Technical requirements for ACTRIS Aerosol Remote Sensing Observational Platforms

22 December 2025 1 / 14 Technical requirements for ACTRIS Aerosol Remote Sensing Observational Platforms Emitter CARS & ARES Version 01 Revision 01 ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 2 / 14 Table of contents APPLICABILITY OF THE DOCUMENT ................................................................................................................. 3 ACRONYMS ...................................................................................................................................................... 3 REFERENCE DOCUMENTS ................................................................................................................................. 3 1 INTRODUCTION ....................................................................................................................................... 4 2 GENERAL CONSIDERATIONS .................................................................................................................... 5 2.1 PRINCIPLES APPLICABLE TO ACTRIS AEROSOL REMOTE SENSING MEASUREMENTS ................................................... 5 2.2 GENERAL REQUIREMENTS FOR THE FACILITY ..................................................................................................... 5 3 TECHNICAL REQUIREMENTS FOR THE AEROSOL HIGH-POWER LIDARS .................................................... 7 3.1 TECHNICAL REQUIREMENTS FOR THE INSTRUMENT ............................................................................................ 7 3.2 REQUIREMENTS RELATED TO THE QUALITY ASSURANCE OF THE MEASUREMENTS..................................................... 8 4 TECHNICAL REQUIREMENTS FOR THE AUTOMATIC SUN/SKY/LUNAR PHOTOMETER ............................ 10 4.1 TECHNICAL REQUIREMENTS FOR THE INSTRUMENT .......................................................................................... 10 4.2 REQUIREMENTS RELATED TO THE QUALITY ASSURANCE OF THE MEASUREMENTS................................................... 11 ANNEX 1. THINGS TO CONSIDER WHEN PURCHASING A NEW LIDAR ........................................................ 12 ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 3 / 14 Applicability of the document These technical requirements apply to ACTRIS Aerosol Remote Sensing Observational Platforms. Acronyms • ACTRIS - Aerosol, Clouds and Trace gases Research InfraStructure • ACTRIS GA – ACTRIS General Assembly • ARES – Aerosol Remote Sensing unit of the ACTRIS Data Centre • ARS – Aerosol Remote Sensing • CARPORT – CARS workflow management portal • CARS - Centre for Aerosol Remote Sensing • CLU – Cloud Remote Sensing unit of the ACTRIS Data Centre • CCRES - Centre for Cloud Remote Sensing • DC – Data Centre • MP – Mobile Platform • NF - National Facility • NRT – Near-real time (less than 3 days from the measurements) • OP – Observational Platform • PI – Principal Investigator • RI Comm – Research Infrastructure Committee • RRT – Real-real time (less than 3 hours form the measurement) • SCC – Single Calculus Chain Reference documents 1. Documentation on technical concepts and requirements for ACTRIS Observational Platforms 2. ACTRIS NF Labelling Plan 3. Descriptions of the workflows between ACTRIS components 4. ACTRIS Data Management Plan 5. CARS implementation plan 6. ACTRIS vocabulary 7. Guidelines for EARLINET-ACTRIS associated stations to access QA services 8. Labelling of the ACTRIS National Facilities operating Aerosol Remote Sensing instruments 9. Measurement Guidelines for aerosol high-power lidars 10. Measurement Guidelines for automatic sun/sky/lunar photometers 11. Standard Operation Procedure for aerosol high-power lidars 12. Standard Operation Procedure for automatic sun/sky/lunar photometer 13. Quality Assurance Procedure for aerosol high-power lidars 14. Quality Assurance Procedure for automatic sun/sky/lunar photometer ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 4 / 14 1 Introduction Aerosol remote sensing instruments as considered by ACTRIS are: a) aerosol high-power lidars; b) automatic sun/sky/lunar photometers; c) automatic low-power lidars and ceilometers. ACTRIS Aerosol Remote Sensing National Facilities operate aerosol high-power lidars and automatic sun/sky/lunar photometers. Note: The technical requirements in this document do not apply to automatic low-power lidars / ceilometers which are currently operated as part of the ACTRIS Cloud Remote Sensing National Facilities ACTRIS Aerosol Remote Sensing National Facilities operate aerosol remote sensing instruments either as Observational Platforms (at fixed site) or as part of a Mobile Platform (movable). In order to be labelled as ACTRIS National Facility, both the Aerosol Remote Sensing Observational Platforms, and the Mobile Platforms operating aerosol remote sensing instruments must undergo the labelling process. The labelling process is described in Labelling of the ACTRIS National Facilities operating Aerosol Remote Sensing instruments Note: The technical requirements in this document do not apply to ACTRIS Mobile Platforms embedding aerosol remote sensing instruments Aerosol remote sensing instruments can also be operated by the EARLINET (aerosol high-power lidars), AERONET (automatic sun/sky/lunar photometers) and E-PROFILE (automatic low-power lidars and ceilometers). Note: The technical requirements in this document do not apply to EARLINET, AERONET and E-PROFILE stations which are not part of ACTRIS. This document describes the requirements for the facility and the instruments, to be fulfilled by the ACTRIS Aerosol Remote Sensing Observational Platforms. ➢ General requirements for the facility are described in Section 2. ➢ Technical requirements for the instruments are presented in Section 3.1 and Section 0. ➢ Technical requirements related to the measurements Quality Assurance are summarized Section 3.2 and Section 4.2. Details can be found in instrument-specific Standard Operation Procedures and in instrument-specific Quality Assurance Procedures. ➢ Things to consider when purchasing a new lidar are presented in Annex 1. ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 5 / 14 2 General considerations 2.1 Principles applicable to ACTRIS aerosol remote sensing measurements ACTRIS Aerosol Remote Sensing Observational Platforms must comply with the following principles: Principle 1: The facility must comply with the general requirements Principle 2: The lidar and the photometer must comply with the specific technical requirements. Principle 3: The protocols for operation, measurement and quality assurance issued by of the Centre for Aerosol Remote Sensing (CARS) and the Aerosol Remote Sensing unit of the ACTRIS Data Centre (ARES) must be applied. If available, calibration and quality assurance tools approved by CARS must be implemented at the National Facility. Principle 4: Participation of the National Facility to QA/QC activities scheduled by CARS is mandatory. In addition, and if necessary, CARS may schedule direct comparisons, site audits, training sessions and/or other actions. Principle 5: Measurements and data workflow recommended by CARS & ARES must be followed. The National Facility has the responsibility to securely and permanently store and archive native data from the instruments and Level 0 data (raw data in the format to be submitted to the DC units). In order to guarantee secure store and archive of such data, the National Facilities should organize their archive in two different physical locations. 2.2 General requirements for the facility The minimum setup of an ACTRIS aerosol remote-sensing station consists of a one-wavelength Raman with polarization discrimination capability, and a sun/sky photometer. The optimum setup of an ACTRIS aerosol remote-sensing station consists of a three-wavelength Raman or high spectral resolution lidar with polarization discrimination capability and an automatic sun/sky and moon photometer (optionally also polarized) according to ACTRIS/AERONET standards, both operating continuously. In order to be evaluated as technically compliant, an Aerosol Remote Sensing must fulfill the following requirements: 1) Synergy requirements An ACTRIS Aerosol Remote Sensing Observational Platform should operate an aerosol high-power lidar and an automatic sun/sky/lunar photometer. These instruments should be collocated, i.e. situated in the same mixed layer in order to measure the same atmosphere. The maximum allowed horizontal distance is 1 km. Although not mandatory, it is advisable that the Aerosol Remote Sensing Observational Platforms also operate a collocated automatic low-power lidar / ceilometer. 2) Technical requirements for the aerosol high-power lidar a) The aerosol high-power lidar must fulfill at least the mandatory technical requirements described in Section 3.1 b) The facility must implement the standard operating procedures as described in Standard Operation Procedure for aerosol high-power lidars ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 6 / 14 c) The facility must implement the QA/QC procedures, as described in Quality Assurance Procedure for aerosol high-power lidars d) The facility must participate in the QA/QC actions scheduled by CARS, as summarized in Section 3.2 3) Technical requirements for the automatic sun/sky/lunar photometer a) The automatic sun/sky/lunar photometer must fulfill at least the mandatory technical requirements described in Section 0. b) The facility must implement the standard operating procedures as described in Standard Operation Procedure for automatic sun/sky/lunar photometer c) The facility must implement the QA/QC procedures, as described in Quality Assurance Procedure for automatic sun/sky/lunar photometer d) The facility must participate in the QA/QC actions scheduled by CARS, as summarized in Section 4.2 4) Other requirements a) The facility must implement the measurement guidelines for the aerosol high-power lidar, as described in Measurement Guidelines for aerosol high-power lidars b) The facility must implement the measurement guidelines for the automatic sun/sky/lunar photometer, as described in Measurement Guidelines for automatic sun/sky/lunar photometers ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 7 / 14 3 Technical requirements for the aerosol high-power lidars The following technical requirements apply to ACTRIS aerosol remote sensing National Facilities and to EARLINET-ACTRIS associated stations. Measurements of aerosol extinction, backscatter and depolarization-ratio profiles are to be performed at least at one wavelength, either 355 or 532 nm. 3.1 Technical requirements for the instrument Technical system parameters such as laser power, telescope aperture, receiver bandwidth and data acquisition system must be chosen such that profiles can be acquired throughout the troposphere up to the lower stratosphere with the required accuracy and temporal and spatial resolution. A separate near-range receiving system is recommended for observations in the lower planetary boundary layer. Configurations may vary to account for climatic circumstances, e.g., the typical height of the boundary layer for the location of the NF. Tab. 1 Summary of mandatory and recommended technical requirements Parameter Mandatory (minimum requirements) Recommended (optimum requirements) Channels 1β + 1α + 1δ at 355 nm or 1β + 1α + 1δ at 532 nm 1β + 1α + 1δ at 355 nm and 1β + 1α + 1δ at 532 nm and 1β at 1064 nm Height resolution raw (recorded signal) ≤ 15 m ≤ 3.75 m Time resolution raw (recorded signal) ≤ 60 s ≤ 10 s Full overlap (m) ≤ 3001 ≤ 200 Minimum altitude range of the 355 raw signal (to be obtained in defined conditions, see below) ≥ 15 km Minimum altitude range of the 532 raw signal (to be obtained in defined conditions, see below) ≥ 15 km Minimum altitude range of the 1064 raw signal (to be obtained in defined conditions, see below) ≥ 10 km Features ⚫ Laser alignment (alignment camera2) ⚫ Polarisation calibration ⚫ Telecover ⚫ Dark signal measurement ⚫ Unattended operation ⚫ Automatic laser alignment ⚫ Automatic polarization calibration 1 This value must be reached in max. 5 years form the initial acceptance, for at least one couple of elastic and Raman channels. The applicability of the overlap correction will be investigated. 2 Only if the assembly of a camera is not possible, alternative “online” control mechanisms for the laser alignment can be approved after verification by CARS. ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 8 / 14 ⚫ Photodetector eye piece3 ⚫ Pretrigger ≥20 µs ⚫ Automatic telecover ⚫ Automatic dark signal measurement ⚫ Photodetector eye piece ⚫ Pretrigger ≥20 µs ⚫ Temperature and humidity control ⚫ Lidar status control ⚫ Eye safety (automatic shut-down) Defined conditions for which the minimum altitude range of the raw signals must be obtained: With clean air in the far range and an averaging time 1 hour: • for 355 and 532 nm with aerosol OD 0.4 in the lower troposphere and a range resolution of 250 m, the SNR in the cross and parallel channels, respectively, must be: o 355 nm: SNR ≥17 (cross) and ≥65 (parallel) at 15 km; o 532 nm: SNR ≥11 (cross) and ≥55 (parallel) at 15 km; • for 1064 nm with aerosol OD 0.13 in the lower troposphere and a range resolution of 500 m the SNR in the total signal must be: SNR ≥9 at 10 Km. Recommendations for purchase of aerosol high-power lidars are provided in Annex 1. 3.2 Requirements related to the Quality Assurance of the measurements Quality control of the aerosol high-power lidar Level 0 data is in the responsibility of the instrument operator, with the support of CARS. ACTRIS high-power aerosol lidars should apply specific calibration and quality assurance measures and tools. Quality assurance measures for aerosol lidars include internal and external check-ups. External check-ups refer to: 1. Direct comparison with a reference lidar systems operated by CARS. Intercomparison measurements with one of the reference lidar systems shall be performed for new systems and after major upgrades if CARS resources allow it. 2. Analysis of the QA tests by CARS. The QA tests will be analyzed regularly by CARS experts in order to check and approve the instrument configuration in the Single Calculus Chain (SCC). QA tests to be performed by the operator and reported to CARS are: Tab. 2 Mandatory Quality Assurance tests to be submitted to CARS: QA test Purpose Periodicity for reporting Telecover test optical alignment Once per year AND Each time the lidar is moved AND 3 Alternative methods to overcome the sensitivity inhomogeneity of the photodetectors can be approved after verification by CARS. ACTRIS Centre for Aerosol Remote Sensing C . A . R . S . 22 December 2025 9 / 14 Each time significant hardware interventions are done to the instrument Rayleigh fit test optical alignment Once per year AND Each time the lidar is moved AND Each time significant hardware interventions are done to the instrument Polarization calibration calibration Each time the lidar is moved AND Each time significant hardware interventions are done to the instrument Zero bin test electronic synchronization Once AND Each time significant hardware interventions are done to the instrument Dark signal measurement electronic distortion subtraction Once AND Each time significant hardware interventions are done to the instrument 3. Site audits. Site audits will be scheduled and performed by CARS for new National Facilities and/or in case of persistent instrumental problems. Internal check-ups refer to: 1. Regular performance of the QA tests. Operators are advised to perform the QA tests (see Tab. 2) as often as possible but at least monthly, and check the instrument’s performance over time. 2. Implementation and use of the QA/QC tools approved by CARS. Specific tools developed by CARS can be downloaded from CARS website. These tools have to be applied regularly based on the recommendations and under the supervision of CARS. Details referring to the QA/QC of the measurements are described in Quality Assurance Procedure for aerosol high-power lidars. Details referring to the operation of the instrument are described in Standard Operation Procedure for aerosol high-power lidars.