Lidar with streak-tube imaging,including hazard detection in marine applications; related optics

1. Field of the invention In some aspects of the invention, a LIDAR subsystem or other means at an elevated position emit thin fan-beam light pulses at a shallow angle, and detect reflected portions of the pulses at a like angle; a streak-tube subsystem or other means image successive reflected portions to detect objects, for example near a water craft if the elevated position is on such a craft (e.g., a mast or high bridge). In some aspects, the imaging means perform the imaging in a way that tightly localizes reflection from a water surface near the objects, to facilitate detecting the objects despite proximity to the surface. Some preferred embodiments apply a correction for energy reduction, or depth errors, near lateral ends of the fan beam; a lenslet array is preferred for applying the correction. Preferably the shallow angle is in a range of approximately one to fifteen degrees, more preferably approximately two to ten degrees, ideally roughly five degrees.