Multi-Frequency and Multi-Polarization Synthetic Aperture Radar for the Larsen-C A-68 Iceberg Monitoring

none6openNunziata, Ferdinando; Buono, Andrea; Migliaccio, Maurizio; Moctezuma, Miguel; Parmiggiani, Flavio; Aulicino, GiuseppeNunziata, Ferdinando; Buono, Andrea; Migliaccio, Maurizio; Moctezuma, Miguel; Parmiggiani, Flavio; Aulicino, Giusepp

Open access data in polar and cryospheric remote sensing

This paper aims to introduce the main types and sources of remotely sensed data that are freely available and have cryospheric applications. We describe aerial and satellite photography, satellite-borne visible, near-infrared and thermal infrared sensors, synthetic aperture radar, passive microwave imagers and active microwave scatterometers. We consider the availability and practical utility of archival data, dating back in some cases to the 1920s for aerial photography and the 1960s for satellite imagery, the data that are being collected today and the prospects for future data collection; in all cases, with a focus on data that are openly accessible. Derived data products are increasingly available, and we give examples of such products of particular value in polar and cryospheric research. We also discuss the availability and applicability of free and, where possible, open-source software tools for reading and processing remotely sensed data. The paper concludes with a discussion of open data access within polar and cryospheric sciences, considering trends in data discoverability, access, sharing and use.A. Pope would like to acknowledge support from the Earth Observation Technology Cluster, a knowledge exchange project, funded by the Natural Environment Research Council (NERC) under its Technology Clusters Programme, the U.S. National Science Foundation Graduate Research Fellowship Program, Trinity College (Cambridge) and the Dartmouth Visiting Young Scientist program sponsored by the NASA New Hampshire Space Grant.This is the final published version. It's also available from MDPI at http://www.mdpi.com/2072-4292/6/7/6183

Ocean remote sensing techniques and applications: a review (Part II)

As discussed in the first part of this review paper, Remote Sensing (RS) systems are great tools to study various oceanographic parameters. Part I of this study described different passive and active RS systems and six applications of RS in ocean studies, including Ocean Surface Wind (OSW), Ocean Surface Current (OSC), Ocean Wave Height (OWH), Sea Level (SL), Ocean Tide (OT), and Ship Detection (SD). In Part II, the remaining nine important applications of RS systems for ocean environments, including Iceberg, Sea Ice (SI), Sea Surface temperature (SST), Ocean Surface Salinity (OSS), Ocean Color (OC), Ocean Chlorophyll (OCh), Ocean Oil Spill (OOS), Underwater Ocean, and Fishery are comprehensively reviewed and discussed. For each application, the applicable RS systems, their advantages and disadvantages, various RS and Machine Learning (ML) techniques, and several case studies are discussed.Peer ReviewedPostprint (published version

Quad-Polarimetric Multi-Scale Analysis of Icebergs in ALOS-2 SAR Data: A Comparison between Icebergs in West and East Greenland

Icebergs are ocean hazards which require extensive monitoring. Synthetic Aperture Radar (SAR) satellites can help with this, however, SAR backscattering is strongly influenced by the properties of icebergs, together with meteorological and environmental conditions. In this work, we used five images of quad-pol ALOS-2/PALSAR-2 SAR data to analyse 1332 icebergs in five locations in west and east Greenland. We investigate the backscatter and polarimetric behaviour, by using several observables and decompositions such as the Cloude–Pottier eigenvalue/eigenvector and Yamaguchi model-based decompositions. Our results show that those icebergs can contain a variety of scattering mechanisms at L-band. However, the most common scattering mechanism for icebergs is surface scattering, with the second most dominant volume scattering (or more generally, clouds of dipoles). In some cases, we observed a double bounce dominance, but this is not as common. Interestingly, we identified that different locations (e.g., glaciers) produce icebergs with different polarimetric characteristics. We also performed a multi-scale analysis using boxcar 5 × 5 and 11 × 11 window sizes and this revealed that depending on locations (and therefore, characteristics) icebergs can be a collection of strong scatterers that are packed in a denser or less dense way. This gives hope for using quad-pol polarimetry to provide some iceberg classifications in the future

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

Quad polarimetric synthetic aperture radar analysis of icebergs in Greenland and Svalbard

Polarimetric synthetic aperture radar (PolSAR) has been widely used in ocean and cryospheric applications. This is because, PolSAR can be used in all-day operations and in areas of cloud cover, and therefore can provide valuable large-scale monitoring in polar regions, which is very helpful to shipping and offshore maritime operations. In the last decades, attention has turned to the potential of PolSAR to detect icebergs in the Arctic since they are a major hazard to vessels. However, there is a substantial lack of literature exploring the potentialities of PolSAR and the understanding of iceberg scattering mechanisms. Additionally, it is not known if high resolution PolSAR can be used to detect icebergs smaller than 120 metres. This thesis aims to improve the knowledge of the use of PolSAR scattering mechanisms of icebergs, and detection of small icebergs. First, an introduction to PolSAR is outlined in chapter two, and monitoring of icebergs is presented in chapter three. The first data chapter (Chapter 4) is focused on developing a multi-scale analysis of icebergs using parameters from the Cloude-Pottier and the Yamaguchi decompositions, the polarimetric span and the Pauli scattering vector. This method is carried out using ALOS-2 PALSAR quad polarimetric L-band SAR on icebergs in Greenland. This approach outlines the good potential for using PolSAR for future iceberg classification. One of the main important outcomes is that icebergs are composed by a combination of single targets, which therefore may require a more complex way of processing SAR data to properly extract physical information. In chapter five, the problem of detecting icebergs is addressed by introducing six state-of-the-art detectors previously applied to vessel monitoring. These detectors are the Dual Intensity Polarisation Ratio Anomaly Detector (iDPolRAD), Polarimetric Notch Filter (PNF), Polarimetric Matched Filter (PMF), reflection symmetry (sym), Optimal Polarimetric Detector (OPD) and the Polarimetric Whitening Filter (PWF). Cloude-Pottier entropy, and first and third eigenvalues (eig1 and eig3) of the coherency matrix are also utilised as parameters for comparison. This approach uses the same ALOS-2 dataset, but also evaluates detection performance in two scenarios: icebergs in open ocean, and in sea ice. Polarimetric modes (quad-pol, dual-pol, and single intensities) are also considered for comparison. Currently it is very difficult to detect icebergs less than 120 metres in length using this approach, due to the scattering mechanisms of icebergs and sea ice being very similar. However, it was possible to obtain detection performances of the OPD and PWF, which both showed a Probability of Detection (PF) of 0.99 when the Probability of False Alarms (PF) was set to 10-5 in open ocean. Similarly, in dual pol images, the PWF gave the best performance with a PD of 0.90. Results in sea ice found eig3 to be the best detector with a PD of 0.90 while in dual-pol mode, iDPolRAD gave a PD of 0.978. Single intensity detector performance found the HV channel gave the best detection with a PD of 0.99 in open ocean and 0.87 in sea ice. In the previous two approaches, only satellite data is used. However, in chapter six, data from a ground-based Ku-band Gamma Portable Radio Interferometer (GPRI) instrument is introduced, providing images that are synchronised with the satellite acquisitions. In this approach, the same six detectors are applied to three multitemporal RADARSAT-2 quad pol C-band SAR images on icebergs in Kongsfjorden, Svalbard to evaluate the detection performance within a changing fjord environment. As before, we also make use of Cloude-Pottier entropy, eig1 and eig3. Finally, we evaluate the target-to-clutter ratio (TCR) of the icebergs and check for correlation between the backscattering coefficients and the iceberg dimension. The results obtained from this thesis present original additions to the literature that contributes to the understanding of PolSAR in cryospheric applications. Although these methods are applied to PolSAR and ground-based radar on vessels, they have been applied for the first time on icebergs in this thesis. To summarise, the main findings are that icebergs cannot be represented as single or partial targets, but they do exhibit a collection of single targets clustered together. This result leads to the fact that entropy is not sufficient as a parameter to detect icebergs. Detection results show that the OPD and PWF detectors perform best in an open ocean setting and using quad-pol mode. These results are degraded in dual-pol mode, while single intensity detection is best in the HV cross polarisation channel. When these detectors are applied to the RADARSAT-2 in Svalbard, the OPD and PWF detectors also perform best with PD values ranging between 0.5-0.75 for a PF of 0.01-0.05. However, the sea ice present in the fjord degrades performance across all detectors. Correlation plots with iceberg size show that a regression is not straightforward and Computer Vision methodologies may work best for this

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Department of Urban and Environmental Engineering (Environmental Science and Engineering)Sea ice closely interacts with the atmosphere and ocean systems. Land fast sea ice (fast ice) is a kind of sea ice attached to the shore, ice shelves, or grounded icebergs. It is widely distributed along the Antarctic coast and acts as an interface between the atmosphere and the ocean, affecting heat balance feedback, thermal insulation effects, and deep water formation depending on the temporal and spatial effects of the environmental conditions. It also plays an important role in the biological aspects of Antarctica. Attached to the Antarctic glacier is strongly associated with calving events of ice shelf as it is physically coupled with glaciers at the terminus. The existing Antarctic fast ice has been mainly focused on the East Antarctic, especially for the research on long-term fast ice. Several case studies for West Antarctic fast ice with satellite images were performed in local areas. Various types of satellite data and detection techniques were utilized to successfully detect fast ice. In addition, long-term fast ice maps specifically focused on the Amundsen sea of West Antarctica were generated to investigate the distribution and variability of fast ice. This thesis reports the results of fast ice detection algorithms that have been developed using various satellite images that can be used for fast ice detection. Along with the use of multiple satellite data, the proposed fast ice detection algorithms can more effectively detect fast ice, which then allows to obtain more accurate fast ice detection and produce long-term fast ice with high accuracy. Especially, the distribution and variability of time-series fast ice in West Antarctica, which is more concentrated in the Amundsen Sea, were analyzed together with bathymetry data and the distribution of glacier icebergs. In order to detect fast ice, machine learning techniques were basically used in this thesis. Two classes (i.e. fast ice and non-fast ice) were classified. Using MODIS images, there was a problem that fast ice was not produced in cloud cover areas and the polar night season, which is winter season in Antarctica. MODIS and AMSR-E satellite data were selectively used to solve the cloud contamination problem. Correlation-related variables were finally added based on the fact that fast ice is motionless for a certain period of time, and fast ice detection was performed at 15-day intervals using the improved input variables. Active microwave sensor data, ALOS PALSAR, was also used to detect fast ice and to validate fast ice detection results. Its high-spatial resolution allows to extract fast ice boundary more accurately. Fast ice detections showed good agreement with available ALOS PALSAR SAR images and MODIS reflectance images. Nearly decade-long fast ice extents were produced in the Amundsen Sea of West Antarctica and analyzed in terms of spatiotemporal variations with bathymetry and icebergs calved from ice shelves in study area. In addition, anomalous fast ice breakup events were examined, which suggests the importance of fast ice on the stability of ice shelves.clos

Hva kontrollerer kalving av breer? Fra observasjoner til prediksjoner

This thesis addresses the process of iceberg calving at the front of tidewater glaciers and tries to clarify what controls the calving of glaciers, from observations in the field to modeling and predictions. Iceberg calving is the detachment of ice from a parent glacier and it makes the glacier very sensitive to its local environment. In turn, calving at a glacier front has a strong impact on the glacier dynamics and can trigger and/or enhance glacier instabilities, acceleration and glacier retreat, making the calving process a crucial factor in glacier dynamics and hence in sea level rise. This thesis is based on field observations, collected throughout 4 years at the front of Kronebreen, Svalbard. A special emphasis has been given to trying various observation techniques: ground-based RADAR, direct observations, seismic monitoring, terrestrial photogrammetry and remote sensing. Using ground-based RADAR we were able to automatically detect 92% of the largest calving events. The percentage detected by seismic monitoring is lower (about 10%) but the technique allows for finer distinction between different calving types and glacier-related seismic events. Seismic equipment also requires less maintenance, less technical expertise and less funding, and can be left in the field for several months. Terrestrial photogrammetry is a very useful tool that can provide glacier dimensions and a continuous monitoring of the general conditions at the front. Finally, direct observations are recommended for the study of calving because it can provide, when used together with terrestrial photogrammetry, both qualitative and quantitative data. The qualitative aspect provides key information for understanding the calving process but is especially hard to obtain with technical methods. The question of seasonal calving variations is also addressed and we show that glacial seismic activity is highly variable throughout the year with recurrent increased activity in autumn, while velocity is low. However this thesis focuses on explaining very short-term variations: the individual calving events. Individual calving events have received so far very little attention in the field and no attention in modeling studies. This thesis was inspired by other studies of complex natural processes in which individual events are all equally considered, large and small, and which emphasize the value of understanding a process at the individual scale, for example the study of earthquakes or forest fires. We first show that general spatial patterns in calving activity can be explained by glacier characteristics like longitudinal stretching rate, which themselves are very linked to the glacier geometry. We then created a simple calving model with the object of understanding what controls the size and timing of calving events. Our simple model, focussing solely on the interplay between calving and its impact on the front stability, manages to reproduce the size and timing distribution of calving events as observed in the field. This result highlights the role of calving on front stability and on calving itself. Front stability is shown to be crucial in the control of calving. Implications of this new finding are that the size distribution of calving depends on the glacier stability: a glacier becoming unstable will produce a higher proportion of large calving events. Beyond a critical glacier stability, calving can become self-sustained and ongoing, leading to very rapid glacier retreat. We propose that the characteristics of the calving event sizes distribution indicate how close a glacier is to rapid retreat. One main point of this thesis is to show the importance of studying calving events at an individual scale to gain more understanding of the process.Denne avhandlingen omhandler kalvingsprosessen i fronten av en tidevannsbre og den forsøker å klargjøre hva som kontrollerer kalving av breer, ved hjelp av feltobservasjoner, modellering og prediksjon. Kalving av isfjell skjer når is brekker av fra en isbre, og kalving gjør breer svært sensitive til det lokale miljøet. Motsatt har også kalvingen ved brefronten en stor innflytelse på breens dynamikk, kalvingen kan initiere eller forsterke ustabilitet, akselerasjon eller tilbaketrekking av breen, hvilket gjør kalvingsprosessen til en sentral faktor for isdynamikken, og for havnivået. Denne avhandlingen er basert på feltobservasjoner som er samlet gjennom fire år ved fronten av Kronebreen på Svalbard. Det er blitt lagt spesielt vekt på å prøve ut forskjellige observasjonsteknikker, bakkebasert RADAR, direkte observasjoner, seismisk monitorering, terrestrisk fotogrammetri, og fjernanalyse. Ved hjelp av bakkebasert RADAR kunne vi detektere 92% av de storste kalvingsepisodene. Prosentandelen for seismisk monitorering er mye lavere, ca 10%, men denne monitoreringen tillater finere distinksjon av forskjellige kalvingsformer og brerelaterte seismiske episoder. Seismisk utstyr krever også mindre ettersyn, mindre teknisk ekspertise og lavere finansiering, og utstyret kan være utplassert i felt uten tilsyn i flere måneder. Terrestrisk fotogrammetri er et svært nyttig verktøy som kan fortelle om breens dimensjoner og som muliggjør en kontinuerlig monitorering av generelle forhold ved fronten. Tilsutt anbefales direkte observasjoner for å studere kalving, fordi disse i kombinasjon med terrestrisk fotogrammetri kan gi både kvalitative og kvantitative data. Det kvalitative aspektet gir essensiell informasjon for forståelsen av kalvingsprosessen, men er spesielt vanskelig å oppnå ved teknologiske metoder. Spørsmålet om sesongbaserte kalvingsvariasjoner er også undersøkt og vi viser at kalvingsaktiviteten er svært variabel gjennom året, med gjentagende økning i aktivitet på høsten når også hastigheten er på sitt laveste. Allikevel fokuserer denne avhandlingen på å forklare de svart raske variasjonene, nemlig individuelle kalvingshendelser. Så langt har det blitt viet svært lite oppmerksomhet mot individuelle kalvingshendelser i felt, og ingen oppmerksomhet innen modelleringsstudier. Denne avhandlingen er inspirert av studier av komplekse prosesser hvor individuelle hendelser er vurdert likeverdige, store som små, og som vektlegger verdien av å forstå prosessen på en skala på individuelt nivå, for eksempel for studier av jordskjelv. Vi viser først at generelle romlige monstre i kalvingsaktivitet kan forklares ved brekarakteristikker som longitudinell tøynings rate (stretching rate), som igjen er knyttet til breens geometri. Vi har laget en enkel kalvingsmodell hvor intensjonen er å forstå hva som kontrollerer størrelse og tidspunkt for kalvingshendelsen. Vår modell, som fokuserer kun på interaksjon mellom kalving og dennes innflytelse på frontstabiliteten, greier å reprodusere størrelses- og tidsfordeling av kalvingshendelser som observert i felt. Dette resultatet fremhever kalvingens rolle på frontstabiliteten og på kalvingen selv. Det viser seg at frontstabiliteten er en essensiell styringsmekanisme for kalvingen. Konsekvensene av dette nye funnet er at størrelsesfordelingen av kalvingshendelsene avhenger av breens stabilitet; en bre som blir ustabil produserer høyere proporsjon av større kalvingshendelser. Over en kritisk brestabilitet vil kalvingen bli selvopprettholdende og vedvarende, hvilket vil medføre en svart rask tilbaketrekning av brefronten. Vi fremsetter en påstand om at karakteristikken av fordelingen av størrelsene på kalvingshendelsene indikerer hvor nært forestående en rask tilbaketrekning er for breen. Et hovedpoeng ved denne avhandlingen er å vise hvor viktig det er å studere kalvingshendelser på en skala på individuelt nivå for å oppnå en bedre forståelse av prosessen.GLACIODY

Polarimetric Synthetic Aperture Radar

This open access book focuses on the practical application of electromagnetic polarimetry principles in Earth remote sensing with an educational purpose. In the last decade, the operations from fully polarimetric synthetic aperture radar such as the Japanese ALOS/PalSAR, the Canadian Radarsat-2 and the German TerraSAR-X and their easy data access for scientific use have developed further the research and data applications at L,C and X band. As a consequence, the wider distribution of polarimetric data sets across the remote sensing community boosted activity and development in polarimetric SAR applications, also in view of future missions. Numerous experiments with real data from spaceborne platforms are shown, with the aim of giving an up-to-date and complete treatment of the unique benefits of fully polarimetric synthetic aperture radar data in five different domains: forest, agriculture, cryosphere, urban and oceans

Investigation of Glacial Dynamics in the Lambert Glacier-Amery Ice Shelf System (LAS) Using Remote Sensing

Numerous recent studies have documented dynamic changes in the behaviors of large marine-terminating outlet glaciers and ice streams in Greenland, the Antarctic Peninsula, and West Antarctica. However, fewer observations of outlet glaciers and ice shelves exist for the East Antarctic Ice Sheet. In addition, most recent surface velocity mappings of the Lambert Glacier-Amery Ice Shelf system (LAS) are derived for the time period of 1997-2000. From this research, surface velocity measurements provide a more extended view of the behavior and stability of the LAS over the past two decades than can be gleaned from a single observational period. This study uses remote sensing to investigate whether significant changes in velocities have occurred from the late 1980’s through the late 2010’s and assesses the magnitude of mass balance changes observed at the grounding line. To accomplish this goal, surface velocities of the LAS from late 1980’s to late 2010’s for three separate time periods are measured. The observed surface velocities of the LAS ranged from 0 to 1300 m yr^-1 during 1988-1990. A slight slowing down is detected in the central Amery Ice Shelf front by analyzing the surface velocity measurements made along the centerlines. The mass balance is the difference between snow accumulation and the outflux of the grounded LAS and is calculated for individual sub-basin during the three time intervals of 1988-1990, 1999-2004, and 2007-2011 to illustrate the mass balance variation under sub-basin level. The flux gates of the Lambert Glacial sub-basin combined with the Mellor Glacial and the Fisher Glacial sub-basin appear to be the largest outlet of the grounded ice of the LAS. The ice mass transported from the interior region through the three flux gates in total is 43.58 Gt yr^-1, 36.72 Gt yr^-1, and 38.61 Gt yr^-1 respectively for the three time intervals above. The sub-basins in the eastern side appear differently than the western side. The outfluxes of the eastern sub-basins vary from 15.85 to 18.64 Gt yr^-1, while the western outfluxes vary from 15.85 to 18.64 Gt yr^-1. The grounded LAS has discharged ice from 84.55 to 81.60 Gt yr^-1 and to 79.20 Gt yr^-1 during 1980s-1990s and 1990s-2000s. Assuming the snow accumulation distribution is stable, the grounded LAS mass lose has increased 2.95 Gt yr^-1 from 1980s to 1990s and 2.40 Gt yr^-1 from 1990s to 2000s. These results indicate insight into the stability of the Amery Ice Shelf over the last few decades