CROSS-CALIBRATION OF THE ROSETTA NAVIGATION CAMERA

This publication describes the radiometric cross-calibration of NavCam with respect to OSIRIS NAC. We estimated the spectral radiance distribution over the OSIRIS filters by fitting an exponential curve to the average nucleus radiance as obtained by the OSIRIS NAC seven bands. From the OSIRIS spectral distribution we used the NavCam sensitivity curve to determine the average nucleus radiance in NavCam broad-band filter. The ratio between the average nucleus radiance and the average nucleus DN (Digital Number) produced the calibration factor which we needed to convert NavCam DN into radiance. The estimated radiometric factor was (7.14±0.07)x10^(-7) and it is suited for processing images acquired with the attenuation filter (FOC_ATT) and HIGH gain mode. In order to check the results we applied that factor to an extended set of NavCam images and analyzed the average nucleus radiance as a function of the phase angle. We then confirmed the consistence of our method.