[Coral-List] PAR sensor/logger (Andrew Trevor-Jones)

Richard Dunne RichardPDunne at aol.com
Fri Aug 24 06:01:19 EDT 2007

To what Andrew says I would add the following caveats.

I notice that Odssey do not give any detail of the calibration of these 
PAR sensors. You will need to ensure that they are calibrated at least 
once a year against a traceable standard. Also even the best PAR sensors 
are only accurate to +/- 5%. Secondly if you are making absolute 
measurements (as opposed to relative measurements) underwater you will 
need to do an immersion effect calibration for a sensor that has been 
calibrated in air. Because of the differences in refractive index 
between air and water a sensor calibrated in air will underread by about 
40% in water. Suppliers of the best underwater sensors (eg. LICOR) 
provide their customers with this immersion effect calibration. To do it 
yourself is very tricky.

References to the immersion effect are:
Tyler and Smith 1970 Measurements of spectral irradiance underwater. 
Gordon and Breach, New Yorl, 103p.
Roemer and Hoagland 1976 Immersion effect anc cosine collecting 
properties of LI-COR underwater sensors. (A study by the University of 
Nebraska for LICOR).

Also you will need to keep the sensor clean when underwater - build up 
of biofilms is a problem for any sensor left in place. Typically 
cleaning once a day is required. Without this, your readings will be 

Richard P Dunne

West Briscoe, Baldersdale, Barnard Castle, Co Durham, DL12 9UP. UK
Tel +44 1833 650059

atj777 at attglobal.net wrote:
> Ruby,
> This question was asked a year or so ago on the list and one great
> option was a logger from Data Flow Systems in New Zealand:
> http://www.odysseydatarecording.com/odyssey_productsview.php?key=6
> I purchased one and it works very well.  It is submersible to 
> 20 metres.  I have taken mine to 30 metres without a problem.
> The only drawback with the logger is that it floats.  This means
> you will need to build something to hold it down.  For mine, I used
> PVC piping and then attached a weight to the base.
> Here is a photograph of the logger at Steve's Bommie on the GBR
> showing the PVC holder and weight:
> http://www.petsforum.com/personal/trevor-jones/Logger_Steves07.jpg
> Andrew.
>> Dear colleagues
>> Can anyone please advise where i could purchase a portable seawater 
>> submersible PAR sensor/logger.
>> So far i have come across PAR sensors which are submersible in 
>> seawater with loggers that are not. The sensors are connected to the
>> loggers by underwater cables.
>> However i would like to place the sensor with the logger at sea to 
>> be retrieved on a weekly/monthly basis
>> Many thanks
>> Ruby
>> Ruby Moothien Pillay (Ph. D.)
>> Project Officer (Oceanography)
>> Mauritius Oceanography Institute
>> France Centre
>> Victoria Avenue
>> Quatre Bornes
>> Mauritius
>> Tel: (230) 427-4434
>> Mobile: (230) 723-8808
>> Fax:(230) 427-4433
>> Website: http://moi.gov.mu
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