- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Towards high throughput assessment of canopy dynamics: The estimation of leaf area structure in Amazonian forests with multitemporal multi-sensor airborne lidar
摘要： Leaf area dynamics offer information about changes in forest biomass and canopy function critical to understanding the role of forests in the climate system and carbon cycle. Airborne small footprint lidar is a potential major source for the detection of variation in leaf area density (LAD), LAD vertical profiles, and total leaf area (leaf area index, LAI), from sites to regional scales. However, the sensitivities of lidar-based LAD and LAI estimation are not yet well known, particularly in dense forests, over landscape heterogeneity, sensor system, and survey differences, and through time. To address these questions, we compared 16 pairs of multitemporal airborne lidar surveys with four different laser sensors across six Amazon forest sites with resurvey intervals ranging from one to nine years. We tested whether the different laser sensors, and the pulse return density of laser sampling (variable between and within each survey) introduce systematic biases. Laser sensors created consistent biases that accounted for up to 18.20% of LAD differences between surveys, but biases could be corrected with a simple regression approach. Lidar pulse return density had little appreciable bias impact when above 20 returns per m2. After correction, repeated mean and site maximum LAI estimates became significantly correlated (R2 ~0.8), while LAD profiles revealed site differences. Heterogeneity and change in LAD structure were detectable at the ecologically relevant 1/4 ha forest neighborhood grid scale, as evidenced by the high correlation of profile variation between surveys, with the strength of correlation (R2 value) significantly decreasing with increasing survey interval (0.74 to 0.16 from one to nine years), consistent with accumulating effects of forest dynamics. Sensor-induced biases trended towards correlation with lidar footprint (beam width). The LAD estimation and bias correction approach developed in this study provides the standardization critical for heterogeneous lidar networks that offer high throughput functional ecological monitoring of climatically important forests like the Amazon.
关键词： Tropical forest monitoring,Forest dynamics,LAI,Lidar,Forest degradation,Leaf area estimation,Leaf area profiles
更新于2025-09-23 15:21:01
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Tropical Forest Tree Species Classification Using Meter-Scale Image Data
摘要： Accurate identification of tropical tree species is critical for studies of forest habitat, composition, biomass, and ultimately a better understanding of the role trees play in climate variability through carbon uptake. The aim of this study was to derive an accurate classification of a tropical forest study site in Costa Rica using high-resolution imagery. A series of corrections for look and view angle, and the utilization of the DigitalGlobe atmospheric compensation procedure (AComp) provided the study with an accurate surface reflectivity dataset from WorldView-3 imagery. A rule-set object-oriented classification schema defined trees in the study area using ENVI-defined tree canopies through a segmentation of the multispectral image. The results show that select WorldView-3 bands, and WorldView-3-specific vegetation indices, can produce an accurate species-level tree classification in a complex tropical forest.
关键词： tree spectra,WorldView-3,Tropical forest mapping,object-oriented classification
更新于2025-09-10 09:29:36
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Estimation of Aboveground Biomass Using Manual Stereo Viewing of Digital Aerial Photographs in Tropical Seasonal Forest
摘要： The objectives of this study are to: (1) evaluate accuracy of tree height measurements of manual stereo viewing on a computer display using digital aerial photographs compared with airborne LiDAR height measurements; and (2) develop an empirical model to estimate stand-level aboveground biomass with variables derived from manual stereo viewing on the computer display in a Cambodian tropical seasonal forest. We evaluate observation error of tree height measured from the manual stereo viewing, based on field measurements. RMSEs of tree height measurement with manual stereo viewing and LiDAR were 1.96 m and 1.72 m, respectively. Then, stand-level aboveground biomass is regressed against tree height indices derived from the manual stereo viewing. We determined the best model to estimate aboveground biomass in terms of the Akaike’s information criterion. This was a model of mean tree height of the tallest five trees in each plot (R2 = 0.78; RMSE = 58.18 Mg/ha). In conclusion, manual stereo viewing on the computer display can measure tree height accurately and is useful to estimate aboveground stand biomass.
关键词： tropical forest,Cambodia,aerial photograph,REDD+,stereo viewing
更新于2025-09-10 09:29:36
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Mapping the Leaf Economic Spectrum across West African Tropical Forests Using UAV-Acquired Hyperspectral Imagery
摘要： The leaf economic spectrum (LES) describes a set of universal trade-offs between leaf mass per area (LMA), leaf nitrogen (N), leaf phosphorus (P) and leaf photosynthesis that influence patterns of primary productivity and nutrient cycling. Many questions regarding vegetation-climate feedbacks can be addressed with a better understanding of LES traits and their controls. Remote sensing offers enormous potential for generating large-scale LES trait data. Yet so far, canopy studies have been limited to imaging spectrometers onboard aircraft, which are rare, expensive to deploy and lack fine-scale resolution. In this study, we measured VNIR (visible-near infrared (400–1050 nm)) reflectance of individual sun and shade leaves in 7 one-ha tropical forest plots located along a 1200–2000 mm precipitation gradient in West Africa. We collected hyperspectral imaging data from 3 of the 7 plots, using an octocopter-based unmanned aerial vehicle (UAV), mounted with a hyperspectral mapping system (450–950 nm, 9 nm FWHM). Using partial least squares regression (PLSR), we found that the spectra of individual sun leaves demonstrated significant (p < 0.01) correlations with LMA and leaf chemical traits: r2 = 0.42 (LMA), r2 = 0.43 (N), r2 = 0.21 (P), r2 = 0.20 (leaf potassium (K)), r2 = 0.23 (leaf calcium (Ca)) and r2 = 0.14 (leaf magnesium (Mg)). Shade leaf spectra displayed stronger relationships with all leaf traits. At the airborne level, four of the six leaf traits demonstrated weak (p < 0.10) correlations with the UAV-collected spectra of 58 tree crowns: r2 = 0.25 (LMA), r2 = 0.22 (N), r2 = 0.22 (P), and r2 = 0.25 (Ca). From the airborne imaging data, we used LMA, N and P values to map the LES across the three plots, revealing precipitation and substrate as co-dominant drivers of trait distributions and relationships. Positive N-P correlations and LMA-P anticorrelations followed typical LES theory, but we found no classic trade-offs between LMA and N. Overall, this study demonstrates the application of UAVs to generating LES information and advancing the study and monitoring tropical forest functional diversity.
关键词： hyperspectral,spectroscopy,West Africa,tropical forest,UAV,Ghana,leaf traits,PLSR,leaf economic spectrum
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Retrieval of Terrain Topography in Tropical Forests Using P-Band Sar Tomography
摘要： This paper presents the results achieved by SAR tomography in estimating digital terrain models under tropical forests. Several airborne data stacks have been processed, they have been gathered on dense forests in central Africa in the framework of the AfriSAR campaign and in South America. The joint exploitation of polarimetry and multibaseline interferometry enabled to separate ground from vegetation above and to analyze it alone. Also, airborne LIDAR measurements were available and provided a reliable comparison. Results indicate that terrain topography in tropical forests can be retrieved by P-Band SAR Tomography to within an accuracy at least comparable to that of LIDAR systems. Furthermore, few meaningful details visible in SAR derived DTMs are missing in LIDAR maps probably due to the high density of the vegetation layer.
关键词： SAR,Tropical,Forest,DEM,TomoSAR,Tomography,DTM
更新于2025-09-09 09:28:46
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Relating Sar Tomography to Tropical Forest Biomass Via Lidar Data
摘要： Forest biomass is a most important parameter in the context of the global carbon cycle. Mapping above ground biomass (AGB) at a global scale contributes to understanding the dynamics of climate change. Tropical forests are extremely important as they store more biomass. In recent years, SAR tomography has been introduced as a new technique that has shown enormous potential in AGB retrieval. A strong linear relationship between in-situ measurements and tomographic power from 30 m above the terrain was discovered by previous studies carried out in French Guiana. However, the two parameters that determine the linear relationship might vary for different tropical forests. Due to the great difficulty in measuring tropical forest AGB by field surveys, in-situ measurements is unfeasible to relate SAR tomography for mapping global forests AGB. For purpose of solving this problem, we investigate the possibility to use LiDAR derived AGB to find the two parameters of the fit line. Experimental results obtained by processing data from the TropiSAR campaign support the feasibility of the proposed concept.
关键词： Tropical Forest,SAR Tomography,Biomass,LiDAR,Back-projection
更新于2025-09-09 09:28:46
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - A Simplified 3D Radiative Transfer Approach for the Retrieval of Chemical and Structural Properties of Individual Tree Crowns from Hyperspectral Data
摘要： In this work, we used hyperspectral remote sensing and a simplified three-dimensional radiative transfer approach to retrieve structural and chemical properties of individual tree crowns (ITCs) from a tropical forest area. First, a Look-Up-Table of simulated ITC reflectance was built by randomly varying parameters of the DART and PROSPECT models. Then, simulated and experimental reflectance of ITCs were compared in terms of spectral similarity. Finally, model parameters that yielded simulations spectrally similar to experimental data were related to sub-pixel fractions and narrow-band vegetation indices computed from the hyperspectral images. DART canopy structural parameters were related to the proportion of non-photosynthetic vegetation (NPV) (R2=0.65), green photosynthetic vegetation (GV) (R2=0.72) and shade (R2=0.34) estimated within ITCs. PROSPECT parameters describing foliar chemical traits such as Chlorophyll a+b (Cab) and Carotenoids (Cxc) were related to the ratio of TCARI/OSAVI (R2=0.77) indices and to the simple ratio between reflectance at 515 nm and 570 nm (R515/R570) (R2=0.42), respectively.
关键词： imaging spectroscopy,tropical forest,DART,traits
更新于2025-09-09 09:28:46
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Improved Characterization of a Tropical Forest Using Polarimetric Tomographic Sar Data Acquired at P Band
摘要： This paper concerns processing techniques for the characterization of a tropical forest using PolTomSAR data at P band. In particular, existing forest biomass estimation methods, relating biomass to sampled tomographic intensity values, are revisited using simple methodological steps and an adaptive tomographic intensity sampling approach. The canopy reflectivity sampling location is determined as a function of the effective forest height and of the tomographic resolution, in order to compensate geometrical mismatches. Moreover, an adaptive polarimetric decomposition technique is used to further decouple the sampled intensity from ground and topographic tomographic scattering effects. The performance of the proposed techniques is assessed using TROPISAR P-band data acquired by the ONERA’s SETHI sensor over the Paracou test site in French Guiana in 2009. Results indicate over this site a substantial reduction of the Above Ground Biomass (AGB) estimation error, with respect to existing techniques.
关键词： BIOMASS mission,Polarimetric SAR Tomography (PolTomSAR),P band,3-D imaging,Tropical forest
更新于2025-09-09 09:28:46