Introduction to SAR Ocean Detection

Synthetic Aperture Radar (SAR) from Sentinel-1 provides all-weather, day-and-night capability for detecting objects at sea, making it ideal for maritime monitoring applications.

Sentinel-1 SAR Features for Ocean Detection

Polarization Modes

  • VV (Vertical-Vertical)
  • VH (Vertical-Horizontal)
  • HH (Horizontal-Horizontal)
  • HV (Horizontal-Vertical)

Different polarizations provide varying sensitivity to different types of objects.

Acquisition Modes

  • Interferometric Wide Swath (IW)
  • Extra Wide Swath (EW)
  • Wave Mode (WV)
  • Stripmap (SM)

Different modes offer varying coverage and resolution options.

ESA SNAP Processing Guide

1. Data Download and Import

Tool: SNAP Desktop

Steps:

  1. Download Sentinel-1 data from Copernicus Open Access Hub
  2. Open SNAP Desktop
  3. Use File > Import > Optical > Sentinel-1
  4. Select the downloaded product

2. Pre-processing

Tools: Radiometric Calibration, Speckle Filtering

Steps:

  1. Apply Radiometric Calibration (Radiometric > Calibrate)
  2. Apply Speckle Filtering (Radar > Speckle Filtering)
  3. Select appropriate filter (e.g., Lee Sigma)
  4. Set filter parameters

3. Land Masking

Tool: Land/Sea Mask

Steps:

  1. Open Land/Sea Mask tool (Raster > Mask)
  2. Select appropriate mask source
  3. Apply mask to remove land areas

4. Object Detection

Tools: Thresholding, Connected Components

Steps:

  1. Apply threshold to identify potential objects
  2. Use Connected Components to identify individual objects
  3. Filter based on size and shape
  4. Export detected objects as vector layer

5. Post-processing

Tools: Classification, Export

Steps:

  1. Classify detected objects (e.g., ships, icebergs)
  2. Calculate object properties (size, orientation)
  3. Export results in desired format

Best Practices

Data Selection

  • Acquisition Mode

    Choose IW mode for general ocean monitoring

  • Polarization

    Use VV for ship detection, VH for iceberg detection

  • Incidence Angle

    Consider angle effects on backscatter

Processing Tips

  • Speckle Filtering

    Balance between noise reduction and detail preservation

  • Threshold Selection

    Adjust based on sea state and target size

  • Validation

    Compare with AIS data or optical imagery when available