Resumé
With the climate changing and the Greenland Ice Sheet (GIS) losing mass at an accelerating rate, the European Space Agency has established the Climate Change Initiative (ESA CCI) project in order to provide selected Essential Climate Variables (ECVs) for the GIS. The ECV presented here is the Ice Sheets (http://www.esa-icesheets-cci.org/) in which four parameters are to be determined: Surface elevation changes (SEC), ice velocities, grounding line locations, and calving front locations. The resulting data sets are to be openly distributed via the CCI web-site in transparent and easy-to-use formats. The production of the final data sets, dating from 1991 - present, is well underway. This presentation will provide a status overview of all four ECV parameters. As a preparation for the final data set computations, all ECVs carried out an open Round Robin (RR) exercise in order to find the most optimal method for producing the most reliable estimates. In the RR, the scientific community was asked to submit their best estimate of the given parameters along with a feedback sheet describing methodology, pre- and post-processing steps, etc. We outline the results of the SEC RR, where 11 participants from various US and European institutions provided estimates over the Jakobshavn Isbræ drainage basin. The participants used either Envisat radar or ICESat laser altimetry, and cross-over (XO), repeat-track (RT), and overlapping footprint analyses were made. Especially one of the results, based on Envisat RT, provided the first evidence for the possibility of using radar altimetry to accurately derive SEC estimates in both interior and margin parts of the GIS. This illustrates the potential for the final SEC product, which will be based on Envisat, Cryosat-2, and Sentinel-3 data. Through inter-comparisons and validation of the submissions, the most optimal method for deriving SEC values was found to be a combination of RT and XO algorithms, exploiting the high spatial resolution of RT and the low errors in XO. Thus, we can create a final data set with a high spatial resolution (5 x 5 km) and minimum errors. We present SEC results based on this combined module, derived from Envisat data. The exact method used for each grid point is determined in an error study of XO, RT and the combination, respectively, thus identifying the most reliable method. Initial results show that both XO and RT observe the thinning along Jakobshavn Isbræ; this places further confidence in the ability of radar data to resolve SEC even along narrow outlet glaciers. As the methods generally agree in margin regions, where surface topography otherwise distorts the signal, this analysis highlights the great potential of using radar altimetry to derive SEC estimates for the entire GIS.
Originalsprog | Engelsk |
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Sider | C11C-06 |
Status | Udgivet - 2013 |
Begivenhed | AGU Fall Meeting 2013 - San Francisco, California, USA Varighed: 9 dec. 2013 → 13 dec. 2013 |
Konference
Konference | AGU Fall Meeting 2013 |
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By | San Francisco, California, USA |
Periode | 9/12/13 → 13/12/13 |
Programområde
- Programområde 5: Natur og klima