Atmospheric correction for airborne sensors: Comment on a scheme used for CASI

In a recent work by Gould and Arnone [Remote Sens. Environ. 61 (1997) 290] the compact airborne spectrographic imager (CASI) was used to map the absorption and scattering properties of a coastal environment. The methodology used in this work is also cited in a number of more recent studies. The authors found large discrepancies between the parameters estimated from measurements (AC9) and from a bio-optical model by Carder et al. [J. Geophys. Res. 104 (1999) 5403]. As a result, they adjusted the backscattering efficiency parameter of the model. We found, however, that the discrepancies may actually be due, at least in part, to an erroneous atmospheric correction used for the airborne data. Because the removal of the surface-reflected sky radiance was neglected, the estimated water-leaving radiance was erroneously augmented and used as the input of the bio-optical model. This caused a scattering overestimate and an absorption underestimate. It is suggested that the surface reflection, unlike for land applications, should always be removed to obtain the water signal for use with such bio-optical models.