Quantifying urban forest structure with open-access remote sensing data sets

Future cities are set to face ever increasing population and climate pressures, ecosystem services offered by urban forests have been recognised as providing significant mitigation for these pressures. Therefore, the ability to accurately quantify the extent and structure of urban forests, across large and highly dynamic cities, is vital for determining the value of services provided and to assess the effectiveness of policy to promote these important assets. Current inventory methods used in urban forestry are mostly reliant on plot networks measuring a range of structural and demographic metrics; however, limited sampling (spatially and temporally) cannot fully capture the dynamics and spatial heterogeneity of the urban matrix. The rapid increase in the availability of open-access remote sensing data and processing tools offers an opportunity for monitoring and assessment of urban forest structure that is synoptic and at high spatial and temporal resolutions. Here we present a framework to estimate urban forest structure that uses open-access data and software, is robust to differences in data sources, is reproducible and is transferable between cities. The workflow is demonstrated by estimating three metrics of 3D forest structure (canopy cover, canopy height and tree density) across the Greater London area (1577 km^{2}). Random Forest was trained with open-access airborne LiDAR or iTree Eco inventory data, with predictor variables derived from Sentinel 2, climatic and topography data sets. Output were maps of forest structure at 100 m and 20 m resolution. Results indicate that forest structure can be accurately estimated across large urban areas; Greater London has a mean canopy cover of ∼16.5% (RMSE 11-17%), mean canopy height of 8.1–15.0 m (RMSE 4.9–6.2 m) m and is home to ∼4.6 M large trees (projected crown area >10 m^{2}Urban forest structureOpen-accessRemote sensingAirborne LiDARiTree EcoSentinel 2). Transferability to other cities is demonstrated using the UK city of Southampton, where estimates were generated from local and Greater London training data sets indicating application beyond geographic domains is feasible. The methods presented here can augment existing inventory practices and give city planners, urban forest managers and greenspace advocates across the globe tools to generate consistent and timely information to help assess and value urban forests

Numerical solutlon of nonllnear boundary value problems with applications, by Milan KubÍĉek and VladimÍr HlavÁĉek, × + 323 pp. Prentice-Hall, Engkewood Cliffs, N.J., 1983; $34.95

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37388/1/690290528_ftp.pd

Computers & chemical engineering, Pergarnon Press, first issued in June 1977; published quarterly, annual subscription 64(withareducedpriceof64 (with a reduced price of 30 for individuals whose institutional library already subscribes)

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37378/1/690240431_ftp.pd

Fluid flow and heat transfer, Aksel L. Lydersen, x + 357 pp., John Wiley & Sons, New york, 1979, $42.50

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37385/1/690280539_ftp.pd

Computational fluid mechanics and heat transfer. By Dale A. Anderson, John C. Tannehill, and Richard H. Pletcher, McGraw-Hill, 1984, 599 + ix pp., $39.95

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37392/1/690310531_ftp.pd

The finite-difference computation of natural convection in a rectangular enclosure

A study is made of the natural convection of a fluid contained in a long horizontal enclosure of rectangular cross section with one vertical wall heated and the other cooled. Two-dimensional motion is assumed. The governing vorticity and energy transport equations are solved by an implicit alternating direction finite-difference method. Transient and steady state isothermals and streamlines are obtained for Grashof numbers up to 100,000 and for height-to-width ratios of 1, 2, and 3.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37342/1/690120129_ftp.pd

An Empirical Ultraviolet Template for Iron Emission in Quasars as Derived from I Zw 1

We present an empirical template spectrum suitable for fitting/subtracting and studying the FeII and FeIII line emission in the restframe UV spectra of active galatic nuclei (AGNs), the first empirical UV iron template to cover the full 1250 - 3090 A range. Iron emission is often a severe contaminant in optical--UV spectra of AGNs. Its presence complicates and limits the accuracy of measurements of both strong and weak emission lines and the continuum emission, affecting studies of line and continuum interrelations, the ionization structure, and elemental abundances in AGNs. Despite the wealth of work on modeling the AGN FeII emission and the need to account for it in observed AGN spectra, there is no UV template electronically available to aid this process. The iron template we present is based on HST spectra of the Narrow Line Seyfert 1, IZw1. Its intrinsic narrow lines (~900 km/s) and rich iron spectrum make the template particularly suitable for use with most AGN spectra. The iron emission spectrum and the line identifications and measurements are presented and compared with the work of Laor et al. We illustrate the application of the derived FeII and FeIII templates by fitting and subtracting the iron emission from UV spectra of four high-z quasars and of the nearby quasar, 3C273. We briefly discuss the small discrepancies between this observed iron emission and the UV template, and compare the template with previously published ones. We discuss the advantages and limitations of the templates and of the template fitting method. We conclude that the templates work sufficiently well to be a valuable and important tool for eliminating and studying the iron emission in AGNs, at least until accurate theoretical iron emission models are developed. (Abridged)Comment: 73 pages including 7 figures, 6 tables. To appear in ApJS. Preprint is also available at http://www.astronomy.ohio-state.edu/~vester/IronEmission

Stability of multilayer extrusion of viscoelastic liquids

A linear stability analysis of multilayer plane Poiseuille flow of Oldroyd-B liquids with shear rate dependent viscosities is performed for an arbitary number of layers. Asymptotic solutions at long wavelengths and numerical solutions at wavelengths of O (1) are obtained for two-dimensional infinitesimal disturbances. The asymptotic solutions are identical for viscoelastic and Newtonian liquids in two- and three-layer flows, except for nearly geometrically symmetric configurations in three-layer flows. Multilayer flows of viscoelastic liquids can be stable at all wavelengths; thus, operating diagrams of stable flows can be constructed. Symmetric and nearly symmetric configurations in three-layer flows are unstable when the core layer is more viscous than the cuter layers. For highly elastic liquids, stability is not influenced by elasticity, whereas shear thinning always destabilizes the flow. The analysis provides guidelines to avoid interfacial instabilities, which originate inside dies of multilayer extrusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/37414/1/690360508_ftp.pd