3.4.8 - GNSS surveying techniques
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Static Surveying
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Today, we will start with static surveying, which is essential for achieving high accuracy in GNSS measurements. Can anyone tell me why we might choose static surveying over other methods?
Maybe because it requires collecting data for a longer time to get accurate results?
Exactly! In static surveying, we collect data continuously for an extended period. The required time depends on factors like satellite visibility and their geometric arrangement. Why do you think the duration is important?
Longer durations mean we can average out errors and get more precise results.
Correct! Longer data collection helps mitigate errors. So remember, the longer the observation, the more accurate the baseline measurements will be. Let's summarize: static surveying is chosen for high accuracy, and it requires more time and careful planning. Any questions?
Rapid Static Surveying
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Now, let's discuss rapid static surveying. This method is known for its speed. Why is that beneficial?
Because it helps us complete surveys more quickly, which is great for engineering projects!
Exactly! Rapid static surveying is perfect for projects requiring quick data collection, like engineering surveys. It works well for control densification. What factors influence the observation time for this method?
Things like the baseline length and the number of visible satellites!
Yes! Especially regarding ionospheric disturbances. Lower disturbances often lead to shorter observation times at night. Remember, this technique balances speed and accuracy. Any final thoughts?
Kinematic Surveying
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Kinematic surveying is where one receiver is stationary while another moves. Why could this method be advantageous?
It allows us to cover more ground quickly, right?
Exactly! It’s great for areas with fewer obstructions. We can collect data efficiently. But what is required for successful kinematic surveying?
We need to maintain a good lock on the necessary satellites as we move!
Correct! Maintaining that lock is vital for accurate data collection. With advancements like On-The-Fly Ambiguity Resolution, this method continues to improve. Can anyone think of a scenario where kinematic surveying could be particularly useful?
Road surveys or mapping applications where you have to move fast!
Exactly! Great connections.
Stop and Go Kinematic Surveying
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Let's explore the stop-and-go kinematic technique. Can someone explain why it's called 'stop and go'?
It collects data only when the receiver is stationary, right?
Exactly! This technique optimizes time between collecting data at stationary points while maintaining satellite tracking during movement. Why might this be advantageous?
We can gather data quickly without needing prolonged static observations!
Precisely! It combines the advantages of static and kinematic methods. However, we must maintain a lock on satellites during the survey. Remember, interruptions can cause the rover to revert to previous known points.
Real-Time Kinematic (RTK) Surveying
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Finally, we have Real-Time Kinematic surveying or RTK. Why is this method preferred in many projects?
Because it offers real-time positioning accuracy!
Right! RTK provides nearly the same positional accuracy as static methods but at a faster rate. Can anyone elaborate on how RTK works?
It requires at least one stationary reference receiver and another moving rover, which communicates through a data link!
Exactly! As long as there's sufficient satellite lock, the rover keeps updating its position as it moves. This makes RTK great for stakeout surveys and other applications needing precision. Any additional notes before we wind up?
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section highlights different GNSS surveying methods, illustrating how each method varies based on location, accuracy requirements, and time efficiency. Techniques like static surveying are discussed for high accuracy, while others like rapid static and kinematic surveying prioritize speed and efficiency.
Detailed
GNSS Surveying Techniques
The Global Navigation Satellite System (GNSS) offers a variety of surveying techniques tailored to specific tasks based on factors like accuracy requirements, time constraints, local terrain, and available facilities. This section delves into several popular GNSS surveying techniques:
1. Static Surveying
This method focuses on obtaining high-accuracy measurements, suitable for control surveys over broad areas. Data is collected continuously from GNSS receivers for a set period, influenced by factors such as satellite visibility and geometry. The longer the observation, the higher the accuracy achieved.
2. Rapid Static Surveying
Rapid static surveying affords a quicker alternative to static surveying, making it ideal for short-range applications such as control densification. By utilizing dual-frequency measurements, this technique resolves ambiguities swiftly without needing an extended observation period. It is beneficial during periods of lower ionospheric disturbances, particularly at night.
3. Kinematic Surveying
This technique involves tracking differential carrier phases when one receiver remains stationary (base) and another moves (rover). It's useful for surveys in unobstructed areas, with shorter observation times and simultaneous data collection allowed. Kinematic surveying is further enhanced by On-The-Fly Ambiguity Resolution (OTF-AR).
4. Stop and Go Kinematic Surveying
Stop and go surveying collects data only when the rover is stationary, providing a balance between speed and precision. Though requiring continuous satellite tracking during movement, this method is effective for detail surveys, especially in areas with minimal signal disruption.
5. Real-Time Kinematic (RTK) Surveying
RTK is a preferred method due to its ability to deliver real-time positioning with high accuracy comparable to static methods. It requires a reference receiver to transmit data to a moving rover, allowing instant positional updates and suitable for applications like stakeout surveying.
Additionally, the advantages and disadvantages of various methods are summarized, highlighting aspects such as equipment costs, accuracy, and time efficiency.
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Overview of GNSS Surveying Techniques
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Chapter Content
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.
Detailed Explanation
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).
Examples & Analogies
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).
Static Surveying
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Chapter Content
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.
Detailed Explanation
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.
Examples & Analogies
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).
Rapid Static Surveying
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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.
Detailed Explanation
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.
Examples & Analogies
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
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Chapter Content
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.
Detailed Explanation
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.
Examples & Analogies
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.
Stop and Go Kinematic Surveying
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Chapter Content
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.
Detailed Explanation
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.
Examples & Analogies
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.
Real-Time Kinematic (RTK) Surveying
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Chapter Content
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.
Detailed Explanation
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.
Examples & Analogies
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.
Differential GNSS (DGNSS) Surveying
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Chapter Content
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.
Detailed Explanation
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.
Examples & Analogies
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.
Key Concepts
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Static Surveying: High-accuracy GNSS method requiring long measurement times.
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Rapid Static Surveying: Faster method suitable for short-distance tasks.
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Kinematic Surveying: Involves stationary and moving receivers to improve data gathering speed.
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Stop and Go Kinematic Surveying: Collects data when stationary, allowing speed and efficiency.
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RTK Surveying: Provides immediate, accurate positioning for staking and other surveying tasks.
Examples & Applications
Using static surveying for establishing control points in a large surveying project.
Utilizing RTK surveying during construction for accurate positioning of foundations.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
In static time, we trust the site, the longer we wait, the baselines are right.
Acronyms
RAPID for Rapid Static
Quick
Accurate
Punctual
In-Demands
economical.
Stories
Imagine a surveyor named Kine who always had to move fast, training a rover to gather data on a journey along scenic roads.
Memory Tools
Remember the S for 'Stop' in stop-and-go—it shows we track the points only when we are slow.
Flash Cards
Glossary
- Static Surveying
A GNSS surveying method that collects continuous data over a period for high accuracy.
- Rapid Static Surveying
A surveying method emphasizing speed with shorter observation times, suitable for short-range applications.
- Kinematic Surveying
A differential tracking technique where one receiver remains stationary while another records data.
- RTK Surveying
Real-Time Kinematic surveying provides real-time positioning with high accuracy using data links between stations.
- Baseline
The distance between two GNSS receivers used in measuring and establishing control points.
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