A warm day with temps hitting 90F, scattered clouds, southerly turning easterly. Occasional dust devils, including one that reportedly went through the UAS operation at the west end of the ISFS array.
Mainly worked on wind profiler power measurements and tweaks to the Metek lidar. Sam made power measurements of both wind profilers, see his separate blog entry for details. The bottom line is the 449 MHz Modular Profiler power was lower than expected, however it wasn't a direct measurement but depended on a test patch antenna which may not be coupling well to the main antenna. This was done so as to minimally disturb the profiler because the rigid cables on the profiler can be tricky to connect and disconnect. Since the profiler is working well (winds to around 4km and RASS to nearly 2km), we aren't concerned about the performance. The 915 MHz profiler check was with a direct measurement and reported the power expected.
The Metek Halo lidar has had some puzzling behavior so I investigated further today. I set up some sector scans across the tall tower. There were echoes around the expected location but were broader than expected being nearly one degree wide (around 77.0 - 77.8 deg azi and 1.5 km range, whereas the windcube response was about 0.1 degree). Also when staring along the ISFS array, the clearest returns are pointed at 79 deg, 0.1 elevation. Pointing at 80 deg and 0 elevation as planned produces regular artifacts. It appears that the azimuth is accurate to about 0.3 deg and the level (elevation) to around 0.1 or 0.2 deg, however there is a little wobble in the trailer with the wind (around 0.1 deg) and a little wobble or hysteresis in the head position. In addition it appears there is some diffusion or sidelobes in the beam. The focal point is about 500 meters (as set by Halo Photonics) and the beam appears to diverge at longer ranges (hence the spread when scanning the tower). When pointing close to the REAL trailer, some of the beam may be skimming or diffracting along the trailer and then hitting the ground further out and thus producing artifacts. For this reason, I've set the stare a little to the north and upwards (79 deg azi and 0.1 elevation). The beam appears to be spread around 0.2 deg or more at the range of the array (1.5 km) which corresponds to about 5 meters. I set up hourly narrow PPI sector scans across the tower and narrow RHIs at 79 deg to keep tabs on these effects, and perhaps enable some analysis of the issue later.
Late afternoon the 449 MHz profiler was drawing 2.96 A and the 915 MHz profiler was drawing 2.47 A.
Power measurements on the 915 MHz profiler (left) and with a test patch on the 449 MHz profiler (right).
Visit to the OU UAS operation near the ISFS array.