Measurements of sea ice by satellite and airborne altimetry
A changing sea ice cover in the Arctic Ocean is an early indicator of a climate in transition, the sea ice has in addition a large impact on the climate. The annual and interannual variations of the sea ice cover have been observed by satellites since the start of the satellite era in 1979, and it h...
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| Format: | Book |
| Language: | English |
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DTU Space
2013
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| Online Access: | https://orbit.dtu.dk/en/publications/2b70450d-62a5-4de2-b255-dec7fc9b5f8b https://backend.orbit.dtu.dk/ws/files/80537655/PhD_SKRose.pdf |
| Summary: | A changing sea ice cover in the Arctic Ocean is an early indicator of a climate in transition, the sea ice has in addition a large impact on the climate. The annual and interannual variations of the sea ice cover have been observed by satellites since the start of the satellite era in 1979, and it has been in retreat every since. The mass balance of the sea ice is an important input to climate models, where the ice thickness is the most uncertain parameter. In this study, data from the CryoSat-2 radar altimeter satellite are used. CryoSat-2 has been measuring the sea ice in the Arctic Ocean since 2010, but there remain uncertainties in the accuracy of its elevation retrieval. A threshold retracker is developed to derive surface elevations and shows good results over the sea ice cover. To validate the satellite measurements, a comparative assessment of sea ice freeboard is presented, where airborne laser altimeter data from DTU Space together with data from the European Space Agency’s (ESA) CryoSat Calibration and Validation Experiment (CryoVEx) and the National Aeronautics and Space Administration’s (NASA) Operation IceBridge (OIB) are used over a first and multi-year ice area. Comparing the modal freeboard heights of 55 cm retrieved from the laser scanner data with the 25 cm retrieved from CryoSat-2 indicates a snow layer of 30 cm, due to the theory that a laser is reflected at the air/snow interface, while the radar is reflected at the snow/ice interface. In the other area, the modal freeboard is found to be 35 cm for both the airborne and satellite data implying, that the radar signal is here reflected from the snow surface, probably due to weather conditions. CryoSat-2 is very sensitive to returns from specular surfaces, even if they appear o_-nadir. This contaminates the “true” signal resulting in o_-ranging elevations. Filtering out these o_-ranging elevations are succeeded and results in more than 60% rejection of CryoSat observations. The correlation between the radar satellite and airborne laser ... |
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