A modern concept for autonomous and continuous measurements of spectral albedo and transmittance of sea ice

Abstract

Abstract Time series of irradiance data measured on sea ice with high temporal and spectral resolution are needed for advancing studies of atmosphere–ice–ocean interaction during different seasons. In particular, more observations of under-ice irradiance are needed to quantify fluxes through snow and sea ice and their seasonality, because the vertical and spectral partitioning of solar radiation are still among the biggest unknowns in today's descriptions of sea-ice related processes. Our current understanding of the interaction of radiation and sea ice is based on only a few data sets, yet this interaction is crucial for describing such processes as sea-ice formation, snow metamorphism, and snow and ice melt, as well as biological productivity and abundance. A modern setup for synchronous, autonomous, continuous, and high temporal-resolution measurements of spectral albedo and transmittance of sea ice is presented. The setup is based on three spectral radiometers, covering a wavelength range from 320 to 950 nm with 3.3 nm spectral resolution. Sensors, data logger, and their setup have worked well in several campaigns under challenging climatic conditions. The longest campaign lasted more than 4 months, without the need for maintenance, and the sensors have shown good performance related to surface contamination, one of the most challenging aspects for radiation measurements. Measured data are of high quality, including details of spectral shapes and high sensitivity to changes in observed snow and ice conditions. All spectra are calibrated for absolute readings, allowing applications in a wide variety of snow and ice studies and their comparison. A sample data set, collected over two weeks in the central Arctic, is presented and shows how the vertical partitioning of irradiance changes during the transition from summer to autumn. The main advantage of the system is its suitability for autonomous and long-term observations over and under sea ice. Furthermore, the setup is portable and robust, and can be easily and quickly installed, which is most valuable for deployment under harsh conditions and also encourages short observation periods. Spectral range and other technical features permit the application of this setup for various interdisciplinary studies, too.