* Video camera with pattern recognition software. In most cases this should work fairly well with white golf balls (white against green = easy to detect. Especially if the dimples are employed in the pattern search.
* Experiment with different wavelengths of light/electromagnetic energy to see if there is some wavelength that highlights golf balls over anything they might be resting on. Then use that wavelength in a scanner (could be a row of sensors like in a photo scanner that would sweep the ground as the golf ball collection vehicle moves forward).
* Perhaps the golf ball has enough of a difference in relative permittivity to make detection possible with some sort of electrostatic field.
* Inertia: feelers that can sense inertia of things they "bump" into.
* Sonic signature -- perhaps reflected sonic waves will have a unique "signature" when from a golf ball. perhaps the dimples will contribute to this, especially if the wavelength is close to the diameter of the dimples, or the depth of the dimples, or the focal length of the dimples, such that some sort of constructive/destructive interference pattern occurs.
* sieve or rake or a combination tuned to the diameter of a golf ball. Perhaps combined with suction that has just enough sucking power to lift a golf ball, but nothing heavier, then the influx product would pass over a sieve that would allow everything to fall through but golf balls which would roll into a bin.
* Monkeys trained to pick-up golf balls and deposit them into a chute whereupon the collection machine would issue a treat.
* Market a line of golf balls with an iron core -- the "social engineering" feat, here, would be to make the new balls so popular that they supplant all other forms of golf ball, and thus making it easy for them to be collected with a powerful magnet.
