Considerations concerning the non-rigid Earth nutation theory

This paper presents the reflections of the Working Group of which the tasks were to examine the non-rigid Earth nutation theory. To this aim, six different levels have been identified: Level 1 concerns the input model (giving profiles of the Earth's density and theological properties) for the calculation of the Earth's transfer function of Level 2; Level 2 concerns the integration inside the Earth in order to obtain the Earth's transfer function for the nutations at different frequencies; Level 3 concerns the rigid Earth nutations; Level 4 examines the convolution (products in the frequency domain) between the Earth's nutation transfer function obtained in Level 2, and the rigid Earth nutation (obtained in Level 3). This is for an Earth without ocean and atmosphere; Level 5 concerns the effects of the atmosphere and the oceans on the precession, obliquity rate, and nutations; Level 6 concerns the comparison with the VLBI observations, of the theoretical results obtained in Level 4, corrected for the effects obtained in Level 5.Each level is discussed at the state of the art of the developments.     

Latitudinal and longitudinal variation of a planetary atmosphere and the occultation experiment

The distribution of neutral and ionized particles about a planet depends, at any time, on angular coordinates (latitude and longitude) as well as altitude. Measurements of the Venusian and Martian atmospheres and ionospheres have been made by means of the ‘occultation’ experiment on-board the Mariner spacecrafts, and the same or similar experiment is planned for future missions to the planets. The conventional method of reducing the residual doppler data assumes spherical symmetry, in which the refractivity of the medium depends only on radius from the center of the planet, or altitude. It is shown that the neglect of angular dependence may introduce serious errors, even for media in which this dependence is slight compared to that in the radial direction, when the plane of motion of the spacecraft about the planet is inclined with respect to the direction of the Earth. The magnitude of the errors may be greatest for a planet such as Mercury and least for Jupiter, if planetary size and atmospheric temperature are the principal factors considered. Mars and Venus being intermediate. These results are most significant for an orbiter in which the orbital plane is inclined to obtain planetary coverage in a matter of months of measurements. Results of calculations for a particular model show that scale height measurements, and, thereby, atmospheric temperature, may be in error by a factor greater than 2 for inclined orbital configurations.     

V. Bücher- und Zeitschriftenschau

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Über das Devon der russischen Tafel

Ohne Zusammenfassung     

Damage phenomenon and petrophysical properties of sandstones at the Phnom Bakheng Temple (Angkor,Cambodia): first investigations and possible conservation measures

Sandstones, clay in the form of bricks and laterite are the building materials used by the Khmer to construct the imposing and magnificent temples in Southeast Asia. Many of these monuments suffer from fracturing, sanding, contour scaling, crust formation and salt weathering. The affinity to weathering is closely connected to the type of material. Two sandstone types classified as feldspathic arenite and quartz arenite of Angkor as well as two arkosic sandstones from Thailand are described and investigated in this study. Important petrophysical properties determined for the different sandstones consist of hydric expansion, thermal expansion, pore radii distribution and ultrasonic velocity. Different investigations such as capillary water uptake, surface hardness, hygroscopic water sorption, and salt resistance tests were undertaken in the laboratory to characterize the various rock types. Observations and quantified damage mapping were done onsite at the Phnom Bakheng Temple. Contour scaling in the form of weathering crusts is one of the main deterioration features observable at the Angkor monuments. Comparisons are made between the building stone, the crust material from the Phnom Bakheng Temple and fresh stone material used for restoration. Significant differences in hydric and especially in thermal expansion of the crust and sandstone have been determined. The results seem to indicate that extensional processes occur, which can be considered a force for detachment (i.e., contour scaling, flaking). In an experimental trial, the hydric and thermal expansion of the weathering crust and the building stone was significantly reduced by using a weak acid for the crust and a swelling inhibitor for the original building stone.     

On the long-term stability of terrestrial reference frame solutions based on Kalman filtering

The Global Geodetic Observing System requirement for the long-term stability of the International Terrestrial Reference Frame is 0.1 mm/year, motivated by rigorous sea level studies. Furthermore, high-quality station velocities are of great importance for the prediction of future station coordinates, which are fundamental for several geodetic applications. In this study, we investigate the performance of predictions from very long baseline interferometry (VLBI) terrestrial reference frames (TRFs) based on Kalman filtering. The predictions are computed by extrapolating the deterministic part of the coordinate model. As observational data, we used over 4000 VLBI sessions between 1980 and the middle of 2016. In order to study the predictions, we computed VLBI TRF solutions only from the data until the end of 2013. The period of 2014 until 2016.5 was used to validate the predictions of the TRF solutions against the measured VLBI station coordinates. To assess the quality, we computed average WRMS values from the coordinate differences as well as from estimated Helmert transformation parameters, in particular, the scale. We found that the results significantly depend on the level of process noise used in the filter. While larger values of process noise allow the TRF station coordinates to more closely follow the input data (decrease in WRMS of about 45%), the TRF predictions exhibit larger deviations from the VLBI station coordinates after 2014 (WRMS increase of about 15%). On the other hand, lower levels of process noise improve the predictions, making them more similar to those of solutions without process noise. Furthermore, our investigations show that additionally estimating annual signals in the coordinates does not significantly impact the results. Finally, we computed TRF solutions mimicking a potential real-time TRF and found significant improvements over the other investigated solutions, all of which rely on extrapolating the coordinate model for their predictions, with WRMS reductions of almost 50%.     

Analysis of Radionuclide Releases from the Fukushima Dai-Ichi Nuclear Power Plant Accident Part I

Part I of this publication deals with the analysis of fission product releases consecutive to the Fukushima Dai-ichi accident. Reactor core damages are assessed relying on radionuclide detections performed by the CTBTO radionuclide network, especially at the particulate station located at Takasaki, 210 km away from the nuclear power plant. On the basis of a comparison between the reactor core inventory at the time of reactor shutdowns and the fission product activities measured in air at Takasaki, especially ⁹⁵Nb and ¹⁰³Ru, it was possible to show that the reactor cores were exposed to high temperature for a prolonged time. This diagnosis was confirmed by the presence of ¹¹³Sn in air at Takasaki. The ¹³³Xe assessed release at the time of reactor shutdown (8 × 10¹⁸ Bq) turned out to be in the order of 80 % of the amount deduced from the reactor core inventories. This strongly suggests a broad meltdown of reactor cores.     

Reflection-constrained 2D and 3D non-hyperbolic moveout analysis using particle swarm optimization

The objective of moveout parameter inversion is to derive sets of parameter models that can be used for moveout correction and stacking at each common midpoint location to increase the signal-to-noise ratio of the data and to provide insights into the kinematic characteristics of the data amongst other things. In this paper, we introduce a data-driven user-constrained optimization scheme that utilizes manual picks at a point on each reflector within a common midpoint gather to constrain the search space in which an optimization procedure can search for the optimal parameter sets at each reflection. The picks are used to create boundary curves which can be derived approximately via an optimization technique or analytically via the derivation of an analytical bounds function. In this paper, we derive analytical forms of bounds functions for four different moveout cases. These are normal moveout, non-hyperbolic moveout, azimuthally dependent normal moveout and azimuthally dependent non-hyperbolic moveout. The optimization procedure utilized here to search for the optimal moveout parameters is the particle swarm optimization technique. However, any metaheuristic optimization procedure could be modified to account for the constraints introduced in this paper. The technique is tested on two-layer synthetic models based on three of the four moveout cases discussed in this paper. It is also applied to an elastic forward modelled synthetic model called the HESS model, and finally to real 2D land data from Alaska. The resultant stacks show a marked improvement in the signal-to-noise ratio compared to the raw stacks. The results for the normal moveout, non-hyperbolic moveout and azimuthally dependent normal moveout tests suggest that the method is viable for said models. Results demonstrate that our method offers potential as an alternative to conventional parameter picking and inversion schemes, particularly for some cases where the number of parameters in the moveout approximation is 2 or greater.