This chapter provides an extensive overview of the use of geophysics in archaeological research and cultural heritage management in Finland, Sweden, Norway, Denmark and Iceland. It discusses the current status, role and acceptance of geophysical methods in each country, and outlines the state-of-the-art based on a synthesis of existing knowledge and experience. The authors consider the past, present and future of archaeo-geophysics in the individual regions, taking into account the academic, curatorial and commercial aspects of their use. This, in turn, serves as the basis for a discussion of the reasons for the varying degrees of acceptance and integration of the methods in each country, and aid the distribution of knowledge and experience gained across Scandinavia and beyond. The practical experience, application and general acceptance are not similar in the different Scandinavian countries. There is a general lack of integrating geophysical (and by extension non-intrusive methods) within the archaeological practice and guidelines. The case studies presented here show a range of archaeological applications of geophysics in Scandinavia, demonstrating how geophysical methods should by no means be considered “new” or “untested”. While there is a need for targeted research, there has also been a challenge in disseminating the already generated knowledge and experiences to other actors within the archaeological community. Some of this can be explained by a lack of trained personnel, domestic competence and archaeological institutions undertaking research into the applicability of geophysical methods, and data-sharing and making reports accessible.

Soil moisture variation is complex and depends on a range of factors, which complicates the formulation of recommendations for GPR surveys. Low amounts of soil moisture produced GPR data of higher quality. However, precipitation rates as well as chronological sequence of precipitation/thawing processes and the GPR survey are of importance. Winter months can offer favorable conditions for GPR surveys if temperatures remain negative over a prolonged time period, allowing for frost to build in the ground. Results of the Borre Monitoring Project (BMP) are valid only for sites with similar settings as Borre; the monitoring approach, however, can be transferred to larger regions with more representative sites.

The Borre Monitoring Project investigated how environmental factors, in particular, precipitation and soil moisture variation as well as different soil and sediment types, affect the quality of GPR data collected for archaeological purposes. To study these questions, regular GPR surveys were conducted over a period of 14 months across a test area covering a hall building at the Iron and Viking Age site of Borre in Norway. In order to obtain in situ measurements of environmental factors relevant for electromagnetic wave propagation including volumetric water content, bulk electrical conductivity, ground temperature, and precipitation, three monitoring stations were erected at the test site. Soil and sediment samples taken from the profiles at the respective monitoring stations were analysed to gain a basic description of their physical and chemical properties. Twelve GPR surveys were conducted roughly once a month between August 2016 and September 2017 and the results clearly indicated differences in the quality of the data collected. To better understand the underlying causes for this variation, GPR data were compared against and integrated with the in situ measurements gathered using the monitoring stations. The results of this analysis emphasised the benefit of dry conditions, which, if prevailing over a longer period of time, proved to generate GPR data of the highest quality. Seasonality could not be attested; instead, data quality was governed by small-scale weather patterns, where the time and intensity of rainfall events prior to the surveys as well as sudden changes in air temperature played a decisive role. While the results of this study are only valid for sites with similar settings such as Borre, they emphasise the importance of considering the environmental factors during all stages of a GPR survey and highlight the need for further studies investigating other settings.

– Usually only GPR reflection amplitudes are imaged, while GPR data contain far more information. – Multi-trace GPR coherency visualisations offer new insights into structures otherwise hardly visible. – Image fusing permits the combined display of different GPR data attributes (amplitude and coherency).

Borre in Norway is famous for its Late Nordic Iron and Viking Age (AD 400-1050) monumental burial mounds. Recently, ground-penetrating radar (GPR) surveys have revealed three large structures close to the mound cemetery. Their unusual layout and size, and location within such a prominent burial site, suggest that they were halls-high-status buildings mentioned in the Nordic sagas. The authors present the GPR results, discuss the buildings' typological classification and provide a preliminary chronological framework. The latter suggests that the buildings coexisted with some of the burial mounds, and raises important questions about the significance of such buildings in Nordic mound-building societies.

The technical advancements of the past decade have rendered motorised, high-resolution ground-penetrating radar (GPR) investigations increasingly popular for archaeological research and cultural heritage management in Norway. However, the agricultural use of most survey areas limits the time available for fieldwork in spring and autumn and thus reduces the method’s potential. An extension of the fieldwork period into the winter season would be desirable. The project “Arkeologi i veien?” aimed to develop practical solutions for efficient motorised GPR surveys on snow and to evaluate to what extent the thickness of the snow cover affects data quality. Four sites with known archaeological remains in the ground have been investigated under snowless conditions and with snow cover. The comparative data analysis showed that GPR surveys can result in useful data even on areas covered with one metre of snow. This study shows that different temperatures and resulting variable snow conditions can have a strong effect on the quality of the generated GPR data. The possibility for GPR measurements on snow offers the opportunity to extend fieldwork into the winter period without conflicting with the growing season; however, local weather and snow conditions have to be closely observed in order to obtain useful prospection data.

Traditionally, ground‐penetrating radar (GPR) measurements for near‐surface geophysical archaeological prospection are conducted with single‐channel systems using GPR antennae mounted in a cart similar to a pushchair, or towed like a sledge behind the operator. The spatial data sampling of such GPR devices for the non‐invasive detection and investigation of buried cultural heritage was, with very few exceptions, at best 25 cm in cross‐line direction of the measurement. With two or three persons participating in the fieldwork, coverage rates between a quarter hectare and half a hectare per day are common, while frequently considerably smaller survey areas at often coarse measurement spacing have been reported. Over the past years, the advent of novel multi‐channel GPR antenna array systems has permitted an enormous increase in survey efficiency and spatial sampling resolution. Using GPR antenna arrays with up to 16 channels operating in parallel, in combination with automatic positioning solutions based on real‐time kinematic global navigation satellite systems or robotic total‐stations, it has become possible to map several hectares per day with as little as 8 cm cross‐line and 4 cm in‐line GPR trace spacing. While this dramatic increase in coverage rate has a positive effect on the reduction of costs of GPR surveys, and thus its more widespread use in archaeology, the increased spatial sampling for the first time allows for the high‐resolution imaging of relatively small archaeological structures, such as for example 25 cm wide post‐holes of Iron Age buildings or the brick pillars of Roman floor heating systems, permitting much improved archaeological interpretations of the collected data. We present the state‐of‐the‐art in large‐scale high‐resolution archaeological GPR prospection, covering hardware and software technology and fieldwork methodology as well as the closely related issues of processing and interpretation of the huge data sets. Application examples from selected European archaeological sites illustrate the progress made.

In September 2010, an exceptionally large cooking-pit site was discovered by means of geophysical prospection at Lunde in Vestfold County, Norway. The site contains in excess of 1000 cooking-pits and is, to date, one of the largest of its kind discovered in Scandinavia. Features known as cooking-pits are ubiquitous on Northern European archaeological sites. Despite research spanning decades, however, the true function and role of this rather non-descript feature type is still debated. Using the results from geophysical prospection, soil analysis, ground-truthing and excavation, this article aims to better understand this phenomenon by evaluating the physical properties revealed from the data, and setting this exceptional site in a wider cultural-historical context. The wider, landscape context is accessible from the large-scale, high-resolution, landscape archaeological prospection case-study approach conducted by Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology (LBI ArchPro). The results suggest that the multi-method approach is essential in such cases, as it is able to challenge the assumptions of the blanket interpretations often applied, and put the site in a cultural and environmental context.

Are they all stray finds? Metal detector finds and the potential for preserved contexts below the plough soil In Vestfold County we have since 2013 seen a marked rise in metal detecting finds being delivered to the county archaeologists by amateur detectorists. These finds are a source of both joy and grief for archaeologists all over Norway. Should we see these finds as noncontextual random finds or do they relate to a more complex situation over which we simply do not have full insight? In this article we discuss the possibilities of investigating sites with clusters of metal detecting finds with geophysical prospection. Two case studies in Vestfold County are presented, both of which have provided clusters of metal finds, and we compare the results from the metal detecting with results from geophysical prospection. By doing so our aim is to contribute to further discussion of the possibilities of preserved archaeological contexts under the plow soil.

Following magnetometry and ground penetrating radar surveys, a geoarchaeological field evaluation was carried out at the Iron Age burial mound of Rom in Slagendalen, Vestfold County, Norway, in order to assess the accuracy of the geophysical data interpretation and to investigate specific questions that have arisen during data interpretation. The evaluation was conducted within the framework of an archaeological excavation campaign in 2013, which enabled direct access to the subsurface materials. The archaeological stratification was recorded by laser scanning using a three-dimensional (3D) single-surface approach, permitting a virtual reconstruction of the excavated part of the mound and facilitating the comparison between excavation and prospection data. Selected sediment sequences were targeted with in situ and laboratory-based measurements for correlation purposes, including magnetic susceptibility, electrical conductivity and water content measurements. Here we present the methodological approach and the results of the geophysical prospection surveys, followed by a geoarchaeological evaluation and a discussion of the impact on the overall archaeological investigation.

S23 Needles in the haystack: Geophysical methods in challenging conditions Lars Gustavsen, Christer Tonning, Arne Anderson Stamnes, Erich Nau, Monica Kristiansen The development of geophysical techniques for archaeological purposes has largely taken place in areas where archaeological features tend to be pronounced, well-defined and, arguably, easily detected by geophysical instruments. Often, however, we are faced with archaeological features which do not readily lend themselves to detection by these methods. This is sometimes compounded by local geomorphological and pedological conditions, which may obscure or mask the archaeological features. This calls for different approaches to how geophysical methods are applied, and it requires comprehensive field observation regimes to verify and understand the geophysical properties of the archaeology. In this session we wish to focus on projects where adverse geological, geomorphological, pedological and archaeological conditions have been encountered. We want to explore how these conditions have affected the geophysical survey results and their archaeological interpretability, to see how these phenomena have been observed through archaeological feedback, and how the results have influenced subsequent field procedures.

This paper describes a processing chain for the semi-automatic mapping of grave mounds from airborne laser scanning (ALS) data. In a digital terrain model (DTM) of the ALS ground points, the automatic method slides a template mound over all positions, and assigns confidence scores to anything resembling a mound. The integer scores range from 1 to 6. By using mound templates with gradually increasing radii from 1.0 to 16m, the method is able to detect all mounds in this range, provided they are visible and well-formed in the DTM. Despite a high number of false positives, the method is a useful tool in semi-automatic, detailed mapping of known grave fields, especially when the number of ground points per square metre is sufficiently large. The method is also able to identify the location of a previously unknown grave field. We discuss possible improvements of the method. The highest potential for better detection performance is in ALS acquisition in the early spring or the late autumn, when leaves are not present.

This project was started in 2002 with the overall aim of developing a cost-effective method for surveying and monitoring cultural heritage sites on a regional and national scale. The project focuses on the development of automated pattern recognition methods for detecting and locating cultural heritage sites. The pattern recognition methods are included in a prototype software called CultSearcher. This software currently supports the following: (1) Search for crop marks and soil marks in optical satellite and aerial imagery; these marks could be levelled grave mounds. (2) Search for pits in airborne laser scanning (ALS) data; these pits could be pitfall traps or charcoal burning pits. (3) Search for heaps in ALS data; these heaps could be Iron Age or Bronze Age grave mounds. This note describes the achievements of the project during 2013. The project is funded by the Norwegian Directorate for Cultural Heritage. In 2013, the semi-automatic method in CultSearcher for the detection of grave mounds was used in detailed mapping of grave mounds in Tønsberg municipality, Vestfold County. Oppland County Administration has continued to use the semi-automatic method in CultSearcher for detailed mapping of archaeological pits, and reports on such mapping in Nord-Fron and Sør-Fron municipalities.

This project was started in 2002 with the overall aim of developing a cost-effective method for surveying and monitoring cultural heritage sites on a regional and national scale. The project focuses on the development of automated pattern recognition methods for detecting and locating cultural heritage sites. The pattern recognition methods are included in a prototype software called CultSearcher. This software currently supports the following: (1) Search for crop marks and soil marks in optical satellite and aerial imagery; these marks could be levelled grave mounds. (2) Search for pits in airborne laser scanning (ALS) data; these pits could be pitfall traps or charcoal burning pits. (3) Search for heaps in ALS data; these heaps could be Iron Age or Bronze Age grave mounds. This note describes the achievements of the project during 2014. The project is funded by the Norwegian Directorate for Cultural Heritage. In 2014, the semi-automatic method in CultSearcher for the detection of grave mounds was used in detailed mapping of grave mounds in the Iron Age grave field at Vang, Oppdal minicipality, Sør-Trøndelag County. The same method was used for detailed mapping of grave mounds in selected areas in Larvik municipality, Vestfold County. In Lesja municipality, Oppland County, a combination of automatic pit detection and automatic heap detection was used in the detailed mapping of charcoal kilns Results from the project was presented at the international CAA conference in Paris, April 2014 and at the national seminar CAA-Norge in Oslo, October 2014. The method for mound detection has been accepted for publication in Journal of Archaeological Science: Reports in 2015.