ZS
Zenith Sky Observations
The zenith prism is pointed to a Zenith Angle of 0°, the iris is opened, FW#1 is set to position 0, FW#2 is set to position 2, and the azimuth tracker is pointed toward the sun. FW#2 is adjusted according to sky intensity. Data is recorded on disk and is printed as previously determined by PN, PD, and PF commands.
A ZS observation consists of seven sets of 20 cycles of the slit mask (a measurement), each cycle taking a reading for 2*0.14 seconds on each wavelength. Intensity data for six wavelengths, and the dark count, from the seven measurements is recorded. The Azimuth and Zenith positions are updated after each measurement. After each measurement O3 is calculated, after the seventh measurement all data is processed, resulting in a single summary set for the total observation.
As a safety feature to prevent damage to the detector, the measurement may terminates if, as a result of varying cloud conditions, FW#2 has initially been set to a low attenuation value and clouds suddenly move out of the field of view.
A ZS measurement takes slightly more than five minutes to complete.