Best Practices for DGNSS (Differential Global Navigation Satellite System)

Systematic field procedures are part of any successful DGNSS survey that guarantees that data obtained is both accurate and reliable. Whether in terms of setting up base and rover stations or the field procedures and collection of data, the same case applies — best practices ensure results are both accurate and reliable. This blog will, therefore, be focusing on some of the most fundamental practices of successful DGNSS surveying.

Pre-survey Preparations

• Ensure all your equipment is properly calibrated, batteries are charged, and software and firmware updates are done before commencing the survey.
• Check the weather forecast and satellite availability and any other factors that might cause interference or obstruction to the measurement, including buildings, trees, power lines, or radio signals. Also, prepare for any contingencies related to the malfunction of equipment, loss of data, and denial of access to the site of interest.
• Locate memory devices (typically SD cards) and verify sufficient storage is available.
• If not familiar with the gear, perform a full setup test, check that the communications are working correctly between devices before heading to the field, or be prepared to troubleshoot later.
• If possible, investigate your field area. Topographic maps, Google Earth Imagery, or pre-trip to the area can dramatically increase your chances of success on your field day. Using this knowledge, plan the base sites, data points and paths to navigate the field site. A good plan will reduce time spent in the field later. Anticipate the number of points to be collected and time associated with the plan.
• Pack all equipment using a checklist.

In-Field Techniques

• Stable and High Ground: Place the base station on stable, solid ground to ensure that it will stay in one place during the entire survey. Put the base station as high as practical. This minimizes multipath from the surrounding area and enables the radio broadcast to the maximum distance. Also, the higher the gain on the antenna, the longer the range.
• Clear Sky View: Mount the base GPS antenna where there will be clear view of the sky in all directions. Not near vertical obstructions like buildings, deep cuttings, site vehicles, towers, tree canopy, etc. This is to ensure that the receiver do not have to deal with messy multi-path signals.
• Check Base Station Regularly: Periodically check the base station to make sure it is functioning correctly and is transmitting data. Ensure that the base is monitored at all time as it can be stolen or knocked down by wind/animals.
• Field Notes: Keeping detailed field notes of the survey, including possible problems or oddities observed in the course of surveying.
• Data Quality Checks: Checking the quality of correction data received from time to time and verifying the positional accuracy obtained from the Rover that should be within the acceptable limits.
• Safety Precautions: Observe precautions for personal safety, especially when working in the vicinity of live traffic, in remote areas, or in bad weather.
• Known Coordinates: Use a location with known and accurate coordinates or establish the position of the base station by precise static observations.
• Power Source: The GNSS receiver should never run out of power. The GNSS receiver has an internal battery that must be charged. Provide external power in order to use continuously for more than a day without losing power at the base station.
• Electromagnetic Interference: Ensure that the base is away from heavy machinery, radio/mobile towers and overhead power lines as the electromagnetic fields associated with these utilities can interfere with the DGNSS signals.

Data Collection Techniques

Effective data collection in a DGNSS survey involves various techniques to ensure precision and reliability. Here are key techniques for data collection during a DGNSS survey:

Static Positioning
Static positioning is a method in DGNSS (Differential Global Navigation Satellite System) surveys that involves collecting data at a fixed point over an extended period to achieve high-precision coordinates. This technique is particularly useful for establishing control points, base station locations, and other critical survey markers that require high accuracy.

Picture 1: DGNSS set to Static Mode

Rapid Static (Fast Static)
Rapid static positioning, also known as fast static positioning, is a technique in DGNSS (Differential Global Navigation Satellite System) surveys that balances the accuracy of static positioning with the efficiency of kinematic methods. It involves shorter observation times than traditional static surveys, making it suitable for projects requiring quick and precise measurements at multiple points.

Real-Time Kinematic (RTK) Surveying
Real-Time Kinematic (RTK) is a high-precision positioning technique used in DGNSS (Differential Global Navigation Satellite System) surveys. RTK provides real-time corrections to the rover receiver, enabling centimeter-level accuracy. This technique is widely used in applications requiring immediate and precise positioning, such as construction, agriculture, and topographic surveys.

Figure 2: The rover is getting real time corrected data from base

Post-Processed Kinematic (PPK)
Post-Processed Kinematic (PPK) is a technique in DGNSS (Differential Global Navigation Satellite System) that provides high-precision positioning by applying differential corrections after data collection. Unlike Real-Time Kinematic (RTK), PPK does not require real-time communication between the base and rover, making it suitable for areas with poor communication infrastructure.

Figure 3: The rover is getting real time corrected data from base

Adhering to best practices in DGNSS surveying is essential for achieving high-precision and reliable results. By meticulously setting up your base and rover stations, continuously monitoring signal quality, and carefully documenting field conditions, you can mitigate potential sources of error. Utilizing techniques like RTK, PPK, static, and rapid static positioning, each suited for specific scenarios, allows for flexibility and precision in various surveying contexts.

This brings us to the end of the blog. I hope this article gained some knowledge for you!

Thank you for reading.

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