Standard Operating Procedure for aerosol high-power lidars

ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 1 / 14 Standard Operating Procedure for aerosol high-power lidars Emitter CARS & ARES Version 01 Revision 09 ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 2 / 14 Table of contents APPLICABILITY OF THE DOCUMENT............................................................................................. 4 ACRONYMS ................................................................................................................................. 4 REFERENCE DOCUMENTS ........................................................................................................... 4 1 INTRODUCTION ................................................................................................................... 5 2 INSTALLATION ..................................................................................................................... 6 2.1 Preparation of the AHL environment .................................................................................................. 6 2.1.1 Instrument location ............................................................................................................................... 6 2.1.2 Environmental temperature and humidity considerations ................................................................... 6 2.1.3 Outgoing window .................................................................................................................................. 7 2.1.4 Connection with a power supply .......................................................................................................... 7 2.1.5 Diffuse reflections ................................................................................................................................. 7 2.1.6 Interference with and from nearby instruments .................................................................................. 7 2.2 Preliminary set up of the instrument .................................................................................................. 7 2.3 On-site installation tests ..................................................................................................................... 8 2.4 Preparation of the operation and maintenance logbook ..................................................................... 8 3 OPERATION ......................................................................................................................... 9 3.1 Check up of the AHL environment ....................................................................................................... 9 3.2 Check up of the lidar ........................................................................................................................... 9 3.2.1 Laser ...................................................................................................................................................... 9 3.3 Switching on the lidar.......................................................................................................................... 9 3.3.1 Laser .................................................................................................................................................... 10 3.3.2 Polarization calibrator ......................................................................................................................... 10 3.3.3 Electronics ........................................................................................................................................... 10 3.3.4 Checking the alignment....................................................................................................................... 10 3.4 Performing the measurements .......................................................................................................... 11 3.4.1 Dark measurement ............................................................................................................................. 11 3.4.2 Normal measurement ......................................................................................................................... 11 3.4.3 Polarization measurement .................................................................................................................. 11 3.5 Finalizing the measurements ............................................................................................................. 11 3.5.1 Submission of the raw data ................................................................................................................. 11 3.5.2 Filling the operation logbook .............................................................................................................. 11 ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 3 / 14 4 MAINTENANCE .................................................................................................................. 12 4.1 Laser.................................................................................................................................................. 12 4.2 Emission optics .................................................................................................................................. 12 4.3 Receiving optics ................................................................................................................................ 12 4.4 Filling the maintenance logbook ....................................................................................................... 12 5 ADDITIONAL RESOURCES ................................................................................................... 13 ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 4 / 14 Applicability of the document These procedures apply to the ACTRIS aerosol remote sensing National Facilities and to the EARLINETACTRIS associated lidar stations. Acronyms ACTRIS - Aerosol, Clouds and Trace gases Research InfraStructure NF - National Facility CARS - Centre for Aerosol Remote Sensing AHL – Aerosol High Power Lidars PMT – Photo Multiplyer APD – Avalanche Photo Doide SCC – Single Calculus Chain ND – Neutral Density EM – Electro Magnetic Reference documents [1]. Labelling of the ACTRIS National Facilities operating Aerosol Remote Sensing instruments [2]. Guidelines for EARLINET-ACTRIS associated stations to access QA services [3]. Technical requirements for ACTRIS Aerosol Remote Sensing Observational Platforms [4]. Technical requirements for ACTRIS Mobile Platforms operating aerosol high-power lidars [5]. Quality Assurance Procedure for aerosol high-power lidars ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 5 / 14 1 Introduction The current document will act as a guideline and does not replace the user manuals and the operator’s personal experience. In case any information does not apply to your lidar instrument, please contact the appropriate representative within CARS for further support: Nikos Siomos » on data handling and processing email: [email protected] Doina Nicolae » on Actris procedures and rules email: [email protected] Volker Freudenthaler » on optics related aspects email: volker.freudent[email protected]-muenchen.de Aldo Almodeo » on instrument operation email: [email protected] Livio Belegante » on instrument operation email: [email protected] All safety procedures that apply within your research institution must be applied and should not be in contradiction with the guidelines found in this document. Before using this document, please read carefully all user manuals from all components and modules that are part or are connected to each lidar instrument. ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 6 / 14 2 Installation 2.1 Preparation of the AHL environment 2.1.1 Instrument location • The AHL instruments are designed for indoor or outdoor use. Based on the technical specifications of each instrument, the operation could be performed in outdoor or indoor conditions. o For outdoor AHL instruments, the installation could be made either outdoor or indoor; o For indoor instruments, the installation should be made in a controlled environment, safe of outdoor environmental factors; • The ALH should be installed in a secured location with limited access for unauthorized persons. • The ALH should be operated only by trained operators. • The installation site should be equipped with a sufficiently large hatch or window for accessing the atmosphere. o the layout of the ALH could be setup for vertical measurements (5° zenith measurements are indicated to avoid specular reflections from cirrus clouds) or could measure under higher zenith angles taking into consideration all eye safety measures that apply for the specific site and location; • The ALH should be installed in a clean environment, safe from dust or other sources of contamination (like reactive gases). • Direct sunlight illumination of the AHL should be avoided. o direct sunlight must never be focused by the telescope, even partially, because this can easily destroy parts of the telescope, the detection box, and the receivers; o direct sun exposure on the telescope tube and surfaces above the telescope (e.g. windows and chimneys) can also be detrimental for the measurements because it can increase the collected solar background; o direct sun exposure applied on parts of the instrument could cause temperature gradients which can affect the alignment; • To reduce the risk of rain contamination during operation, an exterior rain sensor should be installed to monitor the presence of rain drops and humidity. Automatic safety measures are suggested (proximity detectors, laser shutdown during rain episodes, hatch close during rain). 2.1.2 Environmental temperature and humidity considerations • The operating temperature should be kept stable (±2-3°C) to reduce the effects of thermal effects on the frame and opto-mechanics. • The storage and operating relative humidity (RH) should be kept in the range of 30-50% if not otherwise mentioned by the manufacturer of the instrument. https://www.researchgate.net/publication/266475572_The_effect_of_moisture_and_temperature_on_optical_c oatings_used_in_eye-safer_lasers#fullTextFileContent https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3864060/#:~:text=Keep%20optical%20components%20in%20a, with%20plenty%20of%20air%20circulation. https://www.laboratory-supply.net/blog/humidity-control-necessity/ ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 7 / 14 2.1.3 Outgoing window • The outgoing window should be wide enough to accommodate both the telescope dimensions and the outgoing beam. • The walls of the location should be painted black to reduce the diffuse reflection effects (or at least the walls next to the outgoing window). 2.1.4 Connection with a power supply • The laser power supply should be connected to a different power source from the detection power supply. o for three phase power supply, we recommend using each phase for ▪ laser power ▪ detection ▪ AC unit o it is advised to move the laser power supply as far as possible from the detection unit; • Ground loops could affect the signal quality and should be avoided. Authorized personnel should check the electrical setup of the site. https://www.bapihvac.com/application_NOTE/understanding-ground-loops-applicationNOTE/#:~:text=What%20is%20a%20Ground%20Loop,picks%20up%20interference%20currents%20easily. 2.1.5 Diffuse reflections • For indoor AHL, the outgoing lidar beam should be enclosed to reduce the diffuse reflection effects in the vicinity of the ALH unit. o a laser baffle could be installed to reduce the diffuse reflections inside the lidar location; 2.1.6 Interference with and from nearby instruments • Additional instrument that are installed close to the AHL could be a source of EM-interference. We recommend reducing the number of high power instruments installed in the vicinity of the AHL unit. 2.2 Preliminary set up of the instrument • The initial installation of the AHL instrument should be performed with authorized personnel only. • If the AHL instrument is a commercial version, the supplier of the instrument should include a full training course (on site or at the supplier’s location ) before the final delivery. • The supplier of the instrument should provide a full set of manuals that includes all the aspects and units of the AHL. The operator should study all documentation before operating the AHL. ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 8 / 14 • Once the instrument is installed, several aspects related to the layout of the instrument should be considered . o all signal cables should be isolated from all power cables (the signal cables should not touch any other cable to reduce the risk of interference); o in case of Licel detection (many lidar units are equipped with Licel detection modules) the signal detection range should be set to 0-100 mV; ▪ The maximum signal level (near range peak) of the analogue channels should be adjusted by means of neutral density filters to about 50 mV in order to avoid excessive signal induced distortions. ▪ The signal intensity should be set to the desired levels by using ND filters (not the high voltage of the detection). 2.3 On-site installation tests • Once the AHL is set-up, a full set of QA tests should be performed. • The QA tests should include: o Telecover o Rayleigh Fit o Polarization calibration o Zero Bin o Dark signal measurement NOTE: The procedure on how to perform the QA measurements can be found in the “High Power Lidar: QA operation procedures” document. 2.4 Preparation of the operation and maintenance logbook • All lidar related activities should be logged in a centralized logbook. • The logbook should include: maintenance work, lidar upgrades, measurement log (including calibration logs), ND filter replacement, etc. • A logbook template can be found by using the following links (scheduled operation, continuous operation). ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 9 / 14 3 Operation 3.1 Check up of the AHL environment • Before switching on the AHL instrument, it is important to check the integrity of the exit windows (if any). • Check the integrity of all the emission optics that are exposed to dust, humidity or other external factors. • Check all environmental parameters like temperature and humidity (around the AHL premises) to be in the predefined parameters. • Check the atmospheric conditions for low clouds (below 5 km) and rain/snow/fog • Check the weather forecast for the duration of the measurement set (in case of scheduled measurements). o for unattended continuous measurements, the AHL instrument should be equipped with failsafe systems able to properly react to external factors: ▪ switch off the AHL in case of fog ▪ switch off the AHL and close any protective windows in case of rain/snow ▪ switch off the AHL in case of unauthorized movement close to the laser emission ▪ switch off the instrument during the presence of aerial vehicles ▪ automatically switch on the instrument after the factors described above are no longer present ▪ switch off the instrument in case of technical failure (malfunction of the AHL or supporting equipment like heating or cooling) ▪ switch off the instrument in case of smoke ▪ safely switch off the instrument and close the protective windows during power failures ▪ remotely monitor the status of operation for the AHL 3.2 Check up of the lidar Prior to powering on the AHL instrument, it is essential for the operator to conduct a thorough assessment of each individual module. This includes checking the status of the laser, ensuring proper functioning of the detection system, verifying the integrity of the optics, and evaluating the instrument's resilience against potential power failures. 3.2.1 Laser • Check the replacement interval for the laser lamps, filters, water replacement (based on the information provided by the laser manufacturer). • Check the water level and the temperature values of the laser (e.g. harmonic generators, cooling unit) and any other parameters provided by each laser unit (e.g. laser power, humidity inside the laser cavity, coolant flow) and any other parameter indicated by the laser manufacturer in the user manual. 3.3 Switching on the lidar • Remove any covers or shutters from the Emission/Reception unit. • Make sure the laser radiation is not obstructed.