Tag Archives: satellite

Snow in the Atacama Desert

A convincing argument can be made that the Atacama Desert in Chile and Argentina is the driest place on Earth. The average rainfall is one millimetre per year and some weather monitoring stations have never detected rain. This week eighty centimetres of snow fell in the region.

This is what the desert normally looks like:

And this is how it looks now:

The South Pacific is on the left of the image and Chile and Argentina on the right.

It’s difficult to differentiate between cloud and snow in the true-colour image above, but the false-colour image below makes the difference more obvious.

Areas covered in snow are bright white in the visible part of the spectrum and all the visible light detected by the camera in the second image is mapped to the red channel of the image. Ice is very absorbent in the shortwave infrared region that is mapped to the green and blue channels and therefore ice appears bright red.

Snow-covered UK seen from space

In January I posted an image from NASA’s MODIS satellite showing the UK covered in snow. I’m doing the same for the recent snow; these images were taken today (1st December) between 1110 and 1430.

The problem with this image is that snow and clouds are both white so it’s difficult to tell the difference between the two. Luckily NASA also provides some false colour imagery at long wavelengths (670 nanometres, 876nm and 2155nm) that makes this job easier.

Ice is very absorbent in the 2155nm band (shortwave infrared) that is assigned to the red channel of the image, but reflects in the visible red (670nm) and near infrared (876nm) bands that are assigned to the green and blue channels respectively, causing ice to appear cyan. Vegetation is absorbent in both the near and shortwave infrared which leaves it looking green.

Higher resolution imagery is available from the NASA MODIS Rapid Response System.

Rods from God

The problem with bombs is getting them to their target. Dropping them from the air has always been the standard approach (Austrians used air-dropped bombs during the siege of Vienna in 1849), but this is beset by problems. Even stealth aircraft like the B-2 Spirit stealth bomber and the F-22 Raptor stealth fighter are not perfect.

The Rods from God idea did away with aircraft, and with explosives altogether. The concept is very simple: a series of satellites orbit Earth armed with “tungsten telephone poles”. Once a target has been selected and the satellite is overhead, the “pole” is released and pushed towards Earth by a small rocket motor. As the pole falls to Earth from space it requires no fuel; it is powered by gravity alone.

With such a large distance to fall the rod has plenty of time to accelerate, even when the effect of air resistance is taken into account. Hitting the ground at more than ten thousand metres per second (more than 24000 mph) the rod would be able to strike targets buried deep underground.

With a mass of more than eight and a half tonnes, a rod travelling at that speed would have an energy density of fifty million joules per kilogram, far more than TNT (4.6 million joules per kilogram) or nitroglycerin (6.4 MJ/kg). With very little warning of incoming attacks, the weapon’s speed would make it almost impossible to defend against.

Fortunately (or unfortunately, depending on your viewpoint) the Rods from God (or “kinetic bombardment”) system has yet to be deployed. The most recent mention was in a 2003 US Air Force report (PDF) that classified “hypervelocity rod bundles” as a “Post-2015” technology.