Detect Dark Ocean Areas (Image Analyst)

Available with Image Analyst license.

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 parameters values are provided, the Mask Features parameter will be used to create the mask.

    Detect Dark Ocean Areas tool illustration
    Water and land masks for dark ocean areas are shown.

Parameters

LabelExplanationData 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 is specified.

  • Land polygonThe mask input is a land polygon. An inverted mask will be created using this input.
  • Water polygonThe mask input is a water polygon. A mask will be created using this input.
String
DEM Raster
(Optional)

The input DEM.

If the input radar data is not orthorectified, this DEM will be used to orthorectify it.

If the Mask Features parameter value is not provided, 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})
NameExplanationData 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 is specified.

  • LANDThe mask input is a land polygon. An inverted mask will be created using this input.
  • WATERThe mask input is a water polygon. A mask will be created using this input.
String
in_dem_raster
(Optional)

The input DEM.

If the input radar data is not orthorectified, this DEM will be used to orthorectify it.

If the mask_features parameter value is not provided, 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.

  • GEOIDA geoid correction will be made to convert orthometric height to ellipsoidal height (based on EGM96 geoid). This is the default.
  • NONENo 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 and check out ArcGIS Image Analyst extension license
import arcpy
arcpy.CheckOutExtension("ImageAnalyst")
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"

# Execute  
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)

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