WE2.L09 - DESDYNI LIDAR FOR SOLID EARTH APPLICATIONS
DESDynI-Lidar for Solid Earth Applications<br />J. Sauber1, M. Hofton2, R. Bruhn3, S. Luthcke1, B. Blair1<br />1NASA Goddard Space Flight Center<br />2 University of Maryland<br />3 University of Utah<br />Mahalo to Paul Rosen & Jon Ranson<br />
Simulations of DESDynI Lidar performance in Alaska:<br />-Can topography profiles from satellite Lidar advance seismotectonic process studies?<br /><ul><li> “Bald Earth” observations, 10-1 to 100 meters
25 m near contiguous & global georeferenced elevation profiles</li></ul>-Could we use DESDynI-Lidar to constrain coseismic uplift as per DESDynI Science Definition and DESDynI Applications documents?<br /><ul><li>Measuredcoseismic offset from a 1899 M=8 event
Alternate approaches for optimizing DESDynI-Lidar coseismic information </li></ul>DESDynI-Lidar + InSAR fusion for Solid Earth Applications<br />--How could fusion of Lidar-derived elevations into SAR processing be helpful? <br />
Glaciated seismotectonic plate boundary<br />in southern Alaska<br />Alaska<br />How often do 1899 + 1964 happen at the<br /> same time?<br />Is all the uplift due to earthquakes?<br />G of A<br />
Right: Example ICESat Waveform<br />(26 m)<br />Sullivan Anticline<br />Variable Canopy H<br />Terraces<br />BEARS!<br />Ground<br />Above: Photo of marine terraces from coastal region west of Icy Bay (and the Malaspina Glacier) Alaska, 1899 M=8 earthquake aftershock zone<br />Thick coastal forest and brush mask important aspects of the geomorphology on aerial photographs, standard DEM, and C-band synthetic aperture radar (SAR) images.<br />*<br />ICESat penetrates canopy but<br />density of obs. not optimal for SE processes<br />
Topographic map with marine terraces (I-IV) and ground tracks of one pass of DESDynI-Lidar with 5 beams<br />m<br />km<br /><ul><li>DESDynI Lidar Free-Flyer orbital parameters (Jan. 2010):</li></ul>-Altitude: 390 km<br />-Inclination: 97o<br />-5 beam configuration 1-5<br />-10 m post-positioning,<br />(important for fusion with other<br />remote sensing data)<br />I<br />II<br />III<br />5<br />Little River<br />4<br />IV<br />3<br />2<br />25m footprint<br />30m spacing along track<br />850m between beams<br />1<br />
Construction of DESDyn-I Lidar waveforms from NCALM point cloud returns:<br /><ul><li>Lidar waveform parameters:</li></ul>-laser pulse width, 9ns<br />-laser footprint diameter 25m, (1/e2)<br />-waveform vertical resolution 15cm <br />-threshold above simulated <br /> background noise<br /><ul><li>Use NCALM “last stop” point cloud</li></ul>return from “Sullivan” area<br />acquired as part of the NSF STEEP project.<br /><ul><li>For complex waveforms use</li></ul>either centroid or search algorithm to estimate ground return<br />?<br />(G)<br />Ground<br />Above: WGS84 elevation versus waveform amplitude for a simulated waveform from a footprint located along track #1. The returns between the highest and lowest elevation could be due to a variable ground surface (G) or NCALM lidar returns from low-lying brush.<br />
Elevation profile (Centroid in blue) along Track #2,3,4 as a function of latitude with the highest (+) and lowest ( )within footprint elevation above the noise threshold.<br />Track 2<br />Track 3<br /><ul><li>Large offsets between individual terrace levels as well as the slope trends across terraces in a common global reference frame enables more robust comparisons.
Individual terraces occur at lower elevations on the more westerly tracks</li></ul>Track 4<br />I<br />II<br />III<br />Coast<br />III<br />Coast<br />III<br />Coast<br />IV<br />IV<br />IV<br />
Number of NCALM returns in 25 meter footprint as a function of latitude along Track #4.<br />The dashed red line (----) indicates the number of points needed to have 1 return per m2.<br />
Measuring coseismic displacement in large earthquakes:<br />Measurement of near fault uplift/subsidence <br />with Lidar could provide additional constraints on surface expression of slip in an earthquake, especially for upper crustal faults in a SAR “hostile” environment.<br />SO, could we actually measure coseismic offsets with one acquisition of DESDynI of Lidar?<br />An Interferogram of recent Northern Mexico EQ based on ALOS PALSAR (M. Wei and D. Sandwell). One color cycle or fringe is 11.6 cm of line of sight deformation<br />
Use of SAR + Lidar ground control points (GCPs): Lessons learned from Barrow, Alaska study (Atwood et al., 2007): <br />Baseline Refinement: <br /><ul><li>ICESat (55-85m footprint) was useful for ERS-1/2 baseline refinement because elevation were accurate (<10 cm) and topography was modest.
The smaller DESDynI footprint (25 m) with near contiguous along track data and small across track distance would provide denser spatial sampling across an individual SAR scene.
The accurate and denser distribution of elevations (GCPs) could be especially useful outside of SRTM window at high latitudes. </li></ul>Multi-Mosaic stage (DEM creation): ICESAT was useful for distinguishing most accurate DEMS because of the vertical accuracy. DESDynI will additionally provide denser along track and across track sampling across DEMs. <br />Flow chart depicting InSAR processing with ICESat control to produce a DEM. Arrows on right represent steps where ICESat-derived elevations are employed for ground control. The processing steps shown in (a) are applied to each of the three ERS image pairs. The processing steps in (b) pertain to mosaicking of the resulting three DEMs into a single composite DEM.<br />
Lessons Learned and Future work:<br /><ul><li> A ground return search algorithm is under development and testing. An advantage of full waveform Lidar returns (over first and last returns) is that is it easier to associate returns with known vegetation structure of a region. We anticipate that the moderate footprint DESDynI Lidar waveforms will be useful for studying seismotectonic processes.
Coseismic displacements of > 1 m can be measured with one acquisition set and could be used to guide further acquisitions. Based on our previous studies using ICESat elevation profiles, however, DESDynI-Lidar profiles with an earlier InSAR derived DEM will enable recovery of a common mode uplift/subsidence signal. </li>