Reconnaissance techniques . Excavation sites may be determined from aerial photographs, old pictures, maps, documents, or ground features. Some sites - mounds, temples, forts, roads, and ancient cities, may be easily visible at ground level. Aerial photographs may be taken from planes, balloons, or satellite by cameras with remote sensors, infrared film, etc. The high viewpoint reveals outlines of submerged buildings, roads, and fields.
Archaeologists check for clues such as variation of soil color, ground contours, or crop density.
Archaeologists may probe the ground with radar to look for structures or hollows. Electron or proton magnetometers or even mine detectors force currents through the earth to detect unusual features beneath the soil. Magnetometers may be dragged through the sea to locate sunken ships or structures. They also look for agricultural clues such as seeds or field boundaries. Archaeologists carefully remove layers of soil at a site, using trowels or small tools when there's a chance of uncovering an object.