I remotely conducted a few checks on the Windcube lidar today (UT day August 7)
Clock:
The windcube clock was noticed to be 47 seconds too fast. The internal GPS has failed (and Vaisala is having trouble sourcing a replacement) although it did work briefly at the beginning of the campaign so presumably the clock was correct then. At 0214 UT (Aug 7), the settings were adjusted to do a NTP check of the time.nist.gov clock instead of GPS so it should be correct from now on.
Azimuthal bearing check:
0135 UT did a series of slow PPI scans from 70 deg to 80 deg to scan past the ISFS tall tower and array of 4 meter towers.
Assuming that windcube is at 38.040471°N 117.088045°W
- The tall tower is at 38.04376008N 117.069964429W, then according to Google Earth, wrt to the windcube, the tower is at 1628 meters range, bearing 77.0 deg.
- The west end of the ISFS array is about 38.042653°N 117.074279°W, wrt to the windcube, 1235 m range, bearing 78.7 deg.
- The east end of the ISFS array is about 38.043038°N. 117.071518°, wrt to the windcube, 1480m range, bearing 78.9 deg.
The PPI scans showed a target at around 1650m, bearing 76.75 - 76.85 deg (presumably the tall tower), and more targets ranging from 1200m 78.25 deg to 1600m 78.8 deg (presumably the ISFS array). These measurements imply that the windcube bearings may around 0.2 deg too low, although there may be small errors in the GPS locations, and the tower bearings did not account for the guy wires and straps.
Set up a schedule to do this scan once per day around 1215 UT.
Another way to check this is to examine the hourly zero elevation PPI scans since they seem to show the power line to the navigation beacon and probably the towers, although the angular resolution is lower on these scans.
RHI check:
0155 UT did some slow RHI scans from -0.5 deg to 10 deg at 77 deg. These should be later compared to anemometers on the tall tower. These scans should also be examined to see at what elevation the ground is hit since this is difficult to observe on the realtime screen. Set up a schedule to do these scans every 6 hours from 0630 UT.
Note the hourly zero elevation PPI scans may also help with elevation calibration since they seem to hit the ground to the north of the towers, and this could be matched to topography.
Hourly Scans:
Adjusted the hourly intercomparison scans. LROSE seems to have problems plotting the previous west-east and south-north RHIs so switched to north-south and east-west RHIs, with a south to east zero elevation PPI scan in between. There is also a vertical stare of 2 minutes to compare with the UVA Halo lidar (and this also allows an estimate of PBL depth to be determined). In between these hourly scans (and the other scheduled scans mentioned above), the windcube continues to do one-minute PPI scans at 35 deg elevation for VAD wind measurements.