## 1 Introduction
Archaeologists using data products derived from ALS observations need to understand the technology, be aware of its limitations, and be careful not to identify features that are not reliably captured by the ALS observations, or rule out the existence of features not detected by the observations. Our goal here is to use examples taken from archeological research projects to illustrate how ALS technology works, how data are collected, reduced and deliverables produced, and how decisions made at each of these steps impact the ability of the archeologist to answer the research questions. The US National Science Foundation (NSF) National Center for Airborne Laser Mapping (NCALM) has over 15 years of experience of providing research quality LiDAR data for the scientific and engineering communities, and has been collecting ALS data for archaeological applications since 2008 in the US Southwest and Mesoamerica (Table 1. summarizes the project locations, surveyed areas, and nominal shot densities). This paper is based on the analysis of data collected, results from sensor configuration experiments, and lessons learned from the execution of these projects; it is intended to complement and expand information presented in previous instructional works such as [18, 19, 20]. The present work complements the previously cited works in multiple ways with the two main ones being: (1) While the previous works provide brief high level overviews of ALS technology and LiDAR data acquisition their main focus is on how to process, analyze and visualize the data once it is delivered (post-production). In contrast the present work provides a deeper and more complete description of the technology with a focus on the collection and data product generation (pre-production and production) and how the decisions made by the ALS data provider at these stages can affect the ability of an investigator to answer research questions; (2) The cited works are based on the topographic, ecological and anthropological environments of Europe, while this work has been performed in the unique conditions of Mesoamerica. This work is intended to be as complete as a research paper allows, focusing on the archaeological application, however it is not an exhaustive coverage and therefore the reader is \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Project** & **Survey Year** & **Area (km2)** & **Laser Shot Density (s/m2)** \\ \hline Perry Mesa Region, Arizona & 2008 & 40 & 4 \\ Caracol, Belize & 2009 & 194 & 20 \\ Chaco Canyon, New Mexico & 2010 & 40 & 5 \\ Uxbenka, Belize & 2011 & 103 & 12 \\ Mosquitia, Honduras & 2012 & 122 & 15–25 \\ Western Belize & 2013 & 1050 & 15 \\ Mayapan, Mexico & 2013 & 55 & 40–42 \\ Tres Zapotes, Mexico & 2014 & 72 & 12–13 \\ Chichen Itza \& Yuxunah, Mexico & 2014 & 50 & 15 \\ Cansahcab, Mexico & 2014 & 26 & 15 \\ Yaxnohcah, Mexico & 2014 & 90 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Archaeological Airborne Laser Scanning (ALS) survey projects by the National Center for Airborne Laser Mapping (NCALM)referred to the textbook and handbook style works [21, 22, 23] for additional general information on ALS systems and data products. This paper is structured in the following way: In Section 2 we present an overview of ALS technology, data products and nomenclature, which will provide a base for the discussion on how different aspects of the technology affect the final results. Section 3 describes the ALS workflow and how the decisions and considerations made at each step may affect the final products and their usefulness in answering particular research questions. Finally in Section 4 we discuss LiDAR data visualization, analysis, quality assessment and how to evaluate the fidelity of structures evident on elevation rasters or other ALS datasets.