My Google Map Blog

We have recently spent quite a lot of time looking through historical imagery and reported some of the most interesting finds from recent imagery, including:

• The Amtrak train derailment in Philadelphia and a landslide in Salgar, Columbia.
• Flooding in Georgia and Texas.
• Flooding in Brazil.

However, one thing we noticed and found quite frustrating is that if two or more images are captured on the same day of the same area, Google Earth displays them on top of each other and it is impossible to see the ones that are ‘behind’.

In October 2014, Bermuda was hit by hurricane Gonzalo. Google Earth has four images captured on the same day, October 19th, 2014, soon after the hurricane hit. However, the uppermost image is in black and white and there is no way to see the three colour images apart from where they are not overlapped by the ones above them, which for the most part is over the sea. There are two more images on the 20th which also overlap each other, but that is less of a concern as they are of similar quality. We could not identify any evidence of storm damage in any of the images

The four overlapping images of the aftermath of hurricane Gonzalo.

In May, 2014, there was a large wildfire near Lake McClure in California, USA. Google Earth has some imagery of the region captured soon after the fire including, three images all captured on May 31st, 2014. Two of the images are black and white and one is in false colour. False colour imagery is particularly useful for identifying vegetation differences and would probably have been quite helpful in identifying the extent of the fire. Sadly, the false colour image is mostly covered by the two black and white images.

Overlapping images captured soon after the Hunters Fire.

There is also a black and white image from May 30th, and two overlapping images, one black and white and one false colour from June 1st. We think we have identified the extent of the fire by comparing more recent imagery with imagery from before the fire, as well as a bluish patch in the false colour image.

In February 2015, Australia was hit by tropical cyclone Marcia, causing flooding in many places. The Northern Territory towns of Galiwinku and Ramingining have imagery captured soon after the cyclone and again there are overlaps. However, in this case it is not so serious as the quality of the overlapped imagery is similar to the images we can see. The images are not very high resolution, but we can see clear signs of storm damage in both locations.

Ramingining, Australia. You can see trees flattened and on the roofs of houses and some water still on the ground in some places.

The reason why there is a problem with overlapping imagery is because Google dates their imagery to the nearest day. Although the Google Earth timeline is capable of distinguishing dates and times down to a minute, because the images’ date stamps are identical, Google Earth must show both at the same time. The solution would be for Google to add different times to any overlapping images that occur on the same day. It is likely that the actual time the images were captured is known by Google, but if not, a dummy time such as a few minutes after midnight could be used.

To find the locations mentioned in this post in Google Earth use this KML file.

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