In archaeology, the exposure, recording, and recovery of buried material remains. The techniques employed vary by the type of site, but all forms of archaeological excavation require great skill and careful preparation. The process begins with site location, by means of aerial photography, remote sensing, or, commonly, accidental discovery by construction crews. This step is followed by surveying and mapping, site sampling, and developing an excavation plan. The design and execution of an excavation frequently require an interdisciplinary team of experts. The actual digging consists of the removal of surplus dirt and the painstaking examination, through observation, sifting, and other means, of remaining soil, artifacts, and context. Common dig tools include the trowel, penknife, and brush. The excavation phase is followed by artifact classification, analysis, dating, and the publication of results. Excavation may last decades or be a short-term emergency salvage operation (as when a site is threatened by development).