News

A new model of laser beam delay in the atmosphere

11-09-2019

When performing Satellite Laser Ranging (SLR) to artificial Earth satellites, the laser beam passes through the atmosphere twice: from station to satellite and after reflection from the retroreflector from the satellite to the ground station. The laser beam is delayed each time by several up to several dozen meters. The delay occurs primarily in the lowest layer of the atmosphere - the troposphere - and depends to a large extent on atmospheric pressure, and to a lesser extent on the content of water vapor, temperature and carbon dioxide concentration in the troposphere.
The current tropospheric delay models take into account only meteorological measurements performed at laser stations along with measurements of distances to satellites. Currently used models assume full symmetry of the atmosphere above the stations, which leads to systematic errors and degradation of registered ranges in all laser measurements.
Team of scientists from IGiG UPWr. and GFZ Potsdam jointly developed a new model describing how the laser beam is delayed in the atmosphere taking into account the asymmetry of the atmosphere. This is the first model of this type, which is based both on the use of meteorological measurements at stations to calculate the delay towards the zenith, and on numerical weather models to determine the oblique delay towards the satellite because then the laser beam passes through different layers of the atmosphere. For example, the troposphere layer above the equator is much thicker than above the poles, thus the dominant parameter describing the asymmetry is the northern gradient of the tropospheric delay. The developed model also takes into account local conditions around laser stations, e.g. terrain (in mountainous terrain) or the vicinity of water reservoirs.
The laser beam behaves differently in the atmosphere than the electromagnetic wave in the microwave techniques used in Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). In the case of microwave observations, atmosphere asymmetry models have been used for several years. However, laser observations are about 70 times less susceptible to delay due to water vapor content in the atmosphere than microwave observations, while the hydrostatic delay is greater in laser observations than in microwave observations. On the other hand, laser observations can only be made under a cloudless sky, because the laser does not pass through the clouds, while microwave signals from GNSS satellites or extraterrestrial quasars in the VLBI pass through every type of clouds. Hence the need to develop a model of troposphere laser beam delay was addressed the Polish-German team of scientists from IGiG and GFZ. The delay model works for different types of lasers used in satellite observations: green (532 nm), blue (423 nm), near-infrared (846 and 1064 nm) and significantly reduces systematic errors in SLR solutions.


Fig.1. Comparison of horizontal tropospheric delay gradients for microwaves (e.g., GNSS, left) and laser (SLR, right) for the same hour. The upper drawings represent the northern component, and the lower ones - the eastern component - horizontal gradients.


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ESA Awards

08-09-2019

The 7th International Colloquium on Scientific and Fundamental Aspects of GNSS organized by the European Space Agency (ESA) wah held on September 4-6, 2019 at ETH Zürich in Switzerland. During the plenary session crowning the Colloquium, ESA awarded the best papers presenting groundbreaking research using satellite systems, with particular emphasis on the European Galileo system. As many as three awards went to current and former PhD students and employees from IGiG:

MSc. Grzegorz Bury  (PhD Student at IGiG) received an award for the best presentation in the field of Precise Orbit Determination for a paper on developing an analytical "Box-Wing" model of Galileo satellites enabling significant improvement of satellite positioning by elimination of perturbing forces: "Challenges in the modeling of perturbing forces acting on Galileo orbits",

Dr Karina Wilgan (in 2012-2017 PhD Student at IGiG) received an award in the field of Remote Sensing: Troposphere and Weather for a paper on troposphere research using unmanned aerial vehicles - drones recording satellite signals: "Quality assessment of tropospheric estimates from GNSS and meteorological observations on a UAV",

Dr Krzysztof Sośnica (profesor at IGiG) received an award in the field of Fundamental Physics for a paper on measurements of space-time curvature resulting from general relativity using Galileo satellites: "Measurements of the Galileo orbit geometry deformations caused by the general relativity".
More information on the conference can be found on the Colloquium pages:
https://atpi.eventsair.com/QuickEventWebsitePortal/19a07---7th-gnss-colloquium/7th-international-colloquium
Congratulations!

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GNSS Meteorology Workshop 2019

28-08-2019

We kindly invite everyone who is interested in novel applications of GNSS in meteorology to take a part in the workshop "GNSS Meteorology Workshop 2019".

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Best poster award for IGG PhD

21-05-2019

Damian Tondaś, a PhD affiliated to IGIG, was awarded a best poster award at "4th Joint International Symposium on Deformation Monitoring", Athens, Greece. The work "Investigation for mining-induced deformation in Upper Silesia Coal Basin with multi-GNSS in Near Real-Time" demonstrate research linked with the integration of high frequency GNSS permanent observations and InSAR in the area of Upper Silesia Coal Basin. The work is supported by EPOS-PL project.

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Special lectures on seismology

11-04-2019

We kindly invite you to series of lectures by Prof. Eleftheria Papadimitriou and Prof. Vassilios Karakostas from Aristotle University of Thessaloniki, Greece. Both are professors in seismology at the Geophysics Department. Prof. Karakostas has strong expertise in seismology, seismotectonics, tsunami hazards, statistical seismology, seismic hazard assessment. His series of lectures in IGiG will contain the basic theories and knowledge about Seismic waves, Seismometers, Seismological networks and Seismicity. Prof. Papadimitriou is an expert in long-term earthquake prediction, fault plane solutions and stress patterns. She will present the basics of Stress & Strain, Faults & Fault Plane Solutions, Calculations of stress changes and Global Seismotectonics.
The lectures are targeted primary for Master and PhD students, but all interested on the subject are also kindly invited. The seminars will held on 16th, 17th and 18th of April from 16:00 in lecture room I-M. The visit of the guests is part of the ERASMUS+ initiative.