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Rolla, ND | Well there are the Landsat images, used to be there were two different Landsat satellites and one went by each week so there was actually weekly images of the US, now the one is down so we are talking biweekly. That isn't much of a problem unless you end up under a cloud when the satellite goes by. Now some people because they are in the overlaps between passes, actually still do get weekly pictures so it's a little bit luck of the draw.
So there is a shot of your field no less than every two weeks, but not all shots turn out. And you could indeed buy it from either NASA or from various vendors.
Now one that would be good to check with is www.satshot.com. Lanny has the largest set of shots available that I know of. He also provides software for those who buy his product so you are saved that expense. He's changed it a bit, but his software used to be very easy to set up and make zones and such, I haven't worked with his current products, I know they are a little more complicated so I assume they are a little more difficult to learn too, but that's just an assumption.
Now the way he sells shots is one section of land at a time, and you buy a package of so many shots. You can browse and see the shot under low resolution so you can see if all you are getting is a cloud so you don't waste shots.
His "pictures" are a higher resolution than the Landsat is. This is done through use of the computer to increase the resolution much like photo software can increase the sharpness, it isn't perfect, but it actually does do a pretty good job of giving you a useful map at a higher resolution than the Landsat's 30 meter resolution.
Now most commonly, we tend to work in vegetative indexes with sattelite shots, basically that is a function of how much greeen there is. Let's say the parts of the field with pods lost the leaves and the parts without pods didn't (It could be just the opposite, I dont' know what the case was in your fields) Or let's say there was a lot more growth with taller plants and such in the parts with pods, that again would show up well, I suspect the best differential might have been about 3 weeks before maturity.
Now you can see the differences yourself visually, this may show up on a satellite shot, maybe better as a false true color than as a vegetative index shot, that's just a matter of using different bands of the photo. But I kind of doubt if it will show up well, that is because from above, you don't see much of the stems, you look down after the leaves are gone, and what you see isn't mostly stem, it's soil, and dropped leaves and the zones may show up, but not necessarily due to the stems. It could be due to OM differences between the productive and less productive areas, you may actually have just as good or even a better map of the zones taken when the field was basically black dirt rather than have confusing things like dried leaves on the soil surface. I suspect a black dirt shot would actually work pretty good, now you can take the FSA shot and in many cases get a pretty good OM map, maybe not every year but at least some years, the only difference is that the older shots were gray scale, compared to getting some false color today. The grey scale may actually work better and it can be done even with color shots.
I suspect you can indeed get a pretty good map, it would probably only take a little playing around to find what works best. If you are interested the first step is actually to go out while you still can and get some ground truth. Easiest is to take a FSA shot and go out and mark the separations, you may find it follows the FSA map pretty well, maybe not.
Best would be a handheld or laptop with a FSA map as the background but you can do a pretty fair job just by gridding out by hand. Mostly what you want is something marked so when you play with the photos, you can play with the divisions until it breaks in the correct place. Everything is a scale and you basically just need to know where you want the breaks so it gives you what you want.
There are also many higher resolution type of shots out there, Ikonos, or planes or whatever. It may be too late for this year, to order them, usually not everything is routinely shot only those things ordered in advance. If it is still visible, you can even do your own digital photography and calibrate the pictures to get pretty good readings, If it is stem color, you want to take the shot at an angle, and then use the calibrate programs to warp the picture into square with the field. That way you get to see the differences that you wouldn't see from straight down.
One other way you can do this particular thing is to draw the zones with a four wheeler or pickup. But depending on how many there are it might be a lot of work. Basically you would just drive the zone boundaries and log. It wouldn't be bad if there are just several big zones to a field but if it's a patchwork that would probably be too much. But it would be good to do even just a few to get that ground truth to use with any photo.
Marv
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aerial/satellite images
