79 
et al., 1992 and Reagan et al„ 1992) and Dobson UV channel pair for ozone retrieval is performed in much 
the same way. This method is typically used for the mountain top langleys for absolute calibration. 
An automatic calibration is also made on all langley data with aerosol optical thicknesses less than 
0.1 at 670 nm. An iterative algorithm computes the regression and drops all local minimums more than 
10% below the regression. The iteration continues until no more local minimums are identified. The 
resultant Vo is then stored into a file and plots them as a time dependence for that instrument. Note that 
these data are noisy and are used only for identifying trends in the calibration decay between absolute 
mountain top calibrations. 
A second approach ratios various spectral combinations of the langley data sets and plotted as 
regular langleys (Forgan, 1993). This approach is applicable for higher optical thickness conditions. Only 
minimal triplet screening is required to eliminate cloud conditions. The Vos are computed, archived and 
plotted against time. Again this is used as a trend indicator between absolute mountain top calibrations. 
The advantage over the previous method is the significantly greater number of points available for trend 
analysis. 
Intercomparison of automatic instruments is easily accomplished by a routine that searches a 
specified portion of the data base. Having met criteria for a space and time match, sun and sky data are 
automatically inter compared and a table of old and new calibration coefficients is generated. Aureole 
corrected langley plots analysis (Nakajima, 1986) has not been implemented at this writing. 
3.2.2. Time Dependence. The time dependence window serves as the access point for all other 
windows. The aerosol optical thickness, precipitable water, wavelength exponent and calibration trends as 
well as the status indicators may be plotted as a function of time in this window. For a particular 
instrument and location, all or part of the data may be displayed by interactive cursor subsetting. For 
example the dry season data (June to October) from Cuiaba Brazil clearly shows the increase in aerosol 
optical thickness as the burning season commences in August (Figure 1). Subsetting to one day of data 
brings new features to the screen (Figure 2). The GMT time scale in hours is displayed, a color scale of 
local time is drawn, mean 15 min. sun observations are plotted and almucantar (triangles) principle plane 
(squares) and successful inversions (circles and x's) are shown under the time scale. A hatched line above 
the time scale indicates langley data and green vertical bars inside the plot indicate that the wet sensor has 
been activated and no sun data are available. Individual points may be de selected in this window. 
IMOY lJUN IJUL IflUG ISEP I0CT iNOV IDEC IJPIN IFEB 
11994 
Figure 1, The aerosol optical thickness dry season record showing the increase 
in aerosols in August due to regional burning.