That’s the problem addressed by French special forces of the 13th Parachute Dragoon Regiment, known as the 13th RDP, an army regiment entirely dedicated to gathering human intelligence from any theater in peacetime, wartime, or during other crises.
Until recently, the 13th RDP paratroopers were using a ground-detecting system developed over 30 years ago that they found lacking. So, inspired by the reverse sensors that feature on some cars—they are ultrasonic and electromagnetic, with the distance to whatever is behind your vehicle calculated by the time it takes for the waves emitted by the sensors to bounce back to your vehicle—one of the soldiers with hundreds of tandem jumps under his belt had the idea of developing a similar system that would beep at increasingly shorter intervals during his jump the closer he got to the ground.
With some colleagues, he took the concept to France’s Defense Innovation Agency (AID), a specific arm of the French Ministry for the Armed Forces created to discover and develop disruptive technologies. The AID provided him with funding of about $51,000 to work with small French electronics design office Bordelaise Electronique to develop a better system.
The result is DAPCO (Dispositif d’Aide au Poser pour Chuteur Opérationnel), a device that looks like a small box (it’s just 4×4 inches in size) to help operational paratroopers land. DAPCO uses lidar (an acronym for Light Detection and Ranging) technology, which emits a pulsed laser. Given that the speed of light is a known quantity, the time it takes for the light to hit the ground and return to its source will indicate the exact distance from the source (in this case the DAPCO on the paratrooper’s chest) to the ground. This information is also provided by a backlit altimeter on their wrists but the sound signal is more immediately receivable.
Source : https://www.popsci.com/technology/french-special-forces-develop-parachute-tech/