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Title: Interferometric Synthetic-Aperture Radar (InSAR) and Applications


1
Interferometric Synthetic-Aperture Radar (InSAR)
and Applications
Chris Allen (callen_at_eecs.ku.edu) Course website
URL www.cresis.ku.edu/callen/826/EECS826.htm
2
Outline
  • Syllabus
  • Instructor information, course description,
    prerequisites
  • Textbook, reference books, grading, course
    outline
  • Preliminary schedule
  • Introductions
  • What to expect
  • First assignment
  • Radar fundamentals
  • Active RF/microwave remote sensing
  • Electromagnetic issues
  • Antennas
  • Resolution (spatial, range)

3
Syllabus
  • Prof. 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 callen_at_eecs.ku.edu
  • Office 321 Nichols Hall
  • Office hours Tuesdays and Thursdays 200 to
    230 p.m. and 345 to 430 p.m.
  • Course description
  • Description 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.

4
Syllabus
  • Prerequisites
  • Introductory course on radar systems (e.g., EECS
    725)
  • Introductory course on radar signal processing
    (e.g., EECS 744)
  • Textbook
  • Processing of SAR Data by A. HeinSpringer,
    2004, ISBN 3540050434

5
Syllabus
  • Reference 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

6
Grades and course policies
  • The 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 lt 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.
7
Preliminary schedule
  • Course 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 Schedule
  • January 15, 20, 22, 27, 29
  • February 3, 5, (10th to 12th NSF Site Visit),
    17, 19, 24, 26
  • March 3, 5, 10, 12, (17th to 19th Spring Break),
    24, 26, 31
  • April 2, 7, 9, 14, 16, 21, 23, 28, 30
  • May 5, 7
  • Final exam scheduled for Friday, May 15, 130 to
    400 PM

8
Introductions
  • Name
  • Major
  • Specialty
  • What you hope to get from of this experience
  • (Not asking what grade you are aiming for ?)

9
What to expect
  • Course 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 encouraged
  • Students must activate microphone before speaking
  • Please disable microphone when finished
  • Homework assignments will be posted on website
  • Electronic homework submission logistics to be
    worked out
  • We may have guest lecturers later in the semester
  • To break the monotony, well try to take a couple
    of 2-minute breaks during each session (roughly
    every 15 to 20 min)

10
InSAR
11
Your first assignment
  • Send me an email (from the account you check most
    often)
  • To callen_at_eecs.ku.edu
  • 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 youve had

12
SAR image of Los Angeles area
SEASAT Synthetic Aperture Radarf 1.3 GHz PTX
1 kWant 10.8 x 2.2 m B 19 MHz?x ?y 25 m
pol HHorbit 795 km DR 110 Mb/s
13
SEASAT suffered a massive electrical short in one
of the slip ring assemblies used to connect the
rotating solar arrays to the power subsystem.
14
SAR image of Gibraltar
ERS-1 Synthetic Aperture Radarf 5.3 GHz PTX
4.8 kWant 10 m x 1 m B 15.5 MHz?x ?y 30
m fs 19 MSa/sorbit 780 km DR 105 Mb/s
Nonlinear internal waves propagating eastwards
and oil slicks can be seen.
15
PRARE precise range and range rate equipment
16
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
    antennas along-track dimension
  • l 10 m, ?ymin 5 m, ?y 30 m gt ?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

17
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

18
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

19
Ka-band, 4? resolutionHelicopter and plane
static display
f 35 GHz
20
Sandias real-time SAR
21
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, WPr is the
    power intercepted by the receiver, WG is the
    gain of the antenna in the direction of the
    targetR is the range from the antenna to the
    scatterer, m? is the targets radar scattering
    cross section (RCS), m2? is the wavelength of
    the radar signal, m

22
Radar fundamentals (review)
  • Receiver noise power, PN
  • k is Boltzmanns 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

23
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/2?r B 500 MHz

24
Radar range equation example
  • Find Pr
  • Solve in dB
  • Pr(dBm) Pt(dBm) 2?G(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 SNR
  • SNR 156.3 ( 82.5) -73.7 dB or 4.3 ? 10-8

25
Radar fundamentals (review)
  • Signal processing improves SNR
  • Pulse compression gain, B?
  • Assuming ? 20 ?s yields a 40-dB pulse
    compression gain
  • Coherent integration improves SNR by N
  • N 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
    dB
  • Many measurements require SNR gt 10 dB

26
Airborne SAR block diagram
New terminologyMagnitude imagesMagnitude and
Phase ImagesPhase HistoriesMotion compensation
(MoComp)Autofocus
Timing and ControlInertial measurement unit
(IMU)GimbalChirp (Linear FM waveform)Digital-Wa
veform Synthesizer
27
Airborne SAR real-time IFP block diagram
Image-Formation Processor
New terminologyPresum (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)
28
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29
InSAR Coherent Change Detection
30
Backscattering
31
Radar response to extended targets
  • The 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.

32
Factors affecting backscatter
  • The 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 coefficient
  • Air (?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 slope
  • Skews the ??(?) relationship
  • Polarization
  • ??VV ? ??HH ??HV ? ??VH

33
Surface roughness and backscatter
34
Backscatter from bare soil
Note At 1.1 GHz, ? 27.3 cm
35
Backscattering by extended targets
36
Detecting flooded lands
  • Combination of water surface and vertical tree
    trucks forms natural dihedral with enhanced
    backscatter.

37
Detecting flooded lands
38
Doppler shifts and PRF
39
Doppler shifts and radial velocity
  • The signal from a target may be written as
  • ?c 2?fc
  • 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.

40
Doppler shifts and radial velocity
  • The received signal frequency will be
  • Example
  • Consider 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

41
Doppler shifts and radial velocity
  • Given 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
42
Pulse repetition frequencies (PRFs)
The lower limit for PRFs is driven byDoppler
ambiguities
43
Doppler ambiguities
  • To 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.

44
PRF constraints
  • Recapping what weve seen
  • The lower PRF limit is determined by Doppler
    ambiguities
  • The upper PRF limit is determined by the range
    ambiguities
  • Eclipsing
  • Furthermore, 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

45
Spherical Earth calculations
  • Spherical Earth geometry calculations
  • Re Earths average radius (6378.145 km)
  • h orbit altitude above sea level (km)
  • ? core angle
  • R radar range
  • ? look angle
  • ?i incidence angle

46
Spherical Earth calculations
  • Satellite orbital velocity calculations (for
    circular orbits)
  • Re Earths 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)

47
Spherical Earth calculations
  • Swath width geometry calculations
  • Re Earths average radius (6378.145 km)
  • Rn range to swaths near edge
  • Rf range to swaths far edge
  • Wgr swath width on ground
  • Wr slant range swath width
  • ?n core angle to swaths near edge
  • ?f core angle to swaths far edge
  • ?i,m incidence angle at mid-swath

48
PRF constraints
49
PRF constraints
50
PRF constraints
51
Antenna length, velocity, and PRF
  • Given an antenna length, l
  • wavelength, l
  • velocity, v
  • We know
  • The Doppler bandwidth, ?fD, is
  • Therefore PRFmin is

(small angle approximation)
Aircraft casev 200 m/s, l 1 mPRFmin 400
Hz Spacecraft casev 7000 m/s, l 10 mPRFmin
1.4 kHz
Note that PRFmin is independent of l
52
Three moving targets traveling on a runway at the
Patuxent River Naval Air Station.
53
Real-aperture side-looking airborne radar(SLAR)
54
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

where ?p is the compressed pulse duration
?y
?x
?x
55
Side-looking synthetic-aperture radar (SAR)
56
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

57
(No Transcript)
58
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 ?az?R
    (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,

59
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 antennas field of view.

60
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?)

61
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.

62
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.

63
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
G1
July 28, 1999
Aug 5, 1999
A
G2
Aug 2, 1999
Aug 1, 1999
64
Arecibo Observatory
  • Funded by National Science Foundation
  • Operated by Cornell University
  • Located in Puerto Rico
  • 1-MW transmitter
  • f 2.38 GHz, ? 12.6 cm
  • 305-m diameter, non-steerable reflector (Earths
    largest curved focusing dish)

Collects data for radio astronomy
(passive),terrestrial aeronomy (study of Earths
upper atmosphere),planetary radar studies
65
Goldstone Solar System Radar
  • Part of NASA/JPL Deep Space Network (DSN)
  • Located in California
  • Fully-steerable 70-m parabolic reflector 500-kW
    transmitter
  • f 8.560 GHz? 3.5 cm

Operates in both monostatic and bistatic modes
with New Mexicos twenty-seven 25-m antennas Very
Large Array or Arecibo
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