The De-Icing Comparison Experiment (D-ICE): a study of broadband radiometric measurements under icing conditions in the Arctic

Abstract

Abstract. Surface-based measurements of broadband shortwave (solar)\nand longwave (infrared) radiative fluxes using thermopile radiometers are\nmade regularly around the globe for scientific and operational environmental\nmonitoring. The occurrence of ice on sensor windows in cold environments –\nwhether snow, rime, or frost – is a common problem that is difficult to\nprevent as well as difficult to correct in post-processing. The Baseline\nSurface Radiation Network (BSRN) community recognizes radiometer icing as a\nmajor outstanding measurement uncertainty. Towards constraining this\nuncertainty, the De-Icing Comparison Experiment (D-ICE) was carried out at\nthe NOAA Atmospheric Baseline Observatory in Utqiaġvik (formerly\nBarrow), Alaska, from August\xa02017 to July\xa02018. The purpose of D-ICE was to\nevaluate existing ventilation and heating technologies developed to mitigate\nradiometer icing. D-ICE consisted of 20\xa0pyranometers and 5\xa0pyrgeometers\noperating in various ventilator housings alongside operational systems that\nare part of NOAA s Barrow BSRN station and the US Department of Energy\nAtmospheric Radiation Measurement (ARM) program North Slope of Alaska and\nOliktok Point observatories. To detect icing, radiometers were monitored\ncontinuously using cameras, with a total of more than 1\xa0million images of\nradiometer domes archived. Ventilator and ventilator–heater performance\noverall was skillful with the average of the systems mitigating ice formation\n77\u2009% (many >90 \u2009%) of the time during which icing conditions\nwere present. Ventilators without heating elements were also effective and\ncapable of providing heat through roughly equal contributions of waste\nenergy from the ventilator fan and adiabatic heating downstream of the fan.\nThis provided ∼0.6 ∘ C of warming, enough to subsaturate the\nair up to a relative humidity (with respect to ice) of ∼105 \u2009%.\nBecause the mitigation technologies performed well, a near complete record\nof verified ice-free radiometric fluxes was assembled for the duration of\nthe campaign. This well-characterized data set is suitable for model\nevaluation, in particular for the Year of Polar Prediction (YOPP) first\nSpecial Observing Period (SOP1). We used the data set to calculate short-\nand long-term biases in iced sensors, finding that biases can be up to +60 \u2009W\u2009m −2 (longwave) and −211 to +188 \u2009W\u2009m −2 (shortwave). However,\nbecause of the frequency of icing, mitigation of ice by ventilators, cloud\nconditions, and the timing of icing relative to available sunlight, the\nbiases in the monthly means were generally less than the aggregate\nuncertainty attributed to other conventional sources in both the shortwave\nand longwave.