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Remote sensing observations increasingly are used to obtain the detailed information needed about land surface state required for hydrological analyses. However, many of the surface state parameters required for such analyses are related to the vertical structures of surface vegetation and topography, that are often difficult to measure using passive optical and radar remote sensing technologies. A new technology, lidar (light detection and ranging) remote sensing, has proven highly effective for characterizing land surface structure in great detail, including subcanopy topography, canopy height, foliar profile and biomass, among others. In this article, we review the theory and application of lidar remote sensing for characterizing land surface states for hydrological analysis. First we present a brief overview of lidar, and discuss similarities and distinctions between the small-footprint systems commonly used in commercial applications and large-footprint approaches used in research and space-based systems. We next describe common land surface variables that are often used in hydrological analysis and how these are related to vertical structures observable from lidar. Lastly, we present how lidar may be used to recover or parameterize these surface variables; in particular we focus on the observation of forest and topographic structures. Keywords: lidar; remote sensing; canopy structure; laser altimetry; subcanopy topography

[1] ICESat calculations of sea level and mesoscale variability are demonstrated and compared to calculations from TOPEX altimetry. In particular, we examine the accuracy of the ICESat Laser 2a Release 21 GLA15 ocean elevations. A global ICESat ocean elevation bias of −10.0 ± 1.0 cm (low) was found with respect to TOPEX, obtained with a reference mean sea surface (MSS). Dual-satellite (ICESat - TOPEX) crossovers independently verify this bias, having a mean of −11.7 ± 1.8 cm. The origin of this bias is unknown, although it may be related to sea state. Release 21 improvements have mitigated ICESat's thermally-induced day/night laser pointing variations to 1 to 2 cm in elevation. The average daily single-satellite internal crossover RMS is 12 cm for ICESat, 7 cm for TOPEX. ICESat laser altimetry is able to match TOPEX detection of major sea level anomaly and mesoscale variability features on a global scale.

Single-photon-counting laser altimetry is a new measurement technique offering significant advantages in vertical resolution, reducing instrument size, mass, and power, and reducing laser complexity as compared to analog or threshold detection laser altimetry techniques. However, these improvements come at the cost of a dramatically increased requirement for on-board real-time data processing. Reconfigurable computing has been shown to offer considerable performance advantages in performing this processing. These advantages have been demonstrated on the multi-kilohertz micro-laser altimeter (MMLA), an aircraft based single-photon-counting laser altimeter developed by NASA Goddard Space Flight Center with several potential spaceflight applications. This paper describes how reconfigurable computing technology was employed to perform MMLA data processing in real-time under realistic operating constraints, along with the results observed. This paper also expands on these prior results to identify concepts for using reconfigurable computing to enable spaceflight single-photon-counting laser altimeter instruments.

Although laser remote sensing techniques have been applied to a variety of environmental measurement tasks for several decades, it has not been until relatively recently that the promise held by lidar and laser radar has begun to be exploited for global measurements from an Earth-orbiting vantage point. Notwithstanding the successful demonstration of highresolution laser altimetry and cloud/aerosol profiling from orbital platforms in the last decade, full realization of the potential for these techniques to address important Earth science questions awaits the availability of next generation instruments incorporating durable, high-performance laser transmitters and advanced receiver technologies. Some of the most critical, high-impact Earth science measurement applications are enabled by lidar techniques - in some cases uniquely so. This paper describes some of these scenarios and also the philosophy underlying the investment that the US National Aeronautics and Space Administration (NASA) is making in order to pro-actively accelerate technology development in certain key areas that will contribute to our future ability to field advanced laser remote sensing instrumentation in space.

Monitoring of landscapes or sea bottoms by means of laser altimetry or multibeam results in huge amount of data covering the same area in different epochs. Often stable benchmarks are not available in the area covered. We propose a geodetic/geostatistical method to analyze possible deformations in such area out of time series of data. The method is used for a deformation analysis of six consecutive years of laser data covering a dune section on the south-west coast of the island of Texel, the Netherlands.

High-resolution topographic data are essential to mapping and mitigating coastal flooding and erosion hazards. The recent advent of airborne laser altimetry technology allows rapid and inexpensive topographic surveys of large coastal areas.

Airborne scanning laser altimetry (LiDAR) is an important new data source for environmental applications, mapping topographic and surface object heights to high vertical and spatial accuracy over large areas. We present results of a segmentation system for LiDAR data for a reach of the river Severn, UK. The system has been developed to improve the 3 main data required by a leading numerical flood model predicting inundation extent, namely (i) a map of topographic height providing model bathymetry. A comparison with ground control points gives an accuracy of ±17cm (decreasing in the presence of steeply wooded slopes), (ii) the meandering location of the river channel and a suitable height contour which denote the extent of the model domain, and allow immediate finite element mesh generation, and (iii) a map of vegetation height (to an accuracy of ±14cm for grass and cereal crops) which is converted to friction coefficients. Errors due to overlapping swaths are significantly reduced. A 3-class segmentation of vegetation types (short, intermediate and tall) allows optimal height extraction algorithms to be separately applied, and enables realistic conversion to friction coefficients. Short (grass and cereal crops) and intermediate (hedges) vegetation are assumed to be flexible and either emergent or submerged during a flood cycle. Trees (tall vegetation) are modelled as rigid, emergent, stems.

Preface. 1. Why would we use a GIS DataBase and Remote Sensing in Irrigation Management? M.G. Bos. 2. Can WARMAP save the Aral Sea? A. van Dijk, R.N. den Haan. 3. Remote sensing for Inland Water Quality Detection and Monitoring: State-of-the-art application in Friesland waters A.G. Dekker, S.W.M. Peters, R.J. Vos, M. Rijkeboer. 4. Use of remotely sensed Images by SPOT in Hydrologic Modelling N.N. Lorenz. 5. Measuring and analysing of flood waves in Rhine river an application of laser altimetry A.E. Bollweg, R.H. van Heerd. 6. Soil moisture conditions in The Netherlands during the summer of 1995 interpreted from satellite measurements W.G.M. Bastiaanssen, H. Pelgrum, G.J. Roerink, K.L. Soeterik. 7. GIS and watermanagement: Where are we heading to? E.J. van Capelleveen, F.H.W.M. van den Bosch. Index.

The Survey Department of Rijkswaterstaat in The Netherlands makes intensive use of laser altimetry for topographic measurements. A new application is to measure the water level, during flood waves in rivers. As the laser signal reflects differently on water compared to land, a high point density was used. This large data set gives spatial detailed information about the flood wave, the along — and across — track slope of the river and information to derive the water resistance on different vegetation areas.

Derivation of Digital Elevation Models (DEM’s) by ERS SAR interferometry is a promising method for obtaining the necessary elevations for computing accurate terrain corrections in remote, poorly surveyed areas. InSAR DEM’s are especially useful due to the inherent high spatial resolution. In the poster the quality of a SAR derived DEM of an East Greenland area is evaluated based on comparisons to geodetic control points and airborne laser altimetry.

Glacier mass changes are a valuable indicator of climate variability and monsoon oscillation on the underexplored Tibetan Plateau. In this study data from the Ice Cloud and Elevation Satellite (ICESat) is employed to estimate elevation and mass changes of glaciers on the Tibetan Plateau between 2003 and 2009. In order to get a representative sample size of ICESat measurements, glaciers on the Tibetan Plateau were grouped into eight climatically homogeneous sub-regions. Most negative mass budgets of ? 0.77 ? 0.35?m?w.e.?a?1 were found for the Qilian Mountains and eastern Kunlun Mountains while a mass gain of + 0.37 ? 0.25?m?w.e.?a?1 was found in the westerly-dominated north-central part of the Tibetan Plateau. A total annual mass budget of ? 15.6 ? 10.1?Gt?a?1 was estimated for the eight sub-regions sufficiently covered by ICESat data which represents ?80% of the glacier area on the Tibetan Plateau. 13.9 ? 8.9?Gt?a?1 (or 0.04 ? 0.02?mm?a?1 sea-level equivalent) of the total mass budget contributed ?directly? to the global sea-level rise while 1.7 ? 1.9?Gt?a?1 drained into endorheic basins on the plateau.

Laser altimetry of the Moon is now under investigation as a part of the RISE project in the Moon-Orbiting exploration (SELENE; SELenological and ENgineering Explorer) by Japan in 2002–2003. Main objective of this measurement is to construct a precise and global topography of the moon with the 5m vertical resolution and with a center-to-center along-track footprint spacing of 330m. The topography will be a great contribution for addressing several problems of lunar geology and geophysics such as morphological dichotomy, internal structure, isostatic state, and various surface modification processes of the moon.

ICESat satellite laser altimetry provides an unprecedented set of global elevation measurements of the Earth, yielding great detail over ice, land and ocean surfaces. Coastal regions in particular, including seamless land-water transitions, benefit from the small footprint (50 to 90 m), high resolution (40 Hz, ~170 m along-track), and high precision (2 to 3 cm) of ICESat. We discuss the performance and character of ICESat data in three example coastal scenarios: continental coast (Louisiana-Mississippi Gulf Coast, USA, including Lake Pontchartrain), open ocean island (Funafuti, Tuvalu), and an inland river (confluence of Tapajos and Amazon rivers, Brazil). Water elevations are compared to tide gauge heights and to TOPEX and Jason-1 radar altimetry. In demonstrating the utilization of ICESat, we also present examples of: laser waveform shapes over a variety of surface types (water, land, and vegetation); vegetation canopy heights (detecting large-scale destruction from Hurricane Katrina comparing data before and after); sub-canopy surface water; measurements of waves; and examination of along-stream river slope and comparisons of river stage to hydrologically-driven GRACE geoid change.

[1] We present a new method to measure ice thickness of polar sea-ice freeboard heights, using airborne laser altimetry combined with a precise geoid model, giving estimates of thickness of ice through isostatic equilibrium assumptions. In the paper we analyze a number of flights from the Polar Sea off Northern Greenland, and estimate accuracies of the estimated freeboard values to be at a 13 cm level, corresponding to about 1 m in absolute thickness.

The techniques involved in the design and application of laser altimeter instruments are reviewed, including a description of the instrument subsystems required for the range and waveform measurements. Laser pulse transmitters based on the relatively novel technology of diode-pumped solid-state lasers are considered. Various factors affecting laser altimeter instrument performance are discussed. These include the receiver signal-to-noise ratio, atmospheric propagation, and altimeter platform effects. Some examples of laser altimeter data are presented to illustrate the variety of possible instrument applications. >

Apollo 15 and 16 subsatellite observations of lunar limb compressions in the solar wind have been studied statistically by correlating occurrence rates for the compressions with seven topographic parameters derived from Apollo laser altimetry, with the use of a 5-deg x 5-deg selenographic grid. Maximum, rms, and average sunset-facing slopes are significantly correlated with occurrence rates in the source regions, but no correlation with elevation differences is found. Variance percentages suggest that a slope-related source mechanism generates about 6-8% of the limb compressions originating in source areas covered by the laser altimetry. These results confirm the preliminary conclusions of an earlier statistical study, based on Explorer 35 limb-compression observations, which used a coarser 15-deg x 15-deg grid

L'objectif de cette étude est d'estimer le potentiel d'ICESat pour la surveillance des eaux continentales à travers les cas du lac Léman (Suisse et France) et des rivières de la France métropolitaine. / The Ice, Cloud and Land Elevation Satellite (ICESat) laser altimetry mission from 2003 to 2008 provided an important dataset for elevation measurements. The quality of GLAS/ICESat (Geoscience Laser Altimeter System) data was investigated for Lake Leman in Switzerland and France by comparing laser data to hydrological gauge water levels. The correction of GLAS/ICESat waveform saturation successfully improved the quality of water elevation data. First, the ICESat elevations and waveforms corresponding to water footprints across the transition from the land to water were analyzed. Water elevations (2 to 10 measurements) following the land-water transition are often of lesser quality. The computed accuracy for the ICESat elevation measurements is approximately 5 cm, excluding transitions footprints, and 15 cm, including these footprints. Second, the accuracy of ICESat elevation was studied using data acquired on French rivers with a width greater than the size of the ICESat footprint. The obtained root mean square error (RMSE) for ICESat elevations in regard to French rivers was 1.14 m (bias = 0.07 m; standard deviation = 1.15 m), which indicates that small rivers could not be monitored using ICESat with acceptable accuracy due to land-water transition sensor inertia.

The new Dutch national digital elevation model (DEM), acquired with laser altimetry, is almost complete. The Dutch Survey Department fulfils an intermediary function between laser data suppliers and final users of the DEM. One of the most important tasks of the Survey Department is to guarantee the quality of the delivered laser DEMs to the users. For this purpose, a new height error description scheme is developed, allowing to quantify error effects at different scales. Such a new error description scheme was necessary because the former quality description of DEMs was insufficient. The error behaviour of laser altimetry data, acquired by a complex system of different sensors, cannot be expressed by solely two parameters: a bias and a standard deviation. The former and the new error description scheme will be addressed together with methods to quantify the differently scaled error components. Among them are cross correlation techniques, empirical covariance function analysis from geostatistics and 1d strip adjustment. The contractual demands for maximal allowed error amplitudes, derived from real data, will be presented. The benefit of the error description scheme for DEM users will be illustrated by propagating the error components to the height precision of derived products. Summarizing, it can be stated that this paper deals with the height precision of laser altimetry DEMs and the effects of the different error components on the measured heights. This paper does however not aspire to give methods for eliminating or minimizing these errors.