Kipp&Zonen Brewer MkIII - Manual (Page 112)

MKIII OPERATOR’S MANUAL 109
APPENDIX G PRELIMINARY DATA REDUCTION
This section describes how the Brewer software processes the raw photon-count data to determine
ozone (O
3
) and sulphur dioxide (SO
2
) column amounts. Seven of the 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:
( )
6 .. 2 ,
2
1
=
Ч
− Ч
←
i
IT CY
F F
F i
i
where
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
APPENDIX G PRELIMINARY DATA REDUCTION