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We have made measurements in the 60–100 km region using a 2.66‐MHz radar operated as an imaging Doppler interferometer. This allows us to view the entire region within 24° of zenith simultaneously, Doppler‐sorting and then echo‐locating the returns to achieve image resolution of ±3° in zenith angle and ±5 m/s in velocity. The approach is contrasted with conventional beam‐forming radar methods. We assume that the phenomena responsible for the observed weak radar scattering can be described as a distribution of discrete scattering points. Each scattering point is then characterized by its three spatial coordinates, its radial velocity, and the amplitudes and phases of its spectral components measured on a number of independent antennas. We present a series of apparent‐motion profiles from 61 to 87 km, showing the repeatability of the profiles and their evolution in time, followed by a two‐dimensional image of the scattering surface at 85 km, showing the motions of the individual scattering points and their distribution in space. Then we show images of the scattering surfaces from altitudes of 58 to 103 km, every 9 km, showing at each altitude the distribution in the horizontal plane of the locations of the scattering points, the specularity, or aspect sensitivity, of the scattering, and the derived apparent‐motion vectors. A sequence of eight 51‐s frames shows highly structured activity at 103 km.

Imaging Doppler interferometry has been developed as a pulsed-radar technique for obtaining three-dimensional images of mesaspheric scattering. Here we discuss the analysis procedure and algorithms and show the results of processing synthetic data records for a variety of situations. ADAMS ET AL.' IMAGING DOPPLER INTERFEROMETER

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