Category: Optical and atmosphere
Optical Imagery
Optical imagery measures reflected sunlight, providing rich spectral information but being sensitive to clouds and illumination.
Also known as: multispectral imagery, passive optical
Expanded definition
Optical sensors record reflected sunlight in visible and infrared wavelengths. This makes optical imagery intuitive to interpret and useful for vegetation monitoring, water mapping, and land cover classification.
Optical observations depend on illumination and atmospheric conditions. Clouds, haze, smoke, and shadows can block or distort measurements. Low sun angles and seasonal lighting changes also influence pixel values.
Because of this, optical workflows often include cloud masking, atmospheric correction, and normalization steps before doing change detection or machine learning.
Related terms
Cloud Mask
A cloud mask labels pixels likely affected by clouds so they can be excluded or handled differently.
Atmospheric Correction
Atmospheric correction removes or reduces atmospheric effects so scenes are more comparable across time and space.
Reflectance
Reflectance is the fraction of incoming light that a surface reflects, commonly used for analysis and comparison.
TOA (Top-of-Atmosphere)
TOA reflectance is reflectance at the top of the atmosphere, before full atmospheric correction to the surface.
Surface Reflectance (BOA)
Surface reflectance estimates what reflectance would be at the ground after removing atmospheric effects.