As part of the NASA's DESDynI mission, global elevation profiles from contiguous 25 m footprint Lidar measurements will be made. Here we present results of a performance simulation of a single pass of the multi-beam Lidar instrument over uplifted marine terraces in southern Alaska. The significance of the Lidar simulations is that surface topography would be captured at sufficient resolution for mapping uplifted terraces features but it will be hard to discern I-2m topographic change over features less than tens of meters in width. Since Lidar would penetrate most vegetation, the accurate bald Earth elevation profiles will give new elevation information beyond the standard 30-m OEM

Blair, Bryan

Bruhn, Ronald

Hofton, Michelle

Lutchke, Scott

Sauber, Jeanne

NASA Technical Reports Server

DESDynI Lidar for Solid Earth Applications 
Jeanne Sauberl, Michelle Hofton2, Ronald Bruhn3, Scott Luthcke l, and Bryan Blairl 
INASA Goddard Space Flight Center, Greenbelt, MD 20771 
2University of Maryland, College Park, MD 20742 
3University of Utah, Salt Lake City, UT 84112 
Abstract-As part of the NASA's DESDynI mission, global 
elevation profiles from contiguous 25 m footprint Lidar 
measurements will be made. Here we present results of a 
performance simulation of a single pass of the multi-beam 
Lidar instru ment over uplifted marine terraces in southern 
Alaska. The significance of the Lidar simulations is that 
surface topography would be captured at sufficient resolution 
for mapping uplifted terraces features but it will be hard to 
discern I-2m topographic change over features less than tens of 
meters in width. Since Lidar would penetrate most vegetation, 
the accurate bald Earth elevation profiles will give new 
elevation information beyond the standard 30-m OEM. 
I. INTRODUCTION 
Although the primary objective of the DESDyni-Lidar is 
the recovery of vegetation structure for estimation of above 
ground biomass and for ecosystem health, the 25 m 
footprint, contiguous multi-beam data [1] will provide 
important new information on surface topography and 
topographic change. Over the last decade we have 
conducted a number of pre- and post-launch studies that 
support the rationale for the Lidar simulations reported here. 
For example, prior to the launch of the Ice, Cloud and land 
Elevation laser altimeter satellite (ICESat, single laser beam 
with 55-80 m footprints), we used NASA's Airborne 
Topographic Mapper [2] (ATM) to estimate how effective 
individual ICESat footprint data from exact repeat satellite 
tracks would be in recovering ice elevation change over the 
rapidly retreating lakobshavn Glacier. These simulations 
enabled us to identify an approach to successfully use 
ICESat plus InSAR derived digital elevation models (DEM) 
for ice elevation change on mountain glaciers [3,4] Also, 
we have used repeat Laser Vegetation Imaging Sensor 
(L VIS) measurements with full-waveform, 20-m contiguous 
footprints , to quantify pyroclastic and lava flow of a 
stratovolcano in Costa Rica[5]. In another study, near 
Barrow, Alaska, we introduced high quality ICESat derived 
positions into processing of ERS-1I2 data to improve the 
vertical resolution of the InSAR derived DEM by a factor of 
three [6]. An extension of this approach to fuse the 
moderate resolution multi-beam DESDynI-Lidar into 
processing of SAR data for derivation of DEM for a wider 
range of topographic slope and roughness could be 
especially useful outside SRTM coverage. 
The complex plate boundary in southern coastal Alaska 
provides an excellent setting for testing DESDyni 
capabilities to recover fundamental parameters of 
seismotectonic processes. Also, aircraft acquired Lidar and 
SAR data have been acquired in this region in the last 
decade that can be used for simulations. Here we use the 
National Center for Airborne Laser Mapping lidar 
(NCALM) data acquired over marine terraces west of Icy 
Bay ("Sullivan data") in southern Alaska in September 2005 
as part of the NSF STEEP study (www.ig.utexas.edu/steep). 
In this paper, we report on the simulation studies of the 
multi-beam Lidar instrument perfonnance over uplifted 
marine terraces, active faults and folds, and possible uplift 
associated with the 1899 Yakataga seismic event (M=8 ) in 
southern, coastal Alaska. 
II. ApPROACH 
In this performance study we created synthetic waveforms 
by extracting the NCALM point cloud data along one set of 
the DESDyni-Lidar calculated ground tracks (Fig. 1). We 
used a single pass of DESDynI-Lidar satellite ground tracks 
with 5 laser beams and across track spacing of - 850 m to 
geolocate the simulated waveforms. Each ground track had 
individual laser returns spaced 30 m along track (Fig. 1). 
-1 41' 53' -14 1'52' -14 1' 51' -1 41 ' 50' -141 ' 49' 
Fig_ L NCALM-derived topographic map of study region showing the 
marine terrace surfaces (I·IV) and the DESDynI-Lidar (NE-SW) ground 
tracks _ The offset between terrace surface 11 and III is frequently masked 
by alluvial depos its, A subtle offset of 1-2 m between terrace IV and III 
may be due to coseismic displacement associated with the 1899 M=8 
earthquake_ The northern portion of profi le # I crosses the Little River and 
is not included_ Inset: outline of Alaska with study area_ 
https://ntrs.nasa.gov/search.jsp?R=20110013379 2019-08-30T16:08:41+00:00Z
By accounting for sensor characteristics such as footprint 
size and the temporal and spatial distribution of laser 
energy, we generated pseudo-DESDynI waveforms from the 
last return point cloud data (Fig. 2) using the approach 
developed earlier for aircraft LVIS data [7]. Elevation 
measurements are extracted using information obtained in 
the waveform only. The lowest and highest elevations 
within each footprint correspond to the lowest and highest 
detected signals above a predefined threshold. The centroid 
of the waveform has also been extracted to investigate the 
precision and accuracy of this as an elevation measurement 
over the terrace surfaces. These waveform derived metrics 
have been compared to corresponding small-footprint 
elevations to assess their precision and accuracy. 
35 
~ 30 5 
= 
.g 
w 25 >-
v 
@ 
'T 
00 20 C/) 
0 
~ 
15 
0 100 200 300 400 
Amplitude (counts) 
Fig, 2, WGS84 elevation versus waveform amplitude for a simulated 
waveform over a footprint loeated along Track I near the transition from 
near-coastal terrace level IV to the next terrace level. The waveform has 
been simulated assuming DESDynI-like parameters for the observations 
(i,e" laser pulse width (9ns), laser footprint diameter (25m), waveform 
vertical resolution (2ns)), Random noise (2 counts) was also included to 
simulate background noise present in the measurement The range between 
the lowest and highest elevation could be due to a variable ground surface 
or NCALM Lidar returns from low-lying brush (higher curve), 
III. GEODETIC IMAGING OF SEISMOTECTONIC STRUCTURES 
IN SOUTHERN ALASKA 
Between Icy Bay and Cape Yakataga there are four 
marine terraces that range in elevation from approximately 1 
m to 50 m located on the southern flank of the Sullivan 
anticline, and in the footwall of the Sullivan thrust faultS. 
These features trend roughly east-west, a nearly optimum 
orientation for future roughly N-S DESDynI-Lidar ground 
tracks (Fig. 1). The terraces contain evidence for rapid 
uplift during large to great magnitude earthquakes [8]. 
Terrace surfaces are hundreds of meters to over a kilometer 
in width, partly buried by alluvial fans, and separated by 
remnant sea cliffs that mark the former shorelines. The 
Sullivan fault is marked by a prominent escarpment on the 
mountain above the highest terrace level; this feature is 
more evident to the west of the region shown in Fig. 1. The 
thick coastal forest and brush mask important aspects of the 
geomorphology on aerial photographs, standard DEM, and 
C-band synthetic aperture radar (SAR) images, a problem 
that is largely overcome by the NCALM Lidar data [9]. An 
advantage of even the medium footprint DESDynI-Lidar 
data over the standard existing 30 m DEM is the ability to 
see through the vegetation to discern the individual terrace 
heights, features of the escarpment associated with the 
Sullivan fault, and to map out the morphology of the 
Sullivan anticline. Additionally, the DESDynI-Lidar 
derived elevation profiles will be provided in a common 
global reference frame. This will facilitate fusion of this 
data with other DEM and satellite images. 
A. Centroid elevations along jive DESDynI-Lidar ground 
tracks 
The centroid elevation for each footprint has been used to 
create profiles along the 5 tracks shown in Fig. I. For 
example, the Track 2 and 3 profiles (from southwest to 
northeast) in Fig. 3 show offset (in red) of the distinct sloped 
surfaces (blue lines) associated with the 4 different terraces. 
Track 2 
Lldwde 
Track 3 
!~ef!rdc 
Fig. 3 Elevation profiles along Track 2 (top) and Track 3 (bottom) as a 
function of latitude with estimated offset (red) and terrace surface slope 
(blue), 
2 
We examined the centroid elevation plotted in Fig. 3 (blue 
diamond) compared to the highest and lowest elevation 
(above the background noise threshold) from the NCALM 
data. The elevation differences over the flat terrace surfaces 
were generally 2-4 m but over rough areas this difference 
could be larger (up to 9+ m). For the fairly flat terrace 
surfaces, the centroid elevation was generally in the middle 
of the upper and lower elevation bounds from the NCALM 
data. As expect for a 25 m footprint, the upper and lower 
bounds transition regions over faults or the terraces were 
large and variable relative to the centroid. 
The large offsets between individual terrace levels as well 
as the slope trends across terraces in a common reference 
frame enable more robust comparisons. For example, the 
terrace offsets are largest in Track 2 and then the offsets 
become more muted to the west, which cross alluvial fans 
that have formed on the lower terrace level following uplift, 
and partly bury the original sea cliffs (Fig. 1 and 3). In 
general, the individual terraces occur at lower elevations on 
the more westerly tracks, this partly caused by a lateral 
decrease in elevation away from the high points, or apices of 
a temporal sequence of alluvial fans that built out from 
Uttle River onto each terrace level. Only after accounting 
for lateral variations in alluvial fan aggradation on the 
terrace surfaces can we search for evidence of deformation 
and uplift related to earthquake slip or post-glacial uplift 
episodes to the east near Icy Bay. 
The significance of the DESDynI-Udar simulations is that 
surface topography is captured at sufficient resolution for 
mapping uplifted marine terraces, including the alluvial fans 
that built out and buried the marine deposits following 
uplift. Relic sea cliffs at the back of the terraces are also 
resolved as abrupt elevation steps with topographic relief 
dictated by the amount of post uplift burial by alluvial 
processes, and to a lesser degree erosional dissection. 
Although the moderate-scale topographic features are 
captured, uplift on features such as the 1899 berm that are 
just several tens of meters across in width are hard to 
discern in the DESDynI-Udar elevation profiles. 
B. Future steps in waveform simulation over the terraces 
To simulate the DESDynI-Lidar waveforms from aircraft 
point cloud Udar data, returns from all surfaces should be 
included as the full waveform representation is an important 
feature for identifying vegetation structure. The NCALM 
data retains the first and last Udar returns. In the next step 
of our simulation we will include both the first and last 
returns. We will estimate the ground elevation beneath any 
canopy using an automatic search algorithm. As mentioned 
in the Fig. 2 caption, the first (highest) curve may actually 
be reflections from low-lying brush. An advantage of full 
waveform Lidar systems such as LVIS and DESDynI-Lidar 
is that is it easier to associate the various returns with known 
vegetation structure. 
C. Ongoing simulations over fold and fault structures 
covered by glaCiers 
In the late summer of 2005, ATM laser swath E~48M m 
width) data [2] was acquired in coastal, southeastern Alaska 
and it included data from the Malaspina and Seward glaciers 
(https:/lwww.atm.wallops.gov). We used a version of this 
data (ICESSN standard nadir product) with a larger footprint 
size (80 m) to examine the ice characteristics along the 
A TM profile. In the lower Seward the glacier surface 
elevation, along track slope, and within footprint roughness 
and slope were used to identify thrust faults beneath the ice. 
These results are being used to interpret ice velocities 
derived from ALOS PALSAR L-Band InSAR data [9] 
IV. COSEISMIC SLIP RECOVERY SCENARIO FOR A SOUTHERN 
ALASKA EARTHQUAKE 
As summarized in the DESDynI Science Definition 
Document, "in areas where the surface is disrupted over the 
course of a large geophysical event such as coseismic 
displacement and shaking of the surface, the InSAR-derived 
surface deformations measurements cannot be made. It is 
helpful to take advantage of the Lidar to repeat elevation 
transects over the deformed surface to fill in some area of 
disruption." [10] As summarized above, we simulated 
waveforms along DESDynI-Lidar ground tracks over the 
uplifted region associated earlier great earthquakes with just 
one DESDynI-Udar pass assuming a 5 laser beam 
configuration. To estimate coseismic displacements 
following a large earthquake, it would useful to use an 
existing pre-earthquake DEM along with the DESDynI 
Udar over the region. Alternatively, if an off-nadir pointing 
capability exits, repeat targeting of the near-field coseismic 
deformation region would increase the number of transects 
over a short-coseismic interval. This ongoing study is 
enabling us to assess the minimum number of transects 
needed to provide timely, and spatially dense enough, data 
for estimation of earthquake parameters to calculate 
associated stress redistribution and triggered slip on nearby 
faults, inform detailed field studies, and to enable disaster 
managers to assess damage as discussed in the "Use Case 
Scenario" for a Seismic Event in California outlined in the 
Report of the DESDynI Applications Workshop [11]. 
V. SUMMARY 
Since DESDynI-Lidar would penetrate most vegetation, 
the accurate bald Earth elevation profiles will give new 
information beyond the standard 30-m DEM. In our 
southern Alaska study region, the major crustal 
seismotectonic features are roughly perpendicular to the 
satellite ground tracks and the accurate elevation profiles are 
enabling process studies of folds, faults, and marine 
terraces. For a major earthquake with on-land surface 
disruption, such as a thrust-slip event in southern Alaska, 
DESDynI-Udar could provide new and timely near-field 
vertical static displacements when used in combination with 
a pre-earthquake acquired DEM or with some off-nadir 
pointing to previous DESDynI-Udar transects. We have 
found that these new simulations inform prelaunch 
3 
strategies for maximizing our ability to expand the range of 
solid Earth applications for this medium resolution Lidar as 
part of the DESDynI mission. 
REFERENCES 
[1] J.B. Blair, J. Ranson, R. Dubayah, B Coyle, and C. Salerno, Multi-
beam Iidar instrument design, rneasurement capabilities, and technical 
readiness, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract G54-
A-03,2007. 
[2] W. B. Krabill, et aI., Aircraft laser altimetry of elevation changes of 
the Greenland ice sheet, technique and accuracy assessment, J. of 
Geodynamics, 34,357-376,2002. 
[3] J. Sauber, B. Molnia, C. Carabajal, S. Luthcke, and R. Musket(, Ice 
elevations and surface change on the Malaspina Glacier, Alaska, 
Geophys. Res. Left., 32, L23S01, doi:10.1029/2005GL023943, 2005. 
[4] R. R. Muskett, C.S. Lingle, J.M. Sauber, AS. Post, W.V. Tangborn, 
B.T. Rabus, K.A. Echelmeyer, Airborne and spaceborne DEM- and 
laser altimetry-derived surface elevation and volume changes of the 
Bering Glacier system, Alaska, USA, and Yukon, Canada, J. of 
Glaciology, 55(190), 1972-200, 2009. 
[5] M. A Hofton, E. Malavassi, and J. B. Blair, Quantifying recent 
pyroclastic and lava flows at Arenal Volcano, Costa Rica, using 
medium-footprint lidar, Geophy. Res. Lett., 33, L21306, 
doi: 10.1 029/2006GL027822, 2006. 
[6] D. K. Atwood, R. M. Guritz, R. R. Muskett, C. S. Lingle, J. M. 
Sauber, and J. T. Freymueller, DEM Control in Arctic Alaska with 
ICESat Laser Altimetry, IEEE Trans. on Geoscience and Remote 
SenSing, 45(11), 3710-3720,2007. 
[7] J.B. Blair and M.A. Hofton, Modeling large footprint laser altimeter 
returns using high-resolution elevation data, Geophys. Res. Lett. 
26:2509-2512,1999. 
[8] I. Shennan, R. Bruhn, and G. Plafker, Multi-segment earthquakes and 
tsunami potential of the Aleutian megathrust, QSR, 28(1), 7-13,2009. 
[9] R.L. Bruhn, J.M.Sauber, R.R. Forster, and M.M. Cotton, Geosphere-
Cryosphere interactions in the Saint Elias orogen, Alaska and Yukon, 
Eos Trans. AGU, Fall Meeting Suppl. Abstract G52B-94, 2009. 
[10] DESDynl Science Study Group, Deformation, Ecosystem Structure, 
and Dynamics of Ice (DESDynI), A NASA Mission in the NRC 
Decadal Survey Earth Science Applications from Space, Science 
Definition Document, R. Dubayah, B. Hager, and I. Joughin, co-
chairs, 2009. 
[11] A Donnellan, G. Bawden, and J. Rundle, Report of the DESDynI 
Application Workshop, 2009. 
4 


DESDynI Lidar for Solid Earth Applications

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server