TWP/VCEIL/C3 - Degraded hardware

It appears that the sensitivity of the Darwin ceilometer was degrading over a few month 
period leading up to September 2005.  Beginning on September 16, 2005, the instrument 
shifted to a particularly bad state.  Looking at the backscatter data, I do not see nearly as 
great a day-night difference in the background as I expect and there is very little 
sensitivity to clouds.  There was cross talk error noted with that instrument. The ceilometer 
was replaced on December 12.

• Backscatter(backscatter)
• Second lowest cloud base height(second_cbh)
• Third cloud base height(third_cbh)
• Lowest cloud base height detected.(first_cbh)
• background_light
• alt_highest_signal
• Vertical visibility(vertical_visibility)

TWP/VCEIL/C3 - ceilometer lost sensitivity

ceilometer sesitivity decreased suddenly and only very strong cloud reflections are 
observed in the first kilometer.

• Backscatter(backscatter)
• status_string
• status_flag
• sum_backscatter
• Second lowest cloud base height(second_cbh)
• Third cloud base height(third_cbh)
• range
• Lowest cloud base height detected.(first_cbh)
• detection_status
• background_light
• Vertical visibility(vertical_visibility)

TWP/MMCR/C3 - MMCR Power Monitor failure

During this period, the transmit power monitor on the TWTA was not working.  This resulted 
in the power level reading staying at a steady state (approximately 49 dBm).  Normal 
transmitter fluctuations are expected to be on the order of +/- 0.3 dBm.

• Cloud, reflectivity, at altitude(Reflectivity)

• TransmittedRFPower

TWP/SMET/C3 - Reprocess: Tipping bucket rain gauge added

A tipping bucket rain gauge was added to the SMET suite of instruments effective 20060926. 
 Two new variables (count and rain amount) were added at the end of the twpsmet60sC1.b1 
datastream.  When reprocessing of this datastream occurs these variables will be added 
with -9999 (missing) as the value for dates prior to gauge installation.

• base_time

TWP/SMET/C3 - Reprocess: ORG Data has very small rainrate values

The ORG data is collected via analog signal and not digital.  Therefore, we
continuously collect data even when no rain is occurring.  We also capture small events 
such as leaves, large bugs, dust, etc blowing through the measurement path.  Because this 
discrete event occurs quickly the value is usually captured for 1 or 2 seconds.  This 
value is then averaged to the minute producing rainrate on the order of .009 mm/hr or less.  

These values are not indicative of rain and should be removed from the record or summing 
over long periods can bias the climate record.  We will reprocess the data to remove these 
small values.

• precip_sd
• Precipitation maximum(precip_max)
• Precipitation minimum(precip_min)
• Precipitation mean(precip_mean)

TWP/SMET/C3 - Wind Speed data contain offset due to induced voltage

The marine model of the RM Young wind sensor needs twisted pair shielded cable.  The 
manufacturer did not originally supply the pigtail with twisted pair shielded cable.  Use of 
twisted pair shielded cable for the rest of the cable run to the logger was also not 
specified.  This caused an induced voltage in the wind speed line from the wind direction 
excitation.  The induced voltage varied from sensor to sensor and probably changed anytime 
the cable was replaced or parts of the wind sensor were repaired or replaced. The induced 
voltage has been seen to vary from 0.15 m/s to as much as 1.08 m/s.

• up_spd_vec_avg
• lo_spd_vec_avg
• lo_spd_sd
• lo_spd_min
• up_spd_max
• up_spd_sd
• up_spd_min
• lo_spd_arith_avg
• up_spd_arith_avg
• lo_spd_max

TWP/SMET/C3 - Reprocess: Temperature Biased low by 1.06 Degrees

The temperature of the SMET system was biased low by 1.06 Deg C due to a non-precision 
resistor being used int he measurement circuit.  The data will be reprocessed.  Saturation 
Vapor pressure and Vapor pressure will have to be reprocessed also.

Add 1.06 degrees to the temperature data.  

Correct Sat Vap Press using the Buck approximation:
   Es = 6.1121exp((17.502*T)/(240.97 + T) 
where T is the temperature in C.  

Correct Vapor pressure using: E = (RH*Es)/100

• temp_sd
• Mean Air Temperature or Hardware Error(temp_mean)
• Vapor pressure mean(vappress_mean)
• vappress_sd

TWP/VCEIL/C3 - Reprocess: Incorrect serial_number and sum_backscatter fields

Attribute serial_number: In most cases, this field is not representative of the actual 
serial number of the instrument because the value did not change when an instrument changed 
locations or was replaced with a spare.
   
Variable sum_backscatter: An out-of-range condition for the "sum of detected and 
normalized backscatter" was reported as 0 instead of missing (-9999). The valid range is 0 - 
0.0999 /srad.
   
This DQR also applies to a1 level data.

• sum_backscatter

TWP/MPLCMASK/C3 - Cloud layer information in the header is misleading

The comment in the header for cloud_base_layer indicates that the value of -1
indicates that no cloud is detected.  For the above time range, a value of 0 indicates 
that no cloud is detected.

• cloud_base_layer