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51.
The goal of this study was to evaluate whether harmonic regression coefficients derived using all available cloud-free observations in a given Landsat pixel for a three-year period can be used to estimate tree canopy cover (TCC), and whether models developed using harmonic regression coefficients as predictor variables are better than models developed using median composite predictor variables, the previous operational standard for the National Land Cover Database (NLCD). The two study areas in the conterminous USA were as follows: West (Oregon), bounded by Landsat Worldwide Reference System 2 (WRS-2) paths/rows 43/30, 44/30, and 45/30; and South (Georgia/South Carolina), bounded by WRS-2 paths/rows 16/37, 17/37, and 18/37. Plot-specific tree canopy cover (the response variable) was collected by experienced interpreters using a dot grid overlaid on 1 m spatial resolution National Agricultural Imagery Program (NAIP) images at two different times per region, circa 2010 and circa 2014. Random forest model comparisons (using 500 independent model runs for each comparison) revealed the following (1) harmonic regression coefficients (one harmonic) are better predictors for every time/region of TCC than median composite focal means and standard deviations (across times/regions, mean increase in pseudo R2 of 6.7% and mean decrease in RMSE of 1.7% TCC) and (2) harmonic regression coefficients (one harmonic, from NDVI, SWIR1, and SWIR2), when added to the full suite of median composite and terrain variables used for the NLCD 2011 product, improve the quality of TCC models for every time/region (mean increase in pseudo R2 of 3.6% and mean decrease in RMSE of 1.0% TCC). The harmonic regression NDVI constant was always one of the top four most important predictors across times/regions, and is more correlated with TCC than the NDVI median composite focal mean. Eigen analysis revealed that there is little to no additional information in the full suite of predictor variables (47 bands) when compared to the harmonic regression coefficients alone (using NDVI, SWIR1, and SWIR2; 9 bands), a finding echoed by both model fit statistics and the resulting maps. We conclude that harmonic regression coefficients derived from Landsat (or, by extension, other comparable earth resource satellite data) can be used to map TCC, either alone or in combination with other TCC-related variables. 相似文献
52.
Detailed spatial information on the presence and properties of woody vegetation serves many purposes, including carbon accounting, environmental reporting and land management. Here, we investigated whether machine learning can be used to combine multiple spatial observations and training data to estimate woody vegetation canopy cover fraction (‘cover’), vegetation height (‘height’) and woody above-ground biomass dry matter (‘biomass’) at 25-m resolution across the Australian continent, where possible on an annual basis. We trained a Random Forest algorithm on cover and height estimates derived from airborne LiDAR over 11 regions and inventory-based biomass estimates for many thousands of plots across Australia. As predictors, we used annual geomedian Landsat surface reflectance, ALOS/PALSAR L-band radar backscatter mosaics, spatial vegetation structure data derived primarily from ICESat/GLAS satellite altimetry, and spatial climate data. Cross-validation experiments were undertaken to optimize the selection of predictors and the configuration of the algorithm. The resulting estimation errors were 0.07 for cover, 3.4 m for height, and 80 t dry matter ha-1 for biomass. A large fraction (89–94 %) of the observed variance was explained in each case. Priorities for future research include validation of the LiDAR-derived cover training data and the use of new satellite vegetation height data from the GEDI mission. Annual cover mapping for 2000–2018 provided detailed insight in woody vegetation dynamics. Continentally, woody vegetation change was primarily driven by water availability and its effect on bushfire and mortality, particularly in the drier interior. Changes in woody vegetation made a substantial contribution to Australia’s total carbon emissions since 2000. Whether these ecosystems will recover biomass in future remains to be seen, given the persistent pressures of climate change and land use. 相似文献
53.
Himalayan cedar (Cedrus deodara (D. Don) G. Don) due to its long age and wide ecological amplitude in the Himalayan region has strong dendroclimatic potential.
A well replicated ring-width chronology of it, derived from the ensemble of tree-ring samples of two adjacent homogeneous
sites, has been used to reconstruct precipitation for the non-monsoon months (previous year October to concurrent May) back
to AD 1171. This provides the first record of hydrological conditions for the western Himalayan region, India during the whole
of the ‘Little Ice Age’ and latter part of the ‘Medieval Warm Period’. The reconstruction revealed the wettest and the driest
non-monsoon months during the fourteenth and the thirteenth centuries, respectively. The seventeenth century consistently
recorded dry non-monsoon months in the western Himalayan region. Surplus precipitation, especially more pronounced since the
1950s, is recorded in the current century. 相似文献
54.
The mid-Cenomanian fish beds of Nammoura, Mont-Liban district, Lebanon contain a diverse fauna of aquatic and terrestrial vertebrates, a few crustaceans and moderately well-preserved plant remains of which a single species,Sapindopsis anhouryi , was previously described by Dilcher & Basson (1990). We add 11 species of ferns, gymnosperms and angiosperms of which Nammouria cretacea gen. et sp. nov, Nupharanthus cretacea gen. et sp. nov., Sapindopsis libanensis sp. nov. and Nammourophyllum altingioides gen. et sp. nov. are new taxa. The florule differs markedly from both Early Cretaceous and Turonian plant assemblages of the Middle East, thereby representing a distinct stage of the regional floristic evolution. Its phytogeographic affinities are with contemporaneous floras of North America, Central Europe and the Crimea. A combination of such features as xeromorphism, the prevalence of compound leaves, and the presence of deciduous angiosperm components and gymnosperms may indicate climatic conditions similar to those of the present day Mediterranean. 相似文献
55.
56.
Mads Olander Rasmussen Frank-M. Göttsche Doudou Diop Cheikh Mbow Folke-S. Olesen Rasmus Fensholt Inge Sandholt 《International Journal of Applied Earth Observation and Geoinformation》2011
A tree survey and an analysis of high resolution satellite data were performed to characterise the woody vegetation within a 10 × 10 km2 area around a site located close to the town of Dahra in the semi-arid northern part of Senegal. The surveyed parameters were tree species, height, tree crown radius, and diameter at breast height (DBH), for which allometric models were determined. An object-based classification method was used to determine tree crown cover (TCC) from Quickbird data. The average TCC from the tree survey and the respective TCC from remote sensing were both about 3.0%. For areas beyond the surveyed areas TCC varied between 3.0% and 4.5%. Furthermore, an empirical correction factor for tree clumping was obtained, which considerably improved the estimated number of trees and the estimated average tree crown area and radius. An allometric model linking TCC to tree stem crosssectional area (CSA) was developed, which allows to estimate tree biomass from remote sensing. The allometric models for the three main tree species found performed well and had r2-values of about 0.7–0.8. 相似文献
57.
Cédric Véga Sylvie Durrieu 《International Journal of Applied Earth Observation and Geoinformation》2011
This paper presents a method for individual tree crown extraction and characterisation from a canopy surface model (CSM). The method is based on a conventional algorithm used for localising LM on a smoothed version of the CSM and subsequently for modelling the tree crowns around each maximum at the plot level. The novelty of the approach lies in the introduction of controls on both the degree of CSM filtering and the shape of elliptic crowns, in addition to a multi-filtering level crown fusion approach to balance omission and commission errors. The algorithm derives the total tree height and the mean crown diameter from the elliptic tree crowns generated. The method was tested and validated on a mountainous forested area mainly covered by mature and even-aged black pine (Pinus nigra ssp. nigra [Arn.]) stands. Mean stem detection per plot, using this method, was 73.97%. Algorithm performance was affected slightly by both stand density and heterogeneity (i.e. tree diameter classes’ distribution). The total tree height and the mean crown diameter were estimated with root mean squared error values of 1.83 m and 1.48 m respectively. Tree heights were slightly underestimated in flat areas and overestimated on slopes. The average crown diameter was underestimated by 17.46% on average. 相似文献
58.
Roderick J. Bale Iain Robertson Neil J. Loader Mary Gagen Danny McCarroll 《Quaternary Research》2011,76(1):22-29
We present the first near millennium-length, annually resolved stable isotope record from bristlecone pines (Pinus longaeva, D.K Bailey). The carbon isotope ratios from the cellulose of seven trees from the White Mountains of California, corrected for anthropogenic changes in atmospheric chemistry, are used to reconstruct growing season (June through August) precipitation back to AD 1085. Extremely negative isotope results are strongly correlated with proposed severest El Niño events over the last 500 yr, and similar values in the first half of the millennium are used to reconstruct a further 13 strong El Niño events, concentrated in the 12th Century and the mid 13th and 14th Centuries. Ring-width chronologies from adjacent sites in the White Mountains demonstrate a high degree of decadal covariance with the δ13C series, although there are several periods of notable divergence. 相似文献
59.
Extending the Place Glacier mass-balance record to AD 1585, using tree rings and wood density 总被引:1,自引:0,他引:1
Recognizing that climate influences both annual tree-ring growth and glacier mass balance, changes in the mass balance of Place Glacier, British Columbia, were documented from increment core records. Annually resolved ring-width (RW), maximum (MXD), and mean density (MD) chronologies were developed from Engelmann spruce and Douglas-fir trees sampled at sites within the surrounding region. A snowpack record dating to AD 1730 was reconstructed using a multivariate regression of spruce MD and fir RW chronologies. Spruce MXD and RW chronologies were used to reconstruct winter mass balance (Bw) for Place Glacier to AD 1585. Summer mass balance (Bs) was reconstructed using the RW chronology from spruce, and net balance was calculated from Bw and Bs. The reconstructions provide insight into the changes that snowpack and mass balance have undergone in the last 400 years, as well as identifying relationships to air temperature and circulation indices in southern British Columbia. These changes are consistent with other regional mass-balance reconstructions and indicate that the persistent weather systems characterizing large scale climate-forcing mechanisms play a significant glaciological role in this region. A comparison to dated moraine surfaces in the surrounding region substantiates that the mass-balance shifts recorded in the proxy data are evident in the response of glaciers throughout the region. 相似文献
60.