Charlie Jefferson

Surficial materials mapping in Nunavut, Canada with multibeam RADARSAT-2 dual-polarization C-HH and C-HV, LANDSAT-7 ETM, and DEM data

Our study assesses the use of multibeam RADARSAT-2 dual-polarization C-HH and C-HV, LANDSAT-7 ETM+, and Digital Elevation Model (DEM) data for mapping surficial materials in Nunavut, Canada. The RADARSAT-2 images were acquired using standard beam 1 and 7 modes in both ascending and descending orbits. RADARSAT-2 images were filtered to reduce speckle and then orthorectified. Representative training areas of distinct surficial deposits (bedrock, boulders, organic deposits, sand and gravel, thick till with dense vegetation, thick till with sparse vegetation, and thin till) were identified from field information and by interpreting panchromatic aerial photographs and LANDSAT-7 ETM+ images. Maximum likelihood supervised classifications were conducted on the RADARSAT-2 C-HH and C-HV images, individually and combined with LANDSAT-7 ETM+ and (or) DEM data. The best overall classification accuracy was obtained by combining RADARSAT-2 C-HH and C-HV images with LANDSAT-7 ETM+ and DEM data. Confusion between several surface materials was reduced, but confusion between “bedrock” and “boulders” and between “sand and gravel” and “organic deposits” or “thin till” class still remains. Another limitation of the study includes the lack of a field survey to validate training areas for three of the four detailed analysis areas. Nonetheless, this study produced surficial materials maps covering eight 1:250000 scale National Topographic System of Canada sheets that provide important geological information about this remote area.

Basement geology beneath the northeast Thelon Basin, Nunavut: insights from integrating new gravity, magnetic and geological data

ABSTRACT Current models for unconformity‐associated uranium deposits predict fluid flow and ore deposition along reactivated faults in >1.76 Ga basement beneath Mesoproterozoic siliciclastic basins. In frontier regions such as the Thelon Basin in the Kivalliq region of Nunavut, little is known about the sub‐basin distribution of units and structures, making exploration targeting very tenuous. We constructed a geological map of the basement beneath the unconformity by extrapolating exposed features into the subsurface. The new map is constrained by detailed geological, geophysical, and rock property observations of outcrops adjacent to the basin and by aeromagnetic and gravity data over the geophysically transparent sedimentary basin. From rock property measurements, it is clear that the diverse magnetic and density characteristics of major rock packages provide quantitative three‐dimensional constraints. Gravity profiles forward modelled in four cross sections define broad synforms of the Amer Belt and Archean volcanic rocks that are consistent with the structural style outside the basin. Major lithotectonic entities beneath the unconformity include: supracrustal rocks of the Archean Woodburn Lake group and Marjorie Hills meta sedimentary gneiss and associated mixed granitoid and amphibolitic gneiss; the Amer Mylonite Zone and inferred mafic intrusions oriented parallel and sub‐parallel; other igneous intrusions of 2.6 Ga, 1.83 Ga, and 1.75 Ga vintage; and the <2.3 Ga to >1.84 Ga Amer Group. Four main brittle regional fault arrays (040°–060°, 075°–90°, 120°, and 150°) controlled development and preservation of the basin. The reactivated intersections of such faults along fertile basement units such as the Rumble assemblage, Marjorie Hills assemblage, Nueltin igneous rocks, and Pitz formation are the best targets for uranium exploration.

Effects of incidence angles and image combinations on mapping accuracy of surficial materials in the Umiujalik Lake area, Nunavut, using RADARSAT-2 polarimetric and LANDSAT-7 images, and DEM data. Part 1. Nonpolarimetric analysis

This study assesses the use of multibeam RADARSAT-2 multipolarized synthetic aperture radar images (hereafter termed “RADARSAT-2 images”), in combination with LANDSAT-7 Enhanced Thematic Mapper (ETM +) and digital elevation model (DEM) data for mapping surficial materials (bedrock, boulders, organic material, sand and gravel, thick till, and thin till) in Arctic Canada. In particular we tested the effects of RADARSAT-2 incidence angles on classification accuracy. This research contributes to the geoscience framework for mineral exploration in Archean to Paleoproterozoic rocks of the northeast Thelon region of Nunavut. The RADARSAT-2 images were acquired in three west-looking descending beam modes (FQ1, FQ12, and FQ20) with increasing respective incidence angles. A maximum likelihood classification (MLC) was applied to different combinations of RADARSAT-2 and LANDSAT-7 ETM+ images, and DEM data. The incidence angle effect on classification overall accuracies is greatest when only the HH polarized images are used, but is reduced when the HV and (or) VV polarized images are added to the classifier. The best MLC overall accuracy of 85.1% is achieved by combining all polarizations and all incidence angles (beam modes) with LANDSAT-7 ETM+ images and DEM data. The influences of variable environmental conditions (moisture and temperature) on mapping accuracy require further research.

Effects of incidence angles on mapping accuracy of surficial materials in the Umiujalik Lake area, Nunavut, using RADARSAT-2 polarimetric SAR images. Part 2. Polarimetric analysis

Our study assesses the effect of incidence angle on classifications obtained using various polarimetric classifiers applied to polarimetric RADARSAT-2 synthetic aperature radar (SAR) images for mapping surficial materials in Arctic Canada. The RADARSAT-2 polarimetric SAR images were acquired over the Umiujalik Lake test area of Nunavut in three west-looking descending beam modes (FQ1, FQ12, and FQ20) with increasing respective incidence angles. Polarimetric analyses included computation of polarimetric signatures, Wishart supervised classification, as well as Wishart–H/ , Wishart–H/ /A, and Freeman–Wishart unsupervised classifications. Polarimetric signatures helped to understand class separability as a function of the scattering mechanisms of the surficial materials considered in this study. The medium incidence angle (FQ12) image produced the best overall classification accuracy (48.7%) for the Wishart supervised classification. In general, the Freeman–Wishart unsupervised classification produced better areal distribution of surficial materials with the FQ12 and FQ20 images than with the steep angle FQ1 image. More sophisticated classification algorithms are required to combine the multibeam RADARSAT-2 polarimetric SAR images with other geospatial data such as optical images and digital elevation model data. The influences of variable environmental conditions (moisture and temperature) on mapping accuracy of surficial materials also require further research.