Mean annual Secchi depth measurements in the period starting in 1969 provide a measure of water column transparency in the CalCOFI inshore and offshore areas, 1969 - 2004.

The Secchi depth provides a measure of water turbidity. Measurements are made as part of the California Fisheries Cooperative Investigations (CalCOFI). Secchi depth is measured on each station on each cruise. The mean annual is obtained by averaging stations over time and at stations defined as either inshore or offshore.

赛氏盘深度（Secchi depth）是衡量水体浊度的指标。该测量工作作为加州渔业合作调查（California Fisheries Cooperative Investigations, CalCOFI）项目的组成部分实施。每一次科考航次的所有观测站位均会开展赛氏盘深度测量。年平均赛氏盘深度通过对各站位随时间取平均，并针对被划分为近岸或离岸类别的站位分别取平均计算得到。