Digital Zenith Camera Research Articles

A Test of Height Transfer Using Vertical Deflection Measurements by the Digital Zenith Camera VESTA

A Test of Height Transfer Using Vertical Deflection Measurements by the Digital Zenith Camera VESTA

Результаты сравнения астрономо-геодезического и навигационно-геодезического методов определения составляющих уклонения отвесной линии

The authors present the results of comparing the components of deflection of vertical obtained through astronomical-geodetic and navigational-geodetic methods. The first one is based on comparing astronomical and geodetic coordinates of a location. This method has recently been widely implemented in a digital zenith camera systems using a small-sized digital telescope with an astronomical camera based on CCD or CMOS technologies, a high-precision inclinometer and satellite navigation system receiver. In this case, the combination of a telescope, an astronomical camera and an inclinometer enables determining the local direction of the plumb line, expressed by astronomical coordinates, from observations of stars at the zenith and using high-precision star catalogs. The navigational-geodetic method is based on comparing the results of the normal heights’ increments, defined through geometric leveling, and geodetic heights, computed with the relative method of satellite coordinate determinations. For each method, random and systematic components of the error and its confidence bounds were calculated; the absolute values of the deflection of vertical components at two geographically separated points were compared.

Evaluation of quasi-geoid model based on astrogeodetic measurements: case of Latvia

AbstractSince the development of GNSS techniques, the determination of a precise quasi-geoid model has become even more actual. In terms of this project the staff of the Institute of Geodesy and Geoinformatics (GGI) has developed a new quasi-geoid model based on DFHRS (Digital Finite-element Height Reference Surface) approach additionally using astrogeodetic measurements – vertical deflections (VD), which can be observed by a Digital zenith camera. This paper evaluates a quasi-geoid model results based on vertical deflections, as a study area using the territory of Latvia: the standard deviation of the solution is equal to 0.006 m with observation residuals after the adjustment of minimum and maximum differences −0.012 and 0.012 accordingly. The standard deviation of quasi-geoid heights and h-H values from LGIA database is equal to 0.012 m with minimum and maximum differences −0.026 and 0.025 accordingly. The post-processed terrestrial VD observations have been compared to VD derivatives from EGM2008 and GGMplus geopotential models. The developed quasi-geoid has been compared to the national quasi-geoid model LV’14 and to the Scandinavian NKG2015.

Digital zenith camera accuracy analysis scheme based on digital image processing

This article uses a digital zenith camera to perform field measurements to obtain high-precision astronomical longitude and latitude data. To identify the photographed stellar markers, we utilize FFT and digital image processing methods to do CCD star image matching, the establishment of a numerical fit model for star matching, and then the astronomical coordinates of the station against the table decomposition, and finally the use of astronomical geodesy to calculate the vertical deviation of the station and the error in cyclic observation, to test the instrument in the Sensitivity in both directions, astronomical longitude and astronomical latitude.

数字化天顶摄影仪倾角补偿的影响分析

数字化天顶摄影仪倾角补偿的影响分析

THE USE OF THE AUTOMATED DIGITAL ZENITH CAMERA SYSTEM IN ISTANBUL FOR THE DETERMINATION OF ASTROGEODETIC VERTICAL DEFLECTION

The Digital Zenith Camera Systems (DZCSs) are dedicated astrogeodetic instruments used to obtain highly accurate astrogeodetic vertical deflection (VD) data. The first Turkish DZCS, the Astrogeodetic Camera System (ACSYS), was developed in Istanbul, Turkey in 2015. The ACSYS was capable of determining astrogeodetic VDs with an accuracy of ~0.3 arcseconds. However, it had some limitations in observation duration: because of the semi-automated mechanical design, levelling the system towards zenith was a time-consuming process. Since 2016, the ACSYS has been modernized through system upgrades and new technological components. In this paper, we describe the instrument design of the new DZCS-ACSYS2-observation procedures, evaluation of the test data and calculations of these data. The preliminary ACSYS2 astrogeodetic test observations were conducted at Istanbul Technical University (ITU) test station. The standard deviation results of the repeated observations reveal a VD measurement precision of ~0.3 arcseconds for both the North-South and East-West components. To investigate the accuracy of the system, a lightweight total station based-geodetic system-QDaedalus-was also used at the ITU test station. The comparison of the VDs data between ACSYS2 and QDaedalus system shows that the ACSYS2 can produce reliable VDs data.

Analysis of the Influence of Tilt Angle on Star Identification of Digital Zenith Camera

Considering that the tilt angle of the digital zenith camera in the fine state affects the position of the star image on the CCD sensor, this paper established the CCD image coordinate calculation model in the horizontal state according to the principle of quaternion coordinate transformation, and analyzed the influence of the tilt angle on the star map identification combined with the experimental data. The experimental results show that the tilt angle has a significant impact on the position of star imaging, but does not affect the results of star map identification.

PERFORMANCE ANALYSIS OF LATVIAN ZENITH CAMERA

Since finalizing of design in 2016, the digital zenith camera of the University of Latvia was involved in a number of test observations as well as field observations at about 70 different sites. The paper presents analysis of observation results, estimation of instrument’s performance and accuracy. Random and systematic error sources are outlined. Impact of anomalous refraction on vertical deflection determination is discussed. Results of adaptation of GAIA reference star catalog for astrometric data reduction are reported.

基于数字天顶仪的星点图像坐标误差分析

基于数字天顶仪的星点图像坐标误差分析

倾斜状态下数字天顶仪快速定位方法分析

倾斜状态下数字天顶仪快速定位方法分析

粗调平状态数字天顶仪定位方法研究

粗调平状态数字天顶仪定位方法研究

Software development and its description for Geoid determination based on Spherical-Cap-Harmonics Modelling using digital-zenith camera and gravimetric measurements hybrid data

Over several years the Institute of Geodesy and Geoinformatics (GGI) was engaged in the design and development of a digital zenith camera. At the moment the camera developments are finished and tests by field measurements are done. In order to check these data and to use them for geoid model determination DFHRS (Digital Finite element Height reference surface (HRS)) v4.3. software is used. It is based on parametric modelling of the HRS as a continous polynomial surface. The HRS, providing the local Geoid height N, is a necessary geodetic infrastructure for a GNSS-based determination of physcial heights H from ellipsoidal GNSS heights h, by H=h-N. The research and this publication is dealing with the inclusion of the data of observed vertical deflections from digital zenith camera into the mathematical model of the DFHRS approach and software v4.3. A first target was to test out and validate the mathematical model and software, using additionally real data of the above mentioned zenith camera observations of deflections of the vertical. A second concern of the research was to analyze the results and the improvement of the Latvian quasi-geoid computation compared to the previous version HRS computed without zenith camera based deflections of the vertical. The further development of the mathematical model and software concerns the use of spherical-cap-harmonics as the designed carrier function for the DFHRS v.5. It enables - in the sense of the strict integrated geodesy approach, holding also for geodetic network adjustment - both a full gravity field and a geoid and quasi-geoid determination. In addition, it allows the inclusion of gravimetric measurements, together with deflections of the vertical from digital-zenith cameras, and all other types of observations. The theoretical description of the updated version of DFHRS software and methods are discussed in this publication.

Improvement of star identification based on star trace in star images

Abstract Digital zenith camera system is a highly accurate positioning instrument in geodetic astronomy. It can capture 16 star images in one experiment unit in different azimuthal camera orientations and the stars in each star image should be identified using star catalogue. But the amount of calculation is very large, the efficiency of star identification is low. Now, the improvement of star identification is mainly through updating algorithm. Considering that there exist identical stars in these star images, this paper provides a new method to improve star identification. The star trace is deduced taking the earth rotation and instrument rotation into consideration. The errors of star trace are also analyzed. Then select the same stars that appear in the star images taken in the initial position and after rotating one angle. Using the identical stars instead of star catalogue and the star trace to identify the rest stars, the efficiency will get improved. The analysis of experimental data shows that there are many identical stars in these star images. The appearance of one star can be predicted according to the star trace. The star identification get improved by using the same stars in these star images. And it costs less time to identify the stars in star images, but the precision is approximately equal.

基于数字天顶仪的时间标定方法

基于数字天顶仪的时间标定方法

DIGITAL ZENITH CAMERA OF THE UNIVERSITY OF LATVIA

Design of digital zenith camera in Institute of Geodesy and Geoinformatics of the University of Latvia started in 2009. Now, after tests of a prototype, improvements of design and manufacturing of the second version, it has reached operational status. The paper describes construction of camera, features of it‘s control software. Vertical deflection determination results are discussed.

Digital astro-geodetic camera system for the measurement of the deflections of the vertical: tests and results

ABSTRACTThis study introduces the new results of a novel low-cost digital zenith camera system operated in Turkey that uses astronomical and geodetic instrumentation. Currently, it is possible to determine deflections of the vertical (DoV) components by using a vast amount of information gathered from geo-referenced star images, tilt measurements, and Global Navigation Satellite System technology. This new design of an astro-geodetic camera system is used for calculating DoV components with 12 independent solutions on a test station in Istanbul, and additional observations were performed to investigate the external accuracy of the system on a test network. A specific leveling method is developed to align system toward the zenithal direction. The final results of the observations on a test station located in Istanbul indicate that the accuracy of the system is about ±0.19 arc-seconds in latitude and ±0.28 arc-seconds in longitude determination. The system has been further tested on a network with 4 control points that have averagely 20 km baselines. At the test network, the root mean square of the average value of the vertical deflections is calculated as ±0.36 arc-seconds. Furthermore, DoV components are compared with the values that are calculated using global geopotential models.

Метрологические характеристики астрогеодезического измерителя уклонений отвесной линии на основе цифрового зенитного телескопа

Метрологические характеристики астрогеодезического измерителя уклонений отвесной линии на основе цифрового зенитного телескопа

Experiences with the QDaedalus system for astrogeodetic determination of deflections of the vertical

This paper explores the astrogeodetic deflection of the vertical (VD) determination with a light-weight tachymeter-based measurement system called ‘QDaedalus’ developed at ETH Zurich. A description of the relevant components of the system is given to show the set-up and operation. The measuring process including CCD-tachymeter calibration and the astronomical data processing are summarised. The paper then analyses the achievable accuracy of VDs based on new measurement data acquired in Bavaria over several nights. Our measurements were executed atop a pillar on the roof of the TUM and at six stations in the Bavarian Alps (Estergebirge) with highly accurate VDs from previous digital zenith camera measurements available. Our comparisons indicate an accuracy level of 0.15–0.20 arc-seconds for VDs measured with QDaedalus. As a conclusion, our results show that the QDaedalus system is a promising sensor for accurate local astronomical gravity field surveys when a zenith camera is not available.

基于数字天顶仪的视场角分析

基于数字天顶仪的视场角分析

THE ROLE OF ASTRO-GEODETIC IN PRECISE GUIDANCE OF LONG TUNNELS

Abstract. One of prime aspects of surveying projects is guidance of paths of a long tunnel from different directions and finally ending all paths in a specific place. This kind of underground surveying, because of particular condition, has some different points in relation to the ground surveying, including Improper geometry in underground transverse, low precise measurement in direction and length due to condition such as refraction, distinct gravity between underground point and corresponding point on the ground (both value and direction of gravity) and etc. To solve this problems, astro-geodetic that is part of geodesy science, can help surveying engineers. In this article, the role of astronomy is defined in two subjects: 1- Azimuth determination of directions from entrance and exit nets of tunnel and also calibration of gyro-theodolite to use them in Underground transvers: By astronomical methods, azimuth of directions can be determine with an accuracy of 0.5 arcsecond, whereas, nowadays, no gyroscope can measure the azimuth in this accuracy; For instance, accuracy of the most precise gyroscope (Gyromat 5000) is 1.2 cm over a distance of one kilometre (2.4 arcsecond). Furthermore, the calibration methods that will be mention in this article, have significance effects on underground transverse. 2- Height relation between entrance point and exit point is problematic and time consuming; For example, in a 3 km long tunnel ( in Arak- Khoram Abad freeway), to relate entrance point to exit point, it is necessary to perform levelling about 90 km. Other example of this boring and time consuming levelling is in Kerman tunnel. This tunnel is 36 km length, but to transfer the entrance point height to exit point, 150 km levelling is needed. According to this paper, The solution for this difficulty is application of astro-geodetic and determination of vertical deflection by digital zenith camera system TZK2-D. These two elements make possible to define geoid profile in terms of tunnel azimuth in entrance and exit of tunnel; So by doing this, surveying engineers are able to transfer entrance point height to exit point of tunnels in easiest way.