Millimeter-wave radiometry of the earth's surface from Low Earth Orbit (LEO) with a resolution of a few km requires antenna apertures several meters across and sub-second scanning times. Fulfilling these requirements with a mechanically scanned real-aperture antenna presents formidable mechanical challenges. An attractive alternative described here is to use synthetic aperture techniques employing a sparse-array of antennas that trade the mechanical complexity of real-aperture imaging for the electrical complexity of synthetic aperture imaging. We present results of an ESA- sponsored study aimed at seeking the optimum technique for high performance synthetic aperture mm-wave radiometry from LEO.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.