[Coral-List] PAR sensor/logger (Andrew Trevor-Jones)
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:
> 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:
> 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:
>> 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 Moothien Pillay (Ph. D.)
>> Project Officer (Oceanography)
>> Mauritius Oceanography Institute
>> France Centre
>> Victoria Avenue
>> Quatre Bornes
>> Tel: (230) 427-4434
>> Mobile: (230) 723-8808
>> Fax:(230) 427-4433
>> Website: http://moi.gov.mu
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