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A new PC control software for ZLS-Burris gravity meters
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Contents lists available at ScienceDirect
Geodesy and Geodynamics journal homepages: www.keaipublishing.com/en/journals/geog; http://www.jgg09.com/jweb_ddcl_en/EN/volumn/home.shtml
A new PC control software for ZLS-Burris gravity meters Q5
H. Richard Schulz
Q1,2 Steg 8, D-74538 Rosengarten, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 December 2016 Accepted 6 September 2017 Available online xxx
The previous operation of the ZLS-Burris gravity meter using a PDA already provides a significant improvement of the operation of a metal spring gravity meter. But in the practical field work the observer usually wishes more information about the measurement and the collected data. This situation suggested an improvement of the software and computer hardware. The goal was to develop a small useful PC tool that eliminates these deficits. However, it resulted in a very extensive application software, which was developed during 2011e2015. Along the way, some unwanted effects of the original control circuit were detected. Therefore as a last step a complete new control circuit for the feedback system was developed. This new circuit is fast and smooth and without resonance effects to the system. The algorithm parameters can be specifically adapted to the specific gravity meter. The software has a security system that ensures the user, depending on his level of knowledge, a limited access to the software options. Furthermore, a customer project management system is integrated. The observer, the gravity meters, the projects and maps can be assigned. Several ZLS Burris gravity meters can be managed. A large station data management is integrated. Every station has up to more than twenty parameters, such as the mandatory coordinates or supplementary pictures of the station. External storage and documentation of the measurements are possible with extra modules. In addition the maintenance of the gravity meter system is significantly improved. The motor control of the early ZLS Burris gravity meter is also improved. The complete rotation is displayed on the screen. Finally, two survey examples show the advantages of the software related to the accuracy and the time needed for a measurement. © 2017 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: ZLS Burris gravity meter AGES© control software New control circuit Higher accuracy
1. Introduction In April 2007 the author started working with an early ZLS Burris gravity meter (B25 with cable control and dial motor). It was a significant improvement to work with the PDA (Personal Digital Assistant) but the cable was not easy to handle in heavily overgrown areas. In June 2007 the additional Bluetooth® module was on the market and B25 got it.
E-mail address: offi[email protected]. Peer review under responsibility of Institute of Seismology, China Earthquake Administration.
Production and Hosting by Elsevier on behalf of KeAi
After several microgravity surveys first wishes of more information about the measurement came up. Also the data organisation was not user-friendly. Some special PDA properties were also not helpful (e.g. data loss with empty batteries).1 Though there where a lot of critical comments given to Gravity Consult Corporation (represents ZLS in Europe.) The accuracy of the gravity meter was confirmed at the Relative Gravity Measurement Campaign at the BIPM [1]. The main problem of the system gravity meter and separate computer, was the computer. The complete system worked like a black box and was not user-friendly (e. g. no display of saved data). In 2010 the project started to develop a windows based control software for more transparency and better handling. At the
1 Replaced by a Android tablet with UltraGrav2 software. Some of the negative points are eliminated (no data loss, view measured data).
https://doi.org/10.1016/j.geog.2017.09.002 1674-9847/© 2017 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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beginning it was a common project of the Institute of Geosciences of the University Jena applied geophysical department and Applied Gravity. Since 2011 it was a project of Applied Gravity alone. The first idea was to eliminate the critical points of the PDA. It was not planned to change the control circuit. Gradually more wishes arose (GPS, security system, redundant saving, conversion of geographical to UTM coordinates and vice versa, data import opportunities etc.). After 3 years of software development problems with the gravity meter and its system parameters appeared. Meanwhile it was possible to monitor all gravity meter data in real time. With these tools it was recognised that the control circuit had a problem with noise effects. For example: If there were storms at the Bay of Biscay in a distance of about 900 km, it was not possible to observe a correct gravity value. The reason seemed to be an unadapted control circuit. So the last step was now to optimise the control circuit for these circumstances. The original ZLS circuit is a proportional-integralcontroller (PI) [2]. The new one is a dynamic proportionalintegral-derivate controller (PID). It is optimised for a fast and smooth alignment. Finally the now existing control loop is predisposed for microgravity measurements. So all measurements have the quality of microgravity measurements. For more technical details of the ZLS Burris gravity meter see Refs. [2e4]. The reading-out of values is done in terms of frequencies. Thus, the reading line is given as a frequency. All frequencies are converted to mGal. This is made with the original formulas of ZLS and the determined parameters of the
Table 1 Common parts of AGESfield and AGEScont (grey background). AGES Security level AGESfield AGEScont
AGESprocess
Station data base Gravity meter maintenance Client and project administration User administration Separate organised
maintenance. The user has the possibility to display the raw data (frequencies) or the mGal view. With the help of the raw data it is better to identify potential noise due to the characteristic behaviour of the frequencies. 2. AGES structure The software package is named AGES (Applied Gravity Expert system). It consists of three parts (Table 1): Before the start the user has to log in. With the log in, the user receives a security level. The security levels 2 to 5 restrict the access to parts of the software. The user specific security level should depend on the experience and the knowledge of the operator. In the main menu (Fig. 1) contains a button (setting and information) to get more basic information about the software or to change some properties for all parts (Fig. 2). This paper describes the part of AGESfield in more detail. Subsequently a short view of a result of AGEScont is given. The description is based on the availability of all additional modules. 2.1. AGESfield menu The blue button in the main menu of AGES opens the submenu for AGESfield (Fig. 3). On the upper left side of the AGESfield menu are the three main buttons for the measurement. In the upper middle part are the buttons to get more information about saved data. These may be just the observations or a documentation of the whole measurement. It is possible to reprocess the raw data with other parameters. The data can be exported in other formats, backed up or the data structure can be restored. Only with the module redundant saving it is allowed to delete observations, because then it is still possible to restore the data. On the upper right side there are three buttons. Two of them are mostly used functions from AGES settings (check the connection to the gravity meter and change of the user) and one is the direct connection to AGES settings.
Fig. 1. AGESmainmenu.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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Fig. 2. AGES parameters in the submenu AGES settings and information.
Below this main part are three buttons on a white background. Two of them are used to save energy (sleep mode or hibernation) with the third one the software returns to the AGES main menu. At the lower button area there are five buttons (bypass the main menu) for other often used parts of AGESfield. 2.2. Measurement procedure Before starting a new survey or working day the user can change the properties (Fig. 4a, b). This could be the administration data or data collecting properties (the kind of view, earth tide factor or motor behaviour) or technical properties (average time, maximum beam error or standard deviation).
The user might change the dial value for a new area. Therefore a utility allows to calculate the expected dial value based on GPS data or manual input of the latitude (decimal degree) and elevation. With the UTM module it is possible to use the easting and northing data alternatively. Is a motor installed the dial is turned until the calculated counter unit is reached. With the function “motor hunt” the motor turns to the calibration points, until the feedback range is reached. In the last case no latitude input is necessary. Now the software is ready for the measurements in the field (Fig. 3). After selecting a station from the station data base or input of a new station the control circuit for the measurement is started. There are two possibilities to display the data. The simple graphical view
Fig. 3. AGESfield submenu.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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Fig. 4. a. Data collecting properties, b. Technical properties.
(Fig. 5a) shows in an upper line chart the measured gravity and below the standard deviation. Additional information is given with a bubble level (combination of cross- and long-level), the control activities and the relative temperature. All data are in real time. On the blue operator panel are shown the processing time, the average time interval the measured data, the saved data sets, the standard deviation in numeric and at least some control coloured panels for Bluetooth®, correct data stream and the functional port. The numeric display is shown in Fig. 5b. Beside the station name are the buttons for the field book, information about the measurements of the selected station in the past and information of the free hard disk space. Above the station name the administration data are displayed. If the control circuit is optimised the observer has the numeric view and seven charts with the raw data of the
frequency, the difference to the reading line (DHz), the level frequencies, the relative temperature, the observed gravity with its standard deviation and the activity of the duty cycle in DmGal (Fig. 6a, b). The data is saved in the old ZLS format and in its own ZLSmod format. So the user is able to use elder software for the processing. With special modules the data can be saved redundantly or the whole measurement is saved for reprocessing or postprocessing the raw data. 3. Optimised control circuit and AGEScont The optimised control circuit is faster and smoother than the original circuit (Fig. 7). The parameters of this circuit are different for each gravity meter.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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Fig. 5. a. Simple view with charts, blue operator panel and additional information, b. Numerical view with additional information.
But the general behaviour of different gravity meters is the same. This conclusion is based on some tests of the continuous mode with two optimised ZLS Burris gravity meters (B25 and B42). Fortunately, there was a similar weather situation in the Bay of Biscay as in the year the problems with the original circuit were detected. The tests were not really parallel measurements with one computer but measurements with two computers and time lags between 0.7 and about 0.2 s. The noise was not filtered (oscillation). Fig. 8 shows the behaviour of the two ZLS Burris gravity meters B25 and B42. The curve gives the difference to the reading line frequency. The nearest parallel measurement had a time lag of about 0.2 s. Fig. 9 provides nearly the same DHz difference (1 mGal is around 5 Hz). That shows that both optimised control circuits worked correctly.
4. Extra modules There are several options of extra modules such as easier maintenance, UTM module, import and export opportunities, air pressure import, extra calculation of the earth tides, terrain correction with Hammer charts, drift calculation, terrain correction with digital terrain model and GPS positioning. For using a navigation system the station data could be exported to a gpx-file. 5. Advantages of the work with AGESfield The following two examples show impressively the higher accuracy and speed of the measurements.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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Fig. 6. a. Nulling the beam at the reading line (green). Screenshot during the measurement after 26 s. The blue curve shows the real time data. The pink curve shows the average value of 11 s, b. Combination view numeric display and DHz to the reading line.
Fig. 7. The original control circuit (red line) needs 280 s to get a reading. The optimised control circuit delivers a reading after 75 s. The micro oscillation of the original control circuit is bigger then the oscillation of the optimised control circuit.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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Fig. 8. Detailed part of the raw data of two optimised ZLS Burris gravity meters. Green background see Fig. 9.
Fig. 9. Behaviour of two ZLS Burris gravity meters with their individual optimised control circuits (zoomed).
Example 1: The task was to transfer the gravity value from a benchmark to a new station in a laboratory. The distance between both stations was about 18 km. The gravity benchmark is located in a forest beside a busy road. The time for the averaging was 7 s. The desired accuracy was only 100 mGal and it was interest how precise the gravity meter measured within the shortest time. The loop was measured four times, to be sure to get no bad values by driving bad roads, wind, traffic noise and hand transportation. The working time was 5 h without vertical gradient measurement in the laboratory.
Table 2 shows the results of the gravity difference between the two stations. With the achieved accuracy it is possible to reduce the number of loops from four to two. This saves 50% of the time for the same result under normal noise conditions. Example 2: The TLUG (Thüringer Landesanstalt fur Umwelt und Geologie) commissioned Applied Gravity Dr. Schulz to investigate an area of about 22,400 m2 (251 stations with 10 m spacing). The goal of this small survey was to detect density differences.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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Table 2 Measured and corrected gravity differences between gravity benchmark and the new station.
loop
difference (mGal)
1
14.211
2
14.209
3
14.212
4
14.210
drift correction air pressure correction vertical gradient correction
arithmetical mean: 14.2105 mGal corrected variance: 1.666666 x 10-6mGal uncorrected variance: 1.2544 x 10-6mGal
It was often windy, so the averaging time was set to 11 s. No active filter was used (original PID parameters). The complete measuring process for all stations was recorded. With the original parameters of the ZLS PI-loop for high accuracy it would take around 7 min to get a stable value. With the new AGESfield control loop the measurement was finished in around
standard deviation: ±0.00129 mGal standard deviation: ±0.00112 mGal
2 min, so we saved 5 min at every station and 20 h, respectively 2 days of field work in this project. Additionally the accuracy was not reduced. There are no circular lines (5 mGal distance) around stations (Fig. 10b) in the Bouguer anomalies. It was tested down to a isoline distance of 2 mGal with the same result.
Fig. 10. a. Overview Bouguer anomalies, b. Detailed isolines of the Bouguer anomalies.
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Fig. 11. Documentation of the measurement at the station I2 in mGal (green: area of the used values).
Fig. 12. Documentation of the measurement at the station I3 in mGal (green: area of the used values).
The density anomalies become noticeable by varying distance of the gravity isolines. The horizontal derivation is not discussed here. Only the high standard of measurement is shown at the red ellipsoid between the two stations I2 and I3. The area of the red ellipsoid is representative for similar parts of the survey. Figs. 11 and 12 show the complete measuring process for the two stations in mGal (small tick marks of the Y-axis represent 1 mGal). The shown mGal curves show the raw measured data without correction. 6. Conclusion AGESfield is the first step towards improved data processing [5] and the application of the exact terrain correction [6]. The advantages of data acquisition with microprocessors in gravity meters in conjunction with the control software AGES is obvious: This results in complete transparency of the gravity meter measurements (no black box). With the software AGES it is now possible to assess the quality of the measurement while the measurement is ongoing.
The optimised control circuit enables the gravity meter precise and adapted control and ensures accuracy at a high level. Standard deviation smaller than 1 ìGal are achieved under normal field conditions (noise of the traffic or wind up to 3Bft) without a noise filter. Acknowledgement I thank Gravity Consult Corporation for assisting the project with critical statements and discussion. Special thanks go to ZLS for the encrypting algorithm, which made it possible to start this project. References [1] Z. Jiang, V. Palinkas, O. Francis, P. Jousset, J. Makinen, S. Merlet, M. Becker, A. Coulomb, K.U. Kessler-Schulz, H.R. Schulz, Ch. Rothleitner, L. Tisserand, D. Lequin, Relative gravity measurement Campaign during the 8th international comparison of absolute gravimeters (2009), Metrologia 49 (2012) 95, https:// doi.org/10.1088/0026-1394/49/1/014. [2] ZLS Corporation: Manual for ZLS Burris Gravity Meter. Update 201 6/04/1 5.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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[3] G. Jentzsch, H.R. Schulz, A. Weise, Ein bekanntes Prinzip in einem neuen Gravimeter: das automatisierte Burris-Gravimeter, Allg Vermess (avn) (2015) 168e175, 5/2015. [4] G. Jentzsch, H.R. Schulz, A. Weise, The automated Burris gravity meter for single and continuous observation, in: Journal of geodesy and geodynamics, 2017 (this issue). [5] K.U. Kessler-Schulz, H.R. Schulz, Modelling of gravity variations at the microGal Level, in: Proc.Int. Symp. Terrestrial gravimetry - static and mobile measurements, St. Petersburg 22-25 June 2010, 2010. [6] H.R. Schulz, Improvement of the evaluation of micro-gravity data with the help of an integrated software solution with the focus on the improved terrain correction, in: Proc.Int. Symp. Terrestrial gravimetry - static and mobile measurements, St. Petersburg 20-23 September 2007, 2007.
H. Richard Schulz Diploma thesis in geology with a gravity-tectonic focus (TH Darmstadt, Germany) Doctoral thesis with a microgravity-karst focus (TU Darmstadt, Germany) Since 2001 working as a freelancer geoscientist with the focus of all kinds of microgravity measurements (karst, disused mining, 3D microgravity at BIPM, benchmarks for laboratories). Member of EAGE and DGG. Research interests: microgravity in karst regions and disused mining, improvement of the gravity method in the field (data collecting), optimise the gravity calculations at the mGal level.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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Contents lists available at ScienceDirect
Geodesy and Geodynamics journal homepages: www.keaipublishing.com/en/journals/geog; http://www.jgg09.com/jweb_ddcl_en/EN/volumn/home.shtml
A new PC control software for ZLS-Burris gravity meters Q5
H. Richard Schulz
Q1,2 Steg 8, D-74538 Rosengarten, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 December 2016 Accepted 6 September 2017 Available online xxx
The previous operation of the ZLS-Burris gravity meter using a PDA already provides a significant improvement of the operation of a metal spring gravity meter. But in the practical field work the observer usually wishes more information about the measurement and the collected data. This situation suggested an improvement of the software and computer hardware. The goal was to develop a small useful PC tool that eliminates these deficits. However, it resulted in a very extensive application software, which was developed during 2011e2015. Along the way, some unwanted effects of the original control circuit were detected. Therefore as a last step a complete new control circuit for the feedback system was developed. This new circuit is fast and smooth and without resonance effects to the system. The algorithm parameters can be specifically adapted to the specific gravity meter. The software has a security system that ensures the user, depending on his level of knowledge, a limited access to the software options. Furthermore, a customer project management system is integrated. The observer, the gravity meters, the projects and maps can be assigned. Several ZLS Burris gravity meters can be managed. A large station data management is integrated. Every station has up to more than twenty parameters, such as the mandatory coordinates or supplementary pictures of the station. External storage and documentation of the measurements are possible with extra modules. In addition the maintenance of the gravity meter system is significantly improved. The motor control of the early ZLS Burris gravity meter is also improved. The complete rotation is displayed on the screen. Finally, two survey examples show the advantages of the software related to the accuracy and the time needed for a measurement. © 2017 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: ZLS Burris gravity meter AGES© control software New control circuit Higher accuracy
1. Introduction In April 2007 the author started working with an early ZLS Burris gravity meter (B25 with cable control and dial motor). It was a significant improvement to work with the PDA (Personal Digital Assistant) but the cable was not easy to handle in heavily overgrown areas. In June 2007 the additional Bluetooth® module was on the market and B25 got it.
E-mail address: offi[email protected]. Peer review under responsibility of Institute of Seismology, China Earthquake Administration.
Production and Hosting by Elsevier on behalf of KeAi
After several microgravity surveys first wishes of more information about the measurement came up. Also the data organisation was not user-friendly. Some special PDA properties were also not helpful (e.g. data loss with empty batteries).1 Though there where a lot of critical comments given to Gravity Consult Corporation (represents ZLS in Europe.) The accuracy of the gravity meter was confirmed at the Relative Gravity Measurement Campaign at the BIPM [1]. The main problem of the system gravity meter and separate computer, was the computer. The complete system worked like a black box and was not user-friendly (e. g. no display of saved data). In 2010 the project started to develop a windows based control software for more transparency and better handling. At the
1 Replaced by a Android tablet with UltraGrav2 software. Some of the negative points are eliminated (no data loss, view measured data).
https://doi.org/10.1016/j.geog.2017.09.002 1674-9847/© 2017 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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beginning it was a common project of the Institute of Geosciences of the University Jena applied geophysical department and Applied Gravity. Since 2011 it was a project of Applied Gravity alone. The first idea was to eliminate the critical points of the PDA. It was not planned to change the control circuit. Gradually more wishes arose (GPS, security system, redundant saving, conversion of geographical to UTM coordinates and vice versa, data import opportunities etc.). After 3 years of software development problems with the gravity meter and its system parameters appeared. Meanwhile it was possible to monitor all gravity meter data in real time. With these tools it was recognised that the control circuit had a problem with noise effects. For example: If there were storms at the Bay of Biscay in a distance of about 900 km, it was not possible to observe a correct gravity value. The reason seemed to be an unadapted control circuit. So the last step was now to optimise the control circuit for these circumstances. The original ZLS circuit is a proportional-integralcontroller (PI) [2]. The new one is a dynamic proportionalintegral-derivate controller (PID). It is optimised for a fast and smooth alignment. Finally the now existing control loop is predisposed for microgravity measurements. So all measurements have the quality of microgravity measurements. For more technical details of the ZLS Burris gravity meter see Refs. [2e4]. The reading-out of values is done in terms of frequencies. Thus, the reading line is given as a frequency. All frequencies are converted to mGal. This is made with the original formulas of ZLS and the determined parameters of the
Table 1 Common parts of AGESfield and AGEScont (grey background). AGES Security level AGESfield AGEScont
AGESprocess
Station data base Gravity meter maintenance Client and project administration User administration Separate organised
maintenance. The user has the possibility to display the raw data (frequencies) or the mGal view. With the help of the raw data it is better to identify potential noise due to the characteristic behaviour of the frequencies. 2. AGES structure The software package is named AGES (Applied Gravity Expert system). It consists of three parts (Table 1): Before the start the user has to log in. With the log in, the user receives a security level. The security levels 2 to 5 restrict the access to parts of the software. The user specific security level should depend on the experience and the knowledge of the operator. In the main menu (Fig. 1) contains a button (setting and information) to get more basic information about the software or to change some properties for all parts (Fig. 2). This paper describes the part of AGESfield in more detail. Subsequently a short view of a result of AGEScont is given. The description is based on the availability of all additional modules. 2.1. AGESfield menu The blue button in the main menu of AGES opens the submenu for AGESfield (Fig. 3). On the upper left side of the AGESfield menu are the three main buttons for the measurement. In the upper middle part are the buttons to get more information about saved data. These may be just the observations or a documentation of the whole measurement. It is possible to reprocess the raw data with other parameters. The data can be exported in other formats, backed up or the data structure can be restored. Only with the module redundant saving it is allowed to delete observations, because then it is still possible to restore the data. On the upper right side there are three buttons. Two of them are mostly used functions from AGES settings (check the connection to the gravity meter and change of the user) and one is the direct connection to AGES settings.
Fig. 1. AGESmainmenu.
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Fig. 2. AGES parameters in the submenu AGES settings and information.
Below this main part are three buttons on a white background. Two of them are used to save energy (sleep mode or hibernation) with the third one the software returns to the AGES main menu. At the lower button area there are five buttons (bypass the main menu) for other often used parts of AGESfield. 2.2. Measurement procedure Before starting a new survey or working day the user can change the properties (Fig. 4a, b). This could be the administration data or data collecting properties (the kind of view, earth tide factor or motor behaviour) or technical properties (average time, maximum beam error or standard deviation).
The user might change the dial value for a new area. Therefore a utility allows to calculate the expected dial value based on GPS data or manual input of the latitude (decimal degree) and elevation. With the UTM module it is possible to use the easting and northing data alternatively. Is a motor installed the dial is turned until the calculated counter unit is reached. With the function “motor hunt” the motor turns to the calibration points, until the feedback range is reached. In the last case no latitude input is necessary. Now the software is ready for the measurements in the field (Fig. 3). After selecting a station from the station data base or input of a new station the control circuit for the measurement is started. There are two possibilities to display the data. The simple graphical view
Fig. 3. AGESfield submenu.
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Fig. 4. a. Data collecting properties, b. Technical properties.
(Fig. 5a) shows in an upper line chart the measured gravity and below the standard deviation. Additional information is given with a bubble level (combination of cross- and long-level), the control activities and the relative temperature. All data are in real time. On the blue operator panel are shown the processing time, the average time interval the measured data, the saved data sets, the standard deviation in numeric and at least some control coloured panels for Bluetooth®, correct data stream and the functional port. The numeric display is shown in Fig. 5b. Beside the station name are the buttons for the field book, information about the measurements of the selected station in the past and information of the free hard disk space. Above the station name the administration data are displayed. If the control circuit is optimised the observer has the numeric view and seven charts with the raw data of the
frequency, the difference to the reading line (DHz), the level frequencies, the relative temperature, the observed gravity with its standard deviation and the activity of the duty cycle in DmGal (Fig. 6a, b). The data is saved in the old ZLS format and in its own ZLSmod format. So the user is able to use elder software for the processing. With special modules the data can be saved redundantly or the whole measurement is saved for reprocessing or postprocessing the raw data. 3. Optimised control circuit and AGEScont The optimised control circuit is faster and smoother than the original circuit (Fig. 7). The parameters of this circuit are different for each gravity meter.
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Fig. 5. a. Simple view with charts, blue operator panel and additional information, b. Numerical view with additional information.
But the general behaviour of different gravity meters is the same. This conclusion is based on some tests of the continuous mode with two optimised ZLS Burris gravity meters (B25 and B42). Fortunately, there was a similar weather situation in the Bay of Biscay as in the year the problems with the original circuit were detected. The tests were not really parallel measurements with one computer but measurements with two computers and time lags between 0.7 and about 0.2 s. The noise was not filtered (oscillation). Fig. 8 shows the behaviour of the two ZLS Burris gravity meters B25 and B42. The curve gives the difference to the reading line frequency. The nearest parallel measurement had a time lag of about 0.2 s. Fig. 9 provides nearly the same DHz difference (1 mGal is around 5 Hz). That shows that both optimised control circuits worked correctly.
4. Extra modules There are several options of extra modules such as easier maintenance, UTM module, import and export opportunities, air pressure import, extra calculation of the earth tides, terrain correction with Hammer charts, drift calculation, terrain correction with digital terrain model and GPS positioning. For using a navigation system the station data could be exported to a gpx-file. 5. Advantages of the work with AGESfield The following two examples show impressively the higher accuracy and speed of the measurements.
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Fig. 6. a. Nulling the beam at the reading line (green). Screenshot during the measurement after 26 s. The blue curve shows the real time data. The pink curve shows the average value of 11 s, b. Combination view numeric display and DHz to the reading line.
Fig. 7. The original control circuit (red line) needs 280 s to get a reading. The optimised control circuit delivers a reading after 75 s. The micro oscillation of the original control circuit is bigger then the oscillation of the optimised control circuit.
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Fig. 8. Detailed part of the raw data of two optimised ZLS Burris gravity meters. Green background see Fig. 9.
Fig. 9. Behaviour of two ZLS Burris gravity meters with their individual optimised control circuits (zoomed).
Example 1: The task was to transfer the gravity value from a benchmark to a new station in a laboratory. The distance between both stations was about 18 km. The gravity benchmark is located in a forest beside a busy road. The time for the averaging was 7 s. The desired accuracy was only 100 mGal and it was interest how precise the gravity meter measured within the shortest time. The loop was measured four times, to be sure to get no bad values by driving bad roads, wind, traffic noise and hand transportation. The working time was 5 h without vertical gradient measurement in the laboratory.
Table 2 shows the results of the gravity difference between the two stations. With the achieved accuracy it is possible to reduce the number of loops from four to two. This saves 50% of the time for the same result under normal noise conditions. Example 2: The TLUG (Thüringer Landesanstalt fur Umwelt und Geologie) commissioned Applied Gravity Dr. Schulz to investigate an area of about 22,400 m2 (251 stations with 10 m spacing). The goal of this small survey was to detect density differences.
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Table 2 Measured and corrected gravity differences between gravity benchmark and the new station.
loop
difference (mGal)
1
14.211
2
14.209
3
14.212
4
14.210
drift correction air pressure correction vertical gradient correction
arithmetical mean: 14.2105 mGal corrected variance: 1.666666 x 10-6mGal uncorrected variance: 1.2544 x 10-6mGal
It was often windy, so the averaging time was set to 11 s. No active filter was used (original PID parameters). The complete measuring process for all stations was recorded. With the original parameters of the ZLS PI-loop for high accuracy it would take around 7 min to get a stable value. With the new AGESfield control loop the measurement was finished in around
standard deviation: ±0.00129 mGal standard deviation: ±0.00112 mGal
2 min, so we saved 5 min at every station and 20 h, respectively 2 days of field work in this project. Additionally the accuracy was not reduced. There are no circular lines (5 mGal distance) around stations (Fig. 10b) in the Bouguer anomalies. It was tested down to a isoline distance of 2 mGal with the same result.
Fig. 10. a. Overview Bouguer anomalies, b. Detailed isolines of the Bouguer anomalies.
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Fig. 11. Documentation of the measurement at the station I2 in mGal (green: area of the used values).
Fig. 12. Documentation of the measurement at the station I3 in mGal (green: area of the used values).
The density anomalies become noticeable by varying distance of the gravity isolines. The horizontal derivation is not discussed here. Only the high standard of measurement is shown at the red ellipsoid between the two stations I2 and I3. The area of the red ellipsoid is representative for similar parts of the survey. Figs. 11 and 12 show the complete measuring process for the two stations in mGal (small tick marks of the Y-axis represent 1 mGal). The shown mGal curves show the raw measured data without correction. 6. Conclusion AGESfield is the first step towards improved data processing [5] and the application of the exact terrain correction [6]. The advantages of data acquisition with microprocessors in gravity meters in conjunction with the control software AGES is obvious: This results in complete transparency of the gravity meter measurements (no black box). With the software AGES it is now possible to assess the quality of the measurement while the measurement is ongoing.
The optimised control circuit enables the gravity meter precise and adapted control and ensures accuracy at a high level. Standard deviation smaller than 1 ìGal are achieved under normal field conditions (noise of the traffic or wind up to 3Bft) without a noise filter. Acknowledgement I thank Gravity Consult Corporation for assisting the project with critical statements and discussion. Special thanks go to ZLS for the encrypting algorithm, which made it possible to start this project. References [1] Z. Jiang, V. Palinkas, O. Francis, P. Jousset, J. Makinen, S. Merlet, M. Becker, A. Coulomb, K.U. Kessler-Schulz, H.R. Schulz, Ch. Rothleitner, L. Tisserand, D. Lequin, Relative gravity measurement Campaign during the 8th international comparison of absolute gravimeters (2009), Metrologia 49 (2012) 95, https:// doi.org/10.1088/0026-1394/49/1/014. [2] ZLS Corporation: Manual for ZLS Burris Gravity Meter. Update 201 6/04/1 5.
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[3] G. Jentzsch, H.R. Schulz, A. Weise, Ein bekanntes Prinzip in einem neuen Gravimeter: das automatisierte Burris-Gravimeter, Allg Vermess (avn) (2015) 168e175, 5/2015. [4] G. Jentzsch, H.R. Schulz, A. Weise, The automated Burris gravity meter for single and continuous observation, in: Journal of geodesy and geodynamics, 2017 (this issue). [5] K.U. Kessler-Schulz, H.R. Schulz, Modelling of gravity variations at the microGal Level, in: Proc.Int. Symp. Terrestrial gravimetry - static and mobile measurements, St. Petersburg 22-25 June 2010, 2010. [6] H.R. Schulz, Improvement of the evaluation of micro-gravity data with the help of an integrated software solution with the focus on the improved terrain correction, in: Proc.Int. Symp. Terrestrial gravimetry - static and mobile measurements, St. Petersburg 20-23 September 2007, 2007.
H. Richard Schulz Diploma thesis in geology with a gravity-tectonic focus (TH Darmstadt, Germany) Doctoral thesis with a microgravity-karst focus (TU Darmstadt, Germany) Since 2001 working as a freelancer geoscientist with the focus of all kinds of microgravity measurements (karst, disused mining, 3D microgravity at BIPM, benchmarks for laboratories). Member of EAGE and DGG. Research interests: microgravity in karst regions and disused mining, improvement of the gravity method in the field (data collecting), optimise the gravity calculations at the mGal level.
Please cite this article in press as: H.R. Schulz, A new PC control software for ZLS-Burris gravity meters, Geodesy and Geodynamics (2017), https://doi.org/10.1016/j.geog.2017.09.002
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