Impact of bidirectional reflectance distribution function on modis vegetation indices in southeast Asia tropical forests

Copyright © 2017 ISRS, All Rights Reserved. Tropical forests play important roles on global climate and biodiversity. The Moderate Resolution Imaging Spectroradiometer (MODIS), with high temporal resolution, provide a useful tool to study tropical forest dynamics, including seasonality and inter-annual variation. However, optical satellite data have cloud, aerosol and bidirectional reflectance distribution function (BRDF) effects, that create uncertainty in tropical forest studies. In the Amazon, some researchers demonstrated the difficulties in separating true forest dynamics from BRDF artefacts and seasonal cloud and aerosol influences. Lastly, optical reflectance saturation in dense tropical forests may restrict the retrieval of phenology information. In this study, we investigated the impact of BRDF effects on MODIS vegetation indices (VI) in Southeast Asia (SEA) tropical forests, the least studied area compared to other major tropical forests (South America and Central Africa). Moreover, unlike Amazon tropical forests, VI seasonality in SEA forests is not synchronous with sun-sensor geometries. We used 10-year data of daily MODIS BRDF (MCD43A1) collection 6 product, a kernel-driven model product that allows us to retrieve VI values for a range of fixed solar zenith angles (SZA). We compared these with the standard VI products (MOD13A1, MYD13A1) to analyse BRDF influences. The results show significant BRDF effects in all forest sites. Generally, smaller SZA yielded higher VI signals in forests. We found tradeoff's between VI robustness to BRDF effects and saturation that impacted upon the retrievals of phenology parameters

The stability of expanding reactive shocks in a van der Waals fluid

Despite the extensive literature accumulated since the pioneering works of Dyakov and Kontorovich in the 1950s, the stability of steady shocks is still an open question when realistic boundary conditions are accounted. The consideration of a supporting mechanism, which is indeed a necessary condition for shock steadiness, modifies the perturbation shock dynamics in the unstable range. The Noh problem is a suitable example to form steady expanding shocks. This configuration is of great interest to the high-energy-density-physics community because of its direct application to inertial confinement fusion and astrophysics, for which the stagnation of a supersonically converging material via an accretion shock front is ubiquitous. In this work, we extend the generalized Noh problem, both base-flow solution and linear stability analysis, to conditions where endothermic or exothermic transformations undergo across the shock. Within the spontaneous acoustic emission conditions found for a van der Waals gas [J. W. Bates and D. C. Montgomery, The Dyakov-Kontorovich instability of shock waves in real gases, Phys. Rev. Lett. 84, 1180 (2000)], we find that cylindrical and spherical expanding shocks become literally unstable for sufficiently high mode numbers. Counterintuitively, the effect of exothermicity or endothermicity across the shock is found to be stabilizing or destabilizing, respectively.A.C.R. and C.H. work has been supported with project No. PID2019-108592RB-C41 Ministry of Science and Innovation (MCINN). C.H. work has been also supported by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with UC3M (H2SFE-CM-UC3M). A.L.V. work has been supported by the National Nuclear Security Administration of the U.S. Department of Energy

On the stability of piston-driven planar shocks

We present a theoretical and numerical stability analysis for a piston-driven planar shock against two-dimensional perturbations. The results agree with the well-established theory for isolated planar shocks: in the range of hc < h < 1 + 2M2, where h is the Dyakov-Kontorovich (DK) parameter related to the slope of the Rankine-Hugoniot curve, hc is its critical value corresponding to the onset of the spontaneous acoustic emission (SAE) and M2 is the downstream Mach number, non-decaying oscillations of shock-front ripples occur. The effect of the piston is manifested in the presence of additional frequencies occurring by the reflection of the sonic waves on the piston surface that can reach the shock. An unstable behaviour of the shock perturbation is found to be possible when there is an external excitation source affecting the shock, whose frequency coincides with the self-induced oscillation frequency in the SAE regime, thereby being limited to the range hc < h < 1 + 2M2. An unstable evolution of the shock is also observed for planar shocks restricted to one-dimensional perturbations within the range 1 < h < 1 + 2M2. Both numerical integration of the Euler equations via the method of characteristics and theoretical analysis via Laplace transform are employed to cross-validate the results.The work of A.C.R and C.H. has been supported with project TED2021-129446B-C41 (MICINN/FEDER, UE). The work of C.H. has also received support from the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with UC3M (H2SAFE-CM-UC3M). The work of A.L.V. has been supported by the National Nuclear Security Administration of the US Department of Energy

Editorial: Building and delivering real-world, integrated sustainability solutions: Insights, methods and case-study applications

This Research Topic aims to showcase research, development and technology (RDT) work toward devising and delivering integrated solutions that support and enhance the climate smart landscape (CSL)-based approach. This Research Topic comprises 13 articles, including 10 Original Research articles,1 Review, 1 Hypothesis and Theory article, and 1 Technology Report. State-of-the-art modeling approaches and sampling technologies are showcased. Contributed papers present new methodological/technological innovation, findings, and/or insights across four themes: (1) landscape productivity and crop suitability, (2) variable crop requirements for water and nutrients,(3) crop health status, phenology and phenotyping, (4)crop disease assessment and prediction under integrated pest management (IPM) and the CSL approach

Sostenibilidad de las construcciones. Análisis de las herramientas básicas para la evaluación de la ecoeficiencia en los edificios

Al asumir que el resultado inmediato de la actividad de la construcción (los edificios) puede considerarse como una de las causas de contaminación ambiental, en los últimos años se ha despertado un claro interés y compromiso tanto de los técnicos como de las administraciones en proponer directorios de productos y procedimientos que se puedan calificar como "verdes" y cuyo objetivo básico sea minimizar estos efectos negativos. la cantidad de recursos elaborados es amplia, resultando compleja su clasificación. No obstante se distinguen tres tipos de herramientas de diseño, análisis y valoración, las gufas y directorios, las bases de datos de productos y sistemas y las herramientas de análisis y valoración. Dentro de estas últimas se analizan las más relevantes en este campo

Turbulence generation by a shock wave interacting with a random density inhomogeneity field

When a planar shock wave interacts with a random pattern of pre-shock density non-uniformities, it generates an anisotropic turbulent velocity/vorticity field. This turbulence plays an important role at the early stages of the mixing process in the compressed fluid. This situation emerges naturally in shock interaction with weakly inhomogeneous deuterium-wicked foam targets in Inertial Confinement Fusion (ICF) and with density clumps/clouds in astrophysics. We present an exact small-amplitude linear theory describing such interaction. It is based on the exact theory of time and space evolution of the perturbed quantities behind a corrugated shock front for a single-mode pre-shock non-uniformity. Appropriate mode averaging in 2D results in closed analytical expressions for the turbulent kinetic energy, degree of anisotropy of velocity and vorticity fields in the shocked fluid, shock amplification of the density non-uniformity, and sonic energy flux radiated downstream. These explicit formulas are further simplified in the important asymptotic limits of weak/strong shocks and highly compressible fluids. A comparison with the related problem of a shock interacting with a pre-shock isotropic vorticity field is also presented.Comment: This article corresponds to a presentation given at the Second International Conference and Advanced School "Turbulent Mixing and Beyond," held on 27 July - 07 August 2009 at the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy. That Conference Proceeding will be published as a Topical Issue of the Physica Scripta IOP scienc

Diffusion-flame ignition by shock-wave impingement on a supersonic mixing layer

Ignition in a supersonic mixing layer interacting with an oblique shock wave is investigated analytically and numerically under conditions such that the post-shock flow remains supersonic. The study requires consideration of the structure of the post-shock ignition kernel that is found to exist around the point of maximum temperature, which may be located either near the edge of the mixing layer or in its interior, depending on the profiles of the fuel concentration, temperature and Mach number across the mixing layer. The ignition kernel displays a balance between the rates of chemical reaction and of post-shock flow expansion, including the acoustic interactions of the chemical heat release with the shock wave, leading to increased front curvature. The analysis, which adopts a one-step chemistry model with large activation energy, indicates that ignition develops as a fold bifurcation, the turning point in the diagram of the peak perturbation induced by the chemical reaction as a function of the Damköhler number providing the critical conditions for ignition. While an explicit formula for the critical Damköhler number for ignition is derived when ignition occurs in the interior of the mixing layer, under which condition the ignition kernel is narrow in the streamwise direction, numerical integration is required for determining ignition when it occurs at the edge, under which condition the kernel is no longer slender. Subsequent to ignition, for the Arrhenius chemistry addressed, the lead shock will rapidly be transformed into a thin detonation on the fuel side of the ignition kernel, and, under suitable conditions, a deflagration may extend far downstream, along with the diffusion flame that must separate the rich and lean reaction products. The results can be helpful in describing supersonic combustion for high-speed propulsion

Intrinsic climate dependency of ecosystem light and water-use-efficiencies across Australian biomes

© 2014 IOP Publishing Ltd. The sensitivity of ecosystem gross primary production (GPP) to availability of water and photosynthetically active radiation (PAR) differs among biomes. Here we investigated variations of ecosystem light-use-efficiency (eLUE: GPP/PAR) and water-use-efficiency (eWUE: GPP/evapotranspiration) among seven Australian eddy covariance sites with differing annual precipitation, species composition and temperature. Changes to both eLUE and eWUE were primarily correlated with atmospheric vapor pressure deficit (VPD) at multiple temporal scales across biomes, with minor additional correlations observed with soil moisture and temperature. The effects of leaf area index on eLUE and eWUE were also relatively weak compared to VPD, indicating an intrinsic dependency of eLUE and eWUE on climate. Additionally, eLUE and eWUE were statistically different for biomes between summer and winter, except eWUE for savannas and the grassland. These findings will improve our understanding of how light- and water-use traits in Australian ecosystems may respond to climate change

Modeling the effects of climate and land use change on carbon and trace gas budgets over the Amazon Region using NASA satellite products.

Abstract ID: 14. Publicado também on-line