Browsing by Author "Mahmud, Mallik Sezan"

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    Monitoring Arctic Sea Ice from Spaceborne L-band Synthetic Aperture Radar
    (2021-09) Mahmud, Mallik Sezan; Yackel, John; Mahoney, Andy; Howell, Stephen; McDermid, Greg; Moorman, Brian; Murray, Maribeth
    As the Arctic is vast and largely inaccessible, concerns point to the increasing role of innovative earth observation technology for monitoring sea ice environments and conditions. The enhanced capabilities of L-band synthetic aperture radar (SAR) make it a critical technology for developing effective sea ice monitoring strategies. The use of L-band SAR imagery is limited in sea ice research; therefore, it presents a unique opportunity to investigate its advantages and challenges relative to other frequencies. The overarching goal of this research is to characterize the relationship between sea ice geophysical and thermodynamic properties and L-band SAR signatures over the seasonal cycle. To achieve this, L-band SAR imagery was investigated for i) incidence angle induced backscatter variability, ii) snow-covered sea ice thermodynamic monitoring, and iii) newly formed sea ice identification and classification. At first, this doctoral work investigated incidence angle dependency for L-band SAR backscatter and developed an image processing workflow to normalize the incidence angle induced backscatter variability for operation sea ice monitoring. Next, time-series L-band SAR imagery was used to evaluate the first-ever full annual-cycle evolution of L-band backscatter over first-year and multi-year sea ice. Finally, a novel dual-frequency approach was developed to identify newly formed sea ice in the Arctic and demonstrated that a combination of C- and L-band could substantially increase sea ice classification accuracy. This doctoral research provided baseline information on the utility of L-band SAR imagery and demonstrated its advantages over other frequencies for sea ice measurement and monitoring, which will be invaluable to existing, pending and upcoming L-band SAR missions.
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    Sea Ice Melt Onset Dynamics in the Northern Canadian Arctic Archipelago from RADARSAT, 1997-2014
    (2016-01-08) Mahmud, Mallik Sezan; Yackel, John; Beauchamp, Benoit; Howell, Stephen; Hall-Beyer, Mryka
    An algorithm was developed to detect melt onset over Arctic sea ice using high-resolution SAR images from RADARSAT. The algorithm is based on the temporal evolution of the SAR backscatter coefficient (σ⁰), using an ice type specific threshold approach that also corrects for backscatter incidence angle variation. Using 4457 RADARSAT images, the algorithm was applied over sea ice in the northern CAA, thus generating a new time series of melt onset from 1997-2014. The mean annual melt onset date was on YD 164±4 (mid–June). No significant trend was found over the 18-year period, however, variability increased in post-2007 years. An earlier (later) melt onset was associated with increased (decreased) solar energy absorption and subsequently associated in lighter (heavier) September sea ice coverage in the northern CAA. RADARSAT estimates of melt onset were found to be in good agreement but more robust compared to passive microwave and scatterometer estimates.