Control Measurements Between the Geodetic Observation Sites at Metsähovi

The determination of distances consistent with the definition of the base unit of length in the International System of Units (SI), the SI meter, with uncertainties of less than 1 ppm up to 5 km in the open air is a current challenge that is being increasingly required for different applications, including the determination of local ties, calibration baselines, and high precision geodetic metrology in singular scientific and engineering projects. The required knowledge of the index of refraction of the propagating medium at the same level of 1 ppm is a hard limit to the use of precise electronic distance meters, which has motivated the recent development of new two-color, refractivity compensated, electronic distance meter prototypes. As an alternative, the use of Global Navigation Satellite Systems (GNSS) could benefit from their high scale stability although the lack of appropriate estimation of the uncertainties in their sources of error and their unknown propagation into the final result during the data processing has prevented a rigorous uncertainty analysis and, therefore, the use of GNSS for absolute distance determination. Stemming from our initial methodology for a GNSS-Based Distance Meter (GBDM) that was restricted to relatively horizontal baselines and distances up to 1 km only, we have improved the method so that its application range is extended to baselines of up to 5 km with a possibly significant height difference so that it provides the final baseline distance with the corresponding uncertainty derived from the uncertainties in the different error sources rigorously propagated through the equations by which the distance is finally determined. This improved methodology, named as GBDM+, constitutes a significant step forward in the application of GNSS to open air length metrology.

Section: Introductionmentioning

confidence: 99%

GBDM+: an improved methodology for a GNSS-based distance meter

Baselga

García-Asenjo

Garrigues

et al. 2022

“…Although recent efforts [30] achieve relative uncertainties below 10 −6 , these research grade developments are not yet sufficiently stable to rely solely on for the calibration of a baseline. Well established for over 70 years, however, is the calibration procedure by the Finnish Geodetic Institute (FGI) [15,16,31,32]. The so-called Nummela scale transfer is based on a relatively long chain of calibrations.…”

Section: Traceability Of the Reference Lengthmentioning

confidence: 99%

“…Following general principles, in order to provide appropriate test conditions for the highprecision devices discussed before, the uncertainty of the reference should be considerably smaller than 10 −6 l. But baselines whose absolute reference distances are both traceable and known to an uncertainty better than 10 −6 l are extremely scarce. The baseline of the Finnish Geodetic Institute (FGI) at Nummela, Finland [15], has been well established for decades and is the reference for a number of high-precision baselines all over the world, including the newest in Austria [16], Estonia and Lithuania [17]. An alternative calibration route, based on a number of calibrations performed by different traceable distance meters, has been recently applied for the high-accuracy calibration of the novel baseline at Munich, Germany [18], in order to achieve a similar level of accuracy.…”

Section: Introductionmentioning

confidence: 99%

The upgraded PTB 600 m baseline: a high-accuracy reference for the calibration and the development of long distance measurement devices

Pollinger

Meyer

Beyer

et al. 2012

The calibration and verification of high-precision electronic distance meters (EDMs) requires well-characterized and calibrated geodetic baselines. As the length measurements are performed typically over several hundred metres in air, a thorough understanding of the environmental conditions is necessary. In the course of a major refurbishment, the 600 m baseline of the Physikalisch-Technische Bundesanstalt at Braunschweig, Germany, was equipped with a dense environmental sensor network. This paper presents the characterization of this novel reference baseline, including the calibration of the inter-pillar distances, and identifies the major sources of uncertainty for such a length standard. A preliminary expanded standard uncertainty (k = 2) of is deduced for single-slope distance comparisons on the baseline. In the course of a full calibration, the additive constant cEDM of an EDM can currently be determined with an expanded uncertainty of U(cEDM)k = 2 = 6.1 × 10−5 m, and its scale correction sEDM with an expanded uncertainty of U(sEDM)k = 2 = 8.2 × 10−7. As an example, a femtosecond laser-based distance measurement over 600 m on this baseline is presented.

“…The PTB optical sensor was investigated in outdoor environment at the geodetic baseline at Innsbruck [44]. The spectroscopic head (compare figure 3(a)) was integrated into a four-wavelength interferometer to form a refractivitycompensated interferometer capable of measuring geodetic lengths [45].…”

Section: Outdoor Measurementsmentioning

confidence: 99%

Effective humidity in length measurements: comparison of three approaches

Pollinger¹,

Hieta²,

Vainio³

et al. 2012

Humidity is one of the key atmospheric parameters influencing the refractive index of air. Consequently, humidity influences all length measurements whose scale is derived from the speed of light. In this work, we present two laser spectrometers developed for determining the average humidity of air over a long measurement path where local variations may be difficult to measure using conventional sensors. Further, these laser-based systems allow, in principle, good spatial overlap with the beams used in dimensional measurements. The developed systems were compared to each other and to traceable reference sensors during a 65 h measurement campaign. The performance of the systems was investigated under three different conditions: steady state, humidity transient and temperature transient. Both systems were separately tested in outdoor environment at distances up to several hundreds of metres. The measurement results demonstrate that the systems are able to measure the relative humidity below the 4% uncertainty level both in indoor and in outdoor environment.