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Transcript of 1 Interferometric Synthetic-Aperture Radar (InSAR) and Applications Chris Allen ([email protected])...
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Interferometric Synthetic-Aperture Radar (InSAR) and Applications
Chris Allen ([email protected])
Course website URL www.cresis.ku.edu/~callen/826/EECS826.htm
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OutlineSyllabus
Instructor information, course description, prerequisites
Textbook, reference books, grading, course outline
Preliminary schedule
Introductions
What to expect
First assignment
Radar fundamentalsActive RF/microwave remote sensing
Electromagnetic issues
Antennas
Resolution (spatial, range)
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SyllabusProf. Chris Allen
Ph.D. in Electrical Engineering from KU 1984
10 years industry experience
Sandia National Labs, Albuquerque, NM
AlliedSignal, Kansas City Plant, Kansas City, MO
Phone: 785-864-3017
Email: [email protected]
Office: 321 Nichols Hall
Office hours: Tuesdays and Thursdays2:00 to 2:30 p.m. and 3:45 to 4:30 p.m.
Course descriptionDescription and analysis of processing data from synthetic-aperture radars and interferometric synthetic-aperture radars. Topics covered include SAR basics and signal properties, range and azimuth compression, signal processing algorithms, interferometry and coregistration.
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SyllabusPrerequisites
Introductory course on radar systems (e.g., EECS 725)
Introductory course on radar signal processing (e.g., EECS 744)
TextbookProcessing of SAR Databy A. HeinSpringer, 2004, ISBN 3540050434
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SyllabusReference books
Synthetic Aperture Radar Processingby G. Franschetti and R. LanariCRC Press, 1999, ISBN 0849378990
Digital Processing of Synthetic Aperture Radar Databy I. Cumming and F. WongArtech House, 2005, ISBN 1580530583
Spotlight-Mode Synthetic Aperture RadarC. Jakowatz, et al,Springer, 1996, ISBN 0792396774
Synthetic Aperture Radar: Systems and Signal ProcessingJ. Curlander and R. McDonoughWiley, 1991, ISBN 047185770X
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Grades and course policiesThe following factors will be used to arrive at the final course grade:
Homework, quizzes, and class participation 40 %Research project 20 %
Final exam 40 %
Grades will be assigned to the following scale:A 90 - 100 %B 80 - 89 %C 70 - 79 %D 60 - 69 %F < 60 %
These are guaranteed maximum scales and may be revised downward at the instructor's discretion.
Read the policies regarding homework, exams, ethics, and plagiarism.
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Preliminary scheduleCourse Outline (subject to change)
SAR system overview and signal properties 1 weeks(data recording, nonideal motion, layover and shadowing, moving targets)
SAR radar range equation and associated geometries 2 weeks(side-looking, squint, and spotlight modes)
SAR signal processing 3 weeks(range and azimuth compression, range migration, autofocus)
SAR signal processing algorithms 2 weeks(range-Doppler, scaling, omega-k)
Interferometry 6 weeks(registration, decorrelation, phase unwrapping, implementation, terrain mapping, surface velocity mapping, change detection, single-pass vs. multi-pass)
Class Meeting ScheduleJanuary: 15, 20, 22, 27, 29February: 3, 5, (10th to 12th NSF Site Visit), 17, 19, 24, 26March: 3, 5, 10, 12, (17th to 19th Spring Break), 24, 26, 31April: 2, 7, 9, 14, 16, 21, 23, 28, 30 May: 5, 7
Final exam scheduled for Friday, May 15, 1:30 to 4:00 PM
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Introductions
Name
Major
Specialty
What you hope to get from of this experience(Not asking what grade you are aiming for )
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What to expectCourse is being webcast, therefore …
Most presentation material will be in PowerPoint format Presentations will be recorded and archived (for duration of semester)
Student interaction is encouragedStudents must activate microphone before speaking
Please disable microphone when finished
Homework assignments will be posted on websiteElectronic homework submission logistics to be worked out
We may have guest lecturers later in the semester
To break the monotony, we’ll try to take a couple of 2-minute breaks during each session (roughly every 15 to 20 min)
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InSAR
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Your first assignmentSend me an email (from the account you check most often)
Subject line: Your name – EECS 826
Tell me a little about yourself
Attach your ARTS form (or equivalent)
ARTS: Academic Requirements Tracking System
Its basically an unofficial academic record
I use this to get a sense of what academic experiences you’ve had
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SAR image of Los Angeles area
SEASAT Synthetic Aperture Radarf: 1.3 GHz PTX: 1 kWant: 10.8 x 2.2 m B: 19 MHzx = y = 25 m pol: HHorbit: 795 km DR: 110 Mb/s
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SEASAT suffered a massive electrical short in one of the slip ring assemblies used to connect the rotating solar arrays to the power subsystem.
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SAR image of Gibraltar
ERS-1 Synthetic Aperture Radarf: 5.3 GHz PTX: 4.8 kWant: 10 m x 1 m B: 15.5 MHzx = y = 30 m fs: 19 MSa/sorbit: 780 km DR: 105 Mb/s
Nonlinear internal waves propagating eastwards and oil slicks can be seen.
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PRARE: precise range and range rate equipment
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Radar fundamentals (review)ERS-1 Synthetic Aperture Radar
Radar center frequency, f: 5.3 GHz• C-band, = c/f = 5.7 cm
c = 3 x 108 m/s
Antenna dimensions, ant: 10 m x 1 m (width x height)• Approx. beamwidth, /antenna dimension az 0.057 m/10 m = 5.7 mrad or 0.32° el 0.057 m/1 m = 57 mrad or 3.2°• Antenna gain, G 4/(az el)• G(dBi) = 10 log10(G)
dBi is dB relative to isotropic antenna
• G = 4/(0.057 x 0.0057) = 38700 or 46 dBi• Minimum along-track resolution, ymin = ℓ/2
ℓ is antenna’s along-track dimension
• ℓ = 10 m, ymin = 5 m, y = 30 m > ymin
Bandwidth, B: 15.5 MHz• Range resolution (slant range, cross-track), r = c/2B r = c/(2 x 15.5 MHz) = 9.7 m• Ground resolution (cross-track), x = r /sin is the incidence angle
Pulse duration, : 37.1 s• Pulse compression ratio, B = 575 (28 dB)
B(dB) = 10 log10(B)
• Blind range c/2 = 5.6 km
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Radar fundamentals (review)ERS-1 Synthetic Aperture Radar
Sampling frequency, fs: 19 MSa/s, 5 b/sample, I/Q• Nyquist requires fs ≥ 15.5 MSa/s
• fs = 1.23 Nyquist rate (23% oversampling)
Orbit altitude, h: 780 km• Orbital velocity, v,
for Earth, = 398,600 km3/s2
• Ground velocity, vg,
Re = 6378.145 km
• v = 7.46 km/s, vg = 6.65 km/s
• Minimum pulse-repetition frequency, PRFmin = 2v/ℓ
• PRFmin = 2(7460)/10 = 1490 Hz
• 1720 Hz ≥ PRF ≥ 1640 Hz (from ERS specs)
Look angle, : 23°• sin = (1 + h/Re) sin = 26°• Ground resolution, x = r /sin x = 22 m
s/km,hRv e
hRRvv eeg
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Radar fundamentals (review)ERS-1 Synthetic Aperture Radar
Ground swath width, Wgr: 100 km• Slant swath width, Wr = Wgr sin • Wr = 43.8 km
• Echo duration from swath, s = + 2 Wr/c
s = 37.1 s + 292 s = 329.1 s
Data rate, DR: 105 Mb/s• Samples/echo = 329.1 s x 19 MSa/s = 6250 Samples/echo• Sample rate = PRF x Samples/echo• Sample rate = 1640 x 6300 = 10.3 MSa/s• Data rate = Sample rate x bits/sample = 10.3 MSa/s x 10 bits/Sa = 103 Mb/s
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Ka-band, 4″ resolutionHelicopter and plane static display
f: 35 GHz
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Sandia’s real-time SARSandia SAR system
LynxCountry USADate 1998Frequency 15.2 to 18.2 GHzPolarization VVBeamwidth (deg) 3.2 az, 7 el.Slant range 7 to 30 kmSwath width 2600 pixelsTransmit power 320 WNoise equivalent RCS -30 dBsmNF 4.5 dBSampling (8 b @ 125 MS/s)Mode stripmap / spotlightResolution (slant & azimuth) 0.3 / 0.1 mMass 125 lbsProcessing stretchSquint angle (deg) 45 to 135Weather restriction 4-mm/hr rainfall rateUAV platforms Predator, I-GNAT, Prowler IICrewed platforms Blackhawk, KingAir 200
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Radar fundamentals (review)Radar range equation, received signal power, and signal-to-noise ratio
For a monostatic radar system and a point target
Where
Pt is the transmitted signal power, W
Pr is the power intercepted by the receiver, W
G is the gain of the antenna in the direction of the targetR is the range from the antenna to the scatterer, m is the target’s radar scattering cross section (RCS), m2
is the wavelength of the radar signal, m
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22t
rR4
GPP
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Radar fundamentals (review)Receiver noise power, PN
k is Boltzmann’s constant (1.38 10-23 J K-1)
T0 is the absolute temperature (290 K)
B is receiver bandwidth, Hz
F is receiver noise figure
Signal-to-noise ratio (SNR) is
may be expressed in decibels
W,FBTkP 0N
FBTkR4
GPPPSNR
043
22t
Nr
SNRlog10dBSNR 10
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Radar fundamentals (review)Example: Sandia Lynx SAR
Radar center frequency, f = 16 GHz
Transmit power, PT = 320 W (55.1 dBm)
dBm: dB relative to 1 mW
Slant range resolution, r = 0.3 m (1 ft)
Receiver noise figure, FREC = 2.8 (F = 4.5 dB)
Antenna beamwidths, 3.2° x 7°
Range to target, R = 30 km (18.6 miles)
Target RCS, = 0.001 m2 (-30 dBsm) = ° x y
Find the Pr , PN , and the SNR
First derive some related radar parameters
Wavelength, = c/f = 0.01875 m
Antenna gain, G 4/(az el) G = 1840 or 32.6 dBi
Bandwidth, B = c/2r B = 500 MHz
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Radar range equation exampleFind Pr
Solve in dB
Pr(dBm) = Pt(dBm) + 2G(dBi) + 2 (dB) + (dBsm) – 3 4(dB) – 4 R(dB)
Pt(dBm) = 55.1 G(dBi) = 32.6 (dB) = -17.3 (dBsm) = -30
4(dB) = 11 R(dB) = 44.8
Pr(dBm) = -156.3 dBm or 2.3 10-19 W (0.23 aW)
Find PN
Solve in dB
PN(dBm) = kT0(dBm) + B(dB) + F(dB)
kT0(dBm) = -174 B(dB) = 87 F(dB) = 4.5
PN(dBm) = -82.5 dBm or 5.6 pW
Find SNRSNR = – 156.3 – (– 82.5) = -73.7 dB or 4.3 10-8
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22t
rR4
GPP
W,FBTkP 0N
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Radar fundamentals (review)Signal processing improves SNR
Pulse compression gain, BAssuming = 20 s yields a 40-dB pulse compression gain
Coherent integration improves SNR by NN is the number of integrations
N = synthetic-aperture length * PRF / velocity
Synthetic-aperture length, L = az R, L = 1675 m
Assume velocity = 36 m/s (Predator UAV cruise speed is 130 km/h )
Assuming a 1-kHz PRF
N = 46500 or 46-dB improvement
Therefore the SNR from a -30-dBsm target is 12.3 dBMany measurements require SNR > 10 dB
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Airborne SAR block diagram
New terminology:Magnitude imagesMagnitude and Phase ImagesPhase HistoriesMotion compensation (MoComp)Autofocus
Timing and ControlInertial measurement unit (IMU)GimbalChirp (Linear FM waveform)Digital-Waveform Synthesizer
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Airborne SAR real-time IFP block diagram
Image-Formation Processor
New terminology:Presum (a.k.a. coherent integration)Corner-turning memory (CTM)Window Function
Focus and Correction VectorsRange Migration and Range WalkFast Fourier transform (FFT)Chirp-z transform (CZT)
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InSAR Coherent Change Detection
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Backscattering
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Radar response to extended targetsThe preceding development considered point target with a simple RCS, .
The point-target case enables simplifying assumptions in the development.
Gain and range are treated as constants
Consider the case of extended targets including surfaces and volumes.
The backscattering characteristics of a surface are represented by the scattering coefficient, ,
where A is the illuminated area.
A
unitless,p,p;, s0
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22t
rR4
GPP
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Factors affecting backscatterThe backscattering characteristics of a surface are represented by the scattering coefficient,
For surface scattering, several factors affect Dielectric contrast
Large contrast at boundary produces large reflection coefficientAir (r = 1), Ice (r ~ 3.2), (Rock (4 r 9), Soil (3 r 10), Vegetation (2 r 15), Water (~ 80), Metal (r )
Surface roughness (measured relative to )RMS height and correlation length used to characterize roughness
Incidence angle, ()
Surface slopeSkews the () relationship
PolarizationVV HH » HV VH
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Surface roughness and backscatter
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Backscatter from bare soil
Note: At 1.1 GHz, = 27.3 cm
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Backscattering by extended targets
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Detecting flooded lands
Combination of water surface and vertical tree trucks forms natural dihedral with enhanced backscatter.
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Detecting flooded lands
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Doppler shifts and PRF
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Doppler shifts and radial velocityThe signal from a target may be written as
c = 2fc
and the relative phase of the received signal,
A target moving relative to the radar produces a changing phase (i.e., a frequency shift) known as the Doppler frequency, fD
where vr is the radial component of the relative velocity.
The Doppler frequency can be positive or negative with a positive shift corresponding to target moving toward the radar.
rad,R2
2Rk2
Hz,v2
R2
dt
d
2
1f r
D
Rk2tj0
ceEtE
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Doppler shifts and radial velocityThe received signal frequency will be
ExampleConsider a police radar with a operating frequency, fo, of 10 GHz.
( = 0.03 m)
It observes an approaching car traveling at 70 mph (31.3 m/s) down the highway. (v = -31.3 m/s)
The frequency of the received signal will be
fo – 2v/ = fo + 2.086 kHz or 10,000,002,086 Hz
Another car is moving away down the highway traveling at 55 mph (+24.6 m/s). The frequency of the received signal will be
fo – 2v/ = fo – 1.64 kHz or 9,999,998,360 Hz
R2ffff cDc
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Doppler shifts and radial velocityGiven the position, P, and velocity, u, both the radar and the target, the resulting Doppler frequency can be determined
The ability to resolve targets based on their Doppler shifts depends on the processed bandwidth, B, that is inversely related to the observation (or integration) time, T
Instantaneous position and velocity Relative velocity, u
Radial velocity component
uRadar
uTarget
u = uRadar - uTarget
Hz,T1fB D
uRadar uTarget
PRadarPTarget
RRadar path
Target path
u
R (unit vector)^ ^
=
uRadial = u R
uTangential
u
uR = u cos()
fD = 2 u cos() /
^
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Pulse repetition frequencies (PRFs)The lower limit for PRFs is driven byDoppler ambiguities
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Doppler ambiguitiesTo unambiguously reconstruct a waveform, the Nyquist-Shannon sampling theorem (developed and refined from the 1920s to
1950s at Bell Labs) states that exact reconstruction of a continuous-time baseband signal from its samples is possible if the signal is bandlimited and the sampling frequency is greater than twice the signal bandwidth.
Application to radar means that the pulse-repetition frequency (PRF) must be at least twice the Doppler bandwidth. For side-looking SAR (centered about 0 Doppler), the PRF must be twice the highest Doppler shift.
For the case where the Doppler frequency shift will be 250 Hz (a 500-Hz Doppler bandwidth), the PRF must be at least 500 Hz.
[The Nyquist-Shannon theorem also has application to signal digitization in the analog-to-digital converter (ADC) requiring that the ADC sampling frequency be at least twice the waveform bandwidth.]
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PRF constraintsRecapping what we’ve seen—
The lower PRF limit is determined by Doppler ambiguities
The upper PRF limit is determined by the range ambiguities
EclipsingFurthermore, for systems that do not support receiving while transmitting, various forbidden PRFs will exist that will eclipse the receive intervals with transmission pulses, which leads to
where Tnear and Tfar refer to signal arrival times for near and far
targets, is the transmit pulse duration, and N represents whole numbers (1, 2, 3, …) corresponding to pulses
bandwidthDopplertheisf,f2PRF DDmin
rangesunambiguoutheisR,R2
cPRF u
umax
farnear T
NPRF
T
1N
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Spherical Earth calculationsSpherical Earth geometry calculations
Re Earth’s average radius (6378.145 km)
h orbit altitude above sea level (km)
core angle
R radar range
look angle
i incidence angle
i
sin
R
sin
R
sin
hR e
i
e
coshRR2hRRR ee2
e2e
2
Re
Re
NadirPoint
h R
i
Radar Position
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Spherical Earth calculationsSatellite orbital velocity calculations (for circular orbits)
Re Earth’s average radius (6378.145 km)
h orbit altitude above sea level (km)
v satellite velocity
vg satellite ground velocity
standard gravitational parameter (398,600 km3/s2 for Earth)
s/km,hRv e
hRRvv eeg
Re
hRfRn
swath
Radar VelocityAntenna pattern
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Spherical Earth calculationsSwath width geometry calculations
Re Earth’s average radius (6378.145 km)
Rn range to swath’s near edge
Rf range to swath’s far edge
Wgr swath width on ground
Wr slant range swath width
n core angle to swath’s near edge
f core angle to swath’s far edge
i,m incidence angle at mid-swath
enfgr RW
nfr RRW
Re
Re
h Rf
n
f
Rn Wri,m
Wgr
m,igrr sinWW
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PRF constraints
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PRF constraints
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PRF constraints
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Antenna length, velocity, and PRFGiven an antenna length, ℓ
wavelength,
velocity, v
We know
The Doppler bandwidth, fD, is
Therefore PRFmin is
2
v22sin
v2fD
vvv
fD
(small angle approximation)
v2f2PRF Dmin
Note that PRFmin is independent of
Aircraft casev = 200 m/s, ℓ = 1 mPRFmin = 400 Hz
Spacecraft casev = 7000 m/s, ℓ = 10 mPRFmin = 1.4 kHz
fD < 0
ℓv
fD > 0
antenna
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Three moving targets traveling on a runway at the Patuxent River Naval Air Station.
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Real-aperture side-looking airborne radar(SLAR)
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Side-looking airborne radar (SLAR)SLAR systems produce images of radar backscattering mapped into slant range, R, and along-track position.The along-track resolution, y, is provided solely by the antenna. Consequently the along-track resolution degrades as the distance increases. (Antenna length, ℓ, directly affects along-track resolution.)
Cross-track ground range resolution, x, is incidence angle dependent
Ry az
sin2
cx p where p is the compressed
pulse duration
y
xx
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Side-looking synthetic-aperture radar (SAR)
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Synthetic-aperture radar (SAR)Synthetic-aperture radar is an imaging radar concept that was developed in the early 1950s by Goodyear Aircraft Company.
It is remarkable in that when fully processed, SAR images have very fine resolution that are range independent.
Numerous variations of SAR have been derived from the basic concept and these include inverse SAR (ISAR), interferometric SAR (InSAR), and ScanSAR.
The basis concept for SAR appears fairly simple though upon inspection it is more complex.
The core concept may be thought of in at least five different ways:
Synthesized antenna aperture
Doppler beam sharpening
Correlation with reference point-target response
Matched filter for received point-target signal
De-chirping of Doppler frequency shift
Optical focusing equivalent
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Synthetic-aperture radar (SAR)In SAR systems a very long antenna aperture is synthesized resulting in fine along-track resolution.For a synthesized aperture length, L, the along-track resolution, y, is
As with SLAR, the cross-track resolution, x, is incidence angle dependent
L, is determined by the system configuration.For a fully focused stripmap system, Lm = azR (m), where
az is the azimuthal or along-track beamwidth of the real antenna (az /ℓ)
R is the range to the target
For L = Lm, y = ℓ/2 (independent of range and wavelength)
For unfocused SAR, the maximum synthetic aperture length, Lum, is
For L = Lum,
sin2
cx p
L2Ry
)m(,2RLum
)m(,2Rrau
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Synthetic-aperture radar (SAR)In the fully focused stripmap SAR mode, the synthetic-aperture length is determined by the length of the flight path during which a target in the antenna’s field of view.
RRL azm
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Synthetic-aperture radar (SAR)In spotlight mode, the synthetic aperture length L may exceed Lm because the antenna is steered to illuminate the
region of interest as the system passes by, and
where (radians) is the change in aspect angle over which the target is viewed.
For small , y /(2)
m,2sin4
y
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SAR data collection modes
In strip mode, the along-track resolution (y) is determined by synthetic-aperture length (L)
In spotlight mode, y /(2) where (radians) is the change in aspect angle over which the target is viewed.
2/y
L2Ry
RRL az
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Inverse SAR (ISAR)Inverse synthetic-aperture radar (ISAR) (not to be confused
with InSAR) involves forming range-azimuth radar images of a moving target using a stationary radar.
Synthetic aperture formation requires only relative motion and is not restricted to a moving radar system.
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Inverse SAR (ISAR)While primarily used in military applications, ISAR does have scientific value.
Radar images of 3.5-km asteroid 1999 JM8 at a range of 8.5x106 km (22x Earth-Moon separation distance).Images labeled A were produced from data collected by Arecibo and have 15-m range resolution.
Images labeled G produced from data collected by Goldstone. G1 has 38-m resolution, G2 has 19-m resolution.
A
A
G1
G2
Aug 5, 1999 July 28, 1999
Aug 2, 1999Aug 1, 1999
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Arecibo Observatory
Funded by National Science FoundationOperated by Cornell University
Located in Puerto Rico
1-MW transmitterf: 2.38 GHz, : 12.6 cm
305-m diameter, non-steerable reflector (Earth’s largest curved focusing dish)
Collects data for: radio astronomy (passive),terrestrial aeronomy (study of Earth’s upper atmosphere),planetary radar studies
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Goldstone Solar System RadarPart of NASA/JPL Deep Space Network (DSN)
Located in California
Fully-steerable 70-m parabolic reflector500-kW transmitter
f: 8.560 GHz: 3.5 cm
Operates in both monostatic and bistatic modes with New Mexico’s twenty-seven 25-m antennas Very Large Array or Arecibo