Optimizing ground return detection through forest canopies with small footprint airborne mapping LiDAR

Abstract

The capability of airborne LiDAR scanners (ALS) to record returns from the ground surface and other targets occluded by forest canopies has been of great value for geosciences and military operations. In this paper we present preliminary results from efforts aimed to characterize different types of forest canopies and to assess the quantity and quality of potential ground returns obtained through different configurations of small footprint airborne mapping LiDAR systems. The final goal of this work is to provide a methodology that allows for the quantification of the "openness" of a forest canopy and procedures to determine the best configuration of ALS systems that ensures maximum detection of ground returns independent of the many different system designs currently available.

Now You See It… Now You Don’t: Understanding Airborne Mapping LiDAR Collection and Data Product Generation for Archaeological Research in Mesoamerica

“…In general, to achieve optimal canopy penetration several conditions need to be met: (a) the entire surface area needs to be illuminated (ideally more than once from different angles) so that laser pulses are placed in canopy gaps; (b) laser pulses need to have enough energy to make the round trip through the canopy (LiDAR equation); and (c) for discrete LiDAR systems the slant range through the lowest understory vegetation needs to be greater than the width of the laser pulse so that the system range resolution and detector dead time are not detrimental factors for the detection of ground returns [39].…”

Validation of ICESat-2 ATL08 Terrain and Canopy Height Retrievals in Tropical Mesoamerican Forests

“…2), three on the Yucatan peninsula of Mexico, two in Guatemala, one in Belize, and one in the Mosquitia region of Honduras. These HDL reference datasets were collected by the National Center for Airborne Laser Mapping (NCALM) with the specific goal of optimizing canopy penetration to obtain high fidelity and accuracy digital elevation models (DEM) [20]. A total of 97.9% of the HDL validation measurements came from data collected with the Teledyne Optech Titan multispectral lidar [21].…”

Capability Assessment and Performance Metrics for the Titan Multispectral Mapping Lidar

“…NCALM has conducted similar experiments aimed at understanding how to optimize the configuration of lidar systems to maximize the detection of ground returns through canopies in different types of forests [53]. Besides conducting canopy penetration experiments in different kinds of forested environments, NCALM experiments are unique because emphasis has been placed on understanding the pulse energy characteristics of the laser source as a function of the pulse repetition frequency.…”

“…Besides conducting canopy penetration experiments in different kinds of forested environments, NCALM experiments are unique because emphasis has been placed on understanding the pulse energy characteristics of the laser source as a function of the pulse repetition frequency. Previously reported experiments [53] were performed with legacy lidar systems (Optech 3100, Gemini and Aquarius). These systems were powered by Q-switched solid-state laser sources.…”

“…These systems were powered by Q-switched solid-state laser sources. An operational characteristic of such laser sources is that the output laser energy of each laser pulse decreases when the PRF is increased [53]. Based on this characteristic, maximizing canopy penetration with these older systems is achieved by a tradeoff between illuminating as much of the target area as possible, which is directly proportional to the PRF while maintaining enough energy per pulse to ensure the round trip of the laser pulse through the canopy and back to the sensor (which is inversely proportional to the PRF).…”