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December 6, 2006

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Satellite Radar Interferometry and its applicationsPart 1, Radar fundamentals

Guest lecture Remote Sensing (GRS-20306)Wageningen UniversityRamon Hanssen

Delft Institute of Earth Observation and Space Systems

December 6, 2006 2

Contents Part 1 & 2Part 1• Radar background and fundamentals• Imaging radar, SAR• Physics and geometry• ResolutionPart 2• Interferometry, principles• Topography and deformation• Accuracy• Error sources• New processing methodologies: PSI

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Radar background/history

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Early ground based radar

RAdio Detection and Ranging

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Radar mapping of the Moon, Venus, Mars(1946) (1961) (1963)

Main parameters:

•Distance

•Velocity

•Intensity

Retrograde rotation Venus

Improvement of Astronomical unit

2

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Magellan Synthetic Aperture Radar Mosaic of Venus

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Maat Mons, Venus

Magellan Synthetic Aperture Radar

Radar clinometry, altimeter, and backscatter

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Towards imaging radar

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Optical imagery (false color) versus radar imagery

Delft University, AE

Resolution: 4x20 m

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Physics

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Radio waves, active sensor

Wavelength range is cm-m

24 cm 3 cm5 cm

3

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Penetration (weather independent)

C b

and

Radar waves penetrate the atmosphere and clouds

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• Landsat optical• Shuttle L-band radar• What do we see?

Sahara desert

Radar penetrates material with a low dielectric constant (dep. on wavelength)

Here about 3 m.

Sahara, NW Sudan (SIR-A)

Physics

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Physics - Scattering

• Scattering is dominated by wavelength-scale structures

• Wavelength shorter: image brighter• Specular and Bragg scattering• Speckle

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SPECULAR

Radar signal return depends on:

•Slope

•Roughness

•Dielectric constant

Scattering

Smooth Rough

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Physics – scattering phase

Imag

inar

y

Real

Radar pixel phase is superposition of near-random scattering elements:

Unpredictable!

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December 6, 2006 1

Geometry

Terminology • Foreshortening, layover, shadow• Why side-looking?• Incidence angle, • Coordinates range, azimuth

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Fore

short

ening

Layo

ver

Shado

w

Geometry Slant range

Ground range

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Geometry

Fore

short

ening

Layo

ver

Shado

w

JERS-1 data (M.Shimada)

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Resolution I: RAR•Real Aperture Radar

•Resolution dependent on antenna dimension/pulse length

•Beam width (half power width) is ratio wavelength over antenna size:

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Antenna dimensions

1.3 m

10 m

Calculate Ground Resolution

C-band λ= ~0.05 m

D=10 m antenna

Beam angle = 5.10-2/10 = 5.10-3 rad

R=850 km

times 8.5.105 = 42.102[m] = 4.2 km

Dλθ =

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antenna

pulse

2

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antenna

pulse length

pulse repetition

frequency (PRF)

swath

ground range

Slant range

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Improvement of along-track resolution

Synthetic antenna

Physical antenna

Resolution cell

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Improvement in Resolution (Crimea, Ukraine)

Real Aperture Radar Synthetic Aperture Radar

5x14 km pixels 4x20 m pixels

Massonnet and Feigl, 1998

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Resolution II: SAR

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Resolution II (SAR)

• Resolution SAR is inversely proportional with bandwidth

• Azimuth resolution SAR: Half antenna size!

• No influence of satellite height on azimuth resolution SAR image

• Range resolution improvement using chirp waveform

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SAR SLC observationsSLC: Single-Look Complex data

•Single-look: no averaging, finest spatial resolution

•Complex: both real and imaginary (In-phase and quadrature phase) stored

Amplitude PhaseUninterpretable, due to scattering mechanism

Coherent imaging

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End of part 1

December 6, 2006

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Satellite Radar InterferometryPart 2, InSAR, fundamentals and applications

Guest lecture Remote Sensing, Wageningen University

Ramon Hanssen

Delft Institute of Earth Observation and Space Systems

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Interferometric radar (InSAR)

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Radar Interferometry

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Example in 2D: interferogram

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Range

Expressed as phase (radians)

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Range

Expressed as integer cycles + fractional phase

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Reference phase (flat earth phase)

Ellipsoid

-π

+π

Topography will add variation to the “flat earth phase”

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Phase-range relationship

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Phase-height relationship(Far-field approximation)

Ellipsoid

Topographic phase is (inversely) scaled by the perpendicular baseline!

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Amplitude

Reference phase

Topographic phase

RADAR INTERFEROMETRIC OBSERVATIONS

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Phase and topography

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Baseline dependency, height ambiguity

Bperp 173 m, Bt= 1day Bperp 531 m, Bt= 1 day

H2pi=45m H2pi=16m

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Deformation measurements

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Conventional Interferometry: Bam earthquake 26/12/2003

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Conventional Interferometry: Glacier Dynamics (Svalbard, Spitsbergen)

5 KM

LOS

12 day interferogram

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Satellite radar interferometry• Coseismic interferogram, showing deformation Izmit earthquake

• Every color cycle 7.5 cm horizontal motion

• Showing which segment of fault ruptured

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Mauna Loa, Hawaii• Deformation

(inflation) of the Mauna Loa summit

• Position of the magma chamber better determined

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…Very sensitive to deformation

Subsidence Las Vegas due to ground water extraction

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Phase-deformation relationship

Subsidence ∆z

1 cycle LOS deformation is equal to half the physical wavelength

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Topography and deformation

Ellipsoid

Sensitivity to deformation 1000x higher than for topography

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Quality: Phase variance estimation:Coherence

•Optics equivalent to correlation:

•Estimation of coherence:

}|{|}|{|}{

22

21

*21

yEyEyyE⋅

=γ

∑ ∑∑

= =

==N

n

N

nnn

N

nnn

yy

yy

1 12)(

22)(

1

1)(

2)(

1

||||

|||ˆ| γ

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Coherence

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Problems Conventional InSAR• Close satellite orbits required• Sensitive to changing surface backscatter behavior• Sensitive to atmospheric water vapor

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1 day

16618593112Perpendicular baseline (m)

6 years3 years2 years1 yearTemporal baseline

Conclusion:

Conventional InSAR does not work for

•slow deformation, over

•vegetated/wet/changing surfaces,

•in non-arid climate regions

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New processing methodologies

• To resolve the ambiguities• Separate topography and deformation• To detect information in the noise• To estimate/mitigate atmospheric signal• To estimate orbit errors

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Deformationmeasurements:time-seriesapproaches

• Evaluation per point: double-differences

• Opportunistic subsets

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PS principle• Pixels with strong and consistent reflections in

time.• Multi-pass InSAR – time series necessary.• Estimate atmosferic signal:

• Spatially, not temporally correlated.• Independent of baseline. (topography is)

Salt mining Nedmag Veendam

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1992 2004

1992

1992 2004

2004

Formal precision of deformation rate < 1 mm/y

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Interpolated signal

mm/y1992-2004

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28 May 1992

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Case study Harlingen

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Case study Harlingen

mm/year

Local salt mining resulted in subsidence. The dike segment subsided ~5 cm between 1995 and 2001

1992 1995 2001

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Sluices Kornwerderzand

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Case study Kornwerderzand

mm/year

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mm/year

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Case study Marken

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mm/year

0

NAP

-2

-4

-6Compaction

clay

peat

clay

stones

Settlement of peat layers below Markenisland caused a vertical movement of the dikes of ~10 cm between 1992 and 2001

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Case Study Noordoostpolder

Taken from: www.wikipedia.nl

UrkSchokland

Emmeloord

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‘Zetting’