The Earth's radiation enters the instrument at every revolution through a 50 cm x 80 cm aperture. The nominal repeat cycle of 15 min was the driver in selecting the number of detectors per channel and the spin rate (100 rpm). Twelve minutes are allocated to the imaging phase, leaving three minutes for calibration, retrace and stabilization. The 1 km resolution of the High Resolution Visible (HRV) channel is achieved by using 9 broad-band detection elements. The other channels are sampled at 3 km resolution by using 3 narrow-band detection elements per channel.
A combination of a Sun-synchronization
triggering pulse with the master clock signal starts the sampling of detectors signals
which lasts 30 ms. The data are then buffered in a stretching memory and multiplexed
with other necessary data in a 600 ms time frame. The raw data transmission to Earth
at L-band (3.2. Mega bits per second) is continuous.
The data handling system, serving all internal data exchanges through a bus, provides
the data formatting and synchronization tasks, through a modern processor. It also
performs Failure Detection Isolation & Recovery (FDIR), which minimizes the ground
segment workload and allows 24 hour satellite autonomy.