An electrically scanning microwave radiometer (ESMR) is mounted in a flying body orbiting a planet and operative to measure the surface of the planet. A receiving antenna having its cylindrical or multiplicated radiation face is used to scan the surface of the planet along a conical section. A receiver detects the radiation from the planet which is received by the receiving antenna. The detected signals are then integrated by an integrator. The integrated value is converted into a digital value by a signal processor. The digital value is transmitted to an earth station as a measurement signal after it has been formatted. The receiving antenna may be either of a cylindrical phased-array antenna or multiplicated phased-array antenna. The cylindrical and multiplicated faces may be replaced by inverse-directional cylindrical and multiplicated faces, respectively. Further, the receiving antenna may be of a composite or multi-beam type which includes any combination of the aforementioned surfaces. Since the surface of the planet is scanned along the conical section, the incident angle will not be changed even if the width of beam scan is increased. This enables variable incident angle type, multiple polarization type and multiple frequency type ESMRs to be accomplished.
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