The Post Gregorian Upgrade Era

The Gregorian upgrade, which provided a true focus for incoming radio waves plus increased sensitivity and frequency coverage, opened up significant new opportunities in both radio and radar astronomy. In particular, a multi-beam system for, mainly, surveys of atomic hydrogen in the Milky Way and external galaxies were now a possibility. For the newly-named Space and Atmospheric Sciences (SAS), the dual beam capability would allow improved wind and plasma line measurements. Before these improvements could be utilized, the main reflector needed to be repaired and reset, new horns and low noise receivers built and multiple back-end processors designed and constructed. All this was achieved over the next few years with the 7-beam Arecibo L-Band Feed Array (ALFA) being installed in 2004. This was followed by the initiation of a number of extensive surveys. VLBI flourished and several SETI programs were conducted with, sadly, no positive detection. Radar astronomy saw a change in emphasis from the study of planets and satellites to astrometric and imaging observations of asteroids and, when possible, comets. For SAS the LIDAR program flourished with the acquisition of new instruments, and a new HF facility utilizing the 305 m primary reflector was designed and constructed after the HF transmitting facility at Islote on the coast east of Arecibo was destroyed during Hurricane Georges in 1999.