Kevin Rogers

Three-Dimensional UAV-Based Atmospheric Tomography

AbstractThis paper presents a method for tomographically reconstructing spatially varying three-dimensional atmospheric temperature profiles and wind velocity fields based on passive acoustic travel time measurements between a small unmanned aerial vehicle (UAV) and ground-based microphones. A series of simulations are presented to provide an indication of the performance of the technique. The parametric fields are modeled as the weighted sum of radial basis functions (RBFs) or Fourier series, which also allow local meteorological measurements made at the UAV and ground receivers to supplement any time delay observations. The technique has potential for practical applications such as boundary layer meteorology and theories of atmospheric turbulence and wave propagation through a turbulent atmosphere.

Frequency estimation for 3D atmospheric tomography using unmanned aerial vehicles

Spatially varying three-dimensional atmospheric temperature profiles and wind velocity fields may be derived by observing the acoustic signature of an Unmanned Aerial Vehicle (UAV) as it flies over ground-based microphones. The Doppler shift between the UAV and the ground microphones is used to estimate the acoustic propagation times and the atmospheric parameters are then estimated from the derived acoustic propagation times. The estimates may be supplemented by local meteorological measurements made at the UAV and/or the ground receivers. The technique models the atmospheric temperature and wind speed profiles as a 3-dimensional continuous array of Radial Basis Functions. This technique has potential for atmospheric research and practical applications such as boundary layer meteorology, theories of atmospheric turbulence and wave propagation through a turbulent atmosphere. This paper describes how the propagation time and speed of sound is derived from the Doppler frequency. It then describes the method for performing tomographic inversion and then provides simulation results.

Quality Control of Meteorological Data for the Chemical Stockpile Emergency Preparedness Program

The Chemical Stockpile Emergency Preparedness Program Meteorological Support Project ensures the accuracy and reliability of data acquired by meteorological monitoring stations located at seven U.S. Army chemical weapons depots where storage and weapons destruction (demilitarization) activities are ongoing. The data are delivered in real time to U.S. Army plume dispersion models, which are used to plan for and respond to a potential accidental release of a chemical weapons agent. The project provides maintenance, calibration, and audit services for the instrumentation; collection, automated screening, visual inspection, and analysis of the data; and problem reporting and tracking to carefully control the data quality. The resulting high-quality meteorological data enhance emergency response modeling and public safety.

The feasibility of unmanned aerial vehicle-based acoustic atmospheric tomography

A technique for remotely monitoring the near-surface air temperature and wind fields up to altitudes of 1 km is presented and examined. The technique proposes the measurement of sound spectra emitted by the engine of a small unmanned aerial vehicle using sensors located on the aircraft and the ground. By relating projected and observed Doppler shifts in frequency and converting them into effective sound speed values, two- and three-dimensional spatially varying atmospheric temperature and wind velocity fields may be reconstructed using tomography. The feasibility and usefulness of the technique relative to existing unmanned aerial vehicle-based meteorological techniques using simulation and trials is examined.

Improving Unmanned Aerial Vehicle–Based Acoustic Atmospheric Tomography by Varying the Engine Firing Rate of the Aircraft

AbstractIf the acoustic signature of an unmanned aerial vehicle (UAV) is observed as it overflies an array of ground microphones, then the projected and observed Doppler shifts in frequency of the narrowband tones generated by its engine may be compared and converted into effective sound speed values. This allows 2D and 3D spatially varying atmospheric temperature and wind velocity fields to be estimated using tomography. Errors in estimating sound speed values are inversely proportional to the rate of change in the narrowband tones received on the ground. As this rate of change typically approaches zero at least twice per microphone during the UAV’s overflight, errors in the time of flight estimates are typically too large to deliver useful precision to the tomographically derived temperature and wind fields. However, these errors may be reduced by one or two orders of magnitude by continuously varying the engine throttle rate, thereby making the tomographic technique potentially feasible. This is demons...

3D Acoustic Atmospheric Tomography

This paper presents a method for tomographically reconstructing spatially varying 3D atmospheric temperature profiles and wind velocity fields based. Measurements of the acoustic signature measured onboard a small Unmanned Aerial Vehicle (UAV) are compared to ground-based observations of the same signals. The frequency-shifted signal variations are then used to estimate the acoustic propagation delay between the UAV and the ground microphones, which are also affected by atmospheric temperature and wind speed vectors along each sound ray path. The wind and temperature profiles are modelled as the weighted sum of Radial Basis Functions (RBFs), which also allow local meteorological measurements made at the UAV and ground receivers to supplement any acoustic observations. Tomography is used to provide a full 3D reconstruction/visualisation of the observed atmosphere. The technique offers observational mobility under direct user control and the capacity to monitor hazardous atmospheric environments, otherwise not justifiable on the basis of cost or risk. This paper summarises the tomographic technique and reports on the results of simulations and initial field trials. The technique has practical applications for atmospheric research, sound propagation studies, boundary layer meteorology, air pollution measurements, analysis of wind shear, and wind farm surveys.

Acoustic atmospheric tomography using multiple unmanned aerial vehicles

This paper presents a method for tomographically reconstructing atmospheric temperature profiles and wind velocity fields based on acoustic travel time measurements between two or more Unmanned Aerial Vehicles (UAVs). The technique offers mobility and the capacity to monitor hazardous atmospheric environments, otherwise not justifiable on the basis of cost or risk. Simulations, in which the parametric fields of the atmosphere are modelled as a weighted sum of Radial Basis Functions, demonstrate the technique’s potential performance envelope. The approach also allows local meteorological measurements made at the UAVs to supplement any time delay observations. This increases the accuracy of the technique, which has potential for practical applications in boundary layer meteorology, the theory of atmospheric turbulence, and wave propagation through a turbulent atmosphere.

Accurate group velocity estimation for unmanned aerial vehicle-based acoustic atmospheric tomography

Acoustic atmospheric tomography calculates temperature and wind velocity fields in a slice or volume of atmosphere based on travel time estimates between strategically located sources and receivers. The technique discussed in this paper uses the natural acoustic signature of an unmanned aerial vehicle as it overflies an array of microphones on the ground. The sound emitted by the aircraft is recorded on-board and by the ground microphones. The group velocities of the intersecting sound rays are then derived by comparing these measurements. Tomographic inversion is used to estimate the temperature and wind fields from the group velocity measurements. This paper describes a technique for deriving travel time (and hence group velocity) with an accuracy of 0.1% using these assets. This is shown to be sufficient to obtain highly plausible tomographic inversion results that correlate well with independent SODAR measurements.

UAV-based atmospheric tomography using Large Eddy Simulation data

Atmospheric acoustic tomography is used to estimate the 2 or 3 dimensional spatial distribution of temperature and wind in the Atmospheric Boundary Layer. Some applications of these results are atmospheric research, boundary layer meteorology, theories of atmospheric turbulence and wave propagation through a turbulent atmosphere. The tomographic technique described in this paper uses an Unmanned Aerial Vehicle flying over a horizontal array of ground based microphones. The temperature and wind profiles are estimated using tomographic inversion derived from the sound propagation time estimates between the Unmanned Aerial Vehicle and the microphones. Previous papers have reported on this technique for a random atmosphere that is not necessarily realistic. This paper reports on the results from investigations using more realistic atmospheres generated using Large Eddy Simulation.

An Acoustic Tomography Technique for Concurrently Observing the Structure of the Atmosphere and Water Bodies

AbstractThe opacity of water to radio waves means there are few, if any, techniques for remotely sensing it and the atmosphere concurrently. However, both these media are transparent to low-frequency sound (<300 Hz), which makes it possible to contemplate systems that take advantage of the natural integration along acoustic paths of signals propagating through both media. This paper proposes—and examines with theoretical analysis—a method that exploits the harmonics generated by the natural signature of a propeller-driven aircraft as it overflies an array of surface and underwater sensors. Correspondence of the projected and observed narrowband acoustic signals, which are monitored synchronously on board the aircraft and by both sensor sets, allows the exact travel time of detected rays to be related to a linear model of the constituent terms of sound speed. These observations may then be inverted using tomography to determine the inhomogeneous structures of both regions. As the signature of the aircraft ...