3.4.8. GNSS surveying techniques

There are various methods available for some specific tasks, which may be kept in mind while collecting the data from GNSS (Garg, 2021). The technique used in a given location, would however depend on the (i) accuracy requirements, (ii) time to complete the work, (iii) local terrain conditions, and (iv) available facility.

In GNSS surveying, different methods exist to collect data based on specific goals and environmental conditions. The choice of technique will depend on several factors: the precision needed (accuracy requirements), how quickly the work needs to be done (time to complete), the characteristics of the land (local terrain conditions), and the resources that are available (available facility).

Think of choosing a method to cook a meal. If you need a fancy dinner quickly, you might use a pressure cooker (like a rapid static surveying technique). But, if it’s a special occasion and you want the best outcome, you'd spend more time and use the slow-cooking method instead (like static surveying).

This method is used in surveying that requires reasonable high accuracy, e.g., control surveys from local to state-wide area. It will probably continue to be the preferred method, as the receiver at each point collects data continuously for a defined length of time. The duration of data collection will depend on (i) required precision, (ii) number of visible satellites, (iii) satellite geometry (DOP), (iv) single frequency or dual frequency receivers, and (v) distance between the receivers.

Static surveying is the best option for achieving high accuracy, especially for large control surveys that cover local to state regions. In this technique, the survey equipment records data steadily over a set time. Various factors influence how long this recording lasts, including how accurate the results need to be, how many satellites can be seen from that location, their arrangement in the sky which affects geometric accuracy (DOP), whether the system is using one or two frequencies, and how far apart the survey instruments are placed.

Consider taking a group photo with your friends. If you stand still and allow the camera to gather the image slowly, you might get everyone looking great (static surveying). But if you move around quickly, some might blink or turn away (lower accuracy).

The rapid static method is a popular method of GNSS surveying where short-time measurements are taken. As the name suggests, it is easy, quick and efficient. The rapid static technique is well suited for short range applications, such as control densification and engineering surveys or surveying many points.

Rapid static surveying is designed for quick measurements over short distances. It is efficient and user-friendly, making it ideal for tasks like establishing additional control points (control densification) or quick engineering surveys involving multiple locations. This method allows surveyors to collect data quickly without compromising too much on accuracy.

If you're quickly checking how many apples you have by just glancing at your basket instead of counting each one meticulously, that's like rapid static surveying—you're still getting useful information but faster.

Kinematic surveying uses differential carrier phase tracking to record observations simultaneously. It is used in most surveying applications where the base receiver remains stationary and placed at the known point, while the rover receiver will visit the unknown points for a very short time.

Kinematic surveying focuses on tracking changes in position using two types of receivers: a base station at a fixed location and a rover moving to various unknown points. The base collects data while stationary, and the rover gathers data at each visited point for a brief period. This approach allows for real-time location tracking with high accuracy, making it suitable for dynamic environments where quick adjustments are required.

Imagine a detective using a stationary camera to keep watch while their partner checks different locations for clues. The fixed camera provides reliable reference points, while the detective at each spot gathers information quickly.

It is known as stop-and-go technique because only the coordinates of the receiver are used when it is stationary (‘stop’ part) but the receiver continues to function while it is moving (`go’ part) from one stationary station up to the next station.

In stop and go kinematic surveying, the rover periodically stops to gather data while still maintaining a connection with the satellites as it moves. During the 'stop' phase, it collects position data, and while moving, it continues to track satellites, although this data is less critical. This method strikes a balance between speed and accuracy, often used in detailed surveys where many points need to be measured in a limited time.

Think of taking a road trip where you only stop occasionally to snap a photo of landmarks (the stop points), but you keep driving to the next destination (the go part). Each stop gives you meaningful data but not every moment needs to be recorded.

The RTK method is preferred for many survey applications as it provides positioning in real-time. There is no post-processing of the carrier phase data required.

RTK surveying provides immediate position data without the need for lengthy post-survey processing. It relies on a stationary reference receiver that transmits data to a moving rover receiver. This instantaneous correction allows surveyors to obtain data with high accuracy while working, making it ideal for tasks that require immediate results such as construction and land surveying.

RTK surveying is like using a live GPS app that provides turn-by-turn directions instantly, allowing you to get to your destination accurately without waiting for your device to process the route after the fact.

The DGNSS technique requires two identical GNSS units, and is used to improve the accuracy of a standard GNSS. It works by placing a GPS receiver at a known location, called a reference station, and another GNSS unit, known as rover station which is kept at unknown points to determine the coordinates.

DGNSS surveying enhances standard GNSS accuracy by using two receivers: one fixed at a known point (reference station) and another moving to unknown locations (rover). The reference station calculates the error in positioning by comparing GNSS data with its known location and sends this correction to the rover, allowing for improved accuracy at the unknown sites.

It's like having a trusted friend who knows the best shortcuts while you navigate through a new area. They help clarify any mistakes from your GPS by sending you updates based on their knowledge, helping you reach your destination more efficiently.

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