In 1964, the remainder of the NSSP moved to Norman, where it merged with WRL and was renamed the National Severe Storms Laboratory (NSSL). Dr. Edwin Kessler became the first director. In 1969, NSSL obtained a surplus 10-cm pulse-Doppler radar from the United States Air Force. This radar was used to scan and film the complete life cycle of a tornado in 1973. By comparing the film with velocity images from the radar, the researchers found a pattern that showed the tornado beginning to form before it could be visually detected on the film. The researchers named this phenomenon the Tornado Vortex Signature (TVS). Research using this radar led to the concept that would later go on to become the NWS NEXRAD WSR-88D radar network.