Some archaeologists call everything they do out-of-doors fieldwork, but others distinguish between fieldwork, in a narrower sense, and excavation. Fieldwork, in the narrow sense, consists of the discovery and recording of archaeological sites and their examination by methods other than the use of the spade and the trowel. Sites hitherto unknown are discovered by walking or motoring over the countryside: deliberate reconnaissance is an essential part of archaeological fieldwork.
In Europe, a study of old records and place-names may lead to the discovery of long-forgotten sites. The mapping of new and old sites is an essential part of archaeological survey. This process has been brought to a very high standard of perfection, both in the marking of archaeological sites on ordinary topographical maps and in the production of special period maps. The distribution map of artifacts, especially when studied against the background of the natural environment, is a key method of archaeological study.
The formerly earthbound archaeologist has been greatly helped by the development of aerial photography. The application of aerial photography to archaeological investigation began in a small way during World War I, as a side effect of military reconnaissance, and was given further impetus by World War II; the photographic intelligence departments of all the combatant nations were extensively staffed by archaeologists, who then carried their expertise and enthusiasm into the postwar years. The University of Cambridge now has its own department of air photography under J.K.S. St Joseph: using its own pilot and aircraft, it flies photographic missions over Ireland, Great Britain, Denmark, and The Netherlands. The number of new sites discovered each year by aerial photography is very large. Some of these are surface sites, especially partly destroyed sites that show up well in special conditions of light, as in early morning or late evening. But many are sites that could not be found on the ground and that show up in aerial photographs as variations in soil colour or in the density of crop.
Archaeological reconnaissance may be advanced from ordinary surface or aerial methods in a wide variety of ways. A very simple method is tapping the ground to sound for substructures and inequalities in the subsoil. Deep probes have made it possible to trace walls and ditches. The Lerici Foundation of Milan and Rome has had great success with this method since its development of the Nistri periscope, first used in 1957 in an Etruscan tomb in the cemetery of Monte Abbatone. The periscope is inserted into the burial chamber and can photograph the walls and contents of the whole tomb.
Other modern techniques that have been applied to archaeological prospecting employ electricity and magnetic fields (geophysical prospecting). A method of electrical prospecting had been developed in large-scale oil prospecting: this technique, based on the degree of electrical conductivity present in the soil, began to be used by archaeologists in the late 1940s and has since proved very useful. Magnetic methods of prospecting detect buried features by locating the magnetic disturbances they cause: these were introduced in 1957–58 and use such machines as the proton magnetometer, the proton gradiometer, and the fluxgate gradiometer. An American expedition discovered the site of Sybaris in Sicily by magnetic prospecting. Electromagnetic methods have been in use only since 1962; they employ developments of the concepts used in mine detectors. Instruments such as the pulsed-induction meter and the soil-conductivity meter detect magnetic soil anomalies, but only if the features are fairly shallow.