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The information of water level variations in lakes and reservoirs is essential for many applications such as water resources management. The conventional in-situ measurements of water levels based on gauge station are often rarely available or difficult to be shared to the public especially for lakes in the developing countries and transboundary basins. Satellite altimetry provides an alternative solution to obtaining water level variations in lakes. In this study, the laser altimetry product GLAS/ICESat L2 Global Land Surface Altimetry (ICESat-GLA14) data was used to derive water levels in a narrow long-shaped reservoir in the Nile Basin, i.e. Roseires Reservoir in Sudan. A total of 19 water levels were derived from ICESat-GLA14 during the period 2003-2009. Compared with the in-situ measurements, all 19 ICESat-derived water levels had a R2 of 0.88 and RMSE of 138.80 cm. After excluding two water levels (occurred on June 21, 2004 and June 8, 2005) with very large standard deviation (> 1 m), other 17 ICESat-derived water levels were in excellent agreement with in-situ measurements with R2 of 0.99 and RMSE of 16.96 cm. In practical situation, the high standard deviation can be considered as an indicator for unreliable water level which is better excluded for further application. Two problematic water levels showed high overestimation of the in-situ measurements, and they occurred at the lowest water level situations and during rainy season. The exact reason for such high overestimation needs to be investigated in the future study.

This work presents the first results of a research activity aiming to compare estimates of Surface Elevation Changes (SEC) over the Jakobshavn Isbrae basin (Greenland) using different repeat altimetry techniques and different sensors (laser vs. radar altimetry). The goal of this comparison is the identification of the best performing algorithm, in terms of accuracy, coverage and processing effort, for the generation of surface elevation change maps. The methods investigated here are the cross-over and repeat-track. The results of the inter-comparison are here reported and, from a first analysis, it is found that both radar and laser altimetry resolve the surface elevation changes quite well, and that the problems found mainly in the coastal region and along the main trunk can be solved by combining the two methods. The comparison with airborne lidar data from the NASA ICEBridge and the ESA CryoVex campaigns is in progress.

The primary objective of the atmospheric profiling lidar aboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission launched in April 2006 has been studying the climate impact of clouds and aerosols in the atmosphere. However, CALIPSO lidar also collects information about other components of the Earth’s ecosystem, such as polar ice sheets. The purpose of this study is to propose a new technique to provide high resolution of polar ice sheet surface elevation from CALIPSO single shot lidar measurements (70 m spot size). The new technique relies on an empirical relationship between the peak signal ratio and the distance between the surface and the peak signal range bin center to achieve high altimetry resolution. The ice sheet surface elevation results in the region of Greenland and Antarctic compare very well with the Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry measurements. The comparisons suggest that the obtained CALIPSO ice sheet surface elevation by the new technique is accurate to within 1 m. Based on the new technique, the preliminary data product of along-track topography retrieved from the CALIPSO lidar measurements is available to the altimetry community for evaluation.

We present a high-resolution Gravity Recovery and Climate Experiment (GRACE) mascon solution for Gulf of Alaska (GOA) glaciers and compare this with in situ glaciological, climate and other remote-sensing observations. Our GRACE solution yields a GOA glacier mass balance of −65 ± 11 Gt a−1 for the period December 2003 to December 2010, with summer balances driving the interannual variability. Between October/November 2003 and October 2009 we obtain a mass balance of −61 ± 11 Gt a−1 from GRACE, which compares well with −65 ± 12 Gt a−1 from ICESat based on hypsometric extrapolation of glacier elevation changes. We find that mean summer (June–August) air temperatures derived from both ground and lower-troposphere temperature records were good predictors of GRACE-derived summer mass balances, capturing 59% and 72% of the summer balance variability respectively. Large mass losses during 2009 were likely due to low early melt season surface albedos, measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) and likely associated with the 31 March 2009 eruption of Mount Redoubt, southwestern Alaska. GRACE data compared well with in situ measurements at Wolverine Glacier (maritime Alaska), but poorly with those at Gulkana Glacier (interior Alaska). We conclude that, although GOA mass estimates from GRACE are robust over the entire domain, further constraints on subregional and seasonal estimates are necessary to improve fidelity to ground observations.

[1] The recently finalized inventory of Greenland's glaciers and ice caps (GIC) allows for the first time to determine the mass changes of the GIC separately from the ice sheet using space-borne laser altimetry data. Corrections for firn compaction and density that are based on climatic conditions are applied for the conversion from volume to mass changes. The GIC which are clearly separable from the icesheet (i.e., have a distinct ice divide or no connection) lost 27.9 ± 10.7 Gt a−1 or 0.08 ± 0.03 mm a−1 sea-level equivalent (SLE) between October 2003 and March 2008. All GIC (including those with strong but hydrologically separable connections) lost 40.9 ± 16.5 Gt a−1 (0.12 ± 0.05 mm a−1 SLE). This is a significant fraction (~14 or 20%) of the reported overall mass loss of Greenland and up to 10% of the estimated contribution from the world's GIC to sea level rise. The loss was highest in southeastern and lowest in northern Greenland.

NASA flights over southern Greenland in 1991, 1992 and 1993, using a scanning laser altimeter with Global Positioning System (GPS) navigation, have demonstrated a capability to measure ice-surface elevations to an accuracy of 10-15 cm. Flights over Jakobshavns Isbræ revealed winter thickening by several meters between September 1991 and April 1992. By July 1993, surface elevations showed a small additional increase, possibly associated with the cold 1992 summer. Data collected over the ice sheet east of Jakobshavns Isbræ show negligible change over the same period; but further south, at latitude 65 N, the western part of the ice sheet appears to have thickened by up to 2 m between 1980 and 1993. It is clear that such measurements must be continued over many years, both to quantify the effects of inter-annual variability and to measure long-term trends. To this end, we plan to complete a first survey of all major drainage basins on the ice sheet in May-June 1994, and then to resurvey all flight lines at 5a intervals, with more frequent flights over selected routes.

Using the latest laser altimetry and image data from Lunar Reconnaissance Orbiter, this virtual tour visits 10 sites of interest on the moon, from the permanently shadowed floor of Shackleton to the central peak of Tycho and the tire tracks of the astronauts at the landing site of Apollo 17.

The Geoscience Laser Altimetry System (GLAS) is the sole instrument on the ICESat Satellite. On day 230 of 2003, the GLAS Component Loop Heat Pipe (CLHP) entered a slow circulation mode that resulted in the main electronics box reaching its hot safing temperature, after which the entire instrument was turned off. The CLHP had a propylene working fluid and was actively temperature controlled via a heater on the compensation chamber. The slow circulation mode happened right after a planned propulsive yaw maneuver with the spacecraft. It took several days to recover the CLHP and ensure that it was still operational. The recovery occurred after the entire instrument was cooled to survival temperatures and the CLHP compensation chamber cycled on a survival heater. There are several theories as to why this slow circulation mode exhibited itself, including: accumulation of Non-Condensible Gas (NCG), the secondary wick being under designed or improperly implemented, or an expanded (post-launch) leak across the primary wick. Each of these is discussed in turn, and the secondary wick performance is identified as the most likely source of the anomalous behavior. After the anomaly, the CLHP was controlled to colder temperatures to improve its performance (as the surface tension increases with lower temperature, as does the volume of liquid in the compensation chamber) and only precursor pulses occurred later in the mission. After GLAS s last laser failed, in late 2009, a decision was made to conduct engineering tests of both LHPs to try and duplicate this flight anomaly. The engineering tests consisted of control setpoint changes, sink changes, and one similar propulsive Yaw maneuver. The only test that showed any similar anomaly precursors on the CLHP was the propulsive maneuver followed by a setpoint increase. The ICESat Satellite was placed in a decaying orbit and ended its mission on August 30, 2010 in Barents Sea.

CALIPSO satellite has been making global lidar measurements since June 2006 and its lidar, CALIOP, will likely be the only lidar in space during the next several years. Laser altimetry data from space and aircraft-based atmospheric profiling lidars, such as CALIOP, have not been widely used in the community due to their limited vertical sampling resolution (30 meter) and broad laser pulse width (20 ns). This study intends to improve the CALIPSO laser altimetry data quality and provide a highly accurate altimetry data product to the laser altimetry community. In this study, a super-resolution laser altimetry technique has been proposed to provide improved lidar altimetry from a profiling lidar with relatively broad pulse width and slow sampling rate. Application of the technique to CALIPSO data leads to highly accurate CALIPSO land surface elevation measurements. The surface elevations will be derived from near 5-year CALIPSO global observations. The CALIPSO surface elevation results in Northern America derived by the new technique agree with the National Elevation Database (NED) high resolution elevation maps and a comparison suggests that the accuracy of the new CALIPSO land surface elevation measurements is better than 1 meter.

In this paper we will discuss our development progress on a non-scanning, swath mapping laser altimetry system. This paper will discuss the system approach, enabling technologies and instrument concept for the swath mapping laser altimetry.

This presentation will summarize the motivation for space-based laser altimetry, the science requirements for ICESat-2, and the current concept for the ICESat-2 mission. ICESat-2 will employ a photon-counting measurement approach using a high-repetition rate laser in a multi-beam configuration.

This study calibrates the footprint positions of 8.5 million Chang’E-1 and 8.8 million SELENE laser altimetry measurements against accurately known lunar laser reflector locations. The resulting datasets are used to estimate triaxial, biaxial and spherical models of the lunar figure based on the two datasets individually. The equatorial semi-major, minor and polar axes of the Chang’E-1 and SELENE solutions di¤er by 143 m, 3 m and 49 m respectively. The di¤erences between their geometric centers and the lunar center of mass along the three axes are 186 m, 3 m, and 52 m. The complete laser altimetry datasets from the two missions reveal a lunar figure that is more spherical than previously thought. Furthermore, the Chang’E-1 and SELENE solutions are in better agreement with each other than either is with the ULCN 2005 lunar figure.

Two geodetic airborne laser altimeter (ALA) systems coupled to Global Positioning System receivers acquired submeter-resolution topographic profiles of the lower parts of Breidamerkurjökull and Skeidarárjökull, Iceland, in May 1989 and September 1991 (Skeidarárjökull) and of Jakobshavns Isbræ, Greenland, in April 1992. Maximum measured crevasse depths on Breidamerkurjökull, Skeidarárjökull and Jakobshavns Isbræ were 20.7, 36.1 and 50.2 m, respectively. Crevasse spacings were 43 m (45 crevasses km−1) for Breidamerkur jökull, 46–51 m (25 crevasses km−1) for Skeidarárjökull and 20–40 m (lower part) or 50–80 m (upper part) of Jakobshavns Isbræ (27 crevasses km−1). Surface slopes were ~2.4° for the lower 11 km of Breidamerkurjökull, ~0.8° for the lower 10 km of Skeidarárjökull and 1.55° for the lower 28 km of Jakobshavns Isbræ (with a range of 0.55° for the final 17 km to ~6.3° for a steep central part several km in length). Average longitudinal strain-rate values, estimated by assuming a bulk ice temperature of 0°C and a density of 880 kg m−3, ranged from 0.12 a−1 for Breidamerkurjökull, to 0.63 a−1 for Skeidarárjökull; values for Jakobshavns Isbræ fell between 1.3 and 1.7 a−1. Remote sensing of glacier microtopography by ALA offers a potential new tool for determining crevasse morphology, spatial density and spacing, meter-scale local slopes, long-wavelength gradients and derived strain rates.

In this study we address the question of whether regional gravity field modeling techniques of GRACE data can offer improved resolution over traditional global spherical harmonic solutions. Earlier studies into large, equatorial river basins such as the Amazon, Zambezi and others showed no obvious distinction between regional and global techniques, but this may have been limited by the fact that these equatorial regions are at the latitudes where GRACE errors are known to be largest (due to the sparse groundtrack coverage). This study will focus on regions of higher latitude, specifically Greenland and Antarctica, where the density of GRACE measurements is much higher. The regional modeling technique employed made use of spherical radial basis functions (SRBF), complete with an optimal filtering algorithm. Comparisons of these regional solutions were made to a range of other publicly available global spherical harmonic solutions, and validated using ICESat laser altimetry. The timeframe considered was a 3 year period spanning from October 2003 to September 2006.

NASA Goddard Space Flight Center has launched four space based laser instruments for Earth and planetary sciences. Three out of four are single beam laser altimeter systems. We are transitioning into multi-beam swath mapping altimeter systems for high-resolution mapping. This paper will discuss the system approach and enabling technologies for swath mapping laser altimetry.

Satellite platforms utilize altimeters to estimate the elevation of sea ice (freeboard) above the ocean surface, which can be converted into ice thickness. This work analyzes the characteristics and accuracy of these measurements. As a reference, ice thickness can be measured with helicopter-based electromagnetic induction sounding directly. This method assumes, that sea ice can be described as a level plate. Case studies of different types of ice deformations, using a 3D EM forward model, show a local underestimation of true thickness between 40 and 80%, but only a neglible error of mean ice thickness, when using this 1D approach. The comparisons of radar and laser freeboard data show varying penetration depths of radar waves into the snow layer of arctic sea ice. A parametric snow depth is used for the freeboard to thickness conversion, where the difference of laser and radar altimeter did not yield the thickness of the snow layer. The error of mean ice thickness is generally lower than 20% compared to results of the induction method. Spatial averaging of freeboard values at different scales resulted in an insignificant change of the freeboard to ice thickness ratio.

The focus of this paper is on the quantification of ongoing mass and volume changes over the Greenland ice sheet. For that purpose, we used elevation changes derived from the Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry mission and monthly variations of the Earth’s gravity field as observed by the Gravity Recovery and Climate Experiment (GRACE) mission. Based on a stand alone processing scheme of ICESat data, the most probable estimate of the mass change rate from 2003 February to 2007 April equals ?139 ± 68 Gton yr?1. Here, we used a density of 600±300 kgm?3 to convert the estimated elevation change rate in the region above 2000m into a mass change rate. For the region below 2000 m, we used a density of 900±300 kgm?3. Based on GRACE gravity models from half 2002 to half 2007 as processed by CNES, CSR, DEOS and GFZ, the estimated mass change rate for the whole of Greenland ranges between ?128 and ?218 Gton yr?1. Most GRACE solutions show much stronger mass losses as obtained with ICESat, which might be related to a local undersampling of the mass loss by ICESat and uncertainties in the used snow/ice densities. To solve the problem of uncertainties in the snow and ice densities, two independent joint inversion concepts are proposed to profit from both GRACE and ICESat observations simultaneously. The first concept, developed to reduce the uncertainty of the mass change rate, estimates this rate in combination with an effective snow/ice density. However, it turns out that the uncertainties are not reduced, which is probably caused by the unrealistic assumption that the effective density is constant in space and time. The second concept is designed to convert GRACE and ICESat data into two totally new products: variations of ice volume and variations of snow volume separately. Such an approach is expected to lead to new insights in ongoing mass change processes over the Greenland ice sheet. Our results show for different GRACE solutions a snow volume change of ?11 to 155 km3 yr?1 and an ice loss with a rate of ?136 to ?292 km3 yr?1.

Since 2003, the full-waveform laser altimetry system onboard NASA's Ice, Cloud and land Elevation Satellite (ICESat) has acquired a worldwide elevation database. ICESat data are widely applied for change detection of ice sheet mass balance, forest structure estimation, and digital terrain model generation of remote areas. ICESat's measurements will be continued by a follow-up mission. To fully assess the application possibilities of the full-waveform products of these missions, this research analyzes the vertical accuracy of ICESat products over complex terrain with respect to land cover type. For remote areas, validation of individual laser shots is often beyond reach. For a country with extensive geo-infrastructure such as The Netherlands, excellent countrywide validation is possible. Therefore, the ICESat full-waveform product GLA01 and the land elevation product GLA14 are compared to data from the Dutch airborne laser altimetry archive Actual Height model of the Netherlands (AHN). For a total population of 3172 waveforms, differences between ICESat- and AHN-derived terrain heights are determined. The average differences are below 25 cm over bare land and urban areas. Over forests, differences are even smaller but with slightly larger standard deviations of about 60 cm. Moreover, a waveform-based feature height comparison resulted in feature height differences of 1.89 m over forest, 1.48 m over urban areas, and 29 cm over low vegetation. These results, in combination with the presented processing chain and individual waveform examples, show that state-of-the-art ICESat waveform processing is able to analyze waveforms at the individual shot level, particularly outside urban areas.

Sea ice plays an important role in the global climate system by impacting the energy balance of the Earth as well as affecting the oceanic and atmospheric circulations. Recently, large changes have been observed in the Earth's areal coverage of sea ice. However, little is currently known about sea ice thickness particularly at the scales needed for climate research. Spaceborne remote sensing provides the necessary global scale of coverage, but the retrieval of sea ice thickness from space has not been possible until recently with the launch of satellite altimeters of high accuracy and precision. The Ice, Cloud, and land Elevation Satellite (ICESat) is one such laser altimeter with the potential to retrieve the height of the snow plus ice layer above the water level, or sea ice freeboard. The combination of sea ice freeboard data with snow depth retrievals and the assumption of hydrostatic balance allows for the determination of sea ice thickness. The goal of this study is to use data from ICESat to provide sea ice thickness values at the global scale and high spatial resolution needed for climate studies. The work presented in this thesis includes the validation and improvement of ICESat data products, development and validation of sea ice freeboard retrieval algorithms using the ICESat data products, and the development of a method to combine ICESat freeboard retrievals with a snow depth data set to determine sea ice thickness at the 70 m spatial resolution of ICESat. The ICESat data set is used to study sea ice thickness, heat exchange, and ice production in the Arctic Ocean for the 2003-2008 time period. Despite the thinning of the Arctic sea ice cover over the 2003-2008 time period, mean ice growth rates for consecutive fall and winter measurement periods remained relatively constant. An increased ice growth rate which may be expected from a thinner ice cover appeared to be balanced by warmer temperatures. An increased ocean-atmosphere heat flux is also observed due to the thinning of the sea ice cover.

[1] Assimilation of laser altimeter data from the Ice, Cloud and land Elevation Satellite (ICESat) significantly improves the accuracy of ocean tide models for the Ross Ice Shelf (RIS). For the most energetic tidal harmonic, K1, assimilation reduces the root-mean-square error (RMSE) between the model and a set of 16 independent tide records on and near the RIS from 6.0 to 2.8 cm, and the combined RMSE for the six most energetic tidal harmonics from 7.7 to 5.4 cm. When only the six most recent and highest-quality tide records are considered, the combined RMSE is 4.8 cm. This value is close to the uncertainty expected from tidal analyses of the short (∼1–2 month) validation records, indicating that assessing further improvements in tide model accuracy will require development of a higher quality validation data set.

We acquired center-line surface elevations from glaciers in the St Elias Mountains of Alaska/northwestern Canada using aircraft laser altimetry during 2000–05, and compared these with repeat measurements acquired in 2007. The resulting elevation changes were used to estimate the mass balance of 32 900 km2 of glaciers in the St Elias Mountains during September 2003 to August 2007, yielding a value of −21.2 ± 3.8 Gt a−1, equivalent to an area-averaged mass balance of −0.64 ± 0.12 m a−1 water equivalent (w.e.). High-resolution (2 arc-degrees spatial and 10 day temporal) Gravity Recovery and Climate Experiment (GRACE) mass-balance estimates during this time period were scaled to glaciers of the St Elias Mountains, yielding a value of −20.6 ± 3.0 Gt a−1, or an area-averaged mass balance of −0.63 ± 0.09 m a−1 w.e. The difference in balance estimates (altimetry minus GRACE) was −0.6 ± 4.8 Gt a−1, well within the estimated errors. Differences likely resulted from uncertainties in subgrid sampling of the GRACE mass concentration (mascon) solutions, and from errors in assigning an appropriate near-surface density in the altimetry estimates. The good correspondence between GRACE and aircraft altimetry data suggests that high-resolution GRACE mascon solutions can be used to accurately assess mass-balance trends of mountain glacier regions that are undergoing large changes.

Full-waveform digitizer hardware integration within discrete return LIDAR systems provides an enhanced capability to resolve vertical structure within the laser line of sight and potentially classify specific surfaces or objects. However, the subject of waveform signal processing as it applies to surface classification is fairly underdeveloped. This research includes the examination of LIDAR waveform pulse characteristics for known targets and vegetation types. Using these data, a number of signal processing techniques were investigated as precursors to classification engines without prior knowledge of surface slope, or obscuration density. Relevant waveform features were extracted using both Gaussian decomposition method and raw waveform features revealing surface classification distinctions. Preliminary results from this data set indicate that the total integrated waveform energy provides an efficient and rapid methodology for discrimination of vegetation from built surfaces. These results indicate that metrics derived from the full waveforms can be utilized to characterize and classify (to a limited degree) an environment without prior knowledge.

With recent advances in terrain-mapping technologies such as Laser altimetry (LIDAR) and ground based laser scanning, millions of georeferenced points can be acquired within short periods of time. However, while acquiring and georeferencing the data has become extremely efficient, transforming the resulting massive amounts of heterogeneous data to useful information for different types of users and applications is lagging behind, in large part because of the scarcity of robust, efficient algorithms for terrain modeling and analysis that can handle massive data sets acquired by different technologies and that can rapidly detect and predict changes in the model as the new data is acquired.

In this paper we investigate the use of airborne laser altimetry and 3D ground measurements to estimate the position and the attitude of a mobile robot. Our approach is derived from earlier work on matching terrain maps by using local surface signatures. In this paper, we show how point selection strategies improve significantly both the speed and the accuracy of the surface matching algorithm. We also introduce strategies for dealing with missing data - “range shadows” - due to occlusions. We describe in detail the performance of the system in terms of accuracy, speed, and robustness with respect to parameter selection and terrain type as evaluated in five different environments with different ground and airborne sensors. We also describe the performance of the system in real environments with large-scale maps.

In late 2005 the NASA Earth Science Technology Office convened a working group to review decadal-term technology needs for Earth science active optical remote sensing objectives. The outcome from this effort is intended to guide future NASA investments in laser remote sensing technologies. This paper summarizes the working group findings and places them in context with the conclusions of the National Research Council assessment of Earth science needs, completed in 2007.

Since 2003 the spaceborne laser altimetry system on board of NASA’s Ice, Cloud and land Elevation Satellite (ICESat) has acquired a large world-wide database of full waveform data organized in 15 products. In this research three products are evaluated over The Netherlands. For this purpose the raw full waveform product, the derived Gaussian decomposition product and the global land evaluation product are compared to laser data from the Dutch national airborne laser altimetry archive AHN. Using the CORINE land cover 2000 database allows us to compare ICESat to AHN elevation profiles with respect to the land cover classes forest, urban, bare land/low vegetation and water. This comparison shows that a large average height difference of 5.7 m occurs over forest, while much smaller differences of 1.24 m over urban areas, of 0.43 m over bare land/low vegetation and of 0.07 m over water are found. The reason for this large difference over forests is that the standard processing of NASA does not take the position of the last Gaussian mode of the waveform into account. Incorporating results from a full waveform processing procedure allows us to determine improved ICESat profiles. Comparing the improved profiles shows that the average difference with the AHN profiles over forest is reduced to -0.38 m, while the average differences for the other land cover classes do not exceed -0.75 m. Encountered limitations are discussed in the conclusions.

Since 2003 the spaceborne laser altimetry system on board of NASA’s Ice, Cloud and land Elevation Satellite (ICESat) has acquired a large world-wide database of full waveform data organized in 15 products. In this research three products are evaluated over The Netherlands. For this purpose the raw full waveform product, the derived Gaussian decomposition product and the global land evaluation product are compared to laser data from the Dutch national airborne laser altimetry archive AHN. Using the CORINE land cover 2000 database allows us to compare ICESat to AHN elevation profiles with respect to the land cover classes forest, urban, bare land/low vegetation and water. This comparison shows that a large average height difference of 5.7 m occurs over forest, while much smaller differences of 1.24 m over urban areas, of 0.43 m over bare land/low vegetation and of 0.07 m over water are found. The reason for this large difference over forests is that the standard processing of NASA does not take the position of the last Gaussian mode of the waveform into account. Incorporating results from a full waveform processing procedure allows us to determine improved ICESat profiles. Comparing the improved profiles shows that the average difference with the AHN profiles over forest is reduced to -0.38 m, while the average differences for the other land cover classes do not exceed -0.75 m. Encountered limitations are discussed in the conclusions.

International audience; The BepiColombo Laser Altimeter (BELA) has been selected for flight on board the European Space Agency's BepiColombo Mercury Planetary Orbiter (MPO). The experiment is intended to be Europe's first planetary laser altimeter system. Although the proposed system has similarities to the Mercury Laser Altimeter (MLA) currently flying on board NASA's MESSENGER mission to Mercury, the specific orbit and construction of the MPO force the use of novel concepts for BELA. Furthermore, the base-lined range-finding approach is novel. In this paper, we describe the BELA system and show preliminary results from some prototype testing.

We report on progress in developing a new swath mapping laser altimeter measurement approach using multiple laser measurement beams, modulated fiber lasers, photon counting detectors, and event timers for future space missions.

Over the past 80 years, the Rhine-Meuse delta has been mapped extensively by drilling boreholes. These maps are compared with a new detailed digital elevation map of the Netherlands (AHN) that became available in 2004 and is based on very accurate, (sub-decimeter) laser-altimetry data. Examples show, that existing maps can be significantly improved. However, field checks remain a necessity. Therefore, the AHN-data need to be confronted with existing borehole descriptions using a GIS. Geomorphological analysis and geological interpretation of surface elevation patterns now enable us to map larger areas, in greater detail, with greater accuracy, and much faster. It is argued that detailed (≥1 : 50,000) geological mapping of the Netherlands should be resumed, combining the databases of Utrecht University, the National Geological Survey and Alterra.

Flood extent maps derived from SAR images are a useful source of data for validating hydraulic models of river flood flow. The accuracy of such maps is reduced by a number of factors, including changes in returns from the water surface caused by different meteorological conditions and the presence of emergent vegetation. The paper describes how improved accuracy can be achieved by modifying an existing flood extent delineation algorithm to use airborne laser altimetry (LiDAR) as well as SAR data. The LiDAR data provide an additional constraint that waterline (land-water boundary) heights should vary smoothly along the flooded reach. The method was tested on a SAR image of a flood for which contemporaneous aerial photography existed, together with LiDAR data of the un-flooded reach. Waterline heights of the SAR flood extent conditioned on both SAR and LiDAR data matched the corresponding heights from the aerial photo waterline significantly more closely than those from the SAR flood extent conditioned only on SAR data.

Full waveform laser altimetry is a recently developed method to obtain a complete vertical profile of the height of objects in the footprint as illuminated by a laser pulse. The richness of the signal also complicates the processing. One way to improve the processing strategy is to analyze differences of waveforms that should be very similar because they were obtained at approximately the same time and location. Such waveform pairs are still difficult to find. Here it is shown how to use the archive of ICESat space-borne altimetry data over Europe to determine a set of tenths of thousands of at least partial overlapping waveform pairs. The differences in the values of the waveform parameters, median energy, waveform extent, relative returned energy and intensity distribution are determined and discussed. As a case study, three typical pairs of almost perfectly overlapping waveforms are shown, were considerable differences are still occurring. In all three cases an explanation for these differences is found and discussed. Further analysis of the waveform pairs in this database is expected to considerably improve automatic processing of full waveform data.

This paper presents a feasibility study of a laser altimeter conceived as an auxiliary device of an imaging camera to perform stereo pairs correction by high accuracy range measurements. System configuration is compliant to microsatellite constraints and is integrated to a high resolution imaging sensor. System performance analysis is carried out by means of analytical models and computer codes and plots are presented to select key parameters allowing definition of a preliminary laser altimeter configuration.

An high efficiency passively Q-switched Nd:YAG MOPA with 62 mJ of pulse energy, 2.8 ns pulse duration and high temperature stability, suitable for space application was demonstrated.

[1] We present a mathematical model describing the summer melting of sea ice. We simulate the evolution of melt ponds and determine area coverage and total surface ablation. The model predictions are tested for sensitivity to the melt rate of unponded ice, enhanced melt rate beneath the melt ponds, vertical seepage, and horizontal permeability. The model is initialized with surface topographies derived from laser altimetry corresponding to first-year sea ice and multiyear sea ice. We predict that there are large differences in the depth of melt ponds and the area of coverage between the two types of ice. We also find that the vertical seepage rate and the melt rate of unponded ice are important in determining the total surface ablation and area covered by melt ponds.

The paper discuses the elimination of systematic errors from airborne laser scanning data. Systematic errors affect the reliability of the data as well as subsequent processes; their elimination can almost be regarded as mandatory. The paper discusses and models the errors that can be found in airborne laser scanning systems and then analyzes their effect on the reconstructed surface. Following is a presentation of an error recovery model that is based on natural surfaces. The error recovery model is then extended to cope with the adjustment of laser swaths. Some of the topics that are addressed concern the tie and control of information and their incorporation into the model and automation of the process. The paper concludes with a demonstration of the adjustment.