2.1 Radiometric corrections
Comparisons of imagery obtained from multiple acquisition dates
And /or sensor types require radiometric calibration, as spectral information and vegetation indices such as the NDVI (see Section 2.5) are explained by, among several other factors, differences in sensor calibration settings.
2.2 Atmospheric corrections
While radiometric and geometric corrections allow for a more direct comparison of spectral information obtained from multiple sources and dates of remotely sensed imagery, spatial differences in atmospheric conditions between images acquired on different dates can influence spectral reflectance values and vegetation indices such as NDVI.