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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