Abstract
Radiometric calibration of the Dual-Wavelength Echidna® Lidar (DWEL), a full-waveform terrestrial laser scanner with two simultaneously-pulsing infrared lasers at 1064 nm and 1548 nm, provides accurate dual-wavelength apparent reflectance (ρapp), a physically-defined value that is related to the radiative and structural characteristics of scanned targets and independent of range and instrument optics and electronics. The errors of ρapp are 8.1% for 1064 nm and 6.4% for 1548 nm. A sensitivity analysis shows that ρapp error is dominated by range errors at near ranges, but by lidar intensity errors at far ranges. Our semi-empirical model for radiometric calibration combines a generalized logistic function to explicitly model telescopic effects due to defocusing of return signals at near range with a negative exponential function to model the fall-off of return intensity with range. Accurate values of ρapp from the radiometric calibration improve the quantification of vegetation structure, facilitate the comparison and coupling of lidar datasets from different instruments, campaigns or wavelengths and advance the utilization of bi- and multi-spectral information added to 3D scans by novel spectral lidars.
Highlights
Light detection and ranging is an active remote sensing technique using an instrument that emits coherent laser light
This paper addresses these and other challenges for a dual-wavelength, full-waveform terrestrial laser scanner, the Dual-Wavelength Echidna® Lidar (DWEL)
We present a simultaneous calibration of returns from DWEL’s two lasers, which demonstrates how calibration can ensure both radiometric and spectral fidelity in a unified process, providing a pathway for the calibration of other dual- and multi-wavelength terrestrial lidars that may be in various stages of development and application
Summary
Light detection and ranging (lidar) is an active remote sensing technique using an instrument that emits coherent laser light. The radiometric calibration of TLS data faces unique challenges, including: (1) a very large variation in intensity with range that can induce saturation of the detector system by bright targets in the near field and reduced intensities that merge with the noise in the far range; and (2) strong telescopic effects, with defocusing that produces weak signals at near range. This paper addresses these and other challenges for a dual-wavelength, full-waveform terrestrial laser scanner, the DWEL. We conclude by evaluating the calibration accuracy of dual-wavelength point clouds from DWEL, as well as the sensitivity of the calibration accuracy to errors in both range and intensity measurements
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