S-MODE (Sub-Mesoscale Ocean Dynamics Experiment) airborne campaigns
The Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) is a NASA Earth Ventures Suborbital Investigation designed to test the hypothesis that kilometer-scale (“submesoscale”) ocean eddies make important contributions to vertical exchange of climate and biological variables in the upper ocean. To test this hypothesis, S-MODE will employ a combination of aircraft-based remote sensing measurements of the ocean surface, measurements from ships, measurements from a variety of autonomous oceanographic platforms, and numerical modeling. The field campaign will consist of two month-long intensive operating periods (IOPs) that will be preceded by a smaller-scale pilot experiment to test and improve operational readiness and to compare measurements made from different platforms. The pilot experiment was delayed because of the 2020 coronavirus pandemic, and it is currently planned for October-November 2020. 1)
The ocean surface boundary layer that lies at the interface of the ocean and the atmosphere makes up only about 2% of the global oceans, but it plays a critical role in the climate system because it mediates the atmosphere-ocean exchange of important properties like heat, nutrients, oxygen, and carbon. Submesoscale ocean dynamics (horizontal wavelengths of 0.2-25 km, time scales of hours to days) are hypothesized to play an important role in vertical exchange, both between the atmosphere and the surface layer and between the surface layer and the deeper ocean. Our ability to simulate submesoscale ocean dynamics has outpaced our ability to observe them, and recent studies using high-resolution global ocean models suggest that vertical transport of heat by submesoscale variability is indeed a significant factor in the climate system; for example, 2) showed that improved resolution of submesoscale variability leads to changes in mean air-sea heat fluxes in the midlatitudes that are an order of magnitude larger than the global radiation imbalance associated with the greenhouse effect.
The vertical transport of matter and energy in the ocean cannot be accomplished efficiently by the mesoscale and larger-scale flow fields, which have very small vertical velocities (of order 1-10 m/day or less). The transition from the mesoscale dynamical regime to the submesoscale regime is characterized by increasingly strong vertical velocities. The distinctively large vertical velocities occur primarily in ageostrophic secondary circulations across the horizontal surface density gradients, and induce large vertical buoyancy flux (known as restratification) and large biogeochemical fluxes between the euphotic surface layer and underlying gradient layers (e.g., the nutricline). The associated vertical transport is hypothesized to have important consequences for oceanic biology, chemistry, and physics.
Our understanding of submesoscale motions and their vertical exchange comes primarily from numerical simulations. While all models with sufficient resolution predict the existence of submesoscale motions, there are large variations in their quantitative predictions. For example, Figure 1 compares fields of surface relative vorticity (a variable that highlights submesoscales) for two models currently used to simulate the performance of the upcoming SWOT satellite. Although they both show submesoscale fronts and eddies, the higher-resolution ROMS simulation shows a stronger dominance of cyclonic eddies over fronts, while the MITgcm shows a larger seasonal difference between March and September.
These differences highlight the uncertainties in such simulations. The key distinctive features of the submesoscale — the sharp fronts, high vorticity at these fronts and associated large vertical velocities — occur at the smallest scales resolved by the models. Their amplitudes are thus sensitive to resolution (e.g. Figure 1) and to the details of the numerics and damping at the grid scale. Increasing the resolution toward 100 m increases the strength of the submesoscale features, but also brings the grid to the same scales as the parameterized boundary layer turbulence. Proper subgrid schemes to deal with this overlap are still experimental. Furthermore, models and theory indicate both that submesoscale motions are sensitive to the boundary layer turbulence (e.g. turbulent thermal wind) and that the boundary layer turbulence itself is affected by the submesoscale gradients). These effects are only partially included in models.
The physics of air-sea interaction at submesoscales is another poorly constrained factor in simulation of submesoscale dynamics and their associated vertical transport. Submesoscale vorticity can be much larger than the vertical component of Earth’s rotation rate, which can fundamentally alter the wind-driven vertical transports (known as Ekman pumping). In addition, the boundary layer turbulence is primarily forced by air-sea fluxes that are computed from bulk-exchange coefficients that have not been validated at submesoscales. The fluxes can be modulated by the SST (Sea Surface Temperature) gradients at fronts, by the frontal currents themselves and by variations in the surface wave field propagating across the velocity gradients of these fronts. Given these uncertainties, a major goal of S-MODE is to make detailed measurements of the submesoscale variability and compare these with model predictions.
Figure 1: Surface vorticity off Central California in two submesoscale-resolving models in March (left column) and September (right column). Regional ROMS (top row 500 m resolution) and JPL-MITgcm (bottom row, ~ 2km resolution) show different seasonal cycles. The rectangle in the upper left shows our experiment domain. The vorticity has been normalized by the local value of the Coriolis parameter. The inset in the upper-right panel is the normalized vorticity measured by DopplerScatt in the Gulf of Mexico, shown with the same distance scaling and color scale as in the model fields (image credit: NASA/JPL-Caltech)
Science goals and objectives
Model studies (Figure 1) and limited observations indicate that submesoscale vertical exchange is concentrated near km-scale fronts and eddies. High-resolution simulations have outpaced our observational capabilities, but observational techniques have matured rapidly over the past decade. S-MODE seeks to make a comprehensive set of measurements of the dynamical variables needed to validate and discriminate between the high-resolution simulations. To test the hypothesis that submesoscale ocean dynamics make important contributions to vertical exchange in the upper ocean, the S-MODE Science Team has set these science goals:
1) Quantitatively measure the three-dimensional structure of the submesoscale features responsible for vertical exchange.
2) Quantify the role of air-sea interaction and surface forcing in the dynamics and vertical velocity of submesoscale variability.
3) Understand the relation between the velocity (and other surface properties) measured by remote sensing at the surface and that within and just below the surface boundary layer.
4) Diagnose dynamics of vertical transport processes at submesoscales to mesoscales.
Implementation, instruments and platforms
The complexity, size and rapid evolution (hours to days) of submesoscale motions has made them difficult to measure. They are much larger than ships, but small and rapidly evolving compared to typical ship surveys, small for many satellite remote sensing footprints, and difficult to distinguish from inertia-gravity waves because they occur on similar spatial and temporal scales. Over the last decade, new instrumentation and techniques have been developed to overcome these difficulties.
The approach planned for S-MODE is motivated by recent experiments that have shown the benefit of combining multiple, diverse platforms to enable measurements across a range of spatial and temporal. First, satellite remote sensing will inform direct aircraft remote sensing which, in turn, will inform the targeting of in-situ measurements. Second, multiple in-situ platforms, both ships and a variety of autonomous platforms, will be combined to simultaneously measure large values of the km-scale density gradients, vorticity and divergence, that distinguish submesoscale motions from mesoscale and internal wave motions. Third, measurements will be made in a Lagrangian coordinate system, tracking the evolving submesoscale features as they move within the larger, more energetic mesoscale currents.
The nominal study site is centered approximately 150 km offshore of San Francisco (Figures 1-2). There will be a 10-day Pilot campaign late in October 2020, and there will be month-long IOPs (Intensive Operating Periods) in October 2021 and April 2022. The experiment will collect simultaneous measurements using several airborne instruments, including the NASA DopplerScatt instrument, the NASA PRISM instrument [3)], the SIO (Scripps Institution of Oceanography) MASS instrument [4)] and the UCLA MOSES (Multiscale Observing System of the Ocean Surface) instrument. In conjunction with the airborne measurements, in situ data will be obtained using surface drifters, autonomous surface vehicles (Wave Gliders, Saildrones), Lagrangian floats that follow the 3D flow [5)], vertically profiling autonomous underwater vehicles (gliders), and a research vessel. These measurements will be complemented with satellite observations of sea surface height, winds, SST, and ocean color.
One novel and exciting aspect of S-MODE is its focus on measurements of horizontal velocities and their gradients, both from remote sensing and from arrays of in situ platforms. The DopplerScatt instrument [6)], flying on a NASA King Air B200 aircraft, can produce a nearly synoptic map of ocean surface currents over a 100-by-100-km area in a single 4-hour flight. We plan to use arrays of Saildrones [7)] and Wavegliders [8)] carrying ADCPs to estimate horizontal gradients of velocity at kilometer scales, in order to estimate the divergence and vorticity of the horizontal currents. These measurements would be complemented by velocity measurements from gliders, drifters, and the ship. All of the data from the S-MODE program will be made publicly available via the NASA Physical Oceanography Distributed Active Archive Center (PO.DAAC).
S-MODE airborne campaign events and development status
• November 8, 2021: NASA's S-MODE (Sub-Mesoscale Ocean Dynamics Experiment) relies on two aircraft, 17 remote-controlled vehicles, a ship and dozens of drifting instruments to make its detailed study of ocean eddies, currents and whirlpools. The researchers aim to assess how these small, high-energy ocean events contribute to circulation and heat exchange in the upper ocean, and how oceans affect climate change. The tools are stationed in a 7,800 square mile (roughly 20,200 square km) area west of San Francisco Bay, which the researchers call the “S-MODE Polygon.” 9)
- But one of the mission’s most critical tools, its control center, is not on site. The control center is a virtual daily meeting where up to 40 scientists gather to share new data, check in on the mission’s assets and plan where to maneuver their instruments and vehicles to capture the most useful measurements.
Figure 3: The S-MODE Polygon, where the mission’s instruments are stationed, is located off the coast of San Francisco (image credit: Cesar Rocha / University of Connecticut)
- The S-MODE researchers are studying sub-mesoscale ocean processes like eddies – swirling pockets of ocean water that stretch about 6.2 miles (10 km) in distance and often last for only a few days. Because eddies are relatively small and quick-fading, they can be challenging to study. Opportunities to study these processes often spring up with little warning. To study these events, the S-MODE team needs to be able to move their vehicles around quickly and strategically within the polygon.
- For instance, one of the airborne instruments may spot an eddie or whirlpool developing. The scientists may then decide which water measurements they would like to gather, and agree to send the appropriate mission vehicles out to the location of interest. The scientists discuss such decisions at control center meetings.
- During the call, representatives for each of the assets begin by providing their status updates.
- “First, we review the data our assets are seeing in the field that day or the day before, and then decide what is the interesting feature that we want to study,” said Dragana Perkovic-Martin, principal investigator for DopplerScatt, one of S-MODE’s airborne instruments, at NASA’s Jet Propulsion Laboratory. “Based on that decision, we determine which assets we need in that spot and position them in the right area.”
Figure 4: Scientists participate in a control center meeting on October 22 (image credit: NASA)
- The control center was originally going to be hosted in-person at the NASA Ames Research Center in Silicon Valley, California.
- “The idea was for a group of us to work together there to examine the conditions and the data and to update the plan as things unfolded,” said Tom Farrar, S-MODE Principal Investigator and a scientist at Woods Hole Oceanographic Institution in Falmouth, Massachusetts. As COVID-19 cases surged in late summer 2021, the team decided to shift to a virtual format. Now, the only people who are in the field are those who cannot complete their work remotely, like those flying the planes or collecting measurements aboard the ship.
- All of the scientists involved in S-MODE have done traditional field deployments before, Perkovic-Martin said. But few have had experience coordinating an expedition from a virtual control center. The group has adapted quickly with the help of online platforms including Slack, WebEx, email, and Zoom.
- “The control center works in much the same way as originally envisioned, with a group of people trying to take in as much information about what is happening to make decisions about the plan,” Farrar said.
- One of the S-MODE Deputy Principal Investigators, Professor Eric D’Asaro of the University of Washington, leads control center meetings, with the goal of ending each meeting with an updated plan for the next few days.
- “We have benefitted a lot from Eric’s enthusiasm, and his experience in other large field campaigns,” Farrar said. “We have a great team of experts and specialists, and I’m really excited about the coordinated dataset the team is collecting.”
• October 28, 2021: The first of three aircraft participating in the S-MODE campaign has arrived at Moffett Field in California. The NASA King Air B200 aircraft, carrying two science instruments – DopplerScatt and MOSES – landed on October 18th and is preparing for its first flight early in the morning on October 19th. The weather conditions have been changing and incoming storms in northern California are throwing a wrench into our planning for the airborne part of the campaign. 10)
Figure 5: NASA King Air B200 aircraft on arrival at Ames Research Center carrying DopplerScatt and MOSES instruments (image credit: Erin Czech / NASA Ames Research Center)
- My name is Dragana Perkovic-Martin and I am the Principal Investigator for DopplerScatt, an instrument that simultaneously measures ocean vector winds and surface currents. DopplerScatt is a key part of the S-MODE Earth Ventures Suborbital Project. The instrument is currently aboard NASA’s King Air B200 aircraft to collect data for the S-MODE mission. Meanwhile, I am at my pseudo control center at home, following every minute of the deployment, acting as a point of contact for aircraft communications, and jumping in when things go south with DopplerScatt.
- DopplerScatt is a radar and as such it is perfectly happy operating in cloudy conditions since its signals can penetrate the clouds, but it needs the wind to roughen the ocean surface for good data quality. Unlike DopplerScatt, the other instrument aboard this aircraft – MOSES – is an optical instrument (infrared camera to be more precise). That means MOSES can only collect data in clear weather, so no clouds. While high winds and no clouds are not mutually exclusive, the current weather outlook for the week is not great. The science team will have to closely follow forecasts and models and decide at the last moment whether the aircraft should take off. It will be a week at the edge of our seats!
- On Tuesday morning, the King Air B200 took off at 8:20 am for a reconnaissance flight of the S-MODE area. The weather front was coming in and so it was a race between the aircraft and the clouds. The first reports from the aircraft operators were good: the winds were high enough for DopplerScatt to get good data and MOSES was managing to capture data through gaps in the cloud cover.
- A little over four hours later, the King Air B200 landed, delivering the precious data “cargo” to the hangar at NASA Ames, where the DopplerScatt processing machine is housed. The images from the real-time processor aboard the aircraft promise a really good data set. The satellite data obtained by the science team is capturing a very interesting ocean circulation feature within the S-MODE sampling area and the science team is abuzz trying to reposition the autonomous marine robots to capture the feature.
Figure 6: Sea surface temperature images from the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on S/C show a warm water intrusion propagating into the S-MODE area (black polygon) from the western boundary and a cold water filament propagating into the S-MODE area from the northwestern boundary. Left image obtained on October 18th 2021, right image corresponding to October 19th 2021 (image credit: NASA)
- While we prepare for the second flight of the NASA King Air B200 this afternoon, the media is having a field day – coming along to watch, photograph and film our experiments. Today’s flight is aimed at mapping the ocean feature that has formed in the past few days in the northern end of the S-MODE sampling area. The winds are forecast to be just high enough for DopplerScatt to perform its measurements.
Figure 7: Federica Polverari (JPL DopplerScatt operator) in action during S-MODE media day (image credit: NASA)
- Meanwhile, back at my home control center, I’m using a software called FlightAware to track the aircraft while in flight. The display can include weather, and today this shows a patchwork of rain and clouds out there. Fingers crossed that it is not raining at the collection site, as DopplerScatt’s signal is attenuated in rain.
- After the plane took off and arrived at the data collection area, we lost communication as the satellite connection must have been affected by weather in the area.
- We get one more good flight for the DopplerScatt instrument, but it’s bad luck for MOSES. The cloud cover was thick and extended from approximately 5,000 to 24,000 feet, making it impossible for the camera to image the ocean surface. Perhaps we’ll have better luck Friday when cloud conditions appear to be favorable for an early morning flight.
Figure 8: NASA’s King Air B200 aircraft fueling pre-flight on a rainy morning at Moffett Field in California (image credit: NASA)
- There was lots of excitement in the pre-flight instrument power on, as one of the DopplerScatt servers had trouble booting. The DopplerScatt team mobilized over the phone and resolved the issue – sigh of relief! The whole team is glued to their cell phones in the morning, and we may have to investigate the issue upon landing.
- Today’s flight is the first combo experiment of the campaign. The NASA King Air B200 and the Twin Otter aircraft will be flying, carrying the MASS instrument operated by the Scripps Institute of Oceanography (SIO), in addition to autonomous Saildrones and recently ship-deployed drifters. The Saildrones have been sampling the area overnight and are reporting a disappearance of the cold filament. The science folks suspect that the warmer water has pushed the cold filament deeper because it’s not as visible from overhead.
Figure 9: October 22nd 2021 flight tracks by the Twin Otter (red lines) and King Air B200 (blue lines) superimposed on the sea surface temperature map, ship, and Saildrone data collected overnight (image credit: NASA)
- After a frantic back and forth during the flight to identify the source of monitor malfunction on DopplerScatt, things have settled back to normal. The flight was executed successfully and we will perform some more ground trouble-shooting to make sure that DopplerScatt is ready for the next flight, which will probably be on Monday October 25th.
- Hector and Delphine, the instrument operators flying aboard the King Air B200, shared their impressions of the flights from their high-altitude view:
- “The plane flew offshore West of San Francisco and after a cloudy and turbulent takeoff, the ocean appeared perfectly clear at the altitude of 26,000 ft. Operating smoothly thanks to both skills and practice, in coordination with the pilots, we traced an array over the ocean and collected great quality data. When we saw oceanic structures with clean, sharp gradients appearing on our screens we were overjoyed! The months of preparations were starting to pay off. These structures are exactly what we have come to measure. The other aircraft, the Twin Otter, has also joined the data collection and will provide a very useful data comparison. The plane tracks were successfully changed to optimize the overlap of the two data sets. What a great day for S-MODE,” they told me.
- Now quiet resumes while the data are being processed by our teammates. That’s a wrap for the first week of the S-MODE pilot campaign airborne activities!
• October 26, 2021: After a successful test run in May, a NASA campaign is deploying aircraft, a research vessel and several kinds of autonomous ocean robots to study small ocean whirlpools, eddies and currents. 11)
Figure 10: The R/V Oceanus ship docked in Newport, Oregon during S-MODE ship mobilization (image credit: Sommer Nicholas / NASA Ames Research Center)
- Using instruments at sea and in the sky, the Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) team aims to understand the role these ocean processes play in vertical transport, the movement of heat, nutrients, oxygen, and carbon from the ocean surface to the deeper ocean layers below. In addition, scientists think these small-scale ocean features play an important role in the exchange of heat and gases between air and sea. Understanding small-scale ocean dynamics will help scientists better understand how Earth’s oceans slow the impact of global warming and impact the Earth climate system.
- On Oct. 19, the research vessel Oceanus, owned by the National Science Foundation, set sail to an area a hundred nautical miles out to sea off the coast of San Francisco, accompanied by a fleet of several types of autonomous marine research vehicles. For the following three weeks, two aircraft will also fly repeatedly overhead to collect measurements from above while the vessel and the autonomous vehicles samples the ocean below. The eyes-in-the-sky perspective from the aircraft will allow the team to monitor a large swath of ocean at once, as well as direct the research ship and autonomous ocean vehicles in the water to move toward areas of interest.
Figure 11: A map of the ocean floor topography off the coast of San Francisco, California, with black lines outlining the S-MODE study site (image credits: Cesar Rocha, University of Connecticut)
- “The overall goal is to understand vertical transport in the ocean, and how the remote sensing measurements relate to the in situ, or ‘wet,’ measurements,” said Dragana Perkovic-Martin, a radar system engineer at NASA’s Jet Propulsion Laboratory in Southern California.
Aerial Views of the Ocean Surface
- From its vantage 28,000 feet in the air aboard the NASA Armstrong King Air B200, the DopplerScatt instrument bounces radar signals off the ocean to provide information about winds and currents at the surface. The MASS instrument aboard the Twin Otter DHC6 plane flies below the clouds to observe how surface waves move and break. It collects measurements with a complex suite of laser-based and imaging devices, which allow the team to infer ocean currents from these measurements.
Figure 12: Hector Torres from NASA JPL and Delphine Hypolite from the University of California, Los Angeles onboard the AFRC B200 aircraft during the S-MODE flights (image credits: Scott Howe / Ames Flight Research Center)
- “The aircraft instruments provide spatial observations but can’t penetrate the ocean’s surface, while the autonomous vehicles and ship are providing in situ data that will give profiles of the ocean,” said Luc Lenain, an ocean scientist at the Scripps Institution of Oceanography (SIO) at the University of California, San Diego. Used in conjunction, these data show what is happening over an area of the ocean surface and into the depths below.
All Aboard the R/V Oceanus
- While the aircraft collect data on wind, currents and ocean properties from the sky, the ship will be taking similar measurements from the ocean surface. “Since the aircraft-based observations of ocean currents are relatively new, we want to know how they relate to our traditional ways of studying the ocean,” said Andrey Shcherbina, an oceanographer at the Applied Physics Laboratory at the University of Washington and chief scientist on the R/V Oceanus.
Figure 13: Several autonomous marine robots, including these Wave Gliders from Scripps Institute of Oceanography and the Woods Hole Oceanographic Institute, will deploy from R/V Oceanus ship (image credits: Laurent Grare / Scripps Institute of Oceanography)
- The ship will also serve as a launching point for a small fleet of several types of autonomous ocean vehicles. Four Wave Gliders – essentially surfboards with a suite of scientific instruments aboard – will bob up and down on the surface to propel themselves around the study area. Several Saildrones will sail from San Francisco Bay to join the fleet collecting data at the study site. The Saildrones and Wave Gliders will measure a vast array of factors such as ocean currents, wind speed and direction, air and water temperature, salinity, dissolved oxygen, and chlorophyll content.
Figure 14: A type of autonomous marine robot called a Saildrone being deployed from Alameda, California (image credit: NASA, Jesse Carpenter)
- Two kinds of trackers will float freely in the water, providing information about where and how currents are moving and interacting. The drifters remain on the surface, while the Lagrangian Floats follow the underwater ocean currents in three dimensions.
- With all these instruments working in coordination with each other, with the vessel, and with the aircraft, the team hopes to capture rapidly shifting ocean currents and properties within the study area. “Our best bet is to have a lot of instruments sampling this small patch of ocean so that we have a comprehensive multi-faceted view,” said Shcherbina. From this data, the team hopes to learn more about small-scale ocean movements and how these movements may move heat, nutrients and gases within the ocean and between air and sea.
Figure 15: Animation showing the research ship and some of the gliders and floats the S-MODE team will use to study small-scale ocean whirlpools, currents and eddies (image credits: NASA’s Goddard Space Flight Center / Scientific Visualization Studio)
- S-MODE is part of NASA’s Earth Venture Suborbital-3 (EVS-3) program, funded by the Earth System Science Pathfinder (ESSP) Program Office at NASA’s Langley Research Center in Hampton, Virginia, and managed by the Earth Science Project Office (ESPO) at NASA’s Ames Research Center in California’s Silicon Valley.
• May 2021: After being delayed over a year due to the COVID-19 pandemic, a NASA field campaign to study the role of small-scale whirlpools and ocean currents in climate change is taking flight and taking to the seas in May 2021. 12)
Figure 16: Flight crews at NASA's Armstrong Flight Research Center in Edwards, California, flew the Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) installed in the B200 King Air on May 3, 2021 (image credit: Carla Thomas, NASA Armstrong Flight Research center in Edwards, California)
Using scientific instruments aboard a self-propelled ocean glider and several airplanes, this first deployment of the Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) mission will deploy its suite of water- and air-borne instruments to ensure that they work together to show what’s happening just below the ocean’s surface. The full-fledged field campaign will begin in October 2021, with the aircraft based out of NASA’s Ames Research Center in Mountain View, California.
“This campaign in May is largely to compare different ways of measuring ocean surface currents so that we can have confidence in those measurements when we get to the pilot in October,” said Tom Farrar, associate scientist at the Woods Hole Oceanographic Institution in Massachusetts and principal investigator for S-MODE.
Figure 17: Sub-mesoscale ocean dynamics, like eddies and small currents, are responsible for the swirling pattern of these phytoplankton blooms (shown in green and light blue) in the South Atlantic Ocean on Jan. 5, 2021 (image credits: NASA’s Goddard Space Flight Center Ocean Color, using data from the NOAA-20 satellite and the joint NASA-NOAA Suomi NPP satellite)
The S-MODE team hopes to learn more about small-scale movements of ocean water such as eddies. These whirlpools span about 6.2 miles or ten kilometers, slowly moving ocean water in a swirling pattern. Scientists think that these eddies play an important role in moving heat from the surface to the ocean layers below, and vice versa. In addition, the eddies may play a role in the exchange of heat, gases and nutrients between the ocean and Earth’s atmosphere. Understanding these small-scale eddies will help scientists better understand how Earth’s oceans slow down global climate change.
A Self-Powered Surfboard, for Science!
The team is using a self-propelled commercial Wave Glider decked out with scientific instruments that can study the ocean from its surface. The most important gadgets aboard are the acoustic Doppler current profilers, which use sonar to measure water speed and gather information about the how fast the currents and eddies are moving, and in which direction. The glider also carries instruments to measure wind speed, air temperature and humidity, water temperature and salinity, and light and infrared radiation from the Sun.
“The wave glider looks like a surfboard with a big venetian blind under it,” said Farrar.
That “venetian blind” is submerged under the water, moving up and down with the ocean’s waves to propel the glider forward at about one mile per hour. In this way, the wave glider will be deployed from La Jolla, California, collecting data as it travels over 62 miles (100 km) out into the ocean offshore of Santa Catalina Island.
The new data will allow the scientists to estimate the exchange of heat and gases between Earth’s atmosphere and the ocean, and consequently better understand global climate change.
“We know the atmosphere is heating up. We know the winds are speeding up. But we don’t really understand where all that energy is going,” said Ernesto Rodriguez, research fellow at NASA’s Jet Propulsion Laboratory in Pasadena, California, and deputy principal investigator for the airborne parts of S-MODE. It’s likely that this energy is going into the ocean, but the details of how that process works are still unknown. The team thinks that small-scale eddies may help move heat from the atmosphere to the deeper layers of the ocean.
Figure 18: Laurent Grare of the Scripps Institution of Oceanography prepares to recover a Wave Glider during a pre-deployment test. Decked out with solar panels and several scientific instruments, the wave glider will propel itself from Santa Catalina Island farther out to sea (image credits: Courtesy of Benjamin Greenwood / Woods Hole Oceanographic Institution)
Eyes and Scientific Instruments in the Skies
While the Wave Glider continues its slow trek across the ocean’s surface, several airplanes will fly overhead to collect data from a different vantage.
“In an airplane, we can get a snapshot of a large area to see the context of how the bigger- and smaller-scale ocean movements interact,” said Rodriguez.
For example, a ship or wave glider travels slowly along a straight line, taking precise measurements of sea surface temperature at specific times and places. Airplanes move faster and can cover more ground, measuring the sea surface temperature of a large swath of ocean very quickly.
Figure 19: A flight crew prepares for the B200 King Air Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) at NASA’s Armstrong Flight Research Center in Edwards, California. From left to right are Jeroen Molemaker and Scott “Jelly” Howe (image credit: Lauren Hughes, NASA Armstrong)
“It’s like taking an infrared image rather than using a thermometer,” explained Farrar.
Two planes will be used in the May test flights: a B200 plane from NASA’s Armstrong Flight Center in Edwards, California and a commercial plane from Twin Otter International. The B200 is carrying an instrument from NASA JPL called DopplerScatt to measure currents and winds near the ocean surface with radar. The MOSES (Multiscale Observing System of the Ocean Surface) instrument from the University of California, Los Angeles is also aboard to collect sea surface temperature data. On the Twin Otter plane is the MASS (Modular Aerial Sensing System) from the Scripps Institution of Oceanography at the University of California, San Diego, which is an instrument capable of measuring the height of waves on the surface of the ocean.
Figure 20: Delphine Hypolite, MOSES instrument operator from University of California Los Angeles, performs pre-flight checks on the MOSES Camera System at NASA's Armstrong Flight Research Center in Edwards, California (image credit: Lauren Hughes, NASA Armstrong)
The fleet will gain a third member for the October experiments: NASA’s Langley Research Center Gulfstream III plane with JPL’s PRISM (Portable Remote Imaging SpectroMeter), an instrument to measure phytoplankton and other biological material in the water. The October deployments will also use a large ship and some autonomous sailing vessels, called Saildrones, in addition to planes and Wave Gliders.
After nearly a year and a half of delays due to the pandemic, the S-MODE team is excited to get their planes in the sky and the gliders in the water. “It was frustrating,” Rodriguez said, “but the science team hasn’t slowed down. The science keeps progressing.”
S-MODE is NASA’s ocean physics Earth Venture Suborbital-3 (EVS-3) mission, funded by the Earth System Science Pathfinder (ESSP) Program Office at NASA's Langley Research Center in Hampton, Virginia, and managed by the Earth Science Project Office (ESPO) at Ames Research Center.
Mission overview and some background
A major difficulty in simulating Earth’s climate system is that there are interactions across scales, so that the large time and space scales can be sensitive to processes on small scales. As the computational resolution of global ocean models has improved, scientists have begun to suspect that kilometer-scale eddies and fronts, called “sub-mesoscale” variability, have a net effect on ocean-atmosphere heat exchange that is larger than the heating from the greenhouse effect (Su et al. 2018). State-of-the-art computer models agree in predicting that these eddies have important long-term effects on the upper-ocean, but their predictions are sensitive to relatively small details in model physics and implementation. The resolution and detail of these simulations has surpassed our ability to ‘ground truth’ them with spaceborne or in situ sensors. There is thus a pressing need for a comprehensive benchmark data set on these sub-mesoscale motions to address this important source of uncertainty in simulating the global ocean. 13) 14)
This mission will test the hypothesis that submesoscale ocean dynamics make important contributions to vertical exchange of climate and biological variables in the upper ocean. This will require coordinated application of newly-developed in situ and remote sensing techniques, and it will provide an unprecedented view of the physics of submesoscale eddies and fronts and their effects on vertical transport in the upper ocean. The Sub-Mesoscale Ocean Dynamics Experiment (S-MODE) will use measurements from a novel combination of platforms and instruments, along with data analysis and modeling, to test the hypothesis.
Figure 21: Logo of S-MODE (image credit: NASA)
1) J. Thomas Farrar, Eric D'Asaro, Ernesto Rodriguez, Andrey Shcherbina, Erin Czech, Paul Matthias, Sommer Nicholas, Frederick Bingham, Amala Mahedevan, Melissa Omand, Luc Rainville, Craig Lee, Dudley Chelton, Roger Samelson, Larry O'Neill, Luc Lenain, Dimitris Menemenlis, Dragana Perkovic-Martin, Pantazis Mouroulis, Michelle Gierach, David Thompson, Alexander Wineteer, Hector Torres, Patrice Klein, Andrew Thompson, James C. McWilliams, Jeroen Molemaker, Roy Barkan, Jacob Wenegrat, Cesar Rocha, Gregg Jacobs, Joseph D'Addezio, Sebastien de Halleux, and Richard Jenkins, ”S-MODE: The Sub-Mesoscale Ocean Dynamics Experiment,” IGARSS 2020, 26 Sept.-2 Oct. 2020, Virtual Symposium, URL: https://airsea.ucsd.edu/wp-content/uploads/sites/10/2021/02/2020_Farrar-IEEE_IGRSS.pdf
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Thomas Farrar, Eric D'Asaro, Ernesto Rodriguez, Andrey Shcherbina, Erin
Czech4, Paul Matthias, Sommer Nicholas, Frederick Bingham, Amala
Mahedevan, Melissa Omand, Luc Rainville, Craig Lee, Dudley Chelton,
Roger Samelson, Larry O'Neill, Luc Lenain, Dimitris Menemenlis, Dragana
Perkovic-Martin, Pantazis Mouroulis, Michelle Gierach, David Thompson,
Alexander Wineteer, Hector Torres, Patrice Klein, Andrew Thompson,
James C. McWilliams, Jeroen Molemaker, Roy Barkan, Jacob Wenegrat,
Cesar Rocha, Gregg Jacobs, Joseph D'Addezio, Sebastien de Halleux, and
Richard Jenkins, ”S-MODE: The Sub-Mesoscale Ocean Dynamics
Experiment,” IGARSS 2020, 26 Sept.-2 October 2020, Waikoloa, HI,
USA, URL: https://airsea.ucsd.edu/wp-content/uploads/sites/10/2021/02/2020_Farrar-IEEE_IGRSS.pdf
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).