We describe the development of a small profiling float, the ALAMO (Air-Launched Autonomous Micro-Observer), that observes upper-ocean structure over a year. These floats can be launched from any aircraft equipped with an "A-sized" launch tube, or from the door of any other aircraft. Profiling floats have found wide use in the oceanographic community, from their original design in the World Ocean Circulation Experiment (Davis et al., 1992) to their current widespread usage in the Argo program (Riser et al., 2016). The utility of profiling floats derives from their relative affordability and their autonomous nature once deployed. The ALAMO float works on the same principles as the ALACE (Autonomous Lagrangian Circulation Explorer) profiling float designed by Davis et al. (1992), which developed into the SOLO (Sounding Oceanographic Lagrangian Observer) profiling floats used in the Argo program today (Davis et al., 2001). The ALAMO float represents a natural progression of those earlier designs.

In most areas, estimating the presence and distribution of cryptic marine mammal species, such as beaked whales, is extremely difficult using traditional observational techniques such as ship-based visual line transect surveys. Because acoustic methods permit detection of animals underwater, at night, and in poor weather conditions, passive acoustic observation has been used increasingly often over the last decade to study marine mammal distribution, abundance, and movements, as well as for mitigation of potentially harmful anthropogenic effects. However, there is demand for new, cost-effective tools that allow scientists to monitor areas of interest autonomously with high temporal and spatial resolution in near-real time. Here we describe an autonomous underwater vehicle — a glider — equipped with an acoustic sensor and onboard data processing capabilities to passively scan an area for marine mammals in near-real time. The instrument developed here can be used to cost-effectively screen areas of interest for marine mammals for several months at a time. The near-real-time detection and reporting capabilities of the glider can help to protect marine mammals during potentially harmful anthropogenic activities such as seismic exploration for sub-sea fossil fuels or naval sonar exercises. Furthermore, the glider is capable of under-ice operation, allowing investigation of otherwise inaccessible polar environments that are critical habitats for many endangered marine mammal species.

Passive acoustic monitoring (PAM), now widely used for marine mammal research, is typically conducted using hydrophone arrays towed behind ships, providing real-time data from large areas over short time spans (days to weeks), or using fixed autonomous hydrophones, providing non-real-time data from small areas over long time spans (months to years). In contrast, mobile platforms can supply near-real-time data over spatiotemporal scales large in both space and time. These systems are deployed from a vessel, communicate via satellite with shore stations for navigation and control updates, and report in near-real time upon detecting marine mammal or other sounds of interest. Acoustically-equipped gliders are buoyancy-driven devices that are capable of traversing long distances (hundreds to thousands of kilometers) over weeks to months of autonomous operation. Autonomous floats such as QUEphones drift with currents or park on the seafloor, rising to the surface upon detecting sounds of interest. Robot sailboats such as the Roboat use wind to propel themselves quickly over long distances. All platforms can store large datasets and carry additional sensors (e.g., temperature, salinity, chlorophyll, pH, O2), and are therefore well-suited for investigating oceanographic and ecological questions. Advantages and disadvantages of these platforms for various applications will be discussed.