The automated multiwavelength Raman polarization and water-vapor lidar Polly<sup>XT</sup>: the neXT generation

Abstract

Abstract. The atmospheric science community demands autonomous and quality-assured vertically resolved measurements of aerosol and cloud properties. For this purpose, a portable lidar called Polly was developed at TROPOS in 2003. The lidar system was continuously improved with gained experience from the EARLINET community, involvement in worldwide field campaigns, and international institute collaborations within the last 10 years. Here we present recent changes of the setup of the portable multiwavelength Raman and polarization lidar Polly XT and discuss the improved capabilities of the system by means of a case study. The latest system developments include an additional nearrange receiver unit for Raman measurements of the backscatter and extinction coefficient down to 120 m above ground, a water-vapor channel, and channels for simultaneous measurements of the particle linear depolarization ratio at 355 and 532 nm. Quality improvements were achieved by systematically following the EARLINET guidelines and the international PollyNET quality assurance developments. A modified ship radar ensures measurements in agreement with air-traffic safety regulations and allows for 24/7 monitoring of the atmospheric state with Polly XT .

An overview of the first decade of Polly<sup>NET</sup>: an emerging network of automated Raman-polarization lidars for continuous aerosol profiling

“…The data of all channels are acquired with a vertical resolution of 7.5 m in temporal steps of 30 s (laser frequency 20 Hz). Further system details are given by Althausen et al (2009) and Engelmann et al (2016). The specific system setup at each location is given in Table 1.…”

“…Error bars for the automatic retrievals are not presented for clarity of the illustration. Typically, uncertainties are in the range of 5-10 % for the backscatter coefficient and 10-20 % for the extinction coefficient retrieved with the Raman method Baars et al, 2012;Engelmann et al, 2016).…”

“…From the profile of the volume linear depolarization ratio (EARLINET standards, see ) and the backscatter coefficient profile, the particle linear depolarization ratio is calculated. For high quality in the depolarization measurements, a 90 • -calibration is automatically performed for the TROPOS, FMI, and UW systems three times a day since 2012 (for system details and overview see Engelmann et al, 2016, and Table 1). Before the implementation of the 90 • -calibration, the calculation of the linear depolarization ratio was also possible, but needed manual calibration and processing.…”

“…Motivated by the urgent need for robust multiwavelengthRaman-polarization lidars that are easy to operate and allow aerosol typing, a portable lidar system, called Polly, has been developed at the Leibniz Institute for Tropospheric Research (TROPOS) with international partners during the last decade Engelmann et al, 2016). The aim was to develop a sophisticated multiwavelength-Ramanpolarization lidar for scientific purpose, but with the advantages of an easy-to-use and well-characterized instrument with same design, same automated operation, and same centralized data processing in line with the CIMEL Sun photometer of AERONET (Holben et al, 2001).…”

Using paraxial approximation to describe the optical setup of a typical EARLINET lidar system

“…The wide-angle RFOV is not an optimal solution for minimizing the DFO, since in that case (a) the signal will be contaminated with more sky background light, and (b) multiple scattering effects have to be taken into account, especially for case studies of optically thick targets (i.e., water and ice clouds; e.g., Eloranta, 1998;Wandinger, 1998). Nevertheless, there are systems employing two telescopes, one for the short ranges and the other for the far ones, with the short-range one having a wider RFOV angle (e.g., Engelmann et al, 2016). However, such setups are more complicated and their signals demand special treatment during the retrieval processing schemes.…”