A new continuous flow diffusion chamber (CFDC) has been designed and constructed to study the ice nucleation efficiency of natural and anthropogenic aerosol particles over a range of temperatures and supersaturations. The CFDC system at Dalhousie University, Canada is based on the design of Rogers et al. (1988, 1994) at Colorado State University, USA. A steady airflow (2.83 lpm) composed of sheath flows and an aerosol flow passes through the annular gap of the diffusion chamber. The walls of the chamber are ice-covered and are held at different temperatures. Aerosol particles are injected into the center of the gap near the location of maximum supersaturation. Particles greater than 5 µm in aerodynamic diameter are removed with impactors before entry to the chamber. Ice crystals are identified with an optical particle counter at the outlet of the chamber. In this article we report on the ice nucleation results of two mineral dust particles of potential atmospheric relevance, kaolinite and montmorillonite. Our results indicate that kaolinite and montmorillonite act as efficient ice nuclei in deposition/condensation nucleation mode. The onset relative humidity of both kaolinite and montmorillonite mineral dust particles were determined. The percentage of active ice nuclei is higher in montmorillonite compared to kaolinite at each temperature within the experimental conditions. The fraction of active ice nuclei increases with decreasing temperature and also with increasing relative humidity.

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The performance of continuous active sonar (CAS) was compared to conventional pulsed active sonar (PAS) during the TREX13 (Target and Reverberation Experiment 2013) sea trial. The approach was to execute a one-hour CAS run followed closely by a one-hour PAS run to limit the environmental variability between runs and allow a fair comparison. This approach was possible because the sonar source and receiver were fixed to the seabed. A different approach was required for a more recent sea trial, LCAS15 (Littoral Continuous Active Sonar 2015), where the source and receiver were towed from a ship. Ship motion increases variability in sonar performance, therefore a simultaneous comparison of CAS and PAS was desired so that any motion effects were the same for both waveforms. The approach of transmitting CAS and PAS concurrently in two separate frequency bands was taken. The risk with this approach is that potential differences in propagation in the two bands could bias the comparison. A run in which equivalent CAS waveforms were transmitted simultaneously in the two bands was therefore performed to establish a baseline for the performance difference between the bands. Doppler-corrected replicas were required in all of the correlation processing due to the high Doppler sensitivity of the long-duration, wideband CAS waveforms. Preliminary results from the LCAS15 sea trial will be presented.

In recent years, there has been a proliferation of Ocean Observing Systems (OOS) along with a wide distribution of their associated data products. The collected data support scientific research, industry, and government organizations by providing long term measurements of biological, chemical, and physical properties of the ocean environment. However, the collection and distribution of underwater acoustic data poses a potential security risk for naval vessels operating in the vicinity of OOS. The Canadian Forces Maritime Experimental and Test Ranges (CFMETR) provide an underwater tracking facility for naval tests, and are approximately 50 km from hydrophones of the Victoria Experimental Network Under the Sea (VENUS) observatory. Under an existing CFMETR-VENUS agreement, data are diverted during certain naval tests. In order to minimize the frequency of these data diversions, a study is being conducted to investigate acoustic propagation in the Strait of Georgia. The results of acoustic modeling and measurement of transmission loss from CFMETR to VENUS will be presented. A software application called CAVEAT is also presented. The application was developed to integrate the transmission loss results along with other sonar parameters to enable operators at CFMETR to determine the risk of acoustic exposure.

Passive acoustic monitoring (PAM) is often suggested as an effective technology to mitigate impacts from anthropogenic activities; however, the ability to reliably and efficiently detect, locate, and count cetaceans using PAM is still in development. One particularly useful application of PAM is species density estimation, which requires an estimate of the number of individuals involved in a detection event. Efforts have been undertaken to develop methods to directly count the number of vocalizing animals during acoustic detection events. For odontocetes, discrete clicks are almost indistinguishable between individuals, making it more difficult to determine the number of vocalizing animals as the number increases. Using recordings from multiple closely spaced (≈200 m) GuardBuoy sensors deployed on the Canadian Scotian Shelf, cross-sensor correlograms were produced to estimate the number of individual sperm whales, and, as a more challenging case, the number of vocalizing delphinids. Using feature-based multipath reflection discrimination, the raw time series were reduced to a synthetic time series of binary click detections with the multipath arrivals removed. The synthesized click-detection time series were used for the cross-sensor correlograms to generate improved estimates of the number of vocalizing animals as compared with using the raw time series.