The study was intended to eliminate the dorminant source of error in the remote measurement of smoke-stack plumes using lidar, and to improve the data presentation of the lidar transmittance measurement. The use of a special grid-controlled photomultiplier tube and off-gating system has resulted in a large reduction of photomultiplier tube afterpulsing which has been the principal problem limiting the accuracy of plume transmittance measurements. A range-correcting time-squared amplifier has also been developed which permits much faster and more convenient data reduction than formerly possible. The above two developments have been adapted to an existing van-mounted EPA lidar system; and the improved overall system accuracy has been evaluated using both opaque and semi-transparent targets of known transmittance. (Author)