Validation of a daily satellite-derived Antarctic sea ice velocity product: impacts on ice kinematics

Abstract. Antarctic sea ice kinematic plays a crucial role in shaping the polar climate and ecosystems. Satellite passive microwave-derived sea ice motion data have been used widely for studying sea ice motion and deformation processes, and provide daily, global coverage at a relatively low spatial-resolution (in the order of 60 × 60 km). In the Arctic, several validated data sets of satellite observations are available and used to study sea ice kinematics, but far fewer validation studies exist for the Antarctic. Here, we compare the widely-used passive microwave-derived Antarctic sea ice motion product by Kimura et al. (2013) with buoy-derived velocities, and interpret the effects of satellite observational configuration on the representation of Antarctic sea ice kinematics. We identify two issues in the Kimura et al. (2013) product: (i) errors in two large triangular areas within the eastern Weddell Sea and western Amundsen Sea relating to an error in the input satellite data composite, and (ii) a more subtle error relating to invalid assumptions for the average sensing time of each pixel. Upon rectification of these, performance of the daily composite sea ice motion product is found to be a function of latitude, relating to the number of satellite swaths incorporated (more swaths further south as tracks converge), and the heterogeneity of the underlying satellite signal (brightness temperature here). Daily sea ice motion vectors calculated using ascending- and descending-only satellite tracks (with a true ~24 h time-scale) are compared with the widely-used combined product (ascending and descending tracks combined together, with an inherent ~39 h time-scale). This comparison reveals that kinematic parameters derived from the shorter time-scale velocity datasets are higher in magnitude than the combined dataset, indicating a high degree of sensitivity to observation time-scale. We conclude that the new generation of “swath-to-swath” (S2S) sea ice velocity datasets, encompassing a range of observational time scales, is necessary to advance future research into sea ice kinematics.

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Antarctic sea ice variability and trends, 1979–2010

The Cryosphere Discussions ◽

10.5194/tcd-6-931-2012 ◽

2012 ◽

Vol 6 (2) ◽

pp. 931-956 ◽

Cited By ~ 16

Author(s):

C. L. Parkinson ◽

D. J. Cavalieri

Keyword(s):

Indian Ocean ◽

Sea Ice ◽

Ross Sea ◽

Ice Cover ◽

Weddell Sea ◽

The Arctic ◽

Future Research ◽

Positive Trend ◽

Antarctic Sea Ice ◽

Ice Coverage

Abstract. In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978–December 2010 reveal an overall positive trend in ice extents of 17 100 ± 2300 km2 yr−1. Much of the increase, at 13 700 ± 1500 km2 yr−1, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has, like the Arctic, instead experienced significant sea ice decreases, with an overall ice extent trend of −8200 ± 1200 km2 yr−1. When examined through the annual cycle over the 32-yr period 1979–2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 ± 6300 km2 yr−1 in February to a high of 24 700 ± 10 000 km2 yr−1 in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and Western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but differences in the magnitudes of the two trends identify regions with overall increasing ice concentrations and others with overall decreasing ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

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Antarctic sea ice variability and trends, 1979–2010

The Cryosphere ◽

10.5194/tc-6-871-2012 ◽

2012 ◽

Vol 6 (4) ◽

pp. 871-880 ◽

Cited By ~ 292

Author(s):

C. L. Parkinson ◽

D. J. Cavalieri

Keyword(s):

Indian Ocean ◽

Sea Ice ◽

Ross Sea ◽

Ice Cover ◽

Weddell Sea ◽

The Arctic ◽

Future Research ◽

Positive Trend ◽

Antarctic Sea Ice ◽

Ice Coverage

Abstract. In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978–December 2010 reveal an overall positive trend in ice extents of 17 100 ± 2300 km2 yr−1. Much of the increase, at 13 700 ± 1500 km2 yr−1, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has (like the Arctic) instead experienced significant sea ice decreases, with an overall ice extent trend of −8200 ± 1200 km2 yr−1. When examined through the annual cycle over the 32-yr period 1979–2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 ± 6300 km2 yr−1 in February to a high of 24 700 ± 10 000 km2 yr−1 in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but the magnitudes of the two trends differ, and in some cases these differences allow inferences about the corresponding changes in sea ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

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Spatio-temporal variability and decadal trends of snowmelt processes on Antarctic sea ice observed by satellite scatterometers

10.5194/tc-2019-27 ◽

2019 ◽

Author(s):

Stefanie Arndt ◽

Christian Haas

Keyword(s):

Time Series ◽

Sea Ice ◽

Weddell Sea ◽

Passive Microwave ◽

The Arctic ◽

Signal Frequency ◽

Onset Date ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

Perennial Ice

Abstract. The timing and intensity of snowmelt processes on sea ice are key drivers determining the seasonal sea-ice energy and mass budgets. In the Arctic, satellite passive microwave and radar observations have revealed a trend towards an earlier snowmelt onset during the last decades, which is an important aspect of Arctic amplification and sea ice decline. Around Antarctica, snowmelt on perennial ice is weak and very different than in the Arctic, with most snow surviving the summer. Here we compile time series of snowmelt-onset dates on seasonal and perennial Antarctic sea ice from 1992 to 2014/15 using active microwave observations from European Remote Sensing Satellite (ERS-1/2), Quick Scatterometer (QSCAT) and Advanced Scatterometer (ASCAT) radar scatterometers. We define two snowmelt transition stages: A weak backscatter rise indicating the initial warming and metamorphism of the snowpack (pre-melt), followed by a rapid backscatter rise indicating the onset of thaw-freeze cycles (snowmelt). Results show large interannual variability with an average pre-melt onset date of 29 November and melt onset of 10 December, respectively, on perennial ice, without any significant trends over the study period, consistent with the small trends of Antarctic sea ice extent. There was a latitudinal gradient from early snowmelt onsets in mid-November in the northern Weddell Sea to late (end-December) or even absent snowmelt conditions in the southern Weddell Sea. We show that QSCAT Ku-band (13.4 GHz signal frequency) derived pre-melt and snowmelt onset dates are earlier by 25 and 11 days, respectively, than ERS and ASCAT C-band (5.6 GHz) derived dates. This offset has been considered when constructing the time series. Snowmelt onset dates from passive microwave observations (37 GHz) are later by 13 and 5 days than those from the scatterometers, respectively. Based on these characteristic differences between melt onset dates observed by different microwave wavelengths, we developed a conceptual model which illustrates how the evolution of seasonal snow temperature profiles affects different microwave bands with different penetration depths. These suggest that future multi-frequency active/passive microwave satellite missions could be used to resolve melt processes throughout the vertical snow column.

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Spatiotemporal variability and decadal trends of snowmelt processes on Antarctic sea ice observed by satellite scatterometers

The Cryosphere ◽

10.5194/tc-13-1943-2019 ◽

2019 ◽

Vol 13 (7) ◽

pp. 1943-1958 ◽

Cited By ~ 1

Author(s):

Stefanie Arndt ◽

Christian Haas

Keyword(s):

Time Series ◽

Sea Ice ◽

Weddell Sea ◽

Passive Microwave ◽

Spatiotemporal Variability ◽

The Arctic ◽

Signal Frequency ◽

Onset Date ◽

Antarctic Sea Ice ◽

Perennial Ice

Abstract. The timing and intensity of snowmelt processes on sea ice are key drivers determining the seasonal sea-ice energy and mass budgets. In the Arctic, satellite passive microwave and radar observations have revealed a trend towards an earlier snowmelt onset during the last decades, which is an important aspect of Arctic amplification and sea-ice decline. Around Antarctica, snowmelt on perennial ice is weak and very different than in the Arctic, with most snow surviving the summer. Here we compile time series of snowmelt onset dates on seasonal and perennial Antarctic sea ice from 1992 to 2014/15 using active microwave observations from the European Space Agency's (ESA) European Remote Sensing (ERS) 1 and 2 missions (ERS-1 and ERS-2), Quick Scatterometer (QSCAT), and Advanced Scatterometer (ASCAT) radar scatterometers. We define two snowmelt transition stages: a weak backscatter rise, indicating the initial warming and destructive metamorphism of the snowpack (pre-melt), followed by a rapid backscatter rise, indicating the onset of thaw–freeze cycles (snowmelt). Results show large interannual variability, with an average pre-melt onset date of 29 November and melt onset of 10 December, respectively, on perennial ice, without any significant trends over the study period, consistent with the small trends of Antarctic sea-ice extent. There was a latitudinal gradient from early snowmelt onsets in mid-November in the northern Weddell Sea to late (end of December) or even absent snowmelt conditions in the southern Weddell Sea. We show that QSCAT Ku-band-derived (13.4 GHz signal frequency) pre-melt and snowmelt onset dates are earlier by 20 and 18 d, respectively, than ERS and ASCAT C-band-derived (5.6 GHz) dates. This offset has been considered when constructing the time series. Snowmelt onset dates from passive microwave observations (37 GHz) are later by 14 and 6 d than those from the scatterometers, respectively. Based on these characteristic differences between melt onset dates observed by different microwave wavelengths, we developed a conceptual model which illustrates how the seasonal evolution of snow temperature profiles may affect different microwave bands with different penetration depths. These suggest that future multi-frequency active and passive microwave satellite missions could be used to resolve melt processes throughout the vertical snow column of thick snow on perennial Antarctic sea ice.

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Physical and Structural Characteristics of Antarctic Sea Ice

Annals of Glaciology ◽

10.3189/s0260305500002627 ◽

1982 ◽

Vol 3 ◽

pp. 113-117 ◽

Cited By ~ 16

Author(s):

A.J. Gow ◽

S.F. Ackley ◽

W.F. Weeks ◽

J.W. Govoni

Keyword(s):

Sea Ice ◽

Structural Characteristics ◽

Weddell Sea ◽

The Arctic ◽

Mcmurdo Sound ◽

Frazil Ice ◽

Antarctic Sea Ice ◽

Pack Ice ◽

Fast Ice ◽

Ice Production

Observations during February and March 1980 of structures in 66 separate floes in Weddell Sea pack ice show widespread occurrence of frazil ice in amounts not previously reported in sea ice of comparable age and thickness in the Arctic. It is estimated that as much as 50% of the total ice production in the Weddell Sea is generated as frazil. Average floe salinities also appear higher than those of their Arctic counterparts. Comparative studies of fast ice at 28 locations in McMurdo Sound show this ice to be composed almost entirely of congelation ice that exhibits crystalline textures and orientations that are similar to those observed in Arctic fast ice. However, average fast-ice salinities in McMurdo Sound are higher than those reported for Arctic fast ice of comparable age and thickness.

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Organic iodine in Antarctic sea ice: A comparison between winter in the Weddell Sea and summer in the Amundsen Sea

Journal of Geophysical Research Biogeosciences ◽

10.1002/2014jg002727 ◽

2014 ◽

Vol 119 (12) ◽

pp. 2276-2291 ◽

Cited By ~ 12

Author(s):

Anna Granfors ◽

Martin Ahnoff ◽

Matthew M. Mills ◽

Katarina Abrahamsson

Keyword(s):

Sea Ice ◽

Weddell Sea ◽

Amundsen Sea ◽

Organic Iodine ◽

Antarctic Sea Ice

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Analysis Of Interannual Changes In Antarctic Sea-Ice Cover Using Passive Microwave Observations (Abstract only)

Annals of Glaciology ◽

10.3189/s0260305500003256 ◽

1982 ◽

Vol 3 ◽

pp. 350-350

Author(s):

H.J. Zwally ◽

J.C. Comiso ◽

C.L. Parkinson ◽

F.D. Carsey ◽

W.J. Campbell ◽

...

Keyword(s):

Sea Ice ◽

Ross Sea ◽

Open Water ◽

Mean Value ◽

Weddell Sea ◽

Passive Microwave ◽

Average Decrease ◽

Antarctic Sea Ice ◽

Ice Coverage ◽

Ice Concentration

A quantitative comparison of seasonal and interannual Antarctic sea-ice coverage over the four years 1973-76 has been accomplished through the use of passive microwave imagery from the Nimbus-5 satellite. For the entire Southern Ocean both the total ice extent (area with ice concentration greater than 15%) and the actual ice area (the spatially-integrated ice concentration) have decreased over this period of 4 a, but not uniformly in all regions. From 1973 to 1976 the annual-mean value of total ice extent decreased from 13.8 × 106 km2 to 12.1 × 106 km2, yielding an average decrease of 4.0% a−1. The inter-annual difference is greatest during the spring, as the ice decays, with the decrease in the December-mean averaging 8.4% a−1, the largest of any month. The decrease in the November-mean averaged 4.5% a−1. The overall decrease was principally due to the consistent yearly decrease of ice In the Weddell Sea sector (60°W to 20°E). Other sectors show less consistency. For instance, the ice in the Ross Sea sector (130°W to 160°E) increased from 1973 to 1974 and then decreased from 1974 to 1976, and no consistent trend is apparent in the ice extent between 20°E and 160°E. The total ice extent in the Bellingshausen- Amundsen seas sector (60°W to 130°W) actually increased slightly from 1973 to 1976. The area of the open water within the ice pack behaved differently from the total ice area, Increasing each year from February to November but having no clear interannual trend. A detailed analysis of the passive microwave imagery for the Antarctic region is planned for publication in an atlas.

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Antarctic summer sea ice concentration and extent: comparison of ODEN 2006 ship observations, satellite passive microwave and NIC sea ice charts

The Cryosphere Discussions ◽

10.5194/tcd-2-623-2008 ◽

2008 ◽

Vol 2 (4) ◽

pp. 623-647 ◽

Cited By ~ 3

Author(s):

B. Ozsoy-Cicek ◽

H. Xie ◽

S. F. Ackley ◽

K. Ye

Keyword(s):

Sea Ice ◽

Linear Trend ◽

Passive Microwave ◽

The Arctic ◽

Poor Correlation ◽

Sea Ice Concentration ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

Ice Concentration ◽

Ice Edge

Abstract. Antarctic sea ice cover has shown a slight increase in overall observed ice extent as derived from satellite mapping from 1979 to 2008, contrary to the decline observed in the Arctic regions. Spatial and temporal variations of the Antarctic sea ice however remain a significant problem to monitor and understand, primarily due to the vastness and remoteness of the region. While satellite remote sensing has provided and has great future potential to monitor the variations and changes of sea ice, uncertainties remain unresolved. In this study, the National Ice Center (NIC) ice edge and the AMSR-E (Advanced Microwave Scanning Radiometer – Earth Observing System) ice extent are examined, while the ASPeCt (Antarctic Sea Ice Process and Climate) ship observations from the Oden expedition in December 2006 are used as ground truth to verify the two products during Antarctic summer. While there is a general linear trend between ASPeCt and AMSR-E ice concentration estimates, there is poor correlation (R2=0.41) and AMSR-E tends to underestimate the low ice concentrations. We also found that the NIC sea ice edge agrees well with ship observations, while the AMSR-E shows the ice edge further south, consistent with its poorer detection of low ice concentrations. The northward extent of the ice edge at the time of observation (NIC) had mean values varying from 38 km to 102 km greater on different days for the area as compared with the AMSR-E sea ice extent. For the circumpolar area as a whole in the December period examined, AMSR-E therefore underestimates the area inside the ice edge at this time by up to 14% or, 1.5 million km2 less area, compared to the NIC ice charts. These differences alone can account for more than half of the purported sea ice loss between the pre 1960s and the satellite era suggested earlier from comparative analysis of whale catch data with satellite derived data. Preliminary comparison of satellite scatterometer data suggests better resolution of low concentrations than passive microwave, and therefore better fidelity with ship observations and NIC charts of the area inside the ice edge during Antarctic summer.

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A comparison of East Antarctic sea-ice motion derived using drifting buoys and remote sensing

Annals of Glaciology ◽

10.3189/172756401781818374 ◽

2001 ◽

Vol 33 ◽

pp. 139-144 ◽

Cited By ~ 17

Author(s):

P. Heil ◽

C.W. Fowler ◽

J. A. Maslanik ◽

W. J. Emery ◽

I. Allison

Keyword(s):

Sea Ice ◽

Microwave Radiometer ◽

Correlation Method ◽

Weddell Sea ◽

The Arctic ◽

Antarctic Sea Ice ◽

Spatial Coverage ◽

Surface Patterns ◽

Buoy Measurements ◽

Drifting Buoys

AbstractResults of East Antarctic (20−160° E) sea-ice motion derived from drifting buoys (collected in eight selected years between 1985 and 1997) are compared with sea-ice motion derived from sequential images from the 37 and 85.5 GHz channels of the Scanning Multichannel Microwave Radiometer (SMMR, 1979−87) and the Special Sensor Microwave/Imager (SSM/I, 1987−97). For the latitudes of interest, buoys yield velocity fields at 2 hourly resolution/while SMMR and SSM/I provide daily data. The spatial coverage of the drifting buoys is relatively sparse compared to the complete coverage of the southern sea-ice zone by SMMR and SSM/I, but the accuracy of the buoy position is better than ±280 m, while the resolution for the 85.5 GHz channel is only about 12.5 km, and about 25 km for the 37 GHz channel. The buoy measurements represent point motion, equal to the velocity of an individual ice floe, while the satellite data derived via the maximum cross-correlation method represent the motion of surface patterns within a gridcell. Comparison of the mean distributions of daily velocity derived from the datasets shows that while the broad-scale velocity patterns agree, the magnitude of the satellite-derived sea-ice velocities is significantly lower (typically by 40% or less) than the velocities derived from buoy measurements. This is in contrast with previous studies for the Arctic Ocean and the Weddell Sea, Antarctica. To elucidate differences in the velocity magnitude, individual trajectories from a number of drift regimes off East Antarctica are directly compared. Discrepancies between the two datasets are discussed with regard to the difference in spatial resolution of the data, the data-collection and −processing methods and the observed region.

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New estimates of Arctic and Antarctic sea ice extent during September 1964 from recovered Nimbus I satellite imagery

The Cryosphere ◽

10.5194/tc-7-699-2013 ◽

2013 ◽

Vol 7 (2) ◽

pp. 699-705 ◽

Cited By ~ 38

Author(s):

W. N. Meier ◽

D. Gallaher ◽

G. G. Campbell

Keyword(s):

Sea Ice ◽

Satellite Imagery ◽

Arctic Sea Ice ◽

Passive Microwave ◽

The Arctic ◽

Sea Ice Extent ◽

Antarctic Sea Ice ◽

1960S And 1970S ◽

The 1960S ◽

The Antarctic

Abstract. Visible satellite imagery from the 1964 Nimbus I satellite has been recovered, digitized, and processed to estimate Arctic and Antarctic sea ice extent for September 1964. September is the month when the Arctic sea ice reaches its minimum annual extent and the Antarctic sea ice reaches its maximum. Images from a three-week period were manually analyzed to estimate the location of the ice edge and then composited to obtain a hemispheric estimate. Uncertainties were based on limitations in the image analysis and the variation of the ice cover over the three-week period. The 1964 Antarctic extent is higher than estimates from the 1979–present passive microwave record, but is in accord with previous indications of higher extents during the 1960s. The Arctic 1964 extent is near the 1979–2000 average from the passive microwave record, suggesting relatively stable summer extents during the 1960s and 1970s preceding the downward trend since 1979 and particularly the large decrease in the last decade. These early satellite data put the recently observed record into a longer-term context.

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