Saver.net lidar network in southern South America

The South American Environmental Risk Management Network (SAVER-Net) is an instrumentation network, mainly composed by lidars, to provide real-time information for atmospheric hazards and risk management purposes in South America. This lidar network have been developed since 2012 and all its sampling points are expected to be fully implemented by 2017. This paper describes the network’s status and configuration, the data acquisition and processing scheme (protocols and data levels), as well as some aspects of the scientific networking in Latin American Lidar Network (LALINET). Similarly, the paper lays out future plans on the operation and integration to major international collaborative efforts.


INTRODUCTION
In recent years, volcanic activity in the Andes Mountain Range have impacted many countries in the world, primarily Argentina and Chile. These hazards promoted mainly two atmospheric risk management projects (Ministry of Defense -Special Project Nº31554/11 and the SAVER.Net Project.). The first project focused on the development of five lidar deployable stations. The stations were supplemented with ground base instrumentation to monitor atmospheric aerosols and gas constituents (SO 2 , BrO, N 2 O, O 3 , HCHO, H 2 O, by means of MAX-DOAS), solar radiation and meteorological variables. The main goal is the detection of suspended volcanic ash. For this purpose, stations have been strategically distributed across latitudes covering from Patagonia 51°37'S in the South to the central Argentinean region in Buenos Aires from 31°33'S as the northern boundary.
The second project is funded by the government of Japan and provides support for development and assistance to third countries based on a joint funding provided by: Japan International Collaboration Agency (JICA) and the Japan Science and Technology Agency (JST). This support created a Science and Technology Research Partnership for Sustainable Development (SATREPS) to address global issues with practical benefits on both local and global society. The overarching objective of SAVER.Net is to develop an atmospheric hazard and risk management system in Southern South America; focused on aerosol detection and identification as well as monitoring of stratospheric ozone ultraviolet (UV) radiation levels.
This multinational support for science and technological development geared joint efforts between participating institutions: CITEDEF, NIES, UMAG, SMN and the Chilean Meteorological Service (DMC). A common goal across organizations is to use lidar data for providing risk management information.

Hardware description
The Lidar Division at CITEDEF installed the instrumentation on the stations, developing and constructing the lidars on standard 20 ft. containers. These containers are equipped with open hatches at the rooftop, two air conditioning systems, a local area network and electricity connectivity. The roof on each container offers future expansion possibilities for installing additional instrumentation. The container includes office space since the lidar fills out one half of the container divided from the other half by a door.
The lidar network has nine instruments in total from which eight of them can measure depolarization at 532 nm and 355 nm; and one of them contains a telescope fiber-coupled to the spectroscopic box. Four of these instruments are prepared to measure inelastic Raman backscattering returns. And, two of them have high spectral resolution capabilities (HSRL) following the emission and detection scheme described by [1]. Table 1 shows the measurement capabilities. The Lidar emission sub-system in all cases is a Nd:YAG laser (at 1064 nm) doubled (at 532 nm) and tripled (at 355 nm). HSRL Lidars and the one installed in Punta Arenas are based on Continuum Surelite II -10 Hz lasers. However, the lidar in the Bariloche site is based on a Quantel Brilliant B 20 Hz laser and the remaining of them are all based on Continuum Surelite I -30 Hz lasers. See Table 2 for details on laser model, repetition rate and energy per pulse at 1064 nm.  Figure 1 shows the lidar system installed in Punta Arenas, Chile (see Table 1).  Lidars that are only elastic can be easily upgraded to include nighttime Raman detection in photon counting mode.

LIDAR OPERATION DESCRIPTION
The lidars were prepared to operate continuously under all weather conditions in the span of climate conditions from northern Argentina to sub Antarctic regions. Except the HRSLs that measure continuously, the other systems measure every 15 minutes during at least one-minute integrating profiles every 10 seconds (300 shots). This operation mode extends the flash lamp lifetime to one year for the lidar emission sub-system, with the exception of HSRL which requires six flash lamps per year due to their continuous operation.
The Lidar instruments are intended for continuous mode operation but also for intensive observing mode when specific hazardous events occur and then continuous profiling is required. This versatility allows for complementary operations of atmospheric modeling since datasets and level process data can be accessed remotely. Each lidar upload the data to a remote SFTP server every 15 minutes to assure almost real time transfer.
A web server manages and centralize the data through an interactive portal where quick-looks are refreshed illustrating backscattering profiles and lidar retrieved aerosol parameters. The actual quick looks and NetCDF profiles are processed at NIES and have the same format as AD-Net profiles. The online data processing algorithms are described in [2].

LIDAR OPERATION SITES
The lidar site location followed several criteria. Some of them are:  The operation of the lidar should be performed by members of the SAVER.Net Project (in this case CITEDEF, SMN, UMAG)  The site location should be as close as possible to main airports.  The chosen region for installation should contribute improved knowledge on aerosol's optical and microphysical properties as well as their spatial distribution.  The lidar network contours the Andean volcanic belt of Argentina and Chile in Patagonia were several active volcanoes can be found.
Detailed location of the lidar sites can be seen on Table 3 and figure 2

DATA ANALYSIS
One of the main goals of SAVER.Net is to provide operational aerosol information supporting governmental agencies operations for hazards and risk analysis and prevention. For research purposes, lidar datasets are combined to other instrumental datasets (e.g. co-located sunphotometers, radiometers and meteorological stations).
The algorithms to provide lidar information were originally written in MatLab and IDL. Recently, the entire processing platform was upgraded to Python as single open source language to ensure wide distribution and sharing process. The algorithms will deliver in pseudo-real time dynamic structures like atmospheric boundary layer and cloud height and aerosol layers. They will also differentiate spherical from nonspherical backscatters.
In terms of retrieval of aerosol concentration, the network will implement those known and current available inversion methodologies [3][4][5][6][7][8] that can provide an operative solution in pseudo-real time.
By project ends in March 2018 the groups involved in the network will develop a web based platform to distribute datasets and products tailored to risk managers, governmental agencies involved in hazard mitigation and risk assessment [9].

LIDAR OPERATION, TRAINING, AND MAINTENANCE
The instruments are designed to measure continuously but the operator should be ready to deal with shutting down (e.g., to prevent damage due to hail or strong storm) and similarly to restarting the system (e.g., after a blackout lasting longer than the UPS capacity) when necessary. Instruments may also require optical realignment and signal optimization as well as basic maintenance. For this reason, researchers involved leading the lidar development have started training local lidar operators so that after installing and repairing; realigning and other simple routinely measures can be developed by on-site operators.. Furthermore, short courses on lidar signal processing are being prepared to train operators, forecasters and managers on demand of high level data product. Training courses are continuously evolving and improving to cover the majority of data-network users. Recent efforts between the lidar division at CEILAP-CITEDEF and the SMN have focused on preparing distance learning courses in specific topics of SMN interest. Finally, an operation handbook is being prepared for basic on-site operation and maintenance rules and procedures.

CONCLUSIONS AND PERSPECTIVES
Currently seven of nine lidars of the SAVER.Net are operating across different regions of Argentina and Chile. By March 2017 it is expected to have the last two lidars installed on their final locations. This final milestone will fulfill an unprecedented effort to provide a fully operational monitoring network from which several governmental agencies will benefit. After network completion analysis of lidar datasets will be implemented for aerosols transport from local and regional transport events in Argentina and Chile. This way SAVER.Net will contribute and integrate LALINET and other international efforts.