This note describes the new spatial interferometry (SI) capability of the 430-MHz radar system of the Arecibo Observatory (AO). Three limitations exist when the 430-MHz radar is used for observations in the tropospheric and stratospheric regions. First, the AO radar currently has a lower height limitation of approximately 6 km because of the existing transmit/receive switch. Second, fading ground clutter limits the useful data which can be obtained and complicates the analysis. Third, the large mass of the feed system, which slows down beam steering, reduces the temporal resolution of any measurements requiring multiple beam positions. For these reasons, an SI system has been developed which will be shown to reduce these limitations. A brief description of the hardware is provided, and preliminary data are presented.¿ 1997 American Geophysical Union