VHRR (Very High Resolution Radiometer) is a 3 channels device: visible channel is 0.47-0.7 µm, infrared channel is 10.5-12.5 µm and water vapour channel is 5.7-7.1 µm. In the visible channel, the resolution is 2 km. In the infrared and water vapour channels, the resolution is 8 km.
The radiometer scans the earth's surface line by line; each line consists of a series of individual image elements or pixels. For each pixel the radiometer measures the radiative energy of the different spectral bands. This measurement is digitally coded and transmitted to the ground station for pre-processing before being disseminated to the user community.