Comments regarding the NAVCAM calibrations ------------------------------------------ As a part of a comparison of surface properties of comets Wild 2 and Tempel 1, members of the Deep Impact (DI) science team (who are also associated with the PDS Small Bodies Node) examined the NAVCAM calibration, and attempted to reproduce the procedures and the conversion constants that are outlined in the Stardust calibrations. Overall, the DI results were consistent with those used by the Stardust team, with the exception of one constant. This constant is the expected solar flux that should be observed through the optics of the camera. The solar flux that is used by the Stardust team is 168 W/m^2 (as discussed in the calibration document). In an attempt to confirm this value, the DI team took a solar spectrum and computed what the flux should be when combined with the system response profile of the NAVCAM optics. (The optical responses for the camera are included in the table below, which came from the CALIBRPT document in the DOCUMENTS directory.) The result of combining these two curves produces an expected solar flux of 70 W/m^2, which differs from the Stardust result by a factor of 2.4. Because this is such a simple procedure, it is not clear why there is such a large discrepancy between the two determinations. The DI team has attempted to contact Ray Newburn about the discrepancy in this constant, with no success. However, it is important to note that when the constant given in the Stardust calibrations is used, the flux values in the images are more representative of a 4% surface albedo than when the DI constant is used. This indicates that the Stardust results are probably correct as described and the calibrated images presented in this data set have accurate flux levels. It is possible that the DI computations simply did not account properly for the different aspects of the Stardust optical system, and this produces an incorrect measure of the solar flux. NAVCAM System response Wavelen optics CCD QE filter scan mir thruput photon energy nm trans trans ref 400 0.067 0.095 0.00 0.820 0.0000 4.970E-19 425 0.400 0.102 0.00 0.850 0.0000 4.678E-19 450 0.565 0.115 0.00 0.874 0.0000 4.418E-19 475 0.629 0.135 0.40 0.890 0.0302 4.185E-19 500 0.639 0.175 0.72 0.900 0.0725 3.976E-19 525 0.644 0.222 0.91 0.903 0.1175 3.787E-19 550 0.637 0.268 0.92 0.905 0.1421 3.615E-19 575 0.634 0.291 0.93 0.900 0.1544 3.457E-19 600 0.632 0.315 0.93 0.895 0.1657 3.313E-19 625 0.634 0.323 0.92 0.886 0.1669 3.181E-19 650 0.618 0.330 0.92 0.875 0.1642 3.058E-19 675 0.586 0.340 0.89 0.864 0.1532 2.945E-19 700 0.542 0.351 0.90 0.857 0.1467 2.840E-19 725 0.486 0.352 0.86 0.849 0.1249 2.742E-19 750 0.419 0.353 0.96 0.840 0.1193 2.651E-19 775 0.340 0.315 0.92 0.828 0.0816 2.565E-19 800 0.298 0.277 0.95 0.819 0.0642 2.485E-19 825 0.229 0.238 0.95 0.811 0.0420 2.410E-19 850 0.196 0.200 0.76 0.810 0.0241 2.339E-19 875 0.157 0.162 0.74 0.813 0.0153 2.272E-19 900 0.130 0.124 0.74 0.822 0.0098 2.209E-19 925 0.109 0.093 0.36 0.835 0.0030 2.149E-19 950 0.092 0.063 0.00 0.850 0.0000 2.093E-19 975 0.760 0.043 0.00 0.855 0.0000 2.039E-19 1000 0.063 0.022 0.00 0.858 0.0000 1.988E-19