REGIONAL ATMOSPHERIC PROFILING CENTER FOR DISCOVERY

RADIOMETERS

RADIOMETER PHOTO GALLERY

ESSC scientists are measuring the downwelling thermal infrared radiation from the atmosphere, using two ventilated Kipp & Zonen CG4 pyrgeometers atop a twelve-foot tower on the NSSTC Annex rooftop. This vantage point has an unobstructed view of the sky down to the horizon. The CG4 pyrgeometers incorporate an advanced optical and thermal design that eliminates the need for thermistors to measure the dome temperature, and correct for the temperature offset between the dome and the case. The dome shape also enables improved homogeneity in the thin-film solar filter that is deposited on the dome interior; this feature improves the azimuthal uniformity of the sensor responsivity. These two precision sensors are currently collocated to inter-calibrate their relative responsivity over a wide range of air temperatures, sky conditions, and sky temperatures. Results to date indicate excellent agreement between the two sensors (see sample data in Figures A&B). In the raw data, relative offsets rarely exceed 1-2 watt/m2; the largest offsets occur on hot days with clear daylight skies, and during rapid changes in air temperature or sky temperature. These offsets will be substantially reduced after corrections for temperature dependence, non-linearity, and solar leak-through in the thermopile response. Noise levels in the 1-second data are about 0.1 watt/m2 at night and about 0.2-0.5 watt/m2 in sunlight; these noise levels will be negligible after averaging to the 1-minute BSRN standard. Danielle Nuding, ESSC Undergraduate Research Technician, had the primary responsibility for installing the instrumentation and programming the data logger. Stephanie Long, ESSC Undergraduate Research Technician, is monitoring the instruments and analyzing the data. David Bowdle, ESSC Research Scientist, designed the installation and oversees the activity.

DEPSCOR PROGRESS REPORTS
Measurements of Downwelling Infrared Irradiance