Which technique involves transmitting a signal that reflects off retro-reflectors on satellites?

The technique that involves transmitting a signal that reflects off retro-reflectors on satellites is satellite laser ranging. This method utilizes laser beams directed at satellites equipped with retro-reflectors, such as those deployed by the Apollo missions on the Moon. When the laser beam hits the retro-reflector, it is reflected back to the originating point, allowing for precise measurement of the distance between the ground station and the satellite.

This distance measurement is crucial for various applications, including geodesy, monitoring of tectonic plate movements, and satellite orbit determination. The precision of laser ranging contributes to our understanding of Earth’s shape, gravity field, and even the dynamics of Earth's atmosphere.

In contrast, other techniques listed do not primarily focus on the use of retro-reflectors or laser transmission in the same way. For example, lunar laser ranging specifically refers to measurements involving retro-reflectors on the Moon, which could cause confusion. Doppler orbitography focuses on measurements based on frequency changes in received signals caused by the relative motion of satellites, while baseline interferometry typically involves the combination of signals from different locations to measure distances or angles directly, rather than depending solely on reflections from a retro-reflector.