Aeolus data calibration
Aeolus will implement various calibration procedures to obtain the optimum possible accuracy:
- During each shot of the ALADIN instrument, part of the emitted beam is injected into the receivers. This not only ensures that the jitter of the laser frequency is kept at an acceptable level, but also allows the difference in the frequency between the two receivers to be measured.
- Ground echoes are used to remove biases in frequency measurements. This is only really accurate for the Mie receiver. The offsets in the Rayleigh channel are compensated for by using the cross-calibration provided by the shot-to-shot laser measurements.
- In the absence of ground echo, on-board sensor data such as star trackers, gyroscopes and GPS are used to estimate the satellite and Earth Doppler shifts. This allows for a rough compensation of biases. On-board estimates made in this way are reset each time a ground echo is available.
- The frequency response of both receivers is periodically calibrated by scanning the laser transmitter over the dynamic range.