Determination of Vertical Deflection Based on Terestrial Gravity Disturbance Data (A Case Study in Semarang City)

Abstract

Vertical deflection can be determined by geometrical and physical measurement. In geometrical way, vertical deflection is obtained by comparing astronomical coordinate and geodetical coordinate. In physical way, vertical deflection can be computed from gravity measurement. In the past, vertical deflection was computed from gravity anomaly data. Gravity anomaly data measurement is difficult because it need reduction of gravity from surface of the earth to the geoid using orthometric height from spirit level measurement. In modern era, gravity anomaly data may be replaced by gravity disturbance data whose only required gravity and GNSS (Global Navigation Satellite System) measurement. This research aims to determine vertical deflection in Semarang City from terrestrial gravity disturbance data. The gravity data were measured in March of 2016. Formula of Vening Meinesz that usually used for vertical deflection was replaced by new formula that generated from derivation of function of Hotine. Applying gravity disturbance gave vertical deflection of east-west component that were vary from -1.2” to 12.2” while north-south component were vary from -4.2” to 4.2”. Comparing vertical deflection as computed from terrestrial data to as computed from EGM2008 coefficients showed conformity in shape and values. It was concluded that derivation of function of Hotine could be applied for vertical deflection determination from gravity disturbance.

The Influence of the Deflection of the Vertical on Geodetic Surveys in Brazil

“…As stated by Sabri, Sudarsono and Indriana (2019), the θ can be determined by geometric and physical observations. For geometric observations, the θ is obtained by comparing the astronomical and geodetic coordinates (astrogeodetic method).…”

“…Although less common (Sabri, Sudarsono and Indriana 2019), there is the relation between the θ and the geoidal undulation, where the ε is obtained as function of the geoidal undulation change (Figure 4). (5) Vitti (2017) shows an application using equation ( 5) through leveling and geodetic GNSS positioning for the calculation of component ε.…”

“…The global gravitational model (GGM) adopted was the EGM2008 (Earth Gravitational Model 2008) represented by spherical harmonics up to the maximum degree 2190 corresponding a spatial resolution of about 9 km (ICGEM 2019), widely used as reference for studies and comparisons of the θ (Barzaghi, Carrion, Pepe and Prezioso 2016;Hirt 2010a;Osada 2016 andSabri, Sudarsono and Indriana 2019). The International Centre for Global Earth Models (ICGEM 2020) provides a web service to directly obtain the deflection of the vertical (θ) and its components (η, ξ).…”