GTE: a new software for gravitational terrain effect computation: theory and performances

Abstract

The computation of the vertical attraction due to the topographic masses, the so-called Terrain Correction, is a fundamental step in geodetic and geophysical applications: it is required in high-precision geoid estimation by means of the remove–restore technique and it is used to isolate the gravitational effect of anomalous masses in geophysical exploration. The increasing resolution of recently developed digital terrain models, the increasing number of observation points due to extensive use of airborne gravimetry in geophysical exploration and the increasing accuracy of gravity data represents nowadays major issues for the terrain correction computation. Classical methods such as prism or point masses approximations are indeed too slow while Fourier based techniques are usually too approximate for the required accuracy. In this work a new software, called Gravity Terrain Effects (GTE), developed to guarantee high accuracy and fast computation of terrain corrections is presented. GTE has been thought expressly for geophysical applications allowing the computation not only of the effect of topographic and bathymetric masses but also those due to sedimentary layers or to the Earth crust-mantle discontinuity (the so-called Moho). In the present contribution, after recalling the main classical algorithms for the computation of the terrain correction we summarize the basic theory of the software and its practical implementation. Some tests to prove its performances are also described showing GTE capability to compute high accurate terrain corrections in a very short time: results obtained for a real airborne survey with GTE ranges between few hours and few minutes, according to the GTE profile used, with differences with respect to both planar and spherical computations (performed by prism and tesseroid respectively) of the order of 0.02 mGal even when using fastest profiles

Moho Depth and Crustal Architecture Beneath the Levant Basin from Global Gravity Field Model

“…The latter has been simply obtained by computing the gravitational effects of the European Moho model [32] by means of GTE software [33,34]. As it can be seen, for wavelengths smaller than about 20 km, the observation error (blue line) is larger than the Moho signal (red line), which implies that useful information is not retrievable, from GECO, below such a threshold.…”

“…In detail, a complete Bouguer anomaly (see Figure 4a) has been computed by estimating the gravitational effects of topography and bathymetry with the GTE package (a FFT-based software for the computation of the terrain effect) [33,34], using a reference density value of 2670 kg/m 3 . Note that the used gravitational field has a formal resolution of about 10 km.…”

“…The first factor, namely the accuracy of the inversion operator, can be evaluated by means of a simple closed-loop test, where a realistic Moho model in the region of interest, e.g., obtained from the European Moho, is considered. By means of the GTE software [33], the effects, in terms of gravity disturbances, of a synthetic model made of only two layers (i.e., crust and upper Mantle) were computed considering constant densities equivalent to 2850 kg/m 3 and 3250 kg/m 3 , respectively, and separated by the Moho interface. Consequently, the inversion algorithm on the synthetic field is executed.…”

Space-Wise approach for airborne gravity data modelling

“…where δg GGM is the spherical harmonic synthesis of the GGM up to its maximum degree/order L max computed along the aircraft trajectory, while δg RTC is the RTC computed on the same points. Terrain corrections are computed, exploiting fast Fourier transform algorithms, by means of the GTE software (Sampietro et al 2016).…”

A New Tool for Airborne Gravimetry Survey Simulation

“…Both the terrain corrections within this work have been computed using a hybrid algorithm that exploits a combined Fast Fourier Transform-prisms approach, working in spherical approximation [19].…”