Image Processing of Big Data

Discussing computers, computers are of course used to reconstruct the images recorded by observatories, whether terrestrial or orbital, space probes as well as to build images from the radio signals picked up by radio telescopes.

A space telescope has a sensor consisting of a CCD camera (Charge Transfer Device) cooled near absolute zero to reduce the electronic noise. It contains photosites (pixels) that convert the radiation into electrical signals that are stored in a memory space. The signal is then transmitted on the ground by ultra-short radio waves to one of the satellite dishes of the DSN network or directly to an institution in charge of the project. It is then a signal processing program that is responsible for converting it as an image on the screen.

Today, as we have explained, professionals have computer infrastructures and in particular high-performance graphics cards containing thousands of graphics processor cores (GPU) without which they could no longer process the images, so much their size. is important.

There are only three examples. The images taken by the MRO spacecraft in orbit around Mars are each 120 MB, ESO VST is 368 MB.

In 8 years (2000-20008), the Sloan Sky Digital Survey (SDSS), the largest astronomical observation program, recorded 140 TB of images. Thanks to the help of supercomputers, it allowed astronomers to explore the deep universe in 3D up to 1.3 billion light years (z = 0.1). The project continues today as part of the SDSS III with massive spectroscopic analysis, including quasars.

We will take the time to detail these gigantic volumes of data, the bit rates they require and how they are managed in the Big Data article.

Image processing is a specialty in its own right. The images taken by the Hubble Space Telescope for example are recorded in black and white at different wavelengths between 110 to 1100 nm (200-400 nm for the deep sky) through three colored filters, respectively blue, green and red. . It is during the image processing carried out on the ground that the color image is obtained by additive synthesis of the same three fundamental colors.

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