What are non-intrusive archaeological survey techniques, and how are they used to archaeological advantages during excavation

There are a variety of non-intrusive archaeological survey techniques available to archaeologists which can assist excavations before they have begun, during the excavation – bringing clarity to uncovered features, and after – to tie everything together and create a detailed excavation report. Non-intrusive techniques include field walking, sampling, aerial photography, geophysical and geochemical surveys (resistivity and magnetometer surveys) GPR, metal detecting, GIS, and LiDAR (radar acting as its underwater equivalent). The value of each method depends on different variables including the environment, climate, light, time, aim and type of excavation and budget.