Development of a diffuse reflectance probe for in situ measurement of inherent optical properties in sea ice

Abstract

Abstract. Detailed characterization of the spatially and temporally varying inherent optical properties (IOPs) of sea ice is necessary to better predict energy and mass balances, as well as ice-associated primary production. Here we present the development of an active optical probe to measure IOPs of a small volume of sea ice (dm3) in situ and non-destructively. The probe is derived from the diffuse reflectance method used to measure the IOPs of human tissues. The instrument emits light into the ice by the use of an optical fibre. Backscattered light is measured at multiple distances away from the source using several receiving fibres. Comparison to a Monte Carlo simulated lookup table allows, in theory, retrieval of the absorption coefficient, the reduced scattering coefficient and a phase function similarity parameter γ, introduced by Bevilacqua and Depeursinge (1999). γ depends on the two first moments of the Legendre polynomials, allowing the analysis of the backscattered light not satisfying the diffusion regime. The depth reached into the medium by detected photons was estimated using Monte Carlo simulations: the maximum depth reached by 95 % of the detected photons was between 40±2 and 270±20 mm depending on the source–detector distance and on the ice scattering properties. The magnitude of the instrument validation error on the reduced scattering coefficient ranged from 0.07 % for the most scattering medium to 35 % for the less scattering medium over the 2 orders of magnitude we validated. Fixing the absorption coefficient and γ, which proved difficult to measure, vertical profiles of the reduced scattering coefficient were obtained with decimetre resolution on first-year Arctic interior sea ice on Baffin Island in early spring 2019. We measured values of up to 7.1 m−1 for the uppermost layer of interior ice and down to 0.15±0.05 m−1 for the bottommost layer. These values are in the range of polar interior sea ice measurements published by other authors. The inversion of the reduced scattering coefficient at this scale was strongly dependent on the value of γ, highlighting the need to define the higher moments of the phase function. This newly developed probe provides a fast and reliable means for measurement of scattering in sea ice.

Modelled variations of the inherent optical properties of summer Arctic ice and their effects on the radiation budget: A case based on ice cores from CHINARE 2008–2016

“…This result was slightly higher than our results. The results of Mobley et al (1998) and Perron et al (2021) agree with our range. The σ of the DL in Perron et al (2021) was in our range, and the values of Light et al (2008) were smaller than those in the present study.…”

“…CC BY 4.0 License. Perron et al (2021). The values calculated by the same method as used in the present study by Mobley et al (1998) were close to the maximum of our range.…”

“…The results of Light et al (2015) and were obtained in a cold laboratory by simulating the radiative transport in subsections of the sea ice. Meanwhile, the results of Grenfell et al (2006) and Perron et al (2021) are close to the minimum of our range. The σ of ice in Grenfell et al, (2006) was calculated from the ice extinction coefficient, and it was measured in situ using a diffuse reflectance probe in the https://doi.org/10.5194/egusphere-2022-552 Preprint.…”

“…One possible reason for the differences was the uncertainties in the ice microstructure introduced by brine loss during measurement and segmenting. Thus, our Va values of the IL are greater than the values derived from nondestructive methods (e.g., Perron et al, 2021). As a result, the maximum underestimate of Vb was 15-25% and the maximum overestimate of Va was 96-160% when taking the uncertainties introduced by the measurements and brine drainage into account (Wang et al, 2020).…”

From Bright Windows to Dark Spots: Snow Cover Controls Melt Pond Optical Properties During Refreezing

“…For simplicity, the situation without any snow will be referred to as "summer" conditions whereas the snow-covered scenario is referred to as "autumn" conditions. We used typical inherent optical properties for multi-year ice (Katlein et al, 2021;Perron et al, 2021).…”