Project Baseline Haarlemmermeer does horizontal visibility readings with the Dutchi and a small scale Secchimeter. For a vertical reading we use the full scale 20 cm Secchidisk.
Dutchi was especially designed by Ivar Klerks for waters with poor visibility.
Dutchimeter gives more realistic values as to the divers perception of visibility up to 8-10 meters.
Secchi is ideal for scientific purposes and for visibilities of more than 10 meters.
Here you can clearly see the difference between Dutchi on the left where the diver is still visible and Secchi on the right where only the divers light are visible.
That is why we use both and devised a combi-meter as seen in the picture below.
|Full scale Secchi (top) and Combimeter)|
How to read?
You can see a video of such a measurement.
Reading of the Dutchi:
Shine with a 18w HID or equivalent lightsource on the baselinemeter. Until the two thin white lines disappear and the thicker white line is still visible = visibility.
|Use of the Dutchi. (Designed by I.Klerks.)|
Reading of Secchi:
Normally with daylight, but you can also use your divelamp.
Roll out your line until the can barely see the white surfaces. Start reeling in, till you can just see the first contrast of the disc.
try out this Secchi simulator to learn how to work with it, but with sunlight it looks different where the white patches light up more.
You can DOWNLOAD paper versions of a full scale Secchidisk and the easier to carry combi-meter which you can laminate and take it with you underwater.
Our divecomputers or divetimers register the temperature and depth.Pictures taken from a fixed point are key in Project Baseline to show changes through time.
That makes underwatercamera's an important tool, regardless the quality of the camera.
Better one fuzzy picture than no picture at all, unless you have a keen eye and a superb memory to log your dive in a very detailed way.
Things you haven't noticed during a dive, can be found in photo and film material, even months or years later. More detailed photo's can always be used for analyzing.