Multispectral Pixel Saturation Mask¶
Last updated: October 7, 2021
Example imagery¶
This example shows a visual (RGB) WorldView-2 image, taken over Valais Canton, Southern Switzerland. The image on the left is the ARD tile. The image on the right shows the saturated pixels, highlighted in red.
Left: ARD image of snow-covered mountains. Right: pixel saturation mask overlaid on the ARD image.
Overview¶
Highly reflective features such as cloud tops, snow/ice cover, and bright rooftops can overwhelm sensor detectors beyond their capability to register an accurate charge. This is referred to as a saturation state. Pixels determined to be saturated are captured within the multispectral pixel saturation mask.
Pixel saturation is detected in 4 or 8 band multispectral images. Saturation is detected in the multispectral imagery at native resolution (as-collected GSD).
An ARD order delivery includes a raster GeoTiff mask and a vector GeoPackage mask. The vector mask is derived from the raster mask.
| Mask title | File name | File type | Description |
|---|---|---|---|
| Multispectral Pixel Saturation Mask | {acquisitionID}-ms-saturation.tif | Raster | Detects saturated pixels in multispectral images. |
| MS Pixel Saturation Polygons | {acquisitionID}-ms-saturation-mask.gpkg | Vector | Traces the boundaries of saturated pixels. |
How to read the mask data¶
The mask is binary with 1 (True) indicating the presence of saturated pixels and 0 (False) indicated no pixel saturation detected.
Classification/Detection¶
Pixel saturation is identified by pre-determined thresholds in the RGB bands where they are known to start to saturate. Saturation can affect each band separately; it does not have to be bright across all bands (i.e., white in color) to saturate a multispectral sensor.
Use case examples¶
Saturated pixels do not provide an accurate reading of surface reflectance. These pixels should be excluded from further user-based analyses that require accurate reflectance values. This mask provides the ARD data user a convenient tool for excluding such pixels.
Known issues¶
The multispectral saturation mask is not intended for use with panchromatic single-band imagery.