Scientists have long relied on space-based laser instruments to measure Earth’s forests and terrain. These tools typically scan the planet one narrow line at a time. Between those lines lie enormous gaps, leaving millions of acres of land unmapped. A new instrument from NASA aims to close these voids by blending machine learning with an ultra-compact lidar system.
The Concurrent Artificially-intelligent Spectrometry Lidar System, known as CASALS, was developed by researchers at NASA’s Goddard Space Flight Center (GSFC). Supported by the NASA Earth Science Technology Office, the device generates a continuous, three-dimensional swath of the ground below. Unlike legacy systems that use mechanical mirrors to steer lasers, CASALS steers light using wavelength itself.
Non-Mechanical Laser Steering
John Yorks, a physical research scientist at GSFC and the principal investigator for CASALS, described the instrument as featuring a novel transmitter and optical grating system. This design manipulates laser pulses without the heavy, failure-prone motorized mirrors found in older sensors.
Instead of moving parts, CASALS uses a fast-pulsing, tunable seed laser centered at 1040 nanometers. The laser rapidly cycles through 256 unique wavelengths as it pulses through a transmission grating, an optical component with a microscopic pattern of ridges. Physics takes over from there. Because light bends at slightly different angles depending on its exact wavelength, the grating naturally directs each of the 256 pulses into a distinct position across the flight path.
This non-mechanical approach paints a continuous 3D image of the ground. It eliminates the large unmapped gaps left between the isolated tracks of legacy spaceborne lidars. Stripping away moving parts also drastically reduces the instrument’s size, weight, and power requirements. This makes the technology more reliable for the harsh environment of space.
High Sensitivity and Airborne Success
Another key innovation within CASALS is its detector array. This component features a uniquely high Quantum Efficiency, a variable that describes how effectively a detector converts incoming light into an electrical signal. CASALS operates at 80% Quantum Efficiency. This high efficiency means the instrument wastes almost none of the light that makes it back to the sensor.
With such high sensitivity, CASALS can detect much weaker return signals. This allows it to collect useful measurements from darker surfaces or through denser vegetation. The technology has already moved beyond the laboratory. In November 2024, an airborne prototype flew aboard NASA’s B200 King Air aircraft.
The instrument produced science-quality datasets on its first campaign, exceeding the team’s expectations. Yorks noted the impressive performance of the prototype during its initial flight.
I’m very impressed with Guang Yang, Jeffrey Chen, and all our engineers, and how well CASALS performed. This worked really well from the first time we flew it, which is pretty impressive.
Flying at an altitude of roughly five kilometers, the airborne CASALS prototype could distinguish individual tree branches and subtle changes in ground elevation. This capability is thanks to its 22-centimeter horizontal resolution. The team plans to fly CASALS again as part of the Airborne Surface, Cryosphere, Ecosystem, and Nearshore Topography campaign, scheduled for summer 2027.
Path to Space Mission
While the airborne tests were successful, the team must still prepare the technology for space. They plan to make several improvements to CASALS before creating a space-ready prototype. Specific upgrades include widening the instrument’s swath and adding onboard data processing software.
Transitioning from a successful airborne prototype to a fully realized space mission is a challenge, but the CASALS team remains focused. Yorks highlighted the team’s dedication to keeping the project on schedule and optimizing performance.
The team is being funded to improve the performance of the current instrument while simultaneously looking at ways to mature the technologies for a spaceborne version. If successful, CASALS could become the first spaceborne lidar capable of mapping Earth’s forests and terrain as continuous three-dimensional swaths. This would give scientists a dramatically more complete picture of our changing planet.
Source: NASA
