Obscuration measurements of tree canopy structure using a 3D imaging ladar system

Abstract

Recently developed airborne imaging laser radar systems are capable of rapidly collecting accurate and precise spatial information for topographic characterization as well as surface imaging. However, the performance of airborne ladar (laser detection and ranging) collection systems often depends upon the density and distribution of tree canopy over the area of interest, which obscures the ground and objects close to the ground such as buildings or vehicles. Traditionally, estimates of canopy obscuration are made using ground-based methods, which are time-consuming, valid only for a small area and specific collection geometries when collecting data from an airborne platform. Since ladar systems are capable of collecting a spatially and temporally dense set of returns in 3D space, the return reflections can be used to differentiate and monitor the density of ground and tree canopy returns in order to measure, in near real-time, sensor performance for any arbitrary collection geometry or foliage density without relying on ground based measurements. Additionally, an agile airborne ladar collection system could utilize prior estimates of the degree and spatial distribution of the tree canopy for a given area in order to determine optimal geometries for future collections. In this paper, we report on methods to rapidly quantify the magnitude and distribution of the spatial structure of obscuring canopy for a series of airborne high-resolution imaging ladar collections in a mature, mixed deciduous forest.

Characterizing targets and backgrounds for 3D laser radars

“…A straightforward method to calculate the lacunarity is described by Allain and Cloitre 20 , and will be used in this section. In R. Cannata et al 21 the lacunarity metric is used to characterize the obscuration in a series of sets of data from an airborne laser radar sensor into three different classes. …”

Status report on next-generation LADAR for driving unmanned ground vehicles

“…In order to achieve enhanced ionization which is responsive to the arrival of a single photon, they have developed a "Geiger-mode" (GM) avalanche photodiode (APD) array that is integrated with fast CMOS time-to-digital converter circuits at each pixel 5,6 . When a photon is detected there is an explosive growth of current over a period of tens of picoseconds.…”

Medium altitude airborne Geiger-mode mapping LIDAR system

“…Since then, several airborne Geiger-mode LiDAR systems have been developed: JIGSAW, a low altitude foliage penetration (FOPEN) LiDAR shown in Figure 1 [6,7], the Airborne Lidar Research Testbed (ALIRT) a medium altitude mapping LiDAR [8], the High Altitude Lidar Operations Experiment (HALOE) a high altitude imaging LiDAR [9] and the MIT/LL MACHETE a medium altitude FOPEN LiDAR system. DARPA facilitated the transfer of GmAPD technology from MIT/LL to Princeton Lightwave Inc. [10,11], and Boeing Spectrolab [12], in order to establish commercial sources of GmAPD based LiDAR cameras.…”