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Site-dependent effects are accuracy-limiting factors in static and kinematic GNSS-based positioning applications since they cannot be minimized using differential techniques. In general, these effects are separated into signal diffraction, non-line-of-sight (NLOS) signal reception, multipath, and quality of the satellite geometry. In particular, signal diffraction and NLOS reception can lead to huge positioning errors. We present a straight forward approach to mitigate signal diffraction and NLOS reception by forming obstruction adaptive elevation masks, based on terrestrial laser scans. This enables an improvement of the positioning accuracy in high-precision static GNSS applications, even under challenging GNSS measurement conditions. By means of empirical investigations, the approach was tested successfully, and the site-dependent systematic errors can be separated and analyzed. Furthermore, the site-dependent effects and their error sources are assessed in relation to their impact on the accuracy of the positioning solution. We demonstrate that despite poor GNSS measurement conditions, positional accuracies better than 2 mm can be achieved and the ambiguity fixing rate is improved significantly.

Global navigation satellite systems (GNSS) are well suited for attitude determination. The key to high-precision GNSS-attitude determination is the ambiguity resolution. In case of kinematic applications, the rapidity of this process is of particular importance. We present a new instantaneous attitude determination system for GNSS-challenged environments. The single-epoch ambiguity resolution is performed by the ambiguity function method aided by a micro-electro-mechanical system (MEMS), leading to success rates above 99 %. The GNSS/MEMS fusion is realized by the use of an extended Kalman filter. When the system is stationary, a state vector augmentation with a shaping filter reduces systematic effects in the GNSS-attitudes. By means of two field experiments, the system was tested successfully. Despite poor GNSS measurement conditions, it provided reliable and accurate results, with empirical standard deviations in the range of 0.03---0.1 deg for the yaw angle.