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Calibration Targets 5: Around the World

by Timothy Whitehead on May.23, 2017, 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

This is part of a series on calibration targets. Today we are having a look at various calibration targets around the world.

We start in India at the Shadnagar campus of the National Remote Sensing Centre where there are some calibration patterns specifically for satellite calibration:


This site in India is the only calibration site we know of that uses colours.

This site near Zuunmod, Mongolia appears to have been repainted several times.


We don’t know why the angle was changed slightly in the last repaint.

At Salon-de-Provence, France, we find a basic four square pattern:

Next we have a more complex set of patterns at Mount ShongShan, China. One reference states that there are also two rows of squares near this site, each extending over 2 km but we failed to find them.

The Sjökulla Aerial Test Range, Finland was probably designed primarily for aerial photography, but can also be used by satellites.

In South Africa, there is a single white square near Pretoria:


Designed to be exactly 100 m on a side. We don’t know why it wasn’t aligned with the cardinal directions.

The pattern at Peng-Hu, Taiwan was repainted at a different angle:

There are presumably more around the world, but we failed to find a collection listing them all. Also, in many cases temporary patterns are used, using tarpaulins or, in the case of thermal imaging, metal sheets. You can even buy specially made patterns.

There seems to be no universal agreement on what measurement is ideal. We measured some of the squares and four-square patterns:

Zuunmod, Mongolia: Concrete square on which the pattern is painted – 120 m. Painted four-square pattern – 70 m.
Four-square pattern, Salon-de-Provence, France: 60 m.
Four-square pattern, Peng-Hu, Taiwan: 60 m.
White square near Dunhuang, China: 115 m.
Four-square pattern near Boutou, China: 96 m.
White square, South Africa: 100 m.
Four-square pattern, Stennis Space Centre, USA: 50 m.
Four-square pattern, CalVal facility, India: 140 m.

Also useful for calibrating satellites are a number of sites around the globe whose altitude, colour and temperature have been carefully measured. They are typically dried up lake beds in deserts as such areas tend to be very flat and have a consistent temperature for a given time of day and day of year, and have minimal cloud cover. You can find a collection on the USGS website that has been collaboratively measured by many countries around the world. We have included it in the KML below.

To find the above locations, download this KML file.

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Calibration Targets 4: USA

by Timothy Whitehead on May.17, 2017, 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

This is the fourth in our series on calibration targets. Today we are having a look at a number of locations around the USA.

The first is this interesting pattern at Fort Huachuca, Arizona:

We came across this article which mentions patterns at Walker Field, Maryland and Eglin Air Force Base, Florida amongst others. We couldn’t find a ‘Walker Field, Maryland’ on any map, and try as we might, we couldn’t find the pattern at Eglin Air Force Base, Florida. But we did find a number of interesting sights at Eglin Air Force Base.


We are fairly sure this is a test pattern.


We are not certain whether this is a test pattern or serves some other purpose.


Various markings on this airfield appear to be for calibration.

The spots marked ‘H’ on the runways, are, we believe helicopter landing spots. Do any of our readers know what this symbol means:

Landing spot markings on runway.

There are also no less than 14 separate landing fields in the area. There are also a number of other long structures that we think are probably shooting ranges.

Here is a very old pattern at Cuddeback Lake, California:

A calibration pattern at Cuddeback Lake. There are two more that we have marked in the KML.

There are also two large bulls-eyes at Cuddeback Lake, but we are not sure what their purpose is:

A few more examples from around the USA:

Travis Air Force Base, California.


Beaufort Marine Corps Base, South Carolina.


NASA’s Stennis Space Center, Mississippi.

You may also find this article intersting. It was the source of most of the above locations.

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

Next we will be going international. We have found examples in India and South Africa. If you know of any others around the world, please let us know in the comments.

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Calibration Targets 3: China

by Timothy Whitehead on May.16, 2017, 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

This is the third in our series on calibration targets. Note that such targets are used for both satellite imagery as well as imagery captured from aircraft. Today we are looking at some calibration targets in China and other interesting sites found in the same region.

Thank you to GEB reader Kengrok for pointing us to this site showing a variety of patterns:

Next is a set of lines that we covered back in 2011

Nearby is another similar shape, next to a large square. Plain squares are actually quite common for satellite calibration targets, but this particular square probably serves some other purpose as it is not an exact square and is much larger than is typically used.

Here is a smaller square that at first sight appears to have bomb craters on it, but looking back at when it was either being made or repaired, it looks like the patches were always there.

Older image on the left.

Here are what appear to be fake houses used for target practice. The later deterioration might be due to bombs being dropped on them or it might just be weathering, but the older image certainly looks like they were bombed – but again, we may be mistaken.

Here are some large scale markings that look reminiscent of runways, but we believe were never used as such:

For scale, the small square above and bombed houses are marked with arrows.

We believe these next two are either calibration targets for radar, or tests to see if certain patterns can be used to hide objects from radar:

Although it has nothing to do with satellite calibration as far as we know, there is an enormous scale model of a region from the disputed border between China and India. We previously looked at it in 2006.

before
after

Comparison of the scale model (left) and the region it represents (right).

And finally, here is some giant writing:

We don’t know if it is intended to be read by satellites or from passing aircraft. The ground seems fairly flat so we don’t think it is intended to be read from the ground.

For the locations of all the places mentioned in this post, download this KML file

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Calibration Targets 2: Edwards Air Force Base

by Timothy Whitehead on May.10, 2017, 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

A few weeks ago we had a look at some calibration targets used by the classified Corona spy satellites. Today we are looking at a set of calibration targets and other interesting features at Edwards Air Force Base, California.

We start with one of the most obvious features at the site: The largest compass rose in the world. According to Atlas Obscura its purpose is to help with emergency landings. It was created in the 1930’s long before satellites existed and was designated a National Historic Landmark in 1985.


The compass rose points to Magnetic North.

There are several emergency runways painted on the lake bed, and there are also a couple of very large rulers:

(1) A ruler with markings at each quarter mile. (2) Another ruler with numbered markings at each mile.


(1) Another part of the ruler with quarter mile markers. (2) and (3) Markers used for calibration.

There is also a long row of special calibration markers spread out over 18 miles:

Most of the calibration markers are rectangles containing sets of three white bars in different sizes. This one also features three large squares with three different shades of grey:

Many of the markers have old aircraft or vehicles near by. Presumably used for testing how well the satellite or aircraft camera can identify them.


This marker also has a bullseye


An aircraft, helicopter, pressurised tank and other structures probably also used for testing imaging.


A variety of interesting aircraft on show near one of the entrances to the base.


More aircraft on show at one of the entrances.

Be sure to explore the whole base in Google Earth as there is a lot more to see! We have marked some of the interesting stuff we found in this KML file

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Calibration marks for a classified spy mission

by Timothy Whitehead on Apr.14, 2017, 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 interesting article about some mysterious crosses in the Arizona desert around Casa Grande. Also see here. Apparently the crosses were used as calibration targets for the Corona Missions. See here for an analysis of the resolution of the Corona imagery.


A selection of the crosses as seen in Google Earth imagery

We thought it would be interesting to try and find all the crosses in Google Earth imagery. The article referenced the location of one of them, and finding more was relatively easy as they are laid out in a grid pattern with approximately one mile between crosses. We marked quite a few, and then came across a KML file in this thread which included quite a number we had not found. We combined our collection with that KML file and now have a total of 138 markers, and an additional three that we are unsure of and one that we believe was broken up.

Wikipedia says there were originally 272 laid out in a 17×17 grid. 17×17 is 289, so some points on the grid were never filled. It is probable that some points were unsuitable due to unfavourable terrain, or the government was unable to lease the land. Many of the grid points are now residential areas or farm land so some of the crosses were probably removed. Nevertheless, there are still a number within residential areas. The distances between the crosses is not exact, and they don’t all line up exactly. Although most of them have the cross lined up with the cardinal directions, not all of them are so aligned.


The locations of all the markers we were able to find.

See the full collection in Google Earth with this KML file

We will explore other calibration targets around the world in a future post. If you know the locations of any such targets, let us know the coordinates in the comments below.

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