By Air and by Sea: Validating NASA’s PACE Ocean Color Instrument

In autumn 2024, California’s Monterey Bay experienced an outsized phytoplankton bloom that attracted fish, dolphins, whales, seabirds, and – for a few weeks in October – scientists. A team from NASA’s Ames Research Center in Silicon Valley, with partners at the University of California, Santa Cruz (UCSC), and the Naval Postgraduate School, spent two weeks on the California coast gathering data on the atmosphere and the ocean to verify what satellites see from above. In spring 2025, the team returned to gather data under different environmental conditions.

Scientists call this process validation.

Setting up the Campaign

The PACE mission, which stands for Plankton, Aerosol, Cloud, ocean Ecosystem, was launched in February  2024 and designed to transform our understanding of ocean and atmospheric environments. Specifically, the satellite will give scientists a finely detailed look at life near the ocean surface and the composition and abundance of aerosol particles in the atmosphere.

Whenever NASA launches a new satellite, it sends validation science teams around the world to confirm that the data from instruments in space match what traditional instruments can see at the surface. AirSHARP (Airborne aSsessment of Hyperspectral Aerosol optical depth and water-leaving Reflectance Product Performance for PACE) is one of these teams, specifically deployed to validate products from the satellite’s Ocean Color Instrument (OCI).

The OCI spectrometer works by measuring reflected sunlight. As sunlight bounces off of the ocean’s surface, it creates specific shades of color that researchers use to determine what is in the water column below. To validate the OCI data, research teams need to confirm that measurements directly at the surface match those from the satellite. They also need to understand how the atmosphere is changing the color of the ocean as the reflected light is traveling back to the satellite.

In October 2024 and May 2025, the AirSHARP team ran simultaneous airborne and seaborne campaigns. Going into the field during different seasons allows the team to collect data under different environmental conditions, validating as much of the instrument’s range as possible.

Over 13 days of flights on a Twin Otter aircraft, the NASA-led team used instruments called 4STAR-B (Spectrometer for sky-scanning sun Tracking Atmospheric Research B), and the C-AIR (Coastal Airborne In-situ Radiometer) to gather data from the air. At the same time, partners from UCSC used a host of matching instruments onboard the research vessel R/V Shana Rae to gather data from the water’s surface.

Ocean Color and Water Leaving Reflectance

The Ocean Color Instrument measures something called water leaving reflectance, which provides information on the microscopic composition of the water column, including water molecules, phytoplankton, and particulates like sand, inorganic materials, and even bubbles. Ocean color varies based on how these materials absorb and scatter sunlight. This is especially useful for determining the abundance and types of phytoplankton.

The AirSHARP team used radiometers with matching technology – C-AIR from the air and C-OPS (Compact Optical Profiling System) from the water – to gather water leaving reflectance data.

“The C-AIR instrument is modified from an instrument that goes on research vessels and takes measurements of the water’s surface from very close range,” said NASA Ames research scientist Samuel LeBlanc. “The issue there is that you’re very local to one area at a time. What our team has done successfully is put it on an aircraft, which enables us to span the entire Monterey Bay.”

The larger PACE validation team will compare OCI measurements with observations made by the sensors much closer to the ocean to ensure that they match, and make adjustments when they don’t. 

Aerosol Interference

One factor that can impact OCI data is the presence of manmade and natural aerosols, which interact with sunlight as it moves through the atmosphere. An aerosol refers to any solid or liquid suspended in the air, such as smoke from fires, salt from sea spray, particulates from fossil fuel emissions, desert dust, and pollen.

Imagine a 420 mile-long tube, with the PACE satellite at one end and the ocean at the other. Everything inside the tube is what scientists refer to as the atmospheric column, and it is full of tiny particulates that interact with sunlight. Scientists quantify this aerosol interaction with a measurement called aerosol optical depth.

“During AirSHARP, we were essentially measuring, at different wavelengths, how light is changed by the particles present in the atmosphere,” said NASA Ames research scientist Kristina Pistone. “The aerosol optical depth is a measure of light extinction, or how much light is either scattered away or absorbed by aerosol particulates.” 

The team measured aerosol optical depth using the 4STAR-B spectrometer, which was engineered at NASA Ames and  enables scientists to identify which aerosols are present and how they interact with sunlight.

Twin Otter Aircraft

Flying these instruments required use of a Twin Otter plane, operated by the Naval Postgraduate School (NPS). The Twin Otter is unique for its ability to perform extremely low-altitude flights, making passes down to 100 feet above the water in clear conditions.

“It’s an intense way to fly. At that low height, the pilots continually watch for and avoid birds, tall ships, and even wildlife like breaching whales,” said Anthony Bucholtz, director of the Airborne Research Facility at NPS.

With the phytoplankton bloom attracting so much wildlife in a bay already full of ships, this is no small feat. “The pilots keep a close eye on the radar, and fly by hand,” Bucholtz said, “all while following careful flight plans crisscrossing Monterey Bay and performing tight spirals over the Research Vessel Shana Rae.”

Campaign Data

Data gathered from the 2024 phase of this campaign is available on two data archive systems. Data from the 4STAR instrument is available in the PACE data archive  and data from C-AIR is housed in the SeaBASS data archive.

Other data from the NASA PACE Validation Science Team is available through the PACE website: https://pace.oceansciences.org/pvstdoi.htm#

Samuel LeBlanc and Kristina Pistone are funded via the Bay Area Environmental Research Institute (BAERI), which  is a scientist-founded nonprofit focused on supporting Earth and space sciences.

About the Author

Milan Loiacono

Science Communication Specialist

Milan Loiacono is a science communication specialist for the Earth Science Division at NASA Ames Research Center.

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NASA Mars Orbiter Learns New Moves After Nearly 20 Years in Space

The Mars Reconnaissance Orbiter is testing a series of large spacecraft rolls that will help it hunt for water.

After nearly 20 years of operations, NASA’s Mars Reconnaissance Orbiter (MRO) is on a roll, performing a new maneuver to squeeze even more science out of the busy spacecraft as it circles the Red Planet. Engineers have essentially taught the probe to roll over so that it’s nearly upside down. Doing so enables MRO to look deeper underground as it searches for liquid and frozen water, among other things.

The new capability is detailed in a paper recently published in the Planetary Science Journal documenting three “very large rolls,” as the mission calls them, that were performed between 2023 and 2024.

“Not only can you teach an old spacecraft new tricks, you can open up entirely new regions of the subsurface to explore by doing so,” said one of the paper’s authors, Gareth Morgan of the Planetary Science Institute in Tucson, Arizona.

The orbiter was originally designed to roll up to 30 degrees in any direction so that it can point its instruments at surface targets, including potential landing sites, impact craters, and more.

“We’re unique in that the entire spacecraft and its software are designed to let us roll all the time,” said Reid Thomas, MRO’s project manager at NASA’s Jet Propulsion Laboratory in Southern California.

The process for rolling isn’t simple. The spacecraft carries five operating science instruments that have different pointing requirements. To target a precise spot on the surface with one instrument, the orbiter has to roll a particular way, which means the other instruments may have a less-favorable view of Mars during the maneuver.

That’s why each regular roll is planned weeks in advance, with instrument teams negotiating who conducts science and when. Then, an algorithm checks MRO’s position above Mars and automatically commands the orbiter to roll so the appropriate instrument points at the correct spot on the surface. At the same time, the algorithm commands the spacecraft’s solar arrays to rotate and track the Sun and its high-gain antenna to track Earth to maintain power and communications.

Very large rolls, which are 120 degrees, require even more planning to maintain the safety of the spacecraft. The payoff is that the new maneuver enables one particular instrument, called the Shallow Radar (SHARAD), to have a deeper view of Mars than ever before.

SHARAD’s View of Mars During a ‘Very Large Roll’

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Image Details

These two radargrams from the SHARAD instrument on NASA’s MRO reveal how the spacecraft’s new “very large roll” maneuver produces a stronger signal, providing a brighter, clearer picture of the Martian subsurface. Use the slider to compare the 120-degree roll, left, to the standard 28-degree roll. NASA/JPL-Caltech/University of Rome/ASI/PSI

Bigger Rolls, Better Science

Designed to peer from about half a mile to a little over a mile (1 to 2 kilometers) belowground, SHARAD allows scientists to distinguish between materials like rock, sand, and ice. The radar was especially useful in determining where ice could be found close enough to the surface that future astronauts might one day be able to access it. Ice will be key for producing rocket propellant for the trip home and is important for learning more about the climate, geology, and potential for life at Mars.

But as great as SHARAD is, the team knew it could be even better.

To give cameras like the High-Resolution Imaging Science Experiment (HiRISE) prime viewing at the front of MRO, SHARAD’s two antenna segments were mounted at the back of the orbiter. While this setup helps the cameras, it also means that radio signals SHARAD pings onto the surface below encounter parts of the spacecraft, interfering with the signals and resulting in images that are less clear.

“The SHARAD instrument was designed for the near-subsurface, and there are select regions of Mars that are just out of reach for us,” said Morgan, a co-investigator on the SHARAD team. “There is a lot to be gained by taking a closer look at those regions.”

In 2023, the team decided to try developing 120-degree very large rolls to provide the radio waves an unobstructed path to the surface. What they found is that the maneuver can strengthen the radar signal by 10 times or more, offering a much clearer picture of the Martian underground.

But the roll is so large that the spacecraft’s communications antenna is not pointed at Earth, and its solar arrays aren’t able to track the Sun.

“The very large rolls require a special analysis to make sure we’ll have enough power in our batteries to safely do the roll,” Thomas said.

Given the time involved, the mission limits itself to one or two very large rolls a year. But engineers hope to use them more often by streamlining the process.

Learning to Roll With It

While SHARAD scientists are benefiting from these new moves, the team working with another MRO instrument, the Mars Climate Sounder, is making the most of MRO’s standard roll capability. 

The JPL-built instrument is a radiometer that serves as one of the most detailed sources available of information on Mars’ atmosphere. Measuring subtle changes in temperature over the course of many seasons, Mars Climate Sounder reveals the inner workings of dust storms and cloud formation. Dust and wind are important to understand: They are constantly reshaping the Martian surface, with wind-borne dust blanketing solar panels and posing a health risk for future astronauts.

Mars Climate Sounder was designed to pivot on a gimbal so that it can get views of the Martian horizon and surface. It also provides views of space, which scientists use to calibrate the instrument. But in 2024, the aging gimbal became unreliable. Now Mars Climate Sounder relies on MRO’s standard rolls.

“Rolling used to restrict our science,” said Mars Climate Sounder’s interim principal investigator, Armin Kleinboehl of JPL, “but we’ve incorporated it into our routine planning, both for surface views and calibration.”

More About MRO

NASA’s Jet Propulsion Laboratory in Southern California manages MRO for the agency’s Science Mission Directorate in Washington as part of its Mars Exploration Program portfolio. The SHARAD instrument was provided by the Italian Space Agency. Its operations are led by Sapienza University of Rome, and its data is analyzed by a joint U.S.-Italian science team. The Planetary Science Institute in Tucson, Arizona, leads U.S. involvement in SHARAD. Lockheed Martin Space in Denver built MRO and supports its operations.

For more information, visit:

science.nasa.gov/mission/mars-reconnaissance-orbiter

News Media Contacts

Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-2433
andrew.c.good@jpl.nasa.gov

Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov

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NASA’s Webb Digs into Structural Origins of Disk Galaxies

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NASA’s Webb Digs into Structural Origins of Disk Galaxies

Present-day disk galaxies often contain a thick, star-filled outer disk and an embedded thin disk of stars. For instance, our own Milky Way galaxy’s thick disk is approximately 3,000 light-years in height, and its thin disk is roughly 1,000 light-years thick.

How and why does this dual disk structure form? By analyzing archival data from multiple observational programs by NASA’s James Webb Space Telescope, a team of astronomers is closer to answers, as well as understanding the origins of disk galaxies in general.

The team carefully identified, visually verified, and analyzed a statistical sample of 111 edge-on disk galaxies at various periods — up to 11 billion years ago (or approximately 2.8 billion years after the big bang). This is the first time scientists have investigated thick- and thin-disk structures spanning such vast distances, bridging the gap between observers probing the early universe and galactic archaeologists seeking to understand our own galaxy’s history.

“This unique measurement of the thickness of the disks at high redshift, or at times in the early universe, is a benchmark for theoretical study that was only possible with Webb,” said Takafumi Tsukui, lead author of the paper and a researcher at the Australian National University in Canberra. “Usually, the older, thick disk stars are faint, and the young, thin disk stars outshine the entire galaxy. But with Webb’s resolution and unique ability to see through dust and highlight faint old stars, we can identify the two-disk structure of galaxies and measure their thickness separately.”

Image: A Sample of Galaxy Disks (NIRCam)

Data Through Thick and Thin

By analyzing these 111 targets over cosmological time, the team was able to study single-disk galaxies and double-disk galaxies. Their results indicate that galaxies form a thick disk first, followed by a thin disk. The timing of when this takes place is dependent on the galaxy’s mass: high-mass, single-disk galaxies transitioned to two-disk structures around 8 billion years ago. In contrast, low-mass, single-disk galaxies formed their embedded thin disks later on, about 4 billion years ago.

“This is the first time it has been possible to resolve thin stellar disks at higher redshift. What’s really novel is uncovering when thin stellar disks start to emerge,” said Emily Wisnioski, a co-author of the paper at the Australian National University in Canberra. “To see thin stellar disks already in place 8 billion years ago, or even earlier, was surprising.”

A Turbulent Time for Galaxies

To explain this transition from a single, thick disk to a thick and thin disk, and the difference in timing for high- and low-mass galaxies, the team looked beyond their initial edge-on galaxy sample and examined data showing gas in motion from the Atacama Large Millimeter/submillimeter Array (ALMA) and ground-based surveys.

By taking into consideration the motion of the galaxies’ gas disks, the team finds their results align with the “turbulent gas disk” scenario, one of three major hypotheses that has been proposed to explain the process of thick- and thin-disk formation. In this scenario, a turbulent gas disk in the early universe sparks intense star formation, forming a thick stellar disk. As stars form, they stabilize the gas disk, which becomes less turbulent and, as a result, thinner.

Since massive galaxies can more efficiently convert gas into stars, they settle sooner than their low-mass counterparts, resulting in the earlier formation of thin disks. The team notes that thick- and thin-disk formation are not siloed events: The thick disk continues to grow as the galaxy develops, though it’s slower than the thin disk’s rate of growth.

How This Applies to Home

Webb’s sensitivity is enabling astronomers to observe smaller and fainter galaxies, analogous to our own, at early times and with unprecedented clarity for the first time. In this study, the team noted that the transition period from thick disk to a thick and thin disk roughly coincides with the formation of the Milky Way galaxy’s thin disk. With Webb, astronomers will be able to further investigate Milky Way-like progenitors — galaxies that would have preceded the Milky Way — which could help explain our galaxy’s formation history.

In the future, the team intends to incorporate other data points into their edge-on galaxy sample.

“While this study structurally distinguishes thin and thick disks, there is still much more we would like to explore,” said Tsukui. “We want to add the type of information people usually get for nearby galaxies, like stellar motion, age, and metallicity. By doing so, we can bridge the insights from galaxies near and far, and refine our understanding of disk formation.”

These results were published in the Monthly Notices of the Royal Astronomical Society.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

To learn more about Webb, visit:

https://science.nasa.gov/webb

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View/Download all image products at all resolutions for this article from the Space Telescope Science Institute.

View/Download the research results from the Monthly Notices of the Royal Astronomical Society.

Media Contacts

Laura Betz – laura.e.betz@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Abigail Major – amajor@stsci.edu
Space Telescope Science Institute, Baltimore, Md.

Hannah Braun – hbraun@stsci.edu
Space Telescope Science Institute, Baltimore, Md.

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