Selected Science Publications
Using Saildrones to Validate Arctic Sea-Surface Salinity from the SMAP Satellite and from Ocean Models
The Arctic Ocean is one of the most important and challenging regions to observe—it experiences the largest changes from climate warming, and at the same time is one of the most difficult to sample because of sea ice and extreme cold temperatures. Two NASA-sponsored deployments of the Saildrone vehicle provided a unique opportunity for validating sea-surface salinity (SSS) derived from three separate products that use data from the Soil Moisture Active Passive (SMAP) satellite. To examine possible issues in resolving mesoscale-to-submesoscale variability, comparisons were also made with two versions of the Estimating the Circulation and Climate of the Ocean (ECCO) model (Carroll, D; Menmenlis, D; Zhang, H.). The results indicate that the three SMAP products resolve the runoff signal associated with the Yukon River, with high correlation between SMAP products and Saildrone SSS. Spectral slopes, overall, replicate the -2.0 slopes associated with mesoscale-submesoscale variability. Statistically significant spatial coherences exist for all products, with peaks close to 100 km. Based on these encouraging results, future research should focus on improving derivations of satellite-derived SSS in the Arctic Ocean and integrating model results to complement remote sensing observations.
Vazquez-Cuervo, Jorge; Gentemann, Chelle; Tang, Wenqing; Carroll, Dustin; Zhang, Hong; Menemenlis, Dimitris; Gomez-Valdes, Jose; Bouali, Marouan; Steele, Michael. 2021. "Using Saildrones to Validate Arctic Sea-Surface Salinity from the SMAP Satellite and from Ocean Models" Remote Sens. 13, no. 5: 831. https://doi.org/10.3390/rs13050831Download Paper (PDF)
Constraining Southern Ocean CO2 Flux Uncertainty Using Uncrewed Surface Vehicle Observations
Remote, harsh conditions of the Southern Ocean challenge our ability to observe the region's influence on the climate system. Southern Ocean air‐sea CO2 flux estimates have significant uncertainty due to the reliance on limited ship‐dependent observations in combination with satellite‐based and interpolated data products. We utilize a new approach, making direct measurements of air‐sea CO2, wind speed, and surface ocean properties on an Uncrewed Surface Vehicle (USV). In 2019 the USV completed the first autonomous circumnavigation of Antarctica providing hourly CO2 flux estimates. Using this unique data set to constrain potential error in different measurements and propagate those through the CO2 flux calculation, we find that different wind speed products and sampling frequencies have the largest impact on CO2 flux estimates with biases that range from ‐4% to +20%. These biases and poorly‐constrained interannual variability could account for discrepancies between different approaches to estimating Southern Ocean CO2 uptake.
Sutton, A. J., Williams, N. L., & Tilbrook, B. (2021). Constraining Southern Ocean CO2 Flux Uncertainty Using Uncrewed Surface Vehicle Observations. Geophysical Research Letters, 48, e2020GL091748. https://doi.org/10.1029/2020GL091748Download Paper (PDF)
Autonomous Vehicle Surveys Indicate That Flow Reversals Retain Juvenile Fishes in a Highly Advective High‐Latitude Ecosystem
Summer surveys of the Chukchi Sea indicate that high densities of age‐0 gadid fishes, historically Arctic cod (Boreogadus saida) but recently also walleye pollock (Gadus chalcogrammus), dominate the pelagic fish community. Adults are comparatively scarce, suggesting that either overwinter survivorship of age‐0 gadids is low, or that they emigrate to other areas of the Pacific Arctic. To examine population movement, we conducted repeat acoustic surveys with saildrone autonomous surface vehicles equipped with echosounders throughout summer 2018. The saildrones' range and endurance enabled two large‐scale surveys of the U.S. Chukchi shelf. Acoustic backscatter, a proxy for fish density, was highest in regions with sea surface temperatures of 6–8°C, and lowest in areas influenced by recent ice melt. A subarea of the central Chukchi was surveyed a total of four times; backscatter in this subarea increased by > 85% from late‐July to mid‐September. As summer progressed, fish developed more extensive diel vertical migrations and backscatter from individuals doubled. Both changes suggest increases in backscatter were driven primarily by increasing body size. Particle tracking simulations indicated age‐0 gadids were likely retained over the Chukchi shelf by extended periods of wind‐driven southward flow during the survey period before strong northward flow in late fall transported them to the north. These findings suggest that in summer 2018, age‐0 gadids were advected northward to the Chukchi shelf from the northern Bering Sea, where they were retained during a period of growth until late fall before being advected farther north toward the Chukchi and Beaufort shelf breaks.
Levine, R.M., De Robertis, A., Grünbaum, D., Woodgate, R., Mordy, C.W., Mueter, F., Cokelet, E., Lawrence‐Slavas, N. and Tabisola, H. (2021), Autonomous vehicle surveys indicate that flow reversals retain juvenile fishes in a highly advective high‐latitude ecosystem. Limnol Oceanogr. https://doi.org/10.1002/lno.11671Download Paper (PDF)
Use of Saildrone Observations at ECMWF
ECMWF has started assimilating data from wind-powered ocean drones, called saildrones, that have the potential to improve Earth system observation coverage in remote areas. Despite the rapid growth of satellite observations, in-situ data remain vital to numerical weather prediction. Direct measurements of key atmospheric parameters often provide useful adjustments to the analysis in sensitive areas. The impact of such observations is larger in less-observed regions. An article in the spring 2019 issue of the ECMWF Newsletter described the successful launch of 32 drifting buoys with pressure sensors in the northeast Pacific. Saildrone technology is another emerging platform well positioned to improve the coverage in remote areas and to perform targeted observation campaigns in regions of interest.
Dahoui, Mohamed; Pidduck, Emma; Ingleby, Bruce; Isaksen, Lars; de Halleux, Sebastien. “Use of saildrone observations at ECMWF” ECMWF Newsletter. Number 161 - October 2019 https://www.ecmwf.int/en/newsletter/161/news/use-saildrone-observations-ecmwfDownload Paper (PDF)
Evaluation of Unmanned Surface Vehicle Acoustics for Gas Seep Detection In Shallow Coastal Waters
Understanding measurement, monitoring and verification (MM&V) needs in the environmental context of potential subsea carbon dioxide (CO2) storage projects (Carbon Capture and Storage [CCS]) is a challenging task globally. Unmanned surface vehicles (USV) equipped with acoustic sensors are an attractive option for detecting gas leaks due to their spatial and temporal coverage potential. Here, a SIMRAD Wide Band Transceiver Mini acoustic sensor is evaluated for detecting CO2 leaks in shallow coastal water (<20 m depth). Small flows of CO2 (0.34–3.90 tonnes CO2 gas yr−1) were released into the water column. The plumes were detected with the acoustic system with the results highlighting their dynamic nature. A survey simulation model showed that the probability of detecting a leak inside a 5 × 10 km survey area improved depending on the number of leaks within it, with 100 % detection probability for two leaks (>7.8 tonnes CO2 gas yr−1) achieved with a survey time of 600 h. As the number of leaks increased to 40 (> 156 tonnes CO2 gas yr−1) the survey duration reduced to ∼110 h for 100 % probability of detecting a plume. These detection flow rates are well below the upper limits proposed by IPCC (2005) for climate mitigation for a release of 1% in 1000 years for most proposed CO2 storage sites. Regulatory requirements for CCS sites are still evolving to address societal expectations and environmental monitoring needs. This work assists in determining detectable leak rate thresholds that can be detected in the marine environment using acoustic sensors.
Ben Scoulding, Rudy Kloser, Sven Gastauerb, "Evaluation of unmanned surface vehicle acoustics for gas seep detection in shallow coastal waters,” International Journal of Greenhouse Gas Control, Volume 102, November 2020. https://doi.org/10.1016/j.ijggc.2020.103158Download Paper (PDF)
Saildrone-observed Atmospheric Boundary Layer Response yo Winter Mesoscale Warm Spot Along the Kuroshio South of Japan
Using an unmanned sailing vehicle, known as a Saildrone, we observed mesoscale and smaller scale structures of oceanic and atmospheric variables across the Kuroshio south of Japan during the winter of 2018/2019. From December 28 to December 29, 2018, the Saildrone crossed just north of the center of a very warm (∼23∘C) mesoscale spot in the Kuroshio centered around 31.5∘ N, 135.8∘ E. The northerly winter monsoon wind was intensified by ∼2 m s−1 over the mesoscale warm spot (MWS) and accompanied by a submesoscale sea level pressure undulation of ∼1 hPa possibly due to two oppositely rotating ageostrophic vortices. At this time, the wind reached a maximum speed of greater than 12 m s−1 and removed heat from the ocean at a rate of 1141 W m−2. Subsequently (January 3–5, 2019), the Saildrone observed weakening of wind and heat release to the atmosphere on the southern edge of the MWS, which was associated with the approaching low-pressure system over the Kuroshio. The observed submesoscale structures of atmospheric and oceanic variables near the center of the MWS suggest that the atmospheric boundary layer responded to the MWS through the pressure adjustment mechanism in the Kuroshio, where in situ high-resolution measurements have not been performed before.
Nagano, A., Ando, K. "Saildrone-observed atmospheric boundary layer response to winter mesoscale warm spot along the Kuroshio south of Japan," Prog Earth Planet Sci 7, 43 (2020). https://doi.org/10.1186/s40645-020-00358-8Download Paper (PDF)
Evaluation of a New Carbon Dioxide System for Autonomous Surface Vehicles
Current carbon measurement strategies leave spatiotemporal gaps that hinder the scientific understanding of the oceanic carbon biogeochemical cycle. Data products and models are subject to bias because they rely on data that inadequately capture mesoscale spatiotemporal (kilometers and days to weeks) changes. High-resolution measurement strategies need to be implemented to adequately evaluate the global ocean carbon cycle. To augment the spatial and temporal coverage of ocean–atmosphere carbon measurements, an Autonomous Surface Vehicle CO2 (ASVCO2) system was developed. From 2011 to 2018, ASVCO2 systems were deployed on seven Wave Glider and Saildrone missions along the U.S. Pacific and Australia’s Tasmanian coastlines and in the tropical Pacific Ocean to evaluate the viability of the sensors and their applicability to carbon cycle research. Here we illustrate that the ASVCO2 systems are capable of long-term oceanic deployment and robust collection of air and seawater pCO2 within ±2 μatm based on comparisons with established shipboard underway systems, with previously described Moored Autonomous pCO2 (MAPCO2) systems, and with companion ASVCO2 systems deployed side by side.
Christopher Sabine; Adrienne Sutton; Kelly McCabe; Noah Lawrence-Slavas; Simone Alin; Richard Feely; Richard Jenkins; Stacy Maenner; Christian Meinig; Jesse Thomas Erik van Ooijen; Abe Passmore; Bronte Tilbrook, "Evaluation of a New Carbon Dioxide System for Autonomous Surface Vehicles," J. Atmos. Oceanic Technol. (2020) 37 (8): 1305–1317. https://doi.org/10.1175/JTECH-D-20-0010.1Download Paper (PDF)
Saildrone: Adaptively Sampling the Marine Environment
From 11 April to 11 June 2018 a new type of ocean observing platform, the Saildrone surface vehicle, collected data on a round-trip, 60-day cruise from San Francisco Bay, down the U.S. and Mexican coast to Guadalupe Island. The cruise track was selected to optimize the science team’s validation and science objectives. The validation objectives include establishing the accuracy of these new measurements. The scientific objectives include validation of satellite-derived fluxes, sea surface temperatures, and wind vectors and studies of upwelling dynamics, river plumes, air–sea interactions including frontal regions, and diurnal warming regions. On this deployment, the Saildrone carried 16 atmospheric and oceanographic sensors. Future planned cruises (with open data policies) are focused on improving our understanding of air–sea fluxes in the Arctic Ocean and around North Brazil Current rings. The California coastal waters are important for the economy, society (this is the coast of the most populous state in the union), national security (they are the home waters of the Navy’s Pacific fleet), and environment (it is along an eastern boundary current with biologically important upwelling). In the California Current region, the air–land–sea interface is complex, characterized by coastal promontories, upwelling jets and shadows, river plumes, and a narrow continental shelf that affects coastal dynamics producing highly variable sea surface temperature (SST) and concentration of the photosynthetic pigment chlorophyll a (Chl) (Checkley and Barth 2009; Strub and James 1995; Kelly et al. 1998; Brink et al. 2000). Along the U.S. and Mexican west coast, upwelling induces a flux of cold, nutrient-rich, dense, low-in-oxygen, and acidic waters to the surface ocean layers, leading to important air–sea and coastal–open ocean interactions (Sverdrup et al. 1942). Due to its economic importance, the California Current System is one of the most studied and well-monitored upwelling systems in the world, including high-frequency (HF) radar for surface currents, regular oceanographic research cruises, and moored buoys for near-surface meteorological measurements and ocean temperature. Yet, even in this heavily sampled region, there are substantial gaps not filled by the current sampling strategy. Geostationary and polar-orbiting satellites provide discrete glimpses of the spatial structuring at the air–sea interface for a limited subset of environmental parameters. Temporal evolution of features can be provided by moored buoys but the fixed locations limit their use in understanding spatiotemporal structures and spatial scales of dynamical interactions. Other in situ platforms, such as subsurface gliders, floats, and drifters, provide valuable vertical and subsurface oceanographic measurements critical for measuring ocean heat content and transport, ocean velocities, thermohaline circulation, and other oceanographic applications. Wave Gliders provide both surface atmospheric (wind speed and direction, atmospheric pressure, and air temperature) and subsurface oceanographic observations and are able to travel at velocities of typically 0.8 m s‒1. The Saildrone measurements provide significant value to certain types of scientific studies through their design as a solar-powered, movable, steerable platform that samples a wide variety of air–sea-interface and upper-ocean parameters, especially in regions where it is difficult to deploy and maintain other types of assets. Wave Gliders and Saildrones both provide air–sea measurements that address the need for flexible, deployable, movable in situ observational assets, with each vehicle providing different capabilities for different types of scientific investigations. Wave Gliders can provide subsurface observations while Saildrones provide interfacial observations. The Saildrone vehicle’s advantage is for science applications needing rapid spatial sampling (it can travel at up to 4 m s‒1), with additional atmospheric and oceanographic measurements needed to advance research into upwelling dynamics, submesoscale variability, and air–sea fluxes in the vicinity of ocean fronts, diurnal warming modeling, carbon cycling, and biophysical interactions and coupled atmosphere–ocean modeling and data assimilation. It is important to assess the accuracy of Saildrone observations for science. We believe that such an assessment is important for two reasons: first, the Saildrone business model is different from the way research has been previously accomplished. Instead of purchasing equipment, which scientists then maintain, calibrate, and deploy, Saildrone owns and operates the vehicles and sensors, it is the data that are purchased. Second, there may be deployment issues associated with some of the instruments because of the nature of the vehicle. In the following we touch briefly on the former with a bit more discussion devoted to the latter.
Gentemann, C. L., and Coauthors, 2020: "Saildrone: Adaptively Sampling the Marine Environment." Bull. Amer. Meteor. Soc., 101, E744–E762, https://doi.org/10.1175/BAMS-D-19-0015.1.Download Paper (PDF)
Comparison of Satellite-Derived Sea Surface Temperature and Sea Surface Salinity Gradients Using the Saildrone California/Baja and North Atlantic Gulf Stream Deployments
Validation of satellite-based retrieval of ocean parameters like Sea Surface Temperature (SST) and Sea Surface Salinity (SSS) is commonly done via statistical comparison with in situ measurements. Because in situ observations derived from coastal/tropical moored buoys and Argo floats are only representatives of one specific geographical point, they cannot be used to measure spatial gradients of ocean parameters (i.e., two-dimensional vectors). In this study, we exploit the high temporal sampling of the unmanned surface vehicle (USV) Saildrone (i.e., one measurement per minute) and describe a methodology to compare the magnitude of SST and SSS gradients derived from satellite-based products with those captured by Saildrone. Using two Saildrone campaigns conducted in the California/Baja region in 2018 and in the North Atlantic Gulf Stream in 2019, we compare the magnitude of gradients derived from six different GHRSST Level 4 SST (MUR, OSTIA, CMC, K10, REMSS, and DMI) and two SSS (JPLSMAP, RSS40km) datasets. While results indicate strong consistency between Saildrone- and satellite-based observations of SST and SSS, this is not the case for derived gradients with correlations lower than 0.4 for SST and 0.1 for SSS products.
Vazquez-Cuervo, J.; Gomez-Valdes, J.; Bouali, M. "Comparison of Satellite-Derived Sea Surface Temperature and Sea Surface Salinity Gradients Using the Saildrone California/Baja and North Atlantic Gulf Stream Deployments." Remote Sens. 2020, 12, 1839.Download Paper (PDF)
Correcting Non-photochemical Quenching of Saildrone Chlorophyll-A Fluorescence for Evaluation of Satellite Ocean Color Retrievals
Abstract: In vivo chlorophyll fluorescence (ChlF) can serve as a reasonable estimator of in situ phytoplankton biomass with the benefits of efficiently and affordably extending the global chlorophyll (Chl) data set in time and space to remote oceanic regions where routine sampling by other vessels is uncommon. However, in vivo ChlF measurements require correction for known, spurious biases relative to other measures of Chl concentration, including satellite ocean color retrievals. Spurious biases affecting in vivo ChlF measurements include biofouling, colored dissolved organic matter (CDOM) fluorescence, calibration offsets, and non-photochemical quenching (NPQ). A more evenly distributed global sampling of in vivo ChlF would provide additional confidence in estimates of uncertainty for satellite ocean color retrievals. A Saildrone semi-autonomous, ocean-going, solar- and wind-powered surface drone recently measured a variety of ocean and atmospheric parameters, including ChlF, during a 60-day deployment in mid-2018 in the California Current region. Correcting the Saildrone ChlF data for known biases, including deriving an NPQ-correction, greatly improved the agreement between the drone measurements and satellite ocean color retrievals from MODIS-Aqua and VIIRS-SNPP, highlighting that once these considerations are made, Saildrone semi-autonomous surface vehicles are a valuable, emerging data source for ocean and ecosystem monitoring.
Joel P. Scott, Scout Crooke, Ivona Cetinić, Carlos E. Del Castillo, and Chelle L. Gentemann, "Correcting non-photochemical quenching of Saildrone chlorophyll-a fluorescence for evaluation of satellite ocean color retrievals," Opt. Express 28, 4274-4285 (2020) https://doi.org/10.1364/OE.382029Download Paper (PDF)
Air-Sea Fluxes With a Focus on Heat and Momentum
Turbulent and radiative exchanges of heat between the ocean and atmosphere (hereafter heat fluxes), ocean surface wind stress, and state variables used to estimate them, are Essential Ocean Variables (EOVs) and Essential Climate Variables (ECVs) influencing weather and climate. This paper describes an observational strategy for producing 3-hourly, 25-km (and an aspirational goal of hourly at 10-km) heat flux and wind stress fields over the global, ice-free ocean with breakthrough 1-day random uncertainty of 15 W m–2 and a bias of less than 5 W m–2. At present this accuracy target is met only for OceanSITES reference station moorings and research vessels (RVs) that follow best practices. To meet these targets globally, in the next decade, satellite-based observations must be optimized for boundary layer measurements of air temperature, humidity, sea surface temperature, and ocean wind stress. In order to tune and validate these satellite measurements, a complementary global in situ flux array, built around an expanded OceanSITES network of time series reference station moorings, is also needed. The array would include 500–1000 measurement platforms, including autonomous surface vehicles, moored and drifting buoys, RVs, the existing OceanSITES network of 22 flux sites, and new OceanSITES expanded in 19 key regions. This array would be globally distributed, with 1–3 measurement platforms in each nominal 10° by 10° box. These improved moisture and temperature profiles and surface data, if assimilated into Numerical Weather Prediction (NWP) models, would lead to better representation of cloud formation processes, improving state variables and surface radiative and turbulent fluxes from these models. The in situ flux array provides globally distributed measurements and metrics for satellite algorithm development, product validation, and for improving satellite-based, NWP and blended flux products. In addition, some of these flux platforms will also measure direct turbulent fluxes, which can be used to improve algorithms for computation of air-sea exchange of heat and momentum in flux products and models. With these improved air-sea fluxes, the ocean’s influence on the atmosphere will be better quantified and lead to improved long-term weather forecasts, seasonal-interannual-decadal climate predictions, and regional climate projections.
Cronin Meghan F., Gentemann Chelle L., Edson James, Ueki Iwao, Bourassa Mark, Brown Shannon, Clayson Carol Anne, Fairall Chris W., Farrar J. Thomas, Gille Sarah T., Gulev Sergey, Josey Simon A., Kato Seiji, Katsumata Masaki, Kent Elizabeth, Krug Marjolaine, Minnett Peter J., Parfitt Rhys, Pinker Rachel T., Stackhouse Paul W., Swart Sebastiaan, Tomita Hiroyuki, Vandemark Douglas, Weller A. Robert, Yoneyama Kunio, Yu Lisan, Zhang Dongxiao. "Air-Sea Fluxes With a Focus on Heat and Momentum," Frontiers in Marine Science, Vol. 5, 2019, p. 430. DOI: https://www.frontiersin.org/article/10.3389/fmars.2019.00430Download Paper (PDF)
Test of Unmanned Surface Vehicles to Conduct Remote Focal Follow Studies of a Marine Predator
We tested the feasibility of using Saildrone unmanned wind- and solar-powered surface vehicles to conduct remote focal follow studies of northern fur seals Callorhinus ursinus. Using Argos satellite and transmitted GPS locations, the Saildrones followed a fur seal while recording oceanographic conditions and mapping prey abundance and depth distribution using a scientific echosounder. The Saildrones successfully followed 6 fur seals over 2.4 ± 0.2 d (mean ± SE) and 149.7 ± 16.3 km of the foraging path. Median separation distance between the Saildrone and fur seal path was 0.65 ± 0.1 km and average time separation was 9.9 ± 1.4 h, with minimum time separations ranging from 1.9-4.9 h. Time and distance separation were a function of both animal behavior and study design. Our results show that Saildrones can approach satellite tracked marine predators from long distances and follow them over extended periods while collecting oceanographic and prey data. These successful focal follows demonstrate that unmanned surface vehicles are a valuable tool for collecting data on fine-scale relationships between marine predators, their prey, and the environment.
Kuhn CE, De Robertis A, Sterling J, Mordy CW et al. (2020) "Test of unmanned surface vehicles to conduct remote focal follow studies of a marine predator." Mar Ecol Prog Ser 635:1-7. https://doi.org/10.3354/meps13224Download Paper (PDF)
Public Private Partnerships to Advance Regional Ocean Observing Capabilities: A Saildrone and NOAA-PMEL Case Study and Future Considerations to Expand to Global Scale Observing
Partnership between the private sector and the ocean observing community brings exciting opportunities to address observing challenges through leveraging the unique strengths of each sector. Here, we discuss a case study of a successful relationship between the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory (PMEL) and Saildrone to instrument an Unmanned Surface Vehicle (USV) in order to serve shared goals. This case study demonstrates that a private company working with a federal laboratory has provided innovative ocean observing solutions deployed at regional scale in only a few years, and we project that this model will be sustainable over the long-term. An alignment of long-term goals with practical deliverables during the development process and integrating group cultures were key to success. To date, this effort has expanded NOAA’s interdisciplinary observing capabilities, improved public access to ocean data, and paved the way for a growing range of USV applications in every ocean. By emphasizing shared needs, complementary strengths, and a clear vision for a sustainable future observing system, we believe that this case study can serve as a blueprint for public and private partners who wish to improve observational capacity. We recommend that the international scientific community continue to foster collaborations between the private sector and regional ocean observing networks. This effort could include regional workshops that build community confidence through independent oversight of data quality. We also recommend that an international framework should be created to organize public and private partners in the atmospheric and oceanographic fields. This body would coordinate development of observational technologies that adhere to best practices and standards for sensor integration, verification, data quality control and delivery, and provide guidance for unmanned vehicle providers. Last, we also recommend building bridges between the private sector, ocean observing community, and the operational forecast community to consider the future of this new private sector, with goals to determine targeted ocean observing needs; assess the appropriateness of USVs as science platforms, sensors, and data format standards; and establish usage and data quality control and distribution protocols for ocean observing and operational forecasting.
Meinig, C., E.F. Burger, N. Cohen, E.D. Cokelet, M.F. Cronin, J.N. Cross, S. de Halleux, R. Jenkins, A.T. Jessup, C.W. Mordy, N. Lawrence-Slavas, A.J. Sutton, D. Zhang, and C. Zhang. "Public private partnerships to advance regional ocean observing capabilities: A Saildrone and NOAA-PMEL case study and future considerations to expand to global scale observing." OceanObs'19, Front. Mar. Sci., doi: 10.3389/fmars.2019.00448, 2019.Download Paper (PDF)
Using Saildrones to Validate Satellite-Derived Sea Surface Salinity and Sea Surface Temperature along the California/Baja Coast
Abstract: Traditional ways of validating satellite-derived sea surface temperature (SST) and sea surface salinity (SSS) products by comparing with buoy measurements, do not allow for evaluating the impact of mesoscale-to-submesoscale variability. We present the validation of remotely sensed SST and SSS data against the unmanned surface vehicle (USV)—called Saildrone—measurements from the 60 day 2018 Baja California campaign. More specifically, biases and root mean square differences (RMSDs) were calculated between USV-derived SST and SSS values, and six satellite-derived SST (MUR, OSTIA, CMC, K10, REMSS, and DMI) and three SSS (JPLSMAP, RSS40, RSS70) products. Biases between the USV SST and OSTIA/CMC/DMI were approximately zero, while MUR showed a bias of 0.3 ◦C. The OSTIA showed the smallest RMSD of 0.39 ◦C, while DMI had the largest RMSD of 0.5 ◦C. An RMSD of 0.4 ◦C between Saildrone SST and the satellite-derived products could be explained by the diurnal and sub-daily variability in USV SST, which currently cannot be resolved by remote sensing measurements. SSS showed fresh biases of 0.1 PSU for JPLSMAP and 0.2 PSU and 0.3 PSU for RMSS40 and RSS70 respectively. SST and SSS showed peaks in coherence at 100 km, most likely associated with the variability of the California Current System.
Vazquez-Cuervo, J.; Gomez-Valdes, J.; Bouali, M.; Miranda, L.E.; Van der Stocken, T.; Tang, W.; Gentemann, C. "Using Saildrones to Validate Satellite-Derived Sea Surface Salinity and Sea Surface Temperature along the California/Baja Coast." Remote Sens. 2019, 11, 1964. https://doi.org/10.3390/rs11171964Download Paper (PDF)
Long-term Measurements of Fish Backscatter from Saildrone Unmanned Surface Vehicles and Comparison with Observations from a Noise-reduced Research Vessel
Two Saildrone unmanned surface vehicles (USVs) were instrumented with echosounders and deployed in the Bering Sea to make acoustic observations of walleye pollock for 103 days. The Saildrones proved to be a suitable platform for measurement of fish backscatter: they produced high-quality measurements at wind speeds of <10 m s−1. Pollock backscatter measured from the Saildrones was compared to backscatter measured by a noise-reduced research vessel during two “follow-the-leader” comparisons. In a location where pollock were shallowly distributed (30–100 m), there was evidence of depth-dependent avoidance reactions to the ship. This behaviour was not evident in a second comparison, where the fish were primarily deeper than 90 m. Opportunistic comparisons indicate that backscatter where the ship and USVs crossed paths was similar. However, the Saildrones observed higher densities of shallow fish, which is consistent with the diving response inferred in the first follow-the-leader comparison. USVs equipped with echosounders, like all platforms, have inherent strengths (endurance) and limitations (species identification) that should be carefully considered for a given application. USVs can complement traditional ship-based surveys by increasing the spatial and temporal extent of acoustic observations, and their use is likely to become more widespread.
Alex De Robertis, Noah Lawrence-Slavas, Richard Jenkins, Ivar Wangen, Calvin W Mordy, Christian Meinig, Mike Levine, Dave Peacock, Heather Tabisola, "Long-term measurements of fish backscatter from Saildrone unmanned surface vehicles and comparison with observations from a noise-reduced research vessel," ICES Journal of Marine Science, , fsz124, https://doi.org/10.1093/icesjms/fsz124Download Paper (PDF)
An Enhanced Ocean Acidification Observing Network: From People to Technology to Data Synthesis and Information Exchange
A successful integrated ocean acidification (OA) observing network must include (1) scientists and technicians from a range of disciplines from physics to chemistry to biology to technology development; (2) government, private, and intergovernmental support; (3) regional cohorts working together on regionally specific issues; (4) publicly accessible data from the open ocean to coastal to estuarine systems; (5) close integration with other networks focusing on related measurements or issues including the social and economic consequences of OA; and (6) observation-based informational products useful for decision making such as management of fisheries and aquaculture. The Global Ocean Acidification Observing Network (GOA-ON), a key player in this vision, seeks to expand and enhance geographic extent and availability of coastal and open ocean observing data to ultimately inform adaptive measures and policy action, especially in support of the United Nations 2030 Agenda for Sustainable Development. GOA-ON works to empower and support regional collaborative networks such as the Latin American Ocean Acidification Network, supports new scientists entering the field with training, mentorship, and equipment, refines approaches for tracking biological impacts, and stimulates development of lower-cost methodology and technologies allowing for wider participation of scientists. GOA-ON seeks to collaborate with and complement work done by other observing networks such as those focused on carbon flux into the ocean, tracking of carbon and oxygen in the ocean, observing biological diversity, and determining short- and long-term variability in these and other ocean parameters through space and time.
Tilbrook Bronte, Jewett Elizabeth B., DeGrandpre Michael D., Hernandez-Ayon Jose Martin, Feely Richard A., Gledhill Dwight K., Hansson Lina, Isensee Kirsten, Kurz Meredith L., Newton Janet A., Siedlecki Samantha A., Chai Fei, Dupont Sam, Graco Michelle, Calvo Eva, Greeley Dana, Kapsenberg Lydia, Lebrec Marine, Pelejero Carles, Schoo Katherina L., Telszewski Maciej, "An Enhanced Ocean Acidification Observing Network: From People to Technology to Data Synthesis and Information Exchange," Frontiers in Marine Science, Vol. 6. , 2019 p.337 - https://www.frontiersin.org/article/10.3389/fmars.2019.00337Download Paper (PDF)
Comparing Air-Sea Flux Measurements From a New Unmanned Surface Vehicle and Proven Platforms During the SPURS-2 Field Campaign
Abstract Two saildrones participated in the Salinity Processes in the Upper-ocean Regional Study 2 (SPURS-2) field campaign at 10°N, 125°W, as part of their more than six-month Tropical Pacific Observing System (TPOS)-2020 pilot study in the eastern tropical Pacific. The two saildrones were launched from San Francisco, California, on September 1, 2017, and arrived at the SPURS-2 region on October 15, one week before R/V Revelle. Upon arrival at the SPURS-2 site, they each began a two-week repeat pattern, sailing around the program’s central moored surface buoy. The heavily instrumented Woods Hole Oceanographic Institution (WHOI) SPURS-2 buoy serves as a benchmark for validating the saildrone measurements for air-sea fluxes. The data collected by the WHOI buoy and the saildrones were found to be in reasonably good agreement. Although of short duration, these ship-saildrone-buoy comparisons are encouraging as they provide enhanced understanding of measurements by various platforms in a rapidly changing subsynoptic weather system. The saildrones were generally able to navigate the challenging Intertropical Convergence Zone, where winds are low and currents can be strong, demonstrating that the saildrone is an effective platform for observing a wide range of oceanographic variables important to airsea interaction studies.
Dongxiao Zhang, Meghan F. Cronin, Christian Meinig, J. Thomas Farrar, Richard Jenkins, David Peacock, Jennifer Keene, Adrienne Sutton and Qiong Yang, "Comparing Air-Sea Flux Measurements From a New Unmanned Surface Vehicle and Proven Platforms During the SPURS-2 Field Campaign," Oceanography, Vol. 32, No. 2, SPECIAL ISSUE ON SPURS-2: Salinity Processes in the Upper-ocean Regional Study 2 (JUNE 2019), pp. 122-133Download Paper (PDF)
Abrupt Fronts Embedded in Tropical Instability Waves Observed by Saildrones
As part of the Tropical Pacific Observing System (TPOS)-2020 project, two Saildrone Inc. "Saildrones" were deployed in the tropics to assess the capability of these innovative unmanned surface vehicles as potential platforms within the TPOS. Saildrone measurements include wind speed and direction, air- and sea-surface temperature, humidity, barometric pressure, downwelling solar and longwave radiation, surface salinity, upper ocean currents from a RDI-300 KHz workhorse acoustic Doppler current profiler, and a full suite of biogeochemistry measurements. Comparisons between the drone data and surface flux buoys show good agreement, confirming that this platform can make climate-quality meteorological and oceanographic observations. During the 6-month mission, La Niña conditions prevailed, and large-amplitude tropical instability waves propagated along the strong cold-tongue front. Saildrone measurements resolve not only the strong cold-tongue but also abrupt submesoscale fronts. The two Saildrones each traversed the northern edge of the equatorial cold tongue twice. Saildrones observed multiple abrupt fronts equatorward of the cold-tongue front with temperature and salinity changes as large as 1ºC and 0.3 psu, respectively, in less than 1 km. These sharp temperature fronts have the potential to result in large air-sea fluxes because air blowing across these fronts cannot equilibrate with the sea surface on such short length scales. Saildrone, with its high-resolution and adaptive sampling, offers the opportunity to document intense air-sea interaction associated with these abrupt fronts.
Cronin, M. F.; Donohue, K. A.; Zhang, D.; Jenkins, R.; Keene, J., "Abrupt Fronts Embedded in Tropical Instability Waves Observed by Saildrones," American Geophysical Union, Fall Meeting 2018, abstract #OS23F-1695; AGU, 12/2018Download Paper (PDF)
Advances in Ecosystem Research: Saildrone Surveys of Oceanography, Fish, and Marine Mammals in the Bering Sea
Abstract: Saildrones are unmanned surface vehicles engineered for oceanographic research and powered by wind and solar energy. In the summer of 2016, two Saildrones surveyed the southeastern Bering Sea using passive acoustics to listen for vocalizations of marine mammals and active acoustics to quantify the spatial distribution of small and large fishes. Fish distributions were examined during foraging trips of northern fur seals (Callorhinus ursinus), and initial results suggest these prey distributions may influence the diving behavior of fur seals. The Saildrone is faster, has greater instrument capacity, and requires less support services than its counterparts. This innovative platform performed well in stormy conditions, and it demonstrated the potential to augment fishery surveys and advance ecosystem research.
Mordy, C.W., E.D. Cokelet, A. De Robertis, R. Jenkins, C.E. Kuhn, N. LawrenceSlavas, C.L. Berchok, J.L. Crance, J.T. Sterling, J.N. Cross, P.J. Stabeno, C. Meinig, H.M. Tabisola, W. Burgess, and I. Wangen. 2017. "Advances in ecosystem research: Saildrone surveys of oceanography, fish, and marine mammals in the Bering Sea." Oceanography 30(2):113–115,Download Paper (PDF)
Environmental Assessments of Offshore Carbon Capture and Storage (CCS) Sites Using Unmanned Surface Vehicles (USV)
Understanding the environmental context of potential subsea CO2 storage projects is a challenging task that requires the development of risk-based environmental monitoring to address public assurance, as well as regulatory requirements. A core need is an understanding and quantification of background environmental variability in relation to the likelihood of detection from putative release. Unmanned surface vehicle (USV) technology is rapidly evolving, with a number of USV platforms available that can meet a variety of needs in ocean observing. Advanced sensor technologies integrated on USVs promise coverage and flexibility for sustained observations at space and time scales not previously achievable. This paper describes CSIRO research with USVs in support of CCS environmental monitoring studies in Australia. CSIRO utilises a range of autonomous systems, including autonomous underwater vehicles, remotely operated vehicles and robotic profiling floats as part of its observing capabilities. For CCS studies, CSIRO is partnering with Saildrone Inc. to provide a flexible platform that houses a suite of sensors for environmental assessments at offshore CCS sites. The Saildrone platforms have been designed to accommodate sensors for detection of three important monitoring types: seawater carbon dioxide, bubble acoustics and water quality. The Saildrones can be used for long-range reconnaissance in a broad range of sea conditions and with up to 6-month deployment durations. Each Saildrone platform and its science systems can be operated remotely, with data transmitted back to shore via satellite to allow real-time monitoring of changes in the marine environment. The rapid deployment and response of the platform allows for more detailed investigation of features identified during surveys and of anomalies that exceed the known variability in measured variables. The combination of the platform with fixed measurements, such as those collected using more traditional oceanographic moorings, provides new capability to assess variability at CCS sites over a larger survey area than has been possible before. The sensor systems fitted to the Saildrone and the land based calibration and maintenance support facilities are state of the art. The carbon sensor suite delivers pH, pCO2 and dissolved oxygen. It is based on a robust system proven to work in the field over long periods and includes reference gas and transmission of multiple diagnostic parameters to ensure sensor performance and calibrations are maintained. The acoustic sensors use a two-frequency split beam system operating at 38 kHz and 2002 kHz that can detect low concentrations of bubbles in the water column. It will be possible to detect and monitor potential or reported bubble plumes over time to determine the cause. In this way reducing false alarms where under certain circumstances aggregations of fish or zooplankton can be mistakenly interpreted as a bubble plume. Sensors for sub-surface bio-optics to assess water column plankton (chlorophyll and particle backscatter), oceanographic (temperature and salinity) and meteorological data are also incorporated into the real-time data streams delivered from the Saildrone. This paper will provide an overview of the sensor configuration and performance capabilities of the USVs for use in environmental assessments to support CCS. Sea trial and other data including CCS monitoring strategies will be presented. Finally, the paper will discuss potential future uses of the platform for ongoing monitoring of CCS sites.
Marouchos, Andreas and Tilbrook, Bronte and Kloser, Rudy and Ryan, Tim and Passmore, Abe and Van Ooijen, Erik, "Environmental Assessments of Offshore Carbon Capture and Storage (CCS) Sites Using Unmanned Surface Vehicles (USV)," 14th Greenhouse Gas Control Technologies Conference Melbourne 21-26 October 2018 (GHGT-14) . Available at SSRN: https://ssrn.com/abstract=3366344Download Paper (PDF)
Distribution, biomass, and demography of coastal pelagic fishes in the California Current Ecosystem during summer 2018 based on acoustic-trawl sampling
This report provides: 1) a detailed description of the acoustic-trawl method (ATM) used by NOAA’s Southwest Fisheries Science Center (SWFSC) for direct assessments of the dominant species of coastal pelagic species (CPS; i.e., Pacifc Sardine Sardinops sagax, Northern Anchovy Engraulis mordax, Pacifc Mackerel Scomber japonicus, Jack Mackerel Trachurus symmetricus, and Pacifc Herring Clupea pallasii) in the California Current Ecosystem (CCE) o ̇ the west coast of North America; and 2) estimates of the biomasses, distributions, and demographies of those CPS in the survey area between 26 June and 23 September 2018. The survey area spanned most of the continental shelf between the northern tip of Vancouver Island, British Columbia (BC) and San Diego, CA. Throughout the survey area, NOAA Ship Reuben Lasker (hereafter, Lasker) sampled along transects oriented approximately perpendicular to the coast, from the shallowest navigable depth (~30 m depth) to either a distance of 35 nmi or to the 1,000 fathom (~1830 m) isobath, whichever is farthest. Between approximately San Francisco and Pt. Conception, additional acoustic sampling was conducted along 4 nmi-long transects spaced 5-nmi apart using a wind- and solar-powered unmanned surface vehicle (USV; Saildrone, Inc.) in the nearshore where Lasker could not safely navigate.
Kevin L. Stierhoff, Juan P. Zwolinski, and David A. Demer. 2019. "Distribution,biomass, and demography of coastal pelagic fishes in the California Current Ecosystem during summer 2018 based on acoustic-trawl sampling." U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-613Download Paper (PDF)
The Use of Saildrones to Examine Spring Conditions in the Bering Sea: Instrument Comparisons, Sea Ice Meltwater and Yukon River Plume Studies
Abstract: New technologies can help scientists measure and understand Arctic warming, sea ice loss and ecosystem change. NOAA has worked with Saildrone, Inc., to develop an unmanned surface vehicle (USV)—Saildrone—to make ocean surface measurements autonomously, even in challenging high-latitude conditions. USVs augment traditional research ship cruises, mitigate ship risk in high seas and shallow water, and make lower cost measurements. Under remote control, USV sampling strategy can be adapted to meet changing needs. Two Saildrones conducted 97-day missions in the Bering Sea in spring-summer 2015, reliably measuring atmospheric and oceanic parameters. Measurements were validated against shipboard values. Following that, the Saildrone sampling strategies were modified, first to measure the effects of sea-ice melt on surface cooling and freshening, and then to study the Yukon River plume.
D Cokelet, Edward & Meinig, Christian & Lawrence-Slavas, Noah & J Stabeno, Phyllis & W Mordy, Calvin & Tabisola, Heather & Jenkins, Richard & Cross, Jessica. (2015). The Use of Saildrones to Examine Spring Conditions in the Bering Sea: Instrument Comparisons, Sea Ice Meltwater and Yukon River Plume Studies.Download Paper (PDF)
The use of Saildrones to examine spring conditions in the Bering Sea: Vehicle specification and mission performance
Abstract: During recent decades the US Arctic is experiencing a rapid loss of sea ice and subsequently increasingly warmer water temperatures. To better study this economically and culturally important marine ecosystem and the changes that are occurring, the use of new technologies is being explored to supplement traditional ship, satellite and mooring based data collection techniques. Unmanned surface vehicles (USV) are a rapidly advancing technology that has the potential to meet the requirement for long duration and economical scientific data collection with the ability for real-time data and adaptive sampling. In 2015, the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory (NOAA-PMEL), the University of Washington (UW) and Saildrone Inc. (Alameda, California) explored the use of a novel USV technology in the Bering Sea and Norton Sound. Two Saildrones, wind and solar powered unmanned surface vehicles that can be used for extended research missions in challenging environments, were equipped with a suite of meteorological and oceanographic sensors. During the >3 month mission, the vehicles each traveled over 4100 nm, successfully completing several scientific survey assignments. This mission demonstrated the capability of the Saildrone vehicle to be launched from a dock to conduct autonomous and adaptive oceanographic research in a harsh, high-latitude environment.
C. Meinig, N. Lawrence-Slavas, R. Jenkins and H. M. Tabisola, "The use of Saildrones to examine spring conditions in the Bering Sea: Vehicle specification and mission performance," OCEANS 2015 - MTS/IEEE Washington, Washington, DC, 2015, pp. 1-6. https://doi.org/10.23919/OCEANS.2015.7404348Download Paper (PDF)
Hindcast modeling of oil slick persistence from natural seeps
Abstract: Persistence of oil floating in the ocean is an important factor for evaluating hydrocarbon fluxes from natural seeps and anthropogenic releases into the environment. The objective of this work is to estimate the surface residence-time of the oil slick and to determine the importance of wind and surface currents on the trajectory and fate of the released oil. Oil slicks released from natural hydrocarbon seeps located in Green Canyon 600 lease block and its surrounding region in the Gulf of Mexico were analyzed. A Texture Classifying Neural Network Algorithm was used to delineate georectified polygons for oil slicks from 41 synthetic aperture radar images. Trajectories of the oil slicks were investigated by employing a Lagrangian particle-tracking surface oil drift model. A set of numerical simulations was performed by increasing hindcast interval in reverse time order from the image collection time in order to obtain the closest resemblance between the simulated oil pathways and the length and shape of the oil slicks observed in SAR images. The average surface residence-time predicted from the hindcast modeling was 6.4 h (± 5.7 h). Analysis of a linear regression model, including observed oil slick lengths and variables of wind, surface current, and their relative direction, indicated a statistically significant negative effect of wind speed on the surface oil drift. Higher wind speed (> 7 m s-1) reduced length of the oil slicks. When wind and surface currents were driving forces of the surface oil drift model, a good agreement between simulated trajectories and subsequent satellite observations (R2 = 0.9) suggested that a wind scaling coefficient of 0.035 and a wind deflection angle of 20º to the right of the wind direction were acceptable approximations for modeling wind effects in this study. Results from the numerical experimentation were supported by in situ observations conducted by a wind-powered autonomous surface vehicle (Saildrone). Results indicated that the surface currents are, indeed, responsible for stretching oil slicks and that surface winds are largely responsible for the disappearance of the oil slicks from the sea surface. Under conditions of low wind and strong current, natural seeps can produce oil slicks that are longer than 20 km and persist for up to 48 h.
Daneshgar, Samira & Dukhovskoy, Dmitry & Bourassa, Mark & Macdonald, Ian. (2016). "Hindcast modeling of oil slick persistence from natural seeps." Remote Sensing of Environment. 189.Download Paper (PDF)
Shelf-Slope Interactions and Carbon Transformation and Transport in the Northern Gulf of Mexico: Platform Proof of Concept for the Ocean Observing System in the Northern Gulf of Mexico
Abstract: Demonstrating the feasibility of operating the Saildrone in the northern Gulf of Mexico within a high amount of maritime activity, including commercial and recreational fishing, shipping, and oil and gas platforms and associated servicing vessels. Demonstrate the utility of “high-speed” (up to 9 knots) wind-propelled surface vehicles as fast adaptive sampling response tools and to effectively fill in gaps between moorings at separations greater than the local correlation length scales; Collect a dataset that can be used for regional ecosystem model development and for designing the observational systems needed for process studies of shelf-ocean exchange phenomena of import to the carbon cycle in the Gulf.
Howden, Stephan Howden & Lohrenz, Steven & Book, Jeff & Jenkins, Richard & Leonardi, Alan, Meinig, Christian (2015). Shelf-Slope Interactions and Carbon Transformation and Transport in the Northern Gulf of Mexico: Platform Proof of Concept for the Ocean Observing System in the Northern Gulf of Mexico. Northern Gulf Institute Sept 2017 Progress Report. NGI File # 15-NGI2-127. pp 115-122Download Paper (PDF)