2. selection of sar data product for different applications

8/19/2019 2. Selection of SAR Data Product for Different Applications

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iirs

Shashi Kumar

Selection of SAR Data

Product for Different

Applications(SAR Imaging Modes and Data

Format)

Indian Institute of Remote Sensing

(Indian Space Research Organisation)Department of Space, Government of India

04 Kalidas Road, Dehradun - 248 001, U.K.


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Topics

• Different types of

SAR system

•

Imaging platformsand wavelength used

in SAR remote

sensing

• Mode of acquisition

• SAR data format

Figure Source: http://www.scanex.ru/en/publications/pdf/publication50.pdf


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SAR Systems

• Monostatic SAR Systems

• Bistatic SAR Systems

•

Multistatic SAR Systems

http://www.antrix.gov.in/RISAT-1.pdf


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Monostatic SAR

Systems

Single antenna is used to transmit

and receive the electromagnetic

pulses. Currently all the spaceborne

SAR sensors are monostatic SARsystems


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Bistatic

Bistatic radar is defined as a radar where the

transmitter and receiver are spatially separated.The only assumption is that the transmit and

receive antennas are on different platforms.

• TanDEM-X (TerraSAR-X add-on for Digital

Elevation Measurement) opens a new era in space

borne radar remote sensing. The first bistatic SAR

mission, is formed by adding a second, almost

identical spacecraft, to TerraSAR-X and flying thetwo satellites in a closely controlled formation with

typical distances between 250 and 500 m.


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Bistatic


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Bistatic configuration in the TerraSAR-X/F-SAR

spaceborne – airborne SAR experiment.

The trajectory of F-SAR was

designed to be nearly parallel to the

nadir track of TerraSAR-X

http: //elib-v3.dlr .de/55400/1/RoBaKrMo_TGRS10_ieee.pdf

The TerraSAR-X antenna was steered in

high-resolution spotlight mode


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Bistatic Image

K a

u f b e u r e n c i t y s u r r o u

n d e d b y f o r e s t e d a r

e a s a n d f i e l d s


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Mutistatic

Fully active multistatic radar system Semi-active multistatic radar systemKrieger, G.; Moreira, A., "Spaceborne bi- and multistatic SAR: potential and challenges," Radar, Sonar and Navigation, IEE Proceedings - , vol.153, no.3, pp.184,198, June 2006

URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1648537&isnumber=34563

Fully active configuration, each radar has both transmit and receive capabilities

Semi-active systems combine an active illuminator with one or more passive receivers

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1648537&isnumber=34563http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1648537&isnumber=34563


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Radar Bands Commonly Used For Sensing

BAND WAVELENGTH

(cm)

FREQUENCY

GHz (109 Cycles/sec)

Ka 0.75 - 1.1 26.5 - 40

K 1.1 - 1.67 18 - 26.5

Ku 1.67 - 2.4 12.5 - 18X 2.4 - 3.8 8 - 12.5

C 3.8 - 7.5 4 - 8

S 7.5 - 15 2 - 4L 15 - 30 1 - 2

P 30 - 100 0.3 - 1


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Imaging Platforms

• Spaceborne

• Airborne


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Spaceborne SAR

Systems

RISAT-1: April 2012: C-bandRadarsat 1: 1995: C-band

Radarsat 2: 2007: C-band (Quad- pol)

ERS 1: 1991-2000 :C-band

ERS 2: 1995 :C-bandJERS : 1992-98 : L-band

ENVISAT: 2002: C-band

ALOS: 2006: L-band (Quad-pol)

TerraSAR-X: 2007: X-band (Quad-

pol)TanDem-X:2010: X-band (Quad-

pol)

COSMO-SkyMed-1/4 2007 – 2010 – today: X (dual)


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Source: PolSARpro Tutorial;

presentation on

01_polarimetric_airborne_sensors

Airborne SAR Sensors


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Mode of Acquisition

• Scan

• Strip• SpotLight

– Sliding SpotLight(antenna beam is

sliding along theimaged scene) 1mresolution

– Staring SpotLight(antenna steering to a

rotation center insidethe imaged scene) 0.2m resolution

• Interferometric Mode

RISAT-1


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RISAT-1:Imaging Modes of Operation

Risat-1Document Release 3.0 dated 01-Jan 2014

http://nrsc.gov.in/docs/pdf/risat-1.pdf

MRS - Medium Resolution ScanSAR ; FRS- Fine Resolution StripMap;CRS – Coarse Resolution ScanSAR; HRS- High resolution SPOT Light

* Data Products under evaluation


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ScanSAR

ScanSAR data is ideally suited for monitoring

of maritime assets, detection of oil spills,

flood mapping and sea ice, agricultural

mapping, forest mapping

•Also known as “Burst mode” or “Wide Swath

mode”

•Achieves a large swath coverage by periodically

switching the antenna look angle

•Changing Antenna look angle results in have

Multiple Swath•During the look angle transfer, there is no transmit

or receive(off period)

•Allows imaging of a wide swath area at the expense

of azimuth resolution

people.eecs.ku.edu/~callen/826/826_Wurmlinger.ppt


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W i d e S c a n S A R a c q u i s i t i o n o f

t h e G u l f o f B o t h n i a

TerraSAR-X Wide ScanSAR mode provides

an overview of an area of up to 400,000km²

within a single acquisition - anywhere and

independent of weather conditions.

Resolution and Coverage:

Spatial resolution: 40m

Scene size (width x length): 270km

x 200km

Scene length extendable to 1,500km

http: //www.astri um-geo.com/en/5054-discover-terrasar-x-new-imaging-modes

PolSARpro Tutorial; presentation on

01_polarimetric_spaceborne_sensors

Medium Resolution ScanSAR (RISAT 1 Data)


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Medium Resolution ScanSAR (RISAT-1 Data)

Banda

City, UP KenRiver

Yamuna

River

Raibareli

city, UP

Fatehpur

City, UP

Ganga

River

Resolution and

Coverage:

Date: 11-MAR-2013

Incidence Angle: 36.62

Pixel Size: 18 m

Swath: 115 * 115 km

Polarization: HH

InputResolutionAlong

=24m

InputResolutionAcross=18.710m


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Strip Mode

http://geoint2009.crowdvine.com/attachments/0000/5109/Benitz_SAR_Tutorial.pdf

Stripmap modes apply a SAR antenna beam that is alwaysorthogonal to the flight direction

http://geoint2009.crowdvine.com/attachments/0000/5109/Benitz_SAR_Tutorial.pdfhttp://geoint2009.crowdvine.com/attachments/0000/5109/Benitz_SAR_Tutorial.pdf


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Circular Polarization Fine

Resolution Strip MapProducts (CFRS1)

Bhangarh,

Rajasthan

Bandikui City,Rajasthan

Banganga

River,Rajasthan Rail Line

Resolution and

Coverage:

Date: 15-MAR-2013

Spatial resolution: 3*2m

Incidence Angle: 48.706

PixelSpacing:4.5

Scene size: 25*25km

Polarization: RH

RISAT-1 Fine Resolution

StripMap

InputResolutionAlong=13.32

InputResolutionAcross=4.677


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Spot Light

http://geoint2009.crowdvine.com/attachments/0000/5109/Benitz_SAR_Tutorial.pdf

Spotlight-SAR is a mode of SAR operation for obtaining high

resolution by steering the radar beam to keep the target withinthe beam for a longer time and thus form a longer synthetic

aperture.

http://geoint2009.crowdvine.com/attachments/0000/5109/Benitz_SAR_Tutorial.pdfhttp://geoint2009.crowdvine.com/attachments/0000/5109/Benitz_SAR_Tutorial.pdf


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T e r r a S A R - X

S p o t L i g h t a c q u i s i t i o n o

f L i l l e s t r o e m ,

N o r

w a y


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Up to 25cm resolution, scene size

depending on incidence angle, for

example ~ 4km (width) x 3.7km (length) at

60°

The Staring Spotlight mode is

the classical Spotlight mode

with azimuth antenna steering

to a rotation center inside the

imaged scene, i.e. the antenna beam is steered to the scene

center during the complete

datatake.

Staring SpotLight

http://www.eorc.jaxa.jp/ALOS/conf/workshop/jg-sar_ws/s1/01_Moreira.pdf

St i S tLi ht


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T e r r a S A R - X S t a r i n g

S p o t L i g h t a c q u i s i t i o n o f L i l l e s t r o e m , N o r w a y

Staring SpotLight

Up to 25cm

resolution, scenesize depending on

incidence angle,

for example ~ 4km

(width) x 3.7km

(length) at 60°

I t f t i


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Interferometric

Mode

Two SAR images are required

Both the images should be

collected with same SAR

geometry

http://www.lsgi.polyu.edu.hk/geomatics/article/measuring_lar

ge_area_ground_deformations_with_remote_sensing.html

http://www.its.caltech.edu/~ee157

/lecture_note/Interferometry.pdf


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Monostatic Interferometry

Repeat Pass is

used to collect

the data for SAR

interferometric pair


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Bistatic Interferometry

TanDEM-X is the first

bistatic SAR mission, is

formed by adding a second,

almost identical spacecraft, toTerraSAR-X and flying the

two satellites in a closely

controlled formation with

typical distances between 250and 500 m


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Different format of SAR data

• RAW

• SLC

• Multilook

•Geocoded: Terrain Corrected Geo Coded Products

• Polarimetric – Single Polarimetric

– Dual Polarimetric

– Quad-pol – Hybrid Polarimetric

– Stokes format


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SAR Raw DataIn the RAW data, the SAR signal energy

reflected from one single point is spreadalong both azimuth and range direction.Signal Data cannot be viewed as an image

RADARSAT-1

fine beam data

set from the

San Francisco

area


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Single Look Complex SAR Image

SAR image pixel isassociated with a small

area of the Earth’ssurface (called aresolution cell). Each pixel gives a complexnumber that carries

amplitude and phaseinformation about themicrowave field backscattered by all thescatterers (rocks,vegetation, buildingsetc.) within thecorresponding resolutioncell projected on theground. (0.587161,-0.356258)

RADARSAT-2 SLC data for San Francisco area (HH Channel)

SLC D t


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SLC Data

RISAT-2 SLC data (RH Channel)Complex Image

= +

Imaginary Channel

Real Channel


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• Due to the slant-range distortion objects in thenear-range appear compressed relative to far-range. This results in the variation of captured

image scale from near- to far- range. The effect of slant-range distortion is removed by theconversion of slant-range image into the ground-range.

•Multilooking is the process in which square pixelsare generated. The number of looks is determined by the statistics of the images.

Multilook Data


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R A

D A R S A T - 2

I m a g e b e f o r e M u l t i l o o k i n g

R A

D A R S A T - 2

I m a g e a f t e r M u l t i l o o k i n g

Contd …

Azimuth Looks 2Range Looks 1

G d d


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Geocoded Data

Multilooked Terrain

Corrected Geo Coded

SAR intensity images

No need to Georeference

the SAR image

RISAT-1 Geocoded

product in FRS-1 Mode


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Polarimetric

• Single Polarimetric HH/HV/VH/VV

• Dual Polarimetric (Combination of two Polarizations)

• Quad-pol (All the four polarizations)

• Hybrid Polarimetric (Circular transmit and linearreceive)

• Stokes format

Si l P l i t i HH/HV/VH/VV


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Single Polarimetric HH/HV/VH/VV

• Location: India, Port of

Visakhapatnam

• File format: GeoTiff

• Projection: UTM, WGS

84

• Acquisition mode:

SpotLight

• Polarization mode:

Single

• Polarization channel: VV

• Angle of incidence: 41.9

• Date: 12/10/2008

• Look Direction: Right

Terrasar-X High-resolution Spotlight: India, Port of Visakhapatnam


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Dual Polarimetric

FRS-1 VHFRS-1 VV

HH+HV/HH+VV/VV+VH

Q d l


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Quad-polHH+VV+VH+VV

HH HVVV VH

RADARSAT-2 SLC data for San Francisco area


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Scattering Matrix

The scattering matrix is a 2×2 matrix, which

consists of four complex elements, in which the

diagonal elements represent the co-polarized

information while the off-diagonal elementsrepresent the cross-polarized information.

H b id P l i t i


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Hybrid Polarimetric

RISAT-1 CFRS Mode

RHRV

Circular Transmit and Linear Receive (CTLR)

S k F


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Stokes Format

• where S 0, S 1, S 2, S 3 are the four Stokes parameters, E H and E Vare the received horizontal and vertical components of the

electric field vector, Re and Im are the real and imaginary, < >

indicate ensemble averaging.

Ψ is orientation angle and χ is ellipticity

C 1 i i SA


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Chandrayan-1 Mini-SAR data

S 0 S 1 S 2 S 3

Erlanger Crater

St k V t f F ll d P ti ll


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Stokes Vector for Fully and Partially

Polarimetric Data

For a fully polarized plane wave, these Stokes

parameters are related by the identity:

The Stokes vector representation allows for the

description of partially polarized waves where


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2. selection of sar data product for different applications

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