Mapping Greenland Using NASA’s Full- Waveform, Medium/High-Altitude, LVIS Lidar System: Potential 2009 Coverage and Expected Performance Michelle Hofton Department of Geography, University of Maryland, College Park J Bryan Blair NASA Goddard Space Flight Center, Greenbelt, Maryland David Rabine SSAI, Lanham, Maryland

NASA’s Laser Vegetation Imaging Sensor n NASA’s Laser Vegetation Imaging Sensor (LVIS) F Medium/high-altitude, waveform-recording lidar. F Utilizes medium-sized footprints to image topography and surface structure. n Operational since 1997: F Numerous missions for vegetation, solid earth studies. F Flown in Greenland in 2007 in NASA’s P3-B. n LVIS capability for Greenland 2009: F 2 km-wide swath. F 25 m-wide footprints. F 3-4cm range precision F 1-2m horizontal geolocation accuracy. F Contiguous footprints along and across track. F Tx&Return waveforms (10 bit, 1Gsamp/s) for each shot F Quicklook data in 1-2 months, final data in <6 months. F Plenty of link margin to penetrate through clouds. 2 km 10 km Nominal operating mode of LVIS Example LVIS Waveform Collected over Jakobshavn Glacier, 2007 Waveform amplitude (counts) Elevation above ITRF05 ellipsoid (m)

Proposed Greenland Mapping, May 2009 n Proposed LVIS Mapping in Greenland: F 11 flights, 60 ~E-W cross-country flight lines 44 km apart, and 4 ~N-S lines. F 3 week mission on DC-8, ~May F Will illuminate and sample ~5% of Greenland’s surface area. n Each line flown once, cloud issues minimized by flexible planning. n If required, additional flights to cover specifically-targeted areas. n Assumptions: F Using NASA’s DC-8 aircraft F 40,000’ altitude, 400 knot ground speed F 12 hr flights with 10 hrs for science F Thule, Sondrestrom, Keflavik base? 300 km LVIS lines, spaced 44km apart

Coverage Comparisons ICESat Repeat 33 day Coverage LVIS flight track from 9/20/ km Proposed LVIS ‘09 Coverage (3 weeks) 300 km

Swath Corridor n Example 2007 LVIS swath (from 25,000’) in vicinity of Jakobshavn with ICESat L3 (cloud free) footprint locations n From 30-40,000’ flying altitude, LVIS achieves a 2 km- wide swath over all of Greenland n Swath is sufficiently wide to capture all ICESat-1 tracks ICESat L3 Footprint Locations 500m 1km

LVIS Performance in Greenland, 2007 n LVIS data collected on 9/20/07 and 9/21/07 from ~27,000’ in P3-B. n Two ~850km long transects over ice sheet plus ~35 km long transect in the Summit area. n Elevations differences between coincident footprints used to evaluate system performance m 0.00 m 0.01 m 0.08 m 0.11 m 0.06 m Mean difference Standard deviation (1  ) From: Hofton et al. (2008), Geophysical Research Letters, DOI: /2008GL Elevation Differences (m) Percentage in bin (%) With system calibration and multiple GPS base stations, similar performance could be expected in Histograms of elevation differences at coincident LVIS footprints:

Along-track Performance of LVIS Data in Greenland n On average, elevation differences between coincident LVIS footprints had means of 0.0m, but along-transect variations of up to 5 cm occurred (likely caused by errors in the atmospheric model applied in the GPS trajectory calculations). From: Hofton et al. (2008), Geophysical Research Letters, DOI: /2008GL n No obvious degradation in data precision over rough terrain (in this example, the feeder zone of Jakobshavn Glacier)

Comparison of 2007 LVIS Data and ICESat Data n Comparing coincident LVIS (20m footprint) and ICESat (nominal 60m footprint) data in the Summit area. Although there are offsets between the ICESat L3b-h observations and LVIS, the standard deviations of the differences are <7cm (except L3C). From: Hofton et al. (2008), Geophysical Research Letters, DOI: /2008GL035774