LiDAR research results

The first difficulty faced by Veroli scientists planning to conduct archaeological research in Iznik-Nikaia is the lack of a good map of the city and the area. It is necessary for analyzing topography, spatial organization, historic and settlement structure, planning areas for future research and documenting discovery sites. The scientific literature is dominated only by a schematic, simple map, based on a sketch by Foss and Winfield from 1986, which includes: a section of the eastern part of the lake shoreline, an outline of the fortress walls, gates, two main intersecting streets, and the locations of individual, more important historic buildings. . There are also geodetic maps of the city illustrating its contemporary urban layout and street grid. We also have an interesting map by C. Texier from the 1830s, published in 1939, showing the area of ​​settlement of the city at that time, along with the street grid (which differs significantly from the modern one), a quite precise outline of the city walls and with bastions and gates, as well as a theater. The above data regarding the documentation of the city’s topography and layout are complemented by satellite images. However, the schematic nature of the above cartographic studies does not meet the expectations of our current research.

Therefore, one of the initial goals of the “NICAEA 325” project is to create multi-layer documentation of the city of Iznik – Nikaia – Nicaea and its surroundings, especially the areas selected for research in terms of the project issues. For this purpose, modern technologically advanced mapping and measurement functions were used, i.e. photogrammetry, LiDAR, thermal imaging method and multispectral imaging. Their basis is the use of drones with interchangeable components (RGB camera, scanner, thermal camera, multispectral camera), which allow for quick and effective search of large areas from the air, documentation of the area and comprehensiveness of activities.

Photogrammetry is a field of science and technology of spatial measurements, based on the analysis of photographs and raster images of the terrain in order to reproduce its shape, size and color. It is also very helpful for imaging large historic structures such as cities. Aerial photos taken from the aerial ceiling allowed us to create an orthophotomap and a digital terrain model of a large area of ​​the western part of the city and the adjacent eastern shore of the lake along with the historic structures located in this area (Photo 1). A special object located in the water right next to the shore was also documented – the ruins of a sunken basilica (Photo 2). Based on the above form of documentation, it was possible to discover a number of previously unknown submerged archaeological objects and ruins of unidentified buildings (Photos 3, 4, 5, 6).

LiDAR (Light Detection and Ranging) is a distance measurement method that involves illuminating a target with laser light and measuring the object using a sensor that measures differences in the beam return time and wavelength changes. This method allows mapping a three-dimensional terrain model. It was used to visualize the western part of the city, similarly to all other methods we used (Photos 7 and 8).

Thermal imaging is a method of recording, processing and imaging infrared radiation invisible to the eye. The source of this radiation is any object which temperature is above absolute zero. It detects and images temperature differences between an object and its surroundings – for example, a brick or stone wall and the surrounding ground. For this purpose, a thermal imaging camera was used, which generates images based on these temperature differences using infrared radiation in the selected range of electromagnetic waves of the infrared detector installed in the camera (Photos  9-10).

The area of ​​the western part of the city and the adjacent part of the lake was also imaged using an RGB camera (Photos 11-12).

Multispectral imaging is a method that allows the recording of images not only in the visible light range (as in color photography), but also in the microwave, infrared and ultraviolet range, i.e. it records information invisible to the user. Using this method, we imaged the area of ​​the sunken basilica directly adjacent to the ruins (Photo 13) and the vicinity of the North-Istanbul Gate (Photo 14). The above documentation was made in the UTM 35N GPS zone, on the WGS84 ellipsoid, TM ED50 geoid, in the QGIS program. The data obtained using the above methods constitute elements of an even more extensive Geographic Information System, which we are gradually developing in several stages. It will form the basis of our data documentation, expanded to include historical cartographic sources, archival and contemporary aerial and satellite imagery; results of archaeological surface, excavation and underwater research; digital documentation using 3D models and photogrammetry of architectural monuments and movable monuments along with their microplanigraphy; environmental data – geological, geomorphological, palynological and hydrological). In this way, we intend to create a broad database on the basis of which it will be possible to perform a multi-aspect analysis of the functions of discovered architectural objects and the entire settlement complex of the city.