2 3 0 T u y i n tilp cSc c 6 n g trinh nghiSn CLKU V | t ly Dja c4u 2008
NGHIEN eiTU iTNG DUNG LIDAR TRONG NGHIEN ClTU MAY CI
Nguyen Xuan Anh, Le Nhir Quan Viin Vdt ly Dig cdu
18 Hodng Qudc Viet, Cdu gidy, Hd Npi Email: [email protected]
Tom tdt: Trong bdi bdo ndy hi thdng LIDAR (Light Detection and Rgnging) vai irng dung cua nd trong nghien cicu mdy Ci (Cirrus Cloud) dugc di cdp Nghien ciru mdy Ci cd y nghia quan trong bai nd dnh hudmg din trudmg bice xg ciig hi Trdi ddt - Khi quyin, vd vi thi dnh huang din thdi tiit vd khi hdu.
Qug hi thdng LIDAR hgi kinh thu, cdc thdng sd vi mdy Ci dugc xdc dinh bao gom dp cao chdn mdy, dp cao dinh mdy, hi sd tdn xg ngugc, hi sd hdp thu, dp ddy quang hoc, ty li phdn cue. Mpt sd md phdng vi hi thdng LIDAR dugc thuc hien. Phuang dn cdu hinh hi thdng LIDAR di xdc dinh ma trdn Mueller dugc di xudt. Diiu ndy cho phep di sdu nghiin ciru vi mdy Ci, vi du nhu xdc dinh cdu triic vd hudmg phdn bd cdc tinh the bdng trong mdy.
1. Mo-dau Ji He thong LIDAR (Light Detection and Ranging) dugc sir dung nhilu trong nghien
cuu khi quyen. No c6 the do dugc mat do va nhiet do khi quyin theo chieu cao, nghien i cuu may Ci tang cao kliu vuc xich dao, may ting binh luu, ozon ting binh luu, aerosol tang binh luu va tang doi luu, nghien cim khi quyin lop bien, xac dinh hoi nuoc, nghien cuu chuyen dgng roi, cac thanh phin khi khac trong khi quyin [1-11].
Viec tim hieu va nghien cim he thing LIDAR cho thiy day la mgt cong viec phuc tap doi hoi phai co kien thirc chuyen mon ting hgp tir cac nganh co hgc lugng hj, vat ly kW quyen, vat ly laser, thiet bi quang dien tir, lap trinh dilu khiln va xir ly tin hieu. Tren thirc te, he thing LIDAR co ciu true phirc tap va phu thuoc nhilu vao dii tugng nghien cuu.
Trong bai nay, chimg toi xin trinh bay mgt sl kit qua thu dugc qua viec sir dung he thing LIDAR hai kenh cho viec nghien cim may Ci qua chuyin cong tac tim hilu vl he thing LIDAR tai Dai Loan nam 2007. Ciu true bai bao gIm phin nghien cim vai tro cua may Ci, gioi thieu ve he thing va phuang trinh LIDAR quan trie may Ci, mot so kit qua minh hoa, phuong an dl xuit ciu hinh LIDAR do ma tran Mueller.
6 Viet Nam, viec img dung ky thuat LIDAR nghien cim khi quyin noi chung va may Ci noi rieng chua dugc thuc hien. Viec triln khai he thing LIDAR trong nam 2008 6 Vien Vat ly Dia cau se mo ra trien vgng thirc hien cac nghien cim theo huong nay.
Ph^n IV VATLY KM! niiYiiiN 33 j
I Anh huong ciia may CI din thoi tilt khi h au
^ Khoang 30% bl mat trai dit dugc bao phu boi may Ci [12]. May Ci la loai may chira lugng dang ke cac tinh thi bang kich thuoc Ion, dang hinh hgc phuc tap, co do tap trung thap, thuong mong va mau khong tii. May Ci la nhan tl dilu chinh quan trgng can bang birc^xa trong he thing trai dit - khi quyin. May phan xa mgt phin dang kl birc X| mat troi den va dong thoi thu giir thong luong nhiet hing ngoai phat ra tir bl mat trai iit va tang khi quyen duai.
^ Tuy vay, cho den nay, vai tro ciia May Ci anh huong toi thoi tilt, khi hau van la mot trong cac van dk chua dugc tim hilu diy du. Truoc day nguoi ta chi quan tam din sir hinh thanh va tan di cua may Ci theo su biln dii theo thoi gian va khong gian nhung chua xem xet tren quan dilm nhiet dgng iuc hay dgng lire hgc. Qua cac cac thilt bi do dac dat tren may bay chuyen dung va thilt bi do gian tilp img dung ky thuat LIDAR trong nhirng nam gan day, thanh phin ciu tao, cac qua trinh vat ly ciia may Ci dugc nghien cuu sau hon.
Theo cac nghien cuu vat ly va nhimg tinh toan cu thi nguofi ta nhan thay rang may Ci anh huong den truong birc xa ciia he trai dit - khi quyin. Nhimg qua trinh vat ly lien quan den may Ci dan den su lam lanh hay dot nong dang ke len quy mo thang dimg ciing nhu quy mo ngang trong khi quyen. Cac tac dgng do dugc xem la phuang thuc chi phoi qua trinh thay doi khi hau va tac dgng sau sac den he thong thai tiet toan cau, it nhat la den quy mo thai gian dai hon 3 ngay.
Nhu da de cap o tren, may Ci c6 the dugc do dac true tiep hay gian tiep. Tuy nhien, vai cac uu diem ciia ki thuat LIDAR nhu do phan giai cao, do linh hoat Ion (c6 the lap dat 6 tram mat dat, tren may bay, hay tren ve tinh...), nen he thong LIDAR la mgt cong cy hiju ich de nghien cuu sir ton tai va cac dac tinh ciia may Ci.
3. Gioi thieu chung ve LIDAR
LIDAR la thilt bi quan trie tich cue tir xa. Nguyen ly hoat dgng co ban cua he thing LIDAR nghien cim khi quyen la phat tia laser vao khi quyen va nghien cim cac tin hieu quay tro lai dk nhan dugc cac thong tin ve thanh phan va cau true khi quyen. H?
thing LIDAR gIm ba phin chinh la phan phat tin hieu, phan thu tin hieu va phan dilu khien, .xir ly tin hieu. Laser sir dung trong LIDAR 6 giai anh sang cue tim, nhin thiy va hing ngoai. He thing LIDAR quan trac tich circ co nhimg lgi the so voi he thu dgng sir d\ing birc xa tu nhien. Mgt trong nhimg dac diem do la co do phan giai cao theo chieu thing dimg (co thi dat toi vai met).
Nhimg qua uinh vat ly khac nhau trong khi quyin dan din nhimg dang tan xa khac nhau nhu tan xa Rayleigh, Mie hay Raman. Bing viec lira chgn cac qua hinh tan xa khac nhau CO thi giai quylt cac bai toan khac nhau. LIDAR dimg tan xa Rayleigh co kha nSn^
xac dinh profile nhiet do khi quyin len din 90km. LIDAR dimg tan xa Mie nghien cim ve aerosol ting dii luu va binh luu. LIDAR sir dung vach pho cong huong (Resonant lidar) nghien cim su phan bl ciia mgt sl kim loai nhu Na, K, Li, Fe, Ca, Ca+. LIDAR dimg hieu tag Doppler dl xac dinh nhiet do, gio va chuyen dgng rli. LIDAR dimg hieu ung chenh
' V *> ^
J j 2 Tuyln t | p cac c6ng trinh nghidn cu-u Vat ly Dia clu 2008
lech hip thu (DIAL LIDAR) nghien cim vl hoi nuoc, ozone, NO2, CO, SO2. LIDAR tren nguyen ly tan xa Raman nghien cim hoi nuoc, nhiet do, cac chat gay 6^ nhiem, sir suy giam do aerosol. Cin noi them ring moi dang LIDAR deu co uu, nhugc diem rieng va cho din nay viec thilt kl he thing LIDAR van con rat nhieu dieu can nghien cuu.
!;-i:
Laser /
B 9 ph|n quang hpc thu BO nhan quang
May tinh Kiiih thu
^--^' / TAch .song /
• \ \ -
m..
r
/ y* " " BO ph^n phan Uch
Hinh 1. c l u true he thdng LIDAR tai Chung Li, D^i Loan
Tren hinh 1 la ciu true he thing lidar sir dung tai Chung li, Dai Loan. He thing LIDAR nay hoat dgng dua tren tan xa Rayleigh. Dang laser Nd: YaG dugc sir dung phat xung thing dung len khi quyen o buoc song 532nm. Kinh thu (telescope) la dang Newton voi duong kinh 45cm. Tin hieu thu vl, sau khi qua bg Igc, dugc tach lam hai kenh phan cue vuong goc va song song. Cac tin hieu nay dugc khuylch dai bing 2 bg nhan quang va di din thiet bi xir ly tin hieu da ken± cho phep do phan giai 24m.
4. Phu-ffng trich LIDAR •, -^
Phuang trinh LIDAR la phuang trinh co ban xac dinh moi quan he giira sl photon thu nhan dugc voi so photon ma laser phat di, voi sir lan truyen cua tia sang trong khf quyen nen, voi tuong tac vat ly giua anh sang va muc tieu nghien cim, voi he sl hihi dung va cau triic hinh hgc ciia he thong LIDAR, v.v.
Y)k xay dung phuang trimh LIDAR cin phai xac dinh cac qua trinh vat ly dien ra tren co so cac mon co hgc lugng tir, quang phi hgc, vat Iy tan xa (hinh 2). Phuong hinh LIDAR tong quat c6 dang
^si>^^^)-^dKy{i'>iKK^QM)^\A,-{Ta,,R)T{X,R)\\^^^^^
R
trong do:
Ns{/l,R)- so photon se nhan dugc tir khoang each R
(1)
Ph^n I V _ y ^ y ^^j QjjY^N
333
^L (^"i) - so photon do laser phat ra.
/^(<9, R) - he $6 tan xa khii d khoang each R cho goc 0 A/? - do day khoang each tham nhap ciia xung.
A - Dien tich bg thu.
T(R) - he, so Uuyen quang tir nguon phat din khoang each R va hi do tia vl bg thu.
7 - he so hieu qua ciia he thing quang hgc.
G(R) - he so hinh hgc ciia he thing.
NB - so photon nhieu nIn.
Do sir tuong tac giira anh sang vai cac thanh phin khi quyen dac biet phuc tap cho nen khi trien khai phuang trinh LIDAR tong quat sang dang cu thi cho mgt dii tugng nghien cuu can phai xay dung mo hinh hjong tac va tiln hanh don gian hoa. Khi giai phuong trinh ciing phai sir dung nhimg thira nhan, gia thuyet va boi ly do nay ma nghiem ciia phuang hinh dii vdi cac loai LIDAR khac nhau la rit khac nhau.
Thong thuong khi xay dung phuang trinh LIDAR, nguod ta thuong dua ra gia thuylt la tan xa xay ra dgc lap va la tan xa dan. Tan xa dgc lap xay ra khi cac hat chuyen dgng hon loan va tach biet, do do tong nang lugng tan xa khong phu thuoc vao pha va la tong dai so cua cuong do tan xa ciia timg phan hi. Tan xa don xay ra khi mgt photon bi tan xa chi mgt lan.
t h i ticb tut x t
^ Ihi
diin Lidi bi rr-il ihi
Hinh 2. Din giai phuang trinh LIDAR
5. Vi du xu- ly so lieu
Voi muc dich nghien cim may Ci, phuang trinh LIDAR co thi vilt duoi dang sau:
A^(z) = ^ A ' , , ^ e x p -2Ja(z')^z' (2)
^ L 0
trong do: N{z) - sl photon tan xa ngugc. A- he sl phu thuoc vao hieu qua quang hgc he thing. No- sl photon phat di, j3{z) - he sl tan xa ngugc vacr(z) - he sl suy giam.
He sl tan xa ngugc /3{z) va he sl suy giam CT(Z) trong phuang trinh tren bao gom cac thanh phin ciia may va khong khi nhu sau:
334 Tuyen tap cac c6ng trinh nghiSn ciru V | t ly Dja c4u 2008
/3{z) = /3fz) + j3Xz)
a{z) = cT^{z) + o-Xz)
0)
trong do chir c ky hieu cho may va chir r ky hieu cho khong khi.
Doi voi tan xa Rayleigh thi ty so a,, j f ^ = 8;T / 3 .
Tren hinh 3 la bieu dien tin hieu (so photon) hai kenh bg thu ciia mgt thoi diem trong ngay 02/01/2000 tir he thing lidar (Chung Li, Dai Loan). Co the thiy tin hieu tang nhanh tir mat dat len den do cao khoang 1.5km va gan nhu khong doi cho den do cao 9.5km. Tin hieu lai bat dau tang len va gan nhu giii nguyen gia tri cho den do cao khoang 14km thi tin hieu lai bat dau giam. Sir tang giam do Ion ciia tin hieu chung to su ton tai dam may tang cao vod chan may a khoang 9.5km va dinh may la 14km.
binh phuang tin hi?u ngay 02/01/2000
2b
20-
ra o 3
5-
a-
_J
{
10-' ,o" 10
a,Kenh song song
•a ' 10" 10"
b, Kenh vijong g6c
Hinh 3. Tin hieu hai kenh phan cue song song v^ vuong g6c.
Dam may co do cao trung binh khoang 11.75km. Co thi thiy s\r chenh lech ve dp lan tin hieu giua khu vuc trong may va ngoai may a kenh phan cue vuong goc Ion hem so voi kenh song song. De xac dinh ro hon vl do cao chan may, dinh may va mgt sl dac tinh ciia may thi can phai xet them vl su phan bl ciia ti le tan xa ngugc theo do cao.
Ty le tan xa ngugc dugc tinh theo cong thirc:
(4) trong db: ^{. he so tan xa ngugc ciia khong khi
pc: he so tan xa ngugc ciia may
Gia tri ti le tan xa ngugc cung cho thiy chan may 6 khoang 9.5km va dinh may khoang 14km ciing nhu do cao trung binh ciia may khoang 11.75km (xem hinh 4).
Ngoai ra, tu ty le LIDAR va he so tan xa ngugc ciia may xac dinh duoc he sl hip thy cua may theo cong thirc:
G
^^=J => ^.=A-S.
(5)f^^^'Y^^^LYKHlQUY^N
335
Trong do: Sc: ty le LIDAR,
Pc^ he so tan xa ngugc ciia may, Oc: he so hap thu ciia may.
Qua do xac dinh dugc he s l hip thu ciia may: 0.0286. Do diy quang hoc ciia may dugc xac dinh qua cong thirc:
"'op 'i,>p
r , = \a{z')dz'=^ \ S,{z')jB{z')dz' (6)
trong do: Xc: do day quang hgc ciia may o: he so hap thu tong cong p: he so tan xa ngugc tong cong Sc. ty le LIDAR
Do day quang hgc ciia may bing 0.1090. Ty le phan cue A dugc dinh nghia la ti le ciia tin hieu tro lai theo phuong vuong goc voi tin hieu theo phuong song song va dugc tinh boi cong thirc:
•^'^' , (7) trong do: P||: tin hieu song song va P±: tin hieu vuong goc.
Ty le phan cue co lien quan den cac dang ciia tinh the bang. Voi cac hat hinh cau va khong khi, ti le phan cue co gia tri gan bang 0. Cac mo phong voi bang hinh luc giac cho thiy cac gia tri khac cua ty le phan cue. Theo [13,14], doi voi tinh the bang hinh luc giac mong, day, va khii thi ty le phan cue la tuong img la 0,4; 0,5 va 0,6.
^,-,.:•... ,.:.-r,. . . ng^y 02/01/2000 • • - : •.
0 5 10
ty 1? tin X9 ngugc
0 0.1 0.2 0 3 0 4
ty 1? phan ci;c
Hinh 4. Ty le tan xa ngu'O'c (hinh trai) Vci ti le phan eye (hinh phai).
336 Tuyen tap cac cong trinh nghien cij-u Vat ly Dja clu 2008
6. He thong LIDAR xac dinh ma tran MUELLER
He thong LIDAR noi tren chi ghi co hai kenh va khong thi xac dinh toan bo ma tran tan xa ciia doi tugng nghien cim. Boi ly do nay, chiing toi da nghien cuu va thilt kl he thong LIDAR co kha nang xac dinh dugc ma tran Mueller.
Nhu da biet, quan he giira ma tran Mueller va cac thong so Stoke co dang nhu sau'
[s-hMs].
trong do
(8)
S' =
/ ' c ' \
5 ^, S2
\^:J
M
^^00 ^ 0 1 " ^ 0 2 ^ 0 3 ^
W,o W , , W,2 W,3
^20 ^ 2 1 W 2 2 ^ 2 3
V"^30 /W3, W32 m 33 7
Neu coi dii tugng nghien cuu nhu mgt thanh phin trong he quang hgc voi ma tran tan xa la
[A-
•^u -^01
-^10 -^1
•^02 -^03
20 "^21 '^2'^ ^1^
V-^30 S,,
(9)
SyJ
thi CO the dimg ky thuat anh sang phan cue dk tao he quang hoc do duoc cac thong s6 Stoke. Vod 4 do dac khong phu thuoc co thi xac dinh diy dii cac thong sl Stoke va tir do tinh toan ra ma tran Mueller.
M LICAR SIMUUTIOH 1.0
-'••'S
CHJONG TjiNH M 6 P^]i^^G IIDAJ
TJCINQ TAC y<)l l / i l alCJNG
CANCEL
TIN m|u U N TOUY'SN nOMC M 6 I TXUONG
B 6 hHAN FHAT TIN HJ£U
^m Hilu PHAN XA rxONG I M-Sl T W O N G I
e6 fHAN THU Tlh HlSu I
s o CHAN oilu tmin
fHAN M I M AU Lt iO I
T^»iMG KS Hi T> H? THDMG
Hinh 5. Giao dien chuo-ng trinh mo phong LIDAR
^liliiUy-VAT LY KHl QUY^N 337
De nghien cuu mgt each toan dien va he thing ve LIDAR, chimg toi da buoc diu xay dimg chuang Uinh mo phong (giao dien chuang trinh tren hinh 5).
D6i tugng rno phong bao gIm phin cimg thilt bi va dii tugng nghien cim. Nhung mo phong nay rat quan trgng va cin thilt trong viec dinh huong muc tieu nghien cim, lira chgn cau hinh thiet bj phii hgp va la co so cho cong viec xir ly, minh giai sl lieu thu dugc.
7. Ket luan
1. May Ci co vai tro quan trgng anh huong toi khi hau, thoi tilt bod no bao phii toi 30% dien tich be mat qua dat va hap thu song dai tir mat dat, phan xa song ngan Xix birc xa mat troi.
2. He thong LIDAR rat hieu qua trong nghien cim khi quyen, dugc img dung trong nghien cim may, aerosol, ozone, cac thanh phin khi khac, khi quyin lop bien, chuyin dgng roi, song trgng tmong... Vod viec sir dung he thing LIDAR do phan cue hai kenh,
„ mgt so thong so ciia may Ci dugc xac dinh nhu do cao chan may, dinh may, do day quang hgc, he so tan xa ngugc, he so phan cue. Cac thong so nay gop phan lam ro hon vai tro ciia may Ci trong can can birc xa.
3. Viec sir dung ky thuat anh sang phan cue de xac dinh ma tran Mueller se nang cao chat lugng he thong LIDAR, cu the la c6 the xac dinh cau tnic va huong phan bo cac tinh the bang trong may Ci tot hon khi khong sir dung ky thuat nay.
4. Thiet ke he thong LIDAR la mgt cong viec phirc tap can co hieu biet ve vat ly khi quyen, vat ly laser, thiet bi quang hgc va dien hJ, phan mem. De thuc hien cong viec nay cin sir dimg phuong phap he thong, mo phong theo huong doi tugng. Viec lam nay giup dinh huong r5 muc tieu nghien cim, lam ro cac uu diem va nhugc diem ciia timg ciu true phin cimg, tix do se dua ra giai phap toi uu nhat ve phan cimg cung nhu phan mem.
L&i cdm on: Cdc tdc gid xin chdn thdnh cdm on gido su Jan-Bai Nee vd tiin sy Chih-Wei Chiang da cung cdp sd lieu vd tgo diiu kiin hoc tgp, nghiin ciru tgi Dgi hoc Qudc gig Trung uang Chung Li, Ddi Logn.
8. Tai lieu tham khao
1. Omar, A. H., 2001: Observations by the Lidar in-Space Technology Experiment (LITE) of high-altihide cinrus clouds over the equator in regions exhibiting extremely cold temperatures. J. Geophys. Res., 106 (Dl), 1227-1236.
2. Santacesaria V., A. R. MacKenzie and L. Stefanutti, 2001: A climatological smdy of polar stratospheric clouds (1989-1997) from LIDAR measurements over Dumont d'Urville (Antarctica). Tellus (B), 53 (3), 306-321.
3. Douglass L. R., M. R. Schoeberi, S. R. Kawa and E. V. Browell, 2001: A composite view of ozone evolution in the 1995-1996 northem winter polar vortex developed from airborne lidar and satellite observations. J. Geophys. Res., 106 (D9), 9879-9895.
4. Bamaba F, and G. P. Gobbi, 2001: Lidar estimation of h-opospheric aerosol extinction, surface area and volume: Mantime and desert-dust cases. J. Geophys. Res., 106 (D3), 3005-3018.
338 Tuy4n t i p cac c6ng trinh nghldn ci>u V | t ly Pja cJlu 2008
5. Zuev V. v., V. D. Burlakov VD and A. V. El'nikov, 1998: Ten years (1986-1995) of lidar obsen'ations of temporal and veri;ical structure of stratospheric aerosols over Siberia. J. Aerosol Sci., 29 (10), 1179-1187.
6. Devara, P. C. S., and P. E. Raj 1991: Shidy of ahnospheric aerosols m a terrain-induced nochimal boundary layer usmg bistatic lidar. Atmos. Env., 25A, 655-660.
7. Murayama T, H. Okamoto. N. Kaneyasu, H. Kamataki and K. Miura, 1999: Application of lidar depolarization measurement hi the aUnospheric boundary layer: Effects of dust and sea-salt particles. J. Geophys. Res., 104 (D24), 31781-31792.
8. Newsom, R. K. and R. M. Banta, 2002: Shear-flow instability in the stable nochimal boundary layer as observed by Doppler lidar during CASES-99. Submitted to J. Atmos.
Sci.
9. Tumer, D. D., R. A. Ferrare, L. A.Heihnan Brasseur, W. F. Feltz and T. P. Tooman, 2002: Automated retrievals of water vapor and aerosol profiles from an operational Raman lidar. J. Atmos. Ocean Tech., 19, 37-50.
10. A. Zilberman, E. Golbraikhb, and N. S. Kopeika. Validity of Kohnogorov Turbulence at Higher Elevations. Free-Space Laser Communication and Active Laser Illumination III, SPIE Vol. 5160.
11. Bmce M. Gentry, Huailin Chen, Steven X. Li. Wind measurements with 355-nm molecular Doppler lidar. OPTICS LETTERS / Vol. 25, No. 17 / September 1,2000.
12. D. P. Wylie, W. P. Menzel, H. M. Woolf, and K. L. Strabal, "Four years of global cirrus clouds statistics using HIRS," J. Clim. 7, 315-335 (1994).
13. K. Sassen, "The polarization lidar technique for cloud research: a review and current assessment," Bull. Am. Meteorol. Soc. 72,1848-1866 (1991).
14. K. Sassen and B. Y. Cho, "Subvisual-thin cirms lidar dataset for satellite verification and climatological research," J. Appl. Meteorol. 31, 1275-1285 (1992).
ABSTRACT
In this paper, lidar system, and its applicafion for cirrus cloud study were introduced. It was shown that the information about cirrus clouds such as cloud base and top height, optical depth, backscattering ratio, lidar and the depolarization ratios can be derived using lidar system with two detectors. Some simulations of lidar system were done. Our proposal is to design lidar system using polarization technique. Such system can give information about Mueller matrix and thus giving opportunities to understand more about the shape and orientation of cirrus crystals.
