The Geophysics/Surveying Unit uses Trimble 4800 and R8 GNSS Series survey-grade GPS receivers. The GPS equipment includes:

• 2 Trimble R10 GNSS Receivers and 2 Trimble TSC3 Controllers
• 3 Trimble R8 GNSS Rover Receiver and TSC2 Controllers
• 1 Trimble R8 GNSS Base Receiver and TSC2 Controller
• 1 Trimble Trimmark II Radio
• 1 Trimble TDL450L UHF Radio
• 2 UHF Omnidirectional Antennas with a 5dB Gain Tip
• 4 SECO 2.000 meter Fixed-Height Tripods
• 4 SECO Fixed-Height Tripods with Collapsible Center Staff
• 3 Trimble 1.800 meter Carbon Fiber Bipods
• 3 Trimble 2.000 meter Aluminum Bipods
• Trimble Business Center Software

The Geophysics/Surveying Unit performs three primary types of GPS surveys to determine the horizontal and vertical position of discreet points: Static surveys, Real Time Kinematic (RTK) surveys and Post Processed Kinematic (PPK) surveys.

The static survey method requires long occupation times (1 to 8 hours), multiple receivers logging data simultaneously, repeat observations, and significant post-processing to produce final results. The static survey method is the most accurate GPS survey technique available today. The level of accuracy achieved in the final results is based on a number of factors (e.g. equipment type, occupation time, baseline distance, satellite availability and constellation geometry, and physical receiver environment). We primarily use the static survey method when performing our land subsidence measurements.

The Real Time Kinematic (RTK) Survey style requires very short (seconds to minutes) occupation times and no post-processing of the GPS data. However, this method requires that a base station (GPS receiver occupying a location with known coordinates) is operating and broadcasting a correction signal that can be received by the GPS rover receiver. The RTK survey style is used to measure a large number of survey points, in a relatively small geographic area, in a short period of time. There is a decrease in the accuracy of the final result when compared to the static survey style, but these measurements are not normally used for land subsidence monitoring.

The Post Processed Kinematic (PPK) Survey style requires an occupation time of at least thirty seconds. This method is similar to the RTK Survey style but it does not use the broadcasting correction signal from the base station. It uses the static survey data from the base station to post-process the initial point survey data.

The Trimble manufacturer's published errors associated with the Static and Real Time Kinematic Survey Styles for the R8 GNSS and 4800 Series receivers are:

RTK Errors: +/- 1cm + 2ppm Horizontal

+/- 2cm + 2ppm Vertical

Static Errors: 5mm + 1ppm (times baseline length) Horizontal
10mm + 1ppm (times baseline length) Vertical

PPK Errors: 1cm + 1ppm (times baseline length) Horizontal
2cm + 1ppm (times baseline length) Vertical

Trimble R8 RTK Base Station