mapping water features from sar imagery
Post on 28-Jan-2018
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BRAMANTIYO MARJUKI
Mapping Water Features From Synthetic Aperture Radar
Data
REMOTE SENSING
SAR PRINCIPLES
Common Things About SAR
MAPPING WATER FEATURES
Prequisities
Download Data From ASF Vertex
Image Processing Workflow
Water Body Extraction
DISCUSSION
Remote Sensing for OSM Project
COMMON THINGS SAR DATA
Image by : ESA
PASSIVE AND ACTIVE REMOTE SENSING
COMMON THINGS SAR DATA
Image by : ESA MICROWAVE SPECTRUM USED
COMMON THINGS SAR DATA
Image by : ESA SAR Satellite and Sensor Timeline
https://vertex.daac.asf.alaska.edu
https://earthexplorer.usgs.gov
https://www.gportal.jaxa.jp/gp/top.html
https://scihub.copernicus.eu/
COMMON THINGS SAR DATA
Image by : ESA
COMMON THINGS SAR DATA
Image by : ESA
Specular Reflection Surface Reflection
COMMON THINGS SAR DATA
Image by : ESA
Double/Multiple Bounce Volume Scattering
COMMON THINGS SAR DATA
Image by : ESA
Foreshortening
Lay Over
Shadow
Radar Geometric Errors
COMMON THINGS SAR DATA
Image by : ESA
Specular Reflection
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Range Scanning along Satellite Swath
Foreshortening
Layover
Shadow
Surface Reflection
COMMON THINGS SAR DATA
Image by : ESA
Double Bounce
Volume Scattering
MAPPING WATER SAR DATA
QGIS + Orfeo Toolbox (advanced Install using OSGEO4W installer)
Prequisities
MAPPING WATER SAR DATA
QGIS (advanced Install using OSGEO4W installer)
MAPPING WATER SAR DATA
Orfeo Toolbox (advanced Install using OSGEO4W installer)
MAPPING WATER SAR DATA
QGIS + Orfeo Toolbox (advanced Install using OSGEO4W installer)
MAPPING WATER SAR DATA
QGIS + Orfeo Toolbox (advanced Install using OSGEO4W installer)
MAPPING WATER SAR DATA
DATA
We going to use ALOS PALSAR Radiometrically Terrain Corrected
(RTC) data freely available to download from Alaska Satellite Facility
(VERTEX)
RTC Product designed to be GIS-ready, so user doesn’t need to
preprocess the raw data which usually takes time and needs deep
knowledge about SAR theories and SAR Processing sequences
MAPPING WATER SAR DATA
DATA https://vertex.daac.asf.alaska.edu/
MAPPING WATER SAR DATA
WORKFLOW (Two Ways of Mapping)
Import Data
Logaritmic Scale Conversion
Speckle Filtering
Histogram Thresholding
Feature Extraction
Output A
Raster to Vector
Output B
Remove Edge Pixels Error
MAPPING WATER SAR DATA
1. Import Data
MAPPING WATER SAR DATA
2. Despeckle
Note that speckle filtering operation will cause improper
displayed (blank) image when it is not stretched. This effect
happens because speckle filtering leaves very negative pixel value
at the edge of the image, and we must fix it at the next step
MAPPING WATER SAR DATA
3. Remove Edge Pixels Error
(‘Layer Name’>-9999) * ’Layer Name’
MAPPING WATER SAR DATA
2. Despeckle
Pre speckle
Post speckle
MAPPING WATER SAR DATA
3. Log Conversion
10* log10 (Layer Name)
MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Plugin Required
Download from Manage and Install Plugins Menu
MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Plugin Settings
ToleranceTolerance is used to understand if 2 blocks of pixels have similar colors. Example: If the user decides to extract a light green field surrounded by dark green trees to a low value of tolerance must be set. Conversely, if a field that has different shades of yellow is selected to be extracted all at once, the tolerance must be set to a high value.
Approximation
determines how many pixels must be merged in order to speed up the process. If approximation is increased you will immidiatly notice that the trasparent white area that follows your cursor is increased. .
Timeout
If a task is taking more than the timeout value (by default 15 seconds), it will be interrupted.
MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Plugin Settings
Set the Raster to multibandMagicwand only working on Multiband Color Render, so if you just have single band raster, just set it up into multiband, but just use same band for every color pane (RGB just use same band)
Layer Properties>Style>multiband rendering
MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Result
Result automatically saved in polygonpost processing like polygon smoothing still needed
Result can be saved directly into Shapefile or other vector data format supported in QGIS
MAPPING WATER SAR DATA
4.B Histogram Tresholding
Layer Properties >
Histogram
Histogram will have bimodal patterntwo peak of frequency cumulative, the lower peak usually related to accumulation of water related pixel values
MAPPING WATER SAR DATA
4.B Histogram Tresholding
By zooming into the histogram, we could identify the border value of water and land
Which is -15,5
MAPPING WATER SAR DATA
4.B Histogram Tresholding
Return to STYLE Tab, change the color render to singleband pseudocolor, interpolation to discrete, mode to equal interval, and make just two classes
Change the value of first class to -15,5
MAPPING WATER SAR DATA
4.B Histogram Tresholding Result
MAPPING WATER SAR DATA
4.B Histogram Tresholding (make it Permanent)
‘Layer Name’ <= -15.5
MAPPING WATER SAR DATA
4.B Histogram Tresholding (raster to vector)
MAPPING WATER SAR DATA
4.B Histogram Tresholding
Result
Result automatically saved in polygonpost processing like polygon smoothing and cleaning also still needed
Result can be saved directly into Shapefile or other vector data format supported in QGIS
Terima Kasih
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