Unfortunately we don’t have an accepted standard for lidar intensity. It can be loosely defined as the strength of the backscattered echo for each measured point, with the operative word being loosely.
A group of researchers at Oregon State University are trying to change that. From the abstract, “To date, LIDAR intensity data have proven beneficial in a wide range of applications because they are related to surface parameters, such as reflectance. While numerous procedures have been introduced in the scientific literature, and even commercial software, to enhance the utility of intensity data through a variety of “normalization”, “correction”, or “calibration” techniques, the current situation is complicated by a lack of standardization, as well as confusing, inconsistent use of terminology.”
In this paper, the authors first provide an overview of basic principles of LIDAR intensity measurements and applications utilizing intensity information from terrestrial, airborne topographic, and airborne bathymetric LIDAR. Next, they review effective parameters on intensity measurements, basic theory, and current intensity processing methods.
They then define terminology adopted from the most commonly-used conventions based on a review of current literature. Finally, they identify topics in need of further research. Ultimately, the presented information helps lay the foundation for future standards and specifications for LIDAR radiometric calibration.