Sychrov Castle – 3D Georadar Survey of Path Network
Introduction
The regional office of the National Heritage Institute in Liberec is preparing archaeological excavations preceding the planned renewal of the park path network of the state castle in Sychrov. In its preliminary phase, the georadar survey was performed by the company INSET to give archaeologists a better understanding of the history of the site and provide them with information on the layout of underground utilities and other features of potential archaeological importance.
Fig: 3D georadar survey of the area in front of the entrance to the park from the castle. The position of the georadar antenna was tracked by a robotic total station.
Sychrov castle and park
Sychrov state castle, one of the most picturesque and romantic chateaux in the Czech Republic, can be found in the Liberec Region. Its heyday is associated with the influential Rohan family, which came from France and bought the Sychrov estate in 1820. The most recent rebuilding of Sychrov in the Neo-Gothic style was conducted by Duke Camille Rohan during years 1847 – 1862. At the same time, a large park with an area of 26 hectares was founded and designed in the English landscape style.
Fig: Overall view of Sychrov estate from the South-West (photo: J.V.)
Fig: The Habsburg double-headed eagle decorates one of the column head at park viewpoint
The park’s design follows the concept of “Patte d´Oie” – goose leg, created by 3 major axes – vistas from the main chateau terrace through the park to the romantic Arthur´s Castle, the Orangery, and through a 500-m-long pyramidal oak avenue toward the church tower dominating the nearby village of Jenišovice. The set of winding paths criss-crosses the park and leads the visitors to the romantic corners, viewpoints and rest points.
Fig: One of the park’s main axes overlooks the large meadow toward the Orangery
Water Management
With a number of water elements, such as fountains, wells and even a small pond, the estate required sophisticated water management. The progressive waterworks system was designed to bring water from the deep Mohelka river valley up to the water tower and then gravitationally supply the castle and park with water. But a few sketches and the original design of the water supply system and water pipe layout have been lost. As a preliminary measure to protect any historic pipes and other remains of archaeological value against destruction during building activities, the whole network of park paths and open courtyards was inspected before their renewal. The castle administrator, the regional office of the National Heritage Institute in Liberec, entrusted the company INSET with the non-destructive georadar surveying of the Sychrov estate area.
Fig: Exhibition panel with information about the water management system (from the Sychrov castle exhibition); detail of the panel with copy of the design of the water supply system, dated 1896; the water tower situated in the east corner of the park supplied both the castle and the park with water (photo); the park offers visitors a romantic and relaxing atmosphere (photo)
Georadar method
Georadar is a non-destructive method that works by transmitting radio pulses into the ground and receiving responses in the form of reflections from inhomogeneities, such as pipes, cables, walls, voids, etc. Also, changes in environmental properties such as clay content or soil moisture volume can be registered by georadar.
Fig: Scanning the open area between the orangery and a fountain by the means of the 3D GPR MIRA system (photo)
The 3D georadar system MIRA 8 (product of the Swedish company MALĂ, GuideLine Geo group) was used for the survey of the Sychrov estate. MIRA 8, also known as MiniMIRA, is an eight-channel system assembled with 400 MHz antennas with 8 cm separation between channels. For data processing, the software rSlicer was used. Though the 3D georadar method is still new in the Czech Republic, over the last two seasons the company INSET has proved its ability to inspect large areas in high detail (the grid of measured points is 8 x 8 cm), and to reveal even very weak evidence of underground objects.
Fig: Inspection of the main park path, lined with pyramidal oaks (photo)
The survey of the path network at Sychrov estate was carried out in August 2019 and covered the park area, the front courtyard and the farmyard. In 4 days a geophysicist hand-towed a MIRA radar over 11 kilometres of profiles along the paths. Larger open areas were covered with a regular net of parallel swathes 65 cm apart. The total size of measured data exceeded 5 GB. To process and interpret such a quantity of data was both exhausting and time consuming – each particular measured path or area had to be processed individually, not matter how long or short it was. The result of the data processing is a set of time slices in which the detected objects are manually picked and their position interpreted and exported into CAD software to create a complete map of the underground.
Fig: Example of an areal scan showing the position of a utility (probably a power cable)
Results of GPR survey
The survey at Sychrov was focussed mainly on utility detection. In scans, a darker shade of grey represents the higher reflectivity of an underground object. 3D surveys can detect not only perpendicularly crossed linear objects, such as utilities, but also those oriented parallel to a line of direction. Another big advantage of 3D surveys is the opportunity to construct 3D models of the studied subsurface environment, so that the respective positions and depths of different utilities can be viewed when scrolling down in the time/depth axes. Good results in the mapping of underground objects were achieved even in complex areas with a number of water pipes and other utilities laid down at different depths (such areas can be found, e.g., near the main water reservoir in the front courtyard, and along the north facade of the chateau).
Fig. Example of a 3D GPR survey result from the area in front of the north wing of the chateau. Scrolling down through 2D scans reveals a complicated system of underground utilities.
Tree roots are another type of object with high reflectivity that can be detected with a GPR. In the 19th century, Sychrov’s park was planted with many exotic and rare species of fauna. The arboreal value of the park is enormous, and knowledge of the root system extension is essential for its protection.
Fig. Example of the GPR mapping of tree roots under the surveyed path
Discovery of historical construction remains
Discovery of historical construction remains
In the course of the survey, several anomalies with potential archaeological significance were detected. For example, outlines of the historical construction mentioned in the cadastral map from 1843 were discovered in the front courtyard, as well as the outline of another, previously unmentioned building. Other hidden secrets are waiting to be revealed to archaeologists in front of the east wing of the chateau, where several high reflectivity anomalies of unknown origin were detected under the surface using georadar.
Fig: Examples of georadar 2D scans showing the layout of underground utilities and the outlines of construction discovered in the front courtyard.
The results of georadar surveys, presented in the form of a map marked with the position of all detected underground objects and their characterisation, can help archaeologists to plan and, in the future, to perform, excavations prior to the start of any reconstruction works in the park.