**1. Introduction**

Currently, the world's leading authority on global warming issues is the Intergovernmental Panel on Climate Change (IPCC). The IPCC is a scientificpolitical organization, created in 1988 by the United Nations (UN), and received the Nobel Peace Prize in 2007 [1, 2]. Since its foundation, the IPCC has issued five reports (Assessment Reports), the first in 1990, the next ones in 1995, 2001, 2007, and 2014. The next report of IPCC is expected for the year 2022. The IPCC reports have reinforced, with growing evidence, that human influence on Earth's climate is incontestable and that the terrestrial climate system's warming is evident [2].

Aerosols, in particular, can alter the most diverse atmospheric processes, significantly affecting weather and climate. For example, they can absorb or scatter specific solar radiation wavelengths and radiation reflected by the Earth's surface [3]. They can also modify the albedo (ability to reflect solar radiation on a given surface) and the lifetime of clouds [4]. A decrease in the albedo of clouds, for example, can lead to less reflection of radiation from the Sun, contributing to possible global warming effects. In this context, it is expected that the aerosol climatological behavior in the Earth's atmosphere and its influence on climate change processes are of paramount importance.

The World Meteorological Organization (WMO) has encouraged the creation and expansion of networks aimed at atmospheric observations, and ground-based lidar networks have acquired great importance, both for atmospheric monitoring and research. Thus, regional lidar networks' development to research the most diverse atmospheric configurations is strategic. The main fields where groundbased lidar measurements can be applied include [5, 6] atmospheric aerosol optical properties, urban aerosols and pollution, dust and biomass burning transportation, and cloud impacts on climate, planetary boundary layer dynamics, and processes of satellite data validation.

In terms of atmospheric structure, ground base lidars cover from the mesosphere down to the troposphere, through the stratosphere, and inspect each atmospheric layer in question. Under this perspective, laser radars' operation began in the early '70s by observing stratospheric aerosols in Brazil and continued with sodium atoms (Na) concentration in the mesosphere. The stratospheric aerosols and ozone studies followed some years later in Argentina [7] and the late '80s in Cuba. By the late '90s and early 2000, the introduction of the lidar for tropospheric studies began.

We intend to summarize the most significant scientific achievements and developments related to ground-based Lidar remote sensing in South America in the next sections. LALINET's most recent efforts in establishing standard protocols of system configurations, quality assurance, measurements, and data processing also will be approached [7–11]. The chapter organization should first follow the studies

## *Lidar Observations in South America. Part I - Mesosphere and Stratosphere DOI: http://dx.doi.org/10.5772/intechopen.95038*

performed in the mesosphere, followed by the work devoted to the stratosphere, and then we should show the studies related to the troposphere. These sections will be distributed over many specific studies regarding the scientific drives and methodologies employed.
