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These airmass calculations are imbedded within the "equation of time" computations.
A second path-lengthening factor, M2, is also calculated. This airmass corresponds to a layer
height of 22 km.
COMPUTING SINGLE AND DOUBLE RATIOS
At this point the count rates Fi have been corrected and compensated for deadtime, temperature,
and (if applicable) Rayleigh scattering. Four sets of single ratios are formed (recall that these count
rates are in logarithm units, hence a "ratio" is formed by computing the difference):
MS
F
F
←
−
4
5
2
MS
F
F
←
−
5
5
3
MS
F
F
←
−
6
5
4
MS
F
F
←
−
7
6
5
Only the shortest of the five observation wavelengths (306.3 nm, count rate F( 2 )) is significantly
affected by SO
column amounts, so ratios MS( 5) , MS( 6 ), MS( 7 ) will be largely independent of
2
SO
effects.
2
Two higher-order ratios are formed:
MS
MS
3
←
−
8
4
MS
MS
←
−
9
5
Both of these functions have weightings which remove the effects of absorption which are linear
with wavelength. In addition, they are stabilized with respect to small wavelength calibration errors.
The second function is weighted to remove SO
These ratios are written to disk and printer.
DETERMINING O
AND SO
3
The O
amount, MS11, is determined from the logarithms of the count rates for the four longer
3
wavelengths :
MS
−
MS
9
←
11
A
1
M
⋅
where
MS9 is the double ratio described in the previous section
B1 is the extra-terrestrial coefficient for the O3 wavelength combination (instrument-
dependent)
A1 is the differential O3 absorption coefficient for the O3 wavelength combination
(instrument-dependent)
M2 is the path-lengthening factor for an ozone layer of height 22 km.
(includes effects of O
and SO
3
(affected predominantly by O
2 .
MS
⋅
7
0
5 .
MS
1
7 .
MS
⋅
−
⋅
6
FROM DIRECT-SUN DATA
2
B
1
2
MKIII OPERATOR'S MANUAL
APPENDIX G PRELIMINARY DATA REDUCTION
)
2
)
3
7
absorption effects
2
111
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