Ice Sheet Science Questions

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Draft Ice Sheet Science Goals,
Objectives and Requirements
plus
Draft Science Team Terms of Reference
Strawman by KCJ and derived from the draft
Project plan and in particular the Table 3
Tracability matrix. Also culled info from
ISMASS Report and IGOS Theme page 86.
My out-of-thin-air additions are in red
OIB Ice Sheet Program Goals
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Make airborne altimetry measurements over the ice sheets and sea ice to
extend the record of observations begun by ICESat.
Link the measurements made by ICESat, ICESat-2, and CryoSat-2 to allow
accurate comparison and production of a long-term, ice altimetry record.
Use airborne altimetry to monitor key, rapidly changing areas of ice in the
Arctic and Antarctic to maintain a long term observation record, improve
understanding of glacial dynamics, and improve predictive models of sea
level rise and sea ice cover.
In conjunction with altimetry measurements, collecting other remotely
sensed data, improve predictive models of sea level rise and sea ice cover,
especially the following:
Ice thickness and structure;
Bed topography underlying land-based ice;
Bathymetry beneath floating ice shelves;
Snow accumulation and firn structure; and
Other geophysical constraints that will improve estimates of the
geothermal and oceanic heat flux.
Adapt existing instruments for airborne remote sensing of ice by
unmanned aerial systems such as NASA’s Global Hawk.
Provide a well vetted data set with ‘modeler-friendly’ formats to the
research community in a timely fashion
OIB Ice Sheet Science Themes
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What is the flux of ice from the polar ice sheets and what is required to reduce IPCC error
bounds on the contribution of ice sheets to global sea level rise [1]? OIB will collect surface
elevation change data and ice thickness measurements. In combination with available
spaceborne radar interferometry measurements of surface velocity, OIB will yield a precise
assessment of the mass fluxes from the Greenland Ice Sheet and from important sectors of
the Antarctic Ice sheet to reduce error bounds on mass balance assessment.
What causes observed abrupt changes in ice sheet motion? Does a rapid change in a
glacier always lead to a large change in the ice sheet volume [2]? OIB will accurately map
the sea water cavity beneath ice shelves, depth of grounded glaciers below sea level, how
far inland they remain below sea level, and the basal slopes. OIB will inform on subglacial
geology and, in the future, yield indirect measures of geothermal heating. These data will
feed ice sheet process studies and numerical models assessing areas capable of sustained
contribution to sea level rise.
How will the mass balance and dynamics of the ice sheets change in the future [1,2,3]? OIB
surface topography and ice thickness maps will constrain estimates of basal friction and
identify natural pathways for basal water. High fidelity surface digital elevation models
(DEMS) data will refine estimates of the gravitational driving stress that pushes the glacier
forward and will also improve estimates of the subglacial hydrologic potential that
determines the distribution of subglacial water. OIB surface and base digital elevation
models will be a primary input for predictive ice sheet dynamics models.
Is the Greenland Ice sheet, rimmed by outlet glaciers, an analog for the future of the
Antarctic Ice sheet, rimmed by outlet-glacier-fed ice shelves? If so, can lessons learned in
Greenland be extended to predict future behaviors in Antarctica? Are Alaskan/Canadian
glaciers and ice caps an analog for the eventual fates of both Greenland and Antarctica?
Ice Sheet Science Questions
• Where are glaciers continuing to thin and where may they be slowing/
thickening
– How can the ICESat, OIB, Cryosat, ICESat -2 measurements be optimized to characterize
the state of the ice sheets over several decades?
• What are the major forces and mechanisms causing the ice sheets to lose
mass and change velocity, and how are these processes changing over
time?
– How does the ice sheet/glacier surface topography, bed topography, bed geology,
geothermal heat, ice shelves/tongues, and grounding line configurations effect ice
dynamics?
– How and how far are horizontal stresses transmitted in the ice sheet?
– How far downstream do changing processes near the ice divide effect glacier flow
– What is the important scale for measuring geophysical parameters so as to substantially
improve modeling fidelity?
– Where is the subglacial water produced and where is it going?
– What is the sliding law and can repeat measurements be used to refine estimates of the
sliding law parameters?
• How do ocean, sea ice, ice sheet interactions influence ice sheet behavior
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How does the bathymetry beneath ice shelves and the ocean/ice sheet interaction
effect ice sheet/glacier flow dynamics?
How does bathymetry in fjords influence tide-water glaciers about Greenland?
Ice Sheet Science Questions
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When do ice shelves become unstable?
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What creates "granularity" in ice shelves? By granularity, we mean the bumpy texture
that creates the meltwater features that exist on entities like the pre-collapse Larsen B
Ice Shelf. Why should water fill crevasses on Larsen in a geometry such that the
fragments of the ice shelf created during collapse can capsize rather than float "top up"
as a tabular iceberg? This (the development of the proper granularity) is the key
constraint that differentiates a stable ice shelf from an ice shelf that can collapse
explosively.
At what scale are ice rises/rumples important for understanding ice shelf and
upstream ice sheet stability?
• What are yearly snow accumulation rates over the ice sheets?
– How do changing accumulation rates (and hence near surface densities and firn
structure) impact altimetry measurements
• What is the relative importance of ice sheet surface melt, and melt
hydrology on ice sheet mass balance and dynamics?
– What are the surface-melt flow-patterns and how much surface melt drains directly from
the surface and how much drains through channels within the ice sheet?
– How much annual surface melt refreezes in place and how much results in net wastage?
– What is the magnitude and spatial distribution of basal melt/freeze on ice shelves?
• Are there commonalities in bed geomorphology, surface/base hydrology
etc, that can be used to extend IceBridge-derived process-knowledge to
glaciers not overflown by IceBridge?
Ice Sheet Observational Goals
originally in section 1.3.1 of Draft Project Plan
• Monitor changes in Greenland and Antarctic ice-sheet elevations
during the gap in satellite coverage between ICESat-1 and ICESat-2.
• Provide a dataset for cross-calibration and validation of ice-sheet
elevations from satellite lidars (ICESat-1, ICESat-2, DesDynI-Lidar)
and radars (CryoSat-2 and Envisat).
• Provide a dataset for improving the ICESat-1 ice-sheet elevation
time series, including better characterization of ICESat-1 errors.
• Provide a data set for investigating unresolved ice sheet processes
• Provide a dataset for improving numerical models of ice-sheet
dynamics, especially maps of the bed beneath glaciers and ice
shelves.
• Provide a dataset for improving instrument simulation and
performance analysis in support of future missions, such as ICESat-2
and DesDynI-Lidar.
• Support, when feasible, field programs in Greenland and
Antarctica.
• Provide data tailored to support numerical ice-sheet-model intercomparisons
Science Requirements – Spatial Coverage
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Map and characterize the bedrock beneath land-based ice as follows: For Greenland:
establish a 100 km by 100 km grid and provide 10 km by 10 km grids over five major outlet
glacier catchments. For Antarctica, provide mapping over accessible outlet glaciers that
improve numerical models of ice sheet flow according to the priorities in #4. WHAT
PROPERTIES, WHAT ACCURACY
For each target glacier, collect data along the grounding line and along a parallel line 20 km
upstream of the grounding line
Determine bathymetry beneath ice shelves and sub-ice-sheet bedrock topography that
cannot be mapped with radar for target glaciers in Greenland and accessible portions of
Antarctica according to the priorities in #4.
IceBridge shall conduct flight experiments that enable the inter-calibration of the flight
instruments and the characterization of their errors TO WHAT SPECIFICATIONS
X km swath/Scan requirements on altimetry (proposed requirements on swath basal
topography)
Are there requirements for providing photographic data and photogrammetric DEMS?
Observations will be made in Greenland, Antarctica, Alaska and over Canadian Ice Caps.
IceBridge shall fly at least 250,000 total km per year, with 30,000 km per year specifically
along ICESat-1 tracks over sea ice and land ice. WHY THESE NUMBERS
IceBridge shall fly at least 500 km per year as underflights along CryoSat-2 tracks over sea ice
and land ice. THIS NEEDS A CAL/VAL Plan
IceBridge shall, for at least two field seasons, make altimetry measurements along a swath of
the southern limit of the ICESat-1 tracks, enabling direct comparisons of surface elevations
for a large number of ICESat-1 tracks. HOW LONG OF A SWATH
One ice thickness sampling grids for fast glacier/ice stream margins, grounding lines, ice rises
(adaptive gridding strategy?
One continuous ice thickness record around the ice sheet for flux estimates (located where?)
Science Requirements – Temporal
Sampling
• Ice sheet data should be collect in the spring and well prior to melt
onset
• One-time calving events and catastrophic ice shelf collapse events
should receive priority when the event is likely to result in
significant (30%) changes in upstream ice velocity
• Coincidence with field party activities should occur only in the
context of a well documented experiment plan integrated with OIB
objectives
• Cryosat underflights can occur up to one week before or after the
satellite pass (weather requirments?). (NEED CAL VAL PLAN)
• Is there a seasonal measurement requirement
• Is it necessary to collect repeat ice thickness and gravity
measurements? If so, how often
Science Requirements: Measurement
Accuracies
• 20 m vertical ice sheet base height accuracy for all ice covered
terrain
• 100 m vertical accuracy on sub-ice-shelf ocean-cavity thickness with
6 km horizontal sampling
• 10 cm vertical ice sheet surface height accuracy and 2 cm precision
across the scan
• 20 m vertical accuracy on radar internal layers for ice dynamics
(greater than 100 m deep)
• 10 cm vertical accuracy on radar internal layers for firn structure
(less than 100 m deep)
• 10 m horizontal geolocation accuracy
• 10% or 5 cm w.eq. accuracy of surface accumulation rate from snow
radar
• Absolute radiometric accuracy (2 dB) on VHF radar data sufficient
to discriminate basal rock from water
• Elevation measurements that enable determination of surface
slopes to an uncertainty of 0.06° (or about 10 kPa for 1000 m thick
ice).
Science Requirements Data Formats
• Data products formatted and documented for later
integration with earlier spaceborne and airborne data sets
• All data products referenced to WGS 84/polar stereographic
and DD lat long coordinates
• Instrument teams must provide point data. Interpolated grids
are highly desirable but not sufficient
• If gridded data are provided, how does the interpolation
scheme influence model interpretations (resistances to
driving stress are related to gradients in HRij so gridding will
bias derived results)?
Science Requirements on Future Missions
• Provide platform capabilities to extend
measurements spatially and temporally
beyond the reach of current platforms
• Provide 5-10 km wide swath measurements of
all key parameters
• Addition of magnetometer measurements for
characterizing basal sedimentary structures.
Glaciers
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IceBridge Mountain Glacier and Ice Cap Science Requirements
The objectives are:
To monitor changes in selected mountain glacier and ice-cap elevations during the gap in
satellite coverage between ICESat-1 and ICESat-2.
To provide a dataset for cross-calibration and validation of glacier and ice-cap elevations from
satellite lidars (ICESat-1, ICESat-2, DesDynI-Lidar) and radars (CryoSat-2 and Envisat). NEED
CAL/VAL , Mission Continuity Plan
To provide a dataset for improving the ICESat-1 ice-sheet elevation time series, including
better characterization of ICESat-1 errors.
To improve our understanding of tidewater glacier dynamics and the role that they play in the
stability of ice sheets.
To map the bed beneath selected mountain glacier and ice-caps.
Science requirements:
IceBridge shall provide annual surveys of the 50 most important glaciers and ice caps around
the Arctic to sea level rise estimates.
IceBridge shall provide at least 15,000 km of centerline profiles along these glaciers and ice
caps.
IceBridge shall provide swath maps with a 1-m x 1-m lidar point density, 500 meters wide,
with a 30-cm vertical accuracy. WHAT HORIZONTAL ACCURACY
IceBridge shall provide at least 50 crossovers with CryoSat-2 and ICESat tracks.
Science Team Terms of Reference
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Programmatic charge to the Science Team: The IST will work closely with the IceBridge Project
Scientists to provide expert scientific guidance to the IceBridge project in the areas of flight line planning,
measurement strategies, data quality control, and data product development. The Science team will:
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Assist the Project by
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Contribute to the OIB science objectives by
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Final development of the IceBridge Science Definition Document and Level-1 Scientific
Requirements Document;
Evaluation of the IceBridge mission designs in achieving the goals defined by the Science
Definition Document and Level-1 Scientific Requirements Document as requested by the NASA
Program Scientist; and
Support to the IceBridge Program Scientist and Project Scientist in the development of the required
analyses, documents and reporting during the IceBridge project.
Exploiting OIB data in support of a select set of science objectives
Assuring a level of data and meta data reliability, cross-instrument compatibility and accessibility
through use of the data in science investigations
Motivate investigations of all the OIB science objectives by encouraging broad use of the data by
the science community
Compile and regularly update a list of target glaciers for repeat monitoring and for continuation of
the ICESat record
Support OIB objectives by
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4.
Attending 3 team meetings per year
Participating in frequent teleconferences
Providing progress reports before each team meeting to the team leaders in the form of updates to
one-page summaries and which will include a schedule for deliverables.
Evaluating mission plans in the context of the OIB science objectives and specific requirements
Science Team Terms of Reference
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Science Team Organization
– The Program Scientist will appoint an ice sheet and a sea ice team leader for a one-year
rotating term and each will serve as co-chairs of science team meetings.
– Team leaders will be responsible for consolidating documentation, recommendations,
and analyses in support of same from the team, and providing that material to the Project
Scientist
– Team leaders will organize regular telecons and, with the project, organize 3 team
meetings.
– Team meetings will be convened at GSFC or JPL.
– Team members are encouraged to participate in project-organized outreach activities
such as AGU town hall meetings.
– All team members will report to the Program Scientist using the usual mechanism of
annual renewal proposals and as directed by the Program Scientist.
– In contrast to OIB activities to date, neither the team leaders nor the team members are
expected to participate in field deployments unless such work was previously proposed
and approved.
– STILL NEED CLARIFICATION ON THE FUNCTIONAL LINKS TO THE
INSTRUMENT TEAM AND THE SCIENCE WORKING GROUP
Issues and Random Thoughts
• Cal val sensor intercal plan
• Concise explanation/justification on each
objective/requirement
• Update tracability throughout the bullets
• Objectives and Requirements as a check list
for flight planning and instrument priorities
• What are the risks to the gravity measurement
inversions in the presence of undetected basal
marine ice?
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