Detect Dark Ocean Areas (Image Analyst Tools)

Summary

Identifies potential dark pixels belonging to oil spills or algae, and clusters these pixels, while masking out the synthetic aperture radar (SAR) data outside the region of interest.

The tool filters clusters using the Minimum Area parameter, and creates the result as a binary raster. A value of 1 corresponds to dark areas detected and is symbolized in a random color. A value of 0 indicates that no dark areas were detected and is symbolized with full transparency.

Both orthorectified and nonorthorectified radar data are valid inputs. Nonorthorectified radar data results in improved azimuth artifact filtering, since the data is in radar coordinates.

Usage

Optimize area detection by calibrating the input radar data to gamma nought using the Apply Radiometric Calibration tool. This is especially effective in larger radar scenes.
To ensure that only areas in the ocean are detected, provide a value for the Mask Features parameter and use the Feature Type parameter to specify whether the mask is water or land. Alternatively, provide a DEM Raster parameter value, and the tool will use the elevation to determine land and water pixels. Either of these methods can be used to create a land mask.

If both the Mask Features and DEM Raster parameter values are provided, the Mask Features parameter will be used to create the mask.

Water and land masks for dark ocean areas are shown.

Label	Explanation	Data type
Input Radar Data	The input radar data.	Raster Dataset; Raster Layer
Output Raster	The output binary raster of the detected dark ocean areas. A value of 1 corresponds to a detected dark area.	Raster Dataset
Minimum Area (Optional)	The minimum area to be detected. The size cannot be negative. The default value is 10000 square meters.	Areal Unit
Mask Features (Optional)	A land or water polygon feature. This polygon will be used to create a mask.	Feature Layer
Feature Type (Optional)	Specifies the type of polygon the Mask Features parameter value represents. This parameter is required if the Mask Features parameter value is provided. Land polygon—The mask input is a land polygon. An inverted mask will be created using this input. Water polygon—The mask input is a water polygon. A mask will be created using this input.	String
DEM Raster (Optional)	The input DEM. If a Mask Features parameter value is provided, this DEM will be used to project it in radar coordinates. If no value is provided for the Mask Features parameter, this DEM will also be used to create a land mask.	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
Mask Tolerance (Optional)	The buffer distance surrounding the mask created from either the Mask Features parameter or the DEM Raster parameter. The distance cannot be negative. The default value is 100 meters.	Linear Unit

DetectDarkOceanAreas(in_radar_data, out_raster, {min_area}, {mask_features}, {feature_type}, {in_dem_raster}, {geoid}, {mask_tolerance})

Name	Explanation	Data type
in_radar_data	The input radar data.	Raster Dataset; Raster Layer
out_raster	The output binary raster of the detected dark ocean areas. A value of 1 corresponds to a detected dark area.	Raster Dataset
min_area (Optional)	The minimum area to be detected. The size cannot be negative. The default value is 10000 square meters.	Areal Unit
mask_features (Optional)	A land or water polygon feature. This polygon will be used to create a mask.	Feature Layer
feature_type (Optional)	Specifies the type of polygon the `mask_features` parameter value represents. This parameter is required if the `mask_features` parameter value is provided. `LAND`—The mask input is a land polygon. An inverted mask will be created using this input. `WATER`—The mask input is a water polygon. A mask will be created using this input.	String
in_dem_raster (Optional)	The input DEM. If a `mask_features` parameter value is provided, this DEM will be used to project it in radar coordinates. If no value is provided for the `mask_features` parameter, this DEM will also be used to create a land mask.	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
mask_tolerance (Optional)	The buffer distance surrounding the mask created from either the `mask_features` parameter or the `in_dem_raster` parameter. The distance cannot be negative. The default value is 100 meters.	Linear Unit

Code sample

DetectDarkOceanAreas example 1 (Python window)

This example detects dark ocean areas using a land mask.

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

out = arcpy.ia.DetectDarkOceanAreas(
    "IW_manifest_CalG0", "20 SquareKilometers", "land_polygons",
    "LAND", "dem_COP30_ortho.tif", "GEOID", "100 Meters")
out.save("IW_manifest_CalG0_Dspk_DDOA.crf")

DetectDarkOceanAreas example 2 (stand-alone script)

This example detects dark ocean areas using a land mask.

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

# Set local variables
arcpy.env.workspace = r"C:\Data\SAR"
in_radar_data="IW_manifest_CalG0"
out_raster="IW_manifest_CalG0_DDOA.crf"
min_area="20 SquareKilometers"
mask_features= "land_polygons"
feature_type="LAND"
in_dem_raster="dem_COP30_ortho.tif"
geoid="GEOID"
mask_tolerance="100 Meters"

# Run
out = arcpy.ia.DetectDarkOceanAreas(
    in_radar_data, out_raster, min_area, mask_features, feature_type,
    in_dem_raster, geoid, mask_tolerance)
out.save(out_raster)

Environments

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

Licensing information