A Monte Carlo radiative transfer model of satellite waveform LiDAR

Abstract

We present a method and initial results for a model of the interaction of waveform lidar with a three-dimensional canopy representation. The model is developed from the FLIGHT radiative transfer model (North, 1996), based on Monte Carlo simulation of photon transport. Foliage is represented by structural properties of leaf area, leaf angle distribution (LAD), crown dimensions and fractional cover, and the optical properties of leaves, branch, shoot and ground components. Important characteristics of the model are that it can represent multiple scattering of light within the canopy and with the ground surface, simulate the return signal efficiently at multiple wavebands, and model the effects of topography. Spatial and temporal sampling characteristics of the lidar instrument are explicitly modelled. A sensitivity analysis gives expected effects of canopy parameters on the waveform, and indicates potential for retrieval of the canopy properties of fractional cover and leaf area, in addition to height.

Estimating Canopy Gap Fraction Using ICESat GLAS within Australian Forest Ecosystems

“…The large-footprint continuous waveform nature of GLAS data has been suggested to be sensitive to apparent canopy and ground surface reflectance values; that is, canopy returns reflect stronger or weaker than the ground [14]. Radiative transfer analysis partially corroborates these findings [15], but suggests a greater influence is caused by waveforms being more sensitive to within canopy scattering events, which may lead to less energy irradiating the ground surface [16]. Further compounding the misinterpretation issues, the non-uniform footprint energy distribution effectively irradiates targets with higher intensity at the footprint centre.…”

Discrete Anisotropic Radiative Transfer (DART 5) for Modeling Airborne and Satellite Spectroradiometer and LIDAR Acquisitions of Natural and Urban Landscapes

“…A photon, which is scattered in atmosphere or landscape at the (x,y,z) position, can irradiate the LIDAR sensor in directions within the solid angle  (x,y,z), defined by the sensor aperture area ALIDAR. The Monte Carlo (MC) photon tracing method is frequently used for simulating LIDAR signals [60,61]. It simulates multiple scattering of each photon as a succession of exactly simulated single scattering events, and produces very accurate results.…”

Real and Simulated Waveform Recording Lidar Data in Boreal Juvenile Forest Vegetation

“…Absolute validation of MCRT models is difficult, because the effects of the radiative transfer model, vegetation models, and the sensor response cannot be separated from each other. Qualitative comparisons of real and simulated LiDAR data have been reported for space-borne instruments (North et al, 2010), but to our knowledge, quantitative comparisons for small-footprint airborne LiDAR have not been reported before. Our model has some uncertainties, which are related to possible errors in the vegetation modeling, exclusion of wave phenomena (interference, diffraction), improper knowledge on the scattering characteristics of the calibration targets in the hot-spot geometry, and to the simplified sensor model.…”