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16-10-200716-10-2007
APPENDIX G
This section describes how the Brewer software processes the raw photon-count data to determine
ozone (O
) and sulphur dioxide (SO
3
two-character menu commands (SL, SC, DS, ZB, ZC, ZP, M) access a common suite of data
reduction algorithms, as shown in figure G-1.
Figure G.1: Data Reduction Flowchart
CONVERTING RAW COUNTS TO LIGHT INTENSITY
Raw photon counts are automatically retrieved from six wavelength channels (one dark-count
channel, five operational channels.
The computer requests raw photon-count data from the spectrophotometer by transmitting
appropriate command strings, for example:
R, 1, 6, 20 (run the slitmask motor through positions 1 to 6, then back to position 1,
accumulating the counts to six separate channels; repeat this sequence 20 times)
O
(output to the computer the six photon counts measured in the previous R command)
The returned photon-count values are stored in the F() array. These raw values are written to the
printer.
CONVERTING RAW DATA TO COUNT RATES
The core program subtracts the dark count (stored in F(1)) from the operational-wavelength counts,
then scales the result to produce count rates, in counts per second:
2
←
F
i
where
PRELIMINARY DATA REDUCTION
) column amounts. Seven of the
2
(
)
×
−
F
F
i
1
,
×
CY
IT
CY is the number of slitmask cycles (20 in the above example)
IT = 0.1147 is the interval-scaling factor which incorporates slit sampling time
and duty cycle
MKIV OPERATOR'S MANUAL
APPENDIX G PRELIMINARY DATA REDUCTION
=
i
2
..
6
107
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