Light Detection and Ranging (LIDAR) provides remotely sensed information on the vertical structure of forests that is very difficult to obtain either by optical or radar remote sensing techniques. Indeed, forest attributes such as tree height and biomass may be quantified more directly with LIDAR than with other remote sensing means. Recent developments in scanning laser altimetry and small footprint LIDAR systems can provide a very detailed picture of the forest canopy for management purposes or ecological studies. This new GEOIDE research project (RES #502) focuses on the evaluation of algorithms for estimating forest structural and biophysical variables as well as terrain characteristics.

It's 4:00 p.m. on an overcast Thursday afternoon. Jim gets a call form management. They need a Digital Terrain Model (DTM) derived from an airborne survey of a particular area by tomorrow morning. Jim rushes to the nearest surveying company. Within two hours, the aircraft is surveying the area requested and records one hour of data. By that evening data processing has begun and jim findas the DTM on his desk the next morning...

Floods are one of those major natural disasters you can watch on CNN, hopefully occurring somewhere other than where you live. They seem to be happening more often or, at least, being reported more often. Recent large floods such as those on the Mississippi and, in 1997, on the Red River have caused true hardship to the people who live in the affected areas, as well as having destroyed much property, livestock and wildlife...

A simple, lighweight, inespensive, portable airborne laser profiling system has been assembled form off-the-shelf, commercially available components. The system, whitc costs approximately $30,000, is designed to fly aboard small helicopters and single- or twin-engine high-wing aircraft without airframe modification. The system acquires first-return rang and amplitude measurements at data rates up to 2000 hz (operator-controlled) and has an operational envelope up to 300m above terrain. The airborne laser profiling system includes the laser transmitter/receiver, differential GPS receiver, a CCD video camera and recorder, and a laptop computer which interleaves and records the GPS and laser range/amplitude data. The portable airborne laser system (PALS) was designed to acquire fores height measurements along linear flight transects in order to conduct regional or subcontinental fores inventories worldwide. This economical laser system now puts airborne laser mensuration within reach of operational foresters and researchers interested in making rapid forest structure and/or timber surveys in remote areas. PALS has been used to acquire over 5000km of flight transect data over the state of Delaware.

High-resolution airborne laser scaner data offer the possibility to detect and measure individual trees. In this study, an algorithm which estimated position, height, and crown diameter of individual trees was validated with field measurements. Because all the trees in this study were measured on the ground with high accuracy, their positions could be linked with laser measurements, making validation on an individual tree basis possible. In total, 71 percent of the trees were correctly detected using laser scanner data. Because a large partion of the undetected trees had a small stem diameter, 91 percent of the total stem volume was detected.

A method of predicting two forest stand structure attributes, basal area and above ground biomass, from measurements of forest vertical structure was developed and tested using field and remotely sensed canopy structure measurements. Coincident estimates of the vertical distribution of canopy surface area (the canopy height profile), field-measured stand structure attributes were acquired for two data sets. The chronosequence data set consists of 48 plots in stands distributed within 25 miles of Annapolis, MD, with canopy height profiles measured in the field using the optical-quadrat method. The stem-map data set consists of 75 plots subsetted from a single 32 ha stem-mapped stand, with measurements of their valcanopy height profiles made using the SLICER (Scanning Lidar Imager of Canopies by Echo Recovery) instrument, an airborne surface lidar system. Four height indices, maximum, median, mean, and quadratic mean canopy height (QMCH) were calculated from the canopy height profiles ...

This study employed an airborne laser scanner to detect changes of buildings by acquiring a digital surface model DSM data of urban areas. Simple comparison between DSM data sets acquired at different occasions successfully detected building changes without omission errors. A CCD array image simultaneously acquired with the DSM data was also automatically orthorectified with the DSM data and indicated to help revise the building database efficiently. q1999 Elsevier Science B.V. All rights reserved.

Two new techniques for the determination of building models from laser altimetry data are presented. Both techniques work on the original laser scanner data points without the requirement of an interpolation to a regular grid. Available ground plan information may be used, but is not required. Closed solutions for the determination of the parameters of a standard gable roof type building model based on invariant moments of 2 1r2-D point clouds are shown. In addition, the analysis of deviations between point cloud and model does allow for modelling asymmetries such as dorms on a gable roof. By intersecting planar faces nonparametric buildings with more complex roof types can also be modelled. The techniques were applied to a FLI-MAP laser scanner dataset covering an area of 500=250 m2 with a density of more than 5 pointsrm2. Within this region, all but one building could be modelled. An analysis of the variance of the parameters within a group of buildings indicates a precision in the range of 0.1–0.2 m. q1999 Elsevier Science B.V. All rights reserved.

Traditionally, forest inventory in Australia has relied on mapping from medium scale (1:25,000) aerial photography and limited ground survey, with often poor results. This study describes the first trial in Australia of a helicopter-based remote sensing instrument including a: differential global position system; digital video, and laser profiling device, aimed at bridging the gap between mapping and ground survey. Analyses were undertaken to compare laser estimates of tree height, projective foliage cover, crown cover and large-scale video estimates of: stocking, growth stage, and species, with the ground surveys of the same variables. Coefficients of determination (r2) ranged from 0.82 for projective foliage cover to 0.97 for tree height. A Chi-squared analysis of species proportions found no significant difference ground and video data. This study demonstrates that the integration of these technologies has the potential to replace and or supplement some information currently collected from ground surveys. It also has the capacity to generate ground quality information across inaccessible areas at a fraction of the cost of traditional forest inventory in Australia.

Airborne laser scanners have been increasingly used in recent years for the collection ofterrain elevation data especially in wooded areas. The technology demands new processing technologies which have reached a stage of good practical application so far for the interpolatin of groups DTM's. Beyond pure ground DTM's, however, laser scanner data have great potential for other applications suchas creation of digital building models or vegetation analysis. The paper presents the state of the art of interpolation techniques along with a new technique to separate wooded from nonwooded areas even in the special case of off-terrain objects (buildings, rochs) which would normally be eliminated from the ground model. Finally methods are outlined to extract information on forest stands, such as mean stand height, stand density, and tree species, directly from laser scanner data.

Large footprint, waveform sampling lidar altimetry has a number of benefits over traditional, small footprint, single return laser altimetry for the remote sensing of forest structure. Nevertheless, its application has been impeded by a lack of 1) algorithms for converting the lidar data to biophysical measurements, 2) validation of the resulting measurements, and 3) applications demonstrating the utility of the measurements. Over the course of the last five years, we have developed algorithms and software packages for the extraction of height, cover, canopy height profile and light transmittance related measurements, and validated them using field measurements in two contrasting forested ecosystems: eastern deciduous forests in Maryland and North Carolina, USA; and western coniferous Douglas-fir/western hemlock forests at H.J. Andrews Experimental Forest, Oregon, USA. In both...

Lidar remote sensing is a breakthrough technology for forestry applications. Lidar instruments have demonstrated the capability to accurately estimate important forest structural characteristics such as canopy heights, stand volume, basal area and aboveground biomass. This paper provides a brief background on lidar remote sensing, and its current and projected uses in forestry.

A method of predicting two forest stand structure attributes, basal area and aboveground biomass, from measurements of forest vertical structure was developed and tested using field and remotely sensed canopy structure measurements. Coincident estimates of the vertical distribution of canopy surface area (the canopy height profile), and field-measured stand structure attributes were acquired for two datasets. The chronosequence dataset consists of 48 plots in stands distributed within 25 miles of Annapolis, MD, with canopy height profiles measured in the field using the optical-quadrat method. The stemmap dataset...

Recent work has established the utility of waveform sampling lidar for predicting forest structural attributes. Nevertheless, serious obstacles to its wide-spread use still exist. They include the lack of waveform sampling lidar sensors capable of measuring forest canopy structure over large extents, and the practical difficulty of developing widely applicable relationships to predict forest stand structure indices (such as aboveground biomass) from measurements of canopy structure. While the advent of advanced devices such as NASA’s LVIS and VCL sensors will allow the collection of larger datasets than previously possible, neither sensor is capable of collecting spatially comprehensive datasets at the regional scales critical for forest management. Therefore, methods to integrate...

Scanning lidar remote sensing systems have recently become available for use in ecological applications. Unlike conventional microwave and optical sensors, lidar sensors directly measure the distribution of vegetation material along the vertical axis and can be used to provide three-dimensional, or volumetric, characterizations of vegetation structure. Ecological applications of scanning lidar have hitherto used one-dimensional indices to characterize canopy height. A novel three-dimensional...

Studies weti made at 2 rangeland areas in south Texas to mea sure canopy cover and distribution with an airborne laser profiler. In a comparison of laser and ground measurements of canopy cover on the same eighteen 30.5-m segments at the Yturria area, laser measurements of canopy cover ranged from 1 to 89% and were correlated significantly (P = 0.89) with ground measurements (1 to 88%) on the same eighteen 30.5-m segments. Comparisons of laser measurements of canopy cover for 500- and 940-m segments with an average of three 30.5-m ground measurements of canopy cover made within these segments were also significantly correlated (P = 0.95). Topography, vegetation height, and spatial distribution of canopy cover for 6- to 7-km flightlines were also mea sured with the laser profiler. Airborne laser measurements...

Laser scanning with its ability to penetrate vegetation and its extremely high point density allows for a completely new approach to semi-automatically delineate man-made features (“objects”) in forested areas as a basis for the management of such data in a GIS. In this paper, emphasis is laid on the detection of roads and buildings from laser scanning data. The basis of our analysis is the generation of a DTM actually representing the earth surface (no tree tops, no building roofs). From a slope model of the terrain, break lines can be detected by applying standard edge extraction techniques. However, the slope model is still too noisy to deliver “good” (long, continuous) break lines. Thus, a pre-processing step...

Airborne laser Scanning (ALS) is considered as a surface modelling technology. The system is describrd and the results of a series of recent pilot projects are reported. The strengths and weaknesses of Airborne Laser Scanning are considered, and compared with more established technologies. The primary advantage of ALS is the ability to reliably survey through vegetation and to simultaneously record terrain and non-terrain features such as powerlines and tree canopies. In comparing ALS with other technologies it is found to complement rather than displace.

This paper evaluates and discusses the accuracy of laser scanner in DTM (digital terrain model) generation and digital 3-D height model generation in forested areas. High-pulse-rate laser scanners are capable of detecting single trees in a boreal forest zone, since a significant amount of the laser pulses reflect directly from the ground without any interaction with the canopy. This allows for a detailed investigation of forest areas and the creation of a 3-dimensional tree height model. Special emphasis is laid on the optimisation of the selection of ground hits used for the creation of the DTM of future high-pulse-rate laser scanners.

The Laser Vegetation Imaging Sensor LVIS is an airborne, scanning laser altimeter, designed and developed at NASA’s Goddard Space Flight Center GSFC. LVIS operates at altitudes up to 10 km above ground, and is capable of producing a data swath up to 1000 m wide nominally with 25-m wide footprints. The entire time history of the outgoing and return pulses is digitised, allowing unambiguous determination of range and return pulse structure. Combined with aircraft position and attitude knowledge, this instrument produces topographic maps with dm accuracy and vertical height and structure measurements of vegetation. The laser transmitter is a diode-pumped Nd:YAG oscillator producing 1064 nm, 10 ns, 5 mJ pulses at repetition rates up to 500 Hz. LVIS has recently demonstrated its ability to determine topography (including sub-canopy) and vegetation height and structure on flight missions to various forested regions in the US and Central America. The LVIS system is the airborne...

Airborne laserscanner systems are new devices for the assessment of forest stand attributes. Based on experiences with profiling laser systems, it is expected that laserscanners give exact height information on forest stands at reasonable cost and accuracy, which allows the derivation of different important stand attributes like number of trees, tree crowns, tree height, stand structure etc. The paper gives an overview of a research project on the application of airborne laserscanner data for forest inventory purposes. Within the field of assessment of forest stand attributes, the main emphasis is put on horizontal and vertical stand structures. Several approaches for the assessment of horizontal and vertical stand structures are presented. First results are presented and discussed.

Lidar topographic surveys of forested terrain generate XYZ positions for laser returns from numerous points, some on the ground and some from vegetation. Extracting a ground surface model from such data requires ‘virtual deforestation’ (VDF), preferably by automatic means. A simple error budget for lidar topography of forested terrain suggests that the dominant source of error—and the greatest room for improvement—lies in VDF procedures. We discuss a despike VDF algorithm that classifies returns as ground or not-ground on the basis of the geometry of the surface in the neighborhood of each return. The despike algorithm is fully automatic, effective, and can recover breaklines. It fails to identify some negative blunders, rounds some sharp corners off the landscape, and as implemented is slow. There are clear paths to improve its speed. If multiple-return data are available, a no-multiple-returns VDF algorithm robustly defines areas where all returns are ground returns. Many groups are using variations on block-minimum VDF algorithms, but these...