At ACRF's North Slope of Alaska site in Barrow, collocated sky radiometers are being evaluated to refine the methodology that accounts for infrared loss in polar conditions.

In the far northern reaches of Alaska, extended periods of both darkness and daylight occur throughout the year. Additionally, extremely cold weather conditions contribute to a harsh operating environment for research equipment. Therefore, broadband radiometers at the ACRF North Slope of Alaska (NSA) site are equipped with electric heaters inside the ventilators to keep frost and snow from causing interference with the measurements. Unfortunately, both of these issues - heating elements and the lack or surplus of sunlight at certain times of the year - appear to have an effect on correction methods used for known infrared loss problems in broadband shortwave measurements. In August, ARM researchers began a one-year field campaign to obtain the observational data needed for investigating and refining the infrared loss correction methodology for surface broadband measurements acquired at the NSA site.

Anomalous results were discovered during testing of the value added product, ARM Diffuse Correction, when recently applied to NSA data. The correction methodology uses nighttime offset data to establish a correction relationship applied during all hours. However, at NSA the majority of the “nighttime” data occurs during the winter months, while most of the daylight occurs during the summer months under far different ambient conditions. In addition, the existing infrared loss correction methodology was developed without the use of heaters in the ventilators, which were shown to have an effect on the instrument case and dome temperatures.

The Pyranometer Infrared Loss Study will result in comparative data with which to investigate and quantify these effects, both for correcting for infrared loss and effects the current ventilator heaters might be having on the basic measurements. Researchers will also investigate various permutations of the amount of ventilation and heating to perhaps optimize the broadband measurement strategy for NSA. The latter studies will evolve as early results are obtained. Overall, the IOP is targeted at improving both understanding, and the quality and accuracy, of radiative measurements in the polar regions.