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A UK company says it's building a constellation of satellites to gather ultra-high definition (UHD) video of Earth's surface.

London-based Sen hopes to have the first microwave oven-sized spacecraft in orbit by the middle of next year.

The idea is to provide real-time, or at least very timely, video of events unfolding on the planet, such as natural disasters.

Sen already has some UHD cameras in orbit, hosted on a Russian satellite.

These are primarily for inspection purposes, but they're also steerable to look down and so give a sense of what the company's future "EarthTV" concept might look like.

"Each of the satellites will have four cameras to put imagery into context, because that's sort of the way the human brain works," explained Charles Black, founder and CEO of Sen.

"So there'll be wide-angle imagery, from about 250m a pixel to give that country-wide view, all the way down to our highest-resolution imager which is a small telescope that will be able to do 1.5m per pixel," he told 91�ȱ� News.

Sen has laid a multi-million-euro contract with Lithuania's NanoAvionics to assemble five nano-satellites for the network. The payloads to be integrated into those spacecraft will be developed by the London company itself.

To make the videos available quickly, Sen will need access to numerous ground stations.

"We actually compress the high-definition video onboard satellite, which means we can stream it back to the ground and don't need a huge amount of bandwidth.

"We're actually using the same algorithm as Netflix to do the compression. Because we do all that in space, we can get back really high-definition videos just using flight-provenX-band transmitter."

Video from space has been available for some time.

People will be familiar with the live camera views from the space station, and a number of commercial and government operations are currently experimenting with short (20 seconds or so), high-resolution movies of spot scenes.

Moving pictures, obviously, can make it easier to understand what's happening in a location; and the individual frames in a video can be used to make rapid 3D models of landscapes and infrastructure.

As ever, companies are looking for the compelling new business model that can monetise the video capability.

Mr Black expects the EarthTV content to be used in traditional analytics, but he also wants the video to reach a much wider audience and is planning a smartphone app for the general public.

"The great power of video is storytelling. On this app you'll be able to post pictures and make comments and basically get involved as events are unfolding. We think this will be empowering for humanity to witness the evolution of the planet because it is changing every day," Mr Black said.

"There are about 350 natural disasters every year, 70 million people are displaced in the world. These are large events and videos are the best way of telling these stories."

Sen is currently funded through about 40 private investors.

Jonathan.Amos-INTERNET@bbc.co.uk, external and follow me on Twitter: