In the fall of 2012, the American Society of Photogrammetry and Remote Sensing released a valuable addition to literature available to the LiDAR community – The Manual of Airborne Topographic LiDAR. The book can be purchased through the ASPRS bookstore. The manual was edited by Michael Renslow and contains contributions by several experts across various sectors of the LiDAR industry. The book has a wealth of practical information for those in industry who will be involved with LiDAR ranging from acquisition to processing to application. In this review, it is not my intent to provide a critical review of the content, but rather more information of what is included in the book and its relevance.
A few side comments before we get started discussing the content. The book is printed in color, which is very helpful for presenting LiDAR examples. Also, as specified in the title, the focus is airborne LIDAR, not terrestrial LIDAR (static or mobile). Herein is a description of its contents. The full table of contents can be found here: http://www.asprs.org/a/publications/LiDAR_TOC.pdf.
Chapter 1 begins with an introduction by the editor. A very brief history of LiDAR is presented. Traditionally, you would expect to find the glossary at the end of a book; however, a glossary of several key terms has been presented upfront in this text, which is useful to someone new to LiDAR and a good approach.
Chapter 2 discusses the driving technology behind LIDAR. It begins with a discussion of fundamental remote sensing background (electromagnetic spectrum, reflectance, absorbance, etc.). Laser pulse properties, time of flight calculations, and interaction with a surface are then presented. Types of mirrors used for scanning and the subsequent scan patterns on the ground are discussed along with a presentation of the current state of the art systems. This section balances both theoretical and practical considerations in how the technology operates.
Notably, this chapter includes detailed sections discussing recent developments in the industry such as full-waveform LiDAR, flash LiDAR, 3D video panoramic LiDAR, and Geiger mode LiDAR (sometimes referred to as photon LiDAR). There are relatively few references available on these subjects, and even fewer that address it to this level of detail.
Chapter 3 then proceeds to discuss other technologies necessary for LIDAR geo-referencing such as GNSS and Inertial Navigation Systems. The chapter presents the theoretical formulation for direct geo-referencing of kinematic LiDAR followed by strong practical considerations such as calibration requirements (e.g., boresight calibration), GPS errors, survey planning, and more.
Chapter 4 focuses on installation procedures for airborne LIDAR systems covering both rotary wing and fixed wing platforms. The chapter provides an overview of calibration processes as well as QA/QC procedures using ground control points.
Chapter 5, Guidelines for LIDAR data collection, is a very useful chapter discussing critical considerations for flight mission planning (platform, window, height, overlap, point density requirements, etc.) and generation of the flight plan map. Very practical information is provided regarding establishment of ground control. The next main section focuses on in-flight calibration of airborne LIDAR systems and considerations for flat terrain, sloped terrain, and vegetated areas. This is followed by operation guidelines for pilots since they play a critical role in data quality. The final section provides guidance for in-flight quality control with a brief discussion of typical operational mistakes.
Chapter 6 provides a general, efficient step by step workflow (37 major steps identified) for processing airborne LiDAR data. This is written generically so as to not be specific to particular hardware or software vendors. Following the workflow, details are provided for both pre and post processing QA/QC checks. Considerations regarding common filtering and classifying procedures are also presented. The final section of this chapter provides an example of how LiDAR specifications (accuracy and point density) can determine if appropriate features are captured in the dataset. This chapter is very valuable for someone who wants to learn how to process LiDAR data since there are a lot of steps involved and one needs to know what to look for throughout the process.
Chapter 7 begins with a discussion of commercially available ALS systems. The next section presents valuable data management protocols and considerations. The section is organized by a generic LiDAR data flow from acquisition to delivery. A very detailed discussion of the LAS 1.4 specification is then provided. It contains information useful both to end users of the las format as well as programmers supporting las files.
Chapter 8 discusses the relationship between LiDAR and photogrammetry including LiDARgrammetry and combining imagery with LiDAR datasets. There is a discussion on common co-registration algorithms to link images to LiDAR data both by system integration and by feature matching.
Chapter 9 presents the recently released USGS LIDAR base specification 1.0. It also includes a glossary of terminology. However, in addition to the USGS specification, it also provides a discussion of factors affecting LiDAR data accuracy and quality control reporting procedures. Particularly, the QC section discusses statistical considerations related to error reporting that can often be misunderstood by the data user or not properly declared by the data provider.
Chapter 10 provides over 150 pages describing various applications of LIDAR. The first 30 pages outline the derivation of Digital Elevation and Surface models from LIDAR data as TIN, raster and contour products. There is a brief discussion of several types of surface interpolation methods as well as breakline integration. The chapter also provides information on processes such as hydro-flattening and hydro-enforcing. The illustrative examples in this section are very helpful in visually reinforcing the concepts in the National Data Elevation Plan (NDEP) and FEMA flood mapping Guidelines. There is also a discussion of intensity imagery commonly provided with airborne LIDAR datasets, including concepts such as automatic gain control systems and how those influence the resulting data.
The remaining part of the chapter provides information on how LIDAR is being used in forestry, corridor mapping, transportation engineering, flood mapping, building extraction, airport surveying, coastal applications, hydrological applications, and natural hazards. While the majority of these sections are written as overviews with illustrative examples, most provide helpful considerations and insights on the use of LIDAR in that realm. It is particularly worth noting that the section on building extraction discusses, in detail, the theory behind several key algorithms used in geometric feature recognition and extraction.
Appendices. Following the chapters there are 4 appendices.
A. GEIOD height models and vertical datums. This appendix provides background information on the geoid and common datums. It then provides practical advice on usage of a geoid with LiDAR data. It is important to note that at the time of printing, geiod09 was the current geoid model for the conterminous US. However, the NGS recently released Geiod12A to convert ellipsoid heights from NAD83 (2011) to NAVD88. See http://www.ngs.noaa.gov/GEOID/GEOID12A/ for more information.
B. QC process for data users. This appendix provides examples of reflective targets that can be used for quality control purposes.
C. LiDAR metadata. This provides an example of and template for LIDAR metadata. Clear, accurate, and comprehensive metadata is critical to the usability of a dataset and is often overlooked. This template (related to the USGS base specification) will be helpful.
D. List of Acronyms. Self explanatory.
Yes, some information in the book (as any other in our industry) will eventually become outdated given the rapid change of technology development (which is inescapable with LiDAR technology). However, the majority of the text contains very useful information, which will benefit the community for years to come. Thanks to all who made this happen!