Space video cameras to circle globe

Canadian group Urthecast plans to put a 16-satellite constellation in orbit to image the Earth.

Urthecast already has a pair of cameras on the International Space Station, one of which returns short videos.

The new proposal would see free-flying optical and radar sensors circling the globe by the start of the next decade.

Urthecast has asked the UK manufacturer SSTL to make the satellites, and the Spanish concern Elecnor Deimos to design the ground control segment.

The Canadian firm's vision remains the same - to try to push out high volumes of data in easily accessible ways.

It says it wants to drive Earth imagery beyond its traditional customer base, to enable new "Big Data" applications and even social media sharing.

"The goal here is to take vast amounts of Earth observation imagery from multiple sensors, and to put it all on to a very user-friendly, cloud-based platform that allows people then to manipulate the data, to use it, to display it, and to transfer it on to other types of platforms and applications," Wade Larson, Urthecast's president and chief operating officer, told BBC News.

US firm Skybox Imaging, acquired by Google last year, is also building a constellation of video cameras in orbit.
Multiple 'eyes'

One of the innovative aspects of Urthecast's proposed constellation is the intention to pair an optical satellite (which sees the Earth in visible light) with a radar platform (which can see the ground day or night and in all weathers).

Four such pairs would be launched in two planes - one going over the poles, the other plane concentrating its observations on mid-latitudes.

The radar sensor would lead, with the optical camera following about a minute behind.

Earth observation experts have long talked about the advantages that come from such an arrangement.

The all-weather capability of radar means an image of some sort is always guaranteed, while the lead spacecraft can also spot the cloud-free locations to maximise the chances of getting a picture with the following visible camera system.

Urthecast has been working on a radar sensor that will operate simultaneously in the X-band and L-band frequencies, permitting features to be seen on the ground as small as one metre and five metres across, respectively, when the system is put into a "spotlight" mode.

The optical cameras will achieve half-metre resolution, and will be switchable into a video mode, producing short segments of moving imagery at 30 frames per second.

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