The lost castle of Weesp
For 350 years, ‘t Huijs ten Bosch remained lost, until a new archaeological study applying innovative sensor technologies rediscovered the castle.
Goal/research question
The site being studied is the medieval castle ‘t Huijs ten Bosch, built after 1220 and destroyed in 1672. However, it has never been the subject of archaeological investigation, and little is known about the structure itself or the condition of any preserved remains buried beneath the surface. While there are some traces of soil– and crop marks, these don’t offer a strong foundation for answering the key questions surrounding the site.
To address this gap, the project was launched to explore both the use and comparative value of innovative sensor technologies for prospecting, as well as to assess the nature, extent, and state of preservation of the site.
Methodology
To assess the effectiveness of various remote sensing sensors across different seasons, drone footage was captured in February, June, and September 2022. To maximize the amount of information gathered about the site and determine the added value of each sensor, research was conducted using a thermal, multispectral, and optical camera, as well as a LiDAR laser scanner.
Additionally, borehole investigations were carried out, and geophysical surveys using magnetometry and electromagnetic induction (EMI) were conducted.
Results
The geophysical prospection and drone-based remote sensing operations have revealed clear evidence of the castle, including well-defined foundation walls, possible remnants of structures, and a distinct outline of the moat.
Lessons Learned
- Thermal imaging proved useful in both spring and autumn, but the results during winter were limited due to poor image quality, especially in the imagery taken in cold and rainy conditions.
- While thermal images taken in June were less sharp, they still provided valuable data, thanks to significant temperature differences between day and night during that time.
- Thermal imagery captured in september yielded the most detailed results.
- The window for effective multispectral imaging at this site is narrow and highly dependent on annual dryness.
- Both drone photogrammetry and LiDAR-derived Digital Elevation Models (DEMs) can offer comparable precision and accuracy, depending on the conditions.
- The photogrammetry DEM was most accurate during winter captures, when crop height was low.
- LiDAR, on the other hand, is particularly advantageous for its speed in data acquisition and ability to penetrate vegetation, offering sharper imagery than the Digital Elevation Model of the Netherlands (AHN). However, the main contours are visible in both the drone LiDAR and the AHN datasets.
References to reports
- Waagen, J. (2023). In search of a castle: Multisensor UAS research at the Medieval site of ‘t Huijs ten Bosch, Weesp. 4D Research Lab report series, 4. https://doi.org/10.21942/uva.23375486.v2
- Jayasena, R., Lambregts, N., van den Oever, F., & Waagen, J. (2023). Het verdwenen kasteel van Weesp. Een archeologische verkenning naar het dertiende-eeuwse Huis ten Bosch. Amstelodamum, (3), 133.
Colophon
In collaboration with the Monuments and Archaeology Bureau of the Municipality of Amsterdam, Saricon, the 4D Research Lab of the University of Amsterdam, and Hollandia Archaeologists, with the kind cooperation of the landowner.