RADAR IMAGERY:
RADARSAT-1
J. N. Bruning
2/1/08
Outline


General radar history
RADARSAT-1 facts
 Operational



overview
Responses to various surface features
Uses and Examples
Distortions inherent to radar
 How
to overcome/work with these distortions
 What to order?


Processing flow
Radar resources
Satellite RADAR History





Pulsar – ALOS
LIDAR
ERS-1, ERS-2, Envisat
JERS-1
RADARSAT-1
November 4, 1995 by Canadian Government & NASA
 Canada’s 1st Earth observing satellite


Surveillance of Canada’s Arctic and other coastal areas



Shipping routes and natural resources
Radar uninhibited by weather conditions and darkness
RADARSAT-2 launched Dec. 2007, operational spring 2008

Ultra-fine beam mode (3m spatial res.)
RADARSAT-1 Facts

Active sensor (all radar sensors)

Transmit microwave pulses to earth surface, measures amount of energy
that bounces back



Pixel values (intensities) represent ability of target to backscatter (reflect)
pulses: 0-255 digital number
Ability to collect data day or night
One-channel image (RADARSAT-1)

Single microwave frequency (5.3 GHz)
 C-Band, 5.6 cm wavelength

Ability to collect data regardless of atmospheric conditions
Horizontal Polarization (HH)
Combine with multi-date and/or multi-sensor images



Change detection, composite images
RADARSAT-1 Facts …continued
Optical:
Radar:
Landsat
Visible
Adapted from: RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT
ASTER
RADARSAT-1 Facts …continued
SAR:
Synthetic

(space craft motion and
advanced signal process
simulate a larger antenna)
Aperture
(antenna length)
Radar
(Radio Detection and
Ranging, sending out rapid
microwave pulses)
Olmsted, Coert, Alaska SAR Facility: Scientific SAR User’s Guide, July 1993.
RADARSAT-1 Facts …continued

Four technological principles (Coert Olmsted, Scientific SAR User’s Guide, 1993.)
 Antenna
emits EM pulse in a precise direction
 Sensor detects, also with directional precision, the
greatly attenuated echo scattered from a target
 Measure the time delay between emission and
detection
 Scanning directional beam to examine large areas
 Fifth
– spectral analysis of phase controlled signals
RADARSAT-1 Facts …continued

Orbit



Sun synchronous, circles earth 14
times/day, 24 day orbit path repeat
Controls the orientation of the radar
beams with respect to surface features
Stereo-pairs (anaglyphs) and create
DEMs
RADARSAT International
1996. Radarsat Geology
Handbook. Richmond, B.C.
RADARSAT-1 Facts …continued

Image Product Options: 35 possibilities

Positions – cross-track viewing incidence angles 10° - 60°
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT-1 Facts …continued

Temporal resolution



24 day orbit path repeat cycle
With RADARSAT’s suite of beam modes, images can
be acquired for a location every one (high latitudes)
to five (low latitudes) days
Spatial coverage depends on beam mode
RADARSAT International 1996. Radarsat
Geology Handbook. Richmond, B.C.
Beam Mode (35 Possibilities)
Coverage (km) Spatial Res. (m)
ScanSAR Wide (1)
500 x 500
100
ScanSAR Narrow (2)
300 x 300
50
Extended Low (1)
170 x 170
35
Wide (3)
150 x 150
30
Standard (7)
100 x 100
25
Extended High (6)
75 x 75
25
Fine (15)
50 x 50
8
RADARSAT-1 Facts …continued

Data
Transmitted to a local network station, or
 Recorded on board tape recorders and later down linked to
Canadian network station

RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT Response to Various
Surface Features

Radar backscatter (detected intensity) is directly related to
topography, dielectric properties, and surface roughness
Reflection Type:
Image
Appearance:
GREY – speckled
DARK - smooth
Adapted from: RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
BRIGHT
RADARSAT Response to Various
Surface Features
Surface
Roughness
The amount of energy returned is strongly influenced by surface roughness.
RADARSAT can distinguish textural differences created by forest clear-cuts,
agricultural tillage, and crop practices.
Moisture
The amount of moisture in soil or on vegetation affects the amount of SAR
backscatter. Variable moisture levels are represented as tonal variations in
the image.
Land/Water
Boundaries
Smooth water surfaces tend to reflect microwave energy away from the
satellite sensor. Land surfaces tend to be rougher and reflect more energy
back to the satellite. This results in a sharp contrast between land/water
boundaries.
Anthropogenic Anthropogenic features strongly reflect microwave energy back to the SAR
Features
sensor and appear as bright point targets.
Topography
Radar backscatter is greater for slopes facing the radar sensor and less for
slopes facing away from the sensor. This creates a “shaded relief” image
from which geological and geomorphological information can be derived.
Adapted from: RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT-1 Uses

Surface roughness


Moisture


Shipping routes, change detection – drought and flood events
Anthropogenic features


Watershed budget studies, wetland monitoring, seasonal change detection for
lineaments
Land/water boundaries


MTRI road quality study, oil spill monitoring, land cover/land use
Land cover/land use , change detection – agricultural studies
Topography

Geological mapping (including structural information), surface drainage pattern
detection

Two images with different look angles or pass directions can be fused to create
DEMs
RADARSAT-1 Uses …example

Imaging of tropical places
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT-1 Uses …example

Geological mapping: NNW Canada
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT-1 Uses …example

Volcanic lithology: Kamchatka Peninsula, Russia
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT-1 Uses …example

Tree-top geology: Indonesia
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT-1 Uses …example

Oil spill: South Korea
http://earthobservatory.nasa.gov/NaturalHazards/Archive/Dec2007/SouthKorea_ASA_2007345_lrg.jpg
RADARSAT-1 Uses …example

Water resource management: near Boaco, Nicaragua
Image created by J. N. Bruning 10/15/07
RADARSAT-1 Uses …example

Agricultural monitoring: near Lake Nicaragua
Image created by J. N. Bruning 10/17/07
SAR Uses … example

Surface of Venus, as imaged by the Magellan
probe using SAR
Distortions Inherent to SAR

Foreshortening
Layover
Shadowing
Radiometric Effects
Suppression of Structure
Speckle

… How to overcome distortions?





RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
Distortion Inherent to SAR
…Foreshortening

Foreshortening
 The
slant range distance
(1) is smaller than the
actual ground distance (2)
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
Distortion Inherent to SAR
…Layover

Layover
 The
top of the mountain
(B) is viewed before the
bottom of the mountain (A)
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
Distortion Inherent to SAR
…Shadowing

Shadowing
 The
shadow area is not
imaged
RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
Distortion Inherent to SAR
…Radiometric Effects

Sensor-facing slopes are
bright and the leeward
slopes are dark, despite
the valley having
symmetrical slopes and
similar land cover
 Which
way was the sensor
looking?
 Which way was the sensor
traveling?
Adapted from: RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
Distortion Inherent to SAR
…Suppression of Structure

Adapted from: RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
Fusing ascending
imagery with
descending imagery
overcomes lineament
suppression zone
Distortion Inherent to SAR
…Speckle


Definition: Spatially random multiplicative noise due
to coherent superposition of multiple backscatter
sources within a SAR resolution element
Images have grainy appearance
Image from: www.earth.esa.int
Distortion Inherent to SAR …How to
overcome distortions?

Select the appropriate image
 Understand
 Some
 Order

target phenomenology
distortions enhance certain features
>1 image
Processing methods
 Terrain
correction
 Smoothing for speckle reduction
 Multi-date/multi-sensor stacks
 Ascending and descending pair stacks
 … Trial and error
What to order? … continued

Beam modes
 Size
of study area
 At
what scale will your observations be made?
 Mosaic of several images – same look direction
 Type
of features to detect
 Sensitivity
to incidence angle – terrain conditions
 Alignment of features
 Stereo imagery
 Temporal coverage
 Scale of features
 Often
limited by available data for a study location
Processing flow


L0 data - ?
L1 data

ASF convert tool – free download from ASF web site
1.
Terrain correction




2.
Geolocation correction


3.
4.
Requires DEM
Radiometric correction option
Interpolation options
Masking options
Can use DEM
Or… use another program
 ENVI, ERDAS Imagine, ArcGIS
Smoothing (?)
Fusing with other images/data sets
Processing flow … continued

EXAMPLE: Cook Inlet, Alaska RADARSAT (Standard
beam mode, descending orbit)
1. Original Image
2. Terrain Corrected
Adapted from: ASF Convert Manual, pg. 40 – 43.
3. Terrain Corrected &
Geolocation Corrected
Radar Resources

Alaska Satellite Facility
 http://www.asf.alaska.edu/index.html
 Free
JERS-1 mosaics
 SAR FAQ
 Data credit grants (NASA) = free data
 Convert Tool – free SAR data processor
RADARSAT International 1996. RADARSAT
Geology Handbook. Richmond, B.C.
 CROSS

 https://cross.restec.or.jp/cross/CfcLogin.do?locale=en
ASTER
RADARSAT
Questions?
Spectral Resolution



RADARSAT-1 SAR: C-Band, 5.6 cm wavelength
ASTER: 14 Bands (in 3 packages)
QuickBird: 4 Bands