31(3), 207-2/7 Tap chf CAC KHOA HOC VE TRAI D A T 9-2009
KET QUA DANH GIA DO TRE THIEN DINH VA H A M Ll/ONG HOI Nl/dC TONG CONG TANG
DOI LUU Ttr SO LIEU GPS 6 VIET NAM
LE HUY MINH, FREDERIC MASSON, P. LASSUDRIE DUCHESNE, A. BOURDILLON, TRAN THI LAN, PHAM XUAN T H A N H , NGUYEN CHIEN THANG,
TRAN NGOC NAM, HOANG THAI LAN I. Md DAU
Ham lugng hai nude ddng mOt vai trd quan trgng trong cac qua trinh vat ly khi quyen trong pham vi khdng thdi gian rdt rOng, tu cac qua trinh khi hau toan cau tdi cae ye'u td vi khi hau. Ham lugng hgi nude eung bie'n ddi manh nhdt trong .sd cac hgp phdn ciia khi quyen, ngay nay ngudi ta .sii dung nhieu cdng nghe khdc nhau de do dae trong dd cd cdng nghe GPS. Tin hieu dien tu truyen tu ede ve tinh GPS qua tdng dien ly va tdng khi quyen tdi may thu dat tren mat da't bi tre mdt khoang thdi gian nha't dinh so vdi thdi gian truyen trong chan khong. MOi trudng dien ly la mdi trudng tan xa tao nen sy tre khae nhau dd'i vdi hai tdn sd GPS phu thuOc vao mat dO dien tii trong tdng dien ly. Vdi eOng nghe GPS hai tdn sd, viec sii dung cac dd tre nay cd the tinh toan ndng dd dien tii tdng cdng tdng dien ly, vi vay anh hudng ciia tdng dien ly cd the duge tinh toan. Tdng khi quyen (hoac dung ban la tdng dd'i luu) khOng phai la mOi trudng tan xa, trong dai tdn sd sii: dung bdi cOng nghe GPS, anh hudng cua ham lugng hai nude trong tdng ddi luu la nhu nhau dd'i vdi ca hai tdn sd, va viec tinh toan duge dO tre tdng ddi luu lam cho cOng nghe GPS trd thanh mOt cdng cu do ham lugng hoi nude
|2, 4, 8, 10]. Viee tinh toan dd tre va ham lugng hgi nude tdng ddi luu tir sd lieu GPS hien nay thudng diing cac phdn mem chuyen dung nhu phdn mem Gamit [14], phdn mem Bernese, phdn mem Gip.sy- Oasis... Trong khuon khd hgp tac giira Vien Vat ly Dia cdu va Trudng Dai hgc Rennes 1, Trudng Vien thdng Qudc gia Bretagne (COng hda Phap) ba tram thu tin hieu ve tinh GPS lien tue duge dat tai Ha NOi, Hue va thanh phd Hd Chi Minh tir ddu nam 2005 va 2006. Viec su dung sd lieu eua cac tram thu GPS lien tuc nay trong nghien ciiu ndng dO
dien tii tdng cOng tdng dien ly da duge gidi thieu trong fl8, 19|. Bai bao nay trinh bdy nguyen ly chung cua viee tinh toan cac tham sd khi quyen tu sd lieu GPS ndi ehung va ke't qua tinh toan dd tre thien dinh tdng cOng vd hdm lugng hoi nude tdng eOng theo sd lieu ba tram GPS lien tuc d nude ta trong khoang thai gian 2005-2006.
II. CO S6 LY THUYET
Nguyen ly danh gia anh hudng tdng khi quyen len sy truyen tin bieu GPS va xae dinh ham lugng hoi nude tdng cOng tdng ddi luu la xae djnh dO tre ciia tin bieu GPS so vdi truyen trong chan khdng.
DO tre tdng cdng AL gay bdi tdng ddi luu la tich phan dd khiic xa N(l) cua tdng ddi luu dgc theo dudng di L giua anten may thu va ve tinh GPS :
AL = \0-^\N.dl (I)
Dudng di L duge tinh theo nguyen ly Fermat : dudng di ciia tia sang, de di tir mdt diem tdi mOt die'm khae trong mdi trudng dang hudng, tuong irng vdi mOt thdi gian di eye tieu.
DO khiic xa duge bie'u thi vdi gia thie't khdng khi khd ly tudng la ham cua dp sudt timg phdn eila khOng khi "kho" Pd, ciia nhiet dO T va eua dp sudt tung phdn ciia hoi nude Pw :
N = k P,
^7'+k2^^-J+k,
Jl (2)
vdiZj'= 1,00027 modun nghieh diio ciia dd nen eiia khdng khi khO, Z"' = 1,00201 - modun nghieh dao ciia dO nen cua hai nude, k i = 77,60 ±0,05 K/h Pa, k2 = 70,4±2,2K/hPa,k3 = (3,739+0,012).10'K^/hPa.
C6 the vie't lai phuong trinh (2) theo each sd hang thir nhdt chi phu thude dp sudt tdng cdng va khdng phu thudc vdo ty sd (bie'n ddi) giira dp sua't rieng phdn "khd" va "dm" :
N = k,R,p + k^^Z-}+k,^Z-^ (3) vdi Rj = RIM J, k\ • k\ {MJMJ, R - bang sd khi
ly tudng, Mj va M„ - khdi lugng phan tu gam ciia khdng khi khd va khdng khi dm, p - mat dd tdng cdng ciia khdng khi. So hang ddu tien va hai sd hang cudi eiing duge ggi tugng irng la dO khiic xa thiiy tmh ciia khdng khi ky hieu la Nh va dd khiic xa dm ky hieu la N^,. Tap hgp cac hgp phdn khd ciia khi quyen ed the duge nhdm lai trong 1 sd bang duy nha't vi ty le tuang dd'i eiia khi nay dudng nhu khdng ddi theo thdi gian. Cae bift'n thifen do boat ddng ciia con ngudi va bie'n thien theo miia ciia ndng dO khi CO2 (ed 6 ppm/nam va 1,7 ppm/nam) khdng duge chu y tdi trong dang thirc cd dien ciia ki.
Tham sd khi quye'n chinh xac dinh duge tu viee xii ly sd lieu GPS la do tre thien dinh tdng cOng (Zenithal Total Delay - ZTD). Ve phuang dien vat ly nd tuong (rng vdi dd tre thien dinh gay bdi khi quyen trung binh (theo dd'i xung phuang vi). Vi phuang dien toan hgc nd tuong irng vdi trung binh ciia cac dO tre giira mOt tram va cac ve tinh GPS duge ehie'u len thien dinh (theo phuang thang dimg), bie'u tbi nhieu loan lien quan vdi tap hgp khi ciia khi quyen giira mat ddt va ve tinh GPS (tdng dien ly duge tach rieng).
Lugng hai nude tich phan d thien dl'nb (IWP) cd the tinh toan theo mdt qua trinh da duge thie't lap [3] tir eae phep do ap sudt va nhiet dd hi mat vd tir ZTD.
Bude ddu tien la danh gia ddng gdp eiia tap hgp khi bang viec gia sii mdt can bdng thiiy tinh (dd tre thien di'nh thiiy tinh - Zenithal Hydrostatic Delay - ZHD). Cae gia tri tieu bieu eua ZHD co 2,3 m dudi cac dieu kien khi quyen trung binh. ZHD ed the' tinh toan nhd viec do ap sua't d mat da't tu cdng thiic :
p
ZHD = [(0,0022768 + 0,0000015 )m./rPa-' 1 ° , /((0,//)=l-0,00265.cos(2^)-0,000285// ^ ' vdi Po - dp sua't tdng cOng d bd mat, cp - vy dO, H - dd cao tinh tir mat geoid. Dd khdng chac chan trong viee tinh toan ZHD duge dua ra bdi U. Foelsche va G. Kirchengast [12].
ZHD la tdng tap hgp khi ciia khi quye'n d can bang thiiy tTnh trong dd cd hai nude. Ddng gdp eiia bai nude trong ZHD ngu y sai sd cd 3 % tren dd tre thien di'nh udt (Zenithal Wet Delay - ZWD) va duge truyen vao cac tinh toan tie'p theo nhu sai sd d viec do dd dm bang GPS. Sai sd thie't bi ciia cac ddu thu dp sua't rdt nhd, co 0,1 hPa vd khdng tach biet duge (ca 0,23 mm ddi vdi ZHD cd 2,3m). Nhung ddu thu ap sua't khdng lien ke't mdt each be thdng vdi cac tram GPS. Sai sd nOi suy (trudc he't theo dO cao) tu vi tri ciia mOt ddu thu dp sua't tdi vi tri may thu GPS cd the' ed 1 hPa dd'i vdi nhirng dia binh thay ddi manh va mdt ddu thu dp sudt d xa. Cudi ciing cOng thirc tinh ZHD gia sir cOt khi quyen tren die'm do la can bang thuy tmh. Can bang thuy tinh chf rd cac ehuye'n dOng thang dirng trong khi quyen la ed the bd qua.
The'nhung cae md phdng vdi cac md hinh sd khOng thiiy tinh cd dd phan giai cao dudng nhu chi ra dd lech khdi can bang thuy tmh dua tdi nhirng sai sd ldn cd 10 mm trong tinh todn ZHD. J.L. Davis va nnk [9] da chi ra dudi cac dieu kien khi quye'n eye diem nhu bao, gia tO'c thang dirng ed the dat tdi 1 % gia td'e trgng lye, tire la sai .so cd 20 mm. Sai sd pham phai khi ddnh gia ZHD chac chan la mOt trong nhirng ban ehe' chinh eua viec ddnh gid hoi nude bang GPS.
Loai trir ZHD khdi ZTD, chung ta thu duge dd tre udt ZWD. ZWD thay ddi manh giira cac viing kho va cae vung lanh (cd centimet hoac it ban) va d viing xich dao dm udt (de'n 40 em). ZWD eung ty le vdi lugng hai nude tich phan duge bieu dien bang kg/m . De' ddnh gia lugng hoi nude tich phan (Integrated Water Vapour - IWV), cdn chia ZWD cho nhan tii n [6, 7] phu thudc tuye'n thdng dirng ciia ap sudt rieng phdn cua hai nude vd eiia nhiet dd tren tram GPS :
n =
io-
R - k, — — -^• — i , M.. k,M, T,„
r Pjv
dz
0)
m p
\^dz
J j2
vai Mvv - khd'i lugng phan tii gam ciia hai nude, MJ - khd'i lugng phan tu gam ciia khdng khi khd, P„ - dp sudt rieng phdn ciia bai nude, p - mat dd nude ldng, T - nhiet dd.
Nhan tii n thay ddi tuye'n tinh theo T,^, gia tri tieu bie'u cd 6,5 va c6 the thay ddi ban 15 % theo dO cao va theo miia. Cac he sd ki, k2 va k, thu duac
bang thyc nghiem va cac sai sd ciia chiing cd the' bd qua trong tdng hgp sai sd tinh todn IWV. Khi tham dd radio cd mat trong viing gdn tram GPS, n cd the duge tinh toan mdt each tryc tie'p. Khi khdng ed tham dd radio, tdn tai mOt mdi lien he thue nghiem giua nhiet dd be mat va LI. Cdng trinh ciia T.R.
Emarson va nnk [11] eho phep thie't lap cac be sd rieng cho mdi viing d chau Au :
n^
- « i ^^h-Ti
(6)vdi TA - nhiet dO b^ mat (tinh bang dO Kelvin) trir di nhiet do b^ mat trung binh ddi vdi viing (289,76°K ddi vdi viing Dia Trung Hai), ao, ai, a2 - cac he sd tinh toan duge bdi T.R. Emardson va H.J.P. Derks [11]
(tuang irng la 6,324, -0,00177 K"' va 0,000075 K"^
ddi vdi viing Dia Trung Hai).
Cdng thirc ciia Tm vdi ldp phii ddt toan edu duge tinh todn bdi M. Bevis va nnk [3 j tu nhiet dd be mat:
Tm = 10,2+ 0,12* To (7) vdi To - nhiet dd hi mat do bang dO Kelvin.
Sai sd lien quan tdi viec xac dinh n tu nhiet dO be mat chi ddn de'n mOt sai sd ciia IWV cd 1 % [ 12|.
Cudi eiing, IWV bieu thi dO dm trung binh cd mat trong khi quyen tren vi tri tram GPS ; .so sanh IWV do duge bdi GPS, tham dd radio va do birc xa, khdng phat hien sai lech dang ke nao cua do dae bang GPS.
Sy phan tan eae ke't qua do dae giiia GPS va cae thiet bi khdc thay ddi giua 1 va 2 kg/m2. Nhan xet ve dO chinh xac nay ciia viec do dae IWV bdng GPS cho phep coi IWV nhu la dai lugng cd the do duge khdng cdn tim kie'm su cai thien ve ky thuat. Tuang quan ngang ciia IWV ca vdi tram kilomet va vi vay tuong irng vdi cac bdt ddng nhdt eiia tdng giua vdi mdt ty le thdi gian cd tudn. Cac ke't qua nay duge can bdng theo ham sd viing dia ly va cac hoan luu dia phuang cd the ddn de'n cac bie'n thien Idn eiia dO dm. Dinh lugng hda cac tuong quan sai sd khi xac dinh IWV la khd phiic tap, trudc he't do viec xii ly GPS va mang ludi tram tham dd radio thua tbdt. Tuy nhien so .sanh giiJa hai nude tich phan do duge bdng GPS vdi boi nude tich phan tinh toan duge tir cac mO hinh sd dudng nhu chi ra su suy giam theo bam mii ciia tuang quan sai sd vdi dd dai ca 250 km [13].
la cac may thu GPS loai GSV4004A vd GSV4004B vdi ban dien tii thu nhan tin hieu loaiOEM4-G2[22|, vdi hai kie'u anten NOV503 (di vdi may GSV4004A) va NOV533 (di vdi may GSV4004B). Tram Ha NOi tu 4-2005 deh 13-1-2006 dat may GSV4004A, sau dd dat may GSV4004B. Tram Hue dat may GSV4004A, tram Tp Hd Chi Minh dat mdy GSV4004B. Cae tep sd lieu thu nhan tryc tie'p dudi dinh dang *.gps duge chuyen ddi sang eae tep sd lieu RINEX bdng phan mem di kem thie't bi, dinh dang nay se duge sii dung cho cac tinh toan tie'p theo. Ngoai sd lieu ciia ba tram GPS lien tuc d Viet Nam chiing tdi cdn sii dung sd lieu ciia mOt sd tram GPS lien tuc khdc trong khu vyc nhu Pimo (Philippine), Kunm, Wuhn (Trung Qudc), Bako (Indonesia), Terns (Dai Loan)... tu website eua trung tam dich vu GPS qudc te http://sopac.ucsd.edu/cgi-bin/dbDataBySite.egi.
Viee xii ly tai lieu GPS duge thyc hien bang phdn mem GAMIT/GLOBK [14], Trudc he't cdn tinh tga do chinh xac ciia cac tram thu GPS trong he quy ehie'u 1TFR2000 [1]. De tranh phdn nao cac hieu ung da dudng, so lieu tir cac ve tinh ed gde nhin Idn ban 10° duge sii dung. Trudc khi tinh todn dd tre thien dinh tdng cOng va mO hinh cac tham sd khi quyen phii hgp, phdn mem GAMIT ty dOng kiem tra ehdt lugng eua sd lieu dua vao, ne'u sd lieu ed nhieu khoang trdng hoac cd ehdt lugng kem thi sd lieu cua tram bi loai. Viec sii dung them sd lieu cua nhieu tram trong khu vyc trong qua trinh tinh toan, dam bao khi ehdt lugng sd lieu cua mOt sd tram d mdt ngdy ndo dd trong chudi thdi gian tinh toan khOng dam bao, viec xii ly ddi vdi ngay dd vdn duge tie'n hanh va mO hinh khi quyen xay dung duge phan anh duge ca tinh chat khu vyc. Nhu vay chiing ta tinh todn duge ZTD tu phdn mem GAMIT, sau dd ehiing tOi sii dung mo hinh gid tri ap sudt va nhiet dd tu md hinh todn cdu | 5 | de tinh todn dO tre thien dinh thiiy tTnh (ZHD), sau dd loai tru ZHD khdi ZTD chiing ta thu duge do tre thien dinh udt ZWD, tu dd thu duge IWV. De danh gia ke't qua tinh toan ham lugng hoi nude tu sd lieu GPS, ehiing tdi tie'n hdnh so sanh chudi gia tri ham lugng hoi nude trung binh ngdy tu sd lieu GPS vdi sd lieu ham lugng bai nude tir mO hinh tai phan tich 116, 17] tinh d ba vi tri tram GPS tai Ha NOi, Hue vd Tp Hd Chi Minh.
III. SO LIEU vA XLT LY SO UEU Sd lieu diing trong bai bao nay la sd lieu GPS lien tuc ciia ba tram thu GPS d nude ta [18-211. Day
IV. KET QUA vA PHAN TICH Hinh 1 trinh bdy bie'n ddi theo thdi gian ciia dd lech thien dinh tdng cdng tdng khi quyen tinh vdi
SI
2800 -r
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E B
a
H SI2700 —
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2800
2700 ~
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Hinh 1. Biin thien theo thdi gian cua dd lech thien dinh tdng cdng tinh duge tu sd lieu cac tram GPS tai Ha NOi (tren). Hue' (giira) va Tp Hd Chi Minh (dudi)
chudi sd lieu GPS trong khoang thdi gian 2005-2006.
Chiing ta ed the' thdy dd lech thien dinh tdng cdng d ea ba tram Ha Ndi, Hue' va Tp Hd Chi Minh deu ed 2,4 de'n 2,7 in. DO ldn nay hoan toan phd hgp vdi cac ke't qua thu duge tu sd lieu ciia cac tram GPS d
cac nai khae tren the gidi [3, 9]. DO leeh thien dinh tdng cdng bie'n ddi trong mOt ngay vdi bien dO cd chuc centimet, trong khi bien dO giao dOng trong nam cung chi cd 30 cm. Hinh 2 trinh bdy dd lech thien dinh tdng cdng trong ba ngay lien tie'p 107, 108
Q H N
107.0
2700 - r -
2650 - -
2600 —
2550 - -
2500
107.5 108.0 108.5 109.0 Ngay t r o n g n a m
109,5 110.0
HU^
_ — - H
107.0 107.5 108.0 108.5 109.0 Ngay trong nam
109.5 110.0
2700
2500
107.0 107.5 108.0 108.5 109.0 Ngay trong nam
109.5 110.0
Hinh 2. DO tre thien dinh tdng cOng ngay 107-109 (16-18/04/2006) tai Ha NOi (tren), Hue (giiia) vd Tp Hd Chi Minh (dudi)
va 109 tue cae ngay 16-18/04/2006. Chiing ta tha'y md binh khi quyen duge tinh toan cho sd lieu ciia tung ngay, nhung sy bie'n ddi tu ngay ng sang ngay kia la lien tuc, viee tinh todn nhu vay cho ke't qua hgp ly. Cd the' tha'y xu the' bie'n ddi ngay dem ciia ZTD tai ba tram la hoan toan khae biet nhau, dieu nay ngu y bie'n thien cae dieu kien khi quyen trong ngay d ba noi khdc biet nhau va khdng tuong quan vdi nhau. Ciing phai nhdn manh rang chudi ,sd lieu ZTD thu duge d ba tram cdn thie'u nhidu ngay trong bai nam 2005 va 2006, d nhieu doan dieu nay khdng phai do khdng cd sd lieu GPS, ma do cha't lugng eila sd lieu khdng thda man cac dieu kien ciia phdn mem
GAMIT, vdn de nay se duge chiing tOi tim hieu them ea ve xem xet cac tep sd lieu, ca ve cde tham sd dieu chinh trong phdn mem GAMIT. Mac dii chudi sd lieu khOng duge lien tuc nhu mong mudn.
nhung qua phan tieh sd lieu GPS tai ba tram GPS d nude ta trong hai nam 2005-2006 chiing ta quan sat tha'y mOt xu the' bie'n ddi theo miia kha rd ret ; ZTD dat cue dai vao khoang giua nam (thang 8) va eye dai nay rd ret nha't d tram Ha Ndi. va eye tie'u vao khoang ddu nam.
Hinh 3 la bie'n thien theo thdi gian cila ZTD trung binb ngdy tai 3 tram GPS Ha Ndi, Hue vd
2800
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2800
a
2700 +
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Hinh 3. Bie'n thien theo thdi gian eiia dd lech thien dinh tdng cOng trung binh ngay tinh duge tir sd lieu cac tram GPS tai Ha Ndi (tren). Hue (giua) va Tp Hd Chi Minh (dudi)
Tp Hd Chi Minh. Tren hinh 3 chimg ta cd the' tha'y bie'n ddi tir ngay nay sang ngay khae ciia ZTD d ba tram cd sy tuang quan nha't dinh, dieu nay ngu y, ne'u cac bie'n ddi trong ngay eiia ZTD d ba tram ed the' chi gay bdi cac nhieu ddng khi quye'n ed tinh dia phuang, trong khi bie'n ddi hi ngay ng sang ngay kia phai gay bdi cae nhieu ddng khi quyen cd tinh khu vyc rdng ldn ban. Xu the' bie'n ddi nam ciia ZTD quan sat duge tren hinh 3 rd rang ban nhidu.
Do khdng cd so lieu nhiet dd va dp sua't do dae tryc tie'p tai cae tram Ha Ndi, Hue' va Tp Hd Chi
Minh, ehiing tdi da sii dung gia tri nhiet dd va dp sudt tai eae vi tri tram tinh md hinh nhiet dO vd dp sudt toan edu ciia J. Boehm va H. Schuh, mO hinh bieu dien sy bie'n ddi eua nhiet dd va dp sudt trong nam bang cac ham dieu hda cdu duge cac nha trdc dja sir dung phdn mem GAMIT thudng diing. Cae gia tri nhiet dd va ap .sudt tinh theo md binh nay eho phep tinh toan do trd thien dinh thiiy tTnh ZHD nhu da neu d tren va sau dd loai tru ZHD khdi ZTD, chung ta thu duge dO trd thien dinh udt ZWD va tu dd ed the' tinh duge ham lugng hgi nude tdng cdng
(IWV). Ke't qua tinh toan ham lugng hai nude tdng cdng trung binb ngdy tai ba tram Ha NOi, Hue va Tp Hd Chi Minh trinh bdy tren hinh 4. Di kie'm dinh cae ke't qua tinh toan ham lugng hgi nude tu sd lieu GPS, tren hinh 4 chiing tdi cung trinh bdy ham lugng hoi nude tdng cdng tinh tir mO hinh toan edu eiia M.
Kanamitsu va nnk [17] nhu da gidi thieu trong bai bao trudc [20,21].
Bie'n thien theo thdi gian cua ham lugng hai nude tdng cdng d binb 4 hoan toan gidng nhu bien thien theo thdi gian cila dd lech thien dinh tdng eOng ZTD. Dieu nay cung de hieu vi dO lech thien dinh thiiy tTnh ZHD bie'n ddi it theo thdi gian. Tuy nhien cung phai nhdn manh rang di cd md hinh ZHD hgp ly nha't phai dya vao sd lieu do nhiet dO va dp sudt d be mat tai vj tri dat may thu GPS, cae
BJl
50 100 150 200 250 300 350 Ngay - 2005
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Hinh 4. Ham lugng hai nude tdng cdng trung binb ngay tinh tir sd lieu GPS (cac binb thoi rdng) vd tinh tu niO binb toan cdu (cae da'u chii thap) tai Ha NOi (tren). Hue (giiia) va Tp Hd Chi Minh (dudi)
gid tri do dae tryc tie'p nhu vay chac chdn .se bieh ddi theo thdi gian nhieu hon so vdi cac gia tri nhiet dO va dp sua't suy tu md hinh toan cdu. Nhu the' viec xac dinh ham lugng bai nude se cd mdt sai sd he thdng do viee tinh todn ZHD tir md hinh nhiet dd va dp sua't todn cdu. Trong tuang lai ne'u cd sd lieu nhiet do va ap sudt do dae lien tuc tai khu vyc Hd NOi, Hue' va Tp Hd Chi Minh ehiing ta cd the danh gid duge sai sd nay. Bie'n thien ham lugng hoi nude tdng cdng tai Ha Ndi cd xu the'bie'n thien nam rd't rd rang vdi eye dai vao khoang thang 8, d Hue eye dai mudn hon mOt ehiit vao khoang thang 9, d Tp Hd Chi Minh ham lugng bai nude cung eye dai vao khoang giira nam, nhung dinh eye dai khdng rd ret nhu d Hd Ndi va Hue'. Xu the'nay kha phii hgp vdi phan bd lugng
mua trung binh thang thu duge tir quan .sat khi tugng [23]. Bien dd bie'n thien nam cua ham lugng hgi nude tdng cdng tai cac tram Ha Ndi, Hue' va Tp Hd Chi Minh tuong ung bang khoang 50kg/m^ 40kg/m^
va 30kg/m^ ; nhu the' cang vd phia xich dao, bien do bieh thien nam ciia ham lugng hoi nude cang giam. Cye tieu ciia ham lugng hai nude tdng cOng vao khoang thang 1 hoac thdng 2.
Tir hinh 4 chiing ta thdy ham lugng hai nude tdng cOng trung binb ngay tinh duge tir sd lieu GPS tai tram Ha NOi phdn Idn cae ngay ddu cao ban ban cae gid tri tuang irng tinh tir mO hinh toan edu, edn tai cac tram Hue'va Tp Hd Chi Minh, sy chenh lech la nhd ban. Hinh 5 bieu thi dd lech ham lugng hoi
50 100 150 200 250 300 350 50 100 150 200 250 Ngay - 2005 Ngay - 2006
300 350
Hinh 5. DO lech giira ham lugng hgi nude tdng cdng tinh tu sd lieu GPS va tinh tu md hinh toan edu dd'i vdi tram Ha Ndi (tren).
Hue (giua) va Tp Hd Chi Minh (dudi)
150 200 250 Ngay - 2006
300 350
100 150 200 250 Ngay - 2005
100 150 200 250 Ngay - 2006
300 350
nude tdng cdng tinh tu sd lieu GPS va tu md hinh toan cdu. Chiing ta c6 the' tha'y d tram Ha Ndi phdn ldn eae gia trj dd leeh nay deu duang, edn d cac tram Hue'va Tp Hd Chi Minh, sd gia tri dO lech am nhidu ban so vdi tram Ha Ndi, tuy nhien d cae tram Hue' va Tp Hd Chi Minh sd cac gia tri dO leeh duong vdn nhieu ban sd eae gia tri dO lech am. Tai tram Ha NOi do leeh gdn vi tri eye dai giua nam eiing ldn ban tai vi tri eye tieu. DO lech tuyet ddi trung binh giiia ham lugng hoi nude tdng cdng tinh tu .sd lieu GPS va tu md hinh toan cdu ddi vdi cac tram Ha Ndi, Hue' va Tp Hd Chi Minh tinh duge tu chudi .so lieu 2005-2006 tuang ung bdng 11,7 kg/m^ 4,4 kg/m^
va 5,7kg/m .
Chiing ta thdy tren hinh 4, d tram Ha Ndi mac dil sy chenh leeh giiia hai dudng cong ham lugng hoi nude tdng eOng la ldn, nhung xu the' bie'n ddi ciia chiing lai kha phii hgp nhau. De danh gid mirc do phil hgp giira ham lugng hai nude theo sd lieu GPS vd ham lugng hai nude theo mO hinh, chiing tdi tinh he .sd tuong quan giira chiing cho tung nam sd lieu va ke't qua duge trinh bdy d bdng 1. He sd tuong quan dd'i vdi tram Ha NOi d ea hai nam gdn nhu nhau (0,95-0,96), ddi vdi tram Hue la 0,908, dd'i vdi tram Tp Hd Chi Minh tuang quan la nhd hon vdi gid tri trung binb cho ca hai nam la 0,75.
Hinh 6 la bie'u thi sy bie'n ddi theo vy dO cua he sd tuong quan giua IWV tinh tu sd lieu GPS va tinh tiir mO hinh toan cdu, ehiing ta tha'y rd xu the' giam ddn eiia he sd tuong quan khi lai gdn xich dao.
NhiJng ke't qua tren day cho tha'y, khi xii ly sd lieu GPS d phdn mien Bdc nude ta vdi muc dich nghien ciiu dich ehuye'n vd Trai Ddt sii dung md binb khi quye'n toan edu de' hieu chinh anh hudng ciia tdng khi quyen mac dii cd the' Id thich hgp nhung se mde phai mOt sai so cd tinh chat he thdng ; khi xii ly so lieu GPS d phdn mien Nam nude ta, thi viec sir dung mO hinh khi quyen toan cdu de hieu chinh anh hudng cua tdng khi quye'n .se cho sai sd Idn ban.
Bdng 1. He so tUdng quan giiira ham lUdng hdi nude tong cong tinh dudc tU so lieu GPS va tCr
mo hinh toan cau
Tram GPS Nam He sd tuang quan
Ha Ndi 2005 0,960
Hue
Tp Hd Chi Minh
2006 2006 2005
0,952 0,908 0,630
0 , 8 -
0 . 7 -
OR-
1 1 1 ' ^ A 1 1 ^ — " '
^
• 1 - H - -
, 1 . 1
- - ^ - . \ ,
1 t 1 1 1 1 1 1 1 1 1 1
, 1 , \ . 1
10 12 14 16 18
Vy do dia ly (do)
20 22
Hinh 6. Su thay ddi ciia he .so tuong quan giira hdm lugng hoi nude trung binh ngay tinh tu .sd lieu GPS
va tinh tu md hinh toan cdu KET LUAN
Sir dung sd lieu thu thap duge tai ba tram thu tin hieu GPS lien tuc Ha NOi, Hud vd Tp Hd Chi Minh eiing vdi sd lieu ciia mOt sd tram GPS trong khu vuc, dd lech thien dinh tdng cOng va ham lugng hoi nude tdng cdng tdng ddi luu da duge tinh toan trong khoang thdi gian 2005-2006. Cde ke't qua thu duge trong bai bao cd the' riit ra mOt sd ke't luan sau : - Ke't qua tinh toan ZTD tdng khi quyen thu duge tu sd lieu eae may thu GPS lien tuc d nude ta bie'n ddi lien tuc tir ngay ng sang ngay kia trong khoang tu 2,4 de'n 2,75 m, phii hgp ve dO ldn vdi cac ke't qua tinh toan ZTD d nhieu viing khae tren the gidi.
- Ham lugng hgi nude trung binh ngdy bie'n thien manh tu ngay ng sang ngay kia vdi xu the' bie'n thien nam ra't rd ret. Tai tram Ha Ndi IWV dat cye dai vao khoang thang 8, tai Hue' vao khoang thang 9, tai Tp Hd Chi Minh vao khoang thang 7-8 nhung dinh cue dai kem rd rang ban so vdi d Ha Ndi va Hue'; IWV dat cue tieu vao khoang thang 1 hoac thang 2. Bien dd bie'n thien nam cua IWV tai cac tram Ha Ndi, Hue' va Tp Hd Chi Minh tuang iing bang khoang 50kg/m^ 40kg/m^ va 30kg/m^ ; cang gdn xich dao, sy chenh leeh ciia ham lugng hoi nude giira miia khO va miia mua cdng nhd.
- IWV tinh duge tu sd lieu GPS phdn ldn deu Idn ban gia tri md hinh. Dd leeh tuyet dd'i trung binh giiia IWV tinh tU sd lieu GPS vd tu md hinh toan cdu tai Ha NOi, Hue' va Tp Hd Chi Minh ldn lugt bang ll,7kg/m^ 4,4 kg/m^ va 5,7 kg/ml He sd tuang quan trung binh trong 2 nam 2005-2006 giira IWV tinh tu sd lieu GPS va tu mO hinh toan
cdu tai ba tram tren tuang irng la 0,95, 0,91 va 0,75, nghTa la cdng gdn xich dao, sy phii hgp vd xu the' bieh ddi theo thdi gian giira IWV tinh tu .sd lieu GPS vd tir md hinh cang kem, md hinh khi quye'n toan cdu khdng bao ham duge eae nhidu ddng khi quyen ty le nhd phat bien duge d so lieu GPS.
- Thdng tin ve IWV thu duge tir sd lieu GPS la rdt td't, trong tuang lai ne'u cd nhieu tram thu GPS tren lanh thd nude ta va viec tinh toan IWV gdn nhu cap nhat, cd the duge dua vao mO hinh dy bao khi tugng khu vyc de tang them cha't lugng ciia md hinh dy bdo.
Ldi cam dn : bdi bao duge hodn thanh vdi sy trg giiip kinh phi cua di tai nghien ciru ca ban "Xii ly sd lieu ba tram thu GPS lien tue dat tai Ha NOi, Hue' va Tp Hd Chi Minh vdi nhung ung dung co ban trong nghien ciru ndng dd dien tii tdng cdng tdng dien ly d Viet Nam va chuyen ddng vd Trai Ddt d cac viing quan sat", ma so 711906 va de tdi ca'p nhd nude "Ung dung eong nghe vu tru de' danh gia anh hudng eiia tdng dien ly vd tdng khi quye'n tdi do chinh xac khi sii dung tin hieu ve tinh d khu vue Viet Nam".
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S U M M A R Y
Preliminary results of the estimation of the zenith total delay and the integrated water vapour of the
troposphere by GPS data in Vietnam This paper presents the results of the estimation of the zenith delay (ZTD) and the integrated water vapour (IWV) from the Hanoi, Hue and Ho Chi Minh city continuous GPS data during the 2005-2006 period. It is found that the ZTD in Hanoi, Hue and Ho Chi Minh city varies day-to-day in the range of about 2,4-2,7 m and presents a very clearly annual variation. The variations of the GPS IWV are quite similar. The IWV maximum is in August at Hanoi, in September in Hue and in June-July in Ho Chi Minh city, but the IWV maximum in Ho Chi Minh city is not as clear as in Hanoi or in Hue. The IWV minimum is in January or in February. The amplitude of the annual variations of the IWV are about 50 kg/m^
40 kg/m^ and 30kg/m^ in Ha Noi, in Hue and in Ho Chi Minh city respectively, this means that the diffe- rence of the IWVs between the raining and the dry seasons is smaller as near as the equator. The IWV calculated from the GPS data are greater than the one from the NCEP-DOE AMIP-II Reanalysis global model. The mean absolute deviations between the GPS and model IWVs are 11.7 kg/m^ 4.4 kg/m^ and 5.7 kg/m^ in Hanoi, in Hue and in Ho Chi Minh city, but the correlation between the GPS and model IWVs is of 0.95, 0.91 and 0.75 for Hanoi, Hue and Ho Chi Minh city respectively. So the agreement between the GPS and global model IWVs in the South Vietnam is not so good as in the North, this implicates that the small scale atmospheric pertur- bations near the equator could not be included in the global atmospheric model. These results show that the IWV deduced from the GPS data has good quality and could be used for a forecast climatolo- gical model.
Ngdy nhdn bdi : 09-01-2009 Vien Vdt ly dia cdu,
Vien Vdt ly dia cdu Strasbourg (Phdp), Trudng Viin thong qudc gia Bretagne (Phdp),
Trudng Dai hgc Rennes 1 (Phdp), Trudng Dai hgc Khoa hgc Hue, Phdn Vien Vdt ly Tp Ho Chi Minh,