302- EXPLORATION METHODS
EXPLORATION (video link 1, Video link 2)
Exploration is the method by which archaeologists detect unknown sites, and in case of known sites try to know the potential of the site by applying various techniques. In pursuit of such investigations we have to depend on various means and methods.
There are two ways of discovery of the sites :
1. Chance Discovery :
2. Planned Discovery :
Chance Discovery : Partially accidental and involuntary discoveries are known as chance finds, many times lead to the discovery of ancient sites. Chance finds occur as a result of work undertaken by human agency or by natural forces.
Natural Acts : Natural erosion has several times exposed the first traces of lost sites. Wind and water are the chief elements which contribute to natural erosion, leading to exposure of a site.
Rainfall, heavy rain, flood, Sea beaches, Wind action, Earthquake, Volcano eruption etc. , a fall in the level of a lake can expose previously submerged sites. It was in this way that the lake village of Zurich (Switzerland) was discovered.
Man Acts : Human activity is more varied than that of the nature. The diggings for foundation, road laying, canal digging, railways track etc. have brought to light numerous archaeological sites. The great Indus valley site Mohonjodaro was discovered while laying railway track. The accidental discovery of numerous coins and sculptures is well known. Important Mesolithic site of Bagor was discovered while digging the Rajasthan canal.
Man Made Survey :
PROSPECTING AND PRELIMINARY SURVEY
1. Literary Research : Ancient literary works contain a lot of information pertaining to ancient townships, pilgrim places, important routes etc. All kinds of literary works can contribute to the search for sites, but more important are the topographical and geographical works…. Sarswati Pattan – Surwaya, Simhapani – Sihonia, Pashadpalli-Padhawali Kalidasa, Kalhana, Herodotus, Megasthenese, Fahien, Itsing, Marcopolo etc,
2. Maps : Both ancient and modern maps help us in locating vanished sites and monuments. Ruins marked on ordinance survey maps are very useful in locating ancient monuments. Features like temples, forts, dolmens, caves, graves, etc. marked on the maps are very useful in the search for ancient sites.
3. Place Names : Place names have great significance in the archaeological exploration as they often help in locating ancient sites. For example in Andhra Pradesh and Karnataka places having names relating to ash such as Veebhuti Halli, Veebhuti padu, Korivipalli, Budidapadu, Budidapalli, etc. have yielded ashmounds of Neolithic period. Kheda villages in north Indian villages generally have large mounds that perhaps be an ancient site.
4. Oral information : Oral information collected during the exploration of a region for archaeological finds is very useful many times. Local residents have good knowledge of the ruins and ancient finds in the waste lands and agricultural fields. Information gathered from shepherds and cattle grazers are useful in obtaining information about the sites in remote areas and forest and hilly regions.
Ground Level Survey :
1. Traditional and direct Method : Surveying at ground level is the most traditional and the most direct form of prospecting as it presents real picture and potentiality of the site under investigation. In its most basic form , surveying at ground level is carried out on foot. The advantage of survey on foot is that a person can pick up potsherds,metal artifacts , coins , stone tools ,etc. Which are indicators to the presence of a site. Survey of a region can be taken different objectives. Depending on the problem selected , the nature of survey also changes
Physical Survey
Valley to Valley Survey : In case of prehistoric site, main river tributary river, material documentation. River terrace.
Village to village survey : In this survey the area is divided among several small units such as district, Tehsils, blocks, and then from blocks to villages. The explorer has to visit village to village within the block and collect/record all information pertains to antiquity.
2. Scientific Survey :
i) ELECTRICAL RESISTANCE SURVEYING
This method was first applied to detect archaeological structures by Prof R.J.C. Atkinson in 1946. Electrical surveying uses the same variations in humidity which are also applied to the damp marks by aerial photography. Moisture has the property of conducting electricity, which passess through the mineral salts dissolved in the water. So the wetter the soil, the more readily the current will pass through it, and the dryer the region, the poorer the conductivity of the soil. In pits of ancient ditches which collect moisture in the earth resistance to the electrical current will be weak. Conversely, a quickly drying stone wall or a foot-path will be more resistive to electricity. For resistance surveying four electrodes are fixed in equal distance in a line. The two outer electrodes measure the voltage being applied and the two inner electrodes are used to measure the current to estimate the resistance. Alternate current is used to eliminate the electrical charges being formed in the soil strata. If the earth between these two electrodes is abnormally resistant or abnormally conductive (unresistant), the measurements will show irregularities on the resistance graphs drawn to record them. When the selected line is completed the resistance along a parallel line is measured and so on. A comparison of the successive graphs obtained in this way may reveal a construction fairly accurately. This method was successfully used at Naikund in Maharashtra which resulted in the discovery of an iron smelting furnace.
Advantages
Responds to a wide range of archaeological features eg. pits, ditches, structural remains etc.
Excellent response to building remains
Can provide high definition images of archaeological features.
Limitations:
This process runs into difficulties, when it encounters natural pockets of clay or earth in the rock. Stoney soil conceals remains and makes the placing of the electrodes difficult, and rain and pits of organic matter can falsefy the results.
ii) MAGNETIC SURVEYING: Metal Detector
Magnetic surveying is based on the modification of the earths magnetic field by the magnetism of various sources and other buried remains. It is known that if clay is heated in an oven or intense fire, it acquires a magnetic force of its own, and retains it after it cools down. In practice the clay contains varying quantities of iron oxides such as magnetite or hematite, which cause its red colour and their magnetic field align itself with that of the earth as the temperature rises, and remains aligned when the clay cools off again. The result is a localised magnetic disturbance in a given area, the intensity of which can be measured with a magnetometer. This technique is known as thermo -residual technique.
iii) SOUND WAVE SURVEYING:
Acoustic surveys are traditionally carried out by banging the ground with an iron bar, which gives off a hollow or solid sound when it hits the ground and can indicate presence or absence of structures below. Likewise seismic surveying which consist of recording on a seismograph shock waves set up in the earth, can also indicate buried structures. These methods are mainly used after detecting a site to know the nature of the mound and to estimate the extension of the walls and structures before undertaking excavations.
iv) PROBE CHECKING:
. Probe checking is done by T-shaped rods driven in or screwed down by hand to the desired depth and then drawn up again. The presence of soil changes can point out to a grave or habitation site.
v) DRILL METHOD OF SURVEYING:
This is similar to probe checking, but here instead of probes a hole is drilled in the suspected area of hollow structures and tombs and a minature camera and flash gun housed in steel tube is introduced into the drill holes to take photographs of the interiors. Alternatively, a periscope also can be used to inspect the contents
vi) CHEMICAL SURVEYING:
Chemical surveying is chiefly founded on the analysis of phosphates. It is observed that the percentage of potassium nitrates and phosphoric acid increases at the places of human settlement. Chemical analysis of the soil can reveal the presence of prehistoric habitation sites.
vii) AERIAL PHOTOGRAPHY
Aerial photography or aerial surveying is a very useful method in locating ancient sites and monuments. By this method a large area can be surveyed quickly. By this method closely overlapping photographs are taken by special camera, so that nothing is missed. A pair of photographs are taken for each area with stereo cameras, for stereoscopic examination and three-dimensional view. To take aerial photographs an aeroplane is flown over a selected area covering parallel strips of land till the whole area is covered. From the photographs taken in this manner, we can easily identify features looking round, square or rectangular, which probably represent some ancient structures. Ancient habitations could be easily identified due to the discolouration of the mound in comparison to the surrounding area. Completely buried structures also can be identified by observing the differences in relief,
These days Drones are effectively, efficiently used for aerial survey with good quality video imaging techniques.
viii) Remote Sensing
With the advances in the image technologies using aircraft and satellites, now a days it has become common to use remote sensing for detection and study of archaeological sites. Basically, remote sensing means, gathering of information from distance. Remote sensing is used for detection of features or objects from distance. It is common to use satellite imageries for remote sensing. Several countries, including India, have been sending satellites into the space which can transmit the information in the form of the images of the earth. The satellites carry several sensors which can detect various kinds of radiations (or spectrum) that emanate from earth’s surface, when Sun’s radiation is reflected back.
ix) GROUND PENETRATING RADAR (GPR)
RADAR is a acronym for Radio Detection and Ranging. Radar equipment emits micro-waves, which are reflected back by solid objects and absorbed to a great extent by softer material. Radar waves can penetrate earth’s surface to a considerable depth. When we send radar waves into the ground some of the waves are reflected back, depending on the nature of the objects/features in the ground. Thus structures, stones, etc. which are harder material reflect back much of the radiation, while, soft earth, moisture, etc. absorbs the radiation. The reflected waves are collected by the radar antenna and processed to produce an image of the buried features. The GPR are generally mounted on Drone and Planes.
x) SONAR : sound navigation and ranging
Sonar imaging is the use of acoustics to produce images in order to locate objects found underwater. Used in the field of underwater archaeology, Sonar imaging works by sending and receiving signals using a single unit known as a transducer. The transducer emits a sound pulse through the water, which then hits the target and returns to the traducer. This sequence produces an image by measuring the time it takes for the wave to return, as well as the strength of the wave.
xi) LiDAR : Light detection and ranging
is a method for determining ranges(variable distance) by targeting an object or a surface with a Laser and measuring the time for the reflected light to return to the receiver. It can also be used to make digital 3-D representations of areas on the Earth's surface and ocean bottom of the intertidal and near coastal zone by varying the wavelength of light. Lidar can also help to create high-resolution digital elevation models (DEMs) of archaeological sites that can reveal micro-topography that is otherwise hidden by vegetation. The intensity of the returned lidar signal can be used to detect features buried under flat vegetated surfaces such as fields, especially when mapping using the infrared spectrum.
LIDAR has been used in many searching and identifying many MAYA cultures
xii) Thermal Mapping (Infra Red)
The principles behind aerial thermographic imaging in archaeology are relatively simple: due to differences in composition, density, and moisture content, materials on and below the ground surface absorb, emit, transmit, and reflect thermal infrared radiation at different rates. A wide range of archaeological features should all theoretically be visible in a thermal image if (1) there is a sufficient contrast in the thermal properties of archaeological features and the soil matrix or ground cover; (2) the archaeological materials are close enough to the surface to be affected by heat flux; and Put simply, a buried stone wall may heat and cool at a different rate than surrounding soil, and at the right time of day or night, this difference is potentially visible in a thermal image of the surface
As with any geophysical prospection method, researchers should carefully consider the thermal properties of the features or objects they are trying to image versus the properties of the surrounding or overlying matrix, materials. Instances in which there is a large difference in thermal properties between target features and the background will be much more likely to produce good results.
xiii) GIS (Geo-spatial Information System)
Geographic Information Systems has been an important tool in archaeology since the early 1990s. It is a type of database containing geographic data combined with software tools for managing, analyzing, and visualizing those data.
Link 3
Comments