Post by Brent George on Sept 3, 2015 20:20:10 GMT
When a mountain not only gets a name change, but a new height. USA Today
Although you must admit that a mere -10ft (-3.04m) change in height is hardly significant if you account for the error budgets involved. Things like:
- measurement error of height of GNSS unit (say ±0.02m)
- measurement error of thickness of snow cap (say ±0.20m)
- ppm error from base station (assume 40km distant so at 2ppm = 0.08m)
- precision of benchmark height used (say ±0.02m)
- relationship between previous origin of heights to recent origin of heights (say ±0.10m)
- GNS errors - clock; satellite; signal (say ±1.0m)
- Model errors - tropospheric/ionospheric (say ±0.05-0.15m)
- Ephemeris/multipath errors (say ±0.50m)
- (Although some of the above are mitigated depending on the measurements technique used... ;-)
although the main point could be:
- precision of previous height determination (say ±20ft ! = 6.08m)
In summary - a testament to the "1950's" measurement methods as well. Probably by reciprocal vertical angles using precise optical instruments (possibly T3's - remember those?)