Scientific aspects of the global environmental issues had been created largely due to the long-term time series data such as those from Mauna Loa Observatory and large-scale spatial maps such as those from the Total Ozone Mapper on Nimbus 7 Satellite.

Is monitoring the marine environmental changes more difficult than the atmospheric counterpart? There have been various monitoring techniques using ships, buoys, and satellites. However each method has its own limitation. First, it is difficult to reserve a research ship for a specific purpose for long enough to obtain a trend data. Second, the data from limited number of buoys cannot represent the sea, which is inherently more heterogeneous compared to the atmosphere. And third, the satellite cannot directly measure the biochemical substances and time series are frequently interrupted by the cloud coverage.

To supplement these constraints, we used the regularly operated passenger ferries as a monitoring platform, general term of which is the Voluntary Observing Ship (VOS) or the Ship of Opportunity (SOOP). It enables us to conduct monitoring continuously for extended period of time over a wide range. In addition, we have an option of attended observation or in situ experiments because it is a passenger ship.

Among the coastal or marginal seas mentioned in 1., the Seto Inland Sea of Japan has provided an appropriate situation to evaluate the anthropogenic factors including administrative policy making, which has been referred internationally as follows¹⁾. "There is some suggestive evidence. The best experiments Smetacek²⁾ can offer comes from the Seto Inland Sea of Japan. Red tides there increased from 40 a year in 1965 to more than 300 a year in 1973. In 1972 the authorities introduced controls designed to cut the nutrients entering the sea by half. The frequency of red tides peaked in 1975 and has been declining steadily". Therefore, the area including the Seto Inland Sea is one of the key areas to be monitored with respect to the evaluation of the large-scale man-made experiment.