Improving sub-daily strain estimates using GPS measurements

We present an improved GPS analysis strategy that reduces the noise level of GPS-based sub-daily strain measurements by a factor of ∼5 or more and improves sub-daily resolution of positions and baseline estimates by a factor of ∼2-5. These improvements are accomplished by reducing the key sources of error due to diurnal effects from path delays caused by reflections and refractions of the GPS signal near the receiver (multipath), and from tropospheric delays. Errors due to poorly determined tropospheric path delays are mitigated by using the tropospheric parameters estimated in static positioning runs as fixed values. The multipath effects are treated as periodic errors and are mitigated by a modified sidereal filter applied to the phase prior to processing. This combination of path error modeling results in sub-daily strain resolution on the order of ∼0.1 strain for a ∼100km baseline.