Lidar receivers with exquisitely sensitive Geiger-mode detectors are able to detect surfaces even when the line of sight from the lidar sensor to the surface is highly occluded by intervening forest canopy. Additionally, repeated scanning of a region of interest from a diversity of perspectives increases the likelihood of imaging any given surface through at least one substantially unoccluded line of sight. Together, these techniques allow airborne lidar collections to be tailored to achieve comprehensive human activity layer (HAL) data collection, even in areas with dense foliage. We present a study of the performance of a 3DEO lidar for foliage poke-through applications, exploiting both its Geiger-mode sensitivity and agile geo-referenced scanning system. We present two methods for estimating the utility of the resulting 3D point clouds in the HAL, near the ground, based on the spatial statistics of the point clouds. We apply those methods to airborne Geiger-mode lidar data of deciduous forests in Massachusetts and conifers in the US Pacific Northwest. We quantify the completeness of the point clouds as a function of the collection parameters. We then use this analysis to estimate the ideal collection parameters for a Geiger-mode lidar with georeferenced scanning to yield a high-utility data product.
Aerial lidar systems tend to have narrow instantaneous fields of view, with imagers ranging from a single pixel to many tens of thousands of pixels. To collect data over a large area, the narrow lidar field of view (FoV) must be scanned. We present a unique method of scanning a lidar FoV that provides significant flexibility and allows uniform ground coverage, concentrating the system capability only in areas of interest. This method uses a queue of convex polygons, specified in world coordinates. Pre-collection planning tools establish the polygon layout. In flight, the lidar system adaptively collects those polygons that are inside the sensor field of regard, rapidly switching among the polygons as the aircraft flies. This scanning method enables the lidar to accomplish repeated collections of a single target or collections that cover a long straight or meandering path. It also enables collection of corridors with irregular widths, such as power line corridors with bulges at municipal power sub-stations or rail or roadway intersections. In the case of mixed scene types, the system can concentrate more collection time on foliated regions relative to unfoliated regions. Angular diversity can be achieved by sequentially revisiting a single target polygon. Live target tasking is accomplished by adding new targets to the target queue without stopping an ongoing collection. We present scanning simulations and example lidar data collected in flight with this scanning strategy and show some examples of sampling uniformity under the finite bandwidth and acceleration of a real scanning system.
Photon-sensitive lidar receivers enable range measurements at high probability of detection and low false alarm rate using only 5 - 10 detected photons on average per range measurement. This much-reduced link requirement, compared to photodiodes operating in linear mode, holds the promise of much-reduced system volume, mass, and power consumption, while simultaneously enabling longer standoff and higher measurement rates. We present a commercially-available, Geiger-mode lidar system, called Zion, optimized for rapid collection of dense 3D point clouds using small, economical aircraft. The system mass is under 120 kg and it consumes under 1 kW. Zion has operated at ranges between 800 m and 8,000 m. The area collection rate for data products with density of 100 points per square meter exceeds 300 km2/hr at an aircraft altitude of 1,400 m. The maximum usable measurement rate exceeds 10 million points per second. A significant capability of Zion is the agile geo-referenced scanning system, which can point and scan anywhere within a 40 × 40 degree field of regard. Collection efficiency is optimized by scanning only the desired geographic region of interest (e.g. meandering roads and utility corridors) and even in spite of non-ideal aircraft flight path and attitude. The agile, georeferenced scanning allows the flexibility to maximize oblique imaging of structures or to penetrate dense foliage. The collected points are spread evenly across the imaged area, which reduces image artifacts and simplifies processing. This system has flown over 50 flights, and is currently operational.
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