[Coral-List] photoshop trick for sat imagery

Todd Barber reefball at reefball.com
Tue May 20 09:04:35 EDT 2008

Yep....it's a great technique......you can then take the pictures into 
Google Earth and "georeference" them as overlays....you can use the Google 
Earth transparency settings to manipulate views of additional layers.  You 
can even then draw them as paths or mark then with GPS coordinates and 
transfer directly to field GPSs for using during monitoring.

We have found the technique very useful when trying to do comprehensive reef 
survey work over large areas especially when reefs are not well documented. 
Very helpful for would be planners to help avoid these areas when 
development is being considered.

One IMPORTANT thing to note from our experiance is that identified points 
should be ground truthed....there is a tendency for false positives due to 
the occasional cloud on a sunny day, wave shadow...or often a patch of rocky 
outcropping that does not have corals (like newly exposed hard bottom after 
storms).  With a little skill you can usually differentiate between sea 
grasses and reefs but it depends on resolution and color depth of original 

Note to build an even better system....in Google also overlay navigational 
charts, bathemetric lines, and any other available information that can be 
accurately georeferenced.  You can turn them on or off at will or make them 
semi-transparent and really start to develop an accurate understanding of 
what your photos are indicating.

For Google...you can also link any specific point to a web page.  That means 
when you ground truth...take an underwater photo then capture the GPS point 
and later upload the image to the web.  Within Google just link that point 
to that photo and as you are looking at overhead images you can then "zoom 
in" to underwater shots of same location.  Multiple links over time are 
supported so nice for long term monitoring work.

Hope this helps.


Todd R. Barber
Chairman, Reef Ball Foundation

Skype name: toddbarber
Cell Phone 941-720-7549

3305 Edwards Court
Greenville, NC 27858

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----- Original Message ----- 
From: "Don Baker" <reefpeace at yahoo.com>
To: <atolldino at yahoo.com>
Cc: <coral-list at coral.aoml.noaa.gov>
Sent: Monday, May 19, 2008 5:38 PM
Subject: Re: [Coral-List] photoshop trick for sat imagery

Hi Dean,

Bingo!   Someone finally admits that one can 'play' with touched up 
satellite photos of coral reefs.  I have been doing it for awhile now.  High 
density pics work best as the graphic program can 'bring out' underwater 
features that sometimes our human eyes can't recognize and overlook.

Don Baker

Dean Jacobson <atolldino at yahoo.com> wrote: Hi listers:

Today I "discovered" a useful way to filter satellite images using Photoshop 
to reveals relatively deep reefs (below 15 meters).  (I am fortunate to have 
access to 0.6 m Majuro atoll data for ArcMap). I am using Photoshop 6.

Under "images", choose selective color, choose blue, then minimize the black 
slider.  Then choose black, and maximize black slider.  Another iteration 
may be needed.  Then, increase contrast and brightness.  To avoid blowing 
out the shallows and land, first save an extra image layer, make your 
adjustments, and then selectively erase the upper adjustment layer so the 
original pixels show through.

The results were pretty remarkable; it was like having "X-ray vision"... 
well-defined deep reefs magically appeared out of the monotonous dark blue 
lagoon water.  This will work only if the stat image was taken an a calm 
day; a wave chop seems to obscure the deep features.

I discovered this just in time for my coral monitoring season!
I can send some example jpgs upon request.

Dean Jacobson, PhD
College of the Marshall Islands

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Alternate Email: donbjr95 at hotmail.com

"Dedication and motivated direction in achieving specific goals related to 
the care and protection of living things is not necessarily a guaranteed 
formula for success.  Success is, more often than not, a direct result of a 
person's passion in addition to the above formula." [Don Baker, Marine 
Conservationist/Activist, 1998]

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