must be constant through the whole scene
- ILS correction of airborne flight lines must be applied
- the main reason is that the incident sun light can vary by several percents from start to end of an airborne flight line as the sun height varies
- another reason is to correct for transient sun light variations
- this artifact is wavelength-dependent
- Removal of limb brightening must be applied
- the reason is that the path length increases markedly from vertical viewing to oblique viewing across the flight line
- Atmospheric path radiance must be homogeneous
- areas affected by haze must be masked out, or "deglinted"
- if at all possible, areas affected by clouds and their shadows must be masked out.
- atmospheric adjacency effect must be corrected for, if at all possible, but "deglinting" often achieves a good correction.
Optically deep waters must be available in the image
- Cyanobacteria tend to move up towards more light in the evening, and then to move down in the morning as illumination becomes too harsh.
- This also depends on wind conditions.
- Passive RS images are taken at a time when solar illumination is maximum.
- This might be the cause of weird results in many atolls like Fakarava and Tarawa
Sun glints (sea surface clutter) must be totally removed
- Best is to discard images or areas which are too badly affected by sun glint
- Sun glint and Skyglint can have distinctly different spectral properties
- sunglint has the spectral properties of direct sun light, i.e. biased towards the yellow region of the solar spectrum
- skyglint has the spectral properties of the sky light, i.e. usually biased towards the blue region of the solar spectrum for a clear blue sky
- Best deglinting is achieved when the atmosphere is hazy,
- as this strengthens the correlations among bands from NIR through BLUE regions (Mie scattering).
should have been achieved by the nearest neighbor algorithm
Optical properties of water bodies