[Coral-List] Photoquadrat

Frederic Charpentier fcharp at rogers.com
Thu Jul 16 14:39:29 EDT 2009


Just a quick note, hoping that it may be useful. We have been doing photo
transects for a while and had, like you, to either switch cameras or use
more than one model. If you are going to a better model -- as mentioned
before -- the most immediate benefit will be higher resolution.

The only caveat is that the field of view may change from one lens to
another. Because of that, you may end up with photos that cover different
surfaces from one camera to the other and that could throw off your sampling
consistency in CPCE. If that is indeed an issue for you, there is a simple
method to correct the problem (other than having to perform complicated
calculations with focal length, etc...). With the old camera, take a picture
of a ruler resting at the bottom. Make sure to take the picture at the same
distance as you would when doing a transect. Using this photo as reference,
repeat the operation with the new camera and adjust the zoom and distance
from the bottom until the ruler occupies the same area as with the previous
camera. It's a quick and dirty method to insure some scale continuity
between your previous transects and the new ones. 

If you decide to use a different scale in future transects, but still need
to have continuity with the legacy transects, use the ruler trick to
calculate the scale factor from the old photos to the new ones and enter
that scale into CPCE to offset the bias.

I hope this helps.


-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov
[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of eduardo marocci
Sent: Sunday, July 12, 2009 10:54 AM
To: rk.manit at gmail.com; coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Photoquadrat



    Hello Ron,



    We work ourselves in the Abrolhos region, Brazil and also doing FQ and
in the last year we had to change our camara and obtained a satisfactory
result without any damage, so you do not have to worry. If you obtain an
equipment that makes possible more zoom, that only is going to improve the
quality of it photo, without damage for your work.


    Best Regards from Bahia



   Eduardo Marocci
Biólogo - Mestrando em Sistemas Aquáticos Tropicais - UESC Bahia 
emarocci at gmail.com

> Date: Wed, 1 Jul 2009 09:29:49 +0800
> From: rk.manit at gmail.com
> To: coral-list at coral.aoml.noaa.gov
> Subject: [Coral-List] Photoquadrat
> Project Seahorse Foundation for Marine Conservation
> 30 June 2009
> Methodological Question about Photoquadrats for “Coral List”
> The benthic survey component of our coral reef long-term monitoring
> has (again) presented us with some tricky methodological issues, and were
> hoping to consult with this community for advice on how to resolve them.
> are a small marine conservation NGO conducting research on marine
> areas in the central Philippines, with a small team of marine biologists.
> Some background: we piloted a photoquadrat (“PQ”) method in 2007 to
> our older line-intercept method. At each survey site, this PQ method uses
> haphazardly laid 25 m transects, with photos taken every 1 m along the
> transect. We plan to conduct PQ once a year at these sites, all of which
> shallow (~3-4 m depth) with some turbidity.
> Basically, our current digital camera (Sony DSC-P10 Cybershot, 5.0
> megapixels, purchased in 2003) has been malfunctioning and we need to
> replace it. We are very concerned that if we simply bought a new camera
> (with new wide-angle lens etc.) that the photodata we have already
> using this old camera would not be comparable with the newer photodata
> whatever new camera equipment we decide to purchase. Our current wide
> lens is the “MPK-P9 wide version 16 mm/F5.6.” We use CPCE to process the
> images.
> Are photoquadrat methods using this image-processing software sensitive to
> the exact specifications of particular cameras? Or is the software and
> analysis of this kind of data robust to all kinds of equipment? What kind
> considerations do we need to keep in mind when making this decision? Would
> it be ok if just replace our camera with a new set of camera that are of
> different specs on the camera that we are using?
> We would appreciate any advice this community can offer. Thanks!
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> Coral-List at coral.aoml.noaa.gov
> http://coral.aoml.noaa.gov/mailman/listinfo/coral-list

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