The LISST-ST is a submersible field instrument developed for in-situ observation of the size-dependent settling velocity distribution of suspended particles. It incorporates a mechanized settling column and in a settling experiment, a water sample is drawn and trapped. The evolution of the volume concentration near the base of the settling column during the settling experiment is interpreted to estimate settling velocities. Settling velocities are estimated for 8 log-spaced size classes covering the range 1.25-250 microns (Type B), or 2.5-500 microns (Type C). The LISST-ST is designed to carry out multiple settling experiments while submerged. A motorized mechanism operates the doors that control exchange of water between the settling column and the ambient environment. This permits repeated settling experiments. A separate built-in motorized stirrer is used to agitate and flush out settled particles after each settling experiment. In addition to particle size distribution histories with each settling experiment, water pressure and temperature are also recorded. The LISST-ST is a fully autonomous, battery operated, self-contained unit. It is engineered for low power consumption and built to withstand the rigors of field deployment. Easy to program features permit flexibility in duration of experiments, and in operating modes.