## 5 Measurement Campaign  
### Description of the Flight Chain  
[PERSON] et al. [24] have developed a sounding system that combines both the flexibility of the free balloons and the ability to recover the instrumentation such as with tethered balloons. This work was based on the development of a two-balloon system that was used to perform soundings at sea on the ship \"Princesse Alice\" [25] in the early twentieth century. The balloon system used successfully in our  
Figure 6: **(a)** Time series measurement; **(b)** Allan deviation plot on a logarithmic scale showing two different behaviors. First, a linear decay at the beginning (slope = \(-1/2\)) indicating linear decrease in deviation with the averaged number of the data, i.e., efficient white noise reduction and hence improvement in the measurement precision. Second, the instabilities of the instrumental system nevertheless counterbalance the noise reduction given by average and the deviation increases due to undesired drift noise. Figure 7: **(a)** Picarro vs. AMULSE intercomparison. On the upper panel Picarro’s data are plotted in black while AMULSE’s data are in red. The lower panel shows the residual uncertainties which are 7.39% at the higher concentrations and at the beginning of the intercomparison and about 0.01% at lower concentrations. The standard deviation of the uncertainty is equal to 1.2% for all the intercomparison; **(b)** The correlation between the AMULSE and Picarro’s measurements. A linear fit was applied with an adjusted R\({}^{2}\) of 0.99132.  
measurement and described by [PERSON] et al. [PERSON] _et al._ (2011) is a low cost device designed to be easily implemented on any free balloon sounding system to monitor the physico-chemical parameters and characteristics of the atmosphere. The balloon system was tested in 2011 (BLLAST for Boundary Layer Late Afternoon and Sunset Turbulence) and in Passy--France 2015 campaign ([PERSON] _et al._, 2015). The two-balloon (Figure 8a) system is referred to one carrier balloon and one slowing balloon in order to lift up the instrumentation (upward sounding at 5 m/s). Balloons are inflated using tares to ensure good repeatability of ascent and descent balloon speed. The carrier balloon is connected by a wire to the rawinsonde and its separation is triggered either at a specific atmospheric pressure previously fixed before the launch, or via a satellite communication system based on an Iridium element implemented on the AMULSE electronic board or at a specific timeout fixed in advance. When the carrier balloon is released, the instrumentation descends with the slowing balloon (downward sounding at 3.4 m/s was obtained through experimentation and proved to be a good compromise ([PERSON] _et al._, 2015)). A meteorological radiosonde with a GPS probe fixed on the instrumentation and connected to a ground station allows the determination of the landing point which helps recovery of the instrumentation (Figure 8b). A flight simulation software is used to estimate the trajectories and the landing point of the probe. This estimation is based on the forecast vertical profile of horizontal wind with Meteo-France operational Numerical Weather Prediction models Applications de la Recherche a l'Operationnel a Meso-Echelle (AROME) ([PERSON] _et al._, 2015; [PERSON] _et al._, 2015) and Action de Recherche Petite Echelle Grande Echelle (ARPEGE) ([PERSON] _et al._, 2015; [PERSON] _et al._, 2015) at the launching site, the hypothesis on both the ascending/descending speed of the system and the release of the carrier balloon. A measured vertical profile of horizontal wind by the recent sounding can also be used. The trajectories of the balloon are updated in real time by the rawinsonde RS92 measured wind. Figure 9 shows the different stages of the AMULSE flight. In Figure 9a, the AMULSE is well fixed on the two-balloon system and ready to fly (Figure 9b). The two-balloon launch is shown on the Figure 9c.