NASA Earth Scientists Take Flight, Set Sail to Verify PACE Satellite Data

The Importance of Satellite Data Validation

Satellite missions like PACE provide invaluable global observations of Earth's ecosystems and atmospheric conditions. However, the data they collect must be rigorously validated to ensure accuracy. Validation involves comparing satellite measurements with data collected from instruments on or near Earth's surface, confirming that satellite sensors correctly capture environmental variables.

Kirk Knobelspiesse, an atmospheric scientist at NASA’s Goddard Space Flight Center and mission scientist for PACE-PAX, emphasizes that validation is essential for building confidence in satellite observations. Without this step, the reliability of data used by scientists and policymakers to monitor ocean health, atmospheric particles, and clouds would remain uncertain.

This process of validation is critical because once a satellite is launched, its instruments cannot be physically adjusted. Instead, scientists rely on validation campaigns to verify the accuracy of the data and refine the algorithms that interpret satellite measurements. This ensures that the satellite continues to provide reliable information throughout its operational life.

Scope and Scale of the PACE-PAX Campaign

The PACE-PAX campaign, which began in early September 2024, represents the largest validation effort since the satellite's launch. More than 100 scientists operate from three key locations in California: Marina, Santa Barbara, and NASA’s Armstrong Flight Research Center in Edwards.

The campaign employs a combination of platforms—a research vessel and two aircraft—to collect simultaneous data from the ocean surface to high altitudes. This multi-vantage approach allows scientists to capture a comprehensive picture of the ocean and atmosphere, facilitating direct comparisons with satellite data.

This coordinated effort is unique in its scale and complexity, involving several dozen instruments and a diverse team of experts from multiple NASA centers and partner institutions. By collecting data simultaneously from sea level to the stratosphere, the campaign ensures that measurements are temporally and spatially aligned with PACE satellite observations.

Ocean Measurements from the NOAA Research Vessel Shearwater

At sea, the NOAA research vessel Shearwater plays a pivotal role in gathering oceanographic data. Scientists aboard collect water samples to analyze phytoplankton types and their relative abundance, which directly relates to the ocean color data captured by PACE’s hyperspectral Ocean Color Instrument.

Additionally, the vessel measures the optical properties of seawater, providing ground-truth data that help verify the satellite’s ability to detect biological and chemical characteristics of the ocean. These measurements are critical for understanding marine ecosystems and their responses to environmental changes.

Phytoplankton are microscopic organisms that form the base of the ocean food web and play a significant role in carbon cycling. By accurately measuring their abundance and types, scientists can assess ocean health and productivity. The Shearwater’s data help confirm that PACE’s instruments correctly interpret the subtle variations in ocean color that indicate these biological processes.

Atmospheric Observations from Twin Otter and NASA ER-2 Aircraft

Complementing ocean data, atmospheric scientists utilize two aircraft to collect detailed measurements of clouds and aerosols. The Twin Otter, operated by the Naval Postgraduate School, flies at altitudes up to 10,000 feet, sampling cloud droplet sizes and aerosol properties such as particle size and light scattering.

At higher altitudes, NASA’s ER-2 aircraft operates around 70,000 feet, providing a bird’s-eye view above clouds with instruments analogous to those on PACE. These include prototype polarimeters and spectrometers that measure light across visible wavelengths, enabling precise comparisons with satellite data.

The ER-2’s narrower but higher-resolution observations complement the broader satellite perspective, allowing scientists to refine data interpretation methods and improve the accuracy of atmospheric measurements.

The combination of these aircraft platforms enables scientists to capture a vertical profile of atmospheric properties, from near the surface to the stratosphere. This vertical layering is essential for understanding how aerosols and clouds interact and influence climate processes.

Integrating Multi-Platform Data for Robust Validation

The strength of the PACE-PAX campaign lies in its simultaneous data collection across multiple platforms and environments. While the research vessel samples ocean biology and optics, the Twin Otter and ER-2 aircraft gather atmospheric data at different altitudes, all coordinated to observe the same geographic regions as the satellite.

This integrated approach enables scientists to cross-validate measurements, identify discrepancies, and adjust algorithms used to interpret satellite data. As Ivona Cetinic, deputy mission scientist for PACE-PAX, notes, although the satellite’s instruments cannot be modified after launch, the data processing algorithms can be refined to enhance accuracy based on validation results.

Such iterative refinement is crucial for long-term satellite missions, as environmental conditions and instrument performance can change over time. The campaign’s comprehensive data set provides a benchmark against which future satellite data can be compared, ensuring ongoing reliability.

Implications for Climate Science and Environmental Monitoring

Accurate satellite data from missions like PACE are vital for tracking changes in ocean ecosystems, atmospheric composition, and cloud dynamics. These observations inform climate models, support environmental policy decisions, and improve our understanding of Earth’s interconnected systems.

Given the dynamic nature of oceans and atmosphere, ongoing validation campaigns ensure that satellite data remain reliable over time. This is crucial for detecting subtle trends related to climate change, such as shifts in phytoplankton populations or aerosol concentrations, which have far-reaching impacts on global climate and human health.

The PACE mission’s ability to monitor aerosols and clouds also contributes to understanding their role in Earth's energy balance and weather patterns. By improving the accuracy of these measurements, scientists can better predict climate variability and assess the effectiveness of mitigation strategies.

What this means

The PACE-PAX field campaign exemplifies the rigorous efforts required to validate satellite data, ensuring that NASA’s PACE mission delivers precise and trustworthy information about our planet’s oceans and atmosphere. By integrating measurements from sea level to the stratosphere, scientists can confidently interpret satellite observations, enhancing our ability to monitor environmental changes and address global challenges such as climate change. Continued validation campaigns will remain indispensable as satellite technology advances, maintaining the integrity and usefulness of Earth observation data for years to come.