InSAR
and LIDAR
Lecture 10
1. Interferometric Synthetic Aperture
Radar (InSAR or IFSAR)

Is a process whereby radar images of the same location on the
ground are recorded by
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Two antennas of one platform separated by a few meters (single pass),
or
The same radar system at different times (multi-pass or repeat-pass)
Applications on
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Elevation (DEM) derivation (single or multi pass)
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Can be as accurate as DEM from traditional optical photogrammetric
techniques. However, InSAR operate through clouds, day or night.
The first worldwide DEM (99.97%) was acquired in 2000 by SRTM in
2000, not by the photogrammetry
Surface displacement study (multi-pass only)
Examples
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One SAR with 2 antennas (single-pass)
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AIRSAR/TOPSAR
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Along track interferometric mode (ATI)
(L and C)
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Cross track interferometric mode (TXI) (L
or C)
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DEM (3-5 m or 1 m)
Shutter Radar Topographic Mission
(SRTM)
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Ocean current and waves
C band and X band antennas separated by
60 m
One SAR in different times (multipass)
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SIR-C
ERS 1,2
Phase of the wave is the total number of cycles of the wave at any given distance (or
target) from the transmitter, including the fractional part. One cycle of phase is equal to
360 degrees (or 2π).
The phase difference is called the “interferometric phase” and is determined by effectively
subtracting the measured phase at each end of the baseline, and is actually the distance
difference from each receiver to the same target.
Calculate altitude
z ( y )  h    cos 
(1)
(   ) 2   2  B 2  2B cos(90     )   2  B 2  2B sin(    )

 
  (3)
2
(Phase difference)
 2
B ( )
2
(2)
2
z( y)  h 

 2 B sin(    )

 is the fractional phase (value 0-2 radians), λ is wavelength
 cos 
(4)
AIRSAR/TOPSAR
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
Operates from a NASA DC-8 jet. When AIRSAR is
used to create topographic map (DEM), it is called
TOPSAR.
Fully polarimetric imagery (HH, VV, HV, VH) in
three bands:
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C (5.6 cm, 5.26 GHz)
L (24 cm, 1.22 GHz)
P (60 cm, 0.45 GHz)
Spatial resolution of 10 m for 20 MHz radar data and
5 m for 40 MHz data. Multilook post-processing can
be applied to the radar imagery to reduce speckle at
the expense of decreased spatial resolution
Xie, 2002; Xie and Keller, 2006
Both C (5.6 cm) and X (3 cm) bands in the Main
Antenna transmit and receive radar signals, but in
the Outboard Antenna only receive signals.
http://www2.jpl.nasa.gov/srtm/instr.htm
Glaciers are sensitive indicators of climatic change. They can grow and thicken with increasing snowfall
and/or decreased melting. Conversely, they can retreat and thin if snowfall decreases and/or atmospheric
temperatures rise and cause increased melting. Landsat imaging has been an excellent tool for mapping the
changing geographic extent of glaciers since 1972. The elevation measurements taken by SRTM in February
2000 now provide a near-global baseline against which future non-polar region glacial thinning or
thickening can be assessed.
http://www2.jpl.nasa.gov/srtm/alaska.htm
Source for SRTM data

USGS gallery:
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JPL gallery:
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gahttp://srtm.usgs.gov/srtmimagegallery/index.html
http://photojournal.jpl.nasa.gov/mission/SRTM
USGS seamless distribution system (USA 30 m,
globe 90 meter)

http://seamless.usgs.gov/
SRTM coverage map
To download from here http://seamless.usgs.gov/
Displacement
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Interferogram of Landers
earthquake 7.3 magnitude on
June 18, 1992. This is a
remarkable new tech gained
recognition thereafter.
This is from ERS-1
Average displacement along the
fault rupture was 3-4 m,
maximum was 6m.
Each color cycle represents
additional 2.8 cm ground
motion or displacement.
Side info: ASTER Global DEM v2
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This is not from INSAR tech, but It has an alongtrack stereoscopic capability using its near infrared
spectral band and its nadir-viewing and backwardviewing telescopes to acquire stereo image data with
a base-to-height ratio of 0.6. the improved version 2
was just released on October 17, 2011
30 m in pixel size
30 m accuracy in horizontal and 20 m accuracy in
vertical
Free downloaded from
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http://demex.cr.usgs.gov/DEMEX/
http://reverb.echo.nasa.gov/reverb/
2. LIDAR
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LIght Detection And Ranging uses the same principle as RADAR.
The lidar instrument transmits laser out to a target. The transmitted
light interacts with atmosphere and target. Some of this light is
reflected / scattered back to the instrument where it is analyzed.
Use UV, visible, and infrared
Transmitter (laser) and receiver
Distance = C x T /2
Four types
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Ranger finders: it is the simplest lidars, it measures the distance, then create
the topographic map
DIAL: Differential Absorption Lidar is used to measure chemical
concentrations (such as ozone, water vapor, pollutants) in the atmosphere.
Doppler Lidars: it’s used to measure the velocity of a target
Raman LIDAR: can measure gaseous species
Airborne Lidar System

ALTMS
 FLI-MAP
 ALTM
 TopoEye
 ATLAS
(TerraPoint, USA)
(John Chance, USA)
(USA)
(USA)
(USA)
Lidar elevation data of Bristol, UK
http://www.npagroup.co.uk/engenv/engineering/lidar_img1.htm

These data are
collected with
aircraft-mounted
lasers capable of
recording elevation
measurements at a
rate of 2,000 to 5,000
pulses per second and
have a vertical
precision of 15
centimeters (6
inches). After a
baseline data set has
been created, followup flights can be used
to detect shoreline
changes.
Surface and digital terrain model (DTM)
http://www.gisdevelopment.net/technology/rs/ma03234a.htm
digital surface model (DSM) and DTM
DSM
DTM (bare)
Airborne Lidar
http://www.etl.noaa.gov/et2/data/data_pages/texaqs/air_aerosol.html

DIAL laser
measures water
vapor, clouds,
and aerosols by
comparing the
absorption and
scattering of
different laser
pulses on these
atmospheric
species
http://oea.larc.nasa.gov/PAIS/LASE.html
ICESat
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The first LIDAR satellite for Earth launched
1/12/2003
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The Ice, Cloud, and Elevation Satellite (ICESat)
The Geoscience Laser Altimeter System (GLAS)
Two wavelengths: 532 nm and 1064 nm
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532 nm channel: vertical distribution of clouds
and aerosols
1064 nm channel: surface elevation of ice sheets
and sea ice thickness, 15 cm in vertical accuracy.
Ice, Cloud, and Land Elevation Satellite
(ICESat)
Instrument: Geoscience Laser Altimeter System
(GLAS)
Orbit Height: 600 km
Inclination: 94
Laser Wavelengths: 1064 nm and 532 nm
Orbit Repeat: 8 day and 91 day
Transmitted Pulse FWHM : 5 ns
Laser Footprint Diameter on the ground: 70 m
Sample interval on the ground: 170 m
Sample Rate: 40 laser shots per second.
Animation
http://nsidc.org/data/icesat/laser_op_periods.html
ICESat used to validate the SRTM- and
photogrammtry-derived DEMs
Huang et al. 2011
Fig. 5. Elevation profiles along an ICESat ground track over a plateau lake
surface. (a) ICESat ground tracks through the Nam Co Lake (centered at
30.42ºN/90.33 ºE) in 2003. (b) The profiles of ICESat and the two DEMs on
September 27. (c) The elevation difference between DEM and ICESat (DEM
minus ICESat) on September 27.
ICESAT study lake level change
Zhang et al., 2011
Lake Qinghai
Location of Lake Qinghai, and rivers, hydrological and meteorological station sites
The 47 ICESat tracks through Lake Qinghai.
Lake level change
Zhang et al., 2011b
Lake level from in-situ station vs. ICESat data
Absolute average difference=0.06 m
RMSD=0.08 m
ICESat in
SIMBA 2007
0.35
All tracks
Frequency
0.3
Track 0011
0.25
0.2
0.15
0.1
0.05
0
0.2
0.8
1.4
2
2.6
3.2
3.8
4.4
5
5.6
Ice thickness (m)
Snow Freeboard or Ice Thickness (m)
2.30
Freeboard: footprint
Freeboard: 12.5 km running mean
Freeboard: 1 km running mean
Ice thickness: 1 km running mean
1.80
1.30
0.80
0.30
-0.20
-69.0
-69.2
-69.4
-69.6
-69.8
-70.0
-70.2
-70.4
-70.6
-70.8
Latitude (degree)
-71.0
-71.2
-71.4
-71.6
-71.8
-72.0
Xie et al. 2011
CALIPSO
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Cloud-Aerosol Lidar and Infrared Pathfinder
Satellite Observations (CALIPSO), launched
4/28/2006.
Provide a global set of data on aerosol and cloud
properties, radiative fluxes, and atmospheric state.
Equipment:
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Lidar: 632 nm and 1064 nm
Radiometer
Camera
http://www-calipso.larc.nasa.gov/
Calipso instrument
MOLA

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Mars Orbiter Laster Altimeter (MOLA), the first
satellite-based Lidar system, launched on November
7, 1996 on board the Mars Global Surveyor.
Wavelength 1064 nm, 130 m footprint and 330 m
along track spacing (vary with latitude)
To construct a precise topographic map of Mars
S
N
Mars’ south pole has a higher elevation than the north pole by ~6 km.