Michelle Hofton Department of Geography, University of Maryland, College Park

1. 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 mhofton@umd.edu; 301 405 8543 J Bryan Blair NASA Goddard Space Flight Center, Greenbelt, Maryland Bryan.Blair@nasa.gov; 301 614 6741 David Rabine SSAI, Lanham, Maryland

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

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

4. Coverage Comparisons Proposed LVIS ‘09 Coverage (3 weeks) ICESat Repeat 33 day Coverage LVIS flight track from 9/20/07 300 km 300 km

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

6. LVIS Performance in Greenland, 2007 Histograms of elevation differences at coincident LVIS footprints: • LVIS data collected on 9/20/07 and 9/21/07 from ~27,000’ in P3-B. • Two ~850km long transects over ice sheet plus ~35 km long transect in the Summit area. • Elevations differences between coincident footprints used to evaluate system performance. With system calibration and multiple GPS base stations, similar performance could be expected in 2009. Percentage in bin (%) Elevation Differences (m) Mean difference Standard deviation (1) 0.00 m 0.00 m 0.01 m 0.08 m0.11 m 0.06 m From: Hofton et al. (2008), Geophysical Research Letters, DOI:10.1029/2008GL035774

7. Along-track Performance of LVIS Data in Greenland • 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). 204 419 • No obvious degradation in data precision over rough terrain (in this example, the feeder zone of Jakobshavn Glacier) From: Hofton et al. (2008), Geophysical Research Letters, DOI:10.1029/2008GL035774

8. Comparison of 2007 LVIS Data and ICESat Data • 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:10.1029/2008GL035774