Tourists walk past a strange metal structure, which at first glance resembles a huge paper boat, on the recently rebuilt Szaplonczay promenade on the Fonyód plateau, from which, in a unique way, almost the entire Lake Balaton can be seen from Keszthely to Tihany, but in favorable weather conditions, even the Kenese coast can be observed.
Understandably, walkers mostly admire the lake and the opposite Badacsony, but those who also look towards the opposite side of the Bélatelp promenade can also notice the already mentioned gigantic “boat” surrounded by a fence, with a sign in front announcing that it is a “geodesic they see a “base point”, which is used to observe geodynamic and other surface-forming processes.
Geodetic base point on the Szaplonczay promenade in Fonyód; photo: Economx, András Sánta
We were interested in how this structure works, so we contacted the HUN-REN Earth Physics and Space Research Institute with our questions, whose chief scientific colleague, István Bozsó, explained that – as can be seen in the pictures –
THE GEODESIC BASE PRIMARILY CONSISTS OF TWO SO-CALLED CORNER REFLECTORS.
The wonderful structure can work for decades
These corner reflectors were developed in the framework of a tender funded by the European Space Agency (ESA) under the leadership of the HUN-REN Earth Physics and Space Research Institute, in cooperation with the Faculty of Electrical Engineering and Information Technology, Department of Broadband Communications and Electrical Science of the BME.
The corner reflectors are able to reflect the microwave signal emitted by the Sentinel-1 family of satellites orbiting the earth at a low altitude of about 700 kilometers, thereby
THEY FUNCTION AS STABLE DISTRIBUTION POINTS FOR YEARS, EVEN DECADES.
Corner reflectors and base points are completely passive constructions, so they do not need an external energy source for their operation. Two corner reflectors belong to a base point, one is oriented in the direction of the so-called ascending (satellite passage from south to north) and the other in the direction of the so-called descending satellite path (satellite passage from north to south).
The Sentinel–1 satellite monitors the Earth’s surface and provides high-resolution images of the same area every 12 days, and these images can be processed to extract the properties of the signal reflected by the corner reflectors.
By calculating the phase difference of the reflected signals from several recordings and performing a time series analysis, it is possible to infer the satellite component of the surface displacements that occurred compared to a selected reference time and reference base point. By combining the displacements derived from the ascent and descent shots
EAST-WEST AND VERTICAL MOVEMENTS CAN BE IDENTIFIED.
In addition to all this, it is possible to carry out additional measurements on the surface, using the geodetic base point itself, so that these precision geodetic measurements refine the displacements calculated on the basis of satellite data. Furthermore, with periodic measurements, it is also possible to follow the north-south component of the displacements.
The Fonyód corner reflector is not unique
In Hungary, there are a total of four networks managed by the Earth Physics and Space Research Institute, each consisting of 3-4 base points.
- A test network operates in Sopron – where the institute is also located.
- There are three additional “moving” networks in Hungary: Fonyód, Kulcs and Dunaszekcső. These networks are located in areas where significant surface displacements are expected, typically in the form of landslides.
- There are two additional networks in Transylvania, around Szent Anna-tó and Parajd, and another network is being installed in the vicinity of Kovászna.
The mountains on the Balaton coast are collapsing, a good machinist can help a lot
Dangerous loess walls surround Lake Balaton. Their maintenance consumes billions of forints. The collapses around the lake are innumerable.
You can read our previous article HERE →
The loess walls of Balaton are moving
Since it is well known that coastal wall collapses have already occurred in the vicinity of Lake Balaton, for example at Balatonakaratty, Balatonföldvár and Fonyód, we asked the expert whether the location of the Fonyód observation point was justified because another loess wall collapse could occur at the site at any time.
István Bozsó explained in his answer that the Fonyód network was really created to monitor the movement of the seawall:
However, the magnitude of the coastal wall movements we detect is a subsidence of a few mm/year. This is not a negligible surface movement, but it is not a cause for concern, the Fonyód seawall can be said to be relatively stable based on these.
A sudden landslide cannot be predicted
We also learned that new satellite images arrive from the area every 12 days, so real-time monitoring of a landslide is not immediately possible except by the method described above:
“If the earthquake starts almost without any signs, we cannot make any special predictions.”
If, on the other hand, a major earthquake is preceded by a series of more intense surface movements for about one and a half to two months, there is a chance that experts will detect it with the help of satellite images.
The integrity of the structures is not at risk
The geodetic reference point on the Szaplonczay promenade in Fonyód has been surrounded and marked with a sign asking people to preserve the integrity of the structure.
We found out that the tourists comply with the request in a disciplined manner, moreover, the geologists did not experience any damage to the base point networks in Hungary or Transylvania.
Source: www.economx.hu
