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.
We have developed a Geiger-mode lidar system for detecting individual birds in large flocks and tracking them using a real-time processing system. We present initial results of field tests conducted in North Dakota observing large flocks of red-wing black birds and their predators. We analyze the signals and tracks arising from the birds and from a small UAS in the scene. We also present data from testing in Lawrence, Massachusetts observing American Crows in which we tested a real-time processing system. The exquisite sensitivity and rapid measurement rates achievable with Geiger-mode lidars enable rapid surveillance of airspaces for the detection of small targets (cross section of 100 cm2 at 20 percent reflectivity) at operationally relevant standoff (400 - 800 m) with high revisit rates (5 - 10 Hz). The objective of this demonstration was the tracking of over 1000 birds in a flock occupying a volume of interest of (100 m)3 at a standoff of 400 m. We will present initial results from field campaigns observing red-wing blackbirds, predators and American crows.
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.
The image formation process for airborne lidar systems utilizes physical sensor models
in order to create three-dimensional imagery
from range, scanning, position and attitude sensor measurements.
To estimate surface locations from data collected with Geiger-mode lidar systems,
typically range measurements are combined from many laser pulses,
from many camera pixels, over multiple viewing geometries and multiple collection times.
Sharp image formation requires well-calibrated camera and pointing models.
The calibration method presented here utilizes aerial data collections
spanning the full sensor field of regard to iteratively refine the system model parameters
while minimizing relative imagery misplacement.
Step one of the calibration adjusts parameters that only affect image quality
and evaluates image sharpness using, for example, a Sobel sharpness filter.
Step two adjusts parameters affecting image placement.
This calibration method utilizes the vendor-supplied transform code
inside the parameter optimization algorithm
and is therefore independent from the lidar configuration and the physical sensor model.
Utilizing the vendor-supplied transform ensures that the resulting calibration parameters
are interpreted correctly.
To reduce computational burden in step two, the input data from thousands of laser pulses
is condensed into a single effective pulse that is passed through the transform step.
This method has been used to calibrate four different Geiger-mode lidar systems
and has enabled sharp imagery over the full field of regard
prior to incorporating ground control points or performing registration with adjacent imagery.
We present representative results for the Cuchillo lidar system
and discuss execution time requirements and performance limitations.
Based on parallel-plate waveguides (PWWGs), we have developed both passive and active terahertz (THz) sensors, filters, splitters, and switches. We utilize the PPWG since it has excellent waveguiding properties with a simple geometry that allows for incorporation of unique electromagnetic functionalities. A few passive devices are discussed while the focus remains on active devices. The active control is enabled by our innovation to incorporate liquid metals, which can be relocated by application of a small electrical voltage (< 4V), as part of the waveguide geometry itself. The device geometry directly affects the device performance (e.g., frequency band of operation, channel output power). Therefore, by moving the liquid metal, the geometry is reconfigured which results in altering the device function. To show the practicality of these devices to be used for THz wireless communications, we demonstrate the ability of these devices to support a 1 Gb/s data stream on a THz carrier wave and show that this signal can be successfully switched with high modulation depths of ±40 dB. These results show the strong promise of these components to form important signal processing building blocks in the future infrastructure of THz wireless communications.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.