Secchi-disk Observations

BalticSeaNow.info -Secchi-disk. Photo: Kata Kiviluoto

What's a Secchi-disk?

Secchi-disk is a round disc, which is used in Marine Research to measure visibility depth. The disk was developed by the Pope’s scientific advisor Pietro Angelo Secchi in 1865. The idea for the disk came from a white ceramic plate that was dropped in the sea and glowed from the depths. In order to get coherent results the measurements are usually made with a 30 cm disk.

This is how you make an observation

Secchi-observing Photo: Kata Kiviluoto

In order to get comparable results, measure the visibility depth always in the same place and at the same time.

1. The easiest way to start is to choose an achievable place, which you can locate easily time after time.
   
2. Lower the Secchi-disk into the water until it disappears from sight. Note the depth.
3. Lower the disk again into the water so that it disappears from sight. Raise the disk until it reappears again. Note the depth.
4. Calculate the average of these two depths. The outcome of this calculation is the visibility depth.
5. Write down the visibility depth and the time and place of the observation. The place of the observation can be logged either as a GPS reading or as a written description. You can also list other observations together with your Secchi-depths, such as water surface and air temperature and the general description of the prevailing weather.

Submit your observations to balticseanow.info@turkuamk.fi or fill in the observation form .