A Modern Concept for Autonomous and Continuous Measurements of Spectral Albedo and Transmissivity of Sea Ice

Sea ice and its snow cover play a key role in the climate and ecosystems in and beyond both Polar Regions. Especially in the Arctic, significant changes of sea-ice regimes towards higher fractions of younger and thinner sea ice have been observed during the last decades, but the reasons for these changes and their consequences are not yet fully understood. The interaction of solar radiation with snow and ice can drive important feedback processes that affect the sea-ice energy and mass balance. Improving our knowledge about these processes is of critical importance for understanding other physical, biological, and geochemical processes not only in snow and sea ice, but also in the upper ocean. Though several studies on albedo and transmissivity of snow and sea ice have been performed, the knowledge about spectral and total fluxes and their seasonality is still limited, especially under sea ice. But knowledge of how short-wave radiation is partitioned is of high importance when studying biological activity and its seasonal evolution. There is a strong need to quantify how much energy is reflected to the atmosphere, is absorbed in snow and ice, and is transmitted into the ocean, and how is this energy spectrally partitioned. Here we present a modern setup for autonomous, continuous and high temporal resolution measurements of spectral albedo and transmissivity of snow and sea ice. The setup is designed for use under challenging climatic conditions over long times and during different seasons. The measurements are performed using TriOS Ramses spectral radiometers, covering a wavelength range from 330-920 nm. The setup consists of three sensors, measuring incident and reflected radiation above the ice and radiation transmitted through the ice. From these measurements, time series of spectral albedo and transmissivity of snow and sea ice can be derived. The system described has been used successfully on sea ice for both short-term monitoring (days to weeks) and seasonal monitoring from late winter to autumn freeze-up, both with and without routine visits by observers. Beyond a methodological description of sensors and setup, we present sample data sets collected during the last years on Arctic sea ice. The setup has performed well under various conditions and the data sets stand out for high quality data. Comparisons to approved radiation measurements are shown, too. Setup for autonomous and continuous measurements of spectral radiation on sea ice