Measurements of the Velocity Change of a Lightning Return Stroke With Height

A new system is developed to detect optical signals from return stroke channel segments at different heights.The system consists of an optical detector, electric amplifiers and A/D converters with 12 channels.10 channels are used for optical signals, and 2 channels are used for the electric field change and UHF radiation.A silicon-photodiode-array is used as an optical detector.An example in winter positive lightning shows that the two dimensional velocity of a return stroke decreases from 2x10 8 rn/s to 0.3x10 8 rn/s after the propagation of 180 m height.