Polarimetric Synthetic Aperture Radar (SAR) Application for Geological Mapping and Resource Exploration in the Canadian Arctic

The role of remote sensing in geological mapping has been rapidly growing by providing predictive maps in advance of field surveys. Remote predictive maps with broad spatial coverage have been produced for northern Canada and the Canadian Arctic which are typically very difficult to access. Multi and hyperspectral airborne and spaceborne sensors are widely used for geological mapping as spectral characteristics are able to constrain the minerals and rocks that are present in a target region. Rock surfaces in the Canadian Arctic are altered by extensive glacial activity and freeze-thaw weathering, and form different surface roughnesses depending on rock type. Different physical surface properties, such as surface roughness and soil moisture, can be revealed by distinct radar backscattering signatures at different polarizations. This thesis aims to provide a multidisciplinary approach for remote predictive mapping that integrates the lithological and physical surface properties of target rocks. This work investigates the physical surface properties of geological units in the Tunnunik and Haughton impact structures in the Canadian Arctic characterized by polarimetric synthetic aperture radar (SAR). It relates the radar scattering mechanisms of target surfaces to their lithological compositions from multispectral analysis for remote predictive geological mapping in the Canadian Arctic. This work quantitatively estimates the surface roughness relative to the transmitted radar wavelength and volumetric soil moisture by radar scattering model inversion. The SAR polarization signatures of different geological units were also characterized, which showed a significant correlation with their surface roughness. This work presents a modified radar scattering model for weathered rock surfaces. More broadly, it presents an integrative remote predictive mapping algorithm by combining multispectral and polarimetric SAR parameters

Sentinel-1 and RADARSAT Constellation Mission InSAR Assessment of Slope Movements in the Southern Interior of British Columbia, Canada

Landslides are the most common natural hazard in British Columbia. The province has recorded the largest number of historical landslide fatalities in Canada, and damage to infrastructure comes at a great cost. In order to understand the potential impacts of landslides, radar remote sensing has become a cost-effective method for detecting downslope movements. This study investigates downslope movements in the Southern Interior of British Columbia, Canada, with Sentinel-1 and RADARSAT Constellation Mission (RCM) interferometric synthetic aperture radar (InSAR) data. The 2-dimensional time-series analysis with Sentinel-1 ascending and descending InSAR pairs from October 2017 to June 2021 observed distinct earthflow movements of up to ~15 cm/year in the east–west direction. The Grinder Creek, Red Mountain, Yalakom River, and Retaskit Creek earthflows previously documented are still active, with east–west movements of ~30 cm over the past four years. New RCM data acquired from June 2020 to September 2020 with a 4-day revisit capability were compared to 12-day Sentinel-1 InSAR pairs. The 4-day RCM InSAR pairs at higher spatial resolution showed better performance by detecting relatively small-sized slope movements within a few hundred meters, which were not clearly observed by Sentinel-1. The temporal variabilities observed from the RCM InSAR showed great potential for observing detailed slope movements within a narrower time window

3D SAR Speckle Offset Tracking Potential for Monitoring Landfast Ice Growth and Displacement

This study investigates the growth and displacement of landfast ice along the shoreline of the Mackenzie Delta in Northwest Territories, Canada, by synthetic aperture radar (SAR) speckle offset tracking (SPO). Three-dimensional (3D) offsets were reconstructed from Sentinel-1 ascending and descending SAR images acquired on the same dates during the November 2017–April 2018 and October 2018–May 2019 annual cycles. The analysis revealed both horizontal and vertical offsets. The annual horizontal offsets of up to ~8 m are interpreted as landfast ice displacements caused by wind and ocean currents. The annual vertical offsets of approximately −1 to −2 m were observed from landfast ice, which are likely due to longer radar penetration up to the ice–water interface with increasing landfast ice thickness. Numerical ice thickness model estimates supported the conclusion that the cumulative vertical negative offsets correspond to the growth of freshwater ice. Time-series analysis showed that the significant growth and displacement of landfast ice in the Mackenzie Delta occurred between November and January during the 2017–2018 and 2018–2019 cycles

Remote Predictive Mapping of the Tunnunik Impact Structure in the Canadian Arctic using Multispectral and Polarimetric SAR Data Fusion

The 28-km diameter Tunnunik impact structure in northern Victoria Island, Arctic Canada, was mapped using ASTER, Landsat 8, RADARSAT-2 polarimetric synthetic aperture radar (SAR), and Quickbird data. Multispectral analysis was accomplished through band ratios, MNF transform, and spectral matching algorithms, from which 4 distinct spectral units were defined. Polarimetric SAR decompositions also showed different scattering mechanisms for these 4 units indicating different surface roughness properties. These multispectral and polarimetric SAR observations were combined with detailed surface textures and morphological features as visible in very high-resolution Quickbird imagery (61 cm/pixel). Remote sensing parameters and their thresholds for characterizing each unit were implemented into a decision-tree algorithm and a remote predictive geological map was produced. Subsequent field and follow-up laboratory investigations enabled the ground-truthing of these predictions. The geological units were defined as follows: (i) (smooth) fluvioglacial deposits, (ii) (moderately rough) chert-bearing dolostone, (iii) (rough) dolostone, and (iv) (rough) dolostone covered by silicified surfaces. The rough surfaces characterized by multiple scattering in the polarimetric SAR decomposition correspond to the occurrences of weathered carbonate rocks, which are relatively resistant to weathering and form blocky surfaces. This shows that SAR-derived surface roughness properties can greatly contribute to defining geological units by combining with lithological mapping

A Modified Semi-Empirical Radar Scattering Model for Weathered Rock Surfaces

This study presents a modified semi-empirical radar scattering model for weathered rough rock surfaces. Weathered rocks generally have dry surfaces except for a few hours after heavy rain due to their rapid drainage compared to bare soils. We find that the dielectric properties of the rocks themselves and the moisture content of a marginal amount of soil patches in and around the rock surfaces have a negligible effect on radar backscattering. Therefore, radar backscattering from rock surfaces is mainly controlled by surface roughness. Here, we modified the cross-polarization ratio model developed by Oh, which is formulated by only surface roughness parameters with no dependence on soil moisture. Based on LiDAR surface topography data collected from weathered rock surfaces in the Canadian Arctic and corresponding quad-polarimetric RADARSAT-2 synthetic aperture radar (SAR) data, we determined the best fit radar backscattering model for weathered rock surfaces. The modified model was successfully applied to estimate the surface roughness of weathered rock surfaces up to approximately ks = 7 where k is the radar wavenumber (= 2π/λ) and s is the root mean square (RMS) height. This approach avoids the rapid saturation feature observed at ks > 3 in other models

A Polarimetric SAR and Multispectral Remote Sensing Approach for Mapping Salt Diapirs: Axel Heiberg Island, NU, Canada

Remote sensing has revolutionized resource exploration by enabling quick surveillance of large areas. Quad-polarimetric synthetic aperture radar (SAR) is useful for assessing surface roughness, but few studies have applied it for geological mapping. Located in the Canadian Arctic, Axel Heiberg Island is a suitable site for exploring remote predictive geologic mapping techniques that combine quad-polarimetric SAR and multispectral datasets. The island has extensive rock exposure, with little interference from vegetation and snow in late summer. Axel Heiberg Island has the second highest concentration of salt diapirs globally. As a result, it also hosts extensive secondary salt deposits that have been weathered and precipitated away from their source. Because diapirs frequently provide structural traps for petroleum reservoirs, it is important to distinguish between diapiric and non-diapiric salt during early exploration. This study maps diapirs and secondary salts using multispectral data and characterizes them in polarimetric SAR. Diapirs appear rough in C-Band and L-Band radar, whereas the secondary salts appear smooth at both (cm–dm) scales. Field observations confirm salt diapirs are rough at the millimeter–meter scales, whereas secondary salts precipitate on smoother surfaces. These results show that radar can help differentiate between diapiric and secondary salt exposures, which will assist in future resource exploration

Spike Gene Analysis and Prevalence of Porcine Epidemic Diarrhea Virus from Pigs in South Korea: 2013–2022

From late 2013–2022, 1131 cases of porcine epidemic diarrhea (PED) were reported to the Korean Animal Health Integrated System (KAHIS). There were four major outbreaks from winter to spring (2013–2014, 2017–2018, 2018–2019, and 2021–2022), with the main outbreaks occurring in Chungnam (CN), Jeonbuk (JB), and Jeju (JJ). Analysis of the complete spike (S) gene of 140/1131 KAHIS PEDV cases nationwide confirmed that 139 belonged to the G2b genotype and 1 to the G2a genotype. Among them, two strains (K17GG1 and K17GB3) were similar to an S INDEL isolated in the United States (strain OH851), and 12 strains had deletions (nucleotides (nt) 3–99) or insertions (12 nt) within the S gene. PEDVs in JJ formed a regionally independent cluster. The substitution rates (substitutions/site/year) were as follows: 1.5952 × 10−3 in CN, 1.8065 × 10−3 in JB, and 1.5113 × 10−3 in JJ. A Bayesian skyline plot showed that the effective population size of PEDs in JJ fell from 2013–2022, whereas in CN and JB it was maintained. Genotyping of 340 Korean PEDV strains, including the 140 PEDVs in this study and 200 Korean reference strains from GenBank, revealed that only the highly pathogenic non-INDEL type (G2b) was dominant from 2020 onwards. Therefore, it is predicted that the incidence of PED will be maintained by the G2b (non-INDEL) genotype

Protection of Piglets with Maternally Derived Antibodies from Sows Inoculated with an Attenuated Live Marker Classical Swine Fever Vaccine (Flc-LOM-BErns)

Here, we investigated the protective efficacy provided by passive immunity induced by a classical swine fever (Flc-LOM-BErns) vaccine with the newly developed DIVA (Differentiating Infected from Vaccinated Animals) function. Ten pigs (aged 40–60 days) with maternally derived antibodies (MDAs) obtained from sows inoculated with the Flc-LOM-BErns vaccine were challenged with virulent classical swine fever virus (CSFV). Pigs with an MDA titer of 6 log2 induced by the Flc-LOM-BErns vaccine were fully protected against virulent CSFV challenge but not the pigs with an MDA titer under 5 log2. In addition, Flc-LOM-BErns vaccine-derived MDAs successfully differentiated vaccinated pigs by bovine viral diarrhea virus (BVDV) Erns/CSFV Erns antibody detection, functioning as a DIVA

Genetic Diversity of Porcine Group A Rotavirus Strains from Pigs in South Korea

Porcine group A rotavirus (PoRVA; family, Reovirideae) strains cause acute viral gastroenteritis in piglets (especially suckling and weaned pigs), resulting in significant economic losses. In this study, we analyzed the VP7 and VP4 genes of PoRVA isolated between 2014 and 2018 from domestic pigs in South Korea to investigate the prevalence of predominant circulating genotypes (G and P types). The prevalence of the PoRVA antigen in the diarrheic fecal samples was 14.1% (53/377). Further genetic characterization of the VP7 and VP4 genes of 53 PoRVA isolates identified six different G-genotypes and five different P genotypes. The G4 and G9 genotypes were the most common (each 39.6%) in PoRVA-positive pigs, followed by P[7] and P[6] (33.9% and 30.1%, respectively). Because the G5 and G9 genotype vaccines are currently mainly used in South Korea, this result provides valuable epidemiological information about the genetic characteristics of PoRVA circulating on domestic pig farms. Development of a novel PoRVA vaccine that targets the current strains circulating in South Korea may be required for more effective virus control on pig farms