Nghien cOu - Trao doi
Kha nang sur dung ky thuat Radargrammetry trong thanh lap mo hinh so do cao
khu vu^c Hoa Binh
O TRAN THANH H A TnJdng Dgi hgc Md - Dja Chit
T
rong nhGng nam 1960, phuang phdp do ve l$p thi lin diu tien dtftfc Ung dgng cho anh radar bdi L^ Prade de t$n dgng dc UU thi cua anh radar vdi kha ndng thu anh d ban ngdy, lyan dim va khdng phg thudc vdo dc diiu kign thdi tiit Dutfc biit den dUdi thugt ngii "Radar- grammetry", do anh radar cd thi dUtfc so sdnh mdt dch tUdng Ung vdl thuit ngU "Photogram- metry" trong Ilnh vtfc do anh quang hgc. Theo dd,"Radargrammetry" dUtfc djnh nghTa nhtf Id mgt dng nghg nham chiit tdch dc thdng tin hinh hgc cua be mgt thtfc dia tUanh radar.
PhUdng phdp ndy eho phep quan sat va do dge trong khdng gian 3 ehilu dQa tren nguyen ly dong thdi quan sdt hai t i m anh dQpc chyp tQ cde gde chyp khdc nhau cDa cDng mpt d l i tQdng hay mdt b l mat D l khic phyc nhQpc diem eDa InSAR cDng vdi vi^c phdng vd tinh Radarsat nam 1995 thi dnh SAR lap the da dQpc nghien cQu nhilu hPn, cho nen, cac nhd khoa hpc da Qng dyng ky thudt SAR lgp the cho vide khai thdc cde thdng tin dja hinh cung nhQ thdnh ldp DEM (Paillou vd Gelautz 1999). Mgt trong nhQng Ipi t h i cDa Radargrammetry la ft bj dnh hudng bdi khf quyin vi phUPng phdp nay sD dung gid tri bien do (thj sai) de tfnh do cao cDa d l i tupng.
Cd sd ly thuyet va phUdng phap nghidn cdu Tao DEM bang phuang phdp Radargrammetry Doi vdi dnh radar, cac nha nghien cQu da xac dinh mgt s l d u hinh quan trie lgp the ddc thD cho phep tao ra cdc gia tri thj sai giong nhu trong phUdng phap do dnh quang hge ma nhd dd cac gid trj dd cao cd t h i dUge do dac tren cde may ve lap the truyln thong. Hai cau hinh cdp dnh ldp the radar phi biln nhat la cDng phfa (same-side) vd khdc phfa (opposite-side) dugc djnh nghTa dua trdn vj tri tUOng d l i cua radar so vdi khu vuc do ve trong trudng hgp
hai dudng bay. C l u hinh cDng phfa bao gom mdt cap lap the dupc tgo thdnh bdi hai dnh tang dan hogc hai dnh gidm d i n . Trong khi d u hinh khde phfa cung d p cde gdc thj sai, do dd moi quan hd hinh hpc td't hdn d i n d i n thdng tin dja hinh chfnh xac hPn {Toutin vd Gray, 2000).
Trong hinh 1, Si vd S2 Id d c ve tinh, Bx, Bz Id dudng day eP sd theo ngang vd hudng dpc. Gdc 9-|
vd 02 Id gde hinh hay gde giao hdi cDa hai tia ngim.
Rl, R2 Id khodng cdch giQa vd tinh vd dilm do tren mat dat P. Diem P se cd hinh dnh Id P-, vd Pg trong cd hai dnh SAR tQ S^ va S2. Vd dp dQpc ggi id
"chenh lech" khodng each giQa P, vd P2. Neu dilm P coi nhQ bing phang (tdc Id chdnh cao dja hinh h=0) thi khi do P^ vd P2 trDng nhau va khi do dd cao H ( dd cao tQ vd tinh tdi mgt dat) se tdng l l n . Dieu ndy dQpc t h i hien qua cdng thQc {Joutin vd Gray, 2000).
C^=y}x^+{H-hf -yl{x-B,f+[H + B,'hf-tfi + B,y-B^
(1) Hinh 1 : Nguyen ly lap the dnh Radar.
Tdi nguyen vd Mdi trudng | Ky 2-Thing 4/2017 J J
Nhu vay, dfl chlnh xac v l dd cao cfl m l i quan hS tJ IS nghjch vdi gid trj dfl cao h vfl khoing chdnh Iflch dp.
(2)
2 / f B , + 2H^- yJ4H^Bl -<-<^pA
Trong dd:
Vi chdnh cao dja hinh h be hdn rat nhilu so vdi chilu cao bay chyp H nen phQdng trinh (2) se dQpc ddn gidn hda nhQ sau;
Quy trinh thdnh lgp DEM tUdnh Radar Hinh 2: Quy trinh thanh ldp DEM bang phUdng
phap Radargrammetry.
Ket qud thuf nghidm
Khu vQc thQ nghidm dupe thue hidn tgi tinh Hda Binh, Viet Nam. DQ lidu sQ dung trong khu thQc nghiem la dnh TerraSAR kenh X.
Sensor TerraSAR TerraSAR
N g i y chap 3/9/2016 26/7/2016
Ttadigian clinp 6.44"
6.34"
D& phin giil (m)
25 25 Hinh 3; Cap inh vg tinh
TerraSAR-X
Hinh 4: Md hinh so dp cap (DEM)
T i c g i i da ddnh g l i dfl chlnh x i c cDa mfl hinh so dd cao DEM dd thgc hien dga vao c i c diem khong c h l mgt dat d l tien hanh so sanh do tin cay cDa phuang phip xay dflng DEM.
STT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Toa do do cao (m) Didm mat
dat 148.54 286.00 155.05 246.72 305.56 234.67 156.78 105.34 231.32 152.23 123.71 142.41 104.62 98.34 109.31
Mo hmh sd do cao 150.10 288.90 157.11 248.67 307.24 236.03 159.36 108.24 233.51 153.69 125.82 143.93 106.48 99.63 111.47
Chenh cao 1.56 2.90 2.06 1.95 1.68 1.36 2.58 2.90 2.19 1.46 2.11 1.52 1.86 129 2.16 K i t lu$n
Nhin chung, DEM dUpc thanh lap bing phap Radargrammetry cd dp chfnh xdc tUdng d l i cao d khu vUc trung du va miem nDi cd do Idch trung binh so vdi cac diem khong ehe m|t dat khodng 1,5 m. Sd dT nhu vdy Id vi DEM dU0c thanh ldp bing phQdng phap Radargrammetiy thue chd't Id md hinh so be mat (DSM), chQ khdng phai la md hinh so' dp cao (DEM), tQc la nd lu6n chenh so vdi do cao that mdt khodng dung bang chilu eao eua cdc dja vat phD tren mat dd't nhiJ rQng cdy, nhd cDa... Tai khu vQc b i n g phing, nPi md ft ed thuc phD thi do cao cDa DEM Radar- grammetry va cae dilm khing c h l khd gid'ng nhai^
Qua ddy, tae gid nhgn thiy cd t h i sQ dyng DEM dugc thdnh fdp tQ phUdng phdp Radargrammetry cho k i t qud tUdng doi t i t va ehi phf cung ft tin kem hdn so vdi DEM dupe thanh lap b i n g cdng nghd Lidar.B
3 4 Tdi nguyen vd Mdi trLrong | Ky 2 - Thang 4/2017
