AATSR has the same signal channels and embodies exactly the same viewing principle as ATSR-2. These are: thermal channels at 3.7, 10.8, and 12 microns wavelength; and reflected visible/near infrared channels at 0.555, 0.659, 0.865, and 1.61 microns wavelength. Like its predecessors, ATSR-1 and ATSR-2, AATSR has on-board calibration systems for the thermal channels, using two black bodies, viewed every scan, and for the visible channel a sample of solar radiation scattered from a diffuser plate is viewed once per orbit. Unlike ATSR-2 it maintains full digitisation of all channels all the time and has no limited-data-rate operating modes.