Precision Positioning Measurement: A Comprehensive Guide

Summary

Precision positioning measurement is essential for accurate navigation and geolocation. This article explores the impact of tropospheric and ionospheric refraction, as well as multi-path effects on GPS accuracy. We discuss methods to mitigate these influences, ensuring more reliable and precise measurements. Learn about the latest techniques and technologies that enhance GPS accuracy, supported by data and statistics.

Tropospheric Observations

Tropospheric observations can be categorized into dry and wet components. The dry component is influenced by atmospheric pressure and humidity, while the wet component is primarily affected by atmospheric humidity along the signal propagation path.

Dry and Wet Components

• Dry Component: This can be accurately determined using ground-based atmospheric data.
• Wet Component: This is more challenging to measure accurately. For short baselines (less than 50 km), the impact of the wet component is relatively minor.

Ionospheric Refraction

Single-frequency GPS receivers often use ionospheric models provided by navigation data to mitigate the influence of ionospheric refraction. However, these models are not perfect and typically correct about 75% of the ionospheric errors (source).

Dual-Receiver Method

Using two or more receivers to observe the same satellite simultaneously can significantly reduce the influence of ionospheric refraction. This method is particularly effective for short distances between observation stations (less than 20 km). The residual error from ionospheric refraction using this method is minimal, often not exceeding 0.000001.

Tropospheric Refraction Mitigation

To mitigate the effects of tropospheric refraction, several approaches can be employed:

1. Differenced Observables: For observation stations close to each other (less than 20 km), the signal path through the troposphere is similar. By observing the same satellite simultaneously, the tropospheric refraction can be significantly weakened.

Multi-Path Effects

Multi-path effects, also known as multi-path errors, occur when the receiver antenna receives not only the direct signal from the satellite but also reflections from surrounding surfaces. This can cause measurement errors, which vary depending on the nature of the reflecting surfaces.

Impact of Multi-Path Effects

• Code Pseudorange: In a typical reflective environment, the impact on the measured code pseudorange is at the meter level.
• Phase Pseudorange: The impact on the measurement phase pseudorange is at the centimeter level.

In highly reflective environments, the impact can be significantly increased, often leading to signal loss and cycle slips in carrier phase measurements.

Mitigation Strategies

1. Antenna Placement: Place the receiver antenna away from strong reflecting surfaces such as water, smooth flat surfaces, and buildings.
2. Antenna Design: Select an appropriate shape and well-shielded antenna.
3. Observation Time: Extend the observation time to weaken the cyclical impact of multi-path effects.
4. Receiver Design: Improve the GPS receiver circuit design to mitigate multi-path effects.

Conclusion

Precision positioning measurement is a complex field influenced by various atmospheric and environmental factors. By understanding and mitigating the effects of tropospheric and ionospheric refraction, as well as multi-path errors, we can achieve more accurate and reliable GPS measurements. Advanced techniques and technologies continue to enhance the precision of GPS systems, making them indispensable tools in navigation and geolocation.

For more information on GPS accuracy and performance, visit the official GPS website.

Interesting Stats

• The current ionospheric models used in single-frequency GPS receivers correct about 75% of ionospheric errors (source).
• In a typical reflective environment, multi-path effects can impact the measured code pseudorange at the meter level and the phase pseudorange at the centimeter level.

By staying informed about these factors and employing effective mitigation strategies, we can continue to improve the accuracy and reliability of GPS systems.