Vien_tham_vi_ba

2. Vin thm vi ba Vin thm c th c phn thnh 3 loi theo bc sng

s dng:

Vin thm trong di sng nhnthy v hng ngoi

Ngun nng lng s dng lbc x mt tri

Vin thm hng ngoi nhit Ngun nng lng s dng lbc x nhit do chnh vt thpht ra

Vin thm vi ba Hai loi k thut s dng l chng v b ngCh ng: thu bc x tn xhoc phn x t vt thB ng: bc x do chnh vt thpht ra

2.1. Tng quan v vin thm vi bac trng ca vin thm vi ba:

Ph vng vi ba bao gm di bc sng t khong 1cm ti

1m, ln hn bc sng vng nh sng nhn thy v hng

ngoi.

Bc x vi ba c th xuyn qua vng my ph, sng m,

khi bi ch tr khi ma qu to. Trong khi cc bc

sng ln hn th b nh hng bi tn x kh quyn.

c im ny cho php pht hin c nng lng in t

mi iu kin thi tit v mi trng.

Vic thu thp d liu c th thc hin bt k lc no.

2.1. Tng quan v vin thm vi baVin thm vi ba th ng: tng t nh khi nin

vin thm nhit.

Mi vt th u pht nng lng vi ba mt mc no ,

thng l rt nh.

Cc b cm bin vi ba pht hin nng lng vi ba mt cch t

nhin trong trng quan st ca n. Nng lng ny lin quan

n c tnh nhit v m ca vt th hoc b mt .

Cc b cm bin vi ba th ng chnh l thit b o v tuyn

(radiometer) hoc b qut (scanner). Thit b ny hot ng

tng t cc h thng vin thm khc nhng cn c thm mt

ng-ten pht hin v ghi li nng lng in t.

2.1. Tng quan v vin thm vi ba Ngun pht nng lng vi ba cho vin thm vi ba th ng

c th l:

Nng lng t kh quyn

Nng lng phn x t mt b mt

Nng lng pht x t mt b mt

Nng lng pht x t mt b mt khc

Bi v bc sng vi ba ln, nng lng thng yu so vi

cc bc sng quang. Do vy cn trng quan st rng

thu thp nng lng, dn n phn gii khng gian

ca cc b cm bin th ng thng thp.

2.1. Tng quan v vin thm vi ba ng dng ca vin thm vi ba th ng bao gm kh

tng hc (meteorology), thy hc (hydrology) v hi

dng hc (oceanography).

V d:

Trong kh tng hc, ty vo bc sng, vi ba th ng

c s dng o cc thnh phn kh quyn, xc nh

nc v -zn c trong kh quyn.

Trong thy hc, vi ba th ng o m ca t.

ng dng trong hi dng hc bao gm lp bn

bng, gi b mt, pht hin nhim (vt du loang)

2.1. Tng quan v vin thm vi baVin thm vi ba ch ng:

Cc sensor ch ng c ngun bc x in t ca

ring n chiu ri vo mc tiu.

Hai loi sensor ch ng:

Sensor nh (imaging): RADAR

(RAdio Detection And Ranging),

Sensor phi nh (non-imaging):

o cao (altimeter), radar o

tn x (scatterometer).

2.1. Tng quan v vin thm vi ba Sensor nh (imaging): pht tn hiu v tuyn v

pha mc tiu v pht hin phn tn hiu tn x tr li.

mnh yu ca phn tn hiu tn x tr li ny

c o c phn bit cc mc tiu khc nhau, o

thi gian tn hiu truyn i v phn x tr li xc

nh khong cch ti mc tiu.

2.1. Tng quan v vin thm vi ba Sensor phi nh (non-imaging): o cc thng s

theo 1 chiu tuyn tnh ( cao), tri vi sensor nh

biu din theo 2 chiu.

V d:

Radar o cao: truyn cc xung ngn v o thi gian tr round-trip xc nh khong cch gia sensor v mc tiu. Radar o cao thng hng theo nadir thng xung mt t o cao hoc gc ngng.

Radar o tn x (scatterometer): nh lng chnh xc nng lng tn x tr li d on tnh cht ca b mt (g gh hay phng).

2.1. Tng quan v vin thm vi ba RADAR = h thng thit o

khong cch. RADAR bao gm: my pht,

my thu, ng-ten, v mt h thng in t x l v ghi li s liu.

My pht pht lin tip dy xung vi ba (A) tp trung trong bp sng ca ng-ten (B).

ng-ten thu phn phn x (tn x tr li) t cc vt th trong phm vi qut ca bp sng (C).

o thi gian tr gia truyn xung i v nhn tn hiu phn x cho php xc nh khong cch gia radar v mc tiu.

Radar gn trn my bay v chuyn ng, qu trnh ghi li v x l tn hiu phn x to nn nh 2 chiu ca b mt

2.1. Tng quan v vin thm vi ba Ph ca vng vi ba:

rng hn nhiu so vi vng nh sng nhn thy v hng ngoi.

Mt s di bc sng c k hiu bng cc ch ci t Th chin II v vn c s dng ti ngy nay.

2.1. Tng quan v vin thm vi ba Cc bng Ka, K v Ku: bc sng ngn, c s dng

trn cc h thng radar airborne u tin, nay khng cn s dng na.

Bng X: c s dng nhiu trn cc h thng airborne qun s (do thm, lp bn mt t).

Bng C: c s dng trn cc h thng airborne cho nghin cu v c cc h thng spaceborne.

Bng S: s dng trn v tinh Russian ALMAZ. Bng L: s dng trn v tinh SEASAT (M), JERS-1

(Nht), v airborne ca NASA. Bng P: radar bc songs di nht, s dng trn

airborne nghin cu ca NASA.

2.1. Tng quan v vin thm vi ba RADAR hot ng

cc bng khc nhau cho nh khc nhau.

iu ny c ngha l vt th tng tc khc nhau vi nng lng radar ty thuc vo bc sng.

Bng C

Bng L

2.1. Tng quan v vin thm vi ba

RADAR c thit k truyn bc x in t theo phn cc ngang H (horizontally) hay phn cc ng V (vertically).

ng-ten c th nhn tn hiu phn x phn cc ng hay ngang, hay c radar c th nhn c hai. Vy c th c 4 t hp cc phn cc truyn v nhn: HH, VV, HV, VH.

Trong vin thm, s phn cc (polarization) ca bc x in t cng rt quan trng. Phn cc ng hay ngang lin quan n hng ca in trng.

2.1. Tng quan v vin thm vi ba Cng nh thay i bc sng,

ty vo phn cc khi truyn v nhn, bc x tng tc v tn x khc nhau vi b mt.

Hnh pha trn bn tri l hnh tng hp cc kiu phn cc, mi kiu phn cc biu din bng mt mu c bn (red, green v blue).

Kt lun: vi nh radar thu thp c, nu tng hp phn cc v bc sng khc nhau th thu c thng tin khc nhau, b sung nhau v b mt ca mc tiu.

2.2. Hnh hc quan stHnh hc quan st: A: hng bay B: nadir C: Vt chiu ri D: B rng di (across-track

dimension) E: azimuth (along-track

dimension)

Hnh hc quan st side-looking l kiu tiu biu trong cc h thng radar nh (airborne hay spaceborne)

2.2. Hnh hc quan st

A: near range B: far range

2.2. Hnh hc quan st

A: gc ti B: gc nhn C: khong cch ng xin

(slant range distance) D: khong cch mt t

(ground range distance)

2.2. Hnh hc quan st

phn di khng gian L hm ca mt s tnh

cht c trng ca bc x vi ba v tc ng hnh hc.

V d: Khi s dng RAR (Real

Aperture Radar), tng xung n l c truyn i v tn hiu phn x c thu to nh.

2.2. Hnh hc quan st Nh vy, phn gii ph thuc

rng hiu dng ca xung dc theo ng xin v rng bp sng theo hng azimuth.

phn gii ngang tuyn (across-track) ph thuc v rng xung P.

Hai mc tiu s c phn bit nu chng cch nhau cch nhau hn mt na rng xung theo hng b rng di.

phn gii ng xin l hng s, nhng khi c chiu ln mt t, phn gii mt t li ph thuc gc ti. Trong trng hp ny, range cng tng th phn gii mt t cng gim.

2.2. Hnh hc quan st phn gii dc

tuyn (along-track) c xc nh bi rng bp sng bc x vi ba v khong cch ng xin.

rng bp sng (A) chnh l n v o rng ca hnh mu chiu ri (illumination pattern). Khong cch chiu ri cng xa sensor th phn gii dc tuyn cng tng.

Nh minh ha trn hnh, mc tiu 1 v 2 c th c phn bit trong khi mc tiu 3 v 4 cch xa hn nn khng th phn bit c.

2.2. Hnh hc quan st rng bp sng t

l nghch vi di/kch thc ng-ten v cng lin quan n gc m (aperture).

ng-ten cng di th to ra bp sng cng hp v phn gii s tt hn.

C th t c phn gii tt hn nu thu hp rng xung.

phn gii dc tuyn s tt hn nu tng kch thc ng-ten. Tuy nhin kch thc ng-ten b gii hn (1-2m vi ng-ten airborne, 10-15m cho ng-ten trn v tinh)

2.2. Hnh hc quan st Tng phn gii

azimuth: s dng SAR (Synthetic Aperture Radar) v ng dng k thut thu v x l tn hiu c bit.

Mc tiu A i vo bp sng ca radar, tn hiu phn x sau mi xung pht i c ghi li. My bay tip tc di chuyn, cc tn hiu phn x c ghi li trong sut khong thi gian mc tiu nm trong bp sng. Thi im muc tiu ri khi bp sng radar xc nh di ca ng-ten m phng/tng hp.

Phn ln airborne v spaceborne radar l SAR

2.3. Mo dng nh radar Vi mi h thng vin thm, hnh

hc quan st ca radar tt yu dn n mo dng hnh hc trn nh vin thm thu c. Tuy nhin, s khc bit th hin r vi radar nh v radar ch o khong cch.

Mo t l ng xin theo range (slant-range) xy ra vi radar thin v o khong cch ng xin hn l o khong cch b ngang thc trn mt t. Nh vy, t l nh thay i theo range t gn ti xa.

V d: Mc tiu A1 v B1 cng kch thc trn mt t nhng khc nhau trn ng xin range (A2 v B2).Nh vy mc tiu range gn b nn so vi mc tiu range xa.

2.3. Mo dng nh radar

2.3. Mo dng nh radar Hiu ng foreshortening: xy

ra khi bp sng radar chiu ti vt th cao, c mt nghing v pha radar, bp sng chm ti chn trc khi chm nh.

V d: on nghing AB b nn li v

c th hin sai lch bng on AB.

Hiu ng foreshortening cc i xy ra khi mt nghing hng trc din radar (on CD), lc ny di hiu dng ca CD bng 0.

2.3. Mo dng nh radar nh radar ca mt vng i

ni dc vi hiu ng foreshortening.

Vng nh sng mu l ni c hiu ng foreshortening.

2.3. Mo dng nh radar Hiu ng che ph (layover):

xy ra khi bp sng radar chiu ti vt th cao, bp sng chm ti nh (B) trc khi chm chn (A). Nh vy, phn nh s gn hn v pha radar so vi phn chn v che ph phn chn.

Trn nh radar, hiu ng layover trng rt ging vi foreshortening.

Hiu ng layover thng xy ra vi gc ti nh, pha range gn ca vt chiu ri, xy ra khi to nh vng i ni dc.

2.3. Mo dng nh radar nh radar ca mt vng i

ni dc vi hiu ng che ph (layover).

2.3. Mo dng nh radar C hiu ng

foreshortening v layover u dn n bng radar (shadow).

Bng radar xy ra khi bp sng radar khng th chiu ri phn mt t v pha range xa do b che khut bi vt th ng chn.

2.3. Mo dng nh radar Trn nh radar, vng b

bng radar l vng ti mu.

2.3. Tng tc mc tiu v hnh nh

Trn nh radar, mc sng ph thuc phn nng lng phn x tr li t b mt mc tiu.

Cng ca nng lng phn x tr li ph thuc vo tng tc ca nng lng radar vi b mt.

Nng lng phn x c th c coi l hm ca mt s bin v tham s. Cc tham s bao gm:

c tnh ca h thng radar: tn s, phn cc, hnh hc quan st,

c tnh ca b mt: loi ph mt t, a th, a hnh


Cc c tnh ni chung c quan h tng h v khng th tch ring xc nh tc ng ca tng tham s ln hnh nh ca nh radar.

Thay i mt vi tham s c th nh hng ti p ng ca cc tham s khc, v cng nh hng ti cng phn x.

Tuy nhin c th nhm cc tham s ny thnh 3 loi theo s tng tc nng lng radar vi mc tiu:

g gh ca b mt, Quan h gia hng quan st ca radar v dng

hnh hc ca b mt, m v c tnh in ca mc tiu.


g gh ca b mt: quyt nh tng tc ca nng lng vi b mt hoc mc tiu, l yu t chnh to nn cc tng mu trn nh radar.

g gh ca b mt lin quan n s bin thin cao trn mt so vi mt phng, v c o bng thang centimetres (cm).

B mt l g gh hay phng vi radar ph thuc vo bc sng v gc ti.


B mt c coi l phng nu bin thin ca cao nh hn nhiu so vi bc sng.

Khi bin thin ca cao t n di bc sng th b mt c coi l g gh.

Nh vy, hnh nh b mt s l g gh hn nu bc sng ngn, phng hn nu bc sng di hn.

Kt hp vi bc sng, gc ti cng ng vai tr quan trng khi kho st g gh ca b mt.

Vi b mt v bc sng xc nh, b mt s trng bng phng hn vi gc ti tng.


(A) b mt phng phn x nh gng, tng ng vi vng ti hn trn nh.

(B) b mt g gh gy tn x nng lng u theo cc hng, tng ng vi cc tng mu sng.

Cng pha xa ca vt chiu ri (range tng) th nng lng quay tr li sensor cng gim v tng mu trn nh tr nn ti hn.

2.3. Tng tc mc tiu v hnh nhKhi nim gc ti cc b Gc ti v gc quan st l cc

yu t lin quan n hnh hc quan st c nh hng ti tn hiu tn x tr li radar.

Tnh cht hnh hc ca b mt cng c nh hng ti tng tc nng lng radar vi mc tiu v hnh nh ca mc tiu trn nh radar.

Gc ti cc b (A) l gc gia bp sng n v ng trc giao vi ng dc ti im ti (ng dc cc b).

Gc quan st (B) vn khng thay i.

2.3. Tng tc mc tiu v hnh nh Hnh hc quan st v tnh cht

hnh hc ca b mt l yu t quan trng quyt nh tng tc nng lng radar vi mc tiu v tng ng vi sng trn nh radar.

Mi s thay i ca hnh hc quan st s lm ni bt v lm r thm cc c im v a hnh v che ph theo cc cch khc nhau.

V d nh, s thay i ca hnh hc quan st dn n thay i mc ca cc hiu ng foreshortening, layover hay shadow ty vo dc ca b mt, hng v hnh dng

2.3. Tng tc mc tiu v hnh nh Hng quan st (look direction)

ca radar biu din hng ca bp sng radar so vi thnh phn tuyn tnh ca b mt.

Hng quan st c vai tr quan trng i vi hnh nh ca mc tiu trn nh radar, c bit l i vi b mt phng nh cnh ng hay cc dy ni.

V d: (A) hng quan st gn nh vung gc vi b mt, phn ln nng lng ti phn x tr li sensor v thu c hnh nh vi tng mu sng. (B) hng quan st cng nghing so vi b mt, nng lng phn x s yu v hnh nh thu c c tng mu ti.

2.3. Tng tc mc tiu v hnh nh Phn x gc (corner reflection):

xy ra khi gc hng trc din vpha radar.

Nh vy phn ln nng lngtruyn i s phn x tr lisensor.

Phn x gc vi gc phn x phctp thng xy ra mi trng th (ta nh, ph x, cu,) hay cc vch t nhin,

Ni chung, phn x gc lm chohnh nh rt sng trn nh radar.

2.3. Tng tc mc tiu v hnh nh m tc ng ti c tnh in ca vt th. S thay i ca c tnh in c nh hng ti s hp th,

truyn v phn x nng lng in t. Do vy, m nhiu hay t tc ng n vic nng lng

phn x th no t mc tiu v hnh nh xut hin trn nh. Ni chung, phn x tng (nh sng hn) nu m tng. V d: cc mt t hay t trng rau khi t s sng hn khi

kh. Khi mc tiu m hay t, tn x lp trn cng l ch yu

v s cho thy g gh ca b mt. Nu mc tiu kh ro, nng lng radar c th xuyn xung

b mt pha di, cc b mt c th l khng lin tc (tncy rng vi l v cnh) hay ng nht (t, ct hay bng)

Vi mi b mt, bc sng ln th c kh nng xuyn tt hncc bc sng nh.


Tn x khi (volume scattering): Nng lng radar xuyn qua

tng cao nht ca b mt th tnx khi c th xy ra.

Nng lng radar tn x trongmt khi c nhiu mt bao vphn x khc nhau bn trongkhi.

Tn x khi c th lm tng hay gim sng trn nh ph thucvo nhiu hay t nng lng tnx ra ngoi khi v tr li radar.

2.4. Cc c tnh ca nh radarNhiu ht (mui tiu): Tt c cc nh radar u xut

hin nhiu ht mc khcnhau do cc nhiu ngu nhin tcc tn x tr li tc ng lntng cell nh.

Nhiu ht lm gim cht lngnh v lm cho vic gii onnh tr nn kh khn.

Hai cch gim nhiu ht: X l a quan st (multi-look) Lc khng gian (spatial filtering)

2.4. Cc c tnh ca nh radarMulti-look processing: Lin quan ti vic chia bp sng

thnh cc bp ph hp hn. Mi bp ph nhn mt cch

c lp vo i tng. Mi ci nhn nh vy hng ti

mt i tng ht. Cng v ly trung bnh chng vi

nhau th c nh u ra vinhiu ht c gim bt.

Multi-look c thc hin trongqu trnh thu thp d liu.

2.4. Cc c tnh ca nh radarLc khng gian (spatial filtering) Thc hin trn nh u ra trong

mi trng x l nh s (dngmy tnh).

Dch chuyn ca s nh c 3x3 hoc 5x5 qua tng pixel v pdng tnh ton xc nh gitr pixel (trung bnh) nm trongca s .

Thay gi tr ca pixel gia bnggi tr mi.

Tnh ton gi tr trung bnh caca s quanh mi pixel.

2.4. Cc c tnh ca nh radarMo dng xin (slant-range distortion) Hnh nh pha range gn b nn so vi pha range xa. Trong khi , vi hu ht cc ng dng ta u mong

mun nh radar th hin ng kch thc tht. Cn phi chuyn i nh slant-range thnh nh ground-

range th hin ng a hnh v vng ph.

2.4. Cc c tnh ca nh radarAntenna pattern ng-ten radar thng truyn nhiu cng sut hn ti

khu vc gia vt chiu ri dn n cng phn x gia s mnh hn so vi 2 bn ra ca vt chiu ri.

Cn p dng hiu chnh antenna pattern c nhradar ng nht dc theo vt chiu ri.

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Vien_tham_vi_ba