Guislain Bécu, Philippe Massicotte
Since last meeting (= first release of AOP data):
GE2015.ICMP cruise: “Hole Type” from “NA” to “High” for the first (34) profiles - high snow site was actually sampled from the beginning of the sampling efforts,
CDOM and Chl-a concentration.
IOP data include ice camp data only. Amundsen based IOP data are processed by UQAR.
Philippe Massicotte, Guislain Bécu, Simon Lambert-Girard, Marcel Babin
The characteristics of underwater light field are very important drivers of ecosystem functioning:
Primary production
Photo-chemical reactions (photo-degradation)
Energy budget in the water column
Nowadays, measuring downwelling irradiance (\(E_d\)) in open water is pretty straightforward.
In open water, downwelling irradiance (\(E_d\)) is known to decrease exponentially with increasing depth.
\[ Ed(z) = Ed(0) \times e^{-K \times z} \]
\(K\) (\(m^{-1}\)) is the vertical diffuse attenuation coefficient describing the rate at which light decreases with increasing depth.
Important metric used by biologists and to parameter models (need for precise estimates).
Assuming an optically homogeneous water column.
Due to spatial horizontal heterogeneity, measuring vertical light profiles under ice cover presents considerable challenges in comparison to open water.
Note the heterogeneity of the light field.
Under a heterogeneous surface, light transmission can increase to reach a subsurface maximum between 5 and 10 meters.
Obviously, estimating \(K_{Ed}\) under ice represent a considerable challenge.
Influence of the horizontal heterogeneity on measured light.
Due to the horizontal heterogeneity, measured light properties are only valid locally and cannot be generalized to the surrounding environment.
One promising way is to use upwelling radiance (\(L_u\)), which is far less influenced by the surface spatial heterogeneity.
We propose using upwelling radiance attenuation coefficient (\(K_{Lu}\)) as a proxy to reconstruct downwelling irradiance light profiles under a spatially heterogeneous snow/ice environment.
En extensive dataset of light measurements (C-OPS, ACS) done under the landfast ice during the 2016 Green Edge field sampling.
Compare \(K_{Ed}\) and \(K_{Lu}\) from simultaneously collected light profiles during the 2016 Green Edge ice camp mission (\(n = 86\)).
Given that water column is unlikely to be optically homogeneous, attenuation coefficients K were calculated on a 5-meters sliding window.
K were calculated starting at 10 meters to reduce the effect of subsurface light maximum.
A total of 36 120 non-linear models were calculated. 86 profiles \(\times\) 14 depths \(\times\) 15 wavelengths \(\times\) 2 lights (Ed, Lu)
A conservative \(R^2 = 0.99\) was used to filter poor models.
14 942 models were kept for subsequent analysis.
The relationship at higher wavelengths is likely to be affected by the inelastic scattering of water.
Tighter relation in the blue/green regions.
\(E_d\) is not influenced by surface heterogeneity.
Possible workaround:
Reconstruction of Ed(z) profile.
Validate our method with different spatial heterogeneous conditions and water column IOPs generated numerically with 3D Monte-Carlo simulations.
The simulations would include:
The GreenEdge project is funded by the following French and Canadian programs and agencies: ANR (Contract #111112), CNES (project #131425), IPEV (project #1164), CSA, Fondation Total, ArcticNet, LEFE and the French Arctic Initiative (GreenEdge project). This project would not have been possible without the support of the Hamlet of Qikiqtarjuaq and the members of the community as well as the Inuksuit School and its Principal Jacqueline Arsenault. The project is conducted under the scientific coordination of the Canada Excellence Research Chair on Remote sensing of Canada’s new Arctic frontier and the CNRS & Université Laval Takuvik Joint International laboratory (UMI3376). The field campaign was successful thanks to the contribution of J. Ferland, G. Bécu, C. Marec, J. Lagunas, F. Bruyant, J. Larivière, E. Rehm, S. Lambert-Girard, C. Aubry, C. Lalande, A. LeBaron, C. Marty, J. Sansoulet, D. Christiansen-Stowe, A. Wells, M. Benoît-Gagné, E. Devred and M.-H. Forget from the Takuvik laboratory, C.J. Mundy and V. Galindo from University of Manitoba as well as F. Pinczon du Sel and E. Brossier from Vagabond. We also thank Michel Gosselin, Québec-Océan, the CCGS Amundsen and the Polar Continental Shelf Program for their in-kind contribution in polar logistic and scientific equipment.