POSTER SESSION 4
10:30–12:30, Thursday, September 17
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
ABSTRACT 1100 | POSTER 76
MODEL TO ESTIMATE COCCOLITH PIC FROM CROSS-POLARIZED NEAR-FORWARD LIGHT SCATTERING
We present a method to estimate particle inorganic carbon (PIC) from the cross-polarized near-forward scattering by randomly oriented coccoliths from multiple species. Accurate PIC estimation requires precise evaluation of three key terms: the geometric cross-section, scattering efficiency and depolarization within the birefringent crystalline structure of coccoliths.
The geometric cross-section of the coccolith can be estimated as the mean shadow of a flat elliptical disk with a thickness equal to the maximum thickness of the coccolith. Real coccoliths exhibit significant curvature and radial variation in thickness, and their interlocking crystal elements have optical axes that alternate between orientations normal or parallel to their surface. Because the cross-polarization depends on the square of the optical path length difference between the extraordinary and ordinary ray, these structural differences must be accounted for.
Our model captures the average optical behavior of a randomly oriented ensemble of coccoliths by representing each particle as a two-layer elliptical disk. The relative thickness of each layer is determined by the proportion of distinct crystal types for a given species, with each layer corresponding to one dominant crystal orientation.
With this model and precise particle size, shape and distribution measurements, we predict depolarization as a function of PIC concentration for several coccolith species and compare the results with controlled laboratory measurements obtained using a prototype LISST-PIC instrument. The model shows good agreement with experimental observations and is currently within a mean standard deviation of 7%, demonstrating the instrument’s potential for robust estimation of PIC in natural waters.
Georges Fournier, Retired, [email protected]
Qiming Sun, MarSens Research Group, Ghent University, [email protected]
Griet Neukermans, MarSens Research Group, Ghent University, [email protected]
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
