ICESat key findings
ICESat dH/dt
Thinning
Thickening
Most Ice Loss at Rough Steep Margins
ICESat-derived ice loss as a function of slope
Total Ice
Sheet
Loss
Fraction
of Total
175 GT
145 GT
>100%*
18%
132 GT
145 GT
83%
8.5%
68 GT
145 GT
43%
5.1%
40 GT
145 GT
26%
Slope
Fraction
of area
Estimated
Mass Loss
>0.5
°
33%
>1°
>2°
*>3°
there
is a net gain of ice in areas with slopes <0.5°
Slope < 3°
Total -117.5 GT/yr
Slope > 3°
Total -40.4 GT/yr
Zwally, Saba, GSFC
Arctic Sea Ice Observations
Summer sea ice extent is decreasing
faster than predicted by IPCC models.
From ICESat:
Sea ice thickness has decreased by
about 0.70 m;
Area of thick, multiyear ice has
decreased by 42%.
Stroeve et al., 2007
Kwok, 2009
ICESat-2 Mission Concept
In contrast to ICESat design, ICESat-2 will use
micro-pulse multi-beam photon counting
approach
Provides:
Dense cross-track sampling to resolve
surface slope on an orbit basis (different
sampling geometries are currently discussed
with the SDT).
High repetition rate (10 kHz) generates
dense along-track sampling (~70 cm).
Advantages:
Improved elevation estimates over high slope
areas and very rough (e.g. crevassed) areas
Improved lead detection
Current ICESat-2 design:
Current ICESat-2 design:
Flight direction
3km
100 m
3km
Footprint size: 10 m
PRF: 10 kHz (0.7 m)
ICESat vs ICESat-2
Planned ICESat coverage over Jakobshavn glacier.
Actual was 1/3 of this.
Planned
ICESat-2
Spacing
Bridging the gap between ICESat and ICESat-2
The big picture:
Ideally, there is temporal overlap of sequential satellite missions (ideally one year).
IceBridge goal: selective monitoring of ICESat tracks, over both ice sheets and sea
ice. Monitoring key areas that are undergoing rapid and potentially long-term
changes, such as the multiyear sea ice cover in the Arctic.
ICESat established time series of ice sheet
and sea ice thickness changes
IceBridge’s objective is to continue this
time series by flying over key regions every
year until the launch of ICESat-2
CryoSat2 is a radar altimeter but will yield
better spatial and temporal coverage; Xcalibration with IceBridge
ICESat-2 will continue monitoring with
improved measurement concept.
Arctic IceBridge Flights
(1) How can Ice Bridge instruments and flight lines benefit the scientific
analysis of existing ICEsat-1 data?
For grounded ice, we have already collected all the ICESat – airborne coincident data
that can be collected. Ice Bridge can contribute by continuing to support the analysis
of these existing data sets.
Continued monitoring of the cal/val targets used by ICESat (e.g. Track 412 or other
reference tracks) will contribute by placing the ICESat observation period into wider
context, and better characterizing ice sheet change on a variety of time and length
scales.
Monitoring tracks that span a range of surface slope, roughness, and reflectivity
would be ideal.
For sea ice, a major point of interest is the study of snow on sea ice and how this
impacts ice thickness retrievals from laser altimetry data. There are currently three
data sets used to determine snow thickness: passive microwave data, model data, and
climatological data. However, the error sources and biases in each of these methods
are still largely unknown. IceBridge data will provide a valuable data set to determine
errors and biases in these data sets. This will allow us to reanalyze previous ice
thickness estimates from ICESat data and better place the results into the climate
record.
(2) How can Ice Bridge data collections enhance the science transition
from ICESat-1 to ICESat-2?
By continuing the time series along selected tracks, we can place the changes
observed by ICESat into the context of the longer term changes in both the ice
sheets, as well as the sea ice.
Ideally, an instrument with a given set of characteristics used to cross-calibrate
with ICESat would also be used to cross-calibrate with ICESat-2. In practice,
instruments evolve over time. Consequently, it is imperative that altimetry
instruments used in Ice Bridge continue to be well-calibrated and wellchatacterized to maximize ICESat and ICESat-2 cross calibration capability.
ICESat-2 will be at lower orbit than ICESat. Once the ICESat-2 orbit is fixed, line
up some flights with ICESat-2 orbit.
Flight coordination with ICESat-2 calibration instrument MABEL. This will allow
comparison between ICESat-2 like instrument and other airborne laser
altimeters.
(MABEL is ICESat-2 simulator; first flights (primarily engineering in late October; first
science flights April 2011 out of Goose Bay and coordination with IceBridge (focus on ice
sheets); April 2012 (out of Alaska?) will have focus on sea ice).
MABEL April 2011
Goose Bay
(3) How do you think Ice Bridge data could help tie together ICEsat 1/2
and Cryosat science?
Continue to fly laser altimeters with radar altimeter measurements, ideally
at similar frequency as used on CryoSat.
Underflights of CryoSat tracks with both laser and radar altimeters
X-calibration of radar and laser altimeter measurements may allow us to
extrapolate IceBridge data to larger scales.
Coordination with flights of the ASIRAS instrument under CryoSat when
possible.
(4) How can Ice Bridge data best aid planning for ICESat-2?
MABEL data will be instrumental for ICESat-2 algorithm development, i.e.
extraction of geopysical information.
Coordination with IceBridge and its vast array of data sets will enable us to
estimate algorithm performance, errors sources, and uncertainties…..and
improve algorithms….
(5) Incorporate ICESat 1/2 project needs into a decision matrix for
IceBridge flight planning
ICESat / ICESat-2 needs largely fall into repeat flights along selected ground tracks,
and
Cross-calibration flights of opportunity between ASIRAS and MABEL.
Use previously collected ICESat data to identify areas of rapid change and
determine where IceBridge data collections will have the greatest impact.
Could be formalized through a decision matrix developed by the OIB science team.