We performed geophysical and geoarchaeological investigations in the Wadden Sea off North Frisia (Schleswig-Holstein, Germany) to map the remains and to determine the state of preservation of the medieval settlement of Rungholt, especially its southern dyke segment, called the Niedam dyke. Based on archaeological finds and historical maps, Rungholt is assumed to be located in the wadden sea area around the island Hallig Südfall. During medieval and early modern times, extreme storm events caused major land losses, turning cultivated marshland into tidal flats. Especially the 1st Grote Mandrenke (or St. Marcellus’ flood), an extreme storm surge event in 1362 AD, is addressed as the major event that flooded and destroyed most of the Rungholt cultural landscape. Cultural traces like remains of dykes, drainage ditches, tidal gates, dwelling mounds or even plough marks were randomly surveyed and mapped in the tidal flats by several authors at the beginning of the 20th century. Due to the tidal flat dynamics with frequently shifting tidal creeks and sand bars, the distribution of cultural remains visible at the surface is rapidly changing, making it hard to create a comprehensive map of the cultural landscape by surveying. Today, the Niedam dyke area is fully covered by tidal flat sediments, depriving any remains from further archaeological investigation. Since little is known about the precise location or state of preservation of these remains, our investigation aimed at the rediscovery of the medieval dyke system and associated structure with modern and accurate geophysical, geodetical and geoarchaeological methods. Magnetic gradiometry revealed a large part of the medieval dyke, confirming two tidal gates and several terps connected inland with the dyke, providing a detailed example of a Frisian medieval dyke system. Based on our results, the so far inaccurate and incomplete maps of this part of Rungholt can now be specified and completed. Beyond that, seismic reflection profiles give a first depth resolving insight in the remains of the dyke system, revealing a severe threat to the medieval remains by erosion. The site is exemplary for the entire North Frisian coast, that was influenced by multiple flood events in the middle ages to modern times.

Seismic surface-waves may show amplitude resonances at certain frequencies depending on the thickness and elastic parameters of near-surface layers. We investigate if resonance frequencies of Rayleigh-waves, (seismic surface-waves polarized in the vertical plane) can be used to prospect archaeological remains of small-scale buildings such as pit houses. Our test site is a newly detected Viking age village on the island of Föhr (north Germany) where we concentrated on one typical pit house. The results from resonance analysis are compared with magnetic data, ground penetrating radar (GPR) and classical seismic refraction measurements. The method of Rayleigh-wave resonance mapping used in this paper is based on the idea that Rayleigh-wave oscillations on top of anthropogenic structures will show different resonances than on undisturbed soil. We perform spectral analysis of these oscillations to provide information related to the seismic site response. We process single vertical component recordings and map the change in resonance frequency that can be related to the archaeological objects. The test showed that the pit house can be mapped by Rayleigh-wave resonance analysis with a horizontal resolution of~0.6 m. Corresponding computations of the depth of the pit house agree with the results from GPR, magnetic modelling and refraction seismics. A modelling study helped to understand the connection between subsoil shear-wave velocity model and the signal generated by the pit house. The progress of seismic field measurement is slow compared to GPR and magnetometry. However, since seismic methods are based on elastic subsoil parameters, it can be applied in cases where magnetic contrasts are low or GPR fails because of high electromagnetic wave absorption.seismics (Models C, D, F to A, B, E), a change in topsoil velocity (Models E, F), a change in both velocities with the impedance contrast between the two layers kept constant (Model B) and a decrease in the velocity of the stiffer layer (Model C). The spectra show resonance frequencies at about 70 Hz for the Model 2 outside the pit house (Model D) and 45 Hz for Model 1 inside the pit house (Model A), which correlates well with the observation and thus supports the resonance frequency approach.The following effects can be observed: (a) Models A, B, C, and D show a strong maximum in the vertical component together with a sharpFigure 7. (a) Seismic shot gathers from the SH refraction reference profile (position see Figure 3). Picked first arrival times are indicated by blue and red dots. (b) Shear-wave velocity model obtained by the wavefront method. Numbers 1 and 2 indicate the two reference models that correspond to inside and outside the pit. For comparison, the measured magnetic signal of the profile and the location of the modelled prism are shown in (c). 2015. On the ability of geophysical methods to image medieval turf buildings in Iceland. Archaeological Prospection 22(3): 171-186.

In AD 1362, a major storm surge drowned wide areas of cultivated medieval marshland along the north-western coast of Germany and turned them into tidal flats. This study presents a new methodological approach for the reconstruction of changing coastal landscapes developed from a study site in the Wadden Sea of North Frisia.Initially, we deciphered long-term as well as event-related short-term geomorphological changes, using a geoscientific standard approach of vibracoring, analyses of sedimentary, geochemical and microfaunal palaeoenvironmental parameters and radiocarbon dating. In a next step, Direct Push (DP)-based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) were applied at vibracore locations to obtain in situ high-resolution stratigraphic data. In a last step, multivariate linear discriminant analysis (LDA) was successfully applied to efficiently identify different sedimentary facies (e.g., fossil marsh or tidal flat deposits) from the CPT and HPT test dataset, to map the facies' lateral distribution, also in comparison to reflection seismic measurements and test their potential to interpolate the borehole and CPT/HPT data. The training dataset acquired for the key site from coring and DP sensing finally allows an automated facies classification of CPT/HPT data obtained elsewhere within the study area. The new methodological approach allowed a detailed reconstruction of the local coastal landscape development in the interplay of natural marsh formation, medieval land reclamation and storm surge-related land losses.

Hyperbolic diffractions in Ground Penetrating Radar (GPR) data are caused by a variety of subsurface objects such as pipes, stones, or archaeological artifacts. Supplementary to their location, the propagation velocity of electromagnetic waves in the subsurface can be derived. In recent years, it was shown that deep learning tools can automatically detect hyperbola in radargrams using data measured over urban infrastructure, which are relatively clear. In contrast, in this study, we used an archaeological dataset with diverse underground structures. In the first step we used the deep learning network RetinaNet to detect hyperbola automatically and achieved an average precision of 0.58. In the next step, 10 different approaches for hyperbola fitting and thus velocity determination were applied. The derived information was validated with manually determined velocities and apex points. It was shown that hyperbola extraction by using a threshold and a column connection clustering (C3) algorithm followed by simple hyperbola fitting is the best method, which had a mean velocity error of 0.021 m/ns compared to manual determination. The average 1D velocity-depth distribution derived in 10 ns intervals was in shape comparable to the manually determined one, but had a systematic shift of about 0.01 m/ns towards higher velocities.

Det må ikke kopieres fra denne boken i strid med åndsverkloven eller fotografiloven eller i strid med avtaler inngått av KOPINOR, interesseorgan for rettighetshavere til åndsverk.