Technology

Saildrone In Situ Observation: A Single Platform with a Multi-Purpose

Saildrone USVs have proven to be a valuable tool in a multiplatform observation network, but they can also achieve a variety of mission objectives simultaneously, saving money and resources.

By
Saildrone
,
on
April 20, 2020

Inquisitive minds have been observing Earth’s oceans since the dawn of civilization. While observation technologies have improved dramatically from the crude tools used by early ocean explorers, the vastness of the global ocean, the extreme temperatures and weather conditions, and the sheer cost of observation present significant challenges to continuing to advance our understanding of ocean ecosystems, air-sea interactions, and the impact of the ocean on other earth systems. Ships, satellites, submersibles, and autonomous vehicles make observation possible; the remaining challenge is how to make it cost-effective at temporal and spatial scales that can help us address these complex questions.

The Saildrone unmanned surface vehicle (USV) has proven to be a valuable component in a multiplatform observing system—augmenting ship-based fisheries surveys, improving climate models and weather prediction with an array of air, space, surface, and sub-surface platforms, and complementing fixed ocean stations as a tool for cross-calibration and validation—but the vehicle is also multipurpose, capable of collecting data for a range of mission objectives at the same time.

It’s not a coincidence that many of the world’s most robust fisheries are found in the most productive areas of the ocean—the eastern boundary currents like the California Current are affiliated with strong upwelling zones that bring nutrient-rich waters to the surface. Saildrone has performed a number of fisheries surveys off the US West Coast, in the Bering Sea, and the North Sea. Eastern boundary currents are also areas with active frontal boundaries and intense air-sea interactions.

Saildrone mission tracks

Saildrone mission tracks (clockwise from top left): Bering Sea, North Sea, US West Coast, Atlantic Ocean, Pacific Ocean.

Over the course of many missions, saildrones regularly sail back and forth across fronts. While fisheries surveys provide valuable information about the quantity and location of stocks, which is critical to sustainably manage resources, information about the ocean ecosystem in these productive regions can help to improve climate and weather models and increase the value of remote sensing data.

Western boundary currents like the Gulf Stream in the Atlantic Ocean and the Kuroshio Current in the Pacific Ocean are thought to absorb large quantities of carbon dioxide and are of great interest to physical oceanographers and climatologists. These warm, fast-flowing currents transport heat from the equator toward the poles, shedding eddies that carry nutrients normally found in colder, nutrient-rich waters at their poleward side into the subtropics, which attracts phytoplankton and the larger species that feed on them—baleen whales, sharks, turtles, and shellfish. Western boundary currents present conditions that make in situ observation extremely difficult, especially in the winter when carbon fluxes are most active; Saildrone has completed wintertime missions to collect carbon observations in both currents.

The standard Saildrone sensor suite includes science-grade instruments to collect air, sea, and skin temperature, wind speed and direction, relative humidity, barometric pressure, photosynthetically active radiation, salinity, dissolved oxygen, chlorophyll, and wave height and period. Optional sensors include an Acoustic Doppler Current Profiler to measure ocean currents, a single-beam echo sounder to measure fish biomass, and an ASVCO2 developed by NOAA PMEL to measure atmospheric and dissolved partial pressure of carbon dioxide (pCO2).

Saildrone optional sensors
Saildrones can be equipped with a variety of optional insruments in addition to the standard sensor suite (clockwise from top left): SD 1033 is equipped with the NOAA PMEL ASVCO2 sensor just aft of the wing. Further aft is the Eppley PIR to observe longwave radiation; SD 1028 equipped with a ROW; a saildrone equipped with keel-mounted CTDs to observe near-surface temperature gradietns; SD 1036 and SD 1037 equipped with IR pyrometers.

Other sensors that have been successfully integrated into the Saildrone sensor package include a shallow-water multibeam echo sounder and sound velocity profiler, an infrared (IR) pyrometer to measure skin temperature and sky radiation, a Remote Optical Watcher (ROW) to detect hydrocarbons on the surface of the water, and sensors to measure longwave and shortwave radiation. The vehicles are deployable up to 12 months, and even during highly specialized Saildrone missions, they collect a valuable set of metocean data, which could be used by other groups to make simultaneous discoveries.

In some cases, multipurpose missions have been developed across disciplines, in other cases, data from complete missions is released to the public via one of several public portals.

During the 2019 Arctic mission, a fleet of five saildrones observed sea ice to improve ice prediction, measured sea surface temperature (SST) for satellite algorithm development, and studied air-sea carbon interactions in the Chukchi Sea. The mission was operated in partnership with NOAA and NASA. The Saildrone Atlantic to Mediterranean (ATL2MED) mission is a public-private partnership between Saildrone and 12 oceanographic research institutions with several different mission objectives including an eddy survey, cross-calibration of European research infrastructure (RI) sites, and validation of carbon measurements. The mission is supported by the private technology and investment firm PEAK6.

Public-private partnerships and philanthropic support make proprietary Saildrone data sets accessible to a wider audience, either through Saildrone’s own data portal data.saildrone.com or through one of several partner sites, for example, NASA PO.DAAC, NOAA ERDDAP, and EMODnet.

Saildrone data sets
Available data sets on the Saildrone Data Explorer at data.saildrone.com.

Data quality is paramount. Working in close collaboration with our science partners, Saildrone has established a robust and transparent data chain of custody to ensure that each sensor and essential variable is properly understood, and that calibration and validation are tracked during hardware and software design cycles. The Saildrone sensor suite has been developed through rigorous laboratory testing and multiple years of at-sea comparisons correlating Saildrone data with the established standards of ships and buoys. Data is distributed along with CF-compliant metadata that describes in detail every procedure undertaken: each sensor’s initial quality control, drift, calibration, and platform effects.

Saildrone is working toward the deployment of a global fleet of autonomous vehicles for permanent monitoring of Earth’s oceans to enable the science community to achieve the goals set forth by the United Nations Decade of Ocean Science for Sustainable Development. And, we are establishing formal working groups focused on critical areas of ocean observation: surface fluxes, biogeochemistry, fisheries acoustics, and data management to facilitate the involvement of the science community in the growing Saildrone global surface observing network and to promote active cooperation across agencies, institutions, and disciplines.

What could data from a global fleet of saildrones mean to your work? What types of cross-discipline missions could your work benefit from? Contact us to let us know!


Main photo: SD 1030 rendezvous with the Portuguese Navy vessel Gago Coutinho outside the Strait of Gibraltar during the 2020 ATL2MED mission. Courtesy Instituto Hidrográfico.