2015

********************* someone will need to subtract 1.8381 m from the heights

All, I've copied our 2015 Sondy ramp survey vehicle trajectory (April 19th) to the trajectory area. As always, this is the trajectory of the LC phase center of the vehicle antenna. To reduce it to the ramp surface, someone will need to subtract 1.8381 m from the heights. This number accounts for the measured antenna height and for the LC phase center position. > > As a QA measure, I've gotten into the habit of differencing ramp surveys from previous versions. In the case of Sondy, we last surveyed it two years ago. I do this by gridding each trajectory (minus antht/phase center) into 10 m cells, and differencing the resulting grids. The result for this survey is attached. The only significant differences the figure shows are near the southeast edge of the ramp, in a narrow strip which wasn't well-covered by this year's survey. The gridding algorithm I use drapes a spline surface over the trajectory data within an externally-defined boundary (shown in the figure by a black polygon), and in the absence of data near an edge, it extrapolates to the boundary. So this one area of difference is an artifact of the gridding technique, not a real difference in the data. The average difference between the entire 2013 and 2015 surfaces, even with this artifact included, is only 1 cm. So either the combined errors in our survey and antenna height measurements happens to cancel any real geophysical uplift or subsidence (seems unlikely), or the surface is quite stable and our measurements are good. Let's hope it's the latter. > > We got a very similar result (also a 1 cm average height difference) at El Mirage in Fall 2014. Again, the likelihood seems to be that our measurement technique is working well, largely eliminating systematic height errors in these surveys.

From: John Sonntag <john.g.sonntag@nasa.gov> Date: Sun, Apr 19, 2015 at 3:37 PM Subject: notes from ramp survey To: "KyleKrabill@gmail.com" <KyleKrabill@gmail.com> 20150419 BGSF ramp survey xxxx data on xxxx moving xxxx data off usual base station 02QR, 3VSA and 3VYU 3VYD is the vehicle vehicle antenna: Ashtech 701945-01 rev E Antenna height measurements for the vehicle: -mag mount choke-ring antenna was placed on the roof of a Toyota Hilux pickup -Antenna height measurements were made to the very top of the antenna housing, with the vehicle loaded as for the survey -measured height between top of antenna housing and top of chokerings: 3.9 cm -heights measured on paved ramp surface, fairly smooth -pre-survey measurements: 193.9/193.6 cm driver side AVG=193.75 cm 192.8/192.9 cm passenger side AVG=192.85 cm -post-survey measurements: 193.6/193.3 cm driver side AVG=193.45 cm 192.6/192.5 cm passenger side AVG=192.55 cm -average pre-survey height: 193.3 cm -average post-survey height: 193.0 cm -overall average height: 193.15 cm -overall average height to top of chokerings: xxx.xx cm -overall average height to LC phase center: xxx.xx cm