antarctica

A massive iceberg slowly forming – Larsen-C

May 26, 2017

For the past couple of years, scientists have been watching a crack slowly growing in Antarctica’s fourth largest ice shelf, Larsen-C.

The location of the crack. The arrow shows the direction of propagation.

We downloaded some Sentinel-2 images of the location and can see the approximate extent of the crack as of March 2017:

To view them in Google Earth download this KML file. Warning: older computers may struggle to load the images. We tried viewing the overlays in the new Google Earth, but it could only handle one overlay at a time. Trying to open both at once crashed WebGL.

The European Space Agency ESA (which runs the Sentinel program) produced this video showing how they used Sentinel-1 (a radar imaging satellite) to analyse the movement of the ice:

And for some aerial footage, see this video from the British Antarctic Survey (BAS):

While exploring the area in Landsat imagery we were struck by the beauty of the imagery. These two are our favourites:

Sunset in Antarctica.

Beautiful blue ice.

Can we see Antarctic seals in Google Earth?

August 4, 2016

We recently came across this interesting article on the DigitalGlobe blog. It is about using imagery crowd-sourcing site Tomnod to count seals in DigitalGlobe satellite imagery of Antarctica. The very best commercial satellite imagery available today has a resolution of about 30 cm per pixel, with most imagery that we call ‘high resolution’ satellite imagery closer to 50 cm per pixel. This usually means that animals are only a few pixels in an image and difficult or impossible to spot. In the cases where we have seen animals in Google Earth it has typically been in aerial imagery, such as the National Geographic Africa Megaflyover images or areas like the US which have a lot of aerial imagery. And there is, of course, Street View.

Antarctica has the advantage that we are looking for dark spots on a fairly featureless white background, which makes spotting seals possible. Much of Antarctica doesn’t have high resolution satellite imagery but there are some areas that have DigitalGlobe strips of imagery. So, given the tips in the DigitalGlobe blog post, we wondered whether we could find any seals in the imagery.

We aren’t certain if these dark spots are seals, but they do match the description given.

This is rather low resolution imagery but it does look like there might be groups of seals gathered around this crack in the ice.

We are fairly sure this is a positive find and that those are seals.

For the locations above, download this KML file.

Despite looking rather white and boring from a distance, it is well worth zooming in on Antarctica and looking around, as there is a remarkable variety of landscapes formed by glaciers and shifting sea ice. For best results switch to ‘historical imagery’ as it is much easier to find the high resolution patches that way.

We also tried looking for seals with the Tomnod website, but were unsuccessful. Google Earth is a much better interface for this sort of thing as it is much easier to find major features, such as cracks in the ice, then zoom in to them. The actual survey the scientists want, however, has to be done on Tomnod, because Google Earth does not have access to all the imagery that they want searched.

Watching Antarctic Ice Sheets Crack with Landsat Imagery

March 18, 2016

We recently came across this interesting story about an ice shelf in Antarctica which is slowly breaking off. The original story is on the NASA website here. The article features a couple of Landsat images captured in December 2013, and December 2015. However, Landsat imagery is freely available and relatively easy to obtain and put into Google Earth.

Our current favourite method for browsing Landsat imagery is with NASA’s Earth Explorer as it allows you to quickly browse through the imagery available and download low resolution versions, which can easily be put into Google Earth Pro.

In this particular case there is a surprising amount of imagery of the location in question. As we saw when we looked at the coverage that Landsat provides, the imagery is divided into rows and columns that cluster together towards the poles. This means that polar locations actually get covered by several adjacent columns and get imaged every couple of days or so. Most parts of the world only get imaged once every 16 days. However, the poles are also dark for about half the year so there will only be good images during the summer months.

In addition, many of the images have significant cloud cover, so we had to go through them and choose ones that showed a clear view of the location we were interested in. As you can see below we were able to obtain imagery all the way from January 2000 to March 2016. The latest image in the series was captured just last Saturday! (March 12th). There seems to be a bit of a gap in imagery around 2004/2005 but we did not investigate why.

Animation showing the ice crack moving and growing over the years. Larger version

You can see the ice flow like a very slow river. It moves approximately 3.8 km in the 16 year period shown above.

If you wish to explore the imagery in Google Earth you can download this KML file. We have had to crop the Landsat images considerably, showing only the location of interest in order to make the file a reasonable size.

The crack from the story has a precursor in 2000, which was as far back as we could go. However, it only lengthens and widens in 2013, when it starts to look like part of the ice shelf is breaking off.

The default imagery for the location in Google Earth is Landsat imagery from about January 2003.

Average Cloud Cover Map and Map Projections

May 20, 2015

We recently came across this article about a recently released map of average cloud cover for the last 13 years produced by NASA.

The map is provided in the form of an image and a high resolution version can be downloaded from NASA. It would have been nice to view it Google Earth. However, it is provided with a different map projection than is used by Google Earth image overlays. This is usually not much of a problem for small image overlays, but for global maps it is critical. Google Earth image overlays need to be in the Equirectangular Projection. The NASA cloud cover map is provided in the Hammer Projection.

Do any of our readers know of an easy way to convert global images from one projection to another? NASA provides this tool to convert from the Equirectangular Projection to a wide variety of other projections, but it doesn’t convert the other way.

NASA does provide daily and monthly images of cloud cover maps in the Equirectangular Projection. NASA includes the option to download them as KMZ files ready to be viewed in Google Earth.

NASA’s average cloud cover map for April, 2015 as seen in Google Earth. To see it for yourself download this KMZ file

Antarctica is of particular interest. It appears to have three distinct zones of cloud density. We guess that these correspond to:

A region offshore with pack ice.
The coastal ice shelves.
The actual land, which is higher than the ice shelves.

Can any of our readers give a more scientific explanation?

News Roundup: Polar ice caps, poachers and space detectives

October 14, 2014

Polar ice caps

The US National Snow & Ice Data Center (NSIDC) has recently updated their KML files of Arctic and Antarctic ice to include 2014 data. We have looked at their work many times in the past, as you can see here. Also of note is this press release from them explaining that the Arctic sea ice extent is shrinking and the Antarctic sea ice extent is growing. They also indicate this is the 6th lowest amount of ice recorded since they began measurements. Keep in mind that this is minimum and maximum extent of sea ice as measured by satellite and not thickness or total volume.

What interested me most about the animations showing the historical record is how the maximum extent of sea ice seems to be a very different shape each year.

Arctic sea ice extent, September 2014. The pink line is the monthly median sea ice extent 1981-2010

Poachers tracked down with Google Earth

There was an interesting story on Mongabay.com about how a poachers’ camp was identified using the imagery in Google Earth.

The ‘machamba’ (small farm with a few huts) shown in the article.

The interesting part of the story from a Google Earth perspective is that the imagery used was from July 2013 and July 2012, yet it was still useful in tracking down active poachers in 2014. To see the location in Google Earth download this KML

World’s first space detective agency launched.

See the full article here.

Because satellite imagery is being used in court cases more and more frequently, Raymond Harris and Raymond Purdy have launched the world’s first space detective agency. They will specialize in finding and obtaining appropriate satellite imagery for legal cases as well as ensuring that the acquisition and subsequent handling of imagery meets the standards required by courts.