In order to image the interior of the Earth, I often need to deploy seismometers to collect data from a particular area of interest. These deployments can range from a handful of stations to ~100 stations, depending on the depth and size of the structures I want to image.
Roughly speaking, the bigger an area we cover, the deeper we can "see" into the Earth (much like a larger telescope can see farther into the sky). The density of stations within that area controls the resolution of the image we get (you can think of each station as a "pixel"). So, as imaging targets get smaller and/or deeper, we need to put out more and more stations. Each of these stations records continuously for two years or more. They have to run for that long in order to record enough earthquakes. My approach uses earthquakes in much the same way as CAT scans use X-rays, so more earthquakes means better images.
Deploying seismometers is hard work! For a detailed description of what goes into installing a single station, this page by John West details the installation procedure we used during the High Lava Plains project in 2007 - 2010.
New technology holds the promise of greatly simplifying these installations. The seismology group at DTM has been developing a quick deploy box that takes advantage of the small size and improved robustness of these modern sensors and recording devices to eliminate the need for vaults and home-made electronics enclosures. We are currently assembling a 12 station rapid-response instrument pool for volcanic eruptions and major earthquakes that will use the Carnegie quick deploy box.