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Thermal threshold sensitivity test for winter season 2010. The study period is divided in two intervals: (a) 1 April–4 July; (b) 5 July–31 October. TNBP extent retrievals are represented through different colors when using different thresholds, as described in the legend. Yellow circles report the ASAR Envisat co-located retrievals. Black rectangles present a zoom on days (a) 92–93 (2–3 April); and (b) days 232–233 (20–21 August), the case study fully analyzed in Figure 6.
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Polynyas are dynamic stretches of open water surrounded by ice. They typically occur in remote regions of the Arctic and Antarctic, thus remote sensing is essential for monitoring their dynamics. On regional scales, daily passive microwave radiometers provide useful information about their extent because of their independence from cloud coverage an...
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The lack of in situ data has always posed challenges to remote-sensing-data product validation. Herein, the products of sea-ice concentration (SIC) data derived using the arctic radiation and turbulence interaction study (ARTIST) sea ice (ASI) algorithm were evaluated by comparing them with SICs from a high-resolution sea-ice aerial image obtained...
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... The TNB is almost completely covered by sea ice during the winter season from March to October, while the higher temperature during the summer season makes it ice free [24]. The joint effects of strong and persistent katabatic cold winds, i.e., at least 20-25 m/s for at least 12 h, that blow up to 50 m/s from the Nansen ice sheet toward the open ocean, together with the upwelling of warm ocean water and the Drygalski ice tongue blocking action, generate and sustain the opening and growing of the polynya [25], [26]. The morphology, i.e., extent and shape, of the TNB polynya varies on a short temporal range [25]. ...
... The joint effects of strong and persistent katabatic cold winds, i.e., at least 20-25 m/s for at least 12 h, that blow up to 50 m/s from the Nansen ice sheet toward the open ocean, together with the upwelling of warm ocean water and the Drygalski ice tongue blocking action, generate and sustain the opening and growing of the polynya [25], [26]. The morphology, i.e., extent and shape, of the TNB polynya varies on a short temporal range [25]. During winter, very frequent short-term (2-5 days) polynya events alternate with less frequent longer ones (10-15 days). ...
... When available, independent satellite remote sensing information, i.e., space and time collocated optical imagery acquired by the Aqua MODIS mission at 1-km spatial resolution, are used for reference purposes. The cloud-free thermal MODIS imagery within 12 h from the SAR acquisition, are used to obtain IST information on the TNB area, from which the polynya extent and its actual condition, i.e., opening/closing, can be estimated according to the method developed in [25]. For the sake of completeness, the three collocated MODIS images are shown in Fig. 3, which is arranged in a matrix format where rows refer to the three SAR acquisition dates while columns refer to the emissivity channels 31 and 32 and to the IST obtained, as suggested in [25]. ...
In polar regions, coastal polynyas are key drivers for climate since they represent the primary source of ice mass production and oceanic circulation. In this study, multipolarization C-band synthetic aperture radar (SAR) measurements acquired by the Radarsat-2 satellite mission are exploited to observe the Terra Nova Bay (TNB) coastal polynya in the Ross Sea, Antarctica. Incoherent and coherent features, extracted from dual-polarimetric SAR measurements, are used to characterize the TNB coastal polynya under different environmental conditions. The analysis is also supported, when available, by independent optical remote sensing information collected by the thermal infrared channels of the moderate resolution imaging spectroradiometer and by ancillary on-site information about wind and air temperature collected by automatic weather stations. Experimental results show that the SAR plays a key role in providing information about the TNB polynya thanks to its fine spatial resolution and its almost continuous imaging capabilities. In addition, dual-polarimetric SAR offers unprecedented opportunities with respect to single-polarization SAR in performing accurate and unsupervised classification of the area within the polynya. Hence, a more accurate estimation of the polynya extent and the fractional area coverage of sea water within the polynyas obtained.
... The magnitude of the total blowing-snow sublimation and transport reported in that study, which are measured at the Terra Nova Bay in the Ross Sea, are larger than those estimated here at PIG. This is consistent with the fact that katabatic wind events at Terra Nova Bay can be quite strong, being associated with much higher wind speeds than those during the Foehn events discussed here (Aulicino et al., 2018). Blowing-snow sublimation (Fig. 4e) peaks just south and east of the glacier, with values in the range 0.5-0.75 ...
Pine Island Glacier (PIG) has recently experienced increased ice loss that has mostly been attributed to basal melt and ocean ice dynamics. However, atmospheric forcing also plays a role in the ice mass budget, as besides lower-latitude warm air intrusions, the steeply sloping terrain that surrounds the glacier promotes frequent Foehn winds. An investigation of 41 years of reanalysis data reveals that Foehn occurs more frequently from June to October, with Foehn episodes typically lasting about 5 to 9 h. An analysis of the surface mass balance indicated that their largest impact is on the surface sublimation, which is increased by about 1.43 mm water equivalent (w.e.) per day with respect to no-Foehn events. Blowing snow makes roughly the same contribution as snowfall, around 0.34–0.36 mm w.e. d−1, but with the opposite sign. The melting rate is 3 orders of magnitude smaller than the surface sublimation rate. The negative phase of the Antarctic oscillation and the positive phase of the Southern Annular Mode promote the occurrence of Foehn at PIG. A particularly strong event took place on 9–11 November 2011, when 10 m winds speeds in excess of 20 m s−1 led to downward sensible heat fluxes higher than 75 W m−2 as they descended the mountainous terrain. Surface sublimation and blowing-snow sublimation dominated the surface mass balance, with magnitudes of up to 0.13 mm w.e. h−1. Satellite data indicated an hourly surface melting area exceeding 100 km2. Our results stress the importance of the atmospheric forcing on the ice mass balance at PIG.
... For example, Parish and Bromwich (1989) found that katabatic winds originating from the Reeves Glacier upwind of the TNB were detected 250 km offshore in aircraft missions in early November 1987. Being a cold season event (sea ice is not present in the region in the warmer months), when cyclogenesis is more frequent in the Ross Sea (Simmonds et al. 2003), the TNBP area shows considerable seasonal variability (Aulicino et al. 2014(Aulicino et al. , 2018, decreasing from April to August as the regional temperature decreases (Ding et al. 2020). The regular sea ice formation in the TNBP leads to brine rejection, with the salt left behind increasing the density of the water column, resulting in the formation of the High Salinity Shelf Water (HSSW), the densest water mass of the Southern Ocean, and contributing to the formation of the Antarctic Bottom Water (Kurtz and Bromwich 1985;Fusco et al. 2009;Budillon et al. 2011;Castagno et al. 2019). ...
... The methodology of Aulicino et al. (2018), based on MODIS IST, is used in this work to estimate the area of the TNBP. Three MODIS products, over the domain 75.6-74.5°S ...
... This also explains the larger standard deviation in the warmer months. The diurnal variability of the TNBP is controlled by the frequency of occurrence and strength of the katabatic winds (Aulicino et al. 2018). The highest estimated area in the eight-year period is ~ 12,836 km 2 on 31 October 2010, an event discussed in Sect. ...
Polynyas, or ice-free regions within the sea ice pack, are a common occurrence around Antarctica. A recurrent and often large polynya is the Terra Nova Bay Polynya (TNBP), located on the western side of the Ross Sea just off Victoria Land. In this study, we investigate the atmospheric conditions leading to the occurrence of the TNBP and its spatial variability, as estimated using satellite-derived ice surface temperature and sea ice concentration data. A cluster analysis revealed that katabatic winds descending the Transantarctic Mountains, account for about 45% of the days when the TNBP exceeded its 2010-2017 mean extent plus one standard deviation. Warmer and more moist air intrusions from lower-latitudes from the Pacific Ocean, which are favoured in the negative phase of the Southern Annular Mode, play a role in its expansion in the remaining days. This is more frequent in the transition seasons, when such events are more likely to reach Antarctica and contribute to the occurrence and the widening of the polynya. In-situ weather data confirmed the effects of the mid-latitude air intrusions, while sea ice drifts of up to 25 km day-1 cleared the ice offshore and promoted the widening of the polynya starting from the coastal areas. Knowing the atmospheric factors involved in the occurrence of coastal polynyas around Antarctica is essential as it helps in improving their representation and predictability in climate models and hence advance the models’ capabilities in projecting Antarctic sea ice variability.
... Nevertheless, the coarse spatial resolution of PMW sensors (2.5-25 km, dependent on instrument and product) does not allow us to accurately determine the size and shape of the polynya. Several studies have shown the usefulness of satellite thermal imaging (TIR) to characterize areas of the polynya more accurately (Ciappa et al., 2012;Preußer et al., 2015;Hollands and Dierking, 2016;Aulicino et al., 2018;Vincent, 2019). Most TIR radiometers operating from near-polar orbits (e.g. ...
... However, previous observations of the TNBP (e.g. Aulicino et al., 2018) indicate that alternating phases of the opening and closing of the polynya may occur very irregularly throughout the period of March-October with no clear seasonal pattern. ...
... Coastal polynyas are very dynamic, constantly changing environments shaped by the local atmospheric forcing, as well as the surrounding sea ice and oceanic conditions (extent, thickness, compactness and motion patterns of the ice pack, local and regional ocean currents). The available satellite and other data show that the shape and extent of polynyas evolve on a daily or even hourly basis (Kern et al., 2007;Ciappa and Pietranera, 2013;Aulicino et al., 2018), indicating that processes taking place there are nonstationary and very sensitive to changes in the forcing, i.e. atmospheric conditions and sea ice drift. The images analysed here and in similar, satellitebased studies are single snapshots of those evolving systems -or, more precisely, snapshots limited to the ocean surface. ...
Coastal polynyas around the Antarctic continent are
regions of very strong ocean–atmosphere heat and moisture exchange that are
important for local and regional weather, sea ice production, and water mass
formation. Due to extreme atmospheric conditions (very strong offshore
winds, low air temperature, as well as humidity) the surface ocean layer in
polynyas is highly turbulent, with mixing due to combined Langmuir,
wind-induced, and buoyancy-driven turbulence. One of the visible signs of
complex interactions between the mixed-layer dynamics and the forming sea
ice are frazil streaks, elongated patches of high ice concentration
separated by areas of open water. In spite of their ubiquity, observational
and modelling analyses of frazil streaks have been very limited largely due
to the fact that their significance for heat flux and ice production is only
just becoming apparent. In this study, the first comprehensive analysis of
the spatial variability of surface frazil concentration is performed for the
Terra Nova Bay Polynya (TNBP). Frazil streaks are identified in
high-resolution (pixel size 10–15 m) visible satellite imagery, and their
properties (surface area, width, spacing, and orientation) are linked to the
meteorological forcing (wind speed and air temperature). This provides a
simple statistical tool for estimating the extent and ice coverage of the
region of high ice production under given meteorological conditions. It is
also shown that the orientation of narrow streaks tends to agree with the
wind direction, suggesting the dominating role of the local wind forcing in
their formation. Very wide streaks, in turn, deviate from that pattern, as
they are presumably influenced by several additional factors, including
local water circulation and the associated convergence zones. An analysis of
peak wavelengths and directions determined from the images, compared to
analogous open-water wavelengths computed with a spectral wave model,
demonstrates a significant slow-down in the observed wave growth in TNBP.
This suggests an important role of frazil streaks in modifying wind-wave
growth and/or dissipation in polynyas.
... The magnitude of the total blowing snow sublimation and transport reported in that study, which are measured at the Terra Nova Bay in the Ross Sea, are larger than those estimated here at PIG. This is consistent with the fact that katabatic wind events at Terra Nova Bay can be quite strong, being associated with much higher wind speeds than those during the Foehn events discussed here (Aulicino et al., 2018). Blowing snow sublimation (Fig. 4e) peaks just south and east of the glacier, with values in the range 0.5-0.75 ...
Pine Island Glacier (PIG) has recently experienced increased ice loss mostly attributed to basal melt and ocean-ice dynamics. However, atmospheric forcing also plays a role in the ice mass budget, as besides lower-latitude warm air intrusions, the steeply sloping terrain that surrounds the glacier promotes frequent Foehn winds. An investigation of 41-years of reanalysis data reveals that Foehn occurs more frequently from June to October, with Foehn episodes typically lasting about 5 to 9 h. An analysis of the surface mass balance indicated that their largest impact is on the surface sublimation, which is increased by about 1.4 mm water equivalent (w.e.) day−1 with respect to no-Foehn events. Blowing snow makes roughly the same contribution as snowfall, around 0.34–0.36 mm w.e. day−1, but with the opposite sign. The melting rate is three orders of magnitude smaller than the surface sublimation rate. The negative phase of the Antarctic Oscillation and the positive phase of the Southern Annular Mode promote the occurrence of Foehn at PIG. A particularly strong event took place on 09–11 November 2011, when 10-m winds speeds in excess of 20 m s−1 led to downward sensible heat fluxes higher than 75 W m−2 as they descended the mountainous terrain. Surface sublimation and blowing snow sublimation dominated the surface mass balance, with magnitudes of up to 0.13 mm w.e. hr−1. Satellite data indicated an hourly surface melting area exceeding 100 km2. Our results stress the importance of the atmospheric forcing on the ice mass balance at PIG.
... MODIS data have been successfully used also in the detection of polynyas both in the Arctic and Antarctic [23][24][25][26][27][28]. The threshold technology for ice and water separation is a commonly used method to identify sea ice at the verification stage based on MODIS data in polar and mid-high latitude regions [18,29]. ...
High accuracy sea ice monitoring is of great significance in responding to global climate change and guiding safe navigation. The MODIS sensors carried by Aqua and Terra satellites have great potential in high-resolution monitoring of sea ice in polar regions. This study developed an automatic high-accuracy sea ice concentration (SIC) detection algorithm for the MODIS data. We used a machine learning algorithm that combines spectral and texture features to obtain high-precision sea ice recognition results. Then, according to the cloud characteristics in MODIS images and the full coverage of AMSR2 SICs, outlier removal and cloud area filling are carried out. Finally, the SIC result was calculated according to the distribution of ice types. We assessed the accuracy of our high-accuracy SIC product by comparing with the MOD29/MYD29 products and validating with the Landsat 8/9 images. We found that the deviation increased with the decrease of SIC value. The deviation are larger in the ice melting area and the ice edges area, but smaller in the area completely covered by ice. Compared with MOD29/MYD29 SICs, the SICs obtained in this study have higher accuracy, with an average RMSD of 7.64%. It can detect the details of relatively small leads, ice edges and fragmented ice areas. The high-accuracy SIC product we obtained is expected to provide long-term SIC records of high quality.
... Persistent polynyas are key sites of consistent, year-round interactions between atmosphere, sea ice, ocean, ice shelves, and sub-ice-shelf ocean cavities that drive Southern Ocean carbon dynamics [23], [24]; however, in situ observations are sparse due to the logistical constraints of collecting field measurements given the remoteness of Antarctica [25]. Instead, visible (e.g., [16], [26]), thermal (e.g., [27], [28]), and microwave (e.g., [29], [30]) remote sensing techniques have been used to identify and quantify polynya processes in coastal Antarctica. Although multiple remote sensing techniques can identify the presence of polynyas within sea ice, thermal remote sensing, with spatial resolution ∼10 -25 times finer than passive microwave [31], has the unique potential to fingerprint regions of high sea surface temperatures within PIB, which can be used to infer processes that govern sensibleheat polynya evolution. ...
Antarctica’s ice shelves play a critical role in modulating ice loss to the ocean by buttressing grounded ice upstream. With the potential to impact ice-shelf stability, persistent polynyas (open-water areas surrounded by sea ice that occur across multiple years at the same location) at the edge of many ice-shelf fronts, are maintained by winds and/or ocean heat and are locations of strong ice-ocean-atmosphere interactions. However, in situ observations of polynyas are sparse due to the logistical constraints of collecting Antarctic field measurements. Here, we used wintertime (May–August) temperature and salinity observations derived from seal-borne instruments deployed in 2014, 2019, and 2020, in conjunction with thermal imagery from the MODerate resolution Imaging Spectroradiometer (MODIS) and the Landsat 8 Thermal Infrared Sensor (TIRS) to investigate spatial, temporal, and thermal structural variability of polynyas near Pine Island Glacier (PIG). Across the three winters considered, there were 176 anomalously warm (>3σ from background) seal dives near the PIG ice front, including 26 dives that coincided with MODIS images with minimal cloud cover that also showed a warm surface temperature anomaly. These warm surface temperatures correlated with ocean temperatures down to 150 m depth or deeper, depending on the year, suggesting that MODIS-derived surface thermal anomalies can be used for monitoring polynya presence and structure during polar night. The finer spatial resolution (100 m) of TIRS wintertime thermal imagery captures more detailed thermal structural variability within these polynyas, which may provide year-round insight into sub-ice-shelf processes if this dataset is collected operationally.
... Several studies have shown the usefulness of satellite thermal imaging (TIR) to characterize area of the polynya more accurately (Ciappa et al., 2012, Preußer et al., 2015, Hollands and Dierking, 2016, Aulicino et al., 2018, Vincent, 2019. ...
... Coastal polynyas are very dynamic, constantly changing environments shaped by the local atmospheric forcing as well as the surrounding sea ice and oceanic conditions (extent, thickness, compactness and motion patterns of the ice pack, local and regional ocean currents). The available satellite and other data show that the shape and extent of polynyas evolve on a daily 410 or even hourly basis (Kern et al. 2007, Ciappa and Pietranera, 2013, Aulicino et al., 2018, indicating that processes taking place there are nonstationary and very sensitive to changes in the forcing. The images analysed here and in similar, satellitebased studies are single snapshots of those evolving systems -or, more precisely, snapshots limited to the ocean surface. ...
... Most of the scenes cover the entire area of the open water adjacent to the Nansen Ice Sheet. Our analysis ignores openings along and at the extremity of the Drygalski Ice Tongue, as well as any leads external to the polynya, hence the estimated areas (Sp) may be smaller than those estimated on the basis of thermal data for the entire TNB by Ciappa and Pietranera (2012) or Aulicino et al. (2018). In this study, the analysis was also 420 limited to the area of the polynya where frazil streaks are visible. ...
Coastal polynyas around the Antarctic continent are regions of very strong ocean-atmosphere heat and moisture exchange, important for local and regional weather, sea ice production and water mass formation. Due to extreme atmospheric conditions (very strong offshore winds, low air temperature and humidity) the surface ocean layer in polynyas is highly turbulent, with mixing due to combined Langmuir, wind-induced and buoyancy-driven turbulence. One of the visible signs of complex interactions between the mixed layer dynamics and the forming sea ice are frazil streaks, elongated patches of high ice concentration separated by areas of open water. In spite of their ubiquity, observational and modelling analyses of frazil streaks have been very limited, largely due to the fact that their significance for heat flux and ice production is only just becoming apparent. In this study, the first comprehensive analysis of the spatial variability of surface frazil concentration is performed for the Terra Nova Bay Polynya (TNBP). Frazil streaks are identified in high-resolution (pixel size 10-15 m) visible satellite imagery, and their properties (surface area, width, spacing and orientation) are linked to the meteorological forcing (wind speed and air temperature). This provides a simple statistical tool for estimating the extent and ice coverage of the region of high ice production under given meteorological conditions. It is also shown that the orientation of narrow streaks tends to agree with the wind direction, suggesting the dominating role of the local wind forcing in their formation. Very wide streaks, in turn, deviate from that pattern, as they are presumably influenced by several additional factors, including local water circulation and the associated convergence zones. An analysis of peak wave lengths and directions determined from the images, compared to analogous open-water wave lengths computed with a spectral wave model, demonstrates a significant slowdown in the observed wave growth in TNBP. This suggests an important role of frazil streaks in modifying wind-wave growth and/or dissipation in polynyas.
... Despite the coarse resolution of passive microwave data (6.5-25 km), they are routinely used for ice monitoring (Aulicino et al., 2018;Nihashi et al., 2017;Preußer et al., 2019). The higher-resolution thermal infrared (TIR) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) have also proven useful for the retrieval of polynya extent and TIT Preußer et al., 2016Preußer et al., , 2019Willmes & Heinemann, 2017). ...
The North Water Polynya (NOW) is the largest recurrent Arctic coastal polynya. The formation of the NOW is critically dependent on the development of an ice arch that defines its northern boundary. In this study, high‐resolution ENVISAT Advanced Synthetic Aperture Radar data, Sentinel‐1A data, and Moderate Resolution Imaging Spectroradiometer data were employed to identify the spatio‐temporal characteristics of the ice arch during 2006–2019. Polynya pixels were identified based on the thin ice thickness (TIT), using a threshold of TIT <0.2 m, from which the polynya extent, heat flux, and ice production (IP) were estimated. The results show the different locations of the ice arch in different years, with a mean duration of 132 ± 69 days. The average annual polynya extent over the 14 years is ∼38.8 ± 8 × 10³ km², and we found that it is more closely correlated with wind speed during the winter and air temperature during early spring. The average heat flux drops from about 248 W/m² in the winter months to about 34 W/m² in May. The average accumulated IP varies significantly every year, with an average of 144 ± 103 km³, and peak values in March in most years. No apparent interannual trends are shown for the polynya area, heat flux, and IP during 2006–2019. The results also show that IP calculated based on the ice arch data is approximately 25% lower than that obtained by assuming a fixed time, location, and duration for the polynya.
... Alternatively, the simultaneous use of complementary sensors (optical, thermal, and radar) has been thus suggested as the optimal approach for the long-term monitoring of polynyas, and/or the implementation of algorithms to strengthen the final output from the available data [124,131,132]. As, for instance, a multi-band TIR sensor, with at least two bands centered at about 11.0 µm and 12.0 µm, would be feasible to investigate polynyas [124,131]. ...
... Alternatively, the simultaneous use of complementary sensors (optical, thermal, and radar) has been thus suggested as the optimal approach for the long-term monitoring of polynyas, and/or the implementation of algorithms to strengthen the final output from the available data [124,131,132]. As, for instance, a multi-band TIR sensor, with at least two bands centered at about 11.0 µm and 12.0 µm, would be feasible to investigate polynyas [124,131]. ...
In this paper, we present several study cases focused on marine, oceanographic, and atmospheric environments, which would greatly benefit from the use of a deployable system for small satellite observations. As opposed to the large standard ones, small satellites have become an effective and affordable alternative access to space, owing to their lower costs, innovative design and technology, and higher revisiting times, when launched in a constellation configuration. One of the biggest challenges is created by the small satellite instrumentation working in the visible (VIS), infrared (IR), and microwave (MW) spectral ranges, for which the resolution of the acquired data depends on the physical dimension of the telescope and the antenna collecting the signal. In this respect, a deployable payload, fitting the limited size and mass imposed by the small satellite architecture, once unfolded in space, can reach performances similar to those of larger satellites. In this study, we show how ecology and Earth Observations can benefit from data acquired by small satellites, and how they can be further improved thanks to deployable payloads. We focus on DORA—Deployable Optics for Remote sensing Applications—in the VIS to TIR spectral range, and on a planned application in the MW spectral range, and we carry out a radiometric analysis to verify its performances for Earth Observation studies.
