COOL Classroom 2.1

Discover How to Use Secchi Depths

Sechi disks are easy to use and inexpensive to purchase. However, there may be variation in how different people read the depth on a Secchi disk.

Therefore, scientists have also developed censors that could quantify the the amount of light at a certain water depth (Light Penetration/Compensation Depth). As long as the censors are calibrated correctly, any person would get the same reading from the censors.

The problem is that the censors are expensive, which creates a dilemma for scientists. Do they use the easy to use and inexpensive piece of equipment that has a greater possibility of user error or do they use the more expensive piece of equipment that has more accuracy? In fact, scientists came up with a third alternative. They looked at data collected at the same place and time from Secchi disks and from censors and then compared their results. It turns out that the Secchi disk data is almost as accurate as the censor data, but not quite. However, if scientists multiple the Secchi Depth data by 0.96 then they get the values that the censors would have provided to them.

Therefore, scientists use Secchi disks in the field to collect Secchi Depth data and then multiple it by this conversion factor (0.96). They use the new values in their maps and models of where seagrass grow.