Campus Map

Timothy Marston

Principal Engineer





Department Affiliation



B.S. Electrical Engineering, Seattle Pacific University, 2004

M.S. Acoustics, Penn State, 2006

Ph. D. Acoustics, Penn State, 2009


2000-present and while at APL-UW

Utilization of aspect angle information in synthetic aperture images

Plotnick, D.S., and T.M. Martston, "Utilization of aspect angle information in synthetic aperture images," IEEE Trans. Geosci. Remote Sens., 56, 5424-5432, doi:10.1109/TGRS.2018.2816462, 2018.

More Info

1 Sep 2018

Synthetic aperture sonar and synthetic aperture radar involve the creation of high-resolution images of a scene via scattered signals recorded at different locations. Each pixel of the reconstructed image includes information obtained from multiple aspects due to the changing position of the sources/receivers. In this paper, the aspect-dependent scattering at each pixel is exploited to provide additional information about the scene; this paper presents a framework for converting and utilizing multiaspect data, as well as several examples. For sonar data, as is presented here, the aspect dependence may be leveraged to separate objects of interest from the background, to understand the local bathymetry, or for visualizing acoustic shadowing in full circular synthetic aperture sonar images. Several examples of images of the seafloor containing objects of interest are presented for both circular and linear apertures. In addition, the aspect dependence of low-frequency elastic scattering from objects may be used to understand the underlying scattering physics, which is of potential use in fields such as target recognition and nondestructive testing; a laboratory example is presented.

Circular synthetic aperture sonar imaging of simple objects illuminated by an evanescent wavefield

Plotnick, D.S., T.M. Marston, and P.L. Marston, "Circular synthetic aperture sonar imaging of simple objects illuminated by an evanescent wavefield," J. Acoust. Soc. Am., 140, 2839-2846, doi:10.1121/1.4964329, 2016.

More Info

1 Oct 2016

This paper is motivated by the case where an underwater object located within the sediment is illuminated by a grazing acoustic beam below the critical angle. The included experimental work uses a liquid−liquid interface and vertically inverted geometry as a stand-in for the water−sediment boundary. In the super-critical regime sound in the water column refracts into the sediment before scattering. However, for sub-critical illumination a rapidly decaying evanescent wavefield is generated in the sediment near the water−sediment interface. For compact objects located in the sediment near the interface this can result in strong backscattering signals suitable for acoustic image reconstruction using synthetic aperture sonar techniques. Certain properties of the evanescent wavefield such as the vertical phase-locking behavior, the rapid amplitude decay with distance from the interface, and the low-pass filter effect have understandable ramifications for the image formation process and for characteristics of the reconstructed image. In particular, circular imaging techniques require correct placement of the imaging plane to properly focus an object; however, for backscattering (monostatic) evanescent image formation the imaging plane may be placed at the interface and the target will remain in focus regardless of burial depth. A laboratory experiment using simple scatterers is presented.

Volumetric acoustic imaging via circular multipass aperture synthesis

Marston, T.M., and J.L. Kennedy, "Volumetric acoustic imaging via circular multipass aperture synthesis," IEEE J. Ocean. Eng., 41, 852-867, doi:10.1109/JOE.2015.2502664, 2016.

More Info

1 Oct 2016

In this paper, volumetric imaging via multipass circular synthetic aperture sonar (CSAS) is demonstrated using an autonomous underwater vehicle (AUV). A multidimensional aperture is synthesized by performing a series of circular scans at varying grazing angles around targets and coherently combining the backscattering information from the set of scans to form high-resolution volumetric images. A data-driven technique for precision alignment of the individual scans comprising the multipass set enables synthesis of a multidimensional array. To beamform in the vertical dimension using the irregular and undersampled multipass aperture, a compressive-sensing-based approach is adopted which is similar to methods used in analogous synthetic aperture radar tomography applications but modified to accommodate for the wider fractional bandwidth of the synthetic aperture sonar (SAS) system. The modification exploits a joint sparsity assumption in the vertical scattering profile at different subbands and adapts a standard joint sparse solving algorithm to the relevant case in which the sparsity profile is common between solution vectors but the sensing matrices are different. Results are shown for a variety of targets, including proud and obliquely buried unexploded ordnance, a 2-1 solid aluminum cylinder, and a steel oil drum.

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center