VAHCOLI, a new concept for lidars: technical setup, science applications, and first measurements

Abstract

Abstract. A new concept for a cluster of compact lidar systems named VAHCOLI (Vertical And Horizontal COverage by LIdars) is presented which allows to measure temperatures, winds, and aerosols in the middle atmosphere (∼10–110 km) with high temporal and vertical resolution of minutes and some tens of meters, respectively, simultaneously covering horizontal scales from few hundred meters to several hundred kilometers (four-dimensional coverage). The individual lidars (units) being used in VAHCOLI are based on a diode-pumped alexandrite laser currently designed to detect potassium (λ = 770 nm), as well as on sophisticated laser spectroscopy measuring all relevant frequencies (seeder laser, power laser, backscattered light) with high temporal resolution (2 ms) and high spectral resolution applying Doppler-free spectroscopy. The frequency of the lasers and the narrow-band filter in the receiving system are stabilized to typically 10–100 kHz which is a factor of roughly 10−5 smaller than the Doppler-broadened Rayleigh signal. Narrow-band filtering allows to measure Rayleigh and/or resonance scattering separately from the aerosol (Mie) signal, all during night and day. Lidars used for VAHCOLI are compact (volume: ∼1 m3) and are multi-purpose systems employing contemporary electronical, optical, and mechanical components. The units are designed to autonomously operate under harsh field conditions at remote locations. An error analysis with parameters of the anticipated system demonstrates that temperatures and line-of-sight winds can be measured from the lower stratosphere to the upper mesosphere with an accuracy of ±(0.1–5) K and ±(0.1–10) m/s, respectively, increasing with altitude. We demonstrate that some crucial dynamical processes in the middle atmosphere, such as gravity waves and stratified turbulence, can be covered by VAHCOLI with sufficient temporal/vertical/horizontal sampling and resolution. The four-dimensional capabilities of VAHCOLI allow to perform time-dependent analysis of the flow field, for example employing Helmholtz decomposition, and to carry out statistical tests regarding intermittency, helicity etc. First test measurements under field conditions with a prototype lidar being built for VAHCOLI were performed in January 2020. The lidar operated successfully during a six week period (night and day) without any adjustment. These observations covered a height range of ∼5–100 km and demonstrate the capability and applicability of this unit for the VAHCOLI concept.

Ground-based general purpose Doppler-lidar: a technology for Doppler-aerosol measurements and beyond

“…At the same time the potassium layer was observed even though the optics of receiver and telescope have been preliminary and only a low efficiency is achieved. More details about this measurement is given in [8][8] [9]. The Doppler wind is finally measured by tilting the lidar approx.…”

“…The IAP replaces currently the former mobile Doppler lidar by a network of Doppler lidars based on a diode-pumped Alexandrite laser [8]. The main goal of this network called VAHCOLI (Vertical And Horizontal COverage by LIdar) is 4D-sampling of the atmosphere by a network of identical mobile state-of-the-art Doppler lidars.…”

“…Test measurement show that no steering of the laser is required for many hours even though operating with a small field of view. Details on design and manufacturing of the lidar system as well as on the development of a Doppler lidar network consisting of several lidar systems as presented here can be found in [8]. Figure 3 shows the optical system, which we built especially for the remaining space left by the telescope.…”