Kipp&Zonen Brewer MkIII - Manual (Page 108)

MKIII OPERATOR’S MANUAL 105
polished stainless steel or white painted aluminium or steel sheet. It should not extend over the
zenith window or dome.
The Hamamatsu photomultiplier can be fitted to Brewers with serial numbers up to #190 using a
retro-fit kit.
SC: SCAN TEST ON DIRECT SUN
The SC test determines the correct operational setting of the wavelength-adjusting micrometer.
The program takes measurements of O
3
and S0
2
column amounts over an operator-specified
range of micrometer positions (wavelengths) then prints reduced data for each of the positions.
Method:
Before running the SC test you should first ensure that the wavelength calibration is current:
perform an HG (mercury-line calibration). Next, run a DS (direct sun) test to check that the
appropriate neutral-density filter (Filterwheel #2) is in place. Type SC to begin the scan test. In
response to the program prompts enter the minimum, maximum and increment for the stepper-
motor step number - suggested values are 124, 148 and 2 respectively.
Plot the O
3
and SO
2
values as a function of step number.
Table F-4: O
3
and SO
2
column amounts vs. wavelength for a typical Scan Test on direct sun.
Step# [O
3
] [SO
2
]
124 328.4 6.4
126 333.4 5.0
128 336.3 3.6
130 338.4 3.2
132 341.3 2.7
134 345.3 1.7
136 346.4 2.0
138 348.0 2.3
140 344.8 3.5
142 347.1 3.9
144 344.4 5.7
146 342.6 6.9
148 338.9 9.2
The proper operational setting is that step number for which the O
3
value is a maximum; the SO
2
value should have a minimum within 1 or 2 micrometer steps of the O
3
maximum. This operational
setting should be compared with the value currently stored in the instrument Constants File - if the
new value is significantly different and you are confident the instrument is performing correctly then
the instrument Constants File should be updated via the CF command. [Contact the factory before
altering this constant since a complete recalibration may be required.]
The exact position of the peak of the O
3
value does change by 1 or 2 steps depending on the
airmass and the amount of O
3
present. For best results this test should be performed at low
airmass values (mu < 1.5).
INSTRUMENT INTER-COMPARISON CALIBRATION
The Instrument Inter-Comparison Calibration determines the absorption coefficients and
extraterrestrial constants for the measurement of O
3
and SO
2
. These constants are instrument
dependent and must be determined for all instruments prior to O
3
or SO
2
measurements.
The uncalibrated instrument is compared to a certified Brewer reference by the analysis of a large
number of time-coincident direct-sun O
3
observations made by the two instruments.