Cape Farewell Secchi disc and colour

Adding colours You can make any colour from the three primary colours: Red, green and blue

Taking away colours You can change colours by taking some of the colour out....

Try looking at this through a, red filter, a green filter and a blue filter. The red filter takes out green and blue light The green filter takes out red and blue light The blue filter takes out red and green light.

This is useful for finding out how much plankton is in a bit of the ocean. Using a Secchi disc.

Secchi disc - raw Normally, the Secchi disc looks like this from above. Simple black and white.

Secchi disc - filtered Water filters out red light. This leaves more blue and green. Which gives the white bit of the disc a slight cyan tinge. This is exaggerated

Secchi disc - in water The disc is lowered into the water until it is no longer visible. The depth is recorded. This gives an indication of the murkiness of the water. This is exaggerated

Secchi disc - in water Try looking at the disc through a red filter. The white bits go grey. The Secchi depth will be less through a red filter because the water takes out more red light than green and blue This is exaggerated

Secchi disc - in plankton water Plankton absorbs blue light (and some red). So, if there is plankton in the water, the disc looks green. Try looking through a blue filter. This is exaggerated

Secchi disc - more plankton If there is more plankton, more blue light is removed. The disc goes greener. Try looking through a blue filter now. This is exaggerated

Secchi disc - more plankton More plankton will make the disc go out of view at a smaller depth through a blue filter. This is exaggerated