Radiometer intercomparison

Atmospheric boundary layer flow depends on atmospheric stability, which (in wind farms) is typically quantified with tower measurements of temperature profiles. Remote sensing of temperature profiles is possible with microwave radiometers, which will be used in the A2e WFIP2 experiment, and may be useful for improving wind energy forecasting. 

XPIA has two microwave radiometers deployed on the roof of the BAO Visitor Center; their measurements of the temperature and moisture profiles are to be compared with the 300m tower profiles as well as the profiles from the radiosonde launches. One radiometer is from NOAA, the other from CU-Boulder; both are Radiometrics MP-3000A microwave radiometers. (The CU-Boulder system is the same one as used in Friedrich et al., 2012.)

Although the two instruments should be measuring the same thing, we have discovered (thanks to some excellent quick data analysis by Laura Bianco with input from Katja Friedrich and Jim Wilczak) that there is a small offset in the ambient temperature measured between the two instruments, likely due to different surface temperature measurements. 

The radiometer data can be compared to the radiosonde profiles collected in March (based on the 15 deg radiometer scans). Especially at low temperatures (see below, left), there are deviations between the soundings and the radiometer). The mean absolute error between the radiometers and the soundings varies with height (see below, right). The larger disagreements at higher altitudes are to be expected as the sonde drifts away from the radiometer measurement volume.
 

Figure courtesy Laura Bianco

Below is the temperature comparison between the 15 degree averaged scans of the two instruments (based on data between 9 Mar and 5 Apr).

Figure courtesy Laura Bianco

Radiometrics staff have been very helpful in identifying possible sources of these differences, and additional data collection is underway to isolate the source of the deviations and identify best practices for subsequent radiometer deployments.