de Pater, I., P. Palmer, D. L. Mitchell, S. J. Ostro, D. K. Yeomans, and L. E. Snyder (1994). Radar aperture synthesis observations of asteroids. Icarus 111, 489-502.
We report results of Goldstone-VLA, radar aperture-synthesis observations of the mainbelt asteroids 324 Bamberga and 7 Iris and the near-Earth asteroids 1991 EE and 4179 Toutatis. Simultaneous resolution of echoes in both angle and Doppler frequency provide new constraints on the mainbelt asteroids' pole directions: Bamberga's spin vector is within 40 deg. of the south ecliptic pole, and the twofold ambiguity in Iris' pole direction (P. Magnusson, 1989, in Asteroids II, pp. 1180-1190) is resolved in favor of the ecliptic coordinates long = 15 deg., lat = +25 deg. For Bamberga, monostatic and bistatic radar echoes and VLA thermal-emission measurements, also reported here, are consistent with radiometric estimates of Bamberga's size and with the hypothesis that the asteroid is overlain by a regolith having a porosity of ~50%. Our near-Earth asteroid measurements required the development of new on-line VLA software that allows imaging of objects that are in the telescope's "near-field." This software has been successfully tested on Toutatis at a distance of 0.06 AU and will be essential for VLA observations of Earth-approaching comets.