Torsten Geldsetzer

Forecasting for deep slab avalanches

Abstract Avalanches released by deep weak layers are known to be difficult to forecast. This study considers the predictive merit of weather and snowpack data for avalanches that released throughout two winters on layers of faceted crystals. These layers formed above rain crusts in November 1996 and in November 1997 in the Columbia Mountains of western Canada. This study focuses on the first winter, during which the facet layer released an estimated 500,000 tonnes of snow in 700 dry slab avalanches. The facet–crust combinations were the result of a cold air mass cooling a layer of dry snow on top of a rain-wetted layer. The resulting temperature gradient in the dry snow formed a relatively weak layer of facets on top of a hard crust. By early January 1997, the faceted layer from the first winter was buried 1–2.5 m below the surface in many starting zones in the North Columbia Mountains. Most avalanches occurred during or within 2 days of loading by snowfall or wind transported snow. Increases in air temperature over 4–5 days correlated with increased avalanche activity. The effects of warming and cooling on slab stability are discussed, but for thick slabs, current theories do not explain observations of decreased stability. We argue that the fractures that release natural deep slab avalanches may be initiated where the slab is locally thin. Based on rank correlations, the highest ranked predictors of natural avalanches include previous avalanche activity, accumulated snowfall over several days, changes in air temperature over 4–5 days, snowpack properties including a shear frame stability index, and the difference in hardness between the facet layer and the crust.

Surface-Based Polarimetric C-Band Scatterometer for Field Measurements of Sea Ice

A portable surface-based polarimetric C-band scatterometer for field deployment over sea ice is presented. The scatterometer system, its calibration, signal processing, and near-field correction are described. The near-field correction is shown to be effective for both linear polarized and polarimetric backscatter. Field methods for the scatterometer are described. Sample linear polarized and polarimetric backscatter results are presented for snow-covered first-year sea ice (FYI), multiyear hummock ice, and rough melt pond water on FYI. The magnitude of backscatter signature variability due to system effects is presented, providing the necessary basis for quantitative analysis of field data.

Monitoring lake ice during spring melt using RADARSAT-2 SAR

Multipolarized RADARSAT-2 SAR imagery is used to monitor lake ice during the spring melt period. The study area is Old Crow Flats, Yukon, in the Canadian Arctic. HH and HV backscatter from lake ice is shown to have significant temporal variability and interlake diversity. Backscatter thresholds are statistically estimated to discriminate decaying lake ice from open water. A classification methodology is described that uses a HH backscatter threshold to identify initial break-up and a HV backscatter threshold for the main period of break-up. Classification accuracies are >81% ( = 0.189) prior to initial break-up and 66%–97% ( = 0.353–0.868) during break-up. This study demonstrates the potential of RADARSAT-2 imagery and, by extension, other C-band SAR satellites, to provide lake ice break-up information in support of monitoring and reporting requirements, subsequent decision-making, and scientific tasks for the Government of Canada.

All-Season Compact-Polarimetry C-band SAR Observations of Sea Ice

Abstract. Compact-polarimetry (CP) synthetic aperture radar (SAR) observations are presented for major sea ice types in each ice season. CP data for three wide-swath Radarsat Constellation Mission (RCM) modes were simulated and evaluated. Regression models and statistical distances as functions of incidence angles were calculated for 26 CP parameters, based on 969 samples of user-selected homogeneous regions of sea ice. CP parameters, best able to discriminate sea ice types and open water, were quantitatively identified in three incidence angle ranges (19–29°, 30–39°, 40–49°). These parameters will likely provide discrimination of sea ice types and open water for both visual interpretation and automated classification. Several parameter–ice type combinations exhibit novel scattering responses, which present new opportunities for ice type discrimination and for inferring scattering mechanisms. Specifically, phase-related parameters with early-stage ice types provide discrimination for ice type pairings that are difficult with co- or dual-polarized data. CP parameters change with incidence angle, which necessitates the use of certain CP parameters at smaller incidence angles and others at larger incidence angles in wide-swath RCM modes. The Canadian Ice Service will implement CP SAR data in their operational workflows once the RCM is operational. Prelaunch study results provide a valuable resource for early adoption of CP data. Résumé. Des observations SAR en polarimétrie compacte (CP) sont présentées pour les principaux types de glace de mer pour la saison des glaces. Des données en CP pour trois modes à large fauchée de la mission de la Constellation RADARSAT (MCR) ont été simulées et évaluées. Des modèles de régression et des distances statistiques en fonction de l’angle d’incidence ont été calculés pour 26 paramètres en CP d’après 969 échantillons de régions homogènes de glace de mer sélectionnées par l’utilisateur. Les paramètres en CP les plus aptes à distinguer les types de glace de mer et l’eau libre ont été quantitativement identifiés dans trois gammes d’angles d’incidence (19–29 °, 30–39 °, 40–49 °). Ces paramètres permettront probablement la discrimination des types de glace de mer et de l’eau libre, à la fois pour l’interprétation visuelle et la classification automatisée. Plusieurs combinaisons de paramètres et de types de glace montrent de nouvelles réponses de diffusion, présentant ainsi de nouvelles possibilités pour la discrimination du type de glace et pour déduire les mécanismes de diffusion. Plus précisément, les paramètres liés à la phase pour les types de glace à un stade précoce permettent la discrimination du type de glace, ce qui est difficile avec des données copolarisées ou en polarisation double. Les paramètres en CP changent avec l’angle d’incidence, ce qui nécessite l’utilisation de certains paramètres à des angles d’incidence plus petits et d’autres paramètres à des angles d’incidence plus grands dans les modes à large fauchée de la MCR. Le Service canadien des glaces utilisera les données SAR en CP dans leur flux de travaux opérationnels lorsque la MCR sera opérationnelle. Les résultats de l’étude de prélancement fournissent une ressource précieuse pour l’adoption précoce des données en CP.

Analysis of consistency in first-year sea ice classification potential of C-band SAR polarimetric parameters

The consistency in first-year sea ice classification potential of C-band SAR polarimetric parameters was analyzed by comparing the results of two studies conducted for the same ice types under different geophysical settings. The SAR images used in the comparison were acquired at an incidence angle difference of 4°. Probability density functions, grey level parameter images, and classification statistics derived using k-means classifier were used in the comparative analysis. The investigation showed that not all polarimetric parameters exhibit consistency in their classification performance under different geophysical settings. Out of the 20 polarimetric parameters analyzed, 12 demonstrated high levels of classification consistency between the two studies. Among these 12 parameters, only four possessed high classification accuracy and could be applicable for sea ice classification under variable environmental conditions. The parameters that showed the highest classification accuracies in both the studies were found to be inconsistent in their ice type separation capabilities. The signatures of these parameters differed for one or more ice types when compared between the two studies. The utility of these parameters in individual sea ice classification studies is recommended but their relevance in generalized sea ice classification scheme is unclear.

Ocean Wind Study Using Simulated RCM Compact-Polarimetry SAR

Abstract. The incidence angle, wind speed, and wind direction dependence of compact polarimetry (CP) synthetic aperture radar (SAR) parameters are presented for open water. Selected CP parameters are related to C-band geophysical model function (CMOD) output. Wind speeds range between 0 and 24 m/s, and incidence angles range between 18 and 50°. SAR data are coincident with meteorological buoy data. CP parameters are simulated from polarimetric RADARSAT-2 data and emulate data available on the pending RADARSAT Constellation Mission (RCM). Analysis is performed for 20 CP parameters, based on RADARSAT-2 images. Five linear-polarization SAR parameters are included for comparison. Results show robust relationships for CP parameters related to CMOD. For CP parameters unrelated to CMOD, results provide first-, second-, or third-order linear regression models, as functions of incidence angle, wind speed, wind direction, or combinations thereof. These models provide a set of values for comparison with sea ice or other features on, or adjacent to, open water. The results of this study are of value to the Canadian Ice Service of the Meteorological Service of Canada, as well as other government of Canada departments, for implementing CP SAR data in their operational workflows once RCM is launched. Résumé. La dépendance à l’angle d’incidence, à la vitesse et à la direction du vent des paramètres mesurés en polarimétrie compacte (CP) est présentée pour l’eau libre. Les paramètres de CP sélectionnés sont liés aux sorties de la fonction du modèle géophysique en bande C (CMOD). Les vitesses du vent varient entre 0 et 24 m/s, et les angles d’incidence varient entre 18 et 50 degrés. Les données SAR coïncident avec les données des bouées météorologiques. Les paramètres en CP sont simulés à partir des données polarimétriques de RADARSAT-2, et ils simulent les données qui seront disponibles à partir de la mission de la Constellation RADARSAT prévue (MCR). L’analyse est effectuée pour 20 paramètres en CP, sur la base des images RADARSAT-2. Cinq paramètres SAR en polarisation linéaire sont inclus pour comparaison. Les résultats montrent des relations robustes pour les paramètres en CP liés à CMOD. Pour les paramètres en CP non liés à la CMOD, les résultats fournissent des modèles de régression linéaire de première, deuxième ou troisième ordre, en fonction de l’angle d’incidence, de la vitesse et de la direction du vent, ou des combinaisons de ceux-ci. Ces modèles fournissent un ensemble de valeurs de comparaison avec la glace de mer; ou d’autres éléments sur, ou à proximité de, l’eau libre. Les résultats de cette étude seront importants pour le Service canadien des glaces du Service météorologique du Canada, ainsi que pour d’autres ministères du gouvernement du Canada, pour mettre en œuvre les données SAR en CP dans leur flux de travaux opérationnels, une fois la MCR lancée.

Preparation by the Canadian Ice Service for the Operational Use of the RADARSAT Constellation Mission in Their Ice and Oil Spill Monitoring Programs

Abstract. The Canadian Ice Service (CIS) has successfully used airborne and spaceborne synthetic aperture radar (SAR) data extensively for almost three decades in their daily ice and oil monitoring operations. Microwave radars unique ability to penetrate clouds and weather make these types of data invaluable to the CISs support to efficient environmental stewardship and safe operations in Canadian waters. Canadas RADARSAT-1 and RADARSAT-2 platforms have been used by CIS since 1996, with approximately 70,000 image scenes incorporated into the development of operational products in that time. The next generation of the RADARSAT program, the RADARSAT Constellation Mission (RCM), will provide C-band SAR data continuity for CIS and other Canadian SAR users for many years to come when launched in 2018. The RCM will consist of a three satellite constellation, offering improved coverage and new technological advancements, and will provide CIS with a unique opportunity to develop new and improved ice and oil information products. This technical note will discuss the prelaunch preparations planned at the CIS that will enable its operational programs to effectively use the capabilities afforded by this mission at launch and beyond. Résumé. Le Service canadien des glaces (SCG) a abondamment utilisé avec succès des données de radars à synthèse d’ouverture spatiaux et aéroportés pendant près de trois décennies dans leurs opérations quotidiennes pour la surveillance des glaces et de la pollution pétrolière. La capacité unique des micro-ondes radar à traverser les nuages et les conditions météorologiques adverses rend ces types de données précieuses au SCG pour appuyer une gestion efficace de l’environnement et la sécurité des opérations dans les eaux canadiennes. Les plateformes RADARSAT-1 et RADARSAT-2 du Canada ont été utilisées par le SCG depuis 1996 et, jusqu’à présent, environ 70 000 images ont été incorporées dans le développement de produits opérationnels. Lors de son lancement en 2018, la prochaine génération du programme RADARSAT, la mission de la Constellation RADARSAT (MCR), assurera la continuité des données SAR en bande C pour le SCG et les autres utilisateurs canadiens de données SAR pour de nombreuses années à venir. La MCR sera composée d’une constellation de trois satellites, offrant une meilleure couverture, de nouvelles avancées technologiques, et elle fournira au SCG une occasion unique de développer de nouvelles et meilleures informations sur les glaces et la pollution pétrolière. Cette note technique discute des préparatifs de prélancements qui sont prévus au SCG et qui permettront à ses programmes opérationnels d’utiliser efficacement les capacités offertes par cette mission au moment du lancement et au-delà.

Effect of Snow Salinity on CryoSat‐2 Arctic First‐Year Sea Ice Freeboard Measurements

The European Space Agencys CryoSat-2 satellite mission provides radar altimeter data that are used to derive estimates of sea ice thickness and volume. These data are crucial to understanding recent variability and changes in Arctic sea ice. Sea ice thickness retrievals at the CryoSat-2 frequency require accurate measurements of sea ice freeboard, assumed to be attainable when the main radar scattering horizon is at the snow/sea ice interface. Using an extensive snow thermophysical property dataset from late winter conditions in the Canadian Arctic, we examine the role of saline snow on first-year sea ice (FYI), with respect to its effect on the location of the main radar scattering horizon, its ability to decrease radar penetration depth, and its impact on FYI thickness estimates. Based on the dielectric properties of saline snow commonly found on FYI, we quantify the vertical shift in the main scattering horizon. This is found to be approximately 0.07 m. We propose a thickness-dependent snow salinity correction factor for FYI freeboard estimates. This significantly reduces CryoSat-2 FYI retrieval error. Relative error reductions of ~ 11% are found for an an ice thickness of 0.95 m and ~ 25% for 0.7 m. Our method also helps to close the uncertainty gap between SMOS and CryoSat-2 thin ice thickness retrievals. Our results indicate that snow salinity should be considered for FYI freeboard estimates.

Surface-Based Polarimetric C-Band Microwave Scatterometer Measurements of Snow During a Chinook Event

This paper presents a case study of C-band backscatter observations of snow during a Chinook event. A surface-based C-band polarimetric data set collected in February 2006 is used to contrast the polarimetric response to sampled conditions of bare frozen ground, cold snow-covered ground, and snow during a Chinook event. Chinook activity is inherently spatially and temporally variable across the region in winter and produces considerable spatial variability of snow-cover physical properties associated with snow-water-equivalent (SWE) estimates. A temporal analysis of polarimetric backscatter sensed during a Chinook-induced ablation event on February 27, 2006 is used to describe the associated changes in snow conditions and scattering mechanisms. Analysis reveals that the polarimetric surface-based C-band scatterometer data respond to changes in snow parameters associated with the specific ground and snow conditions and to the temporal Chinook ablation event. Use of the copolarizations, cross-polarization, depolarization ratio, copolarization ratio, complex copolarization correlation coefficient, and the copolarized phase difference information show promise in describing changes in snow physical parameters, differing ground and snow conditions, and transitional ablation events, based on differing scattering mechanisms. This paper infers that an increase in volume scattering and fluctuations in surface scattering during the Chinook ablation event may be associated with specific physical changes such as density, crystal structure, and permittivity caused by wind speed. This paper has implications for remotely sensed estimations of snow-covered area (SCA) and SWE. Association of SCA and SWE with backscatter coefficients is not explicit in this paper; however, changes in SWE and snow properties are inferentially linked to changes in backscatter.

Compact Polarimetry in Support of Lake Ice Breakup Monitoring: Anticipating the RADARSAT Constellation Mission

Abstract. Canadas RADARSAT Constellation Mission (RCM) will have the capacity to acquire C-band compact polarimetry (CP) data in all imaging modes over swaths up to 500 km wide. Our study aimed to assess and develop the utility of RCM CP data for the purpose of lake ice breakup monitoring. The breaking ice and open water information content of RADARSAT-2 (R2) polarimetric data and simulated RCM CP data was compared. Despite relative losses in terms of polarization diversity and radiometric sensitivity, RCM-type CP data were concluded to make a good source of information in support lake ice breakup monitoring. For that reason, a CP-based approach, called CP_LakeIceBC, to classify breaking ice and open water for the purpose of lake ice breakup monitoring was developed. CP_LakeIceBC is driven by incidence angle information, uses five CP backscatter variables (RH, RR, RV/RH, RR/RL, and conformity), and is compatible with high- and medium-resolution RCM-type CP products. Application of CP_LakeIceBC to representative simulated products yielded classification accuracies ranging from 73.2 to 99.1% and 60.8 to 99.5% for breaking ice and open water, respectively. Résumé. La mission de la Constellation RADARSAT (MCR) du Canada aura la capacité d’acquérir des données en polarimétrie compacte (CP) en bande C dans tous les modes d’imagerie, sur des fauchées allant jusqu’à 500 km de large. Notre étude visait à évaluer et développer l’utilité des données en CP de la MCR à des fins de surveillance des débâcles lacustres. Le contenu de l’information sur l’eau libre et la rupture des glaces a été comparé à partir de données polarimétriques de RADARSAT-2 (R2) et des données en CP de la MCR. Malgré les pertes relatives en termes de la diversité de la polarisation et de la sensibilité radiométrique, il a été conclu que les données en CP de type MCR sont une bonne source d’information de soutien pour la surveillance des débâcles lacustres. Pour cette raison, une approche fondée sur la CP, nommée CP_LakeIceBC, a été développée afin de classifier la rupture de la glace et l’eau libre à des fins de surveillance de la débâcle lacustre. CP_LakeIceBC est déterminée par l’information sur l’angle d’incidence, elle utilise cinq variables CP de rétrodiffusion (RH, RR, RV/RH, RR/RL et conformité), et elle est compatible avec les produits de CP de type MCR à haute et à moyenne résolution. L’application de CP_LakeIceBC aux produits simulés représentatifs a donné des précisions de classification pour la rupture de la glace et l’eau libre allant de 73,2 % à 99,1 % et de 60,8 % à 99,5 %, respectivement.