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Tag: aster

Scour marks in the Caspian Sea

by Timothy Whitehead on Apr.27, 2016, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

We recently came across this story about scour marks on the floor of the Caspian Sea. It is believed the scour marks are caused by ice that forms in the winter months and is then broken up and blown around scratching the bottom of the shallow sea.

The article states that the featured imagery is from Landsat 8. Landsat 8 imagery is freely available and we have featured it a number of times in the past. We thought it would be interesting to download the images and have a look for ourselves. However, when we used our usual source, the USGS’s Earth Explorer to download a quick preview image, the scratch marks are not visible at all.


Low resolution Landsat 8 image.

So, we decided to download the high quality Landsat imagery, 670 MB download. This includes a number of separate images representing different wavelengths which need to be processed to get a high quality full colour image. Previously, we have used an excellent tool from GeoSage, which at the time was free for non-commercial use. However, that is no-longer the case. So, we decided to see whether or not we could process the imagery with GIMP, an open-source image editing program. We are still learning the best way to do it, so we will not give details at this time, but we were successful and the result is seen below:


High resolution Landsat image processed with GIMP.

We then had a look at ASTER imagery for the same location. ASTER imagery has recently been made freely available and can be easily obtained here. The ASTER imagery looks about the same resolution as the high resolution Landsat imagery, but the ASTER website provides it through a handy KML file and it requires no pre-processing at all. The only disadvantage of ASTER imagery is that there appear to be fewer images of any given location than for Landsat imagery.


ASTER imagery.

The Landsat 8 image is from March 21st, 2016, while the ASTER image is from September 28th, 2015. If you look carefully you can see that the Landsat 8 image has a lot of new scratch marks. There is also an ASTER image available from April 23rd, 2016 which shows almost identical scratch-marks to the Landsat 8 image. So it would appear that the scratch-marks last over multiple seasons.

To see the different images in Google Earth download this KML file. Note that we have cropped the Landsat imagery to make the file size smaller. The ASTER imagery will automatically download from the ASTER site when you view it.

The post Scour marks in the Caspian Sea appeared first on Google Earth Blog.

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NASA and Japan make ASTER imagery available for free

by Timothy Whitehead on Apr.06, 2016, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of the instruments on NASA’s Terra satellite. Although it is a NASA satellite, the instrument belongs to Japan’s Ministry of Economy, Trade and Industry (METI). The instrument was launched in 1999 and has captured more than 2.95 million individual scenes since then. On the first of April this year NASA announced that the full catalogue of imagery is being made available to the public at no cost. The instrument, amongst other things, takes stereoscopic images that enables it to calculate altitudes albeit rather low resolution. The elevation data has always been available to the public at no cost.

The most interesting images have been collected in a gallery found here. You can also see some of the more interesting images in this article and this one.


Mt. Etna, when it erupted in July 2001. The full resolution image and description can be found here.


This image shows the 3D capabilities of ASTER. The full resolution image and description can be found here.

To access the full database of imagery, you can use the MADAS (METI AIST Data Archive System). A really nice feature is that it allows you to download the images as network-linked KML files.

The imagery has a similar resolution to Landsat imagery (approximately 30 m per pixel), so is really only suitable for viewing large scale phenomena. As with Landsat imagery its best use would be to see current events before other satellite imagery becomes available. In December last year we used Landsat imagery to look at the scar made by a tornado near Holly Springs, Mississippi. We found it relatively easy to find an ASTER image of the same region captured on March 28th, 2016, and the scar is still visible. Download this KML file to view it in Google Earth.


The image only covers a small part of the tornado’s track.

The post NASA and Japan make ASTER imagery available for free appeared first on Google Earth Blog.

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