KET QUA BAN PHAT TRIEN HE THONG LIDAR SlT DUNG NGHIEN ClTU SON KHI TAI VIEN VAT LY -

Hoi nghi Khoa hoc ky niem i5 ndm \ ien Khoa hoc vd Cong nghe Viet Nam - Hd Not 10/2010

PHAT TRIEN HE THONG LIDAR SlT DUNG NGHIEN ClTU SON KHI TAI VIEN VAT LY -

NHLTNG

KET QUA BAN

D A U

Nguyfin Thanh Binh, Dinh Van Trung, Dao duy Thang, Nguyen Dinh Hoang, Phung Viet Tiep, Nguyen Dai Hung

Vien Vdt ly - Vien Khog hgc vd Cdng nghe Viet Norn E-mail; tbngiiyen(^iop. vgst. ge. vn

Tom tat:

LIDAR Id ky thudt do dgc tir xg sir dung birc xg laser cho phep do dgc tinh chdt vdt ly dig khi quyen vdi do phdn gidi khdng thdi gion ego. Tgi Vien Vdt ly chiing ddi dd phdt trien mdt he LIDAR 2 budc sdng phuc vu nghien ciru khi quyen vd son khi He LIDAR bcio gdm ; I- Laser xung Nd-YAG cdng sudt cao phdt d budc sdng

1064nm vd 532nm; 2- He thu bcio gdn kinh thien vdn dudng kinh 20cm, he ddu thu qugng dien PMT, APD, he thdng linh kien quang hoc de lgc nhieu nen, bdn tdch chiim phdn cue cho phep tdch tin hieu LIDAR thdnh hai chum cd phuang phdn cue song song vd vudng gdc vdi birc xg Igser cho phep xdc dinh he sd khu phdn cue eug tin hieu LIDAR tir son khi. Cdc ket qud do dgc bgn ddu cho thdy He

LIDAR cd dd nhgy ego, cho phep do dgc phdn bd vd tinh chdt vdt ly ciig son khi tdi do cao tren 20km.

MO DAU

Lidar (Light Detection And Ranging) la ky thuat do dac sir buc xa laser trong mien budc sdng tir ngoai. kha kien va hdng ngoai gan. Viec sir dung ddng thdi cac ky thuat quang phd va quang bgc cho phep irng dung lidar de do dac cac dac trung vat ly cua khi quyen theo khdng gian va thdi gian vdi do phan giai cao.

LIDAR dugc phat trien tir nhiing nam dau ciia thap ky 70 the ky trudc. LIDAR dugc phat trien ban dau chii yeu phuc vy cho myc dich quan sy d cac nude phat trien nhu My, Nga, Nhat. Phap. Dire, Italy. Tay Ban Nha, Trung qudc, Canada Trong thdi gian gan day LIDAR da dugc dan sy hda de phyc vy cac myc tieu dan sy, LIDAR da trd thanh mdt cdng cy khdng the thieu de nghien cim vat ly va boa hgc eiia khi quyen (den do cao 100 km), cac hien tugng khi quyen nhu sdng trgng luc (gravity -wave), phan bd nhiet do dao tren tang quyen trung (mesosphere), hay quan trac mdi trudng nhu xac dinh mat do cua bui. son khi (aerosol), ozone hay cac loai khi thai ddc hai gay d nhiem nhu thuy ngan, SO2, NO2, benzene, toluene...

Tai cac nude phat trien ngudi ta kinh thanh mang ludi LIDAR qudc gia, khu vuc va qudc te nhu mang LIDDAR chau au(Europe LIDAR network EARLENET), mang LIDAR ciia cac nude thude lien bang Xd Viet (CIS-LiNet - lidar net-work), hay mang LIDAR eiia co quan nghien cim khdng gian My - NASA.

Tai Viet Namky thuat LIDAR de phyc vy nghien cun vat ly khi quyen va nghien cim mdi trudng dac biet quan tam. Nam 2007 Vien KHCN Viet Nam giao cho Vien Vat ly thuc hien de tai Xay dyng va phat trien he LIDAR iing dung cho nghien cim son khi. Hien nay de tai da dugc nghiem thu va danh gia xuk sSc. Day la he LIDARdSu tien dugc phat tri6n tai viet Nam. Nhieu don vi nghien ciin khac ciia Vien Khoa hgc va Cdng nghe Viet Nam nhu Vien

Tieu ban: Cong nghe thong tin - Tir dong hod - Cong nghe Vu tru ISBN: 978-604-913-010-6

Vat ly Dia cSu, Vien Cdng nghe Vii try, Vien Cdng nghe Mdi trudng.... dang thyc sy chd dgi sy phat triln va iimg dyng cdng nghe LIDAR cho cac quan tam cua minh.

NGUYEN TAC HOAT DONG VA CAU TAO CUA HE LIDAR

Nguyen tic boat ddng LIDAR cung tuong ty nhu RADAR nhung thay vi hoat ddng trong viing sdng radio LIDAR boat ddng trong miln budc sdng tir tir ngoai den bdng ngoai gin. Ngudi ta cdn ggi LIDAR la Laser RADAR.

MAY PHAT

t '•

ANG TEN PHAT (gian chum) \ 1

LASER Nd:YA

ANGTEN

MAY THU

1

TrBEng dmng

M A Y D O / P H A N T I C K Q U A N G H O C

1

THU THAP DIJLIEU/

MAY TINH

Hinh I: So dd nguyen ly ciia he LIDAR

LIDAR cd ling dyng rat phong phii, tiiy vao mdi ung dyng cy the ma cau tao cy the ciia mdi he LIDAR khac nhau tuy nhien chung deu dugc xay dyng tren mdt nguyen tac chung gdng 2 phan (hinh 2). Phan phat thdng thudng la mdt laser, tuy vao myc dich sir dyng cdng suat laser nay ed the tir vai chyc tdi vai tram mill Joune/xung. Buc xa laser phat vao mdi truong qua he quang hgc se tuong tac vdi thanh phan khac nhau ciia mdi trudng nhu eae phan tir khi. bui. hat son khi, may, cac thanh phan d nhiem... Mdt phan ciia birc xa laser sau khi tuong tac vdi mdi trudng se quay ve he LIDAR. Phan tich cac tin hieu thu dugc nay se cho phep ta xac dinh dugc cac dac trung cua mdi trudng. Phan thu 2 cua he LLIDAR la bd phan anten quang hgc cd kich thude dii Idn de thu nhan tin hieu tir mdi trudng tir khoan each vai tram met tdi hang tram kild met. Thdng thudng anten thu la mdt kinh thien van (telescope) loai Newton hoac Cassegrain cd kich thude tir 20 centimet den hang tram centimet. Ngoai ra anten quang hgc cdn cd cac phin lgc giao thoa cd bang thdng hep ca 1 nm de loai bd nhilu nen la bite xa d cac budc sdng khac vdi budc sdng eiia tin hieu lidar. Tin hieu lidar sau dd se dugc hdi ty vao cac dau do quang, la phan thir ba cua he lidar, thudng la bd nhan quang dien nhanh ddi vdi cac budc sdng trong miln tir ngoai den vimg kha kien va didt thac lu (avalanche photodiode) ddi vdi cac budc sdng trong mien hdng ngoai. Phan thu tu ciia he lidar la mdt he dien tir phirc tap nham khuech dai tin hieu tir cac dau do quang va thyc hien phep do cac tin hieu nay theo che do tuong ty (do ddng) ddi vdi tin hieu lidar tuong ddi manh tan xa tir viing khi quyen tuong ddi gan hay dem photon ddi vdi tin hieu tan xa d khoang each Idn. Do tre At giira thdi diem phat xung laser vao khi quyen va thdi diem do tin hieu lidar

Hoi nghi Khoa hoc ky niem 35 ndm Viin Khoa hoc vd Cong nghe Viet Nam - Hd Noi 10/2010

phanhdi cho phep ta do dugc khoang each D tdi vi tri gay ra tan xa (nghia la ngudn eiia tin hieu lidar) qua mdi lien he D=c*At/2, vdi c la van tdc anh sang. Ta ed the thay ngay rang vdi ddi hdi nghien cim khi quyIn d cac khoang each Idn (nhieu km) vdi do phan giai khdng gian eao (khoang vai chuc met), he lidar phai sir dyng laser cdng suat Idn phat xung ngan, cd vai nano giay, tuong img vdi do phan giai tdi da khoang vai met, cimg mdt he dien tir nhanh, cd 100-300 MHz, va dii nhay dl do tin hieu lidar. Ngoai ra he lidar edn phai cd do dn dinh eao de cd the lay trung binh tin hieu lidar qua hang tram den hang nghin xung laser nham tang ban nira do nhay eiia phep do.

HE LIDAR PHAT T R I E N TAI VIEN VAT LY

He LIDAR phat trien tai Vien vat ly vdi myc dieh nghien cim mdi trudng khi quyen sir dyng phan phat la Laser Nd-YAG (Quantel - Phap) phat d budc sdng co ban 1064nm vdi cdng suat la 360mJ va 180 mJ tai budc sdng 532nm. Chiim laser dugc dua true tiep vao mdi trucmg khi quyen qua he thdng gdm 2 guong laser Ml va M2 (Hinh 2a). Ban nira sdng (A./2) dat trudc chiim laser 532rmi de dinh hudng hudng phan cyc chiim laser, cho phep do tin hieu LIDAR phan eye tai budc sdng nay. Tin hieu LIDAR tir khi quyen dugc thu bang telescope loai Cassegrain cd dudng kinh 8 inch (Meade LX200 - My), f/D=IO. Tai mat phang tieu ciia telescope dat mdt pinhole de giam thi trudng quan sat tranh nhieu quang hgc. Trong phep do chiing tdi thudng sir dyng thi trudng ciia telescope 2 mrad tuong img vdi kicb tbudc ciia pinhold la 4mm. Tin hieu quang sau khi thu dugc tir telescope dugc cho qua guong ludng chiet nham tach tin hieu d budc sdng 532 nm va I064nm. Mdt tinh the phan cyc tacb thanh phan song song va vudng gdc ciia chiim laser cho phep do tin hieu LIDAR phan cyc . Ngoai ra de tranh nhieu quang hgc gay ra bdi cac budc sdng khac vdi budc sdng laser trudc dau thu chiing tdi dat mdt kinh lgc bang hep. Tin hieu quang sau khi di qua kinh lgc bang hep dugc dua vao eae dau thu quang dien la dng nhan quang dien (Hamamatsu 7400U) ddi vdi budc sdng 532 nm va photodiode thac lii (APD - Hamamatsu S9251) ddi vdi budc sdng tir ngoai 1064 rmi. So dd thiet ke khdi thu dugc the hien trong hinh 2b. tin hieu quang hgc sau khi tdi dau thu dugc xir ly va thu nhan dudi hai che do hoac la tuong ty hoac che do dem photon. 0 che do do tuong ty tin hieu dugc dua vao mdt may dao ddng ky sd compact Picosope 200MHz va chuyen qua may tinh qua giao dien USB. 0 che do tuong ty tin hieu LIDAR dugc thu nhan rat de dang tuy nhien che do do nay nhieu Idn chi thich hgp do vdi tin hieu LIDAR Idn, d khoang each gan (<10km). Ddi vdi tin hieu LIDDAR yeu, d khoang each xa chiing tdi sir dyng ky thuat dem photon. Ky thuat nay ddi hdi xir ly tin hieu sau diu thu (PMT hoac APD) bang ky thuat dien tir nhanh va de cac xung photon. Hien nay nay cac bd dim photon cd the sir dyng dugc cho he LIDAR cd gia thanh rit dit (lO.OOOUSD- 20.000USD/kenh tin hieu). Trong he LIDAR nay chiing tdi sir dyng giao ddng ky dl dim photon tuy nhien xung photon sau dau thu thudng ed do ban rdng rit be (~1.5 ns ddi vdi PMT R7400U) de thu nhan dugc xung nay ddi hdi giao ddng ky cd bang thdng Idn, tdc do liy miu cao tren trong khi dd nhiing giao ddng ky nay cd gia thanh cao khdng kem cac bd dim photon da ndi d tren. De thu nhan dugc cac xung photon bdi nhirng giao ddng ky cd gia thanh thip bang ky thuat dien tir chiing tdi keo gian xung ra 10 lan do rdng xung photon sau diu quang hgc thu liic nay khoang 10-15ns cd the thu nhan de dang bdi dao ddng ky cd tin sd liy miu 1 OOMHz. Xung photon dugc dua vao may tinh, nhan dang va dim nhd ky thuat lap trinh qua ngdn ngir Labview.

Tieu ban: Cong nghe thong lin - Tu dong hod - Cong nghe I Ti tru ISBN: 978-604-913-010-6

Khoi phat

Kich thircrc chum dJGiTim

Khoi phat_

1064 nm f _GiKmg

1064 nm

Khoi phat 632 nm

Kich thipo^

chiim (D6 m m

J^

Photodiode trigger

Photodiode trigger

^ ^ H

Ban ni>a Gvcrng song A/2 532 nm

Khoi thu

f/D=10 20 cm

; Chan chum i Thau kinh

Girorng tach ^ J chum 1064/532 ^ j j ™ ^

Phin Ipc giao thoa 607 nm (Tan xa Raman tren Hj)

Hinh 1. Khdi phdt vd khdi thu ciig he LIDDAR Phdt triin tgi Vien Vdt ly

MOT SO KET QUA BAN D A U TREN HE LIDAR PHAT TRIEN TAI VIEN VAT LY He LIDAR ciia chiing tdi cd the do ddng thdi 2 kenh budc sdng 532nm va 1064 nam.

Hinh 3 la ket qua do tir dam may do cao 3000m. chiing tdi sir dyng phuang phap nghic dao Fernald(1984) va Klett(198I) dl chia he sd tan xa 532 nm va 1064 nm. He sd LIDAR, tiic la ti le he sd dap tat tren be sd tan xa ngugc ciia son khi, gia thilt la 70 tai budc sdng 532 nm va 50 tai budc sdng 1064 nm. Gia thilt ring d khoang each tren 3000m tin hieu LIDDAR hoan toan gay ra bdi tan xa ngugc ciia cac phan tir. He sd tan xa ngugc ciia phan tir cd thi dugc tinh nhd sir dyng md hinh khi quyIn MSIS-E-90 (http://omniweb.gsfc.nasa.gov/vitmo/

msis vitmo.html). De phii hgp vdi phuang phap Femal va Klett, he sd tan xa ngugc cd thi tinh bdi tich phan ngugc.

P{z) = PS^) + PS^) = -

z^/'(z)exp{2j[5,(z')-8;r/3]/?„,(z')t/z'}

zlP{z,)ip{z,) + 2 ]sSz')z"'P{z')cx^{2 I[5,(x)-8;r/3]/?„,(x)Jx}6/z'

Trong dd: - Pa(z) la he sd tan xa ngugc d do cao z.

- Pm(z) he sd tan xa ngugc ciia phan tir.

- P(z) la cudng do tin hieu LIDAR thu dugc tir do eao z.

- Sa(z) la ti sd LIDAR ciia son khi.

Hoi nghi Khoa hoc ky niem 35 ndm I 'ien Khoa hoc vd Cong nghe ('let Nam - Hd Noi 10/2010

Tir do eao ZQ nghich dao ket qua sd lieu trong hinh 3 ta dugc ket qua hinh 4. Tir tich phan he sd tan xa ngugc, chiing ta ed the danh gia thdng sd 5 phy tbudc budc sdng dugc dinh nghia bdi Sasano & Browell (1989):

^=-lnL5,(1064)/^^(532)]/ln(l 064/532)

CD

Ul ^

CD

I O

Csj D

T r-fri 1 r

0 1000 2000 3000

Height (m)

Hinh 4 He sd tdn xg ngirgc. Dudng liin net Id kit qud tinh tit boiwcs sdng 532 nm, dudng rdi net ket qud tinh tu kenh budc sdng 1064 nm, dudng chdm chi thdng sd phu thugc budc sdng S

Distance (km)

C

O o

O S

O cr D

b

CO

o en O

5 10

- 1 r — , 1 i I

15 20 25 30

-20 20 «J 60 80 100 120 140 160 180 200

Time (/i,sec)

Hmh 5. Tin hieu cua son khi do tgi birdc sdng 1064 nm

^ Tir ket qua tren cd thi thiy ring thdng sd phu thude budc sdng nhd han hing sd

khi dieu do cho thay rang tinh chat vix ly cua son khi khdng thay ddi theo do cao. son

Tieu ban: Cong nghe thong lin - Tu dong hod - Cong nghe I 'ii tru ISBN: 978-604-913-010-6

KHA NANG HOAT DONG CUA HE LIDAR

He LIDAR cua chimg tdi cd thi do dugc tin hieu LIDAR Idn (cbl do tuong tu) tin hieu LIDAR rit be (chi do dem photon). Do chinh xac ciia phep do da dugc kiem dinh vdi cac md hinh ly thuylt. Tren hinh 5 la tin hieu LIDAR cua son khi do tai budc sdng 1064 nm.

Tren hinh ve dudng den la so lieu thyc nghiem cd the thay rang tin hieu thuc LIDAR thu dugc (1), trong \-iing dd eao tir 5 tdi 25 km hoan toan phii hgp \'di md hinh khi quyen (2), tin hieu khoang each dudi 5 km ed sy sai khac vi d day cd sy tham gia tan xa cac cac hat cd^^kich thude hem, tren 25 km khdng cdn tdn tai cac son khi. Tuy nhien tin bieu ciia he LIDAR van ed thi thu nhan dugc. Nhu vay do chinh xac phep do la hoan toan cd the chap nhan dugc.

He LIDAR la he md, dugc thilt kl theo dang modun, de dang phat trien them cac kenh mdi. Hien nay chiing tdi da hoan thanh phat trien 2 kenh do tin hieu Raman nitoCNi) d 607nm va raman hoi nude d 660mm dl nghien ciiu tinh chat khi quyen va trong tuong lai hoan toan cd the phat trien them nhieu kenh niia phuc vy cho cac muc dich nghien cuu, iing dung khac nhau.

KET LUAN

Chung tdi da thanh cdng trong viec xay dyng he LIDAR dau tien tai Viet Nam nham muc dich nghien cuu mdi trudng khi quyen dac biet la nghien cuu tinh chat vat Iy son khi.

Cac ket qua ban dau cho thay he LIDAR cd giai do rdng, do nhay va do chinh xac eao. Day la he LIDAR dugc thiet ke dudi dang modun ed the de dang thau ddi mdt each linh ddng va phat trien them nhieu modun mdi phyc vu cho nhieu myc dich nghien cuu, ung dyng khac nhau.

Cdng trinh nay hoan thdnh vdi sir hd trg tdi chinh tir Vien Khoa hgc vd Cdng nghe Viet Nam.

TAI LIEU THAM KHAO

1. Klett J.D. 1981, "Stable analytical inversion solution from processing lidar return".

Applied Optics 20, 211-220.

2. F.G. Femald. 1984, "Analysis of atmospheric lidar observations: some comments".

Applied Optics, vol. 23, page 652-653

3. Wandinger U., 2005, in Lidar - Range resolved optical remote sensing of the atmosphere. Ed. by Claus Weitkamp.

4. Jorg Ackermann, 1998, "The extinction to baekscatter ratio of tropospheric aerosol: a numerical suidy", Joumal of atmospheric and oceanic technology, vol. 15, page 1043-1050 5. M. Sicard. A. Comeron. F. Rocadenbosch, A. Rodriguez, C. Munoz, 2009, "Quasi- anahtical determination of noise induced error limits in lidar retrieval of aerosol baekscatter coefficient by the elastic two-component algorithm", Applied Optics vol

48. page 176-182 ' 6. Y. Sasano. E.V. Browell, 1989, "Light scattering characteristics of various aerosol

types derived from multiple wavelength lidar obser\'ations". Applied Optics \ol 28 1670-1679 • ' 7. C. Weitkamp. 2005. "Lidar: range resolved optical remote sensing of the atmosphere",

Springer series in optical science