE bdng ham normalizedDiffereneeO vdi 2 kfinh la B8 vd B4.
- Chi sd NDVI eua Sentinel - 2 va gid tii tdn xg (BKS) cua Sentinel - 1 (cd t h i su dung phdn cue VH hodc W d l tmh todn) dugc k i t hgp vdi nhau (CMB) thdng qua phep tinh:
CMB = (NDVI + j^)/2 (2) Cdng thiic (2) dupc viet lai nhu sau:
CMB = SDVl'BKS-1
(3) Vl gia tri BSK mang gid tri dm nin d l cd thi lay gid tri trung binh cpng tuong duong vdi NDVI tiii BSK dugc them diu dm va nghich dao gia tri, tuc \i lly 1 chia cho BSK vd thfim dau dm phia trudc gid trj mdi. Khi dimg phep biln ddi ndy, gid tri mdi se ding biln vdi NDVI. Ban chat eiia cdng thiic (3) Id kit qua cua phep quy dong mdu sd n h i m tinh todn thuan ti^n hon hong GEE.
Ap dung cdng thiic (3) d l tinh todn CMB, va CMBs dua vdo NDVI ky ti-udc, ky sau vd gia hi tan xa ky trudc, ky sau.
Chi sd biln ddng (NBCI \ D V I and Backscatter Change Index) la ty lfi tinh bdng phin
106 NONG NGHIEP VA PHAT TRIEN N 6 N G THON - KY 1 - THANG 3/2020
KHOA HOC CONG NGHE
NBCI •• - x l 0 0 % (4) hdm (%) giira CMB, va CMB, va dupc tinh toan theo cdng thiic sau day:
CMB^-CMBt CMBt - Ngudng biln ddng:
VI ly thuyit, tai mdt vi tri nhit dinh neu khdng cd su thay doi vl elu tnic b l mdt (hay thay doi hang thdi rimg) thi gid tri NBCI sfi cd gia tri blng 0 (khdng) vd vi tri dd dugc ggi Id on dinh. Khi dd nhirng vi txi cd gia hi nhd hon 0 se Id nhiing noi giam thuc vdt (rimg); ngugc lai nhiing vi tri ed gia tii ldn hon 0 se la nhtrng noi tang thyc vdt (rimg). Tuy nhifin, h-ong tiiuc t l khdng phai nhu vdy bdi thuc vdt ludn ludn thay dii theo thdi gian hong gidi han ma theo quan nifim ehii quan eua con ngudi Id khdng ddi. Chlng han, mdt khu ning ttr nhifin vdn sinh trudng hang ndm, do dd clu tnic b l mat tdn rimg sfi thay ddi, mdu sle cua tan rimg cflng thay ddi...nhung nhiing thay doi dd ehira vtrgt ngudng do con ngudi quy dinh (ning ty nhifin hay khdng phai rimg hr nhifin) nfin ehung (rimg) vdn duge coi Id on dinh. Chinh su thay doi ndy dd lam gid hi phan xa trfin dnh quang hgc vd gid hi tdn xa hfin anh radar se thay doi theo. Ndi mdt each khac, mOt dii tugng dugc coi Id In dinh khi gia tri NBCI ndm hong mdt khoang xung quanh gid tri 0 ggi Id ngirdng In dinh (NV - No change Value), gid hi NBCI nho hon NV duge ggi la ngudng giam (RV - Reduce Value) vd gia tri NBCI ldn hon NV dugc gpi la ngudng tang (IV - Increase Value). Cac gia tii NV, RV va IV dugc xac dinh thdng qua kit qua nghifin ciiu thuc nghifim hen 90 mdu (30 mdu thuc t l dn dinh, 30 mdu thuc t l giam va 30 mdu thuc t l tang).
2.2.3. Phuong phip xac dmh khu vuc mat ning Sau khi xac dinh dugc ngudng biln ddng, anh chi sd biln dpng sfi dugc tai phdn loai theo gid hi RV, NV va IV. Tuy nhifin nghien cun nay chi tap trung
vdo xac dinh khu vyc mat rimg, nfin NBCI se dugc tai phdn loai gom 2 khoang:
- Khoang gia tri RV se dugc thay t h i bdng gid tri 1 (cd biln ddng giam).
- K h o a n g g i a h i N V v a IV s e d u g e t h a y t h i gid tri 0 ( k h d n g cd b i l n d d n g g i a m ) .
K i t q u a tai p h d n loai la m d t r a s t e r c h i i a gid tri 0 v a 1. R a s t e r n a y d u o c e h d n g x I p vdi b a n d o hifin h a n g rimg c u a k y d d u d e x d c d i n h k h u v u e g i a m r u n g . N h i i n g v u n g b i l n d d n g h f i n r a s t e r tai p h d n loai d n g o d i r a n h g i d i 3 loai r i m g h o a c h o n g r a n h gidi 3 loai rimg n h t m g hifin h a n g k h d n g p h a i r u n g s e d u g e loai b d k h o i k i t q u a t i n h todn.
T o d n b d p h u o n g p h a p n g h i e n cihi d u o c rad td t d m tdt b d n g s o d d n h u sau:
H i n h 1. S o d l q u d t r i n h nghifin ciiu 3. KET QUA NDHHI CUU VA IHAO LUAN
3 . 1 . K i t q u a l g c m d y trfin a n h vfi t i n h SentineI-2 Q u y t r i n h lpc m d y d u g e t h y c hifin trfin G E E vdi tdp h g p c a c a n h cd t y lfi m a y c h e p h u d u d i 30%. K i t q u a la a n h S e n t i n e l - 2 Kj d u g c t a o r a ttr 136 c a n h a n h va Kg d u g c t a o r a tir 173 e a n h a n h . Vific loai b d m d y sfi g i u p c h o gia tri N D V I it e h i u a n h h u d n g va tir d d k h d n g l d m sai Ifich k i t q u a x d c d i n h b i l n d d n g r i m g trfin t o d n b d r a n h g i d i c u a tinh Gia Lai.
H m h 2a. A n h S e n t i n e l - 2 k ^ d i u (sau l g c m d y ) H i n h 2 b . A n h S e n t i n e l - 2 k y s a u (sau l g c m d y )
N O N G NGHIEP VA PHAT TRIEN N O N G THON - KY 1 - THANG 3 / 2 0 2 0 107
KHOA HQC CdNG NGHt
De danh gia kha nang phii hop cua vi6c sii dung tap hop anh dg teo ra anh khang co may trong xac dmh bi^n ddng rimg, nhom nghien oiu da tien
hanh phan tich gia tri pho cho timg kenh tren anh ciia mdi ky quan s a t Ket qua danh gia duoc t h i h i e n o b a n g l .
Chi tieu Nho nhat Lonnhat Trung binh Do lech chuan
Kydau Red
0,03 0,56 0,09 0,04
Green 0,05 0,49 0,10 0,02
Blue 0,07 0,47 0,11 0,02
NIR 0,03 0,49 0,12 0,03
phd
Red 0,03 0,55 0,09 0,04
Ky Green
0,05 0,47 0,10 0,02
sau Blue
0,07 0,43 0,11 0,02
NIR 0,03 0,49 0,12 0,03 Bang 1 cho tiily eac chi tifiu thdng kfi gia hi pho
cua cdc kenh hfin anh sau loc mdy cua ky dau vd ky sau Id tuong ding nhau, dac bifit la gid hi trung bmh phd vd do lech chuan giira cde kenh tuong iing cua mdi ky quan sdt Id nhu nhau. Rd rang vific str dung anh tong hgp sau loc may giiia 2 ky quan sat d l so sdnh su biln dii vl gia hi pho dua hfin ehi sd NDVI (dl k i t hop vdi ede ylu t l khac) la phii hgp.
3.2. Kit qua tinh todn cdc chi s i
Chi so NDVI duoc tinh toan bdng cdng thiic (1) cho mdi anh don sau khi lgc bd may, sau do duge
hgp lai vdi nhau blng hdm medianQ hong GEE dl tao ra raster NDVI cho mdi ky quan sat Nhu vay NDVI, dugc tao ra tir 136 NDVI, tiianh phin va NDVIs dugc tao ra tir 173 NDVI, tiidnh phan.
Dtr hfiu tdn xa Sentmel - 1 cua k^ diu dugc tgo ra tii 45 phifin quan sat vd ky sau dugc tao ra hi 45 phifin quan sdt bang hdm medianQ hong GEE.
Dii Ufiu kit hgp giiia chl sd NDVI va gid tri tan xa duge k i t hgp vdi nhau theo cdng thiic (3).
Chi sd biln dpng NBCI dugc tinh toan bdng cdng thiie (4)
Hmh 3al. Sentinel - 1 VH k^ diu (nhd n h i t - 28,5748; Idn n h i t 11,1655)
Hmh 3a2. Sentinel - 1 VH k^ sau (nhd n h i t - 29,6676; ldn n h i t 11,0135)
Hinh 3bl. NDVI k^ diu (nho n h i t -0,394314; ldn Hinh 3b2. NDVI k^ sau (nhd n h i t -0348077; ldn n h i t 0,814148) n h i t 0,820220)
108 NONG NGHIEP VA PHAT TRIEN NONG THON - KY 1 - THANG 3/2020
KHOA HQC CdNG NGHE
Hinh 3cl. Kit hgp k^ diu (nho n h i t -3,75924;
ldn n h i t 6,50000)
Hinh 3c2. Kit hgp k^ sau (nho n h i t -3,80255; Idn n h i t 6,51315)
Hinh 3dl. Chi s i biln dOng {oho n h i t -259874; Idn n h i t 943248). Nhung dilm sdm mdu II nhiing khu vyc c6 chi s i gilm ^V) cao, chd sdng mlu Id nhiing khu vyc c6 chi s i tdng (IV) cao, cdn lgi 11
khu dn dinh (NV) Vific ling dung cdc chi sd d l danh gid str biln ddng giu-a hai ky quan sat, da tiln hanh lap bang thing kfi phan tich cac chi sd nhu a bang 2.
Bang 2 cho thay gid hi cua cdc ehi sd d ky diu vd k^ sau cd su tuong dong cao. Dilu ndy cho phep so sanh sy thay doi gia tri giiia hai ky quan sat tai
Blng 2. Phdn tich d c chi s6
mdt vi tri nhat dmh. Cae ehi tifiu thdng kfi eua ehi sd NBCI ed su khac bifit ldn ve dp lech chuan so vdi BKS, NDVI va CMB. Do Ifich chuan rit eao phan dnh sy khac bifit ldn giua cdc gid tri, ed nghia Id viee phdn bifit su tdng giam ning bdng chi sd NBCI la thtrc hien dugc khi xde dinh dugc ngudng eu the.
Chi aeu Nho nhit Lonnhat Trung binh Do lech chuan
BKS BKS, - 29,91 24,696 -18,88 2,77
BKS, -30 24,48 -16,5 2,95
NDVI NDVI, -0,45
0,84 0,47 0,19
NDVI, -0,42
0,84 0,45 0,2
CMB CMB, -3,76 6,50 0,27 2,49
CMB, -3,8 6,51 0,26 2,49
NBCI - 259.874,00
943.248,00
•5,70 29.932,56
NONG NGHIEP VA PHAT TRIEN NONG THON - KY 1 - THANG 3/2020 109
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3.3. K^t qua xac dinh ogtiOng biin dOng Nguong bien dong duoc xac dinh tren 90 miu thuc te cho chi sd NDVI, tan xa nguoe va gia tri kft hop NDVI va tan xa nguoe. Ket qua cu th^ duoc the hi^n o hinh 4.
; . : I* :>
Hinh 4. Nguong gid h i biln ddng rimg - Ngudng biln ddng ddi vdi ehi sd NBCI: cdc dilm giam rimg cd gia tri tii -127,6 din -36,8 va tap trung nhilu hong khoang tii - 91,2 din - 54,9; cdc dilm rung on dinh cd gia tri tir -39,8 din 43,5 vd tap trung nhilu hong khoang tu -11,9 din 17,2; cae dilm
tdng rimg cd gid hi tir 39,2 dfin 84.9 vd tap liung nhilu hong khoang 49,8 din 76,4.
- Ngudng biln ddng ddi vdi chi sd NDVI: cac dilm giam ning ed gia tri tir -72,0 din 46,7 vd tap trung nhilu hong khoang tir - 69,0 den - 54,9; eac dilm rimg on dinh cd gid tri tii -32,5 din 43,9 va tap trung nhilu hong khoang tii -18,8 din 31,7; cdc dilm tdng rimg cd gid hi tir 46,9 din 81,7 vd tap tinng nhilu hong khoang 54,2 den 75,5.
- Ngudng biln dpng ddi vdi ehi sd BKS: cdc diem giam rimg cd gia tri hi 41,1 den 130,9 vd t^p hung nhilu hong khoang tir 63,5 din 108,3; cac dilm ning on dinh cd gia tri tu - 45,6 den 45,3 va tap trung nhilu hong khoang tii -14,8 din 23,1; cdc dilm tdng rimg ed gid tri tir - 83,2 din - 39,6 va tap trung nhilu trong khoang-72,1 din-45,6.
Nhu vay, cac gia tri tang, on dinh vd giam rimg cua cdc chi so diu ed su giao thoa hong mdt khodng n h i t dinh do vdy ngudng tdng/giam ning dugc xdc dinh la gia tn trung vi cua cac gid tri trong khoang giao thoa (Bang 3).
Chisd NBCI NDVI BKS
Bang 3. BSng xAc dinh ngudng biin dOng rimg Cac gia tri trong khoang giao thoa
Giam - On dinh 35,97; 36,84; 38,93; 39,97 46,7;-32,5
36,85; 41,09; 42,04; 42,61;
42,63; 45,28; 50,47
On dinh - Tang 43,47; 39,23; 43,09; 41,41; 43,54; 42,43 44,1; 46,9
-45,66;-44,39;-39,14 45,69; -44,76; -44,26; -40,7; -39,62
Ngudng tang/giam Giam -37,9 -39,6 42,6
TSng 42,8 45,5 44,3 Bang 3 cho thay, nguong xac dinh bi^n ddng
rung ddi voi timg chi sd duoc xac dinh nhu sau:
- Ddi vdi NBCI: khu vuc rimg 6n dinh khi gia tri NBCI nam trong khoang tii - 37,9 den 42,8; ndu nho hon - 37,9 la mat rimg va neu ldn hon 42,8 la tang rimg;
- Ddi vdi NDVI: khu vuc rimg dn dinh khi gia tri NDVI nam trong khoang ttr - 39,6 den 45,5; neu nho hon - 39,6 la mat rimg va neu ldn hon 45,5 la tang rimg;
- Ddi vdi BKS: khu vuc rimg dn dinh khi gia tri BKS nam trong khoang tir - 44,3 den 42,6; neu nhd hon - 44,3 la tang rimg va neu Ion hon 42,6 la giam rimg.
3.4. Kit qua x4c dinh viing mft rimg Ap dung nguong phan loai d bang 1 ddi vdi timg chi sd NBCI, NDVI va BKS de tao ra cac raster mat
rimg, trong cac raster nay nhiing diim anh cd gia tri bang 1 the hien vi tri mat rimg va nhtmg diim anh c6 gia tri bang 0 la the hien vi tri khdng mat rimg (tang hoac dn dinh). Cac raster mat rimg nay dupc kit hop vol ban do hien trang rimg ciia tinh Gia Lai de loc bd nhiing diim anh ngoai quy hoach 3 loai rimg. Kit qua cho thay chi sd NBCI phat hien dupc 6000 vi tri mat rimg, chi sd NDVI phat hien dugc 6400 vi tri m^t rimg va chi sd BKS phat hien duoc 7200 vi tri mat rimg.
Tir k i t qua xac dinh duoc, nhdm nghiin cuu da tiin hanh lay m i u ngSu nhiin 60 diem phat hiin duoc cua mdi chi sd, sau dd kiem chiing ngoai thi^
dia xem cac vi tri do co phai mat rimg khdng (Bang 4).
Ket qua thdng ke mat rimg phat hien bang chi sd NBCI cho thaiy trong khoang tir dau nam 2018 din giiia nam 2019, toan tinh Gia Lai bj mat di
110 NONG NGHIEP VA PHAT TRIEN NONG THON - KY 1 - THANG 3/2020
KHOA HOC C 6 N G NGHE
3.415,79 ha ning phdn b l d 4.437 Id, 2.022 khoanh, 657 tilu khu, 130 xd vd 16 huy|n, hong dd rimg ty nhifin Id rdng thudng xanh la 1.459,87 ha, rung ty nhifin Id rgng rung la Id 26,82 ha va rimg hong Id 1.929,1 ha (Bang 5).
Bdng 4. Kit qua kilm chiing thyc dja TT
1 2 3
Chisd NBCI NDVI BKS
Sd diim kiim chiing
60 60 60
So diim diing
55 49 45
T y l i
(%)
91,7 81,7 75,0
Hinh 5. Anh v | tinh tnrdc (hli) vd sau (phdi) m i t ning - Kit q u i xdc dinh b l n g chi s i NBCI Blng 5. Kit q u i phdn tich m i t rtmg b l n g chi s6
NBCI
TT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Huyen
Chu Pah Chu Prdng ChuPuh Dik Doa DakPo Diic Co [a Grai la Pa Kbang Kong Chro Krdng Pa Viang Yang -*hu Thien rhanhphd Pleiku FhixaAn iOii Tn xa Ayun
=a one cdng
Rimg trdng (ha) 92,68 712,67 34,14 21,31 98,29 13,65 21,60 21,89 44,42 103,89 24,80 502,93 8,69 67,72 160,42
1.929,10 Rimgtu nhiin la rdng rung la
(ha) 12,60
0,43 0,14 1,27 2,25 4,55 2,15 0,83 0,15
2,45 26,82
Rimgtu nhiin la rdng thudng xanh (ha)
128,23 59,48 6,66 109,99 28,56 267,50 273,82 29,26 48,70 142,05 189,41 151,61 1,39
3,63 19,58 1.459,87
Tdng (ha)
220,91 784,75 41,23 131,44 126,85 282,42 295,42 53,40 93,12 250,49 216,36 655,37 10,23 67.72 164,05 22,03 3.415,79
Bang 5 eho thay difin tich rimg hi mat tap trung nhieu d cdc huyen Chu Prdng (784,75 ha, hong dd:
712,76 ha rimg hong, 59,58 ha rimg hr nhifin la rdng thudng xanh va 12,60 ha rung ttr nhifin Id rpng rung la), Mang Yang (655,37 ha, hong dd: 502,93 ha rimg hdng, 151,61 ha rimg ty nhien Id rdng thudng xanh va 0,83 ha rimg ty nhifin la rdng rung Id). Cac huyfin cd dien tieh rimg hi mat thap gdra: huyfin Phu Thifin (10,23 ha), thi xd Ayun Pa (22,03 ha), huyen Chu Puh (41,23 ha), la Pa (53,40 ha). Cde huyfin cdn lai cd difin tich rimg hi mat phdt hien dugc tir khodng 100 ha din 250 ha. Difin tieh rimg hdng bi mat ehu ylu la rimg san xuat, rimg dugc khai thae de chuyin sang ehu ky hdng rimg mdi, mdt sd difin tieh do hi chdy va chuyen doi eay hdng tir cao su sang hinh thiic sii dung d i t khae.
3.5. Tliao ludn
Tu lieu vifin thdm Sentinel - 1 va Sentinel - 2 diu cd kha ndng phat hien mat rimg vdi dp chinh xae khd cao (tir 75% h d lfin). Tuy nhifin, neu k i t hgp ca 2 loai ndy thi dp chinh xdc se duoc cai thifin hon nhilu (91,7%). Dieu nay cung phii hgp vdi k i t qua nghifin ciiu eua Paulo Amador Tavares (2019) khi su dung cd 2 loai tu hfiu nay d l phdn loai lop phu thue vat dd eho do chinh xde len din 91,07% nhu da ndi d phin md diu. Nhu vdy, vifie iing dung ea anh ve tinh quang hoc vd dii Ufiu vfi hnh radar thi se phat huy dugc the manh eua timg loai anh: chi so NDVI cua anh quang hgc phan anh dac diem Idp phu thyc vdt, chi sd NDVI eang cao thi thyc vdt eang tdt Qohn Weier va David Herring, 2000); eon du lieu radar phan anh ddc diem clu tnic Idp phii thyc vat (OUver, C. vd Quegan, S., 1998), gid tn tan xa d khu vuc cd rimg cao hon d khu vyc dat hong.
4 . KET LUAN
Kit qua nghifin cuu chi ra rdng, sy k i t hgp giira anh vfi tmh quang hgc Sentinel - 2 va anh vfi hnh radar Sentinel - 1 cho kha ndng phdt hifin mat ning d Gia Lai tdt hon so vdi su dung timg loai anh rifing re.
Nhdm nghifin ciiu dd su dung phuong phap lpc mdy hen Google Earth Engme de tao ra anh Senhnel - 2 sach mdy cho ky dau vd ky sau tir 137 vd 176 eanh anh ed ty le mdy dudi 30%. Dtr hfiu radar Sentinel - 1 ky dau va ky sau ciing dtrgc tao ra tir 45 phifin quan sat bang thuat toan medianQ hen GEE. Tir dnh quang hpc, da tinh todn ehi sd NDVI ky dau vd ky sau sau dd kfi't hop vdi gia tn tdn xa nguoe radar (BKS) cua Sentmel - 1 d l tao ra du Ueu kit hpp giira
NONG NGHIEP VA PHAT TRIEN NONG THON - KY 1 - THANG 3/2020 111
KHOA HOC CONG NGHi
NDVI va BKS ky dau va ky sau. Chi sd biin ddng Aperture Radar Data for SEDD+ Applications in duoc tinh toan dua trin sir chinh lich gia tn trin anh Malawi. Land (DOI: 10.3390/land7040116).
k i t hop giiia 2 ky quan sat duoc goi la NBCI. Su 4 Nguyen Thanh Hoan, el al., 2013. Tropical dung 30 miu miit rimg, 30 mSu rimg dn dinh va 30 forest mapping using a combmation of optical and mlu tang rimg de xac dmh nguong biin ddng cho microwave data of ALOS. Intemational Joumal of timg chi sd; (i) Chi sd NBCI co nguong dn dinh tir Remote Sensing.
37,9 din 42,8; (VL) Chi sd NDVI cd nguong dn dinh tir 5. Paulo Amador Tavares, et al., 2019.
39,6 din 45,5; (ui) chi sd BKS cd nguong dn dinh tir - Integration of Sentinel - 1 and Sentinel - 2 for 44,3 din 42,6. Kit qua xac dinh mat rimg bang chi sd ClassiScadon and LULC Mapping in die Urban Area NBCI dat 97,7%, chi sd NDVI dat 81,7% va chi sd BKS ofBelem, Eastem BraziUan Amazon. Sensors.
dat 75,0%. 6 Prasad S. Thenkahail, 2016. Land Resources TAI UBI THAM KHAO Monitoring, Modeling, and Mapphig mth Remote , . , , . r. T^ , „„,„ , , Sensai,g; CRC Press.
1. Alice M.S.Duneux.e/'a/., 2019. Momto/m^ .^ Y ^ j ^ ^ ^ Fernandez-Ordonez, et al., 2009.
forest disturbance usmg change detection on ^^^^^ ^ Geoscience and Remote Sensing, synthetic aperture radar unageiy. SPIE 11139, chapter Forest Inventory usmg Optical and Radar Applications of Machme Learmng. ^ ^ ^ ^ ^ ^^^.^ ^ Q , . io.5772/8330
2. Johannes Reiche, et al., 2019. Combmmg g ^einab Shirvani et al., 2019. A Synergetic satelUte data for better b-op,cal forest momtormg. ^ ^ ^ ^ ^^ Sentinel-l and -2 for Mapping Historical Nature Climate Change 6 (2) : 120 -122. LandsUdes Using Object - Oriented Random Potest
3. Manuela Hirschmugl and Janik Deutscher, ^ OieHyrcanian Forests. Remote Sensing.
2018. Combined Use of Optical and Synthetic
STUDY ON DEFORESTATION DETCCTION IN GIA LAI PROVINCE USING SENTINEI.2 OPTICAL ' SATELLITE IMAGE AND SENTINELrl RADAR DATA
Nguyen Van TW', Tran Quang Bao^, Le Sy Doanh', Pham Van Duan', Nguyen Nam Hai', Tran Xuan Hoa''
^Institute for Forest Ecology and Environment;
" Vietnam National Univertsity of Forestry 'Science and Technology Department of Gia Lai Summary
In this study, NDVI value of the Sentinel - 2 optical sateUite image was integrated with the backscatter value of the Sentmel - 1 SyntheUc - aperture radar data between two periods to detect deforestaUon in Gia Lai province. The early penod is from January 1, 2018 to June 30, 2018 and the later penod is from January 1, 2019 to June 30, 2019. NDVI was calculated from a series of SenUnel-2 scenes with a cloud cover ratio of less than 30%, mcluding 136 scenes of the early penod and 173 scenes of the later period. A median value of backscatter of 45 scenes for each penod were also created for SentineM. Image data processing and analysis is done on Google Earth Engine. The study results show that the probability of detecUng deforestation in Gia Lai with combined data (NBCI) is better than using separate opUcal data (NDVI) or radar backscatter QiKS). Specifically, die accuracy of detecting deforestation with NBCI was 91.7% while it was only 81.7% with NDVI and 75% widi BKS. With the NBCI model integrated with map of forest status in 2017, this study found that 3,415.79 hectares of forest were lost fi-om January 1.2018 to June 30, 2019 in Gia Lai province. This deforestaUon is distributed in 4,437 plots, 2,022 sub compartment. 657 compartment, 130 communes and 16 distticts, of which the evergreen broadleaf natural forest is 1,459.87 hectares, the natural broadleaf deciduous forest is 26.82 hectares and the planted forest is 1,929.1 hectares.
Keywords: Deforestation, Gia Lai. Google Earth Engine, Sentinel -1, Sentinel - 2.
Ngudi phJn biin: TS. Li Anh Hiing Ngiy nhSn bM: 10/01/2020 Ngiy thdng qua phJn biin: 10/02/2020 NgiyduyitdSng: 17/02/2020
112 NONG NGHIEP VA PHAT TRIEN NONG THON - KY 1 - THANG 3/2020
