Blažej Bucha

• PhD
• Slovak University of Technology in Bratislava

LGM2026 is an initiative to develop a suite of lunar surface gravitational maps at 500-m resolution based on 3D density. Long-wavelengths (∼50 km) will be taken from a GRAIL model, while short-scale signals (∼500 m) will be derived from the LOLA topography and a 3D crustal density model. Depicted will be the surface gravitational potential and the...

Change of boundary is a method that iteratively downward continues data from a star-shaped boundary to a regular surface, such as the sphere or the ellipsoid of revolution, and then solves a boundary value problem using the downward continued data on the changed boundary. Although the method belongs to concepts involved in the development of recent...

CHarm is a C library to work with spherical harmonics up to almost arbitrarily high degrees. The library is accompanied by a Python wrapper called PyHarm. This release significantly improves performance of point synthesis and analysis, fixes a few bugs and makes a few modifications of the API. New benchmarks are available at https://www.charmlib....

We present a method to integrate external solid spherical harmonic expansions at geographical grids residing on undulated surfaces. It can be used to evaluate area-mean potential values on planetary surfaces that vary within grid cells. This is in contrast with available methods, which assume cells with a constant spherical radius only. When formul...

This paper reports on the progress in the field of total viewshed computation, which was made by the joint efforts of several Slovak and Czech research institutions. The result of the project is eight total viewsheds calculated for the whole territory of Bohemia (57,000 km2) with a relatively high resolution (grid from 5 × 5 to 320 × 320 m, visibil...

Several kinds of approximation of the gravitational potential of a homogeneous body by truncated spherical harmonics series are in use in physical geodesy. However, only one of them is capable of a representation converging to the true potential in the whole layer between the Brillouin sphere and the Bjerhammar sphere of the body. We aim at providi...

We apply three spherical-harmonic-based techniques to deliver external gravitational field models of the asteroid (101955) Bennu within its circumscribing sphere. This region is known to be peculiar for external spherical harmonic expansions, because it may lead to a divergent series. The studied approaches are (i) spectral gravity forward modellin...

We show that far-zone topography-implied gravitational effects may be accurately computed via external spherical harmonics not only above the limit sphere encompassing all the masses, but also inside it on planetary topographies. Although a rigorous mathematical proof is still missing, our numerical experiments indicate that this is possible, provi...

We present two novel approaches to residual terrain modelling (RTM), one of which is practical and the other rather theoretical. The first provides a solution to the harmonic correction issue and the high-frequency error of the spectral filter problem. As its key feature, cap-modified spectral gravity forward modelling is applied to deliver near-zo...

Cap-modified spectral gravity forward modelling is extended in this paper to the full gravity vector and tensor expressed in the local north-oriented reference frame. This is achieved by introducing three new groups of altitude-dependent Molodensky's truncation coefficients. These are given by closed-form and infinite spectral relations that are ge...

Plain Language Summary Measurement and study of the gravitational force (the g value) is essential for geoscientists concerned with, for example, mineral prospection and investigation of Earth's gravitational field. Most applications require the analyst to remove the gravitational signal caused by the surrounding and remote terrain (mountains and v...

Residual terrain modelling (RTM) plays a key role for short-scale gravity modelling in physical geodesy, e.g. for interpolation of observed gravity and augmentation of global geopotential models (GGMs). However, approximation errors encountered in RTM computation schemes are little investigated. The goal of the present paper is to examine widely us...

Recent numerical studies on external gravity field modelling show that external spherical harmonic series may diverge near or on planetary surfaces. This paper investigates an alternative solution that is still based on external spherical harmonic series, but capable of avoiding the divergence effect. The approach relies on the Runge–Krarup theorem...

Spectral gravity forward modelling is a technique that converts a band-limited topography into its implied grav-itational field. This conversion implicitly relies on global integration of topographic masses. In this paper, a modification of the spectral technique is presented that provides gravity effects induced only by the masses located inside o...

In physical geodesy, the residual terrain modelling (RTM) technique is frequently used for high-frequency gravity forward modelling. In the RTM technique , a detailed elevation model is high-pass filtered in the topography domain, which is not equivalent to filtering in the gravity domain. This in-equivalence, denoted as spectral filter problem of...

We develop a high-resolution regional gravity field model by a combination of spherical harmonics, band-limited spherical radial basis functions (SRBFs) and the residual terrain model (RTM) technique. As the main input data set, we employ a dense terrestrial gravity database (3 – 6 stations per km²), which enables gravity field modelling up to very...

We present global and regional gravity field models to degree 130 based on the GOCE kinematic orbit from the period 01 November 2009 to 11 January 2010. The gravity field models are parameterized in terms of the Shannon and Kaula's spherical radial basis functions. The relation between the unknown expansion coefficients and the kinematic orbit of t...

p>The combined gravity field model EIGEN-6C4 (Förste et al., 2014) is the latest combined global gravity field model of GFZ Potsdam and GRGS Toulouse. EIGEN-6C4 has been generated including the satellite gravity gradiometry data of the entire GOCE mission (November 2009 till October 2013) and is of maximum spherical degree and order 2190. In this s...

Fast spherical harmonic synthesis (SHS) at multiple points based on the lumped coefficients approach is very well-established technique. However, this method cannot be applied to SHS at irregular surfaces, as the points must be regularly spaced and refer to a regular surface such as the sphere or the ellipsoid of revolution. In this paper we presen...

We present a novel graphical user interface program GrafLab (GRAvity Field LABoratory) for spherical harmonic synthesis (SHS) created in MATLAB®. This program allows to comfortably compute 38 various functionals of the geopotential up to ultra-high degrees and orders of spherical harmonic expansion. For the most difficult part of the SHS, namely th...