Observing wind, aerosol particles, cloud and precipitation: Finland's new ground-based remote-sensing network

Abstract

Abstract. The Finnish Meteorological Institute, in collaboration with the University of Helsinki, has established a new ground-based remote-sensing network in Finland. The network consists of five topographically, ecologically and climatically different sites distributed from southern to northern Finland. The main goal of the network is to monitor air pollution and boundary layer properties in near real time, with a Doppler lidar and ceilometer at each site. In addition to these operational tasks, two sites are members of the Aerosols, Clouds and Trace gases Research InfraStructure Network (ACTRIS); a Ka band cloud radar at Sodankylä will provide cloud retrievals within CloudNet, and a multi-wavelength Raman lidar, PollyXT (POrtabLe Lidar sYstem eXTended), in Kuopio provides optical and microphysical aerosol properties through EARLINET (the European Aerosol Research Lidar Network). Three C-band weather radars are located in the Helsinki metropolitan area and are deployed for operational and research applications. We performed two inter-comparison campaigns to investigate the Doppler lidar performance, compare the backscatter signal and wind profiles, and to optimize the lidar sensitivity through adjusting the telescope focus length and data-integration time to ensure sufficient signal-to-noise ratio (SNR) in low-aerosol-content environments. In terms of statistical characterization, the wind-profile comparison showed good agreement between different lidars. Initially, there was a discrepancy in the SNR and attenuated backscatter coefficient profiles which arose from an incorrectly reported telescope focus setting from one instrument, together with the need to calibrate. After diagnosing the true telescope focus length, calculating a new attenuated backscatter coefficient profile with the new telescope function and taking into account calibration, the resulting attenuated backscatter profiles all showed good agreement with each other. It was thought that harsh Finnish winters could pose problems, but, due to the built-in heating systems, low ambient temperatures had no, or only a minor, impact on the lidar operation – including scanning-head motion. However, accumulation of snow and ice on the lens has been observed, which can lead to the formation of a water/ice layer thus attenuating the signal inconsistently. Thus, care must be taken to ensure continuous snow removal.

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

“…Continuous observations are also available at Kuopio, Finland since 2011 (Hirsikko et al, 2014) and Warsaw, Poland since 2013. Profiles of backscatter and extinction coefficients from the regular EARLINET measurement can be found in the EARLINET data base (access via actris.eu) and are regularly published (The EARLINET publishing group [2000][2001][2002][2003][2004][2005][2006][2007][2008][2009][2010]2014).…”

“…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). The Polly systems have been developed for continuous, stand-alone operation in remote environments and were successfully deployed in the high northern latitudes of Finland (> 30 cm snow and < −20 • C, Hirsikko et al, 2014), in the rain forest of the Amazonian Basin with temperatures of > 30 • C and high relative humidity , and under permanent mechanical stress from motor vibrations plus rough sea aboard the research vessel Polarstern (Kanitz et al, 2013a).…”

Turbulent structure and scaling of the inertial subrange in a stratocumulus-topped boundary layer observed by a Doppler lidar

“…34), owned by the Finnish Meteorological Institute and deployed at Mace Head, on the west coast of Ireland (53 • 19 N, 9 • 53 W), from 16 February to 27 March 2012 (Hirsikko et al, 2014). Operating specifications for the Doppler lidar are given in Table 1.…”

“…Post-processing (Hirsikko et al, 2014) then applies background and focus corrections to the signal and provides calibrated attenuated backscatter coefficient profiles, together with uncertainties in the signal, attenuated backscatter and Doppler velocity derived using an approximation to the Cramér-Rao lowerbound method (Rye and Hardesty, 1993) given in O'Connor et al (2010).…”

Correction of water vapor absorption for aerosol remote sensing with ceilometers

“…Several ceilometer networks are operated by national weather services on a 24/7 basis (e.g. Hirsikko et al, 2014). The number of such systems is rapidly growing and is assumed to be a few thousand, but only data of approximately 200 ceilometers are currently available online.…”