Like performing an archaeological excavation, Geophysics surveys are carried out to answer specific questions. Unless something is known about the site already, this question is usually as simple as 'What is there?'. The real question is why are you digging at that particular spot. Whilst geophysics is not as time consuming as excavation, you don't want to be trudging up and down a field if there is a good chance there is nothing there. Therefore geophysics is usually done after other types of survey, which indicate there is something worthwhile to investigate. When talking about sources of information, I will talk about the English system.

One of the best ways to find potential sites is aerial photography. Your local library may have copies of local aerial photographs, the Historic Environment Record at the County Council (HER) will have, but the best place, if you can get them, is the National Monuments Record at Swindon. There is also a good collection of photos online courtesy of Google Earth and Flash Earth. If you can, look at several aerial photographs of the same spot, as different photographs can show up different features. Interpreting Aerial Photographs is like interpreting geophysics data, it takes practice to get it right. Going back to the HER briefly, someone may have already noted something about the area you are interested in. A quick request to the HER may save you doing a survey that has already been done.

Another way to check if the area is suitable for geophysics is to do some field walking. This can be anything from have a quick stoll around a field to see if there is anything of interest, all the way up to total collection in grids. The latter is probably as time consuming as the geophysics itself, but if you do decide to do a total collection, it is worthwhile keeping the same grids for the geophysics so the results can be compared.

Finally, metal detectors can be used to find sites. If there is a good coin scatter (as opposed to a concentrated hoard), there may be an archaeological site worth investigating.

If you intend to do a geophysics survey, you can't just walk into a field and do it, there are potentially several people you need to seek permission from. Firstly there is the landowner. The HER may be able to find out who owns a particular field for you. There may also be a tenant farmer, who has leased the land from the landowner. If you are looking at an average field then that will be the case.

If you are doing a survey on an SSSI or similar designated wildlife area, then you will probably have to contact English Nature, especially if you are marking out your grids using spray paint. English Nature do recommend a brand of spray paint for such sites called Sylvamark.

The other consideration is whether the site has been scheduled. If you are unsure, then contact the county HER. If the site is scheduled, then you will need scheduled monument consent from English Heritage. For a geophysics survey, they are unlikely to turn you down, but they will want a copy of your report for their records within a certain period of time after the survey has been completed.