txspeck wrote:Good question. The only way I know is by trial and error. When fishing, I use a stake out pole to push and feel the bottom, I know this is not the best method but it works. From my past experience, most flats tend to be soft bottom mud and the back of marshes.
Actually the "best" way to "feel" the bottom is just like you describe by using a push pole or something that will let you "feel" the bottom easily without making noise.
Details on how to make out what is in the water in the images in Google is somewhat easy.
Most of the bottom anywhere will be mud and sand of some sort. The shell deposits are scattered depending on the water conditions for the area the shell is in. Not sure why or where shell beds are in the locations they are in but I assume they are near a spot where water can wash parasites into them so they can feed and survive. The fish come and peck at these shells to get parasites and bait attracted to them as well.
If you look at the images in Google Earth (GE) using the history function you will see many of the photos are taken in the winter months as the weather is usually more clear this time of year to get better images.
For example, look at the 11/2011 images and the water is green or blue depending on the depth and bottom. The darker green or blue water areas are of course the deeper areas. The shell beds can be seen as darker "spots" or blotches of different color than the surrounding bottom under water. Grass is harder to see as it is green and blends too easily or the water is not clear enough to make out the grass beds. But you can spot them as a bit darker than surrounding areas.
Grass usually does not grow deep so most of time grass is found shallow or near shore. The fish sit in these grass spots and ambush bait washed over or around it by the current. Sometimes there will be grass, shell and mud all in the same area. The push pole or knowing the area is your best bet if you can't make it out with GE.
If you see an image that you think may be shell as a darker spot, use the history images and compare through the years if the spot gets bigger or smaller or disappears altogether. This way you can tell if the shell is alive or dead or if it is grass and still there.
If you look a the same image in GE (2011) you can zoom in on many shallow areas near shore and see the "spots" or "holes" that flounder or other fish made in the mud bottom. This will give you an idea where fish stage up for future fishing.
You can also make out structure that is normally hidden by the high tide. Fish these and you will usually find fish as they are attracted to anything different on the bay bottom. It's in their nature.
I have found the best thing for me is to review a location I want to fish by studying all images from the past for that area zooming in for best detail. Once I get to the spot I will check the bottom of the areas I saw and had questions about whether there was shell or grass in that area. Once I know I can then go to the map and be able to see it better since I was there first hand and this helps me identify other areas that look about the same in GE. This helps me find similar or new spots to fish.
Sorry this is so long but wanted to give you my insight and how I do it.
I also sent emails with pics I screen captured of GE to Tobin and asked him to confirm if the image I was looking at was in fact shell or grass. He knows most of the bay and his knowledge helps immensely!!
Good luck hope this helps.