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 for the measurement of 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 a 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, which is currently designed to detect potassium (λ=770 nm), and 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 narrowband 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. Narrowband filtering allows for the measurement of Rayleigh and/or resonance scattering separately 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 mechanical components. The units are designed to autonomously operate under harsh field conditions in 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−1, 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, and horizontal sampling and resolution. The four-dimensional capabilities of VAHCOLI allow for the performance of time-dependent analysis of the flow field, for example by employing Helmholtz decomposition, and for carrying out statistical tests regarding, for example, intermittency and helicity. The first test measurements under field conditions with a prototype lidar were performed in January 2020. The lidar operated successfully during a 6-week period (night and day) without any adjustment. The observations covered a height range of ∼ 5–100 km and demonstrated the capability and applicability of this unit for the VAHCOLI concept.

Opinion: Recent Developments and Future Directions in Studying the Chemistry of the Mesosphere and Lower Thermosphere

“…This will ultimately require rocket-borne sampling of the particles in the MLT, either directly or in the form of meteoric residuals in mesospheric ice particles. The COverage by LIdar) instrument (Lübken and Höffner, 2021).…”

Physics in the mesosphere/lower thermosphere: A personal perspective

“…Lidars typically measure at one location only. However, recent developments promise to cover a substantial horizontal region [VAHCOLI = Vertical And Horizontal COverage by LIdar (Lübken and Höffner, 2021)].…”

“…Lidars offer the only method to measure GW and tides quasicontinuously (clear sky conditions provided) from the troposphere to the lower thermosphere, both in temperatures (potential energy) and in winds (kinetic energy). Recent developments in lidar technology promise to extend this capability from local to regional scales (Lübken and Höffner, 2021). Note that the morphology of gravity waves can only be treated correctly if the background wind field is known, which is nowadays the case for some lidars (Baumgarten, 2010;Lübken and Höffner, 2021).…”

“…Recent developments in lidar technology promise to extend this capability from local to regional scales (Lübken and Höffner, 2021). Note that the morphology of gravity waves can only be treated correctly if the background wind field is known, which is nowadays the case for some lidars (Baumgarten, 2010;Lübken and Höffner, 2021).…”

Aerosol measurements in the tropo- and stratosphere by spectral splitting of Rayleigh and Mie signals within a compact lidar of 1 m3

“…For understanding large scale phenomena like gravity waves and tides in the middle atmosphere, the IAP developed VAHCOLI (Vertical And Horizontal COverage by LIdar) [1] a compact and transportable Doppler Lidar platform with daylight capability. The system is capable of studying Mie scattering (aerosols), Rayleigh scattering (air molecules) and resonance fluorescence on free potassium atoms from the troposphere to the lower thermosphere.…”