A pyroelectric detector based nulling infrared radiometer

A chopped pyroelectric infrared radiometer has been developed to improve the accuracy of field measurements of atmospheric emission in the thermal infrared. This poster describes the instrument and its null mode of operation using a built-in miniature blackbody reference. Details are presented on the consequences of nulling operation, the optical layout, the black body reference and temperature measurement, aspects of the digital electronics that perform synchronous demodulation of the detector signal and digital implementation of a PID closed loop controller, and some of the practical design considerations of the instrument. A calibration procedure is given, as well as possible configurations of the instrument to measure hemispherical downwelling radiation or narrow field of view atmospheric or terrestrial radiation. A comparison with the BSRN pyrgeometer at the southern Great Plains ARM site shows good correspondence and a mean difference of 5 W/m^2 (BSRN pygeometer higher) over a period of fifteen days in March of 2000.