Conference Paper

Connecting the Dots between Laser Waveforms and Herbaceous Biomass for Assessment of Land Degradation using Small-footprint Waveform LiDAR Data.

Chester F. Carlson Center for Imaging Sci., Rochester Inst. of Technol., Rochester, NY, USA
DOI: 10.1109/IGARSS.2009.5418078 Conference: IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2009, July 12-17, 2009, University of Cape Town, Cape Town, South Africa, Proceedings
Source: DBLP

ABSTRACT

Measurement and management of vegetation biomass accumulation in ecosystems typically involves extensive field data collection, which can be expensive and time consuming, while leaving the user with relatively crude inputs to intricate biomass models. Light detection and ranging (LiDAR) remote sensing, which provides extensive height measurements of terrain and vegetation, has become an effective alternative to characterize vegetation structure. In this paper, we report on ongoing efforts at developing signal processing approaches to model herbaceous biomass using a new generation of airborne laser scanners, namely full-waveform LiDAR systems. Structural and statistic-based feature metrics are directly derived from LiDAR waveforms at the pixel level and related to plot-level field data. Initial results reveal a definite correlation between the LiDAR waveform and herbaceous biomass. Ongoing research focuses on the links between fractional cover estimated from imaging spectroscopy and woody biomass.

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    • "It is possible that ''first peak'' information, higher than 2 m, was removed in this process. Another difference in this study is that a generic Gaussian modeling algorithm was used to perform composite waveform modeling for waveforms with two peaks or fewer, compared with the expectation maximization algorithm that was used by Wu et al. (2009b). However, the generic Gaussian modeling algorithm performed reasonably well considering the 5% error rate. "
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    ABSTRACT: The mapping of tree species, in general and specifically in diverse savanna environments, is of great interest to ecologists and natural resource managers. This study focused on the fusion of imaging spectroscopy and small footprint waveform light detection and ranging (wLiDAR) data to improve per species structural parameter estimation towards classification and herbaceous biomass modeling. The species classification approach was based on stepwise discriminant analysis (SDA) and used feature metrics from hyperspectral imagery (HSI) combined with wLiDAR data. It was found that fusing data with the SDA did not improve classification significantly, especially compared with the HSI classification results. As for herbaceous biomass modeling, the statistical approach used for the fusion of wLiDAR and HSI was forward selection regression modeling, which selects significant independent metrics and models those to measured biomass. The results indicated that fine scale wLiDAR may not be able to provide accurate measurement of herbaceous biomass, although other factors could have contributed to the relatively poor results, such as the senescent state of grass, the narrow biomass range that was measured, and the low biomass values, i.e., the limited laser-target interactions. We concluded that although fusion did not result in significant improvements over single modality approaches in these two use cases, there is a need for further investigation during the peak growing season.
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    • "The " x-axis " for each waveform corresponds to the time bins, which can be converted to the height above ground, starting from 24.995 m to −8.605 m at increments of 0.15 m. This range was arbitrarily set based on the size of the tree and considering temporally delayed returns due to the multiple scattering of photons [33]. The negative value was used so that multiple scatters could also be included in the simulated waveform, e.g., the minor peak after ground response. "
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    ABSTRACT: A raw incoming (received) Light Detection And Ranging (LiDAR) waveform typically exhibits a stretched and relatively featureless character, e.g., the LiDAR signal is smeared and the effective spatial resolution decreases. This is attributed to a fixed time span allocated for detection, the sensor’s variable outgoing pulse signal, receiver impulse response, and system noise. Theoretically, such a loss of resolution can be recovered by deconvolving the system response from the measured signal. In this paper, we present a comparative controlled study of three deconvolution techniques, namely, Richardson–Lucy, Wiener filter, and nonnegative least squares, in order to verify which method is quantitatively superior to others. These deconvolution methods were compared in terms of two use cases: 1) ability to recover the true cross-sectional profile of an illuminated object based on the waveform simulation of a virtual 3-D tree model and 2) ability to differentiate herbaceous biomass based on the waveform simulation of virtual grass patches. All the simulated waveform data for this study were derived via the “Digital Imaging and Remote Sensing Image Generation” radiative transfer modeling environment. Results show the superior performance for the Richardson–Lucy algorithm in terms of small root mean square error for recovering the true cross section, low false discovery rate for detecting the unobservable local peaks in the stretched raw waveforms, and high classification accuracy for differentiating herbaceous biomass levels.
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    ABSTRACT: Research groups at Rochester Institute of Technology and Carnegie Institution for Science are studying savanna ecosystems and are using data from the Carnegie Airborne Observatory (CAO), which integrates advanced imaging spectroscopy and waveform light detection and ranging (wLIDAR) data. This component of the larger ecosystem project has as a goal the fusion of imaging spectroscopy and wLIDAR data in order to improve per-species structural parameter estimation. Waveform LIDAR has proven useful for extracting high vertical resolution structural parameters, while imaging spectroscopy is a well-established tool for species classification. We evaluated data fusion at the feature level, using a stepwise discrimination analysis (SDA) approach with feature metrics from both hyperspectral imagery (HSI) and wLIDAR data. It was found that fusing data with the SDA improved classification, although not significantly. The principal component analysis (PCA) provided many useful bands for the SDA selection, both from HSI and wLIDAR. The overall classification accuracy was 68% for wLIDAR, 59% for HSI, and 72% for the fused data set. The kappa accuracy achieved with wLIDAR was 0.49, 0.36 for HSI, and 0.56 for both modalities.
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