Extract Water (Image Analyst Tools)

Summary

Finds water bodies using input synthetic aperture radar (SAR) data and a digital elevation model (DEM).

The tool uses the input radar backscatter to determine whether pixels should be classified as water; then creates polygons for water areas. The tool will also create polygons for areas that are not water, which will be considered land areas.

Illustration

Extract Water tool illustration

Usage

Calibrate the input radar data to gamma nought using the Apply Radiometric Calibration tool. This optimizes delineation and classification, especially in large radar scenes.
The input radar data may not align with the output feature class. If the input radar data is not orthorectified, the tool transforms the Output Feature Class parameter value using the DEM Raster parameter. When no DEM is provided, the tool performs a transformation using an ellipsoidal surface. For optimal transformation of the Output Feature Class parameter value, provide an input DEM for the DEM Raster parameter. The input DEM must be in the WGS84 (EPSG:4326) geographic coordinate system.
This tool can also be used to create water polygons or land polygons for input into other SAR tools, such as Detect Bright Ocean Objects and Detect Dark Ocean Areas.

Label	Explanation	Data type
Input Radar Data	The input radar data.	Raster Dataset; Raster Layer
Output Feature Class	The output polygon feature class that depicts water and land polygons.	Feature Class
Minimum Area (Optional)	The minimum area to extract as a water body. The default value is 50,000 square meters.	Areal Unit
DEM Raster (Optional)	The input DEM. If the input radar data is not orthorectified, this DEM will be used to orthorectify the output result. This DEM will also be used to optimize the polygon construction.	Mosaic Layer; Raster Layer
Apply geoid correction (Optional)	Specifies whether the vertical reference system of the input DEM will be transformed to ellipsoidal height. Most elevation datasets are referenced to sea level orthometric height, so a correction is required in these cases to convert to ellipsoidal height. Checked—A geoid correction will be made to convert orthometric height to ellipsoidal height (based on EGM96 geoid). This is the default. Unchecked—No geoid correction will be made. Use this option only if the DEM is provided in ellipsoidal height.	Boolean

ExtractWater(in_radar_data, out_feature_class, {min_area}, {in_dem_raster}, {geoid})

Name	Explanation	Data type
in_radar_data	The input radar data.	Raster Dataset; Raster Layer
out_feature_class	The output polygon feature class that depicts water and land polygons.	Feature Class
min_area (Optional)	The minimum area to extract as a water body. The default value is 50,000 square meters.	Areal Unit
in_dem_raster (Optional)	The input DEM. If the input radar data is not orthorectified, this DEM will be used to orthorectify the output result. This DEM will also be used to optimize the polygon construction.	Mosaic Layer; Raster Layer
geoid (Optional)	Specifies whether the vertical reference system of the input DEM will be transformed to ellipsoidal height. Most elevation datasets are referenced to sea level orthometric height, so a correction is required in these cases to convert to ellipsoidal height. `GEOID`—A geoid correction will be made to convert orthometric height to ellipsoidal height (based on EGM96 geoid). This is the default. `NONE`—No geoid correction will be made. Use this option only if the DEM is provided in ellipsoidal height.	Boolean

Code sample

ExtractWater example 1 (Python window)

This example extracts water polygons larger than 1 square kilometer.

import arcpy
arcpy.env.workspace = r"C:\Data\SAR"

arcpy.ia.ExtractWater("LowNoise_manifest_CalG0_TNR.crf",
    "LowNoise_manifest_CalG0_TNR_Water.shp", "1 SquareKilometer",
    "dem_COP30_ortho.tif", "GEOID")

ExtractWater example 2 (stand-alone script)

This example extracts water polygons larger than 1 square kilometer.

# Import system modules
import arcpy
from arcpy.ia import *

# Set local variables
in_radar=r"C:\SAR\Low Noise_manifest_CalG0_TNR.crf"
out_radar=r"C:\SAR\Low Noise_manifest_CalG0_TNR_Water.shp"
min_area="1 SquareKilometer"
in_dem_raster=r"C:\DEM\dem_COP30_ortho.tif"
geoid="GEOID"

# Run
arcpy.ia.ExtractWater(in_radar, out_radar, min_area, in_dem_raster, geoid)

Environments

Compression, Current Workspace, NoData, Output CONFIG Keyword, Parallel Processing Factor, Pyramid, Raster Statistics, Resampling Method, Scratch Workspace, Snap Raster, Tile Size

Licensing information

Basic: Requires Image Analyst
Standard: Requires Image Analyst
Advanced: Requires Image Analyst