NSA/SONDE/C1 - Increased precision for alt, dp, pres, rh, tdry

The output precision of the following variables was increased 20060929:

   alt	changed from 1m to 0.1m
   dp	changed from 0.1degC to 0.01degC
   pres changed from 0.1 hPa to 0.01 hPa
   RH	changed from 1%RH to 0.01%RH
   tdry changed from .1degC to 0.01degC

Note that the increase in precision does not necessarily imply an increase
in accuracy.  Users are cautioned to continue to use their best scientific
judgement when using these or any other data.

• Dummy altitude for Zeb(alt)
• Dry bulb temperature(tdry)
• Surface dew point temperature(dp)
• Retrieved pressure profile(pres)
• Relative humidity inside the instrument enclosure(rh)

NSA/MWR/C2 - Possible bias on measurements

This instrument was refurbished at the the vendor's facility in 2008 and then sent to the 
SGP for side-by-side comparison with another MWR. During the time the instrument was at 
the SGP, it was noticed that the 23.8-GHz measurements were slightly warmer than those 
from radiometer SN10 operating at the SGP Central Facility. A comparison with radiosonde 
measurements confirmed the slight change in the measurements.

An explanation of the bias and comparison with radiosonde measurements and radiometer SN 
10 is given in the mentor's monthly data  review  for the month of April 2008.

Since there aren't radiosondes at NSA.C2, it is difficult to work around this problem. 
Based on comparison at the SGP, the bias in the 23.8-GHz channel was quantified to be ~1.5 
K. Users can attempt to subtract this amount from the 23.8-GHz measurements. 
Alternatively, use the retrieved PWV and LWV keeping in mind that there is a possible overestimation 
of PWV of ~1 mm.

On 11/16/2009 after a hardware failure of the radiometer a spare radiometer (SN15) was 
installed at the site.

• Sky brightness temperature at 23.8 GHz(tbsky23)

• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)