The PDM-1M mine is one of a series of shallow-water mines employed by the former Soviet ground forces against a river crossing or amphibious threat. All of these munitions have blast effects and are initiated by contact with the watercraft.
The PDM-1M rests untethed on the bottom of the water feature and, with the aid of its weighted ballast plate, remains stationary in currents up to 1.5 m/s.
When laid in groups, PDM-1M mines must maintain a minimum spatial separation of 6 meters to counter sympathetic detonation tendencies.
This mine can be deployed using a variety of vehicles-helicopters, amphibious vehicles, rafts, and bridges- as well as manually.
When vehicles are used, special chutes and stowage equipment are needed.
The primary differences between the PDM-1 and the PDM-1m are that the PDM-1M has no booster and the tilt rod is telescopic.

Text copied from warfare.ru
Photos below (inert version) provided by Jarda.

PDM - 2 :

I have no information on this type yet.