APPLICATION OF THE LANGLEY PLOT METHOD TO THE CALIBRATION OF THE SOLAR BACKSCATTERED ULTRAVIOLET INSTRUMENT ON THE NIMBUS-7 SATELLITE

The concept of the well-known Langley plot technique, used for the cal ibration of ground-based instruments, has been generalized for applica tion to satellite instruments. In polar regions, near summer solstice, the solar backscattered ultraviolet (SBUV) instrument on the Nimbus 7 satellite samples the same ozone field at widely different solar zeni th angles. These measurements are compared to assess the long-term dri ft in the instrument calibration. Although the technique provides only a relative wavelength-to-wavelength calibration, it can be combined w ith existing techniques to determine the drift of the instrument at an y wavelength. Using this technique, we have generated a 12-year data s et of ozone vertical profiles from SBUV with an estimated accuracy of +/-5% at 1 mbar and +/-2% at 10 mbar (95% confidence) over 12 years. S ince the method is insensitive to true changes in the atmospheric ozon e profile, it can also be used to compare the calibrations of similar SBUV instruments launched without temporal overlap.