scholarly journals EVALUATION OF VARIOUS SPECTRAL INPUTS FOR ESTIMATION OF FOREST BIOCHEMICAL AND STRUCTURAL PROPERTIES FROM AIRBORNE IMAGING SPECTROSCOPY DATA

2016 ◽  
Vol XLI-B7 ◽  
pp. 961-966 ◽  
Author(s):  
L. Homolová ◽  
R. Janoutová ◽  
Z. Malenovský
Keyword(s):  
Imaging Spectroscopy ◽  
Beech Forest ◽  
Retrieval Algorithm ◽  
Support Vector ◽  
Spectroscopy Data ◽  
Area Index ◽  
The Czech Republic ◽  
Sensor Field ◽  
Airborne Imaging ◽  
Study Sites

In this study we evaluated various spectral inputs for retrieval of forest chlorophyll content (Cab) and leaf area index (LAI) from high spectral and spatial resolution airborne imaging spectroscopy data collected for two forest study sites in the Czech Republic (beech forest at Štítná nad Vláří and spruce forest at Bílý Kříž). The retrieval algorithm was based on a machine learning method – support vector regression (SVR). Performance of the four spectral inputs used to train SVR was evaluated: a) all available hyperspectral bands, b) continuum removal (CR) 645 – 710 nm, c) CR 705 – 780 nm, and d) CR 680 – 800 nm. Spectral inputs and corresponding SVR models were first assessed at the level of spectral databases simulated by combined leaf-canopy radiative transfer models PROSPECT and DART. At this stage, SVR models using all spectral inputs provided good performance (RMSE for Cab < 10 μg cm<sup>−2</sup> and for LAI < 1.5), with consistently better performance for beech over spruce site. Since application of trained SVRs on airborne hyperspectral images of the spruce site produced unacceptably overestimated values, only the beech site results were analysed. The best performance for the Cab estimation was found for CR bands in range of 645 – 710 nm, whereas CR bands in range of 680 – 800 nm were the most suitable for LAI retrieval. The CR transformation reduced the across-track bidirectional reflectance effect present in airborne images due to large sensor field of view.

scholarly journals EVALUATION OF VARIOUS SPECTRAL INPUTS FOR ESTIMATION OF FOREST BIOCHEMICAL AND STRUCTURAL PROPERTIES FROM AIRBORNE IMAGING SPECTROSCOPY DATA

2016 ◽  
Vol XLI-B7 ◽  
pp. 961-966
Author(s):  
L. Homolová ◽  
R. Janoutová ◽  
Z. Malenovský
Keyword(s):  
Imaging Spectroscopy ◽  
Beech Forest ◽  
Retrieval Algorithm ◽  
Support Vector ◽  
Spectroscopy Data ◽  
Area Index ◽  
The Czech Republic ◽  
Sensor Field ◽  
Airborne Imaging ◽  
Study Sites

In this study we evaluated various spectral inputs for retrieval of forest chlorophyll content (Cab) and leaf area index (LAI) from high spectral and spatial resolution airborne imaging spectroscopy data collected for two forest study sites in the Czech Republic (beech forest at Štítná nad Vláří and spruce forest at Bílý Kříž). The retrieval algorithm was based on a machine learning method – support vector regression (SVR). Performance of the four spectral inputs used to train SVR was evaluated: a) all available hyperspectral bands, b) continuum removal (CR) 645 – 710 nm, c) CR 705 – 780 nm, and d) CR 680 – 800 nm. Spectral inputs and corresponding SVR models were first assessed at the level of spectral databases simulated by combined leaf-canopy radiative transfer models PROSPECT and DART. At this stage, SVR models using all spectral inputs provided good performance (RMSE for Cab < 10 μg cm<sup>&minus;2</sup> and for LAI < 1.5), with consistently better performance for beech over spruce site. Since application of trained SVRs on airborne hyperspectral images of the spruce site produced unacceptably overestimated values, only the beech site results were analysed. The best performance for the Cab estimation was found for CR bands in range of 645 – 710 nm, whereas CR bands in range of 680 – 800 nm were the most suitable for LAI retrieval. The CR transformation reduced the across-track bidirectional reflectance effect present in airborne images due to large sensor field of view.

scholarly journals Comparative analysis of different retrieval methods for mapping grassland leaf area index using airborne imaging spectroscopy

2015 ◽  
Vol 43 ◽  
pp. 19-31 ◽  
Author(s):  
Clement Atzberger ◽  
Roshanak Darvishzadeh ◽  
Markus Immitzer ◽  
Martin Schlerf ◽  
Andrew Skidmore ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Imaging Spectroscopy ◽  
Area Index ◽  
Airborne Imaging

scholarly journals The CCB-ID approach to tree species mapping with airborne imaging spectroscopy

2018 ◽  
Author(s):  
Christopher B Anderson
Keyword(s):  
Tree Species ◽  
Rare Species ◽  
Imaging Spectroscopy ◽  
Class Imbalance ◽  
Accuracy Score ◽  
Spectroscopy Data ◽  
Ecological Data ◽  
Outlier Removal ◽  
Airborne Imaging ◽  
Species Mapping

Background. Biogeographers assess how species distributions and abundances affect the structure, function, and composition of ecosystems. Yet we face a major challenge: it is difficult to precisely map species across landscapes. Novel Earth observations could obviate this challenge. Airborne imaging spectrometers measure plant functional traits at high resolution, and these measurements can be used to identify tree species. Plant traits are often highly conserved within species, and highly variable between species, which provides the biophysical basis for species mapping. In this paper I describe a trait-based approach to species identification with imaging spectroscopy, CCB-ID, which was developed as part of a NIST-sponsored ecological data science evaluation (ECODSE). Methods. These methods were developed using NEON airborne imaging spectroscopy data. CCB-ID classifies tree species using trait-based reflectance variation and decision tree-based machine learning models, approximating a morphological trait and dichotomous key method traditionally used in botanical classification. First, outliers were removed using a spectral variance threshold. The remaining samples were transformed using principal components analysis and resampled by species to reduce common species biases. Gradient boosting and random forest classifiers were trained using the transformed and resampled feature data. Prediction probabilities were then calibrated using sigmoid regression, and sample-scale predictions were averaged to the crown scale. Results. This approach performed well according to the competition metrics, receiving a rank-1 accuracy score of 0.919, and a cross-entropy cost score of 0.447 on the test data. Accuracy and specificity scores were high for all species, but precision and recall scores were variable for rare species. PCA transformation improved accuracy scores compared to models trained using reflectance data, but outlier removal and data resampling exacerbated class imbalance problems. Discussion. CCB-ID accurately classified tree species using NEON imaging spectroscopy data, reporting the best classification scores among participants. However, it failed to overcome several well-known species mapping challenges, like precisely identifying rare species. Key takeaways include (1) training models to maximize metrics beyond accuracy (e.g. recall) could improve rare species predictions, (2) within-genus trait variation may drive spectral separability, precluding efforts to distinguish between functionally convergent species, (3) outlier removal and data resampling exacerbated class imbalance problems, and should be carefully implemented, (4) PCA transformation greatly improved model results, and (5) feature selection could further improve species classification models. CCB-ID is open source, designed for use with NEON data, and available to support future species mapping efforts.

scholarly journals High-Resolution Mapping of Redwood (Sequoia sempervirens) Distributions in Three Californian Forests

2019 ◽  
Vol 11 (3) ◽  
pp. 351 ◽  
Author(s):  
Emily Francis ◽  
Gregory Asner
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Imaging Spectroscopy ◽  
Training Data ◽  
Spectroscopy Data ◽  
Boosted Regression Tree ◽  
High Resolution Mapping ◽  
Resolution Mapping ◽  
Redwood Forests ◽  
Airborne Imaging

High-resolution maps of redwood distributions could enable strategic land management to satisfy diverse conservation goals, but the currently-available maps of redwood distributions are low in spatial resolution and biotic detail. Classification of airborne imaging spectroscopy data provides a potential avenue for mapping redwoods over large areas and with high confidence. We used airborne imaging spectroscopy data collected over three redwood forests by the Carnegie Airborne Observatory, in combination with field training data and application of a gradient boosted regression tree (GBRT) machine learning algorithm, to map the distribution of redwoods at 2-m spatial resolution. Training data collected from the three sites showed that redwoods have spectral signatures distinct from the other common tree species found in redwood forests. We optimized a gradient boosted regression model for high performance and computational efficiency, and the resulting model was demonstrably accurate (81–98% true positive rate and 90–98% overall accuracy) in mapping redwoods in each of the study sites. The resulting maps showed marked variation in redwood abundance (0–70%) within a 1 square kilometer aggregation block, which match the spatial resolution of currently-available redwood distribution maps. Our resulting high-resolution mapping approach will facilitate improved research, conservation, and management of redwood trees in California.

scholarly journals Modelling plant species distribution in alpine grasslands using airborne imaging spectroscopy

2014 ◽  
Vol 10 (7) ◽  
pp. 20140347 ◽  
Author(s):  
Julien Pottier ◽  
Zbyněk Malenovský ◽  
Achilleas Psomas ◽  
Lucie Homolová ◽  
Michael E. Schaepman ◽  
...  
Keyword(s):  
Plant Species ◽  
Species Distribution ◽  
Imaging Spectroscopy ◽  
Added Value ◽  
Leaf Water Content ◽  
Alpine Grasslands ◽  
Distribution Models ◽  
Area Index ◽  
Leaf Chlorophyll ◽  
Airborne Imaging

Remote sensing using airborne imaging spectroscopy (AIS) is known to retrieve fundamental optical properties of ecosystems. However, the value of these properties for predicting plant species distribution remains unclear. Here, we assess whether such data can add value to topographic variables for predicting plant distributions in French and Swiss alpine grasslands. We fitted statistical models with high spectral and spatial resolution reflectance data and tested four optical indices sensitive to leaf chlorophyll content, leaf water content and leaf area index. We found moderate added-value of AIS data for predicting alpine plant species distribution. Contrary to expectations, differences between species distribution models (SDMs) were not linked to their local abundance or phylogenetic/functional similarity. Moreover, spectral signatures of species were found to be partly site-specific. We discuss current limits of AIS-based SDMs, highlighting issues of scale and informational content of AIS data.

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