NDWI
Enhances water using Green and NIR.
NDWI = (Green − NIR)/(Green + NIR)
Best used when: NIR provides a strong water/land contrast.
Shoreline Extraction
Extract a land–water boundary from optical imagery using a water index, thresholding, mask cleanup, and optional edge refinement.
Remote Sensing CoreEnd-User DocumentationTheory + Formula + Parameters1. What This Feature Does
Extract a land–water boundary from optical imagery using a water index, thresholding, mask cleanup, and optional edge refinement.
Cloud workflow: choose data → configure the scientific method → run → review the resulting layer/report. No programming is required.
2. Recommended Workflow
Choose NDWI or MNDWI and map the required bands.
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Choose Otsu or a manual water threshold.
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Choose which side of the threshold represents water.
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Clean the water mask.
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Optionally refine the boundary with Canny or Sobel.
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Review the shoreline geometry against the source image.
3. Theory, Methods & Equations
MNDWI
Uses SWIR instead of NIR and can suppress built-up/soil responses in many settings.
MNDWI = (Green − SWIR)/(Green + SWIR)
Best used when: urban/coastal backgrounds interfere with NDWI.
Otsu Threshold
Automatically selects a split that maximizes between-class variance.
σB²(t)=w0(t)w1(t)[μ0(t)−μ1(t)]²
Best used when: the index histogram shows a useful water/non-water separation.
Manual Threshold
Uses an analyst-defined threshold.
Water = 1 if Index ≥ T (or ≤ T, depending on Water Side)
Best used when: local knowledge or a validated threshold is available.
Canny / Sobel Refinement
Uses image gradients to support a sharper boundary near the threshold-derived water mask.
G = √(Gx²+Gy²)
Best used when: the optical boundary is visually distinct but the mask edge is coarse.
4. Input Data
| Input | Type | Requirement | Description |
|---|---|---|---|
| Input Raster | raster | Required | Multispectral raster used to separate water and land. |
5. Parameters Available in the Application
| Parameter | Default | Choices / Range | How to Use It |
|---|---|---|---|
| Water Index Method | mndwi | MNDWI — Green & SWIR, NDWI — Green & NIR | |
| Green Band | — | — | |
| NIR Band | — | — | Shown for: ndwi |
| SWIR Band | — | — | Shown for: mndwi |
| Water Threshold | otsu | Auto — Otsu, Manual | |
| Manual Index Threshold | 0.0 | -1.0 to 1.0 | Shown for: manual |
| Water Is | greater | Index >= threshold, Index <= threshold | NDWI/MNDWI usually classify water on the greater-than side, but the option is exposed for unusual sensors or preprocessing. |
| Minimum Water Area (pixels) | 100 | 0 to 10000000 | |
| Maximum Water Hole Area (pixels) | 100 | 0 to 10000000 | Fill small holes inside water regions before shoreline extraction. |
| Boundary Refinement | none | Water Mask Boundary — recommended, Canny Edge Assisted, Sobel Edge Assisted | The shoreline always follows the water-mask boundary. Edge-assisted modes snap boundary pixels toward strong image-index edges. |
| Edge Gaussian Sigma | 1.0 | 0.0 to 10.0 | Shown for: canny, sobel |
| Edge Snap Distance (pixels) | 2 | 1 to 20 | Shown for: canny, sobel |
| Minimum Shoreline Length (pixels) | 10.0 | 0.0 to 1000000.0 | |
| Simplify Tolerance (pixels) | 0.5 | 0.0 to 100.0 |
6. Output & Interpretation
The result should be interpreted according to the selected method and the physical meaning of the input data. Preserve source units, coordinate reference information, NoData meaning, acquisition date, and preprocessing level when comparing results.
Scientific interpretation: an algorithm can produce a numerically valid result even when the input data are unsuitable. Always check masks, units, sensor characteristics, spatial resolution and reference data.
7. Best Practices
- Use analysis-ready inputs and remove invalid/cloud/noise artifacts that are not part of the target phenomenon.
- Choose parameters from the physical scale of the data, not only from visual appearance.
- Keep categorical and continuous rasters conceptually separate when selecting interpolation/resampling methods.
- Compare the result with the source image and independent reference information.
- Document the settings used when results will be compared across dates, sensors or study areas.