Sychrov State Castle – Planar 3D Ground-penetrating Radar Survey of the Road Network
In connection with the planned restoration of the road network at the state-owned Sychrov Castle, the National Heritage Institute, the regional branch in Liberec, is preparing a rescue archaeological excavation. As part of it, a non-destructive geophysical survey was conducted in advance of the start of earthworks and construction activities by the company INSET s.r.o.
The archaeological research, together with the geophysical survey, will ensure that there is no damage or destruction to historically valuable records of the development of this significant national cultural monument. Simultaneously, it will provide sufficient documentation and evaluation of all revealed remnants of the gradual development of the site. In addition to the architectural-historical development of the castle itself, this may involve the exploration of the water supply system or older structures that existed on the site before the establishment of Sychrov Castle.
3D ground-penetrating radar measurement using the MIRA system at the entrance area of the park (photo by J. Vidman).
Sychrov Castle and Castle Park
Sychrov Castle, with its picturesque charm, is one of the main tourist attractions in the Liberec region. The flourishing of Sychrov is credited to the Rohan family, who came to Bohemia from France and acquired the local estate in 1820. The last extensive reconstruction of the castle into its present neo-Gothic form took place under Prince Kamil Rohan from 1847 to 1862. The owners of the estate paid exceptional attention not only to their own castle but also to the extensive castle park. The castle park, covering an area of 26 hectares, was established in the English style and served as a model for the creation of several now significant arboretums, such as Průhonice or Konopiště.
Overall view of the castle complex from the southwest (photo: J. Vidman)
The Imperial Eagle adorns the top of the column at the viewpoint.
(Photo by J. Štainbruch)
Park byl koncipován tak, že od zámecké terasy se rozbíhaly průhledy k jednotlivým dominantám: přes velkou louku k oranžerii a severním směrem k Arturovu hradu. Třetí osu parku tvoří příjezdová cesta s 500 m dlouhou alejí pyramidálních dubů, na kterou navazuje alej Rohanka pohledově ukončená věží kostela v Jenišovicích. Kromě hlavních os park protíná síť cestiček, které umožňují návštěvníkům zajímavé průhledy a pohledy.
Průhled od zámku přes velkou louku směrem k oranžerii (foto: J. Štainbruch)
Water Management
The castle complex includes fountains, artificial ponds, and fountains. A distribution system was created for their supply and to provide the castle with water. It was a technically demanding work for its time, as water had to be first brought from the deeply incised valley of the Mohelka River to the water tower and then gravitationally distributed to the individual water features in the castle complex. Unfortunately, there is no map of the actual implementation, except for a few historical records. In order to prevent damage to the historic distribution system and other archaeologically valuable objects during the planned road network renovation, the monument administrator, the National Heritage Institute, commissioned the company INSET s.r.o. to conduct a survey of the affected areas using non-destructive ground-penetrating radar methods.
Exhibition panel providing information about the Sychrov water supply (from the SZ Sychrov exhibition); detail of the exhibition panel with a copy of the distribution plan from 1896; the water tower in the eastern part of the park not only supplied the castle with water but also fed the water features in the park (photo by J. Vidman); during a walk through the park, visitors can enjoy romantic corners and resting places (photo by J. Štainbruch).
Ground-penetrating radar method
Ground-penetrating radar is a method in which high-frequency electromagnetic pulses are transmitted into the surroundings (in this case, into the ground), and reflections from various obstacles are detected. Objects that ground-penetrating radar can detect include pipes, cables, walls, and voids. However, it can also differentiate between different types of environments, such as gravel, clay, and detect changes in environmental properties, such as moisture.
During measurements, the ground-penetrating radar emits electromagnetic pulses into the ground and registers their reflections from various types of obstacles (photo by J. Vidman).
In the case of planar measurements in the Sychrov Castle area, the most modern equipment, the 3D ground-penetrating radar system MIRA from the Swedish manufacturer Malå GeoScience, was used. INSET has been using this device for measurements for only the second year, and it is the only company in the country equipped with this technology. Its biggest advantage over traditional 2D ground-penetrating radars is the multi-channel arrangement of antennas, allowing the coverage of the surveyed area with a dense network of measurement points at 8 x 8 cm and 3D processing of the collected data. As has already been verified at other archaeological sites, this allows for the detection of even subtle manifestations of underground objects. Surveys can be conducted with a very detailed scale on relatively large areas.
3D ground-penetrating radar measurement using the MIRA system on the access road bordered by an avenue of pyramid oaks (photo by J. Vidman).
The ground-penetrating radar survey of the road network in the Sychrov State Castle area took place in August 2019 and covered not only the castle park but also the areas of the honor and economic courtyards. The extent of the task is evident from the fact that geophysicists walked over 11 km of profiles just on the park pathways. Additional kilometers were covered while surveying larger areas, for example, at the park entrance, in front of the orangery, or in the honor courtyard area, where the distance between parallel lines of individual passes of the measuring device was 65 cm. Over 5 GB of data was measured in a total of 4 days. Processing and evaluating such a volume of information were labor-intensive and time-consuming. Each measured section or area, whether it was 100 or 10 meters long, had to be processed separately on the computer into the form of planar scans constructed for individual time/depth levels, thoroughly examined, and evaluated based on specific manifestations.
Display of planar ground-penetrating radar scans in areas measured within the space of the honor courtyard. Darker shades reveal underground objects with higher reflectivity, such as networks or foundations of no longer existing structures.
The results of ground-penetrating radar measurements.
In planar ground-penetrating radar scans, underground objects with higher reflectivity (= electromagnetic signal reflectance) are represented by darker shades. Thanks to 3D technology, it was possible to map networks not only transversely but also longitudinally in the paths' routes, which is challenging with conventional 2D radars. A significant advantage of detailed planar ground-penetrating radar measurements is the ability to construct 3D models of the surveyed environment. Due to the depth scale adjustment, networks stored at various depths from the ground gradually appear in the planar sections. For example, in the area of the northern entrance to the park or around the fountain in the honor courtyard, a branched network of underground utilities was mapped, stored at several depth levels.
The results of planar ground-penetrating radar measurements north of the castle revealed a branched network of underground utilities stored at various depth levels.
Similar to underground networks, tree roots also manifested increased reflectivity in radar sections. It is possible to examine in detail the course, branching, and depth of individual roots or more complex root systems. Given the arboricultural significance of the park, awareness of the extent of the root system of rare trees is important for their protection against damage from construction equipment.
Using ground-penetrating radar, it is possible to map the course of individual roots as well as more complex root systems extending beneath the pathway.
Mapping of extinct objects within the castle complex area
The results of the ground-penetrating radar survey were interesting also in terms of detecting other objects with potential archaeological significance. For example, in the honor courtyard area, it was possible to verify the outlines of a no longer existing structure recorded in the mandatory imperial imprint on the cadastral map from 1843. Additionally, the radar detected the outlines of a completely unknown structure. More surprises await archaeologists in the entrance area to the park along the eastern facade of the castle. Here, too, several 'darker' patterns and spots were detected by the ground-penetrating radar, indicating past interventions in the natural environment.
Výstupem plošných georadarových měření je mapa detekovaných anomálií – podzemních objektů s jejich charakteristikou, která archeologům z Národního památkového ústavu umožní v předstihu před stavebními pracemi naplánovat a následně i zrealizovat záchranný archeologický výzkum a ochránit tak naše historické dědictví.
Video - Sychrov: Film Documentary
Autors: Arnošt Toms, RNDr Jakub Štainbruch Ph.D.
