DEVELOPMENT OF A HIGH-RESOLUTION IMAGING RIOMETER FOR THE MIDDLE AND UPPER-ATMOSPHERE OBSERVATION PROGRAM AT POKER FLAT, ALASKA

An imaging riometer equipped with a 16 x 16-element square array anten na was developed and was installed at Poker Flat, Alaska, to obtain hi gh-resolution two-dimensional images of the cosmic radio noise absorpt ion at 38.2 MHz. This system scans the viewing region of a 200 x 200 k m(2) square of the radio sky at the 90 km altitude every second, using 208 available antenna beams among 256 antenna phasing patterns. The m aximum 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, l eading to more detailed investigation of auroral absorption dynamics t han the existing imaging riometers. After the system check with the fu ll system that was temporarily installed at the CRL Yamagawa observato ry, Japan, in 1994, the final installation was completed and the opera tion started at Poker Flat, Alaska in September 1995. (C) 1997 Elsevie r Science Ltd.