Montana and similar regions contain numerous rivers and lakes that are too small to be spatially resolved by satellites that provide water quality estimates. Unoccupied Aerial Vehicles (UAVs) can be used to obtain such data with much higher spatial and temporal resolution. Water properties are traditionally retrieved from passively measured spectral radiance, but polarization has been shown to improve retrievals of the attenuation-to-absorption ratio to enable calculation of the scattering coefficient for in-water particulate matter. This feeds into improved retrievals of other parameters such as the bulk refractive index and particle size distribution. This presentation will describe experiments conducted to develop a data set for water remote sensing using combined UAV-based hyperspectral and polarization cameras supplemented with in-situ sampling at Flathead Lake in northwestern Montana and the results of preliminary data analysis. A symbolic regression model was used to derive two equations: one relating DoLP, AoP, and the linear Stokes parameters at wavelengths of 440 nm, 550 nm and 660 nm, to chlorophyll-a content, and one relating the same data to the attenuation-to-absorption ratio for 440 nm, 550 nm and 660 nm. Symbolic regression is a machine learning algorithm where the inputs are vectors and the output is an analytic expression, typically chosen by a genetic algorithm. An advantage of this approach is that the explainability of a simple equation can be combined with the accuracy of less explainable models, such as the genetic algorithm.
This paper demonstrates the use of a variable focus MEMS mirror in a frequency-modulated continuous-wave (FMCW) lidar system. The mirror can reveal short range targets that are typically hidden because the lidar was out of focus, and has demonstrated the ability to increase the signal level by over 20 dB for close-range targets. We have also demonstrated the ability to dynamically change the focus of the lidar during each sweep of the galvonometer, thus allowing the resolution of targets at different ranges during each sweep. The electrostatically driven 4 mm diameter mirror has a transition time of less than 1 ms and a focal length that can range from infinity to 56 mm which corresponds to wavefront Zernike fringe defocus coefficient ranging from 0 to 18 μm.
A near-monostatic laser polarimeter has been designed, built, and used to measure angular Mueller matrices characterizing the polarization-dependent reflectance of materials in support of research into polarization lidar. Here we explain the system, show that it has qualitatively similar results as previous complex systems, and show example measurements for red brick, concrete, sheetrock, tar shingles, milled aluminum, and plain steel.
Airborne lidar data for fishery surveys often do not contain physics-based features that can be used to identify fish; consequently, the fish must be manually identified, which is a time-consuming process. To reduce the time required to identify fish, supervised machine learning was successfully applied to lidar data from fishery surveys to automate the process of identifying regions with a high probability of containing fish. Using data from Yellowstone Lake and the Gulf of Mexico, multiple experiments were run to simulate real-world scenarios. Although the human cannot be fully removed from the loop, the amount of data that would require manual inspection was reduced by 61.14% and 26.8% in the Yellowstone Lake and Gulf of Mexico datasets, respectively.
We report the lidar detection of an underwater feature that appears to be a thermal vent in Yellowstone Lake, Yellowstone National Park, USA, with the Montana State University Fish Lidar. The location of the detected vent was 30 m from the closest vent identified in a United States Geological Survey of Yellowstone Lake in 2008. A second possible vent is also presented, and the appearance of both vents in the lidar data is compared to descriptions of underwater thermal vents in Yellowstone Lake from the geological literature.
KEYWORDS: LIDAR, Receivers, Research management, Signal to noise ratio, Water, Signal attenuation, Calibration, Scattering, Pulsed laser operation, Ecosystems
The design of a compact, dual-polarization, nonscanning lidar system intended to fly in a small, single-engine aircraft for airborne study of freshwater marine ecosystems and mapping of fish schools in mountain lakes is discussed. Design trade-offs are presented with special attention paid to selecting the field of view and telescope aperture diameter. Example results and a comparison with a similar existing lidar system are presented.
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