NASA’s CASALS Laser Instrument Could Create 3D Maps of Earth’s Forests From Space

Today’s space-based laser instruments measure Earth’s forests and topography one narrow line at a time from orbit. Between those lines are vast gaps containing millions of acres of land that scientists have never directly measured. NASA’s CASALS instrument combines machine learning with ultra-compact lidar technology to adaptively “sweep” large areas of Earth’s surface. The system could enable space-based sensors to create continuous, true three-dimensional (3D) terrain maps.

How NASA’s CASALS lidar technology works

A team of researchers at NASA’s Goddard Space Flight Center (GSFC) has developed CASALS to eliminate blind spots between lines of lidar data collected across Earth’s surface. The Simultaneous Artificial Intelligence Spectrometer Lidar System, or CASALS, was built with support from NASA’s Earth Science and Technology Office (ESTO) and is designed to map surface features in unprecedented detail.

Rather than mechanically steering lasers with moving mirrors, CASALS uses different wavelengths of light to control where laser pulses travel. This approach creates a continuous 3D swath of Earth’s surface while reducing the need for heavy, failure-prone mechanical components.

John Yorks, a GSFC physics research scientist and CASALS principal investigator, said the instrument uses a new transmitter and optical grating system to steer laser pulses without motorized mirrors.

CASALS relies on a fast-pulsed, tunable “seed” laser centered at 1040 nanometers. The laser rapidly cycles through 256 unique wavelengths as it passes through an optical component with a microscopic ridge pattern known as a transmission grating.

Diffraction then guides the pulses. Because light bends at slightly different angles depending on its precise wavelength, the grating directs each of the 256 pulses to a distinct location along the flight path.

Continuous 3D mapping with fewer moving parts

This non-mechanical design allows CASALS to scan a continuous 3D band of ground. It could eliminate the large unmapped gaps left between the isolated tracks produced by traditional spaceborne lidar systems.

Removing moving parts also reduces the instrument’s size, weight and power requirements, known as SWaP. The simpler design could improve reliability in the harsh environment of space.

A highly sensitive detector for forests and dark surfaces

Another important CASALS innovation is its detector array, which has an unusually high quantum efficiency (QE). Quantum efficiency measures how effectively a detector converts incoming photons into an electrical signal.

CASALS operates at 80% QE, meaning that very little of the light returning to the sensor is wasted. With this level of sensitivity, the instrument can detect weaker return signals and collect useful measurements from dark surfaces and dense vegetation.

NASA tests CASALS aboard an aircraft

The technology has already moved beyond laboratory testing. In November 2024, an airborne CASALS prototype flew aboard NASA’s B200 King Air aircraft. During its first campaign, the instrument produced scientific-quality datasets that exceeded the team’s expectations.

“I’m very impressed with Guang Yang, Jeffrey Chen, and all of our engineers, and with the performance of CASALS. It performed very well and was very impressive from the first time we flew it,” said Yorks.

Flying at an altitude of about 5 kilometers, CASALS can identify individual tree branches and subtle variations in ground elevation with a horizontal resolution of 22 centimeters.

“We can see changes in vegetation structure and surface topography in great detail,” Yorks said.

Next steps toward space-based lidar

The team plans to fly CASALS again during NASA’s Airborne Surface, Cryosphere, Ecosystem, and Coastal Geomorphology (ASCENT) campaign, scheduled for summer 2027.

However, additional development is needed before the technology is ready for space. Researchers plan to improve CASALS, expand its equipment and add onboard data-processing software before building a prototype for space use.

The transition from a successful aircraft instrument to a fully operational space mission is challenging, but the CASALS team is continuing to refine the technology.

“The team has done a great job of coming together and meeting the mission and schedule. We are receiving funding to optimize and improve performance. We are also looking at ways to incorporate and mature the technology used in our airborne instruments to prepare for future spaceborne versions,” Yorks said.

What CASALS could reveal about Earth

If successful, CASALS will be the first spaceborne lidar system capable of mapping Earth’s forests and landscapes as continuous three-dimensional bands rather than isolated profiles. The technology could give scientists a more complete view of how Earth’s vegetation, terrain and landscapes are changing.

See the project entry for more information: NASA TechPort.

Project leader: John Yorks, NASA Goddard Space Flight Center

Sponsoring organizations: NASA’s Decadal Survey Incubation (DSI) program; NASA’s Instrument Incubation Program (IIP); NASA’s Goddard Space Flight Center; the University of California, Santa Barbara; and Virginia Tech and State University.