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An earth radiation budget sensor is proposed which is optimized to yield shortwave and total flux measurements over the entire earth on a spatial scale of ≈500 km without mechanical scanning. The elimination of mechanical scanning reduces instrument complexity and increases reliability and expected operational lifetime. A mosaic array of detectors views the total earth in contiguous elements with 250 km resolution at nadir and gradually increasing resolution towards the edges. The pattern produced at the top of the atmo-sphere is chosen to meet scientific and data reduction goals. The sensor also includes complete earth viewing channels which provide an independent check against the integral of the mosaic detector measurements. An effective spatial scale of ≈500km is achieved by sorting the data according to geographic location and inte-grating over the entire range of outgoing angles at each location. Over a month's period, sufficient data are collected to fill the range of outgoing angles so that it becomes unnecessary to use bidirectional reflectance models to estimate the outgoing flux. All channels, including the complete earth viewing channels, are calibrated by the same source. Calibration against the sun is provided on a regular basis without rotation of the instrument. The detectors to be used are an advanced, low noise version of the active cavity radiometers used on the present ERBE nonscanning instrument. These detectors are sufficiently sensitive so that no imaging optics is required, thus minimizing polarization and spectral flatness problems. The cavity type detectors provide maximum spectral flatness from 0.2 to 50 μ by means of their radiation trapping geometry. Sketches of the proposed instrument and its calibration mechanisms are presented.
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