nonlinear range cell migration (rcm) compensation method for spaceborneairborne forward-looking...
TRANSCRIPT
1
Nonlinear Range Cell Migration (RCM)
Compensation Method for Spaceborne/Airborne
Forward-Looking Bistatic SAR
Zhe Liu , Jianyu Yang, Xiaoling Zhang
School of Electronic Engineering, University of Electronic Science and
Technology of China, Chengdu, 611731, China
Presentation by Zhe Liu
2
Outline
Introduction to the SA-FBSAR and its nonlinear RMC
Nonlinear RCM compensation method
Simulation results
Conclusions and further work
3
Introduction-What is SA-FBSAR
Spaceborne/Airborne Forward-
Looking Bistatic SAR (SA-FBSAR)
Platforms: Transmitter and receiver of
SA-FBSAR are low earth orbit (LEO)
satellite and aircraft, respectively.
Working Modes: Transmitter antenna
works in side-looking or squint-looking
mode; receiver antenna in forward-
looking mode.
Target imaging scene: Target scene is
along the receiver’s forward-looking
direction
transmitter
receiver
Imaging scene
4
Introduction-Emergence of SA-FBSAR
Monostatic
SAR
Bistatic/
Multistatic
SAR(B/M SAR)
Spaceborne
B/M SAR
Airborne
B/M SAR
S-A B/M
SAR
Commu.
satellite Broadcast
satellite Radar
satellite
• Diversity of target information
• High immunity to attacks
• Low cost
• Wide coverage, high SNR
• Platform flexibility
• Power saving
• wide band
• repeated observation
SA-BSAR
with radar
satellite
SA-FBSAR
• attractive potential for
aircraft landing and
navigation
5
Introduction-Emergence of SA-FBSAR
In Nov. 2009, FGAN (German Aerospace Center) launched
the first experiment to test the feasibility of SA-FBSAR.
Fig.1 Imaging result of the first SA-FBSAR feasibility experiment in 2009
6
Introduction-Challenges of SA-FBSAR imaging
· Dramatic geometric difference Satellite height:500-
800km
Aircraft height:1 - 5km
· Essential velocity difference Satellite velocity:7.4 -
7.6km/s
Aircraft velocity:100m/s
· Different working mode
Satellite : side-looking
Aircraft : forward-looking
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Introduction-Challenges of SA-FBSAR imaging
· Dramatic geometric difference
· Essential velocity difference
· Different working mode
Range cell migration
(RCM) features are :
Vary with the target’s
range and azimuth
location
exhibits significant
nonlinearity with target’s
range location
Severe distortion and nonlinear
misregistration will occur, if such
RCM is not properly compensated
8
Introduction-effect of nonlinear RCM on imaging results
Fig2. Imaging result of point targets
(a) original point scatterers (b) without RCM compensation
9
x
y
(a) original area target (b) Without RCMC
Introduction-effect of nonlinear RCM on imaging results
Fig3. Imaging result of area targets
10
Introduction-Our work
Purpose: find a nonlinear two-dimensional RCM
compensation method for SA-FBSAR in frequency
domain
Main idea:
1. Set up SA-FBSAR response spectrum model
2. Deduce nonlinear RCM analytic formula
3. Propose SA-FBSAR nonlinear RCM compensation
method
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Nonlinear RCM Compensation for SA-FBSAR
-system geometric model
Fig.4 SA-FBSAR system geometry
P
0 0Pr
0A
A
0Pz
S
Pv
Sv0Sx
x
y
z
Imaging scene
S
P0 0Sr
xr
Sv T
0Pr
x
0Sr
0 0
, : denote transmitter and receiver platforms, respectively
: reference point scatterer located at 0, ,0
: non-reference point scatterer located at , ,0
, : velocity of platforms
, : range and
S P
S P
A y
A x y
v v
r T 0
0 0 0 0 0
0 0
0 0 0 0 0
0 0
azimuth time distance of A from
, : closest range from platforms to
, : closest range from platforms to
, : azimuth time when is closest to platforms
, : azimuth t
S P
S P
S P
S P
A
r r A
r r A
t t A
t t ime when is closest to platforms
, : the depression angles of platforms' antennaS P
A
12
22
0 0 0
2 2
00 0 0 0 0 0
2. Receiver closest range :
Due to its , targets along range direction are
. Sinc
sin
forward-looking
e sin
mode symmet
, we have . So t
rically
situated 2 he varsinS
P
P
P S
P P P S
r
r
r
r
r
r r r r
0
iance
of receiver's closest range on is . not linear but quadricPr r
2 2
0 0 0
2 2
S 0 0
1. Transmitter closeset range:
Transmitter operates in , and it is asymmetrical with
targets along range direction, the condito
ctg
side-looking mode
ctn holds.
the
gξ 2
vari n
a
S S S
S
r r r r
r r r r
0 0 0
ce of the is about proportional
with target'
transmi
s range
tter's closest a
position, i.e.
pproach linearly
.S Sr r r
.
Origin of nonlinear RCM
0The , which is directly affected by ,
is also .
-variance of the range history in SA-FBSAR
nonlinearly variant with range location
Pr r
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Nonlinear RCM Compensation for SA-FBSAR
-system signal spectrum model
' 2
''
The SA-FBSAR system response after range compression is
, ; ,, exp exp (1), ; ,
2 , ; ,
where is range freqency, is Doppler frequency,
is the range of the
d
d d
d
d
f f r TH f f j drdTj f f r T
f f r T
f f
R t
0
2
' ''
2
0 0
0 022
2 0
SA-FBSAR system about scatterer
2π , , ; ,
, ; , , , ; ,
, ; ,
b
b b
d d t t
d t t d t t
d S
b d S
dS
S
A
f ft R t f t f f r T t
c
t tf f r T f f r T
t t
f r rt f f r T t T
f f fv
c v
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Nonlinear RCM Compensation for SA-FBSAR
- nonlinear RCM analytic formula
After multiplying with conjugate of reference scatterer's spectrum, we get :
;, exp 2 (2)
;
where
RD d AD
d
AD d RD d
RD
ff r TH f f j drdT
Tf f r
2 2
1 2 1 2
0
1 1 22 2
22 2
0 0 0 00 0 0 00
2 2 3 2
0
; , ; (3)
1, , ,
2 sin
11, 1,
2 sin
d RD d RD d RD d RD d RD d
S
RD d RD d RD d
S S Pf d
P S PP P S
RD d AD AD
PZS Pf d PZ S
S
f r f r f r f r f r f r
f v Ff f f
vc F c r f
a t t va v r rff
c rc r f r v
fF v
c
2 22
2 2 0 0
0 0 0 0 0 0
22 2
0 0 0 0 0 0
, ,
,
d d S
Pf d P P S P
S S
PZ P P S P S P
f f rr f r v t t
v v F
r r v t t a v v
15
Nonlinear RCM Compensation for SA-FBSAR
- nonlinear RCM analytical formula
2 2
In (2) (3), due to the forward-looking mode, the coefficients of
range-dependent terms and are significant
comparing with the linear terms. For example, in the SA-FBSAR sy
quad
stem of sim
r
u
ic RD RD
lation system
when 300 , the ratio between the quadric term and linear term is almost 0.1.
SA-FBSAR, RCM not only depends on target's range location (RD-RCM)
and azimuth location (AD-RCM); but also va
r m
ries with the range location nonlinearly.
The nonlinearity in RD-RCM is not just slight deviation from the linear part as the
monostatic spaceborne side-looking SAR; it exhibits evident nonlinear deviation in RCM trajectory.
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Nonlinear RCM Compensation for SA-FBSAR
- nonlinear RCM compensation method
Fig.5 flow chart of nonlinear RCM compensation method for SA-FBSAR
'
RD
RA
AD
T r
0;RA RD d fdf r
'
0
;RD d
RD fd
d
f r
f
,
* *, ;0,0dH f f H f
exp ADj t f
ADa
imaging result
AD-RCMC
RD-RCMC
signal data from SA-FBSAR
1
dfSCFT
, tFT FT
interpo-lation
1
dfFT
1,t fFT FT
12
2
RD d
RD d AD RA
a f r
a f r T r
2exp d RA
RA RA
j f T r
j r T r
modified two-step RCMC method
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Simulation - Parameters
Parameters Transmitter Receiver
Height (km) 514 3
velocity (m/s) 7600 100
azimuth beam width(degree) 0.33 2.9
maximum steering angle(degree) 0.75 15
depression angle (degree) 37 68
beam velocity(m/s) 2100 700
integration duration (s) 0.43
pulse width (μs) 2
central frequency of transmitting
signal (GHz)
9.65
bandwidth of transmitting signal
(MHz)
60
pulse repetition frequency(Hz) 2500
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Simulation - Point scatterers
(a) original point scatterers (b) without RCM compensation
(d) with the proposed method (c) with RCMC Method in Ref[1]
Ref[1]: X.Qiu, D. Hu and C. Ding, IEEE Geosci. Remote Sens. Lett., 4, 735-739, 2008.
Fig.6 Imaging results of 15 point scatters
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Simulation - area target
x
y
Fig. 7 Imaging results of area target
(a) original area target (b) Without RCMC (c) With the proposed RCM
compensation
21
16
.41
6.4
16
.4
16
.81
6.8
16
.8
17
.21
7.2
17
.2
17
.61
7.6
17
.6
18
18
18
18
.41
8.4
18
.4
18
.81
8.8
18
.8
19
.21
9.2
19
.2
19
.61
9.6
19
.6
20
20
20
20
.42
0.4
20
.4
20
.82
0.8
20
.8
21
.22
1.2
21
.2
21
.62
1.6
21
.6
22
22
22
x /m
y/m
-500 -400 -300 -200 -100 0 100 200 300 400 500-100
-50
0
50
100
Fig.8 two-dimensional resolution performance
x/m
y/m
Ai=16.20m2
A=16.34m2
500
100
r
a
x/m
y/m
Ai=18.72m2
A=19.55m2
0
0
r
a
(a) Contour of ideal resolution cell’s area (unit: m2)
(b) target located at (500,100)
(c) target located at (0,0)
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Simulation
From the above simulation results, we could find that:
Uncompensated RCM could deteriorate imaging result severely, cause
nonlinear distortion
RCM compensation method designed for other FBSAR system could not
compensate the nonlinear RCM, thus could not be applied to SA-FBSAR.
The proposed RCM compensation method could effectively compensate the
nonlinear RCM in SA-FBSAR, and all targets are arranged in their originally
correct positions.
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Conclusions & Further work
RCM in SA-FBSAR not only depends on the target’s
two-dimensional space location, but also varies with its
range location nonlinearly. If not properly corrected, RCM
would cause nonlinear distortion in the image and greatly
degrade the imaging quality.
We propose a two-dimensional nonlinear RCMC method
for SA-FBSAR. The validity of the proposed method is
verified.
Further improvement on resolution performance is under
research