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. 2016 Apr 20;16(4):565.
doi: 10.3390/s16040565.

A Comparative Study of the Applied Methods for Estimating Deflection of the Vertical in Terrestrial Geodetic Measurements

Luca Vittuari  1 , Maria Alessandra Tini  2 , Pierguido Sarti  3 , Eugenio Serantoni  4 , Alessandra Borghi  5 , Monia Negusini  6 , Sébastien Guillaume  7
Affiliations

A Comparative Study of the Applied Methods for Estimating Deflection of the Vertical in Terrestrial Geodetic Measurements

Luca Vittuari et al. Sensors (Basel). .

Abstract

This paper compares three different methods capable of estimating the deflection of the vertical (DoV): one is based on the joint use of high precision spirit leveling and Global Navigation Satellite Systems (GNSS), a second uses astro-geodetic measurements and the third gravimetric geoid models. The working data sets refer to the geodetic International Terrestrial Reference Frame (ITRF) co-location sites of Medicina (Northern, Italy) and Noto (Sicily), these latter being excellent test beds for our investigations. The measurements were planned and realized to estimate the DoV with a level of precision comparable to the angular accuracy achievable in high precision network measured by modern high-end total stations. The three methods are in excellent agreement, with an operational supremacy of the astro-geodetic method, being faster and more precise than the others. The method that combines leveling and GNSS has slightly larger standard deviations; although well within the 1 arcsec level, which was assumed as threshold. Finally, the geoid model based method, whose 2.5 arcsec standard deviations exceed this threshold, is also statistically consistent with the others and should be used to determine the DoV components where local ad hoc measurements are lacking.

Keywords: ITALGEO2005; ITRF; QDaedalus; deflection of the vertical; tie vectors.

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Figures

Figure 1
Figure 1
Area of IRA-INAF observatory of Medicina (Northern Italy) (satellite image courtesy of Google Earth®).
Figure 2
Figure 2
Area of the IRA-INAF observatory of Noto (Sicily) (satellite image courtesy of Google Earth®).
Figure 3
Figure 3
Relation between the geoid undulation N and the deflection of the vertical ε. (Adapted from [27]).
Figure 4
Figure 4
Zeiss Ni1 analogic measurement of the height difference between GNSS-ARP and the South leveling bolt at site Medicina. The inset shows the reference height marker: a bolt on top of a 1.5 m coated metal rod hammered into the ground.
Figure 5
Figure 5
Deflection of the vertical (DoV) components ξ (North) and η (East) calculated from the ITALGEO2005 grid at the Medicina site. The orange dot indicates the point where the DoV was estimated using the GNSS-LEV method; the black star identifies the location of the DoV measured using QDaedalus.
Figure 6
Figure 6
DoV components ξ (North) and η (East) calculated from the ITALGEO2005 grid at Noto site. The orange dots indicate the point for which the DoV was estimated using the GNSS-LEV method; the black stars identify the locations where the DoV was measured using QDaedalus.
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