Interferometric Synthetic-Aperture Radar (InSAR) and Applications

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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
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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)

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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 [phone]
• 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.

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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

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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

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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.
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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

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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 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)

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InSAR
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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

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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 MHz?x ?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 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.
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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
  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

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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

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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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Sandias real-time SAR
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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, 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

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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

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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/2?r B 500 MHz

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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

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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

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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
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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)
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InSAR Coherent Change Detection
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Backscattering
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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.

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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

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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 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.

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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

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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
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Pulse repetition frequencies (PRFs)
The lower limit for PRFs is driven byDoppler
ambiguities
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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.

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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

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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

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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)

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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

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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 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
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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

where ?p is the compressed pulse duration
?y
?x
?x
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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 ?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,

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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 antennas field of view.

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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?)

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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.

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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
G1
July 28, 1999
Aug 5, 1999
A
G2
Aug 2, 1999
Aug 1, 1999
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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
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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