We present an evaluation of the novel absolute quantum gravimeters AQG-A02 and AQG-B10 by the French manufacturer Exail with an emphasis on the user's application and outlook for integration into the routine gravity measurements of the German Federal Agency for Cartography and Geodesy (BKG). Since the delivery of these instruments to BKG, test measurements have been performed at the well-established gravity reference stations in Wettzell and Bad Homburg. Our measurements confirm a sensitivity of 500 nm s−2 Hz−1/2 at a quiet site, as specified, equivalent to a precision of 10 nm/s2 after 1-h integration time, and a combined uncertainty on the order of 100 nm/s2, based on a comparison to the local gravity reference function. We conclude that, as of yet, both AQGs do not reach the accuracy of FG5-type gravimeters, but provide advantages for continuous measurements and operation. Despite occasional technical issues with system reliability and pending research on improving the systematic errors, we expect the AQGs will find a central role in BKG's routine gravity measurements in the near future.
This work presents a global, three-dimensional (latitude–longitude–time) model of the refractive index structure constant (), enabling the spatiotemporally correlated simulation of tropospheric delays for space geodetic observations at radio frequencies. The model is based on an ensemble of 100 XGBoost models trained on 21 years of observations from 18,500 GNSS stations, using meteorological variables from ERA5 as features. It effectively captures high-frequency spatial and temporal variations, achieving a mean absolute error of . To simplify the use of the model, monthly average values are computed on a regular
We describe a model that accounts for the phase rotation that occurs when a receiver or transmitter changes orientation while observing or emitting circularly polarized electromagnetic waves. This model extends work detailing Global Navigation Satellite Systems (GNSS) carrier phase wind-up to allow us to describe the interaction of changing satellite orientation with phase rotation in observing radio telescopes. This development is motivated by, and a critical requirement of, unifying GNSS and Very Long Baseline Interferometry (VLBI) measurements at the observation level. The model can be used for either stationary choke ring antennas or steerable radio telescopes observing either natural radio sources or satellites. Simulations and experimental data are used to validate the model and to illustrate its importance. In addition, we rigorously lay out the feed rotation correction for radio telescopes with beam waveguide and full Nasmyth focuses and validate the correction by observing the effect with dual polarization observations. Using this feed rotation model for beam waveguide telescopes, we produce the first phase delay solution for the VLBI baseline WARK30M–WARK12M. We provide a practical guide to using the feed rotation model in Appendix D.
The International Association of Geodesy defined the International Height Reference System (IHRS) in 2015. IHRS will be realised through the International Height Reference Frame (IHRF) primarily by geopotential numbers. On the global scale, a sparse core reference network is utilised to realise the IHRS, but denser realisations (or densifications) are needed to ensure local access and height datum unification. ITRF ellipsoidal heights and a gravimetric (quasi-) geoid model form the basis for a model-based IHRS realisation, which can be enhanced by levelling to improve local accessibility to the global frame and relative uncertainty. This study investigates incorporating levelling observations in the IHRS realisation process and explores potential improvements. A case study over Sweden using an initial model-based IHRS realisation and precise levelling observations from the Baltic Levelling Ring (BLR) project was performed. The levelling network was adjusted relative to the model-based IHRF geopotential numbers using three approaches regarding the a priori variance–covariance matrix for weighting of the observations: constrained adjustment, weighted adjustment with realistic a priori uncertainties, and weighted adjustment with Variance Component Estimation (VCE) to iteratively tune the variance–covariance matrix. It is shown that the model-based IHRS realisation improves significantly. Both the estimated standard uncertainty of the adjusted IHRF geopotential numbers and the relative standard uncertainty between nodal benchmarks are reduced by approximately 40 per cent in the Swedish case. To fully exploit precise levelling observations in the IHRS realisation process, a weighted adjustment, preferably using VCE to optimally combine the initial model-based geopotential numbers and the levelling observations is recommended.
BeiDou Global Navigation Satellite System (BDS-3) PPP-B2b service greatly promotes the real-time precise point positioning applications. However, previous research works have revealed that a nonnegligible satellite-specific clock bias (SCB) exists in the PPP-B2b clock offset, causing the degradation of PPP-B2b positioning performance. In this paper, a single-station-augmented PPP-B2b considering the SCB via BDS-3 short-message communication (SMC) is proposed. Specifically, an easy-to-implement real-time extraction method of single-differenced (SD) SCB is proposed using a single reference station. Then, based on the extracted SCB augmentation information, a new full-rank estimable SCB-weighted model is proposed to enhance the PPP-B2b positioning. In addition, to effectively transmit the SCB augmentation information without regard to Internet, a delicate design of encoding and broadcast strategy is developed via the BDS-3 SMC function. The results show that the extracted SD SCB series of each satellite is highly stable over a certain period of observation arc. The precision of extracted SD SCB series of each satellite varies from 0.11 to 0.28 ns with a mean value of 0.18 ns. In addition, compared with the traditional PPP-B2b model, the proposed SCB-weighted model improves the positioning performance in the static and kinematic applications. Specifically, for the static application, the positioning accuracy of SCB-weighted model exhibits 35.3%, 66.7%, and 48.2% improvements in east, north, and up directions, respectively; the convergence time exhibits a 39.7% improvement. For the kinematic vehicle application, the SCB-weighted model exhibits a faster re-convergence speed. The positioning accuracy is improved from 0.421 to 0.208 m with a 50.6% improvement. In conclusion, the proposed single-station-augmented PPP-B2b using the SCB-weighted model is highly appreciated for enhancing the PPP-B2b positioning performance.
The prolate spheroidal harmonic series is a well-suited tool for gravity modeling of elongated bodies. In this work, the prolate spheroidal harmonic algorithms for forward modeling of the gravitational field of homogeneous polyhedral bodies are presented. The line integral forms of the prolate spheroidal harmonic coefficients are given using the Gauss divergence and the Stokes theorems, and the discontinuities of the prolate spheroidal coordinates are considered in the integral conversions from the volume integrals of the coefficients into the surface and line integrals. The line integral algorithms with normalizations are numerically stable for high- and ultra-high-degree coefficients and both the small and the large eccentric bodies. The method extending exponent of floating-point numbers may need to be applied for ultra-high-degree coefficients. The good convergences and numerical accuracies of the prolate spheroidal harmonic expansions and the numerical stabilities of the line integral algorithms are verified by the numerical experiments for the gravitational field of the homogeneous comet Hartley 2 with 1752 triangular faces shape model, where the harmonic coefficients and expansions are computed up to the truncated degree/order (d/o) 300. Compared with the spherical harmonic expansions, the prolate spheroidal harmonic converges faster for external observation points.
Various vertical reference levels are used in the coastal zone, for various purposes. Being able to transform accurately and efficiently between them is of increasing interest since the need for seamless data over sea and land is growing due to sea-level rise, coastal engineering, and more frequent storm surges. We present a method for simultaneous calculation of models linking the ellipsoid, the geoid, and mean sea level using least-squares collocation. The method includes calculations of interpolated model surfaces together with associated standard error surfaces that provide estimates of the models’ uncertainty. We have applied the method on data from Norway, including sea level data and GNSS/levelling points, and calculated a mean sea surface and a dynamic ocean topography model. The estimated formal errors of the models range 0.4–1.8 cm and 0.5–3.5 cm, respectively. To assess the dynamic ocean topography model, we compared it with satellite altimetry-based datasets. Depending on which dataset used for comparison, we obtained mean differences between −3.2 and (1.2~textrm{cm}) and standard deviations between 4.2 and 5.0 cm at the outer limit of the domain of the estimated models where the distances to the observations are at their longest.
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