This is an excellent presentation on the future of lidar data acquisition and processing by Dr. Qassim Abdullah who works for Woolpert, Inc. He discusses all of the major topics including single photon counting and Geiger mode as well as full waveform and flash. Qassim also contrasts the benefits and limitations of each system. He also looks into the future to predict what the state of the art might be in five years.
This is an important reference for all topics related to airborne lidar data collection.