New Tools for Optical Measurements in Sea Ice
Acknowledgements
This work is funded by the Helmholtz Infrastructure Initiative FRAM, a Sentinel North postdoctoral research fellowship, Takuvik, Université Laval and the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung. We thank the Swedish Polar Research Secretariat (SPRS) and the crew of IB Oden, as well as the Department of Fisheries and Oceans Canada (DFO), Canadian Forces Base Alert, DRDC and Amundsen Science for their field support.
1
Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Germany,
5Bruncin Observation Systems, Croatia,
2
Takuvik Joint International Laboratory (UMI 3376) -- Université Laval (Canada) & Centre National de la Recherche Scientifique (France),
3
Centre d’optique, photonique et laser (COPL), Université Laval, Canada,
4Centre de recherche CERVO, Université Laval, Canada
In-ice profiler with angular resolution
To investigate the vertical decay of light and its changing angular distri- bution within a 2“ hole in sea-ice, we designed and deployed different fo- re-optics for the TriOS RAMSES-ARC hyperspectral radiance sensor.
Christian Katlein 1,2 , Simon Lambert-Girard 2 , Christophe Perron 2 , Raphael Larouche 2 , Yasmine Alikacem 2 , Simon Thibault 3 , Pierre Marquet 3,4 , Marcel Babin 2 , Lovro Valcic 5 , Philipp Anhaus 1 , Mario Hoppmann 1 , Marcel Nicolaus 1
Light measurements in ice
• Currently there is only very limited data on light measurements within sea ice
• In ice light measurements are crucial for the correct determination of the inherent optical properties (IOP)
• The solid nature of sea ice makes non-destructive measurements challenging
To help adress these problems we present the follo- wing novel tools with low impact on the sampled ice
• IMB style multispectral autonomous light sensor chain
• A new in-ice profiler similar to previously used ones, but based on the field proven RAMSES-ARC sensor
• First prototypes of optical sensors for an endoscopic probe allowing in-situ investigations with minimal disturbance of the medium
FRontiers in Arctic marine Monitoring
FRAM
Light sensor chain
For long term monitoring of the in-ice light field, we de- veloped a 2m long chain with 48 multispectral (RGB+PAR) sideward looking irradiance sensors. A prototype was de- ployed in August 2018 at the geographic North Pole and several units of an improved version will be used during MOSAiC.
Sea ice endoscope
A multimodal endoscopic approach for characterizing sea ice optics, physics, biology and biogeochemistry at small scale - Marcel Babin, Session 10, Tuesday morning
Posters:
Development of a reflectance probe to measure sea ice inherent optical properties - Christope Perron
Measurement of in-ice angular radiance distributions Raphael Larouche
On the design of an optical sensor to measure nitrate in sea ice - Yasmine Alikacem
L H L M
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Spectralon RAMSES
ARC
Figure 6: Deployment of the light chain prototype as part of a hyperspectral radiation station during the AO18 expediti- on of icebreaker Oden in the vicinity of the North Pole, August 2018: A) Overview of station setup B) Close up of light sensor chain C) Surface and D) bottom view of deployed light chain.
Figure 2: Different foreoptics holding a spectralon reflectance target in front of the radiance sensor enable the separate measurement of different parts of the radiance disrtibution within sea ice.
Figure 1: Picture of the „irradiance“ foreoptic similar to previously deployed in-ice profilers
Figure 3: Plot of the vertical decay of different components (irradiance ED, vertical rays LV, oblique rays LM, horizontal rays LH) of the radiance distribution in first-year (top row) and multi-year (bottom row) sea ice as measured in May 2018 on landfast ice off CFB Alert in the Lincoln sea. Measurements are normalized to the surface reference sensor. The solid black line depicts the sea ice bottom. Light extinction in interior first-year ice (zi=154cm, zs=17cm) is surprisingly low, while measurements in interior multi-year ice (zi=393cm, zs=44cm) show strong light attenuation.
Figure 11 (left): Vertical profile of measured extinction coefficients
Figure 12 (bottom left): Timese- ries of the measured average ice interior (35-180cm) sideward irradi- ance extinction coefficient.
Figure 13 (bottom middle): Com- parison of light-chain derived light transmittance and light transmit- tance as measured with a TrIOs hyperspectral setup at the same location. TriOS measurements are folded with the respective spectral sensitivities of the channels.
Figure 14 (bottom right): Scatter- plot comparing TriOS and light-chain derived transmittance measurements.
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Figure 5: Raw data of light chain measurements during the deployment in autumn 2018. Four chain segments failed on 3 September and 15 September.
Figure 7: Vertical profiles of sideward irradiance measured in different bands (left) and for different days (right)
Figure 8: Spectral sensitivity of the four channels used on the light chain sensor (TCS3472), as well as reference sensi- tivities of different PAR sensors (thin black curves)
Figure 10: DORT2002 modeled irradiance curves through an icepack similar to the one determined during deployment (left). Modeled chain retrieved extinction coefficents in comparison to beam c and Kd (middle). Irradiance ratios (right)
Figure 9: Coefficient of apparent extinction of sideward irradiance derived from light chain measurements.
Figure 4: Field test of the new IOP senor on land- fast ice in Qiqiktarjuak (Baffin Island)
