Radiometric correction of hemispherical images

Light scattering in fore-optics of imaging radiometric instruments degrades images, the signal of dark pixels is enhanced and that of bright pixels is reduced. A procedure of restoring hemispherical images obtained with a hemispheric view CCD-radiometer is suggested. The circular hemispheric image is projected onto the sphere and Wiener filtering on the sphere is performed. For building the Wiener filter the point spread function of the instrument was measured in the laboratory, and test images of (partially) controlled radiance were measured. The procedure is applied for the correction of hemispherical radiometric images taken under forest canopy. In non-corrected near infrared images the signal of sky pixels in forest canopy gaps near zenith is enhanced 1.4–2.0 times. The applied correction reduces this error to the level of 1.1–1.2. In the red channel these figures are 0.8–0.9 and 0.97–0.99, respectively.