scholarly journals A New Retracking Algorithm for Retrieving Sea Ice Freeboard from CryoSat-2 Radar Altimeter Data during Winter–Spring Transition

2019 ◽  
Vol 11 (10) ◽  
pp. 1194 ◽  
Author(s):  
Xiaoyi Shen ◽  
Markku Similä ◽  
Wolfgang Dierking ◽  
Xi Zhang ◽  
Changqing Ke ◽  
...  
Keyword(s):  
Sea Ice ◽  
European Space Agency ◽  
Early Spring ◽  
Bézier Curve ◽  
Altimeter Data ◽  
Bezier Curve ◽  
Late Winter ◽  
Radar Altimeter ◽  
Depth Level ◽  
Space Agency

A new method called Bézier curve fitting (BCF) for approximating CryoSat-2 (CS-2) SAR-mode waveform is developed to optimize the retrieval of surface elevation of both sea ice and leads for the period of late winter/early spring. We found that the best results are achieved when the retracking points are fixed on positions at which the rise of the fitted Bézier curve reaches 70% of its peak in case of leads, and 50% in case of sea ice. In order to evaluate the proposed retracking algorithm, we compare it to other empirically-based methods currently reported in the literature, namely the threshold first-maximum retracker algorithm (TFMRA) and the European Space Agency (ESA) CS-2 in-depth Level-2 algorithm (L2I). The results of the retracking procedure for the different algorithms are validated using data of the Operation Ice Bridge (OIB) airborne mission. For two OIB campaign periods in March 2015 and April 2016, the mean absolute differences between freeboard values retrieved from CS-2 and OIB data were 9.22 and 7.79 cm when using the BCF method, 10.41 cm and 8.16 cm for TFMRA, and 10.01 cm and 8.42 cm for L2I. This suggests that the sea ice freeboard data can be obtained with a higher accuracy when using the proposed BCF method instead of the TFMRA or the CS-2 L2I algorithm.

scholarly journals Using airborne Ku-band altimeter waveforms to investigate winter accumulation and glacier facies on Austfonna, Svalbard

2013 ◽  
Vol 59 (217) ◽  
pp. 893-899 ◽  
Author(s):  
Robert L. Hawley ◽  
Ola Brandt ◽  
Thorben Dunse ◽  
Jon Ove Hagen ◽  
Veit Helm ◽  
...  
Keyword(s):  
Snow Depth ◽  
European Space Agency ◽  
Synthetic Aperture Radar Image ◽  
Altimeter Data ◽  
Radar Altimeter ◽  
Ice Caps ◽  
Ice Cap ◽  
Space Agency ◽  
Wet Snow ◽  
Airborne Sar

AbstractWinter balance is an important metric for assessing the change on glaciers and ice caps, yet measuring it using ground-based techniques can be challenging. We use the European Space Agency prototype Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) to extract snow depths from the received altimeter waveforms over Austfonna ice cap, Svalbard. Additionally, we attempt to distinguish the long-term firn area from other glacier facies. We validate our results using snow depth and glacier facies characterizations determined from ground-based radar profiles, snow pits and a multi-look satellite synthetic aperture radar image. We show that the depth of the winter snowpack can be extracted from the altimeter data over most of the accumulation zone, comprising wet snow zone and a superimposed ice zone. The method struggles at lower elevations where internal reflections within the winter snowpack are strong and the winter snow depth is less than ∼1 m. We use the abruptness of the reflection from the last summer surface (LSS) to attempt to distinguish glacier facies. While there is a general correlation between LSS abruptness and glacier facies, we do not find a relationship that warrants a distinct classification based on ASIRAS waveforms alone.

Quality Status of the CryoSat Data Products

2020 ◽  
Author(s):  
Erica Webb ◽  
Ben Wright ◽  
Marco Meloni ◽  
Jerome Bouffard ◽  
Tommaso Parrinello ◽  
...  
Keyword(s):  
Sea Ice ◽  
Data Quality ◽  
Positive Impact ◽  
European Space Agency ◽  
Performance Standards ◽  
Radar Altimeter ◽  
Mountain Glaciers ◽  
Space Agency ◽  
And Performance ◽  
Quality Status

<p>Launched in 2010, the European Space Agency’s (ESA) polar-orbiting CryoSat satellite was specifically designed to measure changes in the thickness of polar sea ice and the elevation of the ice sheets and mountain glaciers. Beyond the primary mission objectives, CryoSat is also valuable source of data for the oceanographic community and CryoSat’s sophisticated SAR Interferometric Radar Altimeter (SIRAL) can measure high-resolution geophysical parameters from the open ocean to the coast.</p><p>CryoSat data is processed operationally using two independent processing chains: Ice and Ocean. To ensure that the CryoSat products meet the highest data quality and performance standards, the CryoSat Instrument Processing Facilities (IPFs) are periodically updated. Processing algorithms are improved based on feedback and recommendations from Quality Control (QC) activities, Calibration and Validation campaigns, the CryoSat Expert Support Laboratory (ESL), and the Scientific Community. </p><p>Since May 2019, the CryoSat ice products are generated with Baseline-D, which represented a major processor upgrade and implemented several improvements, including the optimisation of freeboard computation in SARIn mode, improvements to sea ice and land ice retracking and the migration from Earth Explorer Format (EEF) to Network Common Data Form (NetCDF). A reprocessing campaign is currently underway to reprocess the full mission dataset (July 2010 – May 2019) to Baseline-D.</p><p>The CryoSat ocean products are also generated in NetCDF, following a processor upgrade in November 2017 (Baseline-C). Improvements implemented in this new Baseline include the generation of ocean products for all data acquisition modes, therefore providing complete data coverage for ocean users. This upgrade also implemented innovative algorithms, refined existing ones and added new parameters and corrections to the products. Following the completion of a successful reprocessing campaign, Baseline-C ocean products are now available for the full mission dataset (July 2010 – present).</p><p>Since launch, the CryoSat ice and ocean products have been routinely monitored as part of QC activities by the ESA/ESRIN Sensor Performance, Products and Algorithms (SPPA) office with the support of the Quality Assurance for Earth Observation (QA4EO) service (formerly IDEAS+) led by Telespazio VEGA UK. The latest processor updates have brought significant improvements to the quality of CryoSat ice and ocean products, which in turn are expected to have a positive impact on the scientific exploitation of CryoSat measurements over all surface types.</p><p>This poster provides an overview of the CryoSat data quality status and the QC activities performed by the QA4EO consortium, including both operational and reprocessing QC. Also presented are the main evolutions and improvements that have implemented to the processors, and anticipated evolutions for the future.</p>

Quality Status of the CryoSat Data Products

2021 ◽  
Author(s):  
Erica Webb ◽  
Jenny Marsh ◽  
Laura Benzan Valette ◽  
Jerome Bouffard ◽  
Tommaso Parrinello ◽  
...  
Keyword(s):  
Sea Ice ◽  
Data Quality ◽  
Positive Impact ◽  
European Space Agency ◽  
Performance Standards ◽  
Radar Altimeter ◽  
Mountain Glaciers ◽  
Space Agency ◽  
And Performance ◽  
Quality Status

<p>Launched in 2010, the European Space Agency’s (ESA) polar-orbiting CryoSat satellite was specifically designed to measure changes in the thickness of polar sea ice and the elevation of the ice sheets and mountain glaciers. Beyond the primary mission objectives, CryoSat is also valuable source of data for the oceanographic community and CryoSat’s sophisticated SAR Interferometric Radar Altimeter (SIRAL) can measure high-resolution geophysical parameters from the open ocean to the coast.</p><p>CryoSat data is processed operationally using two independent processing chains: Ice and Ocean. To ensure that the CryoSat products meet the highest data quality and performance standards, the CryoSat Instrument Processing Facilities (IPFs) are periodically updated. Processing algorithms are improved based on feedback and recommendations from Quality Control (QC) activities, Calibration and Validation campaigns, the CryoSat Expert Support Laboratory (ESL), and the Scientific Community.</p><p>Since May 2019, the CryoSat ice products have been generated with Baseline-D, which represented a major processor upgrade and implemented several improvements, including the optimisation of freeboard computation in SARIn mode, improvements to sea ice and land ice retracking and the migration from Earth Explorer Format (EEF) to Network Common Data Form (NetCDF). The Baseline-D reprocessing campaign completed in May 2020, and the full mission Baseline-D dataset is now available to users (July 2010 – present). The next major processor upgrade, Baseline-E, is already under development and following testing and refinement is anticipated to be operational in Q3 2021.</p><p>The CryoSat ocean products are also generated in NetCDF, following a processor upgrade in November 2017 (Baseline-C). Improvements implemented in this baseline include the generation of ocean products for all data acquisition modes, therefore providing complete data coverage for ocean users. This upgrade also implemented innovative algorithms, refined existing ones and added new parameters and corrections to the products. Following the completion of a successful reprocessing campaign, Baseline-C ocean products are now available for the full mission dataset (July 2010 – present). Preparations are underway for the next major processor upgrade, Baseline-D.</p><p>Since launch, the CryoSat ice and ocean products have been routinely monitored as part of QC activities by the ESA/ESRIN Sensor Performance, Products and Algorithms (SPPA) office with the support of the Quality Assurance for Earth Observation (QA4EO) service (formerly IDEAS+) led by Telespazio UK. The latest processor updates have brought significant improvements to the quality of CryoSat ice and ocean products, which in turn are expected to have a positive impact on the scientific exploitation of CryoSat measurements over all surface types.</p><p>This poster provides an overview of the CryoSat data quality status and the QC activities performed by the IDEAS-QA4EO consortium, including both operational and reprocessing QC. Also presented are the main evolutions and improvements that have implemented to the processors, and anticipated evolutions for the future.</p>

scholarly journals The European Space Agency’s Earth Explorer Mission CryoSat: measuring variability in the cryosphere

2004 ◽  
Vol 39 ◽  
pp. 313-320 ◽  
Author(s):  
Mark R. Drinkwater ◽  
Richard Francis ◽  
Guy Ratier ◽  
Duncan J. Wingham
Keyword(s):  
European Space Agency ◽  
Ice Sheets ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Radar Altimeter ◽  
Operating Characteristics ◽  
Space Agency ◽  
Explorer Mission ◽  
Arctic Sea ◽  
Ku Band

AbstractCryoSat is currently being prepared for a 2005 launch as the first European Space Agency Earth Explorer Opportunity mission. It is a dedicated cryospheric mission equipped with a Ku-band SIRAL (SAR/Interferometric Radar ALtimeter), whose primary objectives are to measure the variability and trends in the mass of the Arctic sea-ice cover and large terrestrial ice sheets. In this paper, an overview is provided of the mission and of the measurement characteristics of the new SIRAL instrument. Examples of data acquired on recent preparatory campaigns are presented, illustrating the operating characteristics of the key SIRAL modes. Preparatory plans for calibration and validation of CryoSat data are described.

A Subice Suction Corer for Sampling Epontic Ice Algae

1988 ◽  
Vol 45 (3) ◽  
pp. 562-568 ◽  
Author(s):  
Harold E. Welch ◽  
Martin A. Bergmann ◽  
John K. Jorgenson ◽  
William Burton
Keyword(s):  
Sea Ice ◽  
Quantitative Assessment ◽  
Early Spring ◽  
Late Winter ◽  
First Year ◽  
Ice Algae ◽  
Sources Of Error

Standard SIPRE coring was compared with a new Subice Suction Corer and cores taken by diver for the quantitative assessment of epontic (subice) algae on first-year congelation sea ice at Resolute, N.W.T., Canada (≈75°N). The diver cores were probably most accurate but were slow and costly. SIPRE coring was as good as other techniques in late winter and early spring but gave progressively poorer (under) estimates as the season progressed, with up to 90% of the ice algae being lost from SIPRE cores by June. The Subice Suction Corer was fast, easy to operate, cheap, and gave results comparable with samples obtained by diving. Sources of error are discussed.

Distribution and movements of white foxes in northern and western Alaska

1968 ◽  
Vol 46 (5) ◽  
pp. 849-854 ◽  
Author(s):  
David L. Chesemore
Keyword(s):  
Sea Ice ◽  
Bering Sea ◽  
Early Spring ◽  
Aleutian Islands ◽  
Late Winter ◽  
Seasonal Movements ◽  
Alaskan Arctic ◽  
Northern Alaska ◽  
The Bering Sea

White foxes occur on the tundra of northern and western Alaska and predominate on St. Lawrence, St. Matthew, Hall, and Diomede Islands in the Bering Sea. Few white foxes are found on the Pribilof and Aleutian Islands where blue foxes dominate the local fox population. On the Alaskan Arctic Slope, two seasonal movements, the first in the fall when foxes move seaward towards the coast and sea ice, and the second in late winter and early spring when they return inland to occupy summer den sites, occur. Although reported in other arctic areas, no definite records of fox migrations in northern Alaska exist. Distribution records for white foxes in Alaska are summarized.

scholarly journals About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

2015 ◽  
Vol 9 (5) ◽  
pp. 4893-4923 ◽  
Author(s):  
S. Schwegmann ◽  
E. Rinne ◽  
R. Ricker ◽  
S. Hendricks ◽  
V. Helm
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Altimeter Data ◽  
Ice Thickness ◽  
Radar Altimeter ◽  
Growth Season ◽  
Sea Ice Thickness ◽  
Antarctic Sea Ice ◽  
Abstract Knowledge ◽  
Modal Values

Abstract. Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, data come from different sources, and the characteristics of individual sensors differ. Hence, it is important to study the consistency between single sensors in order to develop long and consistent time series over the potentially available measurement period. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on-board Envisat and freeboard measurements from the Synthetic-Aperture Interferometric Radar Altimeter on-board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are comparable over the sea-ice growth season (May–October) and partly also beyond. In general, Envisat data shows higher freeboards in the seasonal ice zone while CryoSat-2 freeboards are higher in the perennial ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regional separated) Southern Ocean differs generally by not more than 2 cm (5 cm, except for the Amundsen/Bellingshausen Sea) between Envisat and CryoSat-2, and the differences between modal freeboard lie generally within ±10 cm and often even below.

scholarly journals A comparison between Envisat and ICESat sea ice thickness in the Antarctic

2020 ◽  
Author(s):  
Jinfei Wang ◽  
Chao Min ◽  
Robert Ricker ◽  
Qinghua Yang ◽  
Qian Shi ◽  
...  
Keyword(s):  
Sea Ice ◽  
European Space Agency ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Radar Altimeter ◽  
Average Deviation ◽  
Absolute Deviation ◽  
Sea Ice Thickness ◽  
Antarctic Sea Ice ◽  
The Antarctic

Abstract. The crucial role that Antarctic sea ice plays in the global climate system is strongly linked to its thickness. While in situ observations are too sparse in the Antarctic to determine long-term trends of the Antarctic sea ice thickness on a global scale, satellite radar altimetry data can be applied with a promising prospect. A newly released Envisat-derived product from the European Space Agency Sea Ice Climate Change Initiative (ESA SICCI), including sea ice freeboard and sea ice thickness, covers the entire Antarctic year-round from 2002 to 2012. In this study, the SICCI Envisat sea ice thickness in the Antarctic is firstly compared with a conceptually new proposed ICESat ice thickness that has been derived from an algorithm employing modified ice density. Both data sets have been validated with the Weddell Sea upward looking sonar measurements (ULS), indicating that ICESat agrees better with field observations. The inter-comparisons are conducted for three seasons except winter based on the ICESat operating periods. According to the results, the deviations between Envisat and ICESat sea ice thickness are different considering different seasons, years and regions. More specifically, the smallest average deviation between Envisat and ICESat sea ice thickness exists in spring by −0.03 m while larger deviations exist in summer and autumn by 0.86 m and 0.62 m, respectively. Although the smallest absolute deviation occurs in spring 2005 by 0.02 m, the largest correlation coefficient appears in autumn 2004 by 0.77. The largest positive deviation occurs in the western Weddell Sea by 1.03 m in summer while the largest negative deviation occurs in the Eastern Antarctic by −0.25 m in spring. Potential reasons for those deviations mainly deduce from the limitations of Envisat radar altimeter affected by the weather conditions and the surface roughness as well as the different retrieval algorithms. The better performance in spring of Envisat has a potential relation with relative humidity.

scholarly journals About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

2016 ◽  
Vol 10 (4) ◽  
pp. 1415-1425 ◽  
Author(s):  
Sandra Schwegmann ◽  
Eero Rinne ◽  
Robert Ricker ◽  
Stefan Hendricks ◽  
Veit Helm
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Altimeter Data ◽  
Ice Thickness ◽  
Radar Altimeter ◽  
Growth Season ◽  
Sea Ice Thickness ◽  
Antarctic Sea Ice ◽  
Abstract Knowledge ◽  
Modal Values

Abstract. Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, the characteristics of individual radar types differ for the available altimeter missions. Hence, it is important and our goal to study the consistency between single sensors in order to develop long and consistent time series. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on board Envisat and freeboard measurements from the Synthetic-Aperture Interferometric Radar Altimeter on board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are in reasonable agreement over the sea-ice growth season (May–October) and partly also beyond. In general, Envisat data show higher freeboards in the first-year ice zone while CryoSat-2 freeboards are higher in the multiyear ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regionally separated) Southern Ocean differs generally by not more than 3 cm (8 cm, with few exceptions) between Envisat and CryoSat-2, and the differences between modal freeboards lie generally within ±10 cm and often even below.

scholarly journals Sources of anions in aerosols in northeast Greenland during late winter

2012 ◽  
Vol 12 (6) ◽  
pp. 14813-14836 ◽  
Author(s):  
M. Fenger ◽  
L. L. Sørensen ◽  
K. Kristensen ◽  
B. Jensen ◽  
Q. T. Nquyen ◽  
...  
Keyword(s):  
Sea Ice ◽  
Long Range ◽  
Atmospheric Aerosols ◽  
Fine Particles ◽  
Chemical Properties ◽  
High Arctic ◽  
Early Spring ◽  
Water Soluble ◽  
The Arctic ◽  
Late Winter

Abstract. The knowledge of climate effects of atmospheric aerosols is associated with large uncertainty, and a better understanding of their physical and chemical properties is needed, especially in the Arctic environment. The objective of the present study is to improve our understanding of the processes affecting the composition of the aerosols in the high Arctic. Therefore size-segregated aerosols were sampled at a high Arctic site, Station Nord (Northeast Greenland), in March 2009 using a Micro Orifice Uniform Deposit Impactor. The aerosol samples were extracted in order to analyze the three water-soluble anions: chloride, nitrate and sulphate. The results are discussed based on possible chemical and physical transformations as well as transport patterns. The total concentrations of the ions at Station Nord were 53–507 ng m−3, 2–298 ng m−3 and 535–1087 ng m−3 for chloride (Cl−), nitrate (NO3-) and sulphate (SO42−), respectively. The aerosols in late winter/early spring, after polar sunrise, are found to be a mixture of long-range transported and regional to local originating aerosols. Fine particles, smaller than 1 μm, containing SO42−, Cl− and NO3−, are hypothesized to originate from long-range transport, where SO42− is by far the dominating anion accounting for 50–85% of the analyzed mass. The analysis suggests that Cl− and NO3− in coarser particles (>1.5 μm) originate from local/regional sources. Under conditions where the air mass is transported over sea-ice at high wind speeds, very coarse particles (>18 μm) are observed and it is hypothesized that frost flowers on the sea ice is a source of very coarse chloride particles in the Arctic.

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