Centre for Earth Observation Science

 

 

Doctor of Philosophy (Ph.D.) Thesis

 

Title

 

On the estimation of physical roughness of a marginal sea ice zone using remote sensing

 

Abstract

 

The surface roughness of both open water and sea ice cover of the marginal ice zone (MIZ) in the Arctic Ocean change as a function of space and time. The MIZ roughness controls many aspects of mass, gas, and energy fluxes across the ocean-sea ice-atmosphere (OSA) interface, all of which are currently being impacted by a changing climate. The rapid reduction of sea ice in the Arctic in the past few decades has resulted in a MIZ consisting of variable sea ice roughness that necessitates improved methods for observations using ice-based, shipborne, airborne, and spaceborne platforms. This thesis is an attempt to provide insight into improved techniques for the detection and classification of various MIZ roughnesses in the southern Beaufort Sea using state-of-the-art in situ and satellite-based microwave remote sensing methods. The analyses of variances of the physical roughness, microwave backscatter and passive microwave emission of the MIZ produce statistically significant, separable classes in the MIZ through a range of spatial and temporal scales.  Polarimetric parameters (coherences and ratios) at C-band (5.5 GHz) have shown potential in discriminating sea ice roughness. A proposed two-dimensional backscattering model of surface roughness by incorporating deviation in the orientation (i.e. the ice slopes) in azimuth and range direction further shows the dependence of circular coherence, a discriminator of roughness, on both the surface roughness and sea ice dielectric properties.

Microwave emission at 37 and 89 GHz and C-band backscatter are shown to be sensitive to the ocean surface wave roughness as defined by the significant wave height, when compared to wind speed. The brightness temperature is significantly correlated with wave height, with the strongest correlations for the horizontal polarization channel at both 37 and 89 GHz. Analysis of AMSR-E brightness temperature at 89 GHz and root-mean-square height (spring to melt onset) shows a significant correlation between the two over spatial scales of 1−4 km. The brightness temperature at horizontal polarization of 89 GHz is also shown to decrease with increasing physical roughness, and is attributed to dominant contributions from a rapidly varying dielectric constant for snow-covered sea ice during the melt season. The results from this analysis suggest that an adequate evaluation of sea ice roughness at sub-pixel scales (< 5.4 km of AMSR-E) requires an improved sea ice roughness model that considers mediating factors (e.g., snow−ice interface water content, air temperature) that affect the dielectric properties and physical roughness of sea ice at high spatial and temporal scales. A combined examination of physical roughness, active polarimetry and passive microwave emission of MIZ at compatible spatial and temporal scales has led to improved understanding of the behavior of the Arctic MIZ.

 

Supervisor

 

Dr. D. G. Barber

Professor, Department of Environment and Geography, University of Manitoba, Winnipeg, Canada

 

Copyright 2014 ©Mukesh Gupta