Hi,
Distances of importance would fall within the 1-2 foot range and the sensor would need to be rugged as it would be used outdoors in summer heat on a daily basis with several hours of operation daily.
How many degrees of detection vertically and what size, shape and material are the obstacles?
I didn't see any direct questions in your post, so what exactly do you need help with, the sensor type or what?
Diesel robot... Makes me think, when something ain't green at all, would it be proper to call it red then?