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WP6: Lidar Calibration Centre

WP6 Objectives

To offer a wide range of services to test and calibrate lidars and ceilometers, starting from the characterization and optimization of single components, to the assessment of the whole system’s performance. At least 20 systems with different configurations will be calibrated (at level of components, blocks, channels), 10 systems will be intercompared to the EARLINET’s reference systems, and 40 operators will be trained to check and maintain the calibration.

Provision of access to the following infrastructure(s): Lidar Calibration Centre (LiCal)  

Description of the infrastructure
Name of the infrastructure (and its installations, if applicable): Lidar Calibration Centre (LiCal), a multi-installation facility:
1.    Lidar Calibration Training Laboratory (LiCalTrain)
2.    Lidar Components Testing Laboratory (LiCoTest)
3.    Mobile reference lidar (POLIS)
4.    Fixed reference lidar (MUSA)
5.    Mobile reference lidar (MUSA-mobile)
6.    Lidar Remote Quality Assurance (LiReQA)
7.    Lidar Check-up Unit (LiCheckUnit)
Location (town, country) of the infrastructure: The National Institute of R&D for Optoelectronics (INOE), located in Magurele, Romania is hosting the Lidar Calibration Training Laboratory and the Lidar Components Testing Laboratory. Ludwig Maximilians University, Meteorological Institute Munich in Germany (LMU) operates the Mobile reference lidar POLIS (at the user’s site), the Lidar Remote Quality Assurance and the Lidar Check-up Unit (at the user’s site). The Institute of Methodologies for Environmental Analysis- National Research Council of Italy (CNR) operates the Reference lidar MUSA in two configurations: at fixed location in Potenza, Italy, and mobile at the user site. The three sites were selected based on the existing infrastructure and expertise, to provide specific services: components characterization and calibration training – INOE, Romania; remote testing, inspection and optimization – LMU, Germany; direct intercomparisons – LMU, Germany and CNR, Italy. An added value of distributing the LiCal installations between three countries is a perfect coverage of all possible lidar sites (in terms of location and instrument configuration), as well as a long-term sustainability.

Web site address: lical.inoe.ro

Annual operating costs (excl. investment costs) of the infrastructure (€): 619977 €/year (unit cost)

Description of the infrastructure: Lidar calibration is a complex process, relying on the quantitative assessment of the instrument’s performance (systematic errors) and its continuous control. LiCal combines a series of direct and remote techniques, involving both the equipment and the operators, to ensure a proper evaluation, maintenance, calibration and operation of the lidar. Each of the seven installations has a specific role in this process, offering together a complete characterization and optimization of lidar instruments. (see Fig. TNA1.1):
•    The Lidar Calibration Training Laboratory (LiCalTrain) operates a multiwavelength depolarization Raman lidar, a scanning depolarization UV lidar, a tropospheric ozone lidar and complementary instrumentation (Scanning Microwave radiometer, C-ToF Aerosol Mass Spectrometer, Aerosol Chemical Speciation Monitor, Aethalometer, Aerodynamic Particle Sizer, Integrating nephelometer), as well as dedicated software tools to test, characterize, calibrate and validate lidar measurements. It is ideal to train the operators how to apply regular check-ups and maintain the calibration.
•    The Lidar Components Testing Laboratory (LiCoTest) has a long expertise in characterizing laser beams and optical components using power and energy meters, Tektronics oscillioscopes, Beam Profiler with M2 option, BeamScope, goniometer and interferometer. This lab also covers spectroscopic ellipsometry measurements and spectral characterization of interferential filters, beam splitters and dichroic mirrors, characterization of the aging process with the Perkin Elmer UV-VIS NIR Spectrometer. Electronic blocks are tested with Agilent and Tektronics pulse/form generators and analysers. This installation delivers full characterization of the optical and electronic components which are part of the transmitter and receiver, essential when assessing the instrumental (systematic) errors.  
•    The mobile reference lidar POLIS measures at two elastic wavelengths - 355 nm and 532 nm  and their N2-Raman shifted wavelengths - 387 nm and 607 nm, and linear depolarisation ratio at 532 nm and 355 nm. It can be easily moved to the user’s site to perform side-by-side intercomparison. It is the only reference lidar with depolarization at 355 nm.
•    The reference lidar MUSA (in fixed or mobile configuration) is a multi-wavelength depolarization Raman with 3 elastic – 1064, 532, 355 nm, 2 Raman – 607, 387 nm, and linear depolarization ratio at 532 nm. It is the only reference instrument operating simultaneously 3 elastic (including the infrared) and 2 Raman channels. The system can be moved at the user site (if the user’s lidar is fixed) or can be operated at the host for longer intercomparisons.
•    The Lidar Remote Quality Assurance (LiReQA) operates dedicated software tools (raytracing for analyzing the transmitter and receiver optics, lidar polarization analysis software, lidar radiation power budget analysis software, analysis of test measurements specialized for individual lidar setups) to perform fault diagnosis of any lidar system.
•    The Lidar Check-up Unit (LiCheckUnit) is a portable unit (laser power meter, polarization analysis instruments for inspection of  transmitter and receiver optics, adapted instruments for checking the alignment of the lidar system, e.g. CCD camera & special optics adapted to the lidar system, lidar pulse simulator for inspection of the detection electronics) which can be used at the user site to inspect and debug the instrument.

Services offered

•    Characterization of basic components (laser, optical and electronic parts) is performed at LiCoTest: laser beam characterization, optical and spectral characterization of lenses, filters, mirrors and fiber optics, spectroscopic  ellipsometry measurements, polarization measurements, paraxial analysis of optical systems, electronic modules synchronization, stability, response time/speed.
•    Assessment of the overall system’s performance is made by side-by-side comparison with POLIS or MUSA, which are both EARLINET reference mobile lidar systems. The availability of the two systems provides a good geographical coverage and reduces time delays between demand and supply. These systems can be used as reference for scientific lidars but also for different instruments (as ceilometers, sunphotometer or in situ measurements), both commercial and scientific.
•    Systematic quality assurance of the optical and electronic chains and fault diagnosis is performed at LiReQA. Users trained at LiCalTrain collects test files and send them to be analysed, collecting feed-backs and recommendations. This ensures a homogeneous characterization of the instruments, and identification of possible biases or instrumental problems. The procedure is applied regularly to check the long-term stability of the systems.
•    Inspection, debugging  and optimization of lidars is performed by LiCheckUnit. This installation relies on the high-level expertise of its operator to identify the cause of improper operation, and find solutions to improve the performances of the lidar.
•    Intensive training to maintain and check the calibration is provided at LiCalTrain, focusing on good practices in lidar measurements and correct application of QA tests for the assessment and optimization of the optical\electronic chains.

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Fig. TNA1.1: Various aspects of lidar calibration, periodicity, and links to LiCal installations

The various installations of LiCal have offered in the last years a significant number of accesses within EARLINET, ACTRIS, ESA-CEOS, ITaRS, as well as for the master and doctoral programs at the Romanian, Italian and German Universities, and national research programs. On average, LiCal installations have hosted about 48 projects (intercomparisons, sample analysis, training, system inspection) and 1260 access days per year, for a number of 51 external users per year, out of which 30 international users. Within the frame of EARLINET and ACTRIS, LiCal has been serving the scientific community (about 20 active lidar stations, regular access), the user community (several lidar/ceilometer operators belonging to weather services and aviation) and the private sector (about 3 companies / developers and integrators). LiCal was also involved in several intercomparison (SLiCE2000, EARLI09, SPALI10, SOLI10, ROLI10, AQUILI12, NALI13, LELI13) and scientific campaigns (ACTRIS SUMMER 2012 Campaign, Charmex EARLINET 72h exercise - Jul. 2012, EMEP summer and winter campaign - Jun.-Jul. 2012 and Jan.-Feb. 2013, Charmex 2013).

This activity strongly contributed to increase the number of available quality assured EARLINET data as demonstrated by the large number of publications collected in the last years (a complete list is reported at www.earlinet.org). In particular EARLINET data have been recently used for aerosol characterization in terms of optical and microphysical properties in conjunction with in situ measurements and transport models (e.g. Pappalardo et al., 2013, Sicard et al., 2012, Wagner et al., 2013, Nicolae et al., 2013). The long-term EARLINET quality assured database is the basis for climatological studies, systematic comparison with models and satellite observations (Mona et al., 2014, Pappalardo et al., 2010). New products were derived as further outcome of this calibration activity, e.g the calibrated linear volume depolarization ratio (Bravo Aranda et al., 2013), the particle linear depolarization ratio (Freudenthaler et al., 2009). At the same time, more and more lidars were upgraded with Raman and depolarization channels.

Up to now LiCal was mainly used by research networks (with a limited number of past accesses). However, the extension of research and operational networks (lidar and ceilometer) in the last years favours an increase of demand for calibration services both from users and manufacturers (generally SMEs). Being unique in Europe and in the world with its reference lidars (POLIS and MUSA), testing and debugging (LiCoTest, LiReQA, LiCheckUnit) and expert training facilities (LiCalTrain), the Lidar Calibration Centre is now able to offer to the external community access to the QA tools, procedures and standards developed by EARLINET and implemented and tested at network level during ACTRIS. Moreover, the new developments foreseen in NA2, will be picked-up by LiCal as soon as they will be fully tested and documented.

Description of work

Modality of access under this proposal: Access will be provided to one or more LiCal installations, based on the user’s request and identified needs. The user has to shortly describe the system to be calibrated and the problems identified / suspected. Facts such as “last calibration date”, “major upgrades”, “expertise of the operators”, “application and recommended measurement accuracy” will be taken into consideration by the LiCal User Selection Panel when recommending and granting access to (a) specific LiCal installation(s).

Physical access

Physical access will be provided by LiCalTrain, LiCheckUnit, POLIS and MUSA. At LiCalTrain (Romania), users (especially new or not very experienced lidar/ceilometer operators, 1-2 persons / station for 5 days) will be trained to apply standard procedures for lidar measurements (lidar alignment,  cleaning of the telescope mirror and optical components, telescope alignment and check-up tools) and correct application of QA tests for the assessment and optimization of the optical\electronic chains (telecover test for optical alignment checkups, depolarization calibration tests and procedures, Rayleigh fit test for alignment checkups, laser trigger-detection synchronization tests). POLIS (Germany) and MUSA-mobile (Italy) will be used for access at the user site (approx. 2 weeks), as reference for direct comparison and intensive training. The choice between the two installations will be made considering the configuration of the system to be calibrated. A report containing the intercomparison result will be sent after analysis. The same services will be provided by MUSA at its original location (Potenza) for users / manufacturers of mobile / portable lidars. To investigate malfunction of their instrument, users will be granted access to LiCheckUnit (Germany). The installation will be moved to the user site location for approx. one week, and the expert will inspect the instrument, identify the causes and recommend solutions. A report containing the findings will be delivered.

Remote access

Remote access will be provided by LiCoTest and LiReQA. At LiCoTest (Romania), users can send samples (components and blocks) to be characterized. At LiReQA (Germany), users can send test data (special format, collected by the operators) to be analysed. In both cases, a report containing the results will be sent back to the user, with recommendations.

For all installations, the modality to declare access costs is on the basis of unit cost, or a combination with actual costs (for POLIS, MUSA-mobile and LiCheckUnit, which involve access at the user site). Unit costs include direct costs and operating personnel costs. Actual costs include shipment of the instruments and travel of the operators to the user site.

Support offered under this proposal

At LiCal, logistic support is routinely offered to the external and international users in terms of travel assistance and fiscal authority. Within the available budget, selected proposals can be provided with support money for travel. For all activities involving training, users are provided with documentation, training material, and have access to lecture rooms, internet, instruments and software. For scientific and technical support, the LiCal experts are directly involved and at the disposal of the users for explanations and clarifications. Access to the characterization, testing and check-up installations helps the users to properly assess the instrumental errors, optimize the systems and quantify the data uncertainty. Access to the hands-on training installations (including during intercomparisons) provides the user with the necessary expertise to properly operate, maintain and calibrate their systems on long term, therefore to allow quantitative measurement of relevant aerosol parameters (Angstrom coefficients, lidar ratio, linear particle depolarization ratio, microphysics).

Outreach to new users

While regular users (e.g. EARLINET stations) are accessing LiCal installations systematically in order to fulfil the agreed standards and ensure homogeneous data quality, it is expected that the number of new users will increase considerably during the project. These are weather services and aviation safety administrations, which are now in the process of implementing such systems for warning or monitoring purposes, as well as lidar/ceilometer developers.  Moreover, within the research community new lidar stations will be soon operational in countries which have recently joined EU or are now in the process (Serbia, Croatia, Republic of Moldova, etc.). In order to promote LiCal and services offered to these new users, advertisement will be done via ACTRIS, ITaRS, EARLINET and own web site, as well as during conferences, workshops and project meetings. Relevant e-mailing lists will be also considered. Dissemination of the TNA achievements will be done based on conference contributions (at least one per TNA project) and papers (at least one ISI paper per year). Reports on results and documentation will include summaries published online, and detailed documentation submitted to the ACTRIS community and following ACTRIS protocols.

Review procedure under this proposal

The transnational access to LiCal installations will be jointly coordinated by the project management team (PMT) and WP6 leader (INOE). INOE will manage and follow-up on the proposals onsite. The call for TNA to LiCal will be an open, continuous call and requests will be accepted at any time from any eligible researcher or research team. The request for accessing LiCal infrastructure will be addressed online to the PMT in the form of a short proposal (template will be available), including the motivation for the access, description of the instrument to be calibrated, problems to be tackled (instrument problem? training? components/blocks characterization? regular testing? overall performance?), people in charge, expected outcomes, etc. Following verification of the proposals by the PMT for formal compliance with EU regulations, INOE will coordinate proposal review with the LiCal User Selection Panel to evaluate and select the proposal according to clearly defined selection criteria. Proposal selection will be based on the scientific quality, priority will be given to new users. It will apply the principles of transparency, fairness and impartiality. The decision on the specific installation(s) to be accessed belongs to the LiCal User Selection Panel, based on the user needs which are expressed in the access proposal. The LiCal User Selection Panel will consist of representatives of the three LiCal partners, and six reputable scientists having expertise in lidar, optics and/or electronics (at least half of them will be independent from ACTRIS-2). The members of the LiCal User Selection Panel will be proposed by the WP leader and appointed by the General Assembly.