Development of a high-resolution imaging riometer for the middle and upper atmosphere observation program at Poker Flat, Alaska

Abstract An imaging riometer equipped with a 16 × 16-element square array antenna was developed and was installed at Poker Flat, Alaska, to obtain high-resolution two-dimensional images of the cosmic radio noise absorption at 38.2 MHz. This system scans the viewing region of a 200 × 200 km 2 square of the radio sky at the 90 km altitude every second, using 208 available antenna beams among 256 antenna phasing patterns. The maximum horizontal spatial resolution is 11 km at 90 km near the zenith over the antenna, which will enable us to resolve fine structures of auroral arcs with widths of the order of tens of kilometers or less, leading to more detailed investigation of auroral absorption dynamics than the existing imaging riometers. After the system check with the full system that was temporarily installed at the CRL Yamagawa observatory, Japan, in 1994, the final installation was completed and the operation started at Poker Flat, Alaska in September 1995.