The latest Landsat images on Earth Engine

I had thought that Google’s big library of satellite images was no longer furnishing us with the latest Landsat images. I was using the same lines of code I always had been, and I could never find images past April 2017.

Well, I figured out what the problem is. The images are there, alright. But they have been reorganized and there are new paths to accessing them. So it was a simple matter to sort out! I went to this website and I clicked on the Landsat libraries I wanted, and voila — I found the new pathways that I need. I tried them out, and yes indeed, I saw Landsat images in the areas I wanted from within the last week (so mid-September 2019).

I had earlier written a blog post decrying the loss of current Landsat images on Earth Engine, and giving undue credit to the Europeans for filling in the gap, to top it all off … glad I have things sorted out now.

 

Those cool sliders that show “before” and “after” images

I wanted to look at some satellite images from Hurricane Dorian, and I found a lot of them — specifically Grand Bahama and the Abaco Islands — up on Google’s big library of satellite images.

It was cool, because when I was for example searching on September 9, there were already images of the Bahamas posted that were captured on September 8. That is quite a quick response time!

I wanted to make a feature where you can slide back and forth between the before-and-after of Hurricane Dorian. I had heard about this new app called Flourish, and lo-and-behold: you can get a slider like that for free. You just have to create an account, and then you upload the “before” and “after” images you want to compare.

Here’s mine comparing Great Abaco Island from August 16 (before) to September 5 (after).

 

You can see that the storm has kicked up a lot of sediment in the water. If that sediment was leached from the land (it kind of looks like it; you can see curls of sediment smoking their way into the water) then that can have repercussions for the land surface of Great Abaco Island.

By the way, did you ever read the “Lost Girl” books? They were set on a deserted speck of the Abaco Islands.

Now, that is a comparison of two images that are just weeks apart in capture; so how about looking at changes in an island’s land surface over a few decades? I made another before-and-after slider image of Tangier Island in the Chesapeake Bay. The “before” image is actually from Landsat, and it is from 1992, so you see it looks quite a bit blurrier than the newer Sentinel-2 image. Times have changed, and so have satellites.

Looks like Tangier has lost quite a bit of ground; both in the north, and on that smaller eastern island. The spit of sand in the south has changed, too.

By the way, have you read “Jacob have I loved”? It’s set on a seemingly fictional Chesapeake island very similar to Tangier and Smith Islands. Oh, it is so good!

 

 

Google Earth Engine no longer adds Landsat images .. WRONG!

EDIT: I have finally discovered the trick to getting the latest Landsat images on Google Earth Engine … which means my whole blog post below is incorrect. I had a feeling it would turn out like this, because honestly? Whenever you start giving too much credit to Europeans, that should be the red flag to let you know, “something ain’t right.”

But I will leave this blog post up, so if anyone else is having the same issues, they can find it and then find the solution here.

Note: if you want to know more about why satellites like Landsat are important, see this animation or this animation.

I used Google Earth Engine to complete a large part of my Ph.D. dissertation.  I needed lots of images taken by satellites. Like, I needed thousands.

There’s a couple ways to get these images (for free!) You can go to a NASA website, and make an order. You have to do a lot of clicking to get it done, and then you have to wait a few days for the order to show up in your email. Then you have to download all the images. They take up a lot of room on your laptop. You have to figure out how to organize them, and then you have to load them into whatever computer program you’re going to use to analyze those images.

Or you can use Google Earth Engine. As much as I hate to give more power and control over to Google, this feature is very helpful. They already have all the millions of satellite images out there uploaded onto the Google servers. Instead of waiting a few days for a NASA order to come through, you can access those images with just a few lines of code in Google Earth Engine. You don’t ever have to download the images to your own computer or laptop, because you can analyze them right there in Earth Engine. The whole process is streamlined, you save so much time, and you don’t clog your harddrive up with huge satellite files.

Well, that’s all in the past now. NASA has apparently given up cooperating with Google Earth Engine. I tried to search if there was an announcement made to that effect, but I didn’t find anything. But it is a fact that if you search for Landsat images on Earth Engine, you will easily dredge up old images, going back to the 1970s. But there are no new images, not for Landsat-7 and not for Landsat-8. In fact, there are no Landsat images past April 30, 2017. Hmmm. I wonder what changes engulfed NASA’s ultimate leadership right around then, so that the ripple effects eventually led to this change in April 2017?

At least, they did not delete all the images that had already been uploaded. So images from the 1970s to April 2017 are still available.

If I’m wrong about this, and the new images are up there somewhere, someone please let me know. I have searched a couple spots on the globe and it is the same every time – nothing new after April 2017.

Yesterday, I searched for Houston in March 2019. I wanted images from the sky of that terrible oil fire that occurred. But I found no Landsat images. However, I realized there was potentially a work-around. The Europeans have launched their own satellites, and thank goodness, because ever since 2016, they have been loading their images from Sentinel-2 onto Google Earth Engine. And they are still loading away — looks like Trump can’t stop them. There were in fact 18 images from the Sentinel-2 satellite for Houston sprinkled between March 1 and April 15, 2019.

Alas for me though — no image showed the black smoke of the fire. That was what I wanted. The fire started on March 17. The first satellite image after the fire (March 18; below) had a thin coverlet of clouds covering Houston, and you can’t see anything through it.

Houston March 18 2019
Sentinel 2 image for Houston, March 18, 2019. Bands: Red, green, blue.

 

The next satellite image came on March 20, but alas again — there’s no more fire to be seen. Do you see black smoke?

Houston March 20 2019
Sentinel 2 image for Houston, March 20, 2019. Bands: short-wave IR, near IR, and blue.

That black dot in these images is supposed to be the location of the company that started the fire, or there-abouts. Zooming in a little closer …

Houston March 20 2019 zoomed
Sentinel 2 image for Houston, March 20, 2019. Bands: short-wave IR, near IR, and blue.

Well, maybe that is black smoke, but I don’t know that it’s going to convince any one.

Sentinel-2 has a band for “coastal aerosol”. Maybe that will be the key to being able to tell where the plume of black smoke is.

My Earth Engine code for getting these images is here.

 

Making maps

I had to verify a fact for my article I’m working on now. It’s about a bunch of polluting power plants being built in a neighborhood in Maryland where mostly Black people live. Having lived in Maryland, I can tell you that this is exactly the sort of thing that Maryland would do.

What the community activists told me was: there is no other place in the United States where you have 3 natural-gas power plants of that size within 2.9 miles of each other. So of course, I wanted to include that in the article, it’s a pretty powerful statistic.

But, no one could show me any report that backed it up.

All I got was a fact-sheet prepared by the non-profit Earthjustice. That fact-sheet said: after all 3 power plants are built, Brandywine will have more power-generating capacity than 99.9% of the country.

This was, first, a more confusing statistic – a lot less clean – compared to the first version. Second, I didn’t have any idea how they’d come up with that figure.

So, I got out my own nifty mapping and GIS skills. I felt so smart!! I have done GIS stuff for 10 years; and the particular program that I used, Google Earth Engine, I used almost every day for the last 2 years of my Ph.D. work. But I haven’t really touched it since I graduated in May. When I pulled it open, I kind of just stared at the screen. I couldn’t remember how to do anything. And it’s only been two months!

But soon I was coding up a storm:

power plant map code

I found a big spreadsheet from the EPA that lists all the power plants in the US. Somehow, I managed to upload that in Earth Engine. Then, I found a shapefile (computer map) of Maryland. Then, I was able to search through the giant EPA spreadsheet, and first pull out only the power plants in Maryland, then only the large ones, then only the fossil fuel-powered ones. It was super great! I’d forgotten I could do all that in Earth Engine, so it was like getting surprise presents one after the other.

Then my script crashed. So I had to redo everything, and I made sure to express my anger in the new script title.

Then, I mapped it all:

power plant map

The black dots are the power plants with a capacity of over 200 megawatts, of all fuel types. There’s one place that has two such plants, by Riviera Beach (the blob south of Baltimore). And the string of 3 black dots, with the red line over them, are the three power plants set to be running in Brandywine by next year.

So the statistic I was able to safely use in the article is: there is no other community in Maryland that will have as many large power plants as Brandywine. It would have been nice to go further and see if this was true for the whole US, but I didn’t have time to visually examine the map; or alternatively, I wasn’t sure how to get Earth Engine to do those calculations for me.

But any case, I’m really happy I was able to do this little bit. And it was worth it for sure to give the article a stronger backing.