the icesat-2 mission: laser altimetry of ice, clouds and land elevation t. markus, t. neumann nasa...
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The ICESat-2 Mission: Laser altimetry of ice, clouds and land elevation
T. Markus, T. Neumann NASA Goddard Space Flight CenterW. Abdalati Earth Science and Observation Center, Univ. of Colorado Boulder
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Draft Level 1 Baseline Science Requirements
ICESat-2 shall produce an ice surface elevation product that enables determination of ice-sheet elevation changes to 0.2 cm/yr accuracy on an annual basis.
ICESat-2 shall produce an ice surface elevation product that enables determination of annual surface elevation change rates on outlet glaciers to an accuracy of better than 0.25 m/yr over areas of 100 km2 for year-to-year averages, and along linear distances of 1 km along-track.
ICESat-2 shall produce an ice surface elevation product that enables resolution of winter (accumulation) and summer (ablation) ice-sheet elevation change to 2.5 cm at 25 km x 25 km spatial scales.
ICESAT-2 shall provide monthly near-repeat surface elevation measurements that enable determination of sea-ice freeboard to an uncertainty of 3 cm at 25 km x 25 km spatial scales for the Arctic Ocean and Southern Oceans.
ICESat-2 shall make elevation measurements for a minimum five-year duration.
ICESat-2 shall produce elevation measurements that enable determination of global vegetation height to 3-m accuracy at 1-km resolution.1
1- Development of a vegetation height model with 1-m accuracy at 1-ha resolution has been identified as a science requirement by the ecosystem structure research community. ICESat-2 will not achieve the vegetation science objectives, but rather will support them to the extent possible without compromising ice science objectives. Results from the ICESat mission suggest that ICESat-2 will be capable of producing a height surface with 3-m accuracy at 1-km spatial resolution, assuming that off-nadir pointing can be used to increase the spatial distribution of observations over terrestrial surfaces.
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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) areasImproved lead detection for sea ice freeboard.
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Ice Sheets and Sea Ice
aSDt and SDT analyzed suitability of micro-pulse multi-beam approach for ice sheets
• Sampling provided by multi-beam is significantly preferable to analog approaches• Amount of improvement directly related to number of beams
• Using nominal 15 cm range accuracy, configuration meets 25 cm/yrover 100 km2 and 2.5 cm over 25 km x 25 km areas.
Testing various approaches to extract freeboard has given biases of < 2.5 cm in freeboard.
Farrell, Markus, Miller, GSFC
Use ATM data (black) over sea ice to simulate ICESat-2 data product (magenta).
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Vegetation Assessment: Preliminary Analysis Approach
Study Area: SERC – a 140m x 900m section of Sigma Space photon-counting data 14 – 10m x 900m profiles extracted.
10 kHz simulation: 10 m footprint moved 70 cm along-track
ICESat-2 vegetation simulations
Concerns with vegetation data: Low energy beams may not penetrate closed canopy; vegetation has low reflectivity.
10 kHz results – n = 115:
s Mean (m) Std Dev (m)A -2.05 4.12B -1.59 4.43C 1.71 5.29
ReferenceA BC
Results:
Plots and data: Ross Nelson, GSFC
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Phase A studies:
1. Engineering design cases (already underway)• Level 1 science requirements do not provide engineering design metrics.• Established ~8 cases as engineering design tool.• Specify environmental conditions (roughness, cloudiness, reflectivity) for
instrument performance modeling.• 2 ice sheet interior, 2 outlet glacier, 2 sea ice, 2 vegetation.
2. Instrument configuration studies (underway; to be completed early 2010)• Select optimal footprint geometry and laser energy distribution• Select optimal pulse repetition rate for optimal
along-track sampling, data volume
4. High Altitude Aircraft (to be ready by 10/2010)• ICESat-2 simulator • Address engineering and science questions• Verification of design models
3. Vegetation Assessment • Rigorous assessment of existing aircraft vegetation data• Vegetation modeling using ICESat-2 design• Identify design choices to improve the prospects for veg. product
Current ICESat-2 footprint pattern
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The ICESat-2 Mission Timeline
• Feb. 2009: Mission Concept Review
• Nov. 2009: δ-Mission Concept Review
• 2009, 2010: Phase A Trade Studies
• May 2012: Mission Critical Design Review
• Oct. 2015: Launch Readiness Date
• 2016: ICESat-2 data collection begins