In fall of 1999 and 2000, the rings of Saturn were imaged using the Arecibo S-band radar system by P. Nicholson, D. Campbell, R. French, G. Black and J.-L. Margot. The image shown is a sum of 5 days of dual-circular polarization data, co-adding both polarizations. The Keplerian velocity profile of the rings results in the outermost or A ring which provides the earliest echo, appearing at a lower Doppler shift than the middle or B ring. This leads to four bright ``crossover'' regions on either side where signal from the two different rings add together, analagous to the north/south ambiguity for radar imaging of rigidly rotating bodies. A pronounced azimuthal asymmetry can be seen: the rings are brighter on the far quadrant on the receding (western) ansa than on the near quadrant of the approaching (eastern) ansa. The most widely accepted explanation of the asymmetry involves gravitational ``wakes'' generated by individual large ring particles, which are distorted by Keplerian shear into elongated structures trailing at angles of about 70 degrees from the radial direction (e.g. Franklin and Colombo 1978).ˆà

A delay-Doppler image of Saturn's rings at a frequency of 2380 MHz (12.6 cm) is compared to a model image constructed by reprojecting a pair of HST images taken at 439 nm. Time delay increases from bottom to top, and Doppler shift increases from left to right. The effective spatial resolution is 2000 km by 15000 km.