Documentation of Urn Graves of Knovíz Culture by RPAS

This paper deals with the documentation, positional determination of urn graves of the Knovíz culture (1200–1000 BC), and geometric and positional determination of tumulus at the archaeological site located near the village Ctiněves, in the Usti region in the Czech Republic. Several hundred urn graves are located in the archaeological site and it is one of the biggest burial sites of Knovíz culture in the Czech Republic. RPAS (Remotely Piloted Aircraft System) was used for the documentation and positional determination of urn graves and tumulus. RPAS was equipped by visible spectral range, two near-infrared range, multispectral and thermal camera (one camera for a single flight). The result is a unique data set documenting this archaeological site. Thanks to the suitable winter and spring conditions in 2016 urn graves and tumulus could be detected on the basis of vegetation symptoms. The paper is also focused on how to process the data and creation of a differential digital surface model.


Introduction
RPAS (Remotely Piloted Aircraft System), UAV (Unmanned Aerial Vehicle) or UAS (Unmanned Aircraft System) are growing in importance due to their versatility in the U.S. Nowadays, for control and piloting, RPAS are equipped with sophisticated micro-instruments such as IMU, gyroscopes, GNSS receivers, wireless image insights, wireless controls, automatic stabilization, flight planners, etc. RPAS can provide not only photographic data, but also other data types like multispectral (with NDVI capability) or thermal data too (depending on sensors and type) [8,2].Bigger RPAS are capable of carrying much more expensive and more accurate devices such as laser scanners, hyperspectral cameras and accurate GNSS receivers [4].The RPAS method of acquisition combines the benefits of close range and aerial photogrammetry [3].RPAS can be used in many areas, such as archaeological surveying [2,11], precision agriculture [13], and mapping [10,7].
RPAS has great benefit for archaeology, documentation of monuments and culture heritage.It is able to carry a variety of sensing devices, it is a versatile instrument, it is capable of very detail imaging of objects and image GSD (Ground Sampling Distance) is in order of cm.This is related to the possibility of creating a digital surface model (DSM) in the order of J. Šedina et al.Documentation of Urn Graves of Knovíz Culture by RPAS.several cm, or in units of dm.For comparison Land Survey Office offers Digital Terrain Model of the Czech Republic of the 5th generation with density of 1.6 points per meter.Another benefit of RPAS is a possibility of thermal imaging due to miniaturization of thermal sensors.Thermal cameras are able to detect subsurface structures to a depth of several cm or dm.For the detection of subsurface structures it is determined diurnal variation of thermal values [2].RPAS are also widely used for a photogrammetric documentation of objects and together with terrestrial imaging we are capable of creating complex photogrammetric documentation [11,1].Furthermore, RPAS are used along with laser scanning and terrestrial photogrammetry to create comprehensive documentation of archaeological sites and objects [9,6].Equally interesting application of RPAS in archaeology is the documentation of the procedure of digs [12].2. At the bottom of the urn grave an urn was found with the ashes of the dead.When ploughing using heavy machinery urns have been damaged and ash of ancestors has served as a source of nutrients for plants.It was possible to detect the urn graves due to a vegetation symptoms.The plants are much greater growth there than the plants in their neighbourhood.A warm winter and spring created great conditions for vegetation symptoms in 2016.A sown grain in the site of urn graves was about 15-20 cm higher than any other grain in their neighbourhood of the 16th June 2016.Urn fields of Knovíz culture are usually small, they seldom have a few dozen graves and bigger one has about 100 urn graves.On this archaeological site there are several hundred of urn graves which makes this site extraordinary.

Archaeological site and subjects of documentation
Figure 2: Urn graves and urns [5].

Used technology RPAS eBee
RPAS (Remotely piloted Aircraft System) eBee (see Figure 3) was used for documentation of the position of urn graves and tumulus.RPAS eBee is a wing type and it is a suitable tool for mapping.EBee system consists of several components: the wing, software for planning flight missions and data processing software.EBee enables to program flight over the area with flight time to about 40 minutes.The usage of this RPAS is wide from mapping, orthophoto creation of high-resolution with pixel size around 3 cm, the creation of a DSM (Digital Surface Model) up to monitoring of vegetation condition (e.g. using vegetation index NDVI -Normalized Difference Vegetation Index).Camera canon S110 is designed for using in precision agriculture and for monitoring and analysis of vegetation cover.The camera captures data in bands NIRRG -NIR, Red and Green as shown in Figure 4.The camera is capable of detailed imaging and an altitude 100 m AGL corresponds to a GSD of 3.5 cm.

multiSPEC 4C
Camera multiSPEC 4C provides data in four bands NIRRERG -NIR, Red Edge, Red and Green.It is thus an appropriate tool for the analysis of vegetation and for use in precision agriculture.GSD at altitude 100 m AGL is about 10 cm. Figure 5 shows spectral bands of four channels of camera multiSPEC 4C.thermoMAP Thermal camera thermoMAP allows to capture thermal video or thermal images in order to create a thermal map of area.The camera extends the capabilities of the entire eBee system, e.g. for remote sensing, archaeological survey and so on.GSD is approximately 18 cm for altitude 100 m AGL.Band response of thermoMAP is shown in Figure 6.shows the differential DSM and the bottom right shows the differential DSM with a height restriction to ± 0.4 m, which very well highlights urn graves and tumulus.Furthermore, in ArcGIS software were created orthophotos NIR -Red (Red band was subtracted from the NIR band).This type of orthophoto was created for the NIR camera Canon PowerShot S110 and for the multispectral camera multiSPEC 4C. Figure 10 shows a process of highlighting urn graves and tumulus on the archaeological site for the camera multiSPEC 4C. Figure 10

Outputs
The project result is a set of thematic maps documenting archaeological site and vector drawing showing the location of the urn graves and the shape and position of the tumulus.Altogether there was found 510 urn graves in the archaeological site, which makes the place one of the biggest archaeological sites of urn graves of Knovíz culture.Maps are created in the coordinate system S-JTSK (EPSG 5514, S-JTSK Krovak EastNorth

Conclusion
In the archaeological site near the Ctiněves village there were found over 500 urn graves of Knovíz culture and it is one of the biggest sites located on the territory of the Czech Republic.RPAS eBee was used for documentation of the archaeological site.Five flights were performed, each using a different camera -VIS, NIR, NIR, multispectral and thermal camera.This gave rise to several orthophotos and a DSM.Furthermore a differential DSM was created in software ArcGIS.Outputs serve for the documentation and for the positional determination of individual urn graves and for the geometric and positional determination of tumulus at the archaeological site.Documentation and positional determination could be made due to vegetation symptoms of urn graves and tumulus.It was caused by favourable conditions for formation of vegetative symptoms during the winter and the spring in the 2016.
Due to these conditions a unique set of data documenting the urn graves of Knovíz culture and tumulus in the archaeological site located near Ctiněves village could be created.

Figure 1 :
Figure 1: Archaeological site.The archaeological site is located near the village Ctiněves, in the Usti region in the Czech Republic and is shown in Figure 1.The survey was conducted by prof.Dr. Ing.Karel Pavelka and Ing.Jaroslav Šedina from the Department of Geomatics, Faculty of Civil Engineering, Czech Technical University in Prague and in collaboration with prof.PhDr.Martin Gojda, PhD. from the Department of Archaeology, Faculty of Arts, University of West Bohemia in Pilsen.The subjects of the survey and documentation are tumulus and urn graves occurring in the archaeological site.Urn graves were identified from the debris of urns in 1969 by the National Museum archaeologist Dr. Sklenář as the urn graves of Knovíz culture from the period 1200 to 1000 BC.Urn grave is circular in shape and deep about 90 cm.Urn graves

J
. Šedina et al.Documentation of Urn Graves of Knovíz Culture by RPAS.

Figure 8 :
Figure 8: Identical point placement in the site.
Figure 9 top left shows the DSM, top right shows the smoothed DSM, bottom left J. Šedina et al.Documentation of Urn Graves of Knovíz Culture by RPAS.
on the top left shows NIR band orthophoto, on the top right is the Red band orthophoto, on the bottom left is the orthophoto NIR -Red and on the bottom right is shown highlighted orthophoto NIR -Red.

Figure 11 :
Figure 11: Comparison of the outputs.

Figure 11 shows
Figure11shows the outputs, from the top left is shown an orthophoto (RGB), NIR (NIRGB), NIR (NIRRG), thermal map, from the top left is shown an orthophoto NIR -Red S110, NIR -Red multiSPEC 4C, Digital Surface Model and Differential Digital Surface Model.Figure11shows that urn graves and tumulus excel at Orthophoto NIR -Red S110 and Orthophoto NIR -Red multiSPEC 4C and they are well visible in the Differential Digital Surface Model and in the Thermal map.In the Thermal map there are urn graves and tumulus much more visible and it has greater contrast with its surroundings than in other outputs.The tumulus and urn graves are also well visible in the Differential Digital Surface Model.