dallas

Google Earth Imagery Update: The Dallas, Texas Tornados

June 20, 2016

Google has recently pushed out another imagery update. Below we show approximate maps of where the new imagery from April, May and June can be found. There is almost certainly older imagery too, but it is harder to find.

June imagery.

May imagery. Red: Recently added imagery. Blue: Imagery as of June 12th.

April imagery. Red: Recently added imagery. Blue: Imagery as of June 12th.

To find the locations in Google Earth download this KML file.

As you can see above the new April imagery is almost exclusively aerial imagery, mostly of the US and a bit of Japan. Clearly aerial imagery takes a bit longer to process than satellite imagery. Strangely we have not yet seen any aerial imagery of Europe this year and very little satellite imagery.
[Correction: There are a few small patches of aerial imagery. ]

On December 26, 2015, there was an outbreak of at least 32 tornados, many of which were in the Dallas, Texas area. There is now some aerial imagery captured on April 28th, 2016, five months after the disaster. Nevertheless, the destruction is still very much in evidence, with the tornado scar over the Garland/Rowlett area visible from quite a high altitude. We have identified the tracks of the three strongest tornados.

We have in the past looked at low resolution imagery of the Garland/Rowlett area using both Landsat imagery and Sentinel imagery, but although we could clearly see the tornado scar, we could not see damage to individual houses.

Below are some ‘before and after’ comparisons. Drag the dividers left and right to compare the imagery.

The above are all from the Garland/Rowlett tornadowhich was the strongest, but we show only a tiny fraction of the damage caused. Be sure to check out the imagery in Google Earth with this KML file as a guide. There is quite a lot of new construction in the area so when looking for damage be sure to compare with historical imagery as a house under construction looks remarkably similar to a severely damaged house.

Sentinel vs Landsat imagery

May 5, 2016

Yesterday we had a look at Snapsat, a useful website for obtaining Landsat imagery. The location we chose was Dallas, Texas and a track made by a tornado in December last year.

We thought it would be interesting to compare the Landsat imagery with the European equivalent – Sentinel imagery.

Landsat 8 captures colour images at 30 m per pixel, but also captures has a panchromatic band at 15 m per pixel, which can be combined (using a process known as pansharpening) with the colour bands to essentially achieve close to 15 m per pixel resolution. Sentinel 2A, on the other hand, captures images in colour at 10 m per pixel and does not use pansharpening. So the Sentinel imagery should be slightly better quality and we found this was indeed the case.

We are still learning the best ways to process imagery and neither image has been processed ideally.

Landsat 8 imagery vs Sentinel 2A imagery.
Images courtesy of USGS/NASA Landsat and Copernicus Sentinel data 2016.

To see the images in Google Earth download this KML file.

Snapsat Beta for Landsat imagery

May 4, 2016

We have previously had a look at how to get Landsat imagery into Google Earth. We have used a number of different techniques over time, but in all cases, obtaining high quality Landsat imagery required a large download (typically over 700 Mb) and several stages of image processing to combine multiple bands into a full colour image.

We recently discovered Snapsat, a website dedicated to making it easier to obtain processed Landsat imagery. In March last year, Amazon announced the availability of Landsat data on Amazon Web Services (AWS). Snapsat builds on the AWS, offering to provide easy access and processing of the Landsat data. It appears to have been set up mid last year not long after the Landsat data was made available on AWS but not much work appears to have been done on it since then. However, it still works well and makes obtaining processed Landsat imagery remarkably easy. Learn how to use it here.

As we mentioned in this post there was a Tornado which struck Dallas, Texas in December last year. There is no imagery yet in Google Earth showing the main path of destruction. So we tried out Snapsat by downloading a Landsat image of Dallas from January 12th. The process was straight forward and only required a download of 107 Mb as opposed to the 772 Mb required to download the same imagery from Earth Explorer. And we can see the track of the tornado.

Tornado track, Dallas, Texas, as seen in Landsat imagery. Ends of the track marked with arrows.

There are, however, a few disadvantages to using Snapsat. The website does not do pansharpening, a process whereby a higher resolution grey-scale image is used in combination with the three colour bands to create a higher resolution image overall. This means that the imagery obtained via Snapsat is not the highest quality possible. Another issue is that the downloaded file does not include Geo-coding information so it cannot be automatically imported into Google Earth Pro. However, since we usually have to crop the imagery anyway, manual positioning is often necessary and not very difficult.

We got the same image from Earth Explorer and used GIMP to process the imagery (very inexpertly) and the result is noticeably sharper because of the pansharpening.

Tornado track, Dallas, Texas, as seen in Landsat imagery, with basic pansharpening via GIMP

To see the two overlays in Google Earth download this KML file.