| 1. |
- Aldenhoff, Wiebke, 1985, et al.
(författare)
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Comparison of ice/water classification in Fram Strait from C- and L-band SAR imagery
- 2018
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Ingår i: Annals of Glaciology. - : Cambridge University Press (CUP). - 0260-3055 .- 1727-5644. ; 59:76pt2, s. 112-123
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Tidskriftsartikel (refereegranskat)abstract
- In this paper an algorithm for ice/water classification of C- and L-band dual polarization synthetic aperture radar data is presented. A comparison of the two different frequencies is made in order to investigate the potential to improve classification results with multi-frequency data. The algorithm is based on backscatter intensities in co- and cross-polarization and autocorrelation as a texture feature. The mapping between image features and ice/water classification is made with a neural network. Accurate ice/water maps for both frequencies are produced by the algorithm and the results of two frequencies generally agree very well. Differences are found in the marginal ice zone, where the time difference between acquisitions causes motion of the ice pack. C-band reliably reproduces the outline of the ice edge, while L-band has its strengths for thin ice/calm water areas within the icepack. The classification shows good agreement with ice/water maps derived from met.no ice-charts and radiometer data from AMSR-2. Variations are found in the marginal ice zone where the generalization of the ice charts and lower accuracy of ice concentration from radiometer data introduce deviations. Usage of high-resolution dual frequency data could be beneficial for improving ice cover information for navigation and modelling.
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| 2. |
- Aldenhoff, Wiebke, 1985, et al.
(författare)
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COMPARISON OF SENTINEL-1 SAR AND SENTINEL-3 ALTIMETRY DATA FOR SEA ICE TYPE DISCRIMINATION
- 2019
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Ingår i: IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium. - 9781538691540
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper near co-incidental Sentinel-1 C-band SAR imagery and Sentinel-3 SRAL Ku-band altimeter data are compared for their capabilities of sea ice type discrimination. Knowledge of sea ice type is important for climate research and safety in Arctic offshore operations. First-year ice is characterised by a low SAR backscatter intensity in both HH and HV polarisation compared to multi-year ice, while the altimeter waveform parameters show high pulse peakiness and peak power compared to multi-year ice. Thus SAR imagery and altimetry can principally discriminate different ice types. The complexity of the backscattered radar signal however impedes a clear separation of the two types for all cases. Cross comparison of the two sensors offers an opportunity of high resolution validation data, which is often lacking for sea ice studies.
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| 3. |
- Carvajal, Gisela, 1983, et al.
(författare)
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Assessment of satellite and ground-based estimates of surface currents
- 2016
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Ingår i: 36th IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2016; Beijing; China; 10-15 July 2016. - New York : IEEE. - 2153-7003. ; 2016-November,, s. Art no 7730220, Pages 4675-4678
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Konferensbidrag (refereegranskat)abstract
- Estimation of surface currents still presents a challenge. In this work validates surface current estimates from the Maximum Cross Correlation (MCC) method, that uses spaceborne radiometer data, against ground-based retrievals from a High Frequency (HF) radar system. Moreover, these datasets have been compared with surface current data from two assimilated satellite products and four weather prediction models. The comparison shows large differences in the spatial resolution and the location of specific features. It is concluded that the variation of the observations may be due to the difference between the measuring or estimated method used in each case and the forces driving them.
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| 4. |
- Heuzé, Céline, 1988, et al.
(författare)
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Optimization of Sea Surface Current Retrieval Using a Maximum Cross-Correlation Technique on Modeled Sea Surface Temperature
- 2017
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 34, s. 2245-2255
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Tidskriftsartikel (refereegranskat)abstract
- Using sea surface temperature from satellite images to retrieve sea surface currents is not a new idea, but so far its operational near-real-time implementation has not been possible. Validation studies are too region specific or uncertain, sometimes because of the satellite images themselves. Moreover, the sensitivity of the most common retrieval method, the maximum cross correlation, to the parameters that have to be set is unknown. Using model outputs instead of satellite images, biases induced by this method are assessed here, for four different seas of western Europe, and the best of nine settings and eight temporal resolutions are determined. The regions with strong currents return the most accurate results when tracking a 20-km pattern between two images separated by 6–9 h. The regions with weak currents favor a smaller pattern and a shorter time interval, although their main problem is not inaccurate results but missing results: where the velocity is too low to be picked by the retrieval. The results are not impaired by the restrictions imposed by ocean surface current dynamics and available satellite technology, indicating that automated sea surface current retrieval from sea surface temperature images is feasible, for pollution confinement, search and rescue, and even for more energy-efficient and comfortable ship navigation.
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| 5. |
- Heuzé, Céline, 1988, et al.
(författare)
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Sea Surface Currents Estimated from Spaceborne Infrared Images Validated against Reanalysis Data and Drifters in the Mediterranean Sea
- 2017
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 9:5, s. Article Number: 422-
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Tidskriftsartikel (refereegranskat)abstract
- Near-real time sea surface current information is needed for ocean operations. On a global scale, only satellites can provide such measurements. This can be done with data from infrared radiometers, available on several satellites, thus giving several images a day. This work analyses the accuracy of such an estimation of surface current fields retrieved with the maximum cross correlation (MCC) method, here used to track patterns of Advanced Very High Resolution Radiometer (AVHRR) brightness temperature between 224 pairs of consecutive images taken between January and December 2015 in the western Mediterranean Sea. Comparison with in-situ drifters shows that relatively small patterns, moving at a slow speed, tracked between images separated by less than four hours give the best agreement. The agreement was strongest in summer, and consistent with low wind, non-eddying situations. When compared to a daily reanalysis field, the averaged satellite-retrieved fields showed good agreement, but not the in-situ drifter data. Drifter data should hence be used to complement satellite-retrieved currents rather than to validate them, since they may measure different components of the surface currents.
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