Hello Again,
Found a great hi-res photo from a new satellite and it is quite spectacular. My wife and I were looking at it and had the same question. Why are certain parts of the ocean bright blue? Shallow water perhaps? We would really like to know. The photo can be seen here: http://blogs.discovermagazine.com/badastronomy/2011/11/22/new-satellite-gets-insanely-hi-res-view-of-earth/
Clear, shallow water over white sand.
From the article:
The image was taken with the Visible Infrared Imager Radiometer Suite, or VIIRS, which, as its names states, takes visible and IR images of the Earth. It can be used to observe hurricanes, fires, ocean surface temperatures, aerosols in the air, volcanoes, and more.
The colors you are seeing are not true colors; they are corrected so that IR can be seen in the visible color spectrum. The pale areas, like coastal regions, are areas of warmer surface temperature.
Stranger
While VIIRS can take both visible and infrared data, it doesn’t actually say it’s a false-color infrared photo.
The light colored areas are the Bahama Banks, a very shallow section of seafloor that does look like that in real life.
There’s nothing in that description that says that infrared was in any way combined with visible light to create the image.
You can see the same effect on Google Maps, which doesn’t use infrared imagery at all. The light blue areas are shallow water.
Surely the different shades of blue in the ocean on Google maps are not directly taken from satellite images though. The shades are supposed to represent the topography of the sea floor, but this is not something you can just see directly from space. The Google oceanic maps clearly are falsely colored. (Which is not to say the pictures linked in the OP are.)
You can see the same effect over shallow water with light-colored bottom (not necessarily sand, although that’s a good example) from the air. If the ocean photographs that way from aircraft (it does: example) I have no idea why pictures from space wouldn’t show the same thing as long as they had sufficient resolution.
Did you look at my link? The areas around the Bahamas (and other places) are clearly demarcated from the rest of the ocean. You can also see the effect from aerial photos of the Bahamas.
It’s kinda what the Bahamas are famous for. The Bahamas sit on top of a shelf called the Bahama Banks. The “normal” blue water is a mile or more deep and the green water is anywhere from a few feet to 100 feet deep. In the last image in the OP, you can see the largest green blob is separated from another by a strip of dark blue. That is called the Tongue of the Ocean, where the shelf drops off abruptly and the water depth goes from 100 feet to 6000 feet.
How bout the Great Lakes. Are they always nice and purty pale blue like that?
off topic: Why is the cloud cover near Florida almost perfectly fitted to the land?
It seems odd to me that it starts and stops along the coastline. What prevents it from forming that way over the water nearby?
Two possibilities. The first is a simple coincidence, it just happens that the photo was taken when the cloud band matched the coastline. Second, land masses have a huge effect on the weather including cloud formation. Land is dryer than the sea (obviously), it transfers heat more readily and so is hotter in summer and cooler in winter than the surrounding ocean, it also has physical features such as valleys, rivers, and mountains that can affect the formation of clouds. It is not unusual to see clouds following mountain ranges, coast lines, rivers etc.
To the OP, that is what sea water looks like around reefs and sandy islands. It is possible the colour is false, but if it is it is an accurate representation.
It’s quite common - often when you’re at the beach you can see that there is lots of cloud over the land but it’s clear out to sea, or vice versa, depending on the relative temperatures of the land and sea, sea breezes and a number of other factors. In this case, the land seems to be warmer than the sea, so the air rises over the land which causes water vapour to condense out of the moist air and form cumulus clouds.
As for the colours on Google Earth/Maps, yes, the shading of the oceans as a whole is totally artifical to show the topography, but in certain areas close to the shore, real imagery is laid on top. You can see that the Bahamas is one of these areas: Google Maps
Real-colour imagery has been overlaid on the shallower areas around the islands (and the Florida Keys, and some other islands nearby).
Yes I did, and my remark was based upon looking at it (and zooming out a bit). I wonder how much you looked at, or thought about, your own link! It is quite clear, as I said, that the ocean basins are artificially shaded to show sea floor topography. What is shown on Google maps is not how the oceans actually look from space.
I do not think it is possible to say, by eyeballing the Google map, whether the light area shown there around the Bahamas is the product of the same artificial shading system used for the rest of the ocean (though it seems consistent with the scheme being used), or whether it is taken direct from the satellite photos, but it seems odd that they would use false coloring for most ocean areas and switch to real satellite images just for the shallow stuff.
Because if they used the real color from the real images to show the deep water, you wouldnt see any topography because the real images don’t show any. Anything deeper than 200? feet give or take would look exactly the same. Once you switch to “fake” photos to show the topography of the ocean bottom you are free to pick a color that makes the most sense/looks the best rather than its “true” color.
Having flown over that shallow stuff a few times, it really does look like that.
Yes, it is perfectly possible. You can clearly see the demarcation line: here it is. (Zoom out for the full effect.)
The non-imagery areas don’t really use different colours at all - just relief shading of the same lilacy-blue colour across the whole globe. The bright turquoise colours only appear on the real photo imagery.
I’m not sure why the Bahamas area gets such a lot of real imagery over the sea. Most other coastal areas have only a very small amount of photo imagery beyond the coast. Example.
I know. That is what I said in paragraph before the one you quote from. That is how I know it has to be false color.
I do not disbelieve that either. My point is that, as they are clearly using false color for the deep oceans and normal continental shelf, and using lighter blues to represent shallower waters, it is impossible to tell, just by eyeballing the Google maps image, whether the light-blue color we see near the Bahamas is is from an actual satellite image or is false color, part of the general scheme they are using to false color the oceans, that happens, in this case, to be similar to the actual color.
Terminus Est’s original claim was that the Google maps image proves that the OP’s images are not false colored. That is not the case, because Google maps itself false-colors oceans.
As I’ve already said and Colophon has also pointed out, the demarcation between real photo-imagery and false color in Google Maps is quite clear.
I have seen similar from aircraft, its not false colouring.
IMO, yes! I would call Lake Michigan an “ocean blue” on a clear day. It changes depending on the weather. I’m right by the beach and have pics in all sorts of weather, and Lake Michigan can be anywhere from sapphire blue to the same shade of gray as a stormy winter sky. Sometimes it’s hard to tell where the water stops and the clouds start, the horizon is barely discernible. My favorite time is when the nearest waterline is frozen over and you can’t tell where the beach ends and the water starts.