Habitats

Drones address an observational blind spot for biological oceanography

Abstract

Marine biological communities are dynamic across many scales in both space and time. Such multi-scale complexity complicates efforts to fully characterize these communities. Critical processes unfold on the order of 0.1–10 kilometers and 0.1–10 days, but conventional oceanographic techniques generally do not observe or model at this scale. Small aerial drones conveniently achieve scales of observation between satellite resolutions and in-situ sampling, and effectively diminish the “blind spot” between these established measurement techniques. Despite this promise, drone-based techniques face challenges inherent to optical oceanography, as well as logistical and regulatory barriers relating to both aerial and marine operations. Such obstacles have slowed adoption of drones for marine biological study, but best practices are emerging alongside new techniques that facilitate robust study designs and rigorous data collection. With such advancements, drones promise to complement conventional approaches in biological oceanography to more fully capture the spatiotemporal complexity of the marine environment.

Citation

Robust ocean color from drones: Viewing geometry, sky reflection removal, uncertainty analysis, and a survey of the Gulf Stream front

Abstract

Accurate and robust retrieval of ocean color from remote sensing enables critical observations of aquatic natural systems, from open ocean biological oceanography, coastal biodiversity, and water quality for human health. In the last decade, studies have increasingly highlighted the important role of small-scale processes in coastal and marine ecology and biogeochemistry, but observation and modeling at these scales remains technologically limited. Unoccupied aircraft systems (UAS, aka drones) can rapidly sample large areas with high spatial and temporal resolution; but the challenge of accurately retrieving ocean color, particularly with common wide field-of-view multispectral imagers, has limited the adoption of this technology. As UAS endurance, autonomy, and sensor capabilities continue to increase, so does this technology’s potential to observe the ocean at fine scales, but only if proper protocols are followed. The present study provides a guide for achieving (1) ideal viewing geometry of UAS-borne ocean color sensors, (2) techniques for the removal of sun glint and reflected skylight to derive water-leaving radiances, (3) characterization of uncertainty in these measurements, and (4) converting water-leaving radiances to remote-sensing reflectance for analytic end products such as chlorophyll a estimates. Documented open-source code facilitates replication of this emerging technique. Using this methodology, we briefly describing fine-scale variability of the Gulf Stream front off North Carolina alongside synoptic satellite data and in situ measurements for comparison. These results demonstrate how UAS-based ocean color measurements complement and enhance conventional ocean observations and modeling to resolve fine-scale variability and close the lacuna between satellite and in situ methods.

Citation

Drone-based monitoring and geomorphology of southern giant petrel nests near Palmer Station, western Antarctic Peninsula

Abstract

Human activities and climate change threaten seabirds globally, and many species are declining from already small breeding populations. Monitoring of breeding colonies can identify population trends and important conservation concerns, but it is a persistent challenge to achieve adequate coverage of remote and sensitive breeding sites. Southern giant petrels (Macronectes giganteus) exemplify this challenge: as polar, pelagic marine predators they are subject to a variety of anthropogenic threats, but they often breed in remote colonies that are highly sensitive to disturbance. Aerial remote sensing can overcome some of these difficulties to census breeding sites and explore how local environmental factors influence important characteristics such as nest-site selection and chick survival. To this end, we used drone photography to map giant petrel nests, repeatedly evaluate chick survival and quantify-associated physical and biological characteristics of the landscape at two neighboring breeding sites on Humble Island and Elephant Rocks, along the western Antarctic Peninsula in January–March 2020. Nest sites occurred in areas with relatively high elevations, gentle slopes, and high wind exposure, and statistical models predicted suitable nest-site locations based on local spatial characteristics, explaining 72.8% of deviance at these sites. These findings demonstrate the efficacy of drones as a tool to identify, map, and monitor seabird nests, and to quantify important habitat associations that may constitute species preferences or sensitivities. These may, in turn, contextualize some of the diverse population trajectories observed for this species throughout the changing Antarctic environment.

Citation