**Post-launch ICESat Science Team Contributions by the Laboratories for
Space Geodesy and Planetary Geodynamics at NASA's Goddard Space Flight
Center**

**David Harding, Scott Luthcke, David Rowlands, Jeanne Sauber, Claudia
Carabajal, and Teresa Williams**

**February 1, 2005**

This document describes post-launch contributions to the ICESat Science
Team by members of Laboratories for Space Geodesy (Code 697) and
Planetary Geodynamics (Code 698) within the Solar System Exploration
Division at NASA's Goddard Space Flight Center. Prior to January, 2005
these organizations were branches within the Laboratory for Terrestrial
Physics (LTP). The work by this group was initiated by Jack Bufton,
ICESat Science Team member and former LTP Associate Chief for Sensors.
Summaries are provided for contributions in two areas, Data Calibration
and Validation, and Science Applications. Additional contributions in
the areas of Instrument Operations, Data Processing and Visualization,
and External Collaborations and Student Training are also listed.

## Contents

**1. Data Calibration and Validation Contributions**

> 1.1 Calibration & Reduction of ICESat Geolocation Errors for Change
> Detection
>
> **1.2 Profile Matching for Geolocation Validation**
>
> **1.3 Waveform Matching for Land Products Validation**

**2. Science Applications Contributions**

> **2.1 Integration of ICESat and SRTM Land Topography Data**
>
> **2.2 Vegetation Height and Biomass from Combined ICESat and SRTM
> Data**
>
> **2.3** **ICESat Observations of Inland Surface Water Stage and
> Slope**
>
> **2.4 ICESat Results for Southern Alaska Glaciers**
>
> **2.5 Ice Sheet Mass Change from a Combination of ICESat and GRACE
> Data**
>
> **2.6 Topographic Changes Associated with the Sumatra Earthquake**

**3. Instrument Operations Contributions**

**4. Data Processing and Visualization Contributions**

**5. External Collaborations and Student Training**

6\. References

1\. Data Calibration and Validation Contributions

1.1 Calibration and Reduction of ICESat Geolocation Errors for Change
Detection

# 

# 1.1.A. Analysis and results

![](media/image1.pct){width="10.166141732283464in"
height="6.95in"}![](media/image2.pct){width="13.082677165354331in"
height="6.95in"}The accurate horizontal and vertical geolocation of the
ICESat Geosciences Laser Altimeter System's (GLAS) surface returns is a
critical issue in the scientific application of these data. Laser
pointing, ranging, timing and orbit errors must be compensated to
accurately geolocate the laser altimeter surface returns. Towards this
end, we have exploited the laser range observations in an integrated
residual analysis to accurately calibrate these geolocation/instrument
parameters *\[Luthcke et al., 2002, 2003a, 2003b\]*. Although we have
applied our techniques to the recovery of all geolocation/instrument
parameters (pointing, ranging, timing and orbit), currently pointing
errors, and errors that manifest themselves as pointing (e.g. field of
view shadowing), represent the dominant geolocation error source.
Furthermore, pointing errors directly impact the calibration of other
geolocation parameters (e.g. range biases). Therefore, the results and
analysis presented here concentrate on the calibration and correction of
pointing errors. The ICESat laser altimeter data have been processed as
direct altimetry from ocean scans (OS) and "round"-the-world scans
(RTWS - continuous OSs for an orbit revolution) along with dynamic
crossovers in order to calibrate, correct and validate laser pointing
biases, along with complex long-period and orbital period variation.
These scans are special spacecraft maneuvers that we have designed to
calibrate pointing errors as accurately as possible *\[Luthcke et al.,
2000\].*

Figure 1 presents the OS and RTWS range residual pointing calibration
results for two representative laser operation periods (L2A and L3A)
using release 18 of the ICESat data products. Laser operations period 2A
(L2A) represents our best performing time period where full Stellar
Referencing System (SRS) pointing corrections were available and
applied. Due to instrument specific problems, full SRS data is not
available for laser operations period L3A. The OS and RTWS range
residual pointing recovery ("effective pointing") accounts for both
transmit and receiver effects such as field of view (FOV) shadowing,
while the SRS accounts for transmit effects. Individual OS range
residual analysis pointing calibration results (left in Figure 1) and
orbital pointing variation recovered from RTWS range residual analysis
(right in Figure 1) demonstrate there are significant long-period and
orbital effective pointing variations remaining in the data. These
remaining effective pointing errors induce significant time varying,
geographically correlated systematic geolocation errors, adversely
impacting such analysis as change detection and range bias estimation.

![](media/image5.pct){width="6.0in" height="1.888976377952756in"}

The calibration results shown in Figure 1 have been used to develop
functional corrections for the observed time varying bias and orbital
variations for both the L2A and L3A periods. These "effective pointing"
corrections account for both transmit and receiver effects, such as
field of view (FOV) shadowing. For a first attempt at this correction,
we have applied a first iteration solution for the time varying bias and
a single average orbital variation correction for each observation
period. The current correction solution (corrv2) results in significant
geolocation accuracy improvement as shown in Figures 2 and 3.
Improvement in Greenland and Antarctica crossover residual statistics
are shown in Figure 2. The Greenland and Antarctica data were not used
in the development of the corrections and provide an independent
assessment. The effective pointing corrections result in significant
improvement in geographically correlated error as shown in the
Antarctica crossover residuals averaged in 5 degree bins (Figure 3).

![](media/image7.pct){width="5.625196850393701in"
height="1.952755905511811in"}

![](media/image9.pct){width="5.193700787401575in"
height="2.098031496062992in"}![](media/image10.pct){width="5.193700787401575in"
height="2.098031496062992in"}

We are currently refining this analysis and correction technique using
release 19 of the ICESat data products. Release 19 includes an
Instrument Star Tracker (IST) distortion correction that accounts for
high-frequency attitude error. The elimination of this high-frequency
IST error has improved our calibrations. Therefore, initial results from
our new L2A calibrations and correction show still further improvement
over the results shown here using this initial release 18 data analysis
*\[Luthcke et al., 2005\].* For example ice sheet crossovers, computed
using L2A release 19 days 275-282, improve from 19.2 cm RMS to 14.6 cm
RMS using our effective pointing corrections. This would then suggest
the corrected data is meeting the 11 cm elevation accuracy mission
requirement, assuming the errors in the crossing tracks are independent.
We are in the process of further validation and then final application
of these corrections into a new release 20 ICESat data product for each
observation period. With these effective pointing corrections applied,
the elevation accuracy for each observation period is expected to meet
the initial mission requirement.

**1.1.B. GEODYN algorithm and software development**

In order to perform the above calibration, correction and error
analysis, extensive GEODYN algorithm and software development has been
performed. GEODYN is an orbit determination and geodetic parameter
estimation software package. It accepts a wide range of tracking data
types including altimetry. Although GEODYN is developed and maintained
in the Laboratory for Space Geodesy (Code 697) at NASA\'s Goddard Space
Flight Center, it is distributed to various university and government
research groups.

GEODYN has the ability to use laser altimetry in the form of ranges to
the Earth\'s surface (direct altimetry) and also in the form of
crossover constraint equations to estimate parameters. GEODYN\'s already
existing laser altimetry capability was expanded for the ICESat mission.
As a result, GEODYN is used by the ICESat mission to determine
sub-arcsecond laser pointing corrections in roll and pitch. The
infrastructure and experience gained from ICESat will benefit future
altimeter missions.

Because ICESat measures attitude at laser observation epochs, GEODYN was
upgraded to use attitude information taken directly at observation times
(as opposed to interpolating at measurement times). This reduces the
effect of jitter. Also, because biases in pointing are likely caused by
thermal effects and therefore unlikely to remain constant over any
significant period of time, GEODYN was given the ability to estimate a
wide range of time dependent pointing parameters. With this suite of
parameters, we were able to account for the time varying pointing biases
and orbital variations induced by thermal mechanical variation, as
discussed above.

**1.2 Profile Matching for Geolocation Validation**

To validate the horizontal accuracy of geolocation solutions derived by
the integrated residual analysis method, we have developed a procedure
for matching elevation profiles to Digital Elevation Models (DEMs) with
moderate resolution (10 to 90 m) for areas with rugged topographic
relief *\[Rowlands et al. (2000), Luthcke et al. (2002)\]*. Footprint
elevations are differenced with the corresponding DEM value, and the
standard deviation of the differences establishes a residual for the
profile as a whole. As profiles are systematically shifted over the
DEMs, the proper geolocation of the profile is established by the
location of the residual minima (Figure 4). We are applying this
approach using U.S. National Elevation Data DEMs produced by the U. S.
Geological Survey and Shuttle Radar Topography Mission (SRTM) DEMs
produced by a joint NASA-NGA mission. The method has documented the
increasing improvement in ICESat geolocation accuracy as refined
calibrations and new data releases are produced *\[Carabajal et al.,
2003\]*. The geolocation accuracy of the upcoming release 20 product,
which will incorporate full pointing calibration corrections, will be
systematically assessed with this method.

![](media/image13.pct){width="6.681102362204724in"
height="5.161023622047244in"}

**1.3 Waveform Matching for Land Products Validation**

ICESat altimeter channel waveforms measure within-footprint relief due
to ground slope and roughness, structures and vegetation cover. In order
to validate waveform-derived elevation parameters, such as highest,
average, and lowest illuminated surfaces within laser footprints, as
well as footprint geolocation results, we have developed a grid-based
waveform simulation capability to compare observed ICESat waveforms to
synthetic waveforms produced from high resolution (1-5 m) Digital
Elevation Models (DEMs) *\[Harding and Carabajal, 2005\]*. We simulate
the instrument's response to complex topographic surfaces, including the
laser far-field energy pattern, boresight field-of-view alignment, and
detector impulse response. Comparison to synthetic waveforms derived
from high-resolution airborne laser mapping data demonstrates that
ICESat waveforms provide detailed and accurate information on the
within-footprint distribution of surface heights (Figure 5). In
addition, the location of maximum correlation between observed and
computed waveforms provides a high-resolution assessment of geolocation
accuracy on a footprint-by-footprint basis. We are now applying this
simulation capability to assess ranging errors due to waveform
distortion introduced by atmospheric forward scattering, waveform
saturation, and field-of-view shadowing.

![](media/image15.png){width="6.125196850393701in"
height="4.186614173228347in"}

### 2. Science Application Contributions

### 

### 2.1 Integration of ICESat and SRTM Land Topography Data

Understanding the quality of land topography data sets, as represented
in Digital Elevation Models (DEMs), is crucial to their use in land
process studies and in detection of topographic changes obtained from
comparison of DEMs acquired at different times. ICESat elevation data
provides a globally distributed data set of very high accuracy that is
being used to independently estimate the vertical accuracy of
continental DEMs with 30 m and 90 m spatial resolution produced by the
joint NASA-NGA Shuttle Radar Topography Mission (SRTM). We have
documented elevation differences between ICESat and SRTM C-band
elevations for various regions of the world with variable topography and
vegetation cover *\[Carabajal and Harding, 2005\]*. In vegetated
regions, ICESat data enables the estimation of radar phase center
elevation biases with respect to top of canopy, waveform centroid, and
underlying ground. Correlations of ICESat to SRTM elevation differences
have been established with local relief, land cover, waveform extent, a
surrogate for canopy height, and waveform relative centroid height, a
surrogate for canopy closure. Regional analyses have been conducted in
southern Alaska, the U.S Pacific Northwest (Figure 6), Amazonia, East
Africa, Tibetan Plateau, Himalayan Mountains, and western Australia.
Future ICESat data product releases will include the SRTM elevation and
local relief for each laser footprint location, facilitating global
analyses using these complimentary elevation measurement systems. This
combination of ICESat and SRTM will produce the most accurate global
land topographic data available for the Earth.

![](media/image16.png){width="5.988188976377953in"
height="3.883464566929134in"}

**2.2** **Vegetation Height and Biomass from Combined ICESat and SRTM
Data**

Although the exchange of carbon between the atmosphere and forested
ecosystems is a vital component of the global carbon cycle, it is a
portion of the cycle that is not well-characterized nor well-understood.
Lidar remote sensing has a unique capability for estimating forest
canopy height, which has a direct and increasingly well-understood
relationship to aboveground carbon storage *\[e.g. Lefsky et al,
2002\]*. While ICESat has collected an unparalleled data set of lidar
waveforms over terrestrial targets, processing of GLAS data to create
reliable estimates of forest height is complicated by sloped-ground
surfaces within the large diameter ICESat footprint that cause waveform
broadening and a resulting overestimate of vegetation height. With
external collaborators, a method has been developed to correct this
broadening effect using SRTM data to quantify local relief at ICESat
footprint locations *\[Lefsky et al., 2005\]*. Biome-specific regression
of estimated tree height, based on ICESat waveform width and SRTM local
relief, versus maximum tree height observed in 63 field plots in three
biomes (Amazonia and the U.S. Southeast and Pacific Northwest) yields a
prediction of 74% of the observed variance (Figure 7, left). For the
Amazon plots, estimated tree height accounts for 74% of the variance in
aboveground biomass, derived from field measurements of stem diameter
and tree height (Figure 7, right). The linear regression relationship
applies to stands having a broad range of aboveground biomass, unlike
passive optical and radar backscatter methods that become insensitive
for stands of moderate to high biomass. Aboveground biomass results for
the U.S. Southeast and Pacific Northwest are in progress. These initial
results demonstrate that combined ICESat and SRTM data has the potential
to provide global inventory data on forest height and aboveground
biomass with accuracies significantly exceeding other currently
available satellite-based observations.

![](media/image17.png){width="3.046456692913386in"
height="2.2216535433070868in"}![](media/image18.png){width="3.1251968503937007in"
height="2.191732283464567in"}

**2.3** **ICESat Observations of Inland Surface Water Stage and Slope**

River discharge and changes in lake, reservoir and wetland water storage
are critical terms in the global surface water balance, yet they are
poorly observed globally and the prospects for adequate observations
from in-situ networks are poor. Measurements of water surface height
(stage), slope, and extent provide a means to remotely monitor inland
water storage and river discharge. ICESat data are being used to
demonstrate the potential for satellite laser altimetry measurements of
these inland water parameters and their contribution to global water
balance monitoring *\[Harding and Jasinski, 2004\]*. For example,
exact-repeat profiling of a portion of the lower Mississippi River on
three dates documents river stage and slope measurement precision of 10
cm and 1 cm per km at and between crossings of channel meanders,
respectively (Figure 8, upper right). Changes in ICESat-derived stage,
average slope of the reach, and local slopes between meander crossings
are observed between the three profiles, and the stage changes correlate
with in-situ gage measurements (Figure 8, lower). Continuing work is
documenting stage and slope retrieval capabilities as a function of
cloud cover (frequency and optical depth) and return signal strength
(dependent on off-nadir angle and water roughness).

![](media/image19.png){width="5.0in" height="4.9374015748031495in"}

**2.4** **ICESat Results for Southern Alaska Glaciers**

The glaciers of the southeastern Alaska coastal region are the largest
temperate glacier meltwater source on Earth and may contribute one third
of the total glacier meltwater entering the global ocean. Since melt
onset and refreeze timing in this region shows a tendency toward earlier
onset and longer ablation seasons, accelerated glacier wastage may be
occurring \[*Ramage and Isaacs*, 2003; *Arendt et al., 2002*\]. Mountain
glaciers generally have rougher surfaces and steeper regional slopes
than the ice sheets for which the ICESat design was optimized. However
we found that by working with well-located individual returns, combined
with earlier geodetic data, we could use ICESat to estimate short-term
elevation change and ice change over the last decade. In three studies
we report elevation changes on two of the largest temperate glacier
systems on Earth, the Bering Glacier and the Malaspina Glacier systems
(Figure 9). Additionally we examined the relation between melting
glaciers, earthquake faulting, and earthquake hazard in this same
region.

# 2.4.a. Wastage of the Malaspina Piedmont Lobe: SRTM versus ICESat (2000-2004)

*Sauber et al.,* *\[2005\]* report and interpret ice elevation change
between a digital elevation model (DEM) derived from the Shuttle Radar
Topography Mission (SRTM C-band) observations in Feb. 2000 and ICESat
Laser 1-3 observations between Feb. 2003 and Nov. 2004. Between 2000 and
2004 ice elevation decreases of 10-30 meters occurred across the central
Malaspina piedmont lobe (Figure 10).

![](media/image22.jpeg){width="5.918897637795276in"
height="3.65748031496063in"}

.

**2.4.b. Elevation change in the Bagley Ice Valley and Bering Glacier
piedmont lobe: aircraft laser altimetry versus ICESat (1995-2004)**

Ongoing retreat of the Bering Glacier since 1905 has been interrupted at
least six times by glacier surges. *Sauber et al.,* *\[2004\]* used
aircraft laser altimetry measurements made in 1995 by *Echelmeyer et
al., \[2002* *NSIDC notes*, *see also* *Arendt et al.,* *2002,
Echelmeyer et al., 1996\]* and ICESat measurements in 2003/2004 to
estimate the elevation changes in the surge reservoir and receiving area
following the most recent (1993-1995) surge. Between 1995 and 2004 we
estimated \>10 meters of elevation increase occurred in the Bagley Ice
Valley accumulation region (Figure 11) and in the upper reaches of the
Bering Glacier piedmont lobe the surface elevation decreased by 27
meters.

![](media/image23.jpeg){width="4.65748031496063in"
height="3.7838582677165356in"}

**2.4.c. Winter elevation increase (2003/2004) from sequential ICESat
measurements across the the snow accumulation regions on the Bagley Ice
Valley and Seward Glacier**

Few direct glaciological observations are available for the source
region of the large Alaska glaciers. Snow accumulation rates have been
largely inferred from low-altitude precipitation and temperature data.
Comparing sequential ICESat observations in the Malaspina source region
(Seward Glacier), we estimated short-term elevation increases of up to 5
meters during the winter of 2003/04. In the Bagley Ice Valley, the snow
accumulation was \~3 meters in the flat regions (Figure 11).

**2.4.d.** **Melting glaciers, earthquake faulting and hazard**

The rapid wastage of southern Alaska glaciers occurs in a region under
going rapid tectonic strain accumulation *\[Sauber et al., 2000; Sauber
and Molnia, 2004\]*. We are using ICESat observations, along with
earlier geodetic data, to estimate the temporal and spatial fluctuations
in ice mass, to evaluate their influence on earthquake hazard, and to
identify surface offset features due to earthquake faulting. For
example, some surface features of the Malaspina Glacier observed with
ICESat may be correlated with the seismically active Malaspina fault
*\[Wiest et al., 2004\].*

**2.5 Ice Sheet Mass Change from a Combination of ICESat and GRACE
Data**

A major goal of the ICESat mission and the NASA Oceans and Ice Program
is to investigate and monitor ice sheet mass balance on scales that
significantly affect sea level. Along with ICESat's observations of
surface height change, the GRACE mission's ultra-precise inter-satellite
range and range rate measurements provide a complementary form of remote
sensing with their ability to detect gravity (mass) change. By its very
nature, temporally varying surface height, *dh/dt*, obtained from
altimetry is a boundary condition that has a somewhat ambiguous
relationship to the underlying mass flux. In addition, altimeter data
acquired over specific narrow surface transects require spatial
filtering and interpolation to deduce height changes over broader
regions. The simultaneous determination of height and gravity from the
ICESat and GRACE missions can reduce many of the ambiguities associated
with the current state of ice sheet mass balance. In addition to our
groups work on improving the ICESat data geolocation accuracy for change
detection, we have also developed unique approaches in GRACE data
processing and mass change recovery. Specifically, we have developed a
capability to recover local/regional gravity changes using non-global
functional representations (i.e. surface anomalies vs. global spherical
harmonics) from the GRACE data *\[Rowlands et al. 2002 and 2005\].* We
are beginning to exploit the unique strengths within our team to process
both the level 1 GRACE and ICESat data. Using unique ICESat and GRACE
analysis approaches we hope to provide an improved methodology to
reliably estimate mass flux over regional (e.g. large glaciers, ablation
zones, etc.) and basin-wide scales. We will assess the utilization of
the ICESat and GRACE data in simultaneous solutions for Antarctic and
Greenland mass flux across co-observed periods.

**2.6 Topographic Changes Associated with the Sumatra Earthquake**

ICESat repeat-profiling detection of elevation change can substantially
contribute to documenting the spatial pattern of crustal deformation
caused by the December, 2004 Sumatra magnitude 9.0 earthquake and
aftershocks. Preliminary modeling by Chen Ji, of the deformation pattern
associated with the main event using teleseismic data shows significant
deformation limited to a 450 km long section of the southern Sunda
Trench, off the west coast of Sumatra (Figure 12). Most of the
deformation is below sea-level; modeled on-land deformation in Sumatra
is relatively small, \< 1 m vertical and \< 3 m horizontal, probably
below ICESat detection capabilities using repeat profiles. However,
based on the spatial distribution of aftershocks, the fault rupture zone
extends an additional 1,000 km northward along the Sunda subduction
zone. Anecdotal reports in this region from the Andaman and Nicobar
Island chains describe uplift by as much as 3 m and and satellite images
document uplift of island-fringing coral reef platforms above sea level.
Four ICESat tracks, with cloud-free data acquired in the fall of 2003
and 2004, cross the Andaman and Nicobar Islands (Figure 12). The spatial
pattern of uplift, documented by exactly repeating these profiles, will
help constrain models of slip distribution on the fault plane, a key to
understanding this event and future subduction zone mega-earthquakes.
Repeat profiling is planned for 2005. Acquisition of these new ICESat
profiles will require the greatest pointing control accuracy achievable,
so as to exactly repeat the prior profiles. Also, the best-possible
calibration of pointing, timing, range, and orbit biases will be needed
to recover the elevation changes along these profiles at the sub-meter
level.

![](media/image24.pct){width="3.5062992125984254in"
height="4.538188976377953in"}![](media/image25.pct){width="2.0661417322834645in"
height="2.66259842519685in"}![](media/image26.png){width="1.4263779527559055in"
height="4.192913385826771in"}

**3. Instrument Operations Contributions**

Following L1A operations, developed round-the-world scan calibration
methodology to document waveform skew introduced by FOV shadowing and
establish orbital variation in transmitted beam and receiver pointing
(Luthcke, Harding)

Following L1A operations, contributed to revision of on-board gain
algorithm to reduce the level and frequency of waveform saturation
(Harding, Carabajal, Sauber)

Following L1A operations, provided Alaska examples over steep, glaciated
terrain to Instrument team for revision of GLAS data acquisition
algorithm (Sauber)

Following L2A operations, documented truncation of broad waveforms for
areas of steep slopes and/or tall vegetation and recommended waveform
compression correction which was adopted (Harding, Sauber)

Following L2A operations, identified incorrect implementation of range
gating associated with off-nadir targets of opportunity causing data
loss and recommended correction which was adopted (Harding)

Following L2C operations, recommended methodology for daily monitoring
of gain algorithm performance and waveform saturation which was adopted
(Harding, implemented by Saba)

Following L1A and L2A operations, coordinated reporting and integration
of observations related to FOV offsets associated with temperature
changes (Harding, Luthcke, Carabajal))

For L2 observations, coordinated targeting ICESat on calibration sites
for vegetation cover and inland water (Harding, Lefsky, Carabajal)

For L3A observations, coordinated targeting ICESat on Mount St. Helens
during period of renewed volcanic activity (Harding)

For L3B observations, coordinated targeting ICESat on Andaman and
Nicobar Island chains to determine topographic changes (uplift,
subsidence, tilting) associated with Sumatra M9.0 earthquake and
aftershocks (Harding)

**4. Data Processing and Visualization Contributions**

Established appropriate threshold level for definition of alternate
signal start and end (Harding)

Identified missing or miss-specified parameters in GLA structures
including alternate signal start offset, and beam azimuth and
co-elevation angles (Harding, Carabajal)

Documented and validated GLA orientation parameters and their
relationship to the GLAS optical bench including track azimuth, transmit
beam azimuth and co-elevation, and footprint azimuth (Carbajal, Harding)

Revised and documented alternate Gaussian waveform fitting to
significantly improve representation of complex waveforms by preserving
six peaks and constraining base level (Harding, implemented by Roberts)

Recommended and specified improvements to GLAS Data Visualizer,
including save/restore of plot parameters and export of footprint
latitude and longitude (Harding, implemented by SCF staff)

Evaluated flagging of saturated land returns and recommended revised
implementation to properly identify saturated returns and provide a
measure of degree of saturation (Harding, not yet implemented)

Evaluated Gaussian fitting correction for saturated returns (fit leading
edge and preserve area) and identified problems with the implementation
(Harding, in on-going collaboration with SCF staff)

Recommended and specified use of SRTM 90 m DEM as source to provide GLA
land elevation values (Harding, Carabajal, Sauber, implemented by SCF
staff but not yet included in data releases)

**5. External Collaborations and Student Training**

All members of the team have supported external users in their
understanding and use of the ICESat data products, and have
significantly contributed to the production of release notes that
facilitate data use by outside collaborators and the general research
community. Specifically, explanations have been provided on geolocation
accuracy, the spatial and temporal coverage for land products, the
definition and method of production for land and waveform product
parameters, and best use of products to achieve specific objectives.
Team members have also contributed to outreach efforts by presenting
information on the general objectives of the mission, calibration
efforts and scientific results at workshops, university seminars, and
international meetings. External collaborations, all of which include
student training in the use of ICESat data, resulting in presentations
at scientific conferences include:

1*. Darius Mitchell, Case Western Reserve,* EGU-AGU presentation,
Mitchell, D. J. Sauber, D. Harding, C. Carabajal, W. Krabill, S.
Manizade, J. Bufton, 2003, Expected ICESat measurement of glacier
elevation change, Geophysical Research Abstracts, v. 5, 04153, European
Geophysical Society.

2\. *Katy Wiest, University of Texas at El Paso,* AGU presentation,
Wiest, K.R., J.M. Sauber, A. A. Velasco, D.L. Doser, and J.M. Hurtado,
2004, The relationships between earthquakes, faults and recent glacier
fluctuations in southern Alaska, *Eos Trans. AGU*, *85(47),* Fall Meet.
Suppl. Abstract S53A-0179.

3\. *Reiji Muskett, University of Alaska*, IGARSS presentation, Muskett,
R., C. Lingle, R. Guritz, D. Atwood, J. Sauber, R. Gens, N.
LaBell-Hamer, and B. Kerrin, 2004, DEM control in Arctic Alaska with
ICESat altimetry.

4\. *Michael Lefsky, Colorado State University*, AGU presentation,
Lefsky, M.A., Harding, D.J., Warren, W.B., and Keller, M., 2004,
Estimating forest canopy height from Geoscience Laser Altimeter System
waveforms and Shuttle Radar Topography Mission digital elevation models,
*Eos Trans. AGU, 85*(47), Fall Meet. Suppl., Abstract C21B-07.

**6.** **References**

Arendt, A.A., K.A. Echemeyer, W.D. Harrison, C.S. Lingle, and V. B.
Valentine, 2002, Rapid wastage of Alaska glaciers and their contribution
to rising sea level, *Science*, 297, 382-386.

> Carabajal, C.C., D.J. Harding, J.L. Bufton, S.B. Luthcke and D.D.
> Rowlands, 2003, ICESat Geolocation and Land Products Validation: Laser
> Altimetry Profile and Waveform Matching, International Archives of
> Photogrammetry, Proceedings of the ISPRS workshop on 3D mapping from
> InSAR and Lidar, WG I/3-WGII/2, Portland OR.

Carabajal, C.C., and D.J. Harding, 2005, ICESat Validation of SRTM
C-Band Digital Elevation Models, *Geophysical Research Letters*, ICESat
topical issue, submitted.

Echemeyer et al., 1996, Airborne surface profiling of glaciers: A case
study in Alaska, *Journal of Galciology*, 42(142), 538-547.

Harding, D.J., and Carabajal, C.C., 2005, Validation of ICESat Waveform
Observations of Within-footprint Canopy Structure and Ground Relief,
*Geophysical Research Letters*, ICESat topical issue, submitted.

Harding, D.J., and Jasinski, M.F., 2004, ICESat Observations of Inland
Surface Water Stage, Slope, and Extent: a new Method for Hydrologic
Monitoring, *Eos Trans. AGU, 85*(47), Fall Meet. Suppl., Abstract
C21B-05.

Lefsky, M.A., W.B. Cohen, D.J. Harding, G.G. Parker, S.A. Acker, and
S.T. Gower, 2002, Lidar remote sensing of aboveground biomass in three
biomes, *Global Ecology and Biogeography*, 11(5): 393-399.

Lefsky, M.A., Harding, D.J., Cohen, W.B., Keller, M., Carabajal, C.C.,
2005, Estimating forest canopy height and aboveground bimass from ICESat
waveforms and Shuttle Radar Topography Mission digital elevation models,
*Geophysical Research Letters*, ICESat topical issue, submitted.

Luthcke, S.B., Carabajal, C.C and D.D. Rowlands, 2002, Enhanced
Geolocation of Spaceborne Laser Altimeter Surface Returns: Parameter
Calibration from the Simultaneious Reduction of Altimeter Range and
Navigation Tracking data, *Journal of Geodynamics*, Vol. 34, No. 3-4,
pp. 447-475.

Luthcke, S.B., D.D. Rowlands, F.G. Lemoine, N.P. Zelensky and T.A.
Williams, 2003, GPS-based Precision Orbit Determination for a New Era of
Altimeter Satellites: Jason-1 and ICESat, Proceedings from the Flight
Mechanics Symposium, NASA Goddard Space Flight Center

Luthcke, S.B., D.D. Rowlands, C.C. Carabajal, D.J. Harding, J.L. Bufton
and T.A. Williams, 2003, ICESat Laser Altimeter Pointing, Ranging and
Timing Calibration From Integrated Residual Analysis: A Summary of Early
Mission Results, Proceedings from the Flight Mechanics Symposium, NASA
Goddard Space Flight Center.

Luthcke, S.B., Rowlands, D.D., McCarthy, J.J., Stoneking, E. and Pavlis,
D.E., 2000, Spaceborne Laser Altimeter Pointing Bias Calibration From
Range Residual Analysis, *Journal of Spacecraft and Rockets*, Vol. 37,
No. 3, pp. 374-384.

Luthcke et al., 2005, Calibration and reduction of ICESat geolocation
errors and the impact on change detection, *Geophysical Research
Letters*, ICESat topical issue, submitted.

Ramage, J. M., and B. L. Isacks, 2003, Interannual variations of
snowmelt and refreeze timing on southeast-Alaska icefields, U.S.A.,
*Journal of Galciology*, 49(164), 102-116.

Rowlands, D. D., C. C. Carabajal, S. B. Luthcke, D. J. Harding, J. M.
Sauber, and J. L. Bufton, 2000, Satellite Laser Altimetry: On-Orbit
Calibration Techniques for Precise Geolocation, *The Review of Laser
Engineering*, Vol. 28, No. 12, pp. 796-803.

Rowlands, D.D., R.D. Ray, D.S. Chinn, F.G. Lemoine, 2002, Short-arc
analysis of intersatellite tracking data in a gravity mapping mission,
*Journal of Geodesy*, 76, pp. 307-316.

Rowlands, D.D., S.B. Luthcke, S.M. Klosko, F.G.R. Lemoine, D.S. Chinn,
J.J. McCarthy, C.M. Cox, O.B. Anderson, 2005, Resolving mass flux at
high spatial and temporal resolution: 'mascon' estimation using GRACE
intersatellite measurements, *Geophysical Research Letters*, in press.

Sauber, J., G. Plafker, B.F. Molnia, and M.A. Bryant, 2000, Crustal
deformation associated with glacial fluctuations in the eastern Chugach
Mountains, Alaska, *Journal of Geophysical Research*, 105(B4),
8055-8077.

Sauber, J. M., and B. Molnia, 2004, Glacier ice mass fluctuations and
fault instability in tectonically active southern Alaska, *Global and
Planetary Change,* Topical Issue "Ice Sheets and Neotectonics", eds.
T.S. James, T.H. Jacka, A. Morelli, and R. Dietrick, 42, 279-294.

Sauber, J., B. Molnia, and D. Mitchell, 2003, ICESat Observations of
southern Alaska Glaciers, *Eos Trans. AGU,* 84(46), Fall Meeting Suppl.,
Abstract C31D-07.

Sauber, J., B. F. Molnia, S. Luthcke, D. Rowlands, D. Harding, C.
Carabajal, J.M. Hurtado, and G. Spada, 2004, Southern Alaska glaciers:
spatial and temporal variations in ice volume, *Eos. Trans. AGU*,
85(47), Fall Meet. Suppl., Abstract, C22A-03.

Sauber, J., B. Molnia, C. Carabajal, S. Luthcke, and R. Muskett, 2005,
Elevation change (2000-2004) on the Malaspina Glacier, Alaska,
*Geophysical Research Letters*, ICESat topical issue, submitted.

Wiest, K.R., J.M. Sauber, A. A. Velasco, D.L. Doser, and J.M. Hurtado,
2004, The relationships between earthquakes, faults and recent glacier
fluctuations in southern Alaska, *Eos Trans. AGU*, *85(47),* Fall Meet.
Suppl. Abstract S53A-0179.