M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Prospecting - CSATHÓ Beáta, PATTANTYUS-Á. Miklós: Possibilities and experiences of geophysical prospecting at archaeological sites in Hungary

In the radar image the structures consisting of a material of larger dielectric constant (metals, wall remains, etc.) produces many reflected waves, while the surrounding soil absorbs the majority of the waves. The reflected signals appear in densely shaded bands, by means of which the wall remains can be distinguished in the image. Two radar profiles are presented in Photo 2: the results of foreign and Hungarian measurements. It is, of course, well-known that the determination of the depth is problematic (Ujszászi, 1983) and is also very much influenced by the moisture content of the soil (Bruce, 1984). For the different depths of investigation transmitter and receiver antennae operating at various frequencies are needed which makes the archaeological utilization of this expensive equipment even more difficult. There is no radar equipment available in Hungary though their application in archaeological prospecting would be advantageous and economical (Pattantyús—Á., 1985). Other methods The application and experiments of other geophysical methods are also known in archaeological geophysics (Aitken, 1974) of which little experience is available in Hungary. Such is, for example, the measurement of soil susceptibility measured in shallow boreholes at an archaeological site; this type of measurement is suitable for complementing magnetic maps. Only in some cases, however, has this been employed for archaeological purposes in Hungary (Csókás and Takács, 1983). The method of aerial photography and its interpretation (see in this volume: Turkeve) should also be mentioned here - although it is not a purely geophysical method - as the basic method for the discovery of archaeological sites (Erdélyi, 1982). This method should be utilized before starting almost all archaeological surveys. Unfortunately, there have been only a few examples for this in Hungary during the past years and its application is becoming general in practice only nowadays (Erdélyi and Sági, 1985). Data processing and display Although it is essential in archaeological pn specting to be able to survey and interpret the applied geophysical methods easily, additional computer processing of the data is also necessary. One reason for this is the relatively large quantity of data: due to the small separation of stations more than 1000 data can be measured a day. The other reason is that by filtering the vast quantity of data and by displaymg them in various ways far more information can be obtained. Computer data processing is especially important in a noisy environment. Since the computer data recording of the majority of our currently used instruments is not solved, field pre-processing and displaying is not possible either. However, the subsequent computer processing of the measured data is possible since the excavation generally takes place only a year after the geophysical prospecting. In addition to plotting (resistivity and magnetic maps and profiles) computer processing has an important role in filtering the data system. During the processing of magnetic maps, a high-pass filter is used to remove the low-frequency effects (e. g. the effect of changes in soil quality) and to enhance the high-frequency effects characteristic of the archaeological objects. The gradient calculated from measurements of two sensor heights has the same purpose. The application of the smoothing (low-pass) filter for resistivity maps eliminates the noise caused by inhomogeneitie

s around the electrodes. These two filtering procedures described above are suitable for the processing of almost all data systems. If the resultant maps still do not reflect the expected effects