In this paper, the Pockels sensing system consists of a pulse laser and a CCD camera for measuring the instantaneous two-dimensional potential distribution on a 25.4 mm square area with a 50 (mu)m sampling pitch. The temporal resolution is 3.2 ns which is determined by the pulse width of the laser emission. The transient change in the potential distribution of a positive surface streamer propagating in atmospheric air is measured with this system. The electric field and the charge distributions are also calculated from the measured potential profile. The propagating direction component of the electric field near the tip of the propagating streamer reaches 3 kV/mm. When the streamer stops, the potential distribution along a streamer forms an almost linear profile with the distance from the electrode, and its gradient is about 0.5 kV/mm.
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