IASI optics

The IASI concept is based on the Michelson interferometer. The Earth-incoming radiation is directed into the instrument by the Scan mirror that is attached to the scan mechanism. The position of the scan mirror defines the pixel that is acquired.

The beam is then focused by mirrors M1 and M2 into the interferometer composed of a movable corner cube (CC1) attached to the corner cube mechanism (CCM) and a fix corner cube (CC2). The beam is split by means of the beam splitter. The emitted beams are refocused by the mirrors M3 and M4 to generate and direct the interference fringes into the detection unit (Cold box subsystem).

The cold box subsystem includes several Dichroic Plates allowing the incoming light to be focussed in three spectral bands B1, B2 and B3, each of them including four detectors. The analog signal is then sent from the detectors into the Main acquisition subsystem that includes the A/D converter and transfers the digital signal to the processor unit (DPS). The DPS performs the on board calibration, the Fourier transforms and generates the scientific telemetry to be downloaded in the form of a source packet.

The instrument includes two other electronic units, one ensuring the control of the Corner mechanism and its associated compensation device, the other one ensuring the scan mechanism control. The Corner cube mechanism generates the internal IASI synchronisation signal called the ASE. One cycle of the ASE corresponds to a position acquisition (i.e. one position of the scan mirror, acquisition of four pixels times three bands).

The scan mechanism is also synchronised to the ASE. One scan cycle corresponds to 64 ASE cycles (i.e. eight seconds). For each interferometer recording (i.e one cycle of the corner cube) the sampling is synchronised to a signal generated by a reference laser.

The IASI also includes an infrared imager.