A Review of LIDAR Radiometric Processing: From Ad Hoc Intensity Correction to Rigorous Radiometric Calibration

Abstract

In addition to precise 3D coordinates, most light detection and ranging (LIDAR) systems also record “intensity”, loosely defined as the strength of the backscattered echo for each measured point. 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, we 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, we review effective parameters on intensity measurements, basic theory, and current intensity processing methods. We define terminology adopted from the most commonly-used conventions based on a review of current literature. Finally, we identify topics in need of further research. Ultimately, the presented information helps lay the foundation for future standards and specifications for LIDAR radiometric calibration.

Specular Reflection Effects Elimination in Terrestrial Laser Scanning Intensity Data Using Phong Model

“…A number of studies have been successfully conducted to derive a corrected intensity that is merely related to the scattering properties of the scanned target by correcting the effects of incidence angle and distance. The irregular TLS distance effect is strongly dominated by instrumental factors (e.g., aperture size, automatic gain control, amplifier for low-reflective surfaces, and a brightness reducer for near distances [1]) and differs significantly among different systems. The distance effect does not completely follow the inverse square range function from the radar range equation [18][19][20].…”

“…The intensity value is the momentary amplitude of the return signal, which can be derived from the analog electrical signal output of the photodetector or digitized waveform [1]. Theoretically, surfaces of higher reflectance will reflect a greater portion of the incident laser radiation, thereby increasing the backscattered signal power and further the intensity [1]. Therefore, the intensity is a source of information closely associated with the reflectance properties of the scanned surface [2][3][4].…”

“…In addition to the conventional precise 3D coordinates, TLS systems simultaneously measure the power of the backscattered laser signal of each scanned point and record it as an intensity value. The intensity value is the momentary amplitude of the return signal, which can be derived from the analog electrical signal output of the photodetector or digitized waveform [1]. Theoretically, surfaces of higher reflectance will reflect a greater portion of the incident laser radiation, thereby increasing the backscattered signal power and further the intensity [1].…”

Towards High-Definition 3D Urban Mapping: Road Feature-Based Registration of Mobile Mapping Systems and Aerial Imagery

“…The laser footprint increases significantly as the incidence angle increases and, therefore, the quality of data is affected [51]. Although the effects of distance and incidence angle on laser intensity would ideally be modeled individually, different laser scanners from different manufacturers can show completely different responses [49]. The transmitted energy, intensity bit depth, amplification of low-reflectivity surfaces, and aperture size are some instrumental factors that affect the intensity measurements and differ between manufacturers.…”

“…Various research groups have used this value to differentiate between asphalt and painted parts of the road surface [45]. However, the reflected laser signal is significantly affected by the scanning geometry, mainly the distance and the laser incidence angle to the target surface [47][48][49][50]; therefore, it cannot be directly used for road marking extraction. In MMS scanning, where the distance between the scanner and target is relatively close, and the target surface is larger than the footprint of the laser beam, the range dependence can be expressed as 1/R 2 , where R is the range [47].…”