NSA/DL/C1 - Changing elevation angles in PPI scans

After the system was installed, the mentor set up the PPI scans with a prescribed 
elevation angle of 70 deg. After a couple of weeks of operation we noted that the actual reported 
elevation angles in the PPI scan files (i.e. nsadlppiC1.b1) differed from the prescribed 
angle.
The PPI scans were initially setup by specifying 8 evenly spaced azimuth angles between 0 
to 360deg at an elevation angle of 70 deg. The reported elevation angles at each of these 
azimuth angles were:

70.02 70.04 73.25 70.04 70.02 70.00 70.02 70.00

The small deviations on the order of a few hundredths of a degree are not of significant 
concern. The one outlier (73.25) is, however, a problem.
We note that the Streamline Pro that is operated at NSA differs from the other DLs that 
ARM currently operates in that scanning is limited to +/- 20 from zenith. Thus, the mentor 
suspected that the problem might be due to the fact that we were attempting to scan at 
the limit of the system's field-of-regard. Accordingly, the PPI elevation angle was changed 
from 70 to 75 deg at about 0030 UTC on 20140820. As a result, the elevation angles no 
longer contain outliers. Thus, PPI scans for the NSA system will continue to use a 75 deg 
elevation angle until further notice.

If you are using these data to compute wind profiles you should check for consistency 

in the elevation angles. You may want to throw out any beams with inconsistent 
elevation angles.

• elevation