Norbert Zehentner

Graz University of Technology | TU Graz · Institute of Geodesy

The Gravity Recovery Object Oriented Programming System (GROOPS) is a software toolkit written in C++ that enables the user to perform core geodetic tasks. Key features of the software include gravity field recovery from satellite and terrestrial data, the determination of satellite orbits from global navigation satellite system (GNSS) measurements...

ITSG‐Grace2018 is a new series of GRACE‐only gravity field solutions based on reprocessed GRACE observation data (L1B RL03) and the latest atmosphere and ocean dealiasing product (AOD1B RL06). It includes unconstrained monthly and constrained daily solutions, as well as a high‐resolution static gravity field. Compared to the previous ITSG release,...

We demonstrate that the Swarm mission serves as an interesting source of global gravimetric data to fill gaps and periods not covered by the GRACE and GRACE-FO missions, be it with reduced spatial resolution. We illustrate that major geophysical signals that take place during such periods can be observed by Swarm at regional scales. For the first 5...

This article describes the raw observation approach as implemented at Graz University of Technology to determine GNSS products like satellite orbits, clocks, and station positions. To assess the performance of the approach, 15 years (2003–2017) of observations from a network of 245 globally distributed IGS stations to the GPS constellation were pro...

Compared to the ITSG-Grace2016 release, multiple improvements within the processing chain have been implemented: updated background models, co-estimation of tides and stochastic modeling of satellite orientation measurements. The ITSG-Grace2018 release is based on Level-1B Release 03 data and the AOD1B Release 06 dealiasing product. It includes unc...

This Technical Note intends to: i) provide guidelines for GPS data screening or weighting strategies to efficiently mitigate ionosphere-induced artifacts in the gravity field; ii) recommend the inclusion of measured or modelled non-gravitational accelerations in the production of the gravity field models (WP421 to WP424); and iii) conclude on the a...

Many global navigation satellite system (GNSS) applications, e.g. Precise Point Positioning (PPP), require high-quality GNSS products, such as precise GNSS satellite orbits and clocks. These products are routinely determined by analysis centers of the International GNSS Service (IGS). The current processing methods of the analysis centers make use...

Gravity field recovery from high-low satellite to satellite tracking has been applied successfully to former gravity missions like CHAMP and GOCE. The process to derive gravity field estimates from GNSS observations is separated into two steps. First kinematic orbits for the LEO satellite are derived from the GNSS measurements. Subsequently the kin...

Many global navigation satellite system (GNSS) applications, e.g. Precise Point Positioning (PPP), require high-quality GNSS products, such as precise GNSS satellite orbits and clocks. These products are routinely determined by analysis centers of the International GNSS Service (IGS). The current processing methods of the analysis centers make use...

Many global navigation satellite system (GNSS) applications, e.g. Precise Point Positioning (PPP), require high-quality GNSS products, such as precise GNSS satellite orbits and clocks. These products are routinely determined by analysis centers of the International GNSS Service (IGS). The current processing methods of the analysis centers make use...

The Swarm satellites continue to provide high-quality hl-SST data. We use these data to derive the time-varying gravity field of the Earth at 1500km resolution, on a monthly basis since December 2013. We combine the gravity field solutions computed with the data of all three satellites, as provided by the Astronomical Institute (ASU), Astronomical...

The Swarm satellite mission provides important information regarding the temporal changes of Earth’s gravity field. Several European institutes routinely process Swarm GPS data to produce kinematic orbits, which forms the basis for the estimation of monthly gravity fields. Each institute follows a different gravity field estimation approach and all...

Observing temporal changes of gravity has become a vital source of information about changes in the system Earth. Currently these variations are observed by the satellite mission Gravity Recovery and Climate Experiment (GRACE). Besides this mission no other technique is capable of providing the same resolution, both in space and time. Although a fo...

The Gravity Field And Climate Experiment (GRACE) has granted invaluable insight into the redistribution of surface mass, by providing monthly snapshots of the Earth’s gravity field. Highly dynamic events like floods, which can build up and drain on time scales from hours to weeks, are however difficult to resolve with this comparatively coarse samp...

It is of great interest to numerous geophysical studies that the time series of global gravity field models derived from Gravity Recovery and Climate Experiment (GRACE) data remains uninterrupted after the end of this mission. With this in mind, some institutes have been spending efforts to estimate gravity field models from alternative sources of...

The Earth’s Magnetic Field and Environment Explorers (Swarm), launched in November 2013, aim at improving the knowledge of the geomagnetic field. Nevertheless, the data gathered by the Global Positioning System (GPS) and star tracker instruments are also useful for geodetic applications, in particular to measure large-scale temporal variations of E...

The GPS instruments on-board the three Earth’s Magnetic Field and Environment Explorer (Swarm) satellites provide the opportunity to measure the gravity field model at basin-wide spatial scales. In spite of being a geo-magnetic satellite mission, Swarm’s GPS receiver collects highly accurate hl-SST data (van den IJssel et al., 2015), which has been...

Compared to the predecessor ITSG-Grace2014, multiple improvements within the processing chain have been implemented: updated background models, instrument data screening, improved accelerometer calibration, improved numerical orbit integration, and covariance function estimation. The ITSG-Grace2016 gravity field model consists of two parts: (1) Unc...

SWARM is an ESA mission of three satellites to study the geomagnetic field, each equipped with a GPS receiver, which were successfully placed in orbit in November 2013. Over the year 2014, there were several changes in the processing of Swarm GPS data that improved the quality of obtained gravity field solutions. Although the accuracy and resolutio...

Precise orbit determination is an essential part of the most scientific satellite missions. Highly accurate knowledge of the satellite position is used to geolocate measurements of the onboard sensors. For applications in the field of gravity field research, the position itself can be used as observation. In this context, kinematic orbits of low ea...

Although the main purpose of the SWARM satellites is to study the Earth's magnetic field, they are also well suited to study a second component of the system Earth, the gravity field. The Earth's gravity field can be investigated by analyzing satellite orbits. Fortunately the satellites are equipped with geodetic grade GPS receivers for the purpose...

Since the launch of the European Space Agency’s (ESA) Gravity field and Ocean Circulation Explorer (GOCE) satellite in 2009 and its end in 2013, a sequence of official GOCE gravity field models was released. One of the series of models follows the so called time-wise approach (EGM_TIM). They are purely based on GOCE obser- vations such that they ar...

Kinematic orbit determination for Low Earth Orbiting satellites is one of the core elements in gravity field recovery from GNSS tracked satellites. The accuracy of the kinematic orbit positions directly determines the achievable accuracy in terms of gravity field results. We apply a precise point positioning approach based on raw GNSS observations,...

Different approaches have been proposed to bridge the possible gap between GRACE and GRACE-FO. One of these methods is Satellite-to-Satellite tracking in high-low mode. The main part of this approach is the kinematic orbit determination of Low Earth orbiters. GNSS observations are utilized to determine the satellite orbit without using any apriori...

The ITSG-Grace2014 GRACE-only gravity field model consists of a high resolution unconstrained static model (up to degree 200) with trend and annual signal, monthly unconstrained solutions with different spatial resolutions as well as daily snapshots derived by using a Kalman smoother. Apart from the estimated spherical harmonic coefficients, full v...

After more than 4.5 years in orbit, the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission ended with the reentry of the satellite on 11 November 2013. This publication serves as a reference for the 5th gravity field model based on the time-wise approach (EGM_TIM_RL05), a global model only determined from GOCE observations. Du...

The SLR observations to spherical geodetic satellites, e.g., LAGEOS-1/2, Starlette, Stella, AJISAI and LARES, provide remarkable information about the temporal variations of the very long wavelength part of the Earth's gravity field. As opposed to the low Earth orbiting satellites tracked by GPS high-low satellite-to-satellite tracking (GPS hl-SST)...

GRACE is undoubtedly one of the most important sources to observe mass transport on global scales. However, GRACE has outlived its predicted life time and the satellite system is showing signs of fatigue. As the value of any geophysical or environmental record is proportional to the length of the time series, the geo-scientific communities are seri...

The restricted sensitivity of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) gradiometer instrument requires satellite gravity gradiometry to be supplemented by orbit analysis in order to resolve long-wavelength features of the geopotential. Several approaches have been proposed to exploit the kinematic GPS-derived GOCE orbit...

Kinematic orbit determination based on GNSS measurements is a core element for gravity field determination from Low Earth Orbiting Satellites as for example GRACE and GOCE. Presently used algorithms for kinematic orbit determination are based on observation combinations, like for example the ionosphere-free combination or double differences. In thi...

After the launch of the European Space Agency's (ESA) Gravity field and Ocean Circulation Explorer (GOCE) satellite in 2009, the fourth generation of ESAs official Earth's gravity field models were computed within ESA funded High-level Processing Facility (HPF). From the time series of November 2009 to June 2012 effectively two years of 1HZ sampled...

The restricted sensitivity of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) gradiometer instrument requires satellite gravity gradiometry to be supplemented by orbit analysis in order to resolve long-wavelength features of the geopotential. Several approaches have been proposed to exploit the kinematic GPS-derived GOCE orbit...

One method for gravity field determination is satellite-to-satellite tracking(SST) in high-low mode. Therefore GPS (Global Positioning System) observations are used to estimate precise orbit positions and these are then used to gain the desired information about the earth's gravity field. In this context several approaches exist. One of them is the...

Estimating the time-variable gravity field signal has become an important task in climate research. Different scientific communities rely on the produced time series of gravity field information to investigate for example ice melting, changes in water storage or the effects of heavy earthquakes. Today the only measurement system which can provide t...