I'd like to show you how to download Landsat 8 Satellite Imagery from the United States Geological Survey website. You can just do a search online for USGS Landsat 8 data, something like that if you want to find it, or you can go to the URL EarthExplorer.usgs.gov. Either way, I'm sure you'll be able to find it. So, that will bring you to this interactive web explorer type interface, where you can zoom and pan to different parts of the world, search for satellite imagery, and then download it. So, I'm going to search for San Francisco. Just type that in, hit "Enter" and you'll see that that comes up right away. So, I'm going to click on that. So, that's shown up on my map. So, I can zoom into that area. Now, I can optionally put a date range in here. I believe what it will do is list the results in reverse chronological order, and since I'm interested in recent data, I'm not going to bother putting in a date range there, but you could. For example, say I'm only interested in imagery from July or August from 2016 or whatever it happens to be. I'm just going to leave that blank and click the dataset button. So, that opens up a list here. I can expand the Landsat options, and I'm going to go with Landsat collection 1 level-1. If I expand that, I'm going to select Landsat 8, and so now I'll click the "Results" button. Here on the left you can see the different imagery that's available that meet the criteria that I've specified. So, this is for the San Francisco area. I didn't set a date, so it's giving me lots of different options here. As you look at the results of your search, a couple of things that you may want to keep in mind are the time of year and the amount of cloud cover that there is. So, depending on what it is that you're trying to map, you may want to have say the vegetation in full leaf, because that's what you're interested in looking at. So, that might mean getting an image from the summer months, or maybe you don't want the leaves to be on the trees, and you want to be able to see the ground underneath, then you might want something from the winter months. Unless of course you live in an area that has a lot of snow, then in the winter you're going to be able to see as snow, and so that's not going to work. So, you may want to go with a spring or fall. So, that's definitely going to be a factor is what time of year you want to look at and also cloud cover. When you're using something like Landsat 8, that's using visible and your close to visible wavelengths that are affected by clouds, so in other words they don't penetrate clouds. So, if there's cloud cover over your image, then you're not going to be able to see anything under those clouds. So, when you look at the thumbnails, you can easily see major amounts of clouds, you can also filter the imagery for cloud cover if you want. So, that's just a couple of things that you may want to keep in mind as you look through the results. So, if I scroll down here I see some imagery from September. Here's an image that looks like it has a lot of cloud cover in it, because you can actually see the clouds off the coast. I think that's pretty common in San Francisco. If I keep going, I see one here from June, first 2018. That looks like it might be a pretty good candidate. So, a couple things I'll just mention is, you'll see this little footprint here, if I click that, and it will show me the coverage of that image. So that's the footprint on the Earth of how much of that image covers the Earth, which can be extremely useful especially it's common that you'll have a study area that spans more than one image, you want to make sure that you get all of the images that you need for your project. If you click "Show Browse Overlay", and if I turn off the footprint, that will actually give you a quick snapshot of what that image looks like, which is another quick visual way being able to make sure that it looks the way you expect it to, and whether or not there's any clouds present. Then, I can click here for download options. So, you'll notice there's a dialog box that's popped up here that gives me different options for downloading, but that it's asking for me to log into my account in order to complete the download process. You have to have an account in order to be able to download data. It's free. It's really easy to set up. I'm not going to walk through it here. I already have an account, so I'm going to login and then continue with the download procedure. So, you notice here that there are different options for downloading. The first few are really just to download a snapshot of the satellite image. So, one of the things that we'll kind of tip you off is that when the image is only six megabytes, it means that it's really just kind of a- it's not a full resolution multi-spectral image. It's just as a little tiny JPEG picture, that you can use for reference later if you want to. The full data is the one at the bottom here. If we click "Download Level-1 GeoTiff data product", and you'll notice that it's 910 megabytes, that's what will tell you that this is the full dataset. Something that's a large number like that. I'll just go ahead and click "Download". So, you can browse to wherever you want to store that file. I'm just going to keep it here on my demo drives. You'll notice that the file name is fairly long, that's including information about the image itself. So, things like that are embedded in here are the file on the path and the date and so on, and you'll notice that it's a tar.gz file extension. So, that's a TAR or a tape archive file format and GZ means that it's being compressed, so we can download that, but we're going to then have to use a utility to be able to convert it from a TAR format into one that we can use inside our GIS software. So, I'll click "Save". So, as this file is almost a gigabyte, it may take a few minutes to download, depending on your internet speed and your bandwidth. Okay. Through the magic of editing, I speed up that little process. Here's our completed file. As you can see, this as a tar.gz file format. What that means is we have to take it out of that TAR format, so that's a format that's used to kind of collect a bunch of files and put them together, in a similar way to a zip if you're familiar with that. So, we have to take it out of a tar format and decompress edge by taking it out of the GZ format. So, the utility that I like to use for this is called 7-Zip. It's free, you can download it, and it's straightforward and it's one of the few utilities that I've found that you can easily convert a tar format and decompressed very simply. So, I'll show you how that works. So, since I have it installed already, all I have to do is right-click on this file, and you'll see that I have 7-Zip here, and I can say extract here, and that's been completed, and you'll notice that this file is now about 1.7 gigabytes. So, what that's done is it's uncompressed the file or decompress. I'm never quite sure what the right way of saying that is, but it's expanded it. Let's put it that way. So, now we've taken our compressed dataset, we've expanded it. So, now that's the full dataset. So, it's no longer got the GZ extension, but now we still have to convert it from a tar format. So, we just right-click again, select 7-Zip, and then say extract here. So, now we've decompressed it, and we've converted it from the original tar format into the actual image files that we'll want to be able to access and use in our GIS software. This may take a couple of minutes, because these are fairly large files, they're raster, they're satellite images, so they're fairly big. But be patient, and it should hopefully work correctly. Now, it's complete, which is great. So, these are all the files that were bundled up and compressed, and put together and packaged up for us by the USGS. Now, we've turned them into a format that we can now use inside our GIS software.
