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

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 temporalresolution 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.

Development and calibration of an automatic spectral albedometer to estimate near-surface snow SSA time series

“…Even though these values are weak, the correction successfully removes the decreasing trend in the shorter wavelengths of the visible (400 to 600 nm) that affects the evening acquisition. Albedo measurements by Nicolaus et al (2010) show a similar artifact. Such a trend is visible throughout the time series at large SZA and the collector response correction usually performs well by recovering a nearly constant value as expected.…”

“…(2) Use of optical switch instead of two or more spectrometers is a good option. It is cost effective and avoids the need of inter-calibration of the spectrometers (Nicolaus et al, 2010) which may drift independently over time (France et al, 2011) However, it involves mechanical parts and is subject to switching delay and reproducibility errors. This strategy allowed us to deploy two measurement heads located a few meters apart which provided evidence of spatial difference during some periods.…”

“…Long-term monitoring of spectral albedo requires fully automatic instruments with a good robustness to cope with the Antarctic conditions (Wuttke et al, 2006;Salzano et al, 2016). With the advent of cheaper and compact spectrometers free of mechanical parts (Kantzas et al, 2009;Nicolaus et al, 2010), operating such instruments in Antarctic conditions is becoming easier.…”

A New Remotely Operated Sensor Platform for Interdisciplinary Observations under Sea Ice

“…Sea ice plays a major role in the earth's climate system by controlling fluxes of energy and momentum between the atmosphere and the polar oceans (Solomon, 2007). Despite the harsh climatic conditions sea ice also harbors a complex ecosystem which is tightly coupled to the response of polar sea ice to global climate change (Melnikov, 1997;Quillfeldt et al, 2009). Sea ice extent has been decreasing dramatically throughout the last decades, particularly in the Arctic (Stroeve et al, 2012).…”

Development and evaluation of a driver circuitry for miniature spectrometers used in cold environments

“…Solar radiation not only contributes to the melting of sea ice but also helps to shape the species and biomass of the marine plankton in the Arctic. Therefore, great efforts have been made to measure solar radiation distribution above or below the Arctic sea ice [7,8]. A fiber optic spectrometry system is proposed to measure spectral intensity of solar radiation at different depths of sea ice, autonomously and year-roundly [9].…”