Presentation on theme: "RADAR IMAGERY: RADARSAT-1 J. N. Bruning 2/1/08. Outline General radar history RADARSAT-1 facts Operational overview Responses to various surface."— Presentation transcript:
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 1 st 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.)
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
RADARSAT-1 Facts …continued Olmsted, Coert, Alaska SAR Facility: Scientific SAR User’s Guide, July 1993. 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)
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
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-1 Facts …continued 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 Beam Mode (35 Possibilities)Coverage (km)Spatial Res. (m) ScanSAR Wide (1)500 x 500100 ScanSAR Narrow (2)300 x 30050 Extended Low (1)170 x 17035 Wide (3)150 x 15030 Standard (7)100 x 10025 Extended High (6)75 x 7525 Fine (15)50 x 508 RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
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.
Radar backscatter (detected intensity) is directly related to topography, dielectric properties, and surface roughness RADARSAT Response to Various Surface Features Adapted from: RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C. GREY – speckled DARK - smooth BRIGHT Reflection Type: Image Appearance:
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. MoistureThe 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 Features Anthropogenic features strongly reflect microwave energy back to the SAR sensor and appear as bright point targets. TopographyRadar 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 MTRI road quality study, oil spill monitoring, land cover/land use Moisture Watershed budget studies, wetland monitoring, seasonal change detection for lineaments Land/water boundaries Shipping routes, change detection – drought and flood events Anthropogenic features 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
Imaging of tropical places RADARSAT-1 Uses …example RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C.
RADARSAT-1 Uses …example RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C. Volcanic lithology: Kamchatka Peninsula, Russia
RADARSAT-1 Uses …example RADARSAT International 1996. Radarsat Geology Handbook. Richmond, B.C. Tree-top geology: Indonesia
Oil spill: South Korea RADARSAT-1 Uses …example 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 Image created by J. N. Bruning 10/17/07 Agricultural monitoring: near Lake Nicaragua
SAR Uses … example Surface of Venus, as imaged by the Magellan probe using SAR
Foreshortening Layover Shadowing Radiometric Effects Suppression of Structure Speckle … How to overcome distortions? Distortions Inherent to SAR 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.
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? Distortion Inherent to SAR …Radiometric Effects 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. ASCENDING ORBIT Fusing ascending imagery with descending imagery overcomes lineament suppression zone DESCENDING ORBIT
Definition: Spatially random multiplicative noise due to coherent superposition of multiple backscatter sources within a SAR resolution element Images have grainy appearance Distortion Inherent to SAR …Speckle Image from: www.earth.esa.int
Distortion Inherent to SAR …How to overcome distortions? Select the appropriate image Understand target phenomenology Some distortions enhance certain features Order >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 Requires DEM Radiometric correction option Interpolation options Masking options 2. Geolocation correction Can use DEM Or… use another program ENVI, ERDAS Imagine, ArcGIS 3. Smoothing (?) 4. Fusing with other images/data sets
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