Downloading data from the USGS Earthexplorer

all right so this is sort of part 1 of 2 for our practicum for a week 3 of our week to week 3 of computational archaeology so in this first part this is going to be standalone video just showing you how to access the USGS geospatial data data portal that's also known as Earth Explorer so what you need to do is to load up your favorite web browser and point it to earth Explorer USGS govt and once you get over there what you need to do is first you need to create a an account if you don't have one already so there should be a register button over here now I've already logged in so you don't see it and you know you have to go through a few steps tell them how you're going to use the data if you're a student in the class obviously you're gonna do it in an educational context needs a freak out you just set it up with username and password then make sure you log in and as soon as you've locked in now you're pretty much ready to go to access and download free geospatial data from the United States government so this is what you should see when you first open this and login it's by default zoom down into like basically the center of the United States there's a couple of different ways you can navigate so if you see once your mouse cursor goes into the map area it turns into a hand so you can click and pan by dragging click and hold and drag it around the scroll wheel will work to zoom in now you can also zoom in and zoom out with these tools over here you can change of how it looks if you really wanted to sort of the base layer that you're looking at over here probably that default is good enough and so what you don't want to do is to navigate to the part of the world that you want to see if they have any data for and then you'll put in some bounding boxes like so so here I just randomly clicked around in the sort of I guess Midwest Upper Midwest of the United States you can see each one of these pins is a sort of vertex of a virtus of this square polygon and I can put as many or as you know few pins as I want you'll see they'll show up over here with their latitude longitude coordinates if you made a mistake just go over here and you can X out of that like so and you'll see they'll sort of delete them one by one you can also click the add coordinates and type them in very precisely here so you can add each pin individually if you for example have a GPS point you know very precisely that's the corner of the area that you're interested in you can certainly do that as well the other thing that you can do is to sort of search you can do a couple of different things you can actually click this tab and you can actually upload a shapefile or a KML file which is what you would export from from Google Earth shape file is a standard vector format that's sort of the bounding box of the area that you're interested in and you can upload that and it will just use that as the bounding box on the other hand you can go to the tab that says geo coder and you can in a couple of other sort of identifying features the most useful one is probably address place so that's actually what we're going to do here first we're going to search for the city that is closest to the little project area that we're using in project 1 which is in Calabria Italy in the town that we're going to search for is called bola Marina so that is B OVA space ma RI and a so you type it into that box and you hit show and it should show you the actual address here and a lot of devotees you can click on it and it should zoom right in there and it should have a pin already in place so I'm gonna use a scroll wheel to zoom way in so I can show you so there it is this is the little town of lorina so this is where I stay in the summer times when I'm out doing field work and just over here to the to the east of it is a valley this is the south of Valley and this is the valley that you're gonna use for actually quite a few of the projects in this semester so this by default has now been added as a coordinate so that's totally cool we can then go in and click a couple other coordinates and really all we care about is just getting the main center part of the valley this is the town of bola or upper bola so you might want to put the pin on bova and you know make it sort of parallel and maybe the other pin can be on probably Medina and between all of these things maybe want to extend these so we get you know the entire coastline that's pretty good like so you know it doesn't have to be exactly the way I've done it here because what it's going to do is to show you the overlap of any GIS tiles that they have for download any GIS tiles that actually overlap in any way with this area will show up in the search so once we're happy with our coordinates and again we can drag them we can add additional ones we can delete the new ones you know as soon as we're ready to do it what we can do is to go down to the very bottom here and click where it says datasets and this is where we get an opportunity to choose what kind of data would want to search for and as you can see they have quite a few different varieties of them so later on this semester we'll deal with imagery specifically we'll deal with Landsat imagery also we'll talk a little bit about imagery from commercial satellites and declassified data so these are like you know Cold War spy images so you know at this moment you can take a moment in and sort of click through some of these things just to see what they are but what we really want to do right now for project one is download some digital elevation data and you can see there's several of these some of these are just for North America or in fact specifically just for this one is just for Alaska but the one that we're particularly interested in is SRTM which stands for shuttle radar topography mission and this is a global data set and it is actually available free of charge from the USGS and a 30 meter spatial resolution which means ever pixal is gonna cover a swath 30 by 30 meters which is actually pretty high resolution for a global data set so it's a super useful data set it's actually pretty accurate because it was done by a radar system that is an active sensor so that literally the Space Shuttle was a two devices one would pulsed the radar signal down the other would wait for it to bounce off the surface and and return and based on the timing between when it was sent and when it bounced you can know pretty precisely the average elevation within that 30 millimeter pixel so what we want to do is to get the one that is SRTM one arcsecond global and your clue here is arcsecond so we know that it's going to be a latitude longitude system and angular measurement systems so that's going to be our base initial import and later on figure out reproject it and when we get halfway through the course into grass so all I'm going to do is to put a check mark over here and once we're cool you can add additional criteria so you can actually put you know if you know some other like specific ID numbers you can put them there but typically it's just sort of useful once you check the box just to go straight to results and in our case we've just got one one that overlaps and if you want to double check you have a couple of tools over here pretty useful as the footprint tool and it actually shows the coverage of that individual tile so obviously since this is a global data set you can't get the whole world at one so you'd be here for days and days and get terabytes of information so they break them up into these one arcsecond tiles and you know you can actually get you know basically like a mosaic if you wanted to cover all of southern of kelabra you need to get the one that was up here the one that was over here and the one that was over here you can download them individually and composite them back together in your GIS and we'll cover that again later on in class but for now this is the one the only one that we really need is the one that covers our little project area of San Pasquale Valley so that's the footprint over here is a Browse overlay so it actually gives you a sort of scale back miniature view of what the data actually is this is pretty useful specifically or especially if you're getting imagery data and you can actually see what it actually is and there are a couple of other things you can compare if there's for example imagery from one date versus another you can put them a list to compare so you can choose the best one you can look at the metadata which is essentially like you know the date that it was captured the day it was published the corners and you know the coordinates of the corners and if you are a little bits of information again depending on what kind of data you'll get some other information here so that's also potentially pretty useful to look at but for us at this particular point what we want to do is to go to the download options tab so click that button and you'll see that there are actually three different formats that we can download them in now depending on which GIS software you're using it may be advantageous to pay you know one of these versus the other for us we're going to pick geo TIFF geo tip is a pretty standard accepted raster format for most GIS systems and so that's what we're going to do it UJS reads these in just fine click the download button and it may say waiting and then it's good download it but default it's just going to put it into the downloads folder of your computer you might get a little pop-up that asks you where to download it so that could be a useful thing once this guy is finished downloading then we're basically ready to go we can continue to search for different data sets so we can go back over here clear our SRTM and we could continue to search for you know other different kinds of data sets if we really wanted to but for us all we really wanted that SRTM so work done we can essentially close out of that what I will do briefly before ending this first part of the practicum is to show you how you'd want to organize your data set so I've opened up my download folder and what we want to do is to find this one and it has a very strange name and 37 underscore e01 5 underscore 1 arc AR c underscore v3 dot TIFF and what this is is saying the tile is north 37 east 0 15 there's one arcsecond coverage and it's the version 3 SRTM the most up-to-date most recent version of the SRTM data set so that's how you will identify it if you download more than one it might say you know the one just north of this will be north 38 east 15 the one just to the east moving north 37 east 16 right so or 14 whichever way the numbers go so that's how you will sort of in your mind organize how you're going do all this stuff now what we want to do is to open up our what we wanna do is open up our QGIS projects folder that we made last time so here's my one from last time QGIS project Lula then we have SPV survey if you recall in there we have raster and vector so why go into the raster folder and here at this in this case we just have one orthos tip tip and we can pull this one directly in here now real best practice would be to make a new folder that says de m or elevation or something like that and then to put our SRTM into there and technically we should have one that says imagery let's actually type the entire word imagery like so and we can put San Pasquale orthos in here so you should already be in your mind going oh we just move psycho squad ortho into a new folder that might do something to our GIS project when we open it up so if we go back here just one folder up and we open our SPV survey q GS project file it's going to open q GS and then it's gonna say handle bad lairs San Pasquale ortho sucked if it means you can't find it now because I moved it and it doesn't know where that file is so what we can do here is we can highlight it and then we can click browse and what we need to do is to go into our project folder SPB Survey go now into raster and our new folder imagery and then say it is San Pasquale orthos on TIF and then click OK and now we configure and so you'll see I'm right back where we left off last week my 2017 structures outline is in there it styled exactly the way I last lifted and now that we told it where the orthos are the orthophoto is it knows where those are and can display them as well

Channel: Isaac Ullah

Views: 10,282

Rating: 4.875 out of 5

Keywords: GIS, Tutorials, GRASS, QGIS

Id: nAj3LlaLNVM

Length: 14min 4sec (844 seconds)

Published: Thu Feb 06 2020