mapping water features using radar SAR imagery, example using ALOS PALSAR RTC Product, free download at ASF VERTEX

1. BRAMANTIYO MARJUKI
Mapping Water Features From
Synthetic Aperture Radar
Data
REMOTE SENSING

2. 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

3. COMMON THINGS SAR DATA
Image by : ESA
PASSIVE AND ACTIVE REMOTE SENSING

4. COMMON THINGS SAR DATA
Image by : ESA MICROWAVE SPECTRUM USED

5. 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/

6. COMMON THINGS SAR DATA
Image by : ESA

7. COMMON THINGS SAR DATA
Image by : ESA
Specular Reflection Surface Reflection

8. COMMON THINGS SAR DATA
Image by : ESA
Double/Multiple Bounce Volume Scattering

9. COMMON THINGS SAR DATA
Image by : ESA
Foreshortening
Lay Over
Shadow
Radar Geometric Errors

10. COMMON THINGS SAR DATA
Image by : ESA
Specular
Reflection
AzimuthScanning
alongSatelliteOrbit
Range Scanning along
Satellite Swath
Foreshortening
Layover
Shadow
Surface
Reflection

11. COMMON THINGS SAR DATA
Image by : ESA
Double Bounce
Volume
Scattering

12. MAPPING WATER SAR DATA
QGIS + Orfeo Toolbox (advanced Install using OSGEO4W installer)
Prequisities

13. MAPPING WATER SAR DATA
QGIS (advanced Install using OSGEO4W installer)

14. MAPPING WATER SAR DATA
Orfeo Toolbox (advanced Install using OSGEO4W installer)

15. MAPPING WATER SAR DATA
QGIS + Orfeo Toolbox (advanced Install using OSGEO4W installer)

16. MAPPING WATER SAR DATA
QGIS + Orfeo Toolbox (advanced Install using OSGEO4W installer)

17. 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

18. MAPPING WATER SAR DATA
DATA https://vertex.daac.asf.alaska.edu/

19. 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

20. MAPPING WATER SAR DATA
1. Import Data

21. 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

22. MAPPING WATER SAR DATA
3. Remove Edge Pixels Error
(‘Layer Name’>-9999) * ’Layer Name’

23. MAPPING WATER SAR DATA
2. Despeckle
Pre speckle
Post speckle

24. MAPPING WATER SAR DATA
3. Log Conversion
10* log10 (Layer Name)

25. MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Plugin Required
Download from
Manage and
Install Plugins
Menu

26. MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Plugin Settings
Tolerance
Tolerance 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.

27. MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Plugin Settings
Set the Raster to multiband
Magicwand 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

28. MAPPING WATER SAR DATA
4.A Feature Extraction
MagicWand Result
Result automatically saved
in polygon
post processing like polygon
smoothing still needed
Result can be saved directly
into Shapefile or other vector
data format supported in QGIS

29. MAPPING WATER SAR DATA
4.B Histogram Tresholding
Layer Properties >
Histogram
Histogram will have
bimodal pattern
two peak of frequency cumulative,
the lower peak usually related to
accumulation of water related pixel
values

30. 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

31. 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

32. MAPPING WATER SAR DATA
4.B Histogram Tresholding Result

33. MAPPING WATER SAR DATA
4.B Histogram Tresholding (make it Permanent)
‘Layer Name’ <= -15.5

34. MAPPING WATER SAR DATA
4.B Histogram Tresholding (raster to vector)

35. MAPPING WATER SAR DATA
4.B Histogram Tresholding
Result
Result automatically saved
in polygon
post processing like polygon
smoothing and cleaning also still
needed
Result can be saved directly
into Shapefile or other vector
data format supported in QGIS

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