Field procedure and data collection tool: Towards controlling GPS multipath error for mapping within urban semi-closed areas

Multipath error, a significant challenge in GNSS positioning, arises from signals reaching the receiver via multiple paths, thus biasing range and location. This paper presents a new tool and charting method, using a predefined model, to mitigate multipath effects in pseudorange measurements within U-shaped urban obstructions. The model incorporates obstruction dimensions and receiver location, utilizing L1 and L2 carrier frequencies. Focusing on pseudorange errors caused by multipath at obstruction distances of 7–52 m, the study determines optimal observation times for various satellite systems and signal combinations. Charts are provided to determine the optimum observation time for the maximum required attainable accuracy, obstruction ratios (D/H), and angles (α). Results showed that total error decreased with longer observation times (10–120 minutes), ranging from 2 mm to 18.1 cm. Higher D/H ratios (closer obstructions) correlated with larger errors. Smaller obstruction angles generally yielded smaller errors, especially with longer observation times. The study produced a new charting tool to determine optimal observation time based on desired accuracy, D/H ratio, and α, aiming to minimize multipath error in obstructed environments. This tool aids in selecting optimal GPS antenna placement, measurement time, and expected accuracy in environments where reflection coefficients are difficult to determine.