Suppression of Systematic Errors of Electronic Distance Meters for Measurement of Short Distances

Abstract

In modern industrial geodesy, high demands are placed on the final accuracy, with expectations currently falling below 1 mm. The measurement methodology and surveying instruments used have to be adjusted to meet these stringent requirements, especially the total stations as the most often used instruments. A standard deviation of the measured distance is the accuracy parameter, commonly between 1 and 2 mm. This parameter is often discussed in conjunction with the determination of the real accuracy of measurements at very short distances (5–50 m) because it is generally known that this accuracy cannot be increased by simply repeating the measurement because a considerable part of the error is systematic. This article describes the detailed testing of electronic distance meters to determine the absolute size of their systematic errors, their stability over time, their repeatability and the real accuracy of their distance measurement. Twenty instruments (total stations) have been tested, and more than 60,000 distances in total were measured to determine the accuracy and precision parameters of the distance meters. Based on the experiments’ results, calibration procedures were designed, including a special correction function for each instrument, whose usage reduces the standard deviation of the measurement of distance by at least 50%.

Mathematical Model and Calibration Procedure of a PSD Sensor Used in Local Positioning Systems

“…ToA and ToF are used in systems based on interferometry [ 2 ], time of flight cameras [ 3 , 4 ] or ultrasound [ 5 ], in which the sender and receiver share hardware and can detect when the signal is emitted and received, and therefore, measure signal flight time or the phase difference of arrival (PoA-PDoA). The sender and the receiver are distant, so they must be synchronized in order to obtain the propagation times.…”

Error in hydraulic head and gradient time-series measurements: a quantitative appraisal

“…Estimating the positioning errors of total stations is even more complicated due to the combination of EDM and angle sensors (Walker and Awange, 2018). Braun et al (2015) thoroughly investigated the accuracy and precision of industrystandard EDM devices over a well-calibrated distance of 40 m. They found that the accuracy varied from 0-4 mm, with some devices showing dependence on the measurement Figure 3. Illustration of the influence that the instrument resolution has on the measurement error: a continuous, time-variable head is measured at discrete time intervals by instruments with analogue-to-digital conversion resolution of 5, 2 and 0.1 mm.…”

“…distance. We use the precision of 0.5 mm stated by Braun et al (2015) for our error analysis (Table 1).…”

“…Open GMI may suffer from a time delay in the water level response to changes in subsurface pore pressure, either because the well screen is partially clogged or improperly sized or because the well volume is so large that water cannot flow fast enough through the surrounding porous media and well screen to allow equilibration of the water level inside the well with the groundwater pressure (e.g., Hvorslev, 1951). In low-permeability materials like compacted peat or finegrained sediments, time lags can be on the order of hours or even longer, which precludes the registration of the response to rapid processes such as for example river flooding events (Hanschke and Baird, 2006) but also to water level changes induced by pumping, ocean tides or atmospheric pressure changes (e.g., Bredehoeft, 1967). Observation wells may also take appreciable time to readjust after the water level inside was raised by water displaced by inserting measurement instruments.…”

Author response to SC2

“…Open GMI may suffer from a time delay in the water level response to changes in subsurface pore pressure, either because the well screen is partially clogged or improperly sized or because the well volume is so large that water cannot flow fast enough through the surrounding porous media and well screen to allow equilibration of the water level inside the well with the groundwater pressure (e.g., Hvorslev, 1951). In low-permeability materials like compacted peat or finegrained sediments, time lags can be on the order of hours or even longer, which precludes the registration of the response to rapid processes such as for example river flooding events (Hanschke and Baird, 2006) but also to water level changes induced by pumping, ocean tides or atmospheric pressure changes (e.g., Bredehoeft, 1967). Observation wells may also take appreciable time to readjust after the water level inside was raised by water displaced by inserting measurement instruments.…”