TES Calibration Update

Space View Starting on OCK 12581, the normal MGS mapping orientation was rotated 16 degrees as a fuel saving measure. As a result, TES could no longer use the -90 pointing angle for the space view used for calibration because a portion of Mars could find its way into the field of view (FOV). With this spacecraft orientation change, the space view was switched to a +74 pointing angle, which would ensure that Mars would not enter into the TES FOV for the space calibration observations. Unfortunately, the TES pointing mirror is only designed to clear the shroud from pointing angles of -90 to +70. Observations that stepped the mirror at 1 degree intervals confirm that all 6 detectors from the spectrometer do not experience vignetting to a pointing angle of no more than +72. At the pointing angle of +74 used for TES OCKS 1258126794, TES detectors 3 and 6 detect an additional 4.5 x 10 and 2 x 10 W cm sr cm respectively between 400 and 800 cm (Figure 1). This effect is less for detectors 2 and 5 (1 x 10 W cm sr cm) and is not detected in TES detectors 1 and 4. There does not appear to be any effect on the TES visible and thermal bolometers. The result is an apparent negative radiance for cold temperature observations, such as space, polar caps, and the Martian atmosphere. The magnitude of this error on the calibrated radiance data is dependent on the wavenumber and magnitude of radiance of the target. The largest errors are near 600 cm and for cold targets. Polar/nighttime surface temperature determination and atmospheric temperature retrievals are significantly affected and warm surface temperature atmospheric opacity retrievals and spectroscopy are not affected in a significant manner. There are several reasons for this, including the magnitude of the error diminishes with increasing signal, the relative proportion of the error is smaller with increasing signal, and radiance is a power function of temperature. Temperature errors at 667 cm for an average of all 6 detectors are -3 K, -4 K, and -8 K for 200, 180, and 150 K temperatures respectively. At 250-450 cm these errors are somewhat lower; -2 to -4 K.