Cryosphere Applications

Synthetic aperture radar (SAR) provides large coverage and high resolution, and it has been proven to be sensitive to both surface and near-surface features related to accumulation, ablation, and metamorphism of snow and firn. Exploiting this sensitivity, SAR polarimetry and polarimetric interferometry found application to land ice for instance for the estimation of wave extinction (which relates to sub surface ice volume structure) and for the estimation of snow water equivalent (which relates to snow density and depth). After presenting these applications, the Chapter proceeds by reviewing applications of SAR polarimetry to sea ice for the classification of different ice types, the estimation of thickness, and the characterisation of its surface. Finally, an application to the characterisation of permafrost regions is considered. For each application, the used (model-based) decomposition and polarimetric parameters are critically described, and real data results from relevant airborne campaigns and space borne acquisitions are reported

Safety and efficacy of tenecteplase in patients with wake-up stroke assessed by non-contrast CT (TWIST): a multicentre, open-label, randomised controlled trial

Background: Current evidence supports the use of intravenous thrombolysis with alteplase in patients with wake-up stroke selected with MRI or perfusion imaging and is recommended in clinical guidelines. However, access to advanced imaging techniques is often scarce. We aimed to determine whether thrombolytic treatment with intravenous tenecteplase given within 4·5 h of awakening improves functional outcome in patients with ischaemic wake-up stroke selected using non-contrast CT. Methods: TWIST was an investigator-initiated, multicentre, open-label, randomised controlled trial with blinded endpoint assessment, conducted at 77 hospitals in ten countries. We included patients aged 18 years or older with acute ischaemic stroke symptoms upon awakening, limb weakness, a National Institutes of Health Stroke Scale (NIHSS) score of 3 or higher or aphasia, a non-contrast CT examination of the head, and the ability to receive tenecteplase within 4·5 h of awakening. Patients were randomly assigned (1:1) to either a single intravenous bolus of tenecteplase 0·25 mg per kg of bodyweight (maximum 25 mg) or control (no thrombolysis) using a central, web-based, computer-generated randomisation schedule. Trained research personnel, who conducted telephone interviews at 90 days (follow-up), were masked to treatment allocation. Clinical assessments were performed on day 1 (at baseline) and day 7 of hospital admission (or at discharge, whichever occurred first). The primary outcome was functional outcome assessed by the modified Rankin Scale (mRS) at 90 days and analysed using ordinal logistic regression in the intention-to-treat population. This trial is registered with EudraCT (2014–000096–80), ClinicalTrials.gov (NCT03181360), and ISRCTN (10601890). Findings: From June 12, 2017, to Sept 30, 2021, 578 of the required 600 patients were enrolled (288 randomly assigned to the tenecteplase group and 290 to the control group [intention-to-treat population]). The median age of participants was 73·7 years (IQR 65·9–81·1). 332 (57%) of 578 participants were male and 246 (43%) were female. Treatment with tenecteplase was not associated with better functional outcome, according to mRS score at 90 days (adjusted OR 1·18, 95% CI 0·88–1·58; p=0·27). Mortality at 90 days did not significantly differ between treatment groups (28 [10%] patients in the tenecteplase group and 23 [8%] in the control group; adjusted HR 1·29, 95% CI 0·74–2·26; p=0·37). Symptomatic intracranial haemorrhage occurred in six (2%) patients in the tenecteplase group versus three (1%) in the control group (adjusted OR 2·17, 95% CI 0·53–8·87; p=0·28), whereas any intracranial haemorrhage occurred in 33 (11%) versus 30 (10%) patients (adjusted OR 1·14, 0·67–1·94; p=0·64). Interpretation: In patients with wake-up stroke selected with non-contrast CT, treatment with tenecteplase was not associated with better functional outcome at 90 days. The number of symptomatic haemorrhages and any intracranial haemorrhages in both treatment groups was similar to findings from previous trials of wake-up stroke patients selected using advanced imaging. Current evidence does not support treatment with tenecteplase in patients selected with non-contrast CT. Funding: Norwegian Clinical Research Therapy in the Specialist Health Services Programme, the Swiss Heart Foundation, the British Heart Foundation, and the Norwegian National Association for Public Health

Classification of Fram Strait Sea Ice by Synthetic Aperture Radar

Space-borne synthetic aperture radar (SAR) systems are essential for operational monitoring of sea ice in polar regions. Radar polarimetry is a powerful niche within remote sensing, allowing investigations of various sea ice types’ scattering properties. Full-polarimetric and compact polarimetry SAR measurements may hence allow improved sea ice type characterization and discrimination capabilities aiding operational sea ice services. In this talk,we disseminate results from remote sensing measurements of sea ice collected under the Norwegian Young Sea Ice 2015 (N-ICE2015) field campaign that took place January to June 2015 in the Fram Strait. In particular, we focus on multifrequency SAR studies, involving acquisitions from ALOS-2 (L-band), Radarsat-2 (C-band), and TerraSAR-X (X-band), and give some directions for future research. First, an analysis of full-polarimetric L-, C-, and dual-polarization (HH/VV) X-band SAR data recorded over lead ice revealed that by combining the scattering entropy and co-polarization ratio we can successfully separate newly formed sea ice from open water and thicker sea ice within all three frequencies throughout the winter and spring season. The polarization difference exhibits less incidence angle dependency and shows to provide additional discrimination support. X- and L-band SAR acts complementary to the more regular acquisitions in C-band in terms of characterizing the newly formed sea ice types and surface structure. Second, asemi-coherent backscatter model is used to interpret the space-borne SAR data acquisitions of the Fram Strait sea ice. Specifically, full-polarimetric L-,C-, dual-polarization (HH/VV) and full-polarimetric X-band SAR is compared to model output. Constrained to simultaneous in-situ observations from the campaign, the model is able to reproduce the backscatter from lead ice and ice floes well for the individual frequency bands. For open water leads, unexpectedly high backscatter values are observed in L-band compared to C-band. Possible explanations relating to the sea ice formation process are discussed. Third, an automatic sea ice classification algorithm developed for near real-time services on full-polarimetric SAR measurements has been tested for X-, C-, and L-band data. Spatial and temporal coincident sea ice freeboard measurements of an airborne laser scanner as well as sea ice thickness data were used to validate the classification results. It was found that the number of multipolarization SAR parameters could be reduced from18 to 9, for all three frequencies, whilst still maintaining the 96.9% sea ice classification accuracy. The set of parameters that were found most useful in L-band was slightly different compared to those for the other two frequencies. Next, exploring a supervised classification scheme, we which to includemore full-polarimetric ALOS-2 L-band SAR scenes from the N-ICE campaign. Our goal is to investigate which multipolarization SAR parameters that are most useful for operational services, aiming at high accuracy sea ice classification under various environmental conditions and imaging geometries

Assessment of Polarimetric Variability by Distance Geometry for Enhanced Classification of Oil Slicks Using SAR

In this paper, we introduce a new approach for investigation of polarimetric Synthetic Aperture Radar (PolSAR) images for oil slick analysis. Our method aims at enhancing discrimination of oil types by exploring the polarimetric features that can be produced by processing PolSAR scenes without dimensionality reduction. Taking advantage of a mixture description of the interactions among classes within the dataset and a characterization of their intra- and inter-class variability, our algorithm is able to quantify the areal coverage of different elements. These estimates can be used to hence improve classification. Experimental results on a PolSAR dataset acquired by unmanned aerial vehicle (UAV) on oil slicks in open water show the capacity of our method

Polarimetric decomposition analysis of Sea Ice data

International audienc

ExtremeEarth: The Polar Use Case

The Polar Use Case in ExtremeEarth aims to address these issues through the development of a range of valuable tools. Deep learning algorithms will be developed to extract valuable sea ice and iceberg information from the ever increasing volumes of data collected by the Copernicus Sentinel satellite constellations. These new algorithms will be implemented on the Polar Thematic Exploitation Platform (Polar TEP) providing processing resources to produce the new information products. New data sets will be released for training and validating the new algorithms. Linked data tools will extend the capabilities for data access and discovery with semantic catalogue services that scale to the volumes of big data produced in the project. Frontend services, such as the PolarTEP and the Norwegian Meteorological Institute ice charts, will provide simple user access to browse and query the data generated