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Welcome to CLARREO Pathfinder

Advancing Climate Science Through Unprecedented Accuracy

CLARREO Pathfinder’s data will help us better understand Earth’s changing climate. CLARREO Pathfinder (CPF) data will do this by taking highly accurate measurements of sunlight reflected by Earth and the Moon. These measurements, which will be anchored to international standards, will be five to ten times more accurate than those from existing sensors. CPF will have the unique ability to maintain its high accuracy throughout its lifetime. CPF will also showcase novel techniques in transferring its high accuracy to other sensors monitoring Earth. Higher accuracy means greater certainty in our measurements, which makes it possible to detect Earth’s subtle climate change trends decades sooner than otherwise possible, and provides the knowledge needed to make informed decisions in response.

CLARREO Pathfinder mission patch showing the instrument on the ISS.
Clouds over the Atlantic Ocean

Earth’s climate is complex and dynamic.

CPF will take high accuracy measurements of reflected sunlight needed to help us better understand Earth’s climate system.

Sunlight reflected off the Earth

The spectral content of reflected sunlight carries climate information back to space.

CPF measurements will be sensitive to changes in reflected sunlight, which are representative of changes in several vital climate variables. This is essential to detect and understand changes in Earth’s climate.

Close-up of the Sun

CPF will measure reflected sunlight better than current Earth-viewing sensors.

CPF will use scans of the Sun and other detailed calibration measurements to achieve unprecedented accuracy that will be 5-10 times better than existing sensors.

Satellites around the Earth

Other instruments need a high accuracy reference to more confidently monitor climate.

CPF will demonstrate how to transfer its high accuracy, which will be tied to international standards, to other Earth-viewing sensors.

The Moon

CPF will improve the Moon as a calibration standard.

CPF’s measurements will improve the calibration accuracy of the Moon, a stable calibration target, which will also help other in-orbit instruments.


NASA innovates for the benefit of humanity.

Earth’s climate is changing. What remains a mystery is how quickly, to what extent, and the exact nature of the consequences. CPF’s unparalleled measurement accuracy and novel analysis techniques are critical steps toward detecting climate trends decades sooner than is otherwise possible. Earlier climate change detection and increased confidence in climate projections supported by CPF can result in significant economic, social, and defense benefits.  CPF will help to improve life on Earth through its innovative technology and high accuracy climate measurements.



Measuring sunlight reflected by Earth helps us learn about the Earth climate system. CPF’s data will be the first step in helping us make measurements at sufficiently high accuracy to be sensitive to Earth’s changing climate. These measurements are a crucial step toward better equipping policymakers, so they can make more informed decisions about how to effectively respond to climate change.



CPF’s high accuracy means that it can serve as an on-orbit reference for other satellite instruments. CPF will demonstrate the capability to transfer its unparalleled high accuracy to other Earth-viewing satellites using a novel inter-calibration technique. This improves accuracy and consistency among satellite measurements.



The surface of the Moon is a highly stable reference that researchers use to track satellite sensor performance throughout the sensor’s lifetime. This is done by measuring the amount of sunlight that reflects off the Moon. Having highly accurate measurements of the Moon from space that are tied to international standards, improves this key calibration standard for a large number of Earth-monitoring instruments.



A climate record is a series of data points that tell us about climate variability over time. Currently, we obtain these records using measurements from different instruments that overlap in time to provide a continuous long-term data record. Relying on overlapping measurements, however, means that gaps in the continuous record limit our understanding of climate variability. The high accuracy attained by CPF reduces the susceptibility to gaps in measurements.



A clearer understanding of how much and how fast climate is changing helps us respond more effectively to climate-related disasters such as rising sea levels, a concern that impacts the U.S. military and coastal communities. CPF advances our understanding to begin solving this mystery decades sooner than we can currently.