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. A new concept for a cluster of compact lidar systems named VAHCOLI (Vertical And Horizontal COverage by LIdars)is presented, which allows for the measurement of temperatures, winds, and aerosolsin the middle atmosphere (∼ 10–110 km) with high temporal and verticalresolution of minutes and some tens of meters, respectively,simultaneously covering horizontal scales from a few hundred meters toseveral hundred kilometers (“four-dimensional coverage”).The individual lidars (“units”) being used in VAHCOLI arebased on a diode-pumped alexandrite laser, which iscurrently designed to detect potassium (λ=770 nm), and onsophisticated laser spectroscopy measuring all relevant frequencies (seeder laser,power laser, backscattered light) with high temporal resolution (2 ms)and high spectral resolution applyingDoppler-free spectroscopy. The frequency of the lasers andthe narrowband filter in the receiving system are stabilizedto typically 10–100 kHz, which is a factor of roughly 10−5 smallerthan the Doppler-broadened Rayleigh signal. Narrowbandfiltering allows for the measurement of Rayleigh and/or resonance scatteringseparately from the aerosol (Mie) signal during both night and day.Lidars used for VAHCOLI are compact (volume: ∼ 1 m3)and multi-purpose systems which employ contemporary electronic, optical, and mechanicalcomponents. The units are designed to autonomously operate under harsh field conditions inremote locations. An error analysis with parameters of the anticipated systemdemonstrates that temperatures and line-of-sight windscan be measured from the lower stratosphere to the upper mesospherewith an accuracy of ±(0.1–5) K and ±(0.1–10) m s−1, respectively,increasing with altitude.We demonstrate that some crucial dynamical processes in the middle atmosphere, such as gravitywaves and stratified turbulence, can be covered by VAHCOLIwith sufficient temporal, vertical, and horizontal sampling and resolution.The four-dimensional capabilities of VAHCOLI allow for the performance oftime-dependent analysis of the flow field,for example by employing Helmholtz decomposition, and for carrying outstatistical tests regarding, for example, intermittency and helicity.The first test measurements under field conditions with a prototype lidarwere performed in January 2020. The lidar operated successfully during a 6-week period (night and day) withoutany adjustment. The observations covered a height range of ∼ 5–100 km and demonstrated the capabilityand applicability of this unit for the VAHCOLI concept.

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