RASTA is a W-band pulsed Doppler cloud radar (95GHz) – its characteristics are given in the table below. RASTA is capable of retrieving the 3D wind field, i.e. the three components of the wind on the vertical plane below/above the aircraft (3/6 antenna configuration), by combining independent Doppler velocity measurements from the multi-beam antenna system (we retrieved the 3 components of the wind in the aircraft’s referential, Vx is the along track wind, Vy is the cross-track wind and Vz the vertical wind). These three components can be converted into Earth referential horizontal wind components (U, V). Once the Doppler velocity is unfolded and corrected from aircraft’s motion and the reflectivity calibrated it is possible to retrieve both dynamical and microphysical cloud properties.
RASTA’s Nyquist velocity depends on the operation mode (see below). Therefore, the Doppler velocity measured by RASTA must be corrected from “folding”, which means that all Doppler velocities are measured into the Nyquist interval. The aircraft motion vector is then projected along the radial direction, and added to the Doppler measurement to remove the aircraft motion component. This component is actually added, because the aircraft motion results in an apparent Doppler contribution of opposite sign. We then use the in-situ data at the closest range to the aircraft to unfold the first measured Doppler velocity along a radial direction. Then we apply a gate to gate correction along the radial, allowing for a maximum difference of 10% of the maximum velocity between successive range gates.
| Distance (ambiguous velocity) Resolution (pulse length) | 6 Km (19.71m/s) | 7.5 Km (15.76 m/s) | 9 Km (13,14 m/s) | 12 Km (9.85 m/s) | 15 Km (7.88 m/s) | 18 Km (6.57m/s) |
| 15 m (100ns) | 400 | 500 | 600 | 800 | – | – |
| 30 m (200s) | 200 | 250 | 300 | 400 | 500 | – |
| 60 m (400ns) | 100 | 125 | 150 | 200 | 250 | 300 |
| 120 m (800ns) | – | – | – | – | 125 | 150 |
| 3-6 antennas | I and Q available | |||||
| Frequency (GHz) | 95 (3.2mm) | Z and V computed using pulse-pair technique | ||||
| Integration time (ms) | 250ms to 1s | |||||
| Energy (kW) | 1.5 | |||||
| Antenna size (cm) | 45 (0.6° beam width) and 30 (0.8°) | |||||
| Sensitivity at 1km (dBZ) (depends on configuration) | Down backward: -32 / Nadir: -35 / Down transverse: -32 / Zenith -28 | |||||
| Weight (kg)/dimensions (cm) | 110/82x102x150 | |||||
| Any antenna can be disactivated/activated in real time to adapt to the mission purpose | ||||||