4 research outputs found
Improved retrieval of land ice topography from CryoSat-2 data and its impact for volume-change estimation of the Greenland Ice Sheet
A new methodology for retrieval of glacier and ice sheet elevations and
elevation changes from CryoSat-2 data is presented. Surface elevations and
elevation changes determined using this approach show significant
improvements over ESA's publicly available CryoSat-2 elevation product (L2
Baseline-B). The results are compared to near-coincident airborne laser
altimetry from NASA's Operation IceBridge and seasonal height amplitudes from
the Ice, Cloud, and Elevation Satellite (ICESat).
Applying this methodology to CryoSat-2 data collected in interferometric
synthetic aperture mode (SIN) over the high-relief regions of the Greenland
Ice Sheet we find an improvement in the root-mean-square error (RMSE) of 27
and 40 % compared to ESA's L2 product in the derived elevation and
elevation changes, respectively. In the interior part of the ice sheet, where
CryoSat-2 operates in low-resolution mode (LRM), we find an improvement in
the RMSE of 68 and 55 % in the derived elevation and elevation changes,
respectively. There is also an 86 % improvement in the magnitude of the
seasonal amplitudes when compared to amplitudes derived from ICESat data.
These results indicate that the new methodology provides improved tracking of
the snow/ice surface with lower sensitivity to changes in near-surface
dielectric properties.
To demonstrate the utility of the new processing methodology we produce
elevations, elevation changes, and total volume changes from CryoSat-2 data
for the Greenland Ice Sheet during the period January 2011 to January 2015.
We find that the Greenland Ice Sheet decreased in volume at a rate of 289 ± 20 km3a−1, with high interannual variability and spatial
heterogeneity in rates of loss. This rate is 65 km3a−1 more
negative than rates determined from ESA's L2 product, highlighting the
importance of CryoSat-2 processing methodologies.</p
Time-evolving mass loss of the Greenland Ice Sheet from satellite altimetry
Mass changes of the Greenland Ice Sheet may be estimated by the input–output
method (IOM), satellite gravimetry, or via surface elevation change rates
(dH/dt). Whereas the first two have been shown to agree well in
reconstructing ice-sheet wide mass changes over the last decade, there are
few decadal estimates from satellite altimetry and none that provide a
time-evolving trend that can be readily compared with the other methods.
Here, we interpolate radar and laser altimetry data between 1995 and 2009 in
both space and time to reconstruct the evolving volume changes. A firn
densification model forced by the output of a regional climate model is used
to convert volume to mass. We consider and investigate the potential sources
of error in our reconstruction of mass trends, including geophysical biases
in the altimetry, and the resulting mass change rates are compared to other
published estimates. We find that mass changes are dominated by surface mass
balance (SMB) until about 2001, when mass loss rapidly accelerates. The onset
of this acceleration is somewhat later, and less gradual, compared to the
IOM. Our time-averaged mass changes agree well with recently published
estimates based on gravimetry, IOM, laser altimetry, and with radar altimetry
when merged with airborne data over outlet glaciers. We demonstrate that,
with appropriate treatment, satellite radar altimetry can provide reliable
estimates of mass trends for the Greenland Ice Sheet. With the inclusion of
data from CryoSat-2, this provides the possibility of producing a continuous
time series of regional mass trends from 1992 onward
Four decades of Antarctic surface elevation changes from multi-mission satellite altimetry
We developed a multi-mission satellite altimetry analysis over the Antarctic
Ice Sheet which comprises Seasat, Geosat, ERS-1, ERS-2, Envisat, ICESat and
CryoSat-2. After a consistent reprocessing and a stepwise calibration of the
inter-mission offsets, we obtained monthly grids of multi-mission surface
elevation change (SEC) with respect to the reference epoch
09/2010 (in the format of month/year) from 1978 to 2017. A validation with independent elevation
changes from in situ and airborne observations as well as a comparison with a
firn model proves that the different missions and observation modes have been
successfully combined to a seamless multi-mission time series. For coastal
East Antarctica, even Seasat and Geosat provide reliable information and,
hence, allow for the analysis of four decades of elevation changes. The
spatial and temporal resolution of our result allows for the identification
of when and where significant changes in elevation occurred. These time
series add detailed information to the evolution of surface elevation in such
key regions as Pine Island Glacier, Totten Glacier, Dronning Maud Land or
Lake Vostok. After applying a density mask, we calculated time series of mass
changes and found that the Antarctic Ice Sheet north of 81.5∘ S was
losing mass at an average rate of -85±16 Gt yr−1 between 1992 and
2017, which accelerated to -137±25 Gt yr−1 after 2010.</p