The sky radiometer housing was designed so that rain and spray would not reach the lens.Ī common approach for providing a two-point calibration is to use a constant temperature hot target and an ambient (cold) temperature target. The sky-viewing radiometer was contained in an unheated external housing attached to the side of the sensor housing. This algorithm was based on minimizing errors in the correction for nonunity emissivity of the blackbody, the use of two different sky- and sea-viewing radiometers, and the window correction. The housing temperature was reset on a daily basis to 5 K above the highest air temperature of the previous day.
This provided a stable, dry environment for the internal radiometer and the blackbody. The CIRIMS housing was insulated and maintained at a constant temperature within a range of approximately 0.1 K about the set temperature (standard deviation 0.1 K) by means of an integrated thermoelectric heater/cooler unit and circulation fan. Schematic overview of the CIRIMS radiometers showing internal instrument configuration. Photometers are similarly divided into luminance and illuminance versions.įigure 25. Instruments with intentionally broad spectral coverage are called broadband radiometers. Radiometers are divided into radiance and irradiance subclasses. They might therefore more properly be called spectral transmissometers (or reflectometers). In spite of the inclusion of “photo” in the name, the human photopic spectral response function (the V-lambda curve) is generally not employed in the use of spectrophotometers. This term is generally applied to neither radiometers nor photometers but to transmissometers or to reflectometers-instruments measuring an optical property-which scan over a range of monochromatic wavelengths. They are used to measure the spectral flux, irradiance, or radiance received by them. Some narrow spectral interval radiometers are made which scan the position of their narrow spectral interval across the spectrum. When the shape of the spectral response of a broadband radiometer is made to match the human spectral photopic efficiency function, the V-lambda curve, it is called a photometer. Others perform measurements only over a narrow spectral interval. Some radiometers measure over a large wavelength range. Others measure the flux received from a large range of solid angles. Some radiometers measure the radiant flux contained in a beam having a known solid angle and cross-sectional area. Radiometer is the term given to an instrument designed to measure radiant flux. Ross McCluney, in Encyclopedia of Physical Science and Technology (Third Edition), 2003 IX.A Introduction
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