Wave focusing of energetic swell fields can result in small‐scale variations associated with coherent interference that can be important for nearshore circulation and beach dynamics. However, coherent interference is difficult to measure with conventional in situ instruments and is not accounted for in operational wave models. As a result, such effects are generally ignored. In this work, we analyze X‐band radar observations collected at Ocean Beach, San Francisco using a Wigner‐Ville or coupled‐mode spectrum, to show how long‐dwell remote sensing technology allows us to identify coherent wave interference. Our analysis demonstrates that during energetic swell events, the nearshore wave field consists of two noncollinear, but coherent, swell patterns that originate from the same offshore source but are directionally separated due to refraction over the San Francisco Bar. The length scale of the associated alongshore wave height variability (200 m) is consistent with the wavenumber separation obtained from the coupled mode analysis. This confirms that the small‐scale variability is primarily due to coherent interference. In addition, our analysis shows that the shoreline exhibits a strong localized response near the radar site on the 200 m scale, which suggests that coherent interference effects can affect wave‐driven nearshore transport processes and localized erosion.

Vessel traffic management systems can be employed for environmental management where vessel activity may be of concern. One such location is in San Francisco Bay where a variety of vessel types transit a highly developed urban estuary. We analyzed vessel presence and speed across space and time using vessel data from the Marine Monitor, a vessel tracking system that integrates data from the Automatic Identification System and a marine-radar sensor linked to a high-definition camera. In doing so, we provide data that can inform collision risk to cetaceans who show an increased presence in the Bay and evaluation of the value in incorporating data from multiple sources when observing vessel traffic. We found that ferries traveled the greatest distance of any vessel type. Ferries and other commercial vessels (e.g., cargo and tanker ships and tug boats) traveled consistently in distinct paths while recreational traffic (e.g., motorized recreational craft and sailing vessels) was more dispersed. Large shipping vessels often traveled at speeds greater than 10 kn when transiting the study area, and ferries traveled at speeds greater than 30 kn. We found that distance traveled and speed varied by season for tugs, motorized recreational and sailing vessels. Distance traveled varied across day and night for cargo ships, tugs, and ferries while speed varied between day and night only for ferries. Between weekdays and weekends, distance traveled varied for cargo ships, ferries, and sailing vessels, while speed varied for ferries, motorized recreational craft, and sailing vessels. Radar-detected vessel traffic accounted for 33.9% of the total track distance observed, highlighting the need to include data from multiple vessel tracking systems to fully assess and manage vessel traffic in a densely populated urban estuary.

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There is growing evidence that smaller vessels not required to broadcast data via the Automatic Identification System (AIS) contribute significant noise to urbanized coastal areas. The Marine Monitor (M2), a vessel tracking system that integrates AIS data with data collected via marine radar and high-definition camera, was employed to track all vessel types (regardless of AIS data availability) in a region of San Francisco Bay (SFB) where high-speed ferry, recreational, and commercial shipping traffic are common. Using a co-located hydrophone, source levels (SL) associated with 565 unique vessel passages were calculated and resultant cumulative daily sound exposure levels across the study area were modeled. Despite large ships primarily having the highest SLs, ferries and motorized recreational craft contributed noise to the largest area in two frequency bands of interest. The M2 provided data without the need for an on-site observer and enabled a systematic analysis of all relevant vessel types which showed that non-AIS vessels should not be excluded from consideration, especially in a highly urbanized estuary like SFB. This research provides an assessment of underwater radiated noise from all common vessel types in SFB suitable for informing habitat quality and threat evaluation for local cetacean species.

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