NASA’s CASALS lidar maps ground in 3D strips, tested by plane

From orbit, today’s laser instruments measure Earth’s forests and terrain one narrow line at a time. Between those lines lie enormous gaps, including millions of acres that scientists never directly measure. On a flight over the Great Cypress Swamp in Delaware on November 12, 2024, the instrument’s data showed tree canopy tops, the ground and the low vegetation in separate colors, all from a single continuous image.

The trick is in the light. Conventional lidars steer their laser with moving mirrors. CASALS, developed with support from NASA’s Earth Science Technology Office, uses a fast-pulsing “seed” laser centered at 1040 nanometers that cycles through 256 wavelengths. It sends this light through a transmission grating, a component with a microscopic pattern of ridges. Because light bends at slightly different angles depending on its wavelength, the grating sends each of the 256 pulses to a different position across the flight path. The result is a swath of ground rather than a single track, and no moving parts are needed to produce it.

That design also matters for reliability. Motorized mirrors are heavy and prone to failure, and removing them drastically reduces the instrument’s size, weight and power requirements, which the team considers important for the harsh environment of space. The detector array adds a second advantage: it operates at 80% quantum efficiency, meaning it converts almost all of the returning light into an electrical signal. The team says this lets CASALS pick up much weaker return signals, which helps it measure darker surfaces or ground under denser vegetation.

What this changes, and for whom, depends on the next steps. Scientists who study forests, terrain and changing ecosystems would gain a far more complete map than today’s isolated profiles provide. For now, the benefit is limited to aircraft flights: the team plans to fly CASALS again in the ASCENT campaign, scheduled for summer 2027, and has not announced when a spaceborne version could fly. Before that, it intends to widen the swath and add onboard data processing software.

The team’s confidence rests on a first campaign that, in the words of Yorks, “worked really well from the first time we flew it.” At roughly five kilometers’ altitude, CASALS already distinguishes individual tree branches and subtle changes in ground elevation, thanks to its 22-centimeter horizontal resolution. Turning that performance into a satellite still means a redesign of the swath and the processing, and NASA presents the outcome as conditional on success.