Under international agreements, a world-wide network of Port Meteorological Officers (PMO's) are involved in keeping the fleet of international voluntary observing ships (VOS) in tact. The duties of the PMO's consist of:

• recruiting new volunteers
• inspection of ships' meteorological equipment
• instruction to observers

Stationed in De Bilt (The Netherlands), two PMO's look after the ships that visit the Dutch ports, among which one of the world's largest ports: Rotterdam.