Similarity search is a popular technique for seismic signal processing, with template matching, matched filters, and subspace detectors being utilized for a wide variety of tasks, including both signal detection and source discrimination. Traditionally, these techniques rely on the cross‐correlation function as the basis for measuring similarity. Unfortunately, seismogram correlation is dominated by path effects, essentially requiring a distinct waveform template along each path of interest. To address this limitation, we propose a novel measure of seismogram similarity that is explicitly invariant to path. Using Earthscope’s USArray experiment, a path‐rich dataset of 207,291 regional seismograms across 8452 unique events is constructed, and then employed via the batch‐hard triplet loss function, to train a deep convolutional neural network that maps raw seismograms to a low‐dimensional embedding space, where nearness on the space corresponds to nearness of source function, regardless of path or recording instrumentation. This path‐agnostic embedding space forms a new representation for seismograms, characterized by robust, source‐specific features, which we show to be useful for performing both pairwise event association as well as template‐based source discrimination with a single template.

Three-dimensional (3D) FLASH Laser Radar (LADAR) sensors are unique due to the ability to rapidly acquire a series of two dimensional remote scene data (i.e. range images). Principal causes of 3D FLASH LADAR range estimation error include spatial blur, detector blurring, noise, timing jitter, and inter-sample targets. Unlike previous research, this paper accounts for pixel coupling by defining the range image mathematical model as a 2D convolution between the system spatial impulse response and the object (target or remote scene) at a particular point in time. Using this model, improved range estimation is possible by object restoration from the data observations. Object estimation is performed by deriving a blind deconvolution Generalized Expectation Maximization (GEM) algorithm with the range determined from the estimated object by a normalized correlation method. Theoretical derivations and simulation results are verified with experimental data of a bar target taken from a 3D FLASH LADAR system in a laboratory environment. Simulation examples show that the GEM improves range estimation over the unprocessed data and a Wiener filter method by 75% and 26% respectively. In the laboratory experiment, the GEM improves range estimation by 34% and 18%over the unprocessed data and Wiener filter method respectively.

The global positioning system (GPS) generally provides worldwide high-accuracy positioning. However, GPS requires lines of sight to multiple satellites and may be blocked or jammed, hence backup navigation techniques are of interest. Navigation via signals of opportunity uses existing radio infrastructure as ad hoc navigational beacons. A mobile receiver determines its position by computing a time difference of arrival (TDOA) between signal reception time at the mobile and at a reference receiver. The drawback is that this requires communication between the reference and mobile receivers. In this paper, we show that multicarrier modulation is an ideal candidate for a navigation signal of opportunity. We show that communication between the reference and mobile can be very minimal for multicarrier modulation compared to other modulation types, since the block structure inherently aids synchronization of the two received signals. Simulations are used to quantify the performance of the TDOA estimate as a function of the SNR and the bandwidth between the reference and the mobile.