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.
Dutchi meter with three lines.
How to read?
We place the visibilitymeter at a fixed measurepoint and attach a simple reel or spool on which distance markers are placed at each meter or half meter. We swim backwards and unreel the line.
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 glimps of the disc.
You can DOWNLOAD paper versions of a full scale Secchidisk and the easier to carry combi-meter (Dutchi and Secchi), which you can laminate and take it with you underwater.
Depth and Temperature
Our divecomputers or divetimers register depth and temperature, but beware that the temperature sampling time of a divecomputer, usually is about every 20 seconds. This means you can spend a minute or more waiting for a proper temperature measurement. Also the sensor is mostly right on your arm, preventing water to pass by the sensor quickly.
There is a faster and easier way!
I recommend using an ordinary garden alcohol (no mercury) thermometer. You only have to check the deviation with a calibrated thermometer.
The alcohol thermometer:
– Withstands depths upto 30 meters (100 ft)
– Fast readout.
– Easy to put away in your pocket or on your harness.
Pictures and their importance.
Aside from taking pictures of a fixed point / station, which are key in Project Baseline to show changes through time, just take random pictures of underwater features, plants, animals and insignificant looking areas on the bottom.
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.
You will discover things, you hadn’t noticed during diving, because you simply can’t see and memorize everything. It’s good for braintraining though.
Check out the image below.
Spot the freshwater snale Planorbis planorbis and the fish leach Piscicola geometra