A rigorous and accurate GPS survey is a process that begins with project planning. This is followed by data gathering, data reduction and finally post-processing. The Alignment Engineering Group employs two software packages for this purpose.
LEICA's SKI-Pro software was part of the original equipment purchase. It is a windows-based, largely automated suite of programs that is used for all observation related tasks and for analysing real-time data (RTK mapping). It is not as flexible as desired for tasks requiring very high accuracy such as tying a station in to a well defined reference frame at the sub-centimeter level (absolute accuracy). Using data of observation sessions on two days in December 2001 (Campaign 1), differences in coordinate components to the chosen reference sites reached values far over the sought for centimeter.
BERNESE V. 4.2 GPS software was acquired in February 2002 to perform in depth analysis and long-term studies. Bernese is a platform independent software package based on standard FORTRAN-77 and FORTRAN-90 modules that are being driven by a menu system. The data analysis can be automated to a large extent by means of batch processes of the Bernese Processing Engine (BPE). The highest accuracy requirements are met by processing dual frequency code and phase measurements as well as by modeling or introducing models for the ionospheric and tropospheric signal delay, antenna phase center variations, and ocean tide loading effects as examples. Bernese constitutes a state-of-the-art scientific software package which is also being employed worldwide by survey agencies to evaluate permanent local or regional GPS networks.
The Alignment Engineering Group is also completing the combination of GPS baseline solutions with terrestrial surveying observations such as precise leveling height differences and laser tracker or total station triplet observations. The SLAC adjustment package LEGO is being extended to accept baselines and their covariance matrices.