Algorithms used in the Airborne Lidar Processing System (ALPS)

Open-File Report 2016-1046
By:  and 



The Airborne Lidar Processing System (ALPS) analyzes Experimental Advanced Airborne Research Lidar (EAARL) data—digitized laser-return waveforms, position, and attitude data—to derive point clouds of target surfaces. A full-waveform airborne lidar system, the EAARL seamlessly and simultaneously collects mixed environment data, including submerged, sub-aerial bare earth, and vegetation-covered topographies.

ALPS uses three waveform target-detection algorithms to determine target positions within a given waveform: centroid analysis, leading edge detection, and bottom detection using water-column backscatter modeling. The centroid analysis algorithm detects opaque hard surfaces. The leading edge algorithm detects topography beneath vegetation and shallow, submerged topography. The bottom detection algorithm uses water-column backscatter modeling for deeper submerged topography in turbid water.

The report describes slant range calculations and explains how ALPS uses laser range and orientation measurements to project measurement points into the Universal Transverse Mercator coordinate system. Parameters used for coordinate transformations in ALPS are described, as are Interactive Data Language-based methods for gridding EAARL point cloud data to derive digital elevation models. Noise reduction in point clouds through use of a random consensus filter is explained, and detailed pseudocode, mathematical equations, and Yorick source code accompany the report.

Suggested Citation

Nagle, David B., and Wright, C. Wayne, 2016, Algorithms used in the Airborne Lidar Processing System (ALPS): U.S. Geological Survey Open-File Report, 2016–1046, 45 p.,

ISSN: 2331-1258 (online)

Table of Contents

  • Acknowledgments
  • Abstract 
  • Introduction
  • Workflow Overview
  • Slant Range Measurement 
  • Waveform Analysis 
  • Point Projection
  • Random Consensus Filter (RCF)
  • Coordinate Transformations
  • Gridding
  • Manual Editing
  • References Cited
  • Appendix A. Source Code
Publication type Report
Publication Subtype USGS Numbered Series
Title Algorithms used in the Airborne Lidar Processing System (ALPS)
Series title Open-File Report
Series number 2016-1046
DOI 10.3133/ofr20161046
Year Published 2016
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) St. Petersburg Coastal and Marine Science Center
Description x, 45 p.
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details