Essentially a telescope with a focal length of 3650 mm, Meteosat's main piece of equipment is the radiometer, an instrument which is sensitive to some visible and thermal radiation. The radiometer carefully scans the Earth's surface by taking data about every piece of land as if it were reading a book line by line. Each "line" that the satellite scans is translated into a series of individual picture elements or pixels. For each pixel, the radiometer measures the energy of the different spectral bands. This measurement is digitally coded and transmitted to the ground station. The coding gives each radioactive intensity level a certain grey value giving Meteosat pictures the look of a black-and-white photograph. Meteosat pictures, however, should not be regarded as true photographs; they are a series of picture elements, and each element comprises a certain digital value according to the measured energy.