I am not sure what you mean by the 'extension of the adjacenty effect'. The FLAASH help describes this setting: Click the Use Adjacency Correction toggle button to specify whether or not to use adjacency correction. Unlike most atmospheric correction models, the FLAASH model accounts for both the radiance that is reflected from the surface that travels directly into the sensor and the radiance from the surface that is scattered by the atmosphere into the sensor. The distinction between the two accounts for the adjacency effect (spatial mixing of radiance among nearby pixels) caused by atmospheric scattering. More accurate reflectance. The ratio of radiant energy reflected by a body to the energy incident on it, usually denoted as a percentage. retrievals result when adjacency correction is enabled; however, there may be occasions when it is desirable to ignore this effect. Turning adjacency correction off sets ρe = ρ in Equation (1). The pixel size you specify in the help does affect this setting.

Hi MariM, Adjacency effect is more o less the contribution of other pixels in ground to the radiance measured around the pixel of interest. So, my question is, which is the maximum distance that one pixel can be to influence the pixel of interest. For example, in some software you can set maximum of 200 pixels. Or adjacency effect in FLAASH only accounts to atmospheric diffuse reflectance? I mean, photons without ground contact. Regards! Laura

The documentation for "The FLAASH model" discusses this: "Spatial averaging is performed using a point-spread function that describes the relative contributions to the pixel radiance from points on the ground at different distances from the direct line of sight."