Estimation of source-detector separation in an optical measurement system

A method comprising:

• directing, by an optical measurement system, a light source to emit a first light pulse toward a target, the first light pulse having a first wavelength;
• directing, by the optical measurement system, the light source to emit a second light pulse toward the target, the second light pulse having a second wavelength that is different from the first wavelength;
• determining, by the optical measurement system, a plurality of temporal distributions of photons included in the first light pulse and the second light pulse and detected by a detector after the photons are scattered by the target;
• and
• determining, by the optical measurement system based on the plurality of temporal distributions and a source-detector distance estimation model, a distance between the light source and the detector.