Global Positioning System (GPS) and Global Navigation Satellite System (GNSS)
GPS, the first passive one-way ranging satellite system to become operational, is an excellent mapping and survey tool wherever there is satellite reception. It is a central technology for Seisland, being used for our mapping and survey activities. As a corporate philosophy, Seisland has continually invested in the latest-available technologies.
Our first use of GPS dates back to 1995, when we began complementing the total station by using the accurate positioning that GPS enabled. Today, we also incorporate other satellite systems (GLONASS and soon Galileo) plus satellite-based augmentation, together referred to as GNSS, to increase availability, reliability and accuracy.
Seisland currently uses Leica Viva GS14 & GS10 GNSS and Leica GX1230GG GNSS dual-frequency receivers, which can provide centimetre accuracy under good satellite reception. In seismic surveying, the standard goal is to position the source/receiver points to sub-metre accuracy in three dimensions.
GNSS has two main uses for us. The first comes during the control survey at the beginning of a seismic program, in which survey reference points are established. Second is for the layout of the specific source/receiver points in the field, as well as all the field culture collected for the program map. The new data is added to the program map at the end of each day.
For the majority of Seisland’s geophysical field surveys, we use real-time kinematic (RTK) GNSS for positioning the source/receiver locations. RTK consists of using corrections from a base station transmitted to the “rover”, or GNSS surveyor, in real time. The measurements are done on the carrier phase and, with the ambiguity being resolved, centimetre-to-decimetre positioning accuracy can be achieved.
Seisland uses RTK GNSS on the majority of its geophysical programs for establishing the locations of the source/receiver points. When necessary – in environments with degraded GNSS signals, such as areas with heavy canopy or narrow valleys – the GNSS data is supplemented with INS, LiDAR and/or barometry.