These utility trucks carrying a radar dish are familiar sights on the Great Plains, and have been spotted nationwide participating in other meteorological studies. There are two basic DOWs, built sometime around 1993. They are the brainchild of OU (now NCAR) scientist Josh Wurman. The units are now based in Boulder, Colorado and are owned by a partnership of universities.
The radars are used to gather extremely high resolution (both temporal and spatial) data of storm structure. From this data it is possible to make theories that give us a better understanding of how tornadoes and other severe weather forms.
A third DOW (Rapid-DOW) has recently been built using a phased-array radar. It allows a near-continuous look at a storm, and can be identified by its large, flat panel rather than the familiar radar dish.
A new fleet of mobile radars (actually, two) is now in existence, thanks to a partnership between NSSL, OU, TTU, and TAMU. These are called SMART Radars, and may be mistaken for DOWs. They're based in Norman, Oklahoma, where the DOWs used to reside.
Actually, they were built in 1994-5 as a joint NSSL/OU facility, and first deployed during VORTEX on a supercell in NC Kansas on 12 May 95. I drove the Field Coordinator (FC) that day and warmly remember the conversation between the brainchildren Erik Rasmussen, Jerry Straka, Kathy Kanak (Jerry's wife), and Josh Wurman (and I believe Lou Wicker) as we drove home that evening reminiscing about the events and ideas that led to the DOW conception and this historical first deployment. Other historic deployments that followed in 1995 included the 16 May multiple-tornadic storm near Hanston KS, 2 Jun 95 infamously researched tornado near Dimmitt TX, and 8 Jun 95 wedge near Allison TX.