Full Waveform Analysis for Long-Range 3D Imaging Laser Radar

Abstract

The new generation of 3D imaging systems based on laser radar (ladar) offers significant advantages in defense and security applications. In particular, it is possible to retrieve 3D shape information directly from the scene and separate a target from background or foreground clutter by extracting a narrow depth range from the field of view by range gating, either in the sensor or by postprocessing. We discuss and demonstrate the applicability of full-waveform ladar to produce multilayer 3D imagery, in which each pixel produces a complex temporal response that describes the scene structure. Such complexity caused by multiple and distributed reflection arises in many relevant scenarios, for example in viewing partially occluded targets, through semitransparent materials (e.g., windows) and through distributed reflective media such as foliage. We demonstrate our methodology on 3D image data acquired by a scanning time-of-flight system, developed in our own laboratories, which uses the time-correlated single-photon counting technique.

High precision laser ranging by time-of-flight measurement of femtosecond pulses

“…the achievable precision of TOF measurement has been limited by the bandwidth of the available photo-detection electronics, which is currently in the picosecond range or the equivalent of a few hundred micrometers in distance [3,4]. Time gating with single-photon detectors or postprocessing of TOF electric signals enables improvement in the measurement precision [5,6]. Nonetheless, the fidelity of the converted electric pulse signal is degraded by the thermal phase drift as well as amplitude-to-phase conversion of photo-detection electronics, limiting the phase-detector resolution to a 0.1 ps level at best [7].…”

Full-Waveform Terrestrial Laser Scanning for Extracting a High-Resolution 3D Topographic Model: a Case Study on an Area of Archaeological Significance

“…Usually, various types of digital products can be obtained from full-waveform laser data: high precision DTMs (Digital Terrain Models) and DSMs (Digital Surface Models) [Hug et al, 2004], vegetation density maps and derived canopy height models [Pirotti et al, 2013a]. In addition to the production of high precision terrain models for topographic purposes, this new generation of laser scanners is fully employed for urban classification and city modeling, as well as surveys in architectural and archaeological contexts [Doneus et al, 2009]; some experimental systems have even been tested recently for security and safety purposes [Wallace et al, 2010]. The technical potential of full-waveform terrestrial systems is widely used for investigations in geological environments, where considerable distances can be achieved (up to 6 kilometers with the Riegl VZ-6000), and forestry applications.…”

Sub-bin histogram peak detection for the direct time-of-flight SPAD-based laser ranging systems with millimeter range precision

“…Simply introducing a TDC with smaller LSB would be highly impracticable and almost impossible, because it needs more complex circuits, wider chip area, higher power assumptions and memory resources for histogram storage. Interpolation has emerged as a promising alternative to estimate objects' distance more precise than the limited TDC LSB [6] [7]. However, the balance between the performance and algorithm complexity must be kept very carefully, otherwise the designer in doing so will work against the broader goals: reducing the complexity and price of SPAD sensor of great performance.…”