Wet Path Delay Corrections from Line-of-Sight Observations of Effelsberg’s Water Vapour Radiometer for Geodetic VLBI Sessions

Water vapour induced excess path lengths in electromagnetic waves have been one of the most unmanageable errors in space geodesy, such as GPS and VLBI. The difficulty mainly comes from the highly variable distribution of atmospheric water vapour both in time and space. In general, these wet path delays cannot be estimated accurately by atmospheric models that are conventionally used in space geodetic applications. In the last few decades, water vapour radiometry has shown great potential for measuring atmospheric water vapour content. However, the wet path delay retrieval processes are strongly dependent on radiosonde data, although periodic radiosonde observations are rarely available in the vicinity of water vapour radiometers (WVRs). Radiosonde observations are weather profiles from balloon starts which are transmitted by radio signals. On the other hand, the possibility of using a numerical weather model (NWM) instead of a radiosonde has been on the increase in recent years. NWM can provide meteorological profiles for those places where radiosonde data is not available. The focus of this thesis is mainly on the improvement of the wet path delay corrections in geodetic VLBI sessions using the WVR observations at the 100m Effelsberg radio telescope. Compared to other WVRs, the Effelsberg one has a great advantage in terms of observation. It always points at the same direction as the VLBI antenna because it has been installed on the prime focus cabin of the telescope. However the Effelsberg station does not make periodic radiosonde observations. To overcome this weakness, the numerical weather model of the European Centre of Medium Range Weather Forecasts (ECMWF) was introduced. It provides meteorological profiles over Effelsberg such as atmospheric pressures, temperatures, and water vapour pressures. Those profiles were processed by a radiative transfer model, which calculates theoretical measurements of brightness temperature and converts them into wet path delays. These two models were combined to be compared with WVRobserved wet path delays. For a better comparison between wet path delays from the WVR and the models, zenith wet delays (ZWDs) were used. As the results of the comparison illustrate, ZWDs from the models showed higher values than the WVR-measured ones by roughly 30 mm. For comparison with GPS-derived values, average offsets and standard deviations of the models and the WVR were -4.3±11.0 mm and -44.8±24.0 mm, respectively. From these ZWD comparisons it was found that further corrections to the WVR ZWDs are necessary. In addition, the noisy behaviour of the raw WVR ZWD measurements should be smoothed by a running mean method before application. In addition, averaged offsets between the models and the WVR measurements should be determined for the correction of individual sessions. However, already at this step it became obvious that the instrumental calibrations of the radiometer are far from being mature resulting in erroneous absorption profiles. ZWDs from the WVR measurements with different levels of corrections were applied as corrections to the wet components of the atmospheric refraction in the five geodetic VLBI sessions. Impacts on baseline repeatability and height precision by these were investigated. As the results show, the baseline repeatability was improved in terms of Root Mean Squared Error (RMS) when the offset correction was applied. However, the improvement was less than one percent. Although the repeatability of the height component was improved in terms of Weighted RMS (WRMS) with respect to the short term mean height by a factor of 2, the height component itself showed a larger deviation from the original value than that expected from the ZWD corrections. A possible reason is that the estimation of the many parameters in the least squares adjustment can easily affected the height parameter. The conclusion of this study is that the Effelsberg WVR observations are not perfectly suited for wet path delay corrections yet. This is mainly due to the imperfectness of instrumental calibration. Further studies based on an increased number of WVR data with better internal calibrations seems to be necessary to make a final judgment regarding the usefulness of the WVR for wet path delay corrections in geodetic VLBI.Zur Korrektur von feuchtebedingten Laufzeitverzögerungen mit dem co-linearen Wasserdampfradiometer in Effelsberg für geodätische VLBI-Messungen Wasserdampfinduzierte Refraktionseffekte der elektromagnetischen Wellen stellen die zurzeit größte Fehlerquelle bei Messverfahren der Satellitengeodäsie, wie z.B. GPS und VLBI, dar. Die Problematik rührt hauptsächlich her von der stark variierenden Verteilung von atmosphärischem Wasserdampf sowohl in der Zeit als auch im Raum. Im Allgemeinen können diese Laufzeitverzögerungen durch den feuchten Anteil der Atmosphäre nicht exakt genug durch atmosphärische Modelle berechnet werden, die herkömmlich in Satellitengeodäsieanwendungen genutzt werden. In den vergangenen Jahrzehnten hat die Wasserdampfradiometrie ein großes Potential entwickelt, um den atmosphärischen Wasserdampfbestandteil zu messen. Allerdings ist der Prozess der Umrechnung von gemessenen Helligkeitstemperaturen in Laufzeitverzögerungen stark von gleichzeitig durchgeführten Radiosondenmessungen abhängig. Dabei werden die Messergebnisse von an aufsteigenden Ballons befestigten Wettersensoren für verschiedene Druckstufen per Radiosignal ausgesendet. Leider werden periodische Radiosondenbeobachtungen aber nur selten in der Nähe des Wasserdampfradiometers (WVR) durchgeführt. Dem gegenüber besteht seit einigen Jahren die Möglichkeit, ein numerisches Wettermodell anstelle der Radiosondenergebnisse zu nutzen. Ein numerisches Wettermodell kann meteorologische Profile für solche Orte liefern, wo eine Radiosonde nicht verfügbar ist. Der Schwerpunkt dieser Dissertation liegt hauptsächlich auf der verbesserten Bestimmung der Laufzeitverzögerungen durch den feuchten Anteil der Atmosphäre in der geodätischen VLBI, wobei die Wasserdampfradiometerbeobachtungen am Radioteleskop in Effelsberg genutzt werden. Verglichen mit anderen Wasserdampfradiometern hat dieses Instrument große Vorteile hinsichtlich der Messwertgewinnung. Es zeigt immer in dieselbe Richtung wie die VLBI-Antenne, weil es im Primärfokus des Teleskopes installiert ist. In oder in der Nähe von Effelsberg werden jedoch keine Radiosondenbeobachtungen durchgeführt. Um diese Schwäche zu beheben, wurde ein numerisches Wettermodell des European Centre for Medium Range Weather Forecasts (ECMWF) für die Bestimmung von Kalibrierwerten herangezogen. Es liefert für das Radioteleskop in Effelsberg meteorologische Daten wie z.B. Druck, Temperatur und Wasserdampfdruck. Solche Profile wurden in einem Strahlungsübertragungsmodell verarbeitet, welches theoretische Messungen der Helligkeitstemperatur ermittelt und diese in Laufzeitverzögerungen durch den feuchten Anteil der Atmosphäre umwandelt. Um die Laufzeitverzögerungen durch den feuchten Anteil der Atmosphäre aus Wasserdampfradiometermessungen und die Modelle besser vergleichen zu können, wurden alle Laufzeitverzögerungen durch den feuchten Anteil der Atmosphäre auf die Zenitrichtung (Zenith Wet Delays, ZWD) bezogen. Der Vergleich hatte zum Ergebnis, dass die ZWDs der Modelle einen um ca. 30 mm höheren Wert zeigten als jene, die mit einem Wasserdampfradiometer gemessen wurden. Im Vergleich zu GPS-abgeleiteten ZWDs betrugen die durchschnittlichen Offsets der Modelle und des Wasserdampfradiometers -4.3±11.0 mm beziehungsweise -44.8±24.0 mm. Diese ZWDVergleiche haben gezeigt, dass eine Korrektur der WVR ZWDs erforderlich ist. Außerdem hatte es den Anschein, dass die rohen WVR-ZWD-Messungen geglättet werden sollten, um das Rauschen des Instruments zu reduzieren. Für die Fehlerkorrektur wurden außerdem in jeder einzelnen Session durchschnittliche Offsets zwischen den Modellen und den Wasserdampfradiometern berechnet und angesetzt. Allerdings zeigte sich schon hier, dass die interne Kalibrierung des Instruments einige Defizite aufwies und die Ergebnisse dadurch in ihrer Genauigkeit eingeschränkt waren. Die Korrekturen an den Laufzeitverzögerungen in Zenitrichtung aus verschiedenen Ansätzen wurden in fünf geodätischen VLBI-Sessionen verwendet und die Auswirkungen auf die Basislinienwiederholbarkeit und Höhengenauigkeit untersucht. Es stellte sich heraus, dass die Basislinienwiederholbarkeit bei manchen Basislinien verbessert werden konnte, wenn Offsets an den gemessenen WVR-Ergebnissen angebracht wurden. Die Verbesserung war jedoch kleiner als 1 Prozent. Obwohl die Höhengenauigkeit, ausgedrückt als Root Mean Squared Error (RMS) und Weighted RMS (WRMS), um den Faktor 2 verbessert werden konnte, zeigte die Höhenkomponente selbst eine größere Ablage von den Ursprungswerten als erwartet. Als Ursache dafür wurde die Vielzahl der zu schätzenden Parameter und ihre zum Teil hohen Korrelationen identifiziert. Die Schlussfolgerung dieser Untersuchung ist somit, dass die Waserdampfradiometerbeobachtungen in Effelsberg noch nicht gänzlich für die Fehlerbehebung der Laufzeitverzögerungen durch den feuchten Anteil der Atmosphäre geeignet sind, was hauptsächlich auf die Unvollkommenheit einer instrumentellen Kalibrierung zurückzuführen ist. Es werden weitere Studien mit einer größeren Zahl von WVR- Messwerten mit einer verbesserten Kalibrierung des WVR notwendig sein, um die Zweckmäßigkeit des Wasserdampfradiometers für die Fehlerbehebung der Laufzeitverzögerungen durch den feuchten Anteil der Atmosphäre in der geodätischen VLBI abschließend nachweisen zu können

The Environmental Consequences of Globalization: A Country-Specific Time Series Analysis

The dynamic relationships among trade, income and the environment for developed and developing countries are examined using a cointegration analysis. Results suggest that trade and income growth tend to increase environmental quality in developed countries, whereas they have detrimental effects on environmental quality in most developing countries. It is also found that for developed countries, the causal relationship appears to run from trade and income to the environment ─ a change in trade and income growth causes a consequent change in environmental quality, and the opposite relationship holds for developing countries.Developed countries, Developing countries, Environmental quality, Globalization, Time-series analysis, Trade,

The Environmental Consequences of Globalization: A Country-Specific Time-Series Analysis

The dynamic relationships among trade, income and the environment for developed and developing countries are examined using a cointegration analysis. Results suggest that trade and income growth tend to increase environmental quality in developed countries, whereas they have detrimental effects on environmental quality in most developing countries. It is also found that for developed countries the causal relationship appears to run from trade and income to the environment - a change in trade and income growth causes a consequent change in environmental quality, and the opposite relationship holds for developing countries.Developed countries, Developing countries, Environmental quality, Globalization, Time-series analysis, Trade, Environmental Economics and Policy, International Relations/Trade,

KASI Combination Center Report

This report presents the activities of the Korea Astronomy and Space Science Institute (KASI) as an IVS Combination Center during 2012, and it sketches the intended tasks for 2013

Treating Motion as Option with Output Selection for Unsupervised Video Object Segmentation

Unsupervised video object segmentation (VOS) is a task that aims to detect the most salient object in a video without external guidance about the object. To leverage the property that salient objects usually have distinctive movements compared to the background, recent methods collaboratively use motion cues extracted from optical flow maps with appearance cues extracted from RGB images. However, as optical flow maps are usually very relevant to segmentation masks, the network is easy to be learned overly dependent on the motion cues during network training. As a result, such two-stream approaches are vulnerable to confusing motion cues, making their prediction unstable. To relieve this issue, we design a novel motion-as-option network by treating motion cues as optional. During network training, RGB images are randomly provided to the motion encoder instead of optical flow maps, to implicitly reduce motion dependency of the network. As the learned motion encoder can deal with both RGB images and optical flow maps, two different predictions can be generated depending on which source information is used as motion input. In order to fully exploit this property, we also propose an adaptive output selection algorithm to adopt optimal prediction result at test time. Our proposed approach affords state-of-the-art performance on all public benchmark datasets, even maintaining real-time inference speed

COMPARISON OF FOOT MORPHOLOGY AND PREFERRED SHOE FOR IMPROVING RUNNING SHOE FITTING

The purpose of this study was to compare the shoe internal space and foot shapes of different type for increasing sense of shoe fitting. 347 healthy subjects (male=160; female=187) without any pathological conditions of the foot participated in this study. 11 pairs of running shoes have different size (230-280mm) with same material and appearances were prepared and the shapes of shoe last were also measured for these shoes. In order evaluating the sense of shoe fitting, 6 fit indicators were analysed by comparing the shape of shoe last with foot morphology. We could find that people with wider feet tend to wear tighter shoes and narrower feet preferred to wear looser shoes that seems to significantly affect by the experience. And the sense of shoe fitting was significant different from gender and foot type which can be used as important data for recommending shoe size and to make customized shoe

Measurement-based Close-in Path Loss Modeling with Diffraction for Rural Long-distance Communications

In this letter, we investigate rural large-scale path loss models based on the measurements in a central area of South Korea (rural area) in spring. In particular, we develop new close-in (CI) path loss models incorporating a diffraction component. The transmitter used in the measurement system is located on a hill and utilizes omnidirectional antennas operating at 1400 and 2250 MHz frequencies. The receiver is also equipped with omnidirectional antennas and measures at positions totaling 3,858 (1,262 positions for LOS and 2,596 positions for NLOS) and 4,957 (1,427 positions for LOS and 3,530 positions for NLOS) for 1400 and 2250 MHz, respectively. This research demonstrates that the newly developed CI path loss models incorporating a diffraction component significantly reduce standard deviations (STD) and are independent of frequency, especially for LOS beyond the first meter of propagation, making them suitable for use with frequencies up to a millimeter-wave.Comment: 5 pages, 5 figure

Leveraging Spatio-Temporal Dependency for Skeleton-Based Action Recognition

Skeleton-based action recognition has attracted considerable attention due to its compact skeletal structure of the human body. Many recent methods have achieved remarkable performance using graph convolutional networks (GCNs) and convolutional neural networks (CNNs), which extract spatial and temporal features, respectively. Although spatial and temporal dependencies in the human skeleton have been explored, spatio-temporal dependency is rarely considered. In this paper, we propose the Inter-Frame Curve Network (IFC-Net) to effectively leverage the spatio-temporal dependency of the human skeleton. Our proposed network consists of two novel elements: 1) The Inter-Frame Curve (IFC) module; and 2) Dilated Graph Convolution (D-GC). The IFC module increases the spatio-temporal receptive field by identifying meaningful node connections between every adjacent frame and generating spatio-temporal curves based on the identified node connections. The D-GC allows the network to have a large spatial receptive field, which specifically focuses on the spatial domain. The kernels of D-GC are computed from the given adjacency matrices of the graph and reflect large receptive field in a way similar to the dilated CNNs. Our IFC-Net combines these two modules and achieves state-of-the-art performance on three skeleton-based action recognition benchmarks: NTU-RGB+D 60, NTU-RGB+D 120, and Northwestern-UCLA.Comment: 12 pages, 5 figure