Twenty Years of Experience Running Calibration Baseline

Transcription

1 Environmental Engineering 10th International Conference eissn / eisbn Vilnis Gediminas Technical University Lithania, April 2017 Article ID: enviro DOI: Twenty Years of Experience Rnning Calibration Baseline Arnas Bga 1, Raimndas Ptrimas 2 1,2 Calibration Laboratory, Institte of Geodesy, Vilnis Gediminas Technical University, Lithania s: 1 arnas.bga@vgt.lt (corresponding athor); 2 raimndas.ptrimas@vgt.lt Abstract. The athors of the paper are sharing their 20 years of experience in sing Kyviškės Calibration Baseline. The Kyviškės Calibration Baseline (1320 m) is the longest calibration baseline in Lithania. The baseline is calibrated reglarly with 5 7 years period. The first time these measrements were performed in 1997 and repeated in 2001, 2007, 2008 and The same Kern Mekometer ME5000 EDM (electronic distance measrement) instrment was sed for all the measrements performed. By bilding additional pillar aside from the baseline pillars the Kyviškės Baseline was converted to a triangle-shaped test field in The reslts confirm good stability of the baseline, which is now sed for calibration of the EDM instrments, total stations and GNSS (global navigation satellite system) receivers. Keywords: calibration, baseline, EDM, length measrement. Conference topic: Technologies of Geodesy and Cadastre. Introdction EDM instrments calibration is a poplar topic and every srveyor shold be concerned abot his instrment calibration periodically (Hazelton 2009). Calibration laboratory of Institte of Geodesy at VGTU (Vilnis Gediminas Technical University) has established and is rnning Kyviškės Calibration Baseline since 1996 (Jokela et al. 1999). The same Kern Mekometer ME5000 EDM instrment was sed for all the measrements performed. The prpose of bilding calibration baseline was to establish calibration facilities for EDM instrments. Six observation pillars were fndamented on the grassland on the Western side of the Kyviškės airfield. Calibration of the Kyviškės Calibration Baseline is done on the reglar basis at approximate 5 years interval. Repeated high precision measrements with traceability to Finnish National Standard are essential in validating new measrement standards. The original baseline was first measred in Jne 1997 in co-operation between the Institte of Geodesy of VGTU and the Finnish Geodetic Institte (FGI). Since 1997 a for more calibrations of the Kyviškės Calibration Baseline were performed by cooperating FGI and VGTU. Baseline calibration reslts proved stability of the baseline and sitability for EDM instrments calibration. Calibration laboratory of VGTU is accredited for EDM instrments calibration by Lithanian National Accreditation Brea since Metrological activities at the VGTU are gided by qality management system and meet the reqirements of ISO standards. The srveying activities are becoming increasingly international recently. Srveyors take part in the international projects and participate in the tenders where positioning techniqes are applied. Moreover, the accredited calibration and testing laboratories have to demonstrate their proficiency. The proficiency testing (comparative calibration or testing) is an important way of meeting the reqirements of the international standards in the area of qality assrance of the laboratory reslts. Therefore the EDM calibration baselines in different contries are reqired. Along with establishing of the seventh pillar and extending the calibration baseline to a triangle-shaped test field in 2000 the preconditions were created to se baselines for testing GPS receivers, theodolites, total stations and laser scanners. Facilities and baseline calibration Calibration laboratory of Institte of Geodesy, VGTU owns two baselines for EDM instrment verification and calibration. The shorter one (15 m length) is sitated in the premises of the VGTU abd therefore is ofeten called VGTU calibration baseline. The Kyviškės Calibration Baseline is 1320 m length and is located 15 km otside Vilnis in the Kyviškės Airport (ICAO code EYVK). It is a regional airport managed by VGTU and sed mainly for VGTU Aviation Institte pilot training prposes. Kyviškės Calibration Baseline was calibrated by Finnish Geodetic Institte 5 times: in 1997, 2001, 2007, 2008 and The transfer standard sed for Kyviškės Calibration Baseline was Kern ME5000 high precision EDM instrment with prism reflector, calibrated at the Nmmela Standard Baseline. The lengths at Kyviškės are traceable to the definition of the metre. The Nmmela Standard Baseline in Finland, measred reglarly with the Väisälä interference comparator, and the qartz gage system determining the scale in it, are essential measrement standards in the traceability chain (Jokela et al. 2009) Arnas Bga, Raimndas Ptrimas. Pblished by VGTU Press. This is an open-access article distribted nder the terms of the Creative Commons Attribtion (CC BY-NC 4.0) License, which permits nrestricted se, distribtion, and reprodction in any medim, provided the original athor and sorce are credited.

2 Bga, A.; Ptrimas, R Twenty years of experience rnning calibration baseline The prpose of establishing the Kyviškės Calibration Baseline was to create calibration facilities for the EDM instrments. A sitable site was selected in the Kyviškės airfield (fnctioning since 1947), which is still sed for pilots training. The Kyviškės airfield was assigned to the VGTU in The flat nobstrcted area of the airfield is very fitting for the calibration baseline. The area of the airfield and the Kyviškės Calibration Baseline was fenced by metal net limiting possible access for strangers. The pillars of the baseline are fndamented 3.25 m below the grond srface. An inslated steel pipe is anchored sing reinforced concrete. The soil in Lithania never freezes bellow 1.5 m in winter. The topsoil textre is mostly composed of sand and sandy loam in Kyviškės, which is typical for this part of Lithania. 6 observation pillars are bilt in line deflecting arond 10 from the North Soth direction. The baseline extends p-slope with an approximate grade of 0.5% from 1 to 6 pillar. Fig. 1. Orthophoto of the Kyviškės Calibration Baseline The distances from the first to the following pillars are 100 m, 360 m, m, 1300 m and m respectively. 10 more calibration line combinations are possible from other than the first pillar. The seventh pillar was bilt in 2000 on the eastern side of the rnway, 644 m to 949 m from the other pillars (Būga et al. 2008). By bilding the seventh pillar additional 6 observable distances in the test field were created (Fig. 1). All the seven observation pillars are not protected from the direct Sn. Therefore portable mbrellas covering EDM instrments and thermometers are sed dring snny days. Observation pillars are located in line from North to Soth, it makes observer feel comfortable dring the measrements as Sn mostly shines to his back. The Kyviškės Calibration Baseline is the longest (1320 metres) calibration baseline in Lithania and among the several ones most freqently calibrated in Erope recently. The Kyviškės Calibration Baseline was established by the Institte of Geodesy, VGTU in 1996 for the calibration of the EDM instrments (Jokela et al. 1999). The Finnish Geodetic Institte together with the Institte of Geodesy, VGTU are measring the Kyviškės Calibration Baseline in 5 7 year cycles. In EDM precision measrements accrate and precise meteorologic parameter measrements are essential. Temperatre mst be measred in the shade at both interval ends: at the instrment and the reflector. Temperatre is measred at instrment and reflector height. The atmospheric pressre mst be measred at the instrment for each interpillar distance. To obtain a higher accracy calibration, atmospheric pressre can also be observed at the reflector, for each inter-pillar interval. The significance of errors in the meteorological observations on the EDM distance can be smmarised as follows: an error in temperatre of 1 C affects the distance by 1ppm. An error in pressre of 1hPa 2

3 Bga, A.; Ptrimas, R Twenty years of experience rnning calibration baseline affects the distance measrement by 0.3ppm. Hmidity has only a small effect on EDM measrements. An error in the partial water vapor pressre of 1 hpa cases 0.04 ppm impact on distance measrements. Relative hmidity (%) or partial water vapor pressre of observations can be taken to frther improvement of the accracy of the calibration (Pollinger et al. 2012; Reger 1990). The Figre 2 presents variations in the length of the Kyviškės Calibration Baseline with reference to the mean vale of all five baseline calibrations dring ,8 0,6 0,4 Length variation, mm 0,2 0-0,2-0, ,6-0, Baseline length, m Fig. 2. The Kyviškės Baseline length variations The Figre 3 presents variations in the length of the VGTU Calibration Baseline with reference to the mean vale of all three baseline calibrations dring ,0 Length variation, mm 0,5 0,0-0,5-1, , Baseline length, m Fig. 3. VGTU Baseline length variations 3

4 Bga, A.; Ptrimas, R Twenty years of experience rnning calibration baseline EDM instrments calibration dring Calibration Laboratory is permanently sing Kyviškės Calibration Baseline for EDM instrments calibration. This means that calibration baseline is visited at least once every second week EDM instrments at the Calibration laboratory were calibrated since its establishment till the end of Different total station models and handheld laser distance meters broght for calibration are listed in Table 1 and 2. Table 1. Distribtion of calibrated total stations (listed by prodcer) dring Geodimeter 1 1 GeoMax Leica Nikon Sokkia Spectra precision 1 3 Topcon Trimble Table 2. Distribtion of calibrated handheld laser distance meters (listed by prodcer) dring Bosch 1 5 Leica Disto A* Leica Disto D* Leica Disto Lite Leica Disto Classic Spectra Precision Stabila Other Nmber of calibrated instrments is related to the steps taken by Metrologic Inspection. More active raids of Metrologic Inspection to check validity of instrments verification means more clients at Calibration Laboratory becase instrment calibration is normally done along with instrment verification. Calibration ncertainty estimation Lately some improvement to process of estimation of calibration ncertainties was introdced. Instrment constants and errors are determined dring EDM instrment calibration process. Instrment constant is determined by performing series of measrements at seven baseline intervals. Measrements are done in three trns (Ptrimas 2010). One trn is composed of three measred intervals s 1, s2, s3 on a straight line (Fig. 4). Instrment constant is compted sing formla: Fig. 4. Intervals measred for instrment constant determination 1 r Ci r i = 1 C =, (1) 4

5 Bga, A.; Ptrimas, R Twenty years of experience rnning calibration baseline where C i = S3 S1 S2, r nmber of trns, S i mean vales of measred intervals. Total ncertainty of mean constant is obtained sing formla: C r 1 2 = C i r, (2) i= 1 where C = S3 S1 S2 d ; d + ncertainty contribtion estimate de to electronic digital indicator resoltion is 0.29 mm when vale of indicator division is 1 mm, from formla: Si standard ncertainty of mean interval is compted S i = n ( S j S) j= 1 ( 1) n n 2, (3) 1 n where S = S i, here S j vale of measred interval, n nmber of interval measrements. n i= 1 If C C, then instrment constant is corrected with vale C and new vale is entered to the instrment s memory. Instrment calibration is contined sing five intervals (20, 360, 760, 960, 1320 m) of Kyviškes calibration baseline. Systematic calibration correction for every measred interval is compted sing formla: V = S S, (4) S E i where S E interval etalon vale, S mean vale of measred interval. Total ncertainty of calibration correction is compted: i V d E S AP At Z i = , (5) here d = 0.29 mm ncertainty contribtion estimate de to electronic digital indicator resoltion; E etalon line ncertainty contribtion according to calibration certificate; S mean correction ncertainty contribtion compted from (3) formla; AP ncertainty contribtion de to atmospheric pressre inflence, compted from (6) formla; ncertainty contribtion de to air temperatre inflence, compted from (7) formla; At z= 0.21 mm ncertainty contribtion de to centering of the instrment and reflector. Standard ncertainty de to atmospheric pressre and air temperatre are compted from formlas: AP 79 S 10 = t 6 p ; (6) At 79 P S 10 = ( t) 2 6, (7) here p ncertainty of the atmospheric pressre measrement is 2 hpa; t ncertainty of the air temperatre measrement is 0.5 C. The reported expanded ncertainty of mean correction is stated as the standard ncertainty of measrement mltiplied by the coverage factor k = 2 (EA-4/ ), which for a normal distribtion corresponds to a coverage probability of approximately 95%: t U = k V. (8) Calibration laboratory after performed calibration is prodcing a certificate of calibration where calibration reslts with expanded ncertainties are listed. Together with the calibration reslts a compted new vale of the reflector constant together with expanded ncertainty is provided. 5

6 Bga, A.; Ptrimas, R Twenty years of experience rnning calibration baseline Conclsions The Kyviškės Calibration Baseline is a national measrement standard for calibration of EDM instrments in Lithania. The Kyviškės Calibration Baseline was calibrated five times dring the last twenty years. The reglar calibrations proved good stability of the pillars and reliability of the baseline. The length variation of the baseline sections dring 5 measrement cycles is within ±0.7 mm. The obtained total ncertainty of the baseline is in the interval between ±0.3 mm and ±0.9 mm. The Kyviškės Calibration Baseline measrements in allowed for accmlating sfficient data set to be sed for the ftre analysis of stability, repeatability, reprodcibility and inflence of the weather conditions. The experience that was gained dring twenty years of operation will be sed in frther activities of the Calibration Laboratory. Calibration Laboratory calibrates approximately 47 total stations and 33 handheld laser distance meters a year. Additionally GNSS receivers, theodolites, levelling instrments, laser scanners are calibrated at Kyviškės Calibration Baseline and shorter baseline located at the laboratory. References Būga, A.; Jokela, J.; Ptrimas, R Traceability, stability and se of the Kyviskes calibration baseline the first 10 years, in the 7th International Conference Environmental Engineering: selected papers, May, 2008 Vilnis, Lithania. Vol. III: Vilnis: Technika, ISBN EA-4/ Expression of the ncertainty of measrement in calibration. Eropean co-operation for Accreditation. 79 p. Hazelton, N. W. J Instrment calibration for the 21st Centry. Presented at the MSPS 57th Annal Meeting, St. Clod. 22 p. Jokela, J.; Petroškevičis, P.; Tlevičis, V Kyviškės calibration baseline. Reports of the FGI, 99:3, p. 15. Jokela, J.; Häkli, P.; Būga, A.; Ptrimas, R On tracebility of long distances, in Proceedings of XIX IMEKO World Congress Fndamental and Applied Metrology, 6 11 September, 2009, Lisbon, Portgal, Pollinger, F.; Meyer, T.; Beyer, J.; Doloca, N. R.; Schellin, W.; Niemeier, W.; Jokela, J.; Hakli, P.; Abo-Zeid, A.; Meiners-Hagen, K The pgraded PTB 600 m baseline: a high-accracy reference for the calibration and the development of long distance measrement devices, Measrement Science and Technology 23: p. [online], [cited 31 October 2016]. Available from Internet: stacks.iop.org/mst/23/ Ptrimas, R Elektroninių tolimačių kalibravimo metodika. VGTU, Geodezijos instittas, Kalibravimo laboratorija. Vilnis. 18 p. Reger, J. M Electronic distance measrement: an introdction. 3rd totally revised ed. Berlin: Springer-Verlag. 266 p. 6