GRW/VCEIL/M1 - Receiver failure

The AMF VCEIL had lower-than-normal laser transmitter power, ~84%, so the instrument was 
replaced with a spare on 4/22. The spare VCEIL had just been repaired but began to display 
receiver failure warnings.

Diagnostic information was sent to Vaisala and we discussed either replacing the receiver 
with the one from the original VCEIL (with the degraded transmitter) or replacing the 
transmitter in the original VCEIL with the one from the spare. Vaisala recommended the 
latter because the original VCEIL is a much newer unit.

On 5/16, the site operator replaced the transmitter in the original VCEIL with the one 
from the spare, realigned the optics, recalibrated the laser, and put the instrument back 
into service, successfully correcting the problem.

The data during this period were intermittently incorrect, containing warning flags and 
alarms and unreasonable cloud base heights.

• Aerosol backscatter coefficient at 355 nm(backscatter)
• Lowest cloud base height detected.(first_cbh)
• Millivolts at internal ADC input (0 to 2500)(background_light)
• Third cloud base height(third_cbh)
• Altitude of highest signal(alt_highest_signal)
• Second lowest cloud base height(second_cbh)
• Vertical visibility(vertical_visibility)

GRW/MWR/M1 - Loose mirror

The data from the MWR were suspicious and became progressively worse. The problem was 
traced back to the fact that the screw that keeps the mirror in place had become loose and 
the mirror was freely rotating. 

The mirror was tightened on 6/9/2009, however the measurements were noisy until 6/16, when 
the instrument was rebooted and all the connections checked. 

Measurements between 5/1 and 6/9 should not be used. Data between 6/9 and 6/16 are usable, 
although they are very noisy.

• Sky brightness temperature at 23.8 GHz(tbsky23)
• 31.4 GHz sky signal(sky31)
• 23.8 GHz blackbody+noise injection signal(bbn23)
• MWR column precipitable water vapor(vap)
• Averaged total liquid water along LOS path(liq)
• 31.4 GHz blackbody(bb31)
• 23.8 GHz sky signal(sky23)
• 31.4 GHz blac2body+noise injection signal(bbn31)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• 23.8 GHz Blackbody signal(bb23)

• 31.4 GHz sky brightness temperature derived from tip curve(tbsky31tip)
• 23.8 GHz Blackbody signal(bb23)
• 23.8 GHz blackbody+noise injection signal(bbn23)
• 23.8 GHz sky signal(tipsky23)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 23.8 GHz sky brightness temperature derived from tip curve(tbsky23tip)
• 31.4 GHz blac2body+noise injection signal(bbn31)
• 31.4 GHz sky signal(tipsky31)
• 31.4 GHz blackbody(bb31)
• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)