Simulation of the CryoSat-2 satellite radar altimeter sea ice thickness retrieval uncertainty

Tonboe, Rasmus; Pedersen, Leif Toudal; Haas, Christian

doi:10.5589/m10-027

Cited by 21 publications

(45 citation statements)

References 24 publications

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“…The latter ones often cause highly negative freeboard values because the range estimate is no longer associated with the nadir return. Underestimation of freeboard for mixed ice cases has been demonstrated in a simulation study based on CryoSat-2 parameters [36]. To reduce biases in freeboard retrievals due to ambiguous waveforms, returns with increased PP and peak power over FYI or waveforms with widened leading edge are usually discarded for sea ice thickness retrievals in standard gridded products [3,37].…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of Radar Altimeter Waveform to Changes in Sea Ice Type at Resolution of Synthetic Aperture Radar

2019

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Radar altimetry in the context of sea ice has mostly been exploited to retrieve basin-scale information about sea ice thickness. In this paper, we investigate the sensitivity of altimetric waveforms to small-scale changes (a few hundred meters to about 10 km) of the sea ice surface. Near-coincidental synthetic aperture radar (SAR) imagery and CryoSat-2 altimetric data in the Beaufort Sea are used to identify and study the spatial evolution of altimeter waveforms over these features. Open water and thin ice features are easily identified because of their high peak power waveforms. Thicker ice features such as ridges and multiyear ice floes of a few hundred meters cause a response in the waveform. However, these changes are not reflected in freeboard estimates. Retrieval of robust freeboard estimates requires homogeneous floes in the order of 10 km along-track and a few kilometers to both sides across-track. We conclude that the combination of SAR imagery and altimeter data could improve the local sea ice picture by extending spatially scarce freeboard estimates to regions of similar SAR signature.

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Section: Discussionmentioning

confidence: 99%

Sensitivity of Radar Altimeter Waveform to Changes in Sea Ice Type at Resolution of Synthetic Aperture Radar

2019

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“…The CryoSat simulation, taking a surface elevation corresponding to the minimum 10% or 25% of values within a patch, is less successful, significantly overestimating R at representative footprint sizes (e.g., R > 6 for minimum 10% values over deformed ice and R > 5 over level ice). The mechanism by which the thinnest ice dominates the CryoSat return is not a simple “percentage minimum” as used in this simulation, however, but is dependent on surface roughness [ Tonboe et al , 2010, p. 64]: “The high backscatter magnitude from the thinnest ice within the footprint largely determines the elevation of the effective scattering surface” and has a significant effect down to very low percentage area coverage of the thinner ice type. Though it should be borne in mind that the CryoSat radar penetrates the snow layer, unlike the laser measurements considered here, it is clear that such characteristics will significantly affect CryoSat's ability to correctly report ice thickness over the varied ice terrain which forms the vast majority of Arctic pack ice.…”

Section: Discussionmentioning

confidence: 99%

“…As before, a circular patch of a given diameter is run over the data at half‐radius increments in both x and y directions. For surface elevation, we also calculate the result using the minimum value within each patch, as recent work suggests that CryoSat retrievals are largely determined by the thinnest ice within a footprint [ Tonboe et al , 2010]. ICESat is assumed to return the mean surface elevation within a footprint over snow covered surfaces [ Kwok et al , 2007] and we calculate the mean within each patch accordingly.…”

Section: Comparing Draft and Surface Elevationmentioning

confidence: 99%

“…Unfortunately, the only time this is less problematic, the summer, when all the snow masking the ice surface has melted, is also the time when radar altimeters cannot determine ice freeboard due to the presence of liquid water on the ice. The chosen ice and water densities also play a role, as does the prevalence of deformed ice, a mixture of ice types within the altimeter footprint and other important, radiometric, issues highlighted in recent work [ Tonboe et al , 2009, 2010].…”

Section: Introductionmentioning

confidence: 99%

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The relation between Arctic sea ice surface elevation and draft: A case study using coincident AUV sonar and airborne scanning laser

Doble¹,

Skourup²,

Wadhams³

et al. 2011

J. Geophys. Res.

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[1] Data are presented from a survey by airborne scanning laser profilometer and an AUV-mounted, upward looking swath sonar in the spring Beaufort Sea. The air-snow (surface elevation) and water-ice (draft) surfaces were mapped at 1 × 1 m resolution over a 300 × 300 m area. Data were separated into level and deformed ice fractions using the surface roughness of the sonar data. The relation (R = d/f ) between draft, d, and surface elevation, f, was then examined. Correlation between top and bottom surfaces was essentially zero at full resolution, requiring averaging over patches of at least 11 m diameter to constrain the relation largely because of the significant error (∼15 cm) of the laser instrument. Level ice points were concentrated in two core regions, corresponding to level FY ice and refrozen leads, with variations in R attributed primarily to positive snow thickness variability. Deformed ice displayed a more diffuse "cloud," with draft having a more important role in determining R because of wider deformed features underwater. Averaging over footprints similar to satellite altimeters showed the mean surface elevation (typical of ICESat) to be stable with averaging scale, with R = 3.4 (level) and R = 4.2 (deformed). The "minimum elevation within a footprint" characteristic reported for CryoSat was less stable, significantly overestimating R for level ice (R > 5) and deformed ice (R > 6). The mean draft difference between measurements and isostasy suggests 70 m as an isostatic length scale for level ice. The isostatic scale for deformed ice appears to be longer than accessible with these data (>300 m).Citation: Doble, M. J., H. Skourup, P. Wadhams, and C. A. Geiger (2011), The relation between Arctic sea ice surface elevation and draft: A case study using coincident AUV sonar and airborne scanning laser,

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“…One of the techniques used for determining sea-ice thickness from satellite altimetry is to measure sea-ice surface elevation relative to nearby leads (narrow cracks in the ice) to calculate ice freeboard and convert the freeboard to ice thickness. This technique assumes hydrostatic equilibrium, which may not be always true [15]. Sea-ice freeboard is calculated by subtracting the surface elevation of leads from the surrounding sea-ice surface elevations.…”

Section: A Sea Icementioning

confidence: 99%

Fine-Resolution Radar Altimeter Measurements on Land and Sea Ice

Patel

Paden

Leuschen

et al. 2015

IEEE Trans. Geosci. Remote Sensing

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Satellite radar altimeter (RA) measurements are important for continued monitoring of rapidly changing polar regions. In 2010, the European Space Agency launched CryoSat-2 carrying SIRAL, a Ku-band RA with objectives of determining the thickness and extent of sea ice and the topography of the ice sheets. One difficulty with Ku-band radar surveys over snow and ice is unknown penetration of RA signal into snow cover. Improving our understanding of the interactions of RA signals with snow and ice is needed to produce accurate elevation products. To this end, we developed a low-power, ultrawideband (12-18 GHz) RA for airborne surveys to provide fine resolution measurements capable of detecting both scattering from the surface and layers within sea ice and ice sheets. These measurements provide a means of identifying the dominant scattering location of lower resolution RA measurements comparable to satellite-based instruments. We generated two products: a full-bandwidth waveform (FBW) to identify scattering targets at fine resolution and a reducedbandwidth waveform (RBW) to represent conventional RA measurements. Retrackers are used to generate height estimates over various surface conditions for comparisons. Over ice sheets, the leading-edge tracker provided consistent ice-surface elevation measurements between the FBW and RBW results; however, there were significant differences between the results from the centroid tracker. Over sea ice, the location of the dominant return between the results from snow-covered sea ice is highly variable. This paper provides an overview of RA surveys in polar regions, a description of the CReSIS system, and a discussion of the results.

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Simulation of the CryoSat-2 satellite radar altimeter sea ice thickness retrieval uncertainty

Cited by 21 publications

References 24 publications

Sensitivity of Radar Altimeter Waveform to Changes in Sea Ice Type at Resolution of Synthetic Aperture Radar

Sensitivity of Radar Altimeter Waveform to Changes in Sea Ice Type at Resolution of Synthetic Aperture Radar

The relation between Arctic sea ice surface elevation and draft: A case study using coincident AUV sonar and airborne scanning laser

Fine-Resolution Radar Altimeter Measurements on Land and Sea Ice

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