Abstract
Single-epoch relative GPS positioning has many advantages, especially for monitoring dynamic targets. In this technique, errors occurring in previous epochs cannot affect the position accuracy at the current epoch, but careful processing is required, and resolving carrier phase ambiguities is essential. Statistical ambiguity resolution functions have been used to determine the best values of these ambiguities. The function inputs include as a minimum the known base station position, the approximate roving antenna position, and the dual-frequency carrier phase measurements from both receivers. We investigate different solutions to find the ambiguity function inputs that achieve the highest ambiguity resolution success rate. First, we address the rover seed position. A regionally filtered undifferenced pseudorange coordinate solution proves better than a double-differenced one. Multipath errors approximately repeat themselves every sidereal day in the case of static or quasi-static antennas; applying a sidereal filter to the pseudorange-derived positions mitigates their effects. Second, we address the relative carrier phase measurements, which for medium to long baselines are significantly affected by ionospheric propagation errors imperfectly removed during differencing. In addition to the International GNSS Service ionospheric model, we generate a local pseudorange-based ionospheric correction. Applying this correction improves the quality of the phase measurements, leading to more successful ambiguity resolution. Temporally smoothing the correction by means of a Kalman filter further improves the phase measurements. For baselines in the range 60–120 km, the mean absolute deviation of single-epoch coordinates improves to 10–20 cm, from 30–50 cm in the default case.
Highlights
Using single-epoch GPS positioning has many advantages in high-multipath and restricted sky visibility situations, especially when monitoring dynamic targets where sudden and unpredictable movements occur
This suggests that the majority of the improvement seen in solution 3KF compared with the original solution 1 is the result of improved seed coordinates combined with more compatible local ionospheric corrections, with the latter being a significant factor affecting the availability of solutions
More significant improvement arises from parameterising the local ionospheric model as a zenith delay rather than using satellite-specific terms, because the single zenith parameter is more precise and robust
Summary
Using single-epoch GPS positioning has many advantages in high-multipath and restricted sky visibility situations, especially when monitoring dynamic targets where sudden and unpredictable movements occur In this technique, each data epoch is processed independently and so measurement errors and outages occurring in previous epochs cannot affect the current epoch’s accuracy. Strict attention must be paid to the other positioning errors such as receiver dependent biases, satellite dependent biases and signal propagation biases i.e. ionospheric and tropospheric delays These errors must be eliminated to ensure correct ambiguity resolution and obtain the highest possible accuracy. We develop a local code pseudorange-based ionospheric zenith delay correction model to augment the IGS 2D ionospheric model These models are used to provide improved a priori roving antenna coordinates and corrected double-difference carrier phase observations. We examine the use of Kalman filtering to reduce noise in the local ionospheric model by temporal smoothing
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