# Three-Dimensional Wind Measurements with the Fibered Airborne Coherent Doppler Wind Lidar LIVE
## 3 Results  
### Flight Test Campaign  
Objectives of the test campaign were to evaluate LIVE lidar behavior in an aeronautical environment, to validate its performance (range and velocity measurements), and to validate LIVE 3D wind field measurements by comparisons with wind measurements from other ground based wind profilers, such as ultra high frequency (UHF) radar and ground based lidar.  
Acquisitions of LIVE lidar took place on 20, 21 February 2019, during two flights over two geographical areas of interest: a mountainous area around the city of Lannemezan and a plain area around the city of Fauga. Near Lannemezan, the Atmospheric Research Center (CRA) had two radar wind profilers operating, an UHF and a very high frequency (VHF) radar. Their data will enable Lidar measurements to be validated at high altitudes. Near Fauga, Onera has a center where a WindCube 100S (commercial Lidar from Leosphere) was operated to compare ground based lidar with airborne lidar measurements in the boundary layer. Flight altitudes of 3 km, 5 km and 7 km were used during these flight tests. Figure 6 shows LIVE lidar installed inside the ATR42 of SAFIRE, with a red aluminum plate covering the hole in the aircraft floor over the rear bottom porthele. Under this plate is the gimbal deflection turret, and over it is the lidar telescope. All optical electronic components are inside the grey racks of the bay, with the black computer on the bottom and its display deployed for operator use on top.  
As explained in the lidar signal processing chapter, displays for a short time (0.3 s) averaging of CNR and velocity along the line of sight are processed in real time thanks to GPU computing (Figure 7). The CNR is a useful coherent lidar signal quality criterion [16]. In the usual case of detection noise being limited by shot noise, the accuracy of the measured wind speed is theoretically proportional to:  
\[\sigma_{v}=\frac{1}{f(CNR)\sqrt{N}}, \tag{1}\]  
where \(N\) is the number of averaged pulses and \(f\) is an increasing function depending on lidar configuration.  
Figure 6: Picture of LIVE lidar installed inside the ATR42.  
Figure 7 shows an example of the on-board real time display. Figure 7a shows the real time display of CNR: the horizontal axis is the line of sight number (the real time display shows two complete conical scanning patterns) and the vertical axis is the range from the lidar. The CNR display first exhibits a blind zone due to the reflection of the laser pulse on the optics, followed by a low CNR area (in blue) due to low aerosol density at high altitudes. Then, the laser pulse reaches the top of the boundary layer at 1.5 km from the lidar, and a high level of lidar signal is obtained to the ground, where a strong reflection occurs at 3.3 km from the lidar. The distance from which ground reflection is obtained varies because of landforms. Figure 7b shows the real time display of wind velocity versus line of sight number. The velocity display shows a rainbow pattern mainly due to aircraft speed projection on the conical scan of the line of sight. At 700 m to 1200 m from the lidar, the real time velocity display contains many outliers due to low CNR in this range.