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ZB, ZC, ZS Zenith Sky Observations
ZB, ZC, and ZS are variations of the same command, and are used when sky conditions are
known and it is desirable to keep the observations separated.
ZB is usually used in clear sky conditions (Zenith Blue), ZC is used under cloudy conditions
(Zenith Cloud), and ZS is used when conditions are unknown (as is a schedule).
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 O
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.
ZP initiates a variation of the ZS command in which the Azimuth Tracker is rotated to an
angle perpendicular to the sun.
A ZS measurement takes slightly more than five minutes to complete.
See Appendix A.
ZE
Zero Zenith Prism
ZE positions the zenith prism to its zero-step position, or ZA=180°. The zenith reference is
found, and the prism is then moved back a constant number of steps from the zero-step
position.
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MKIII OPERATOR'S MANUAL
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