scholarly journals Interacciones entre índice de área foliar, densidad del dosel y precipitación efectiva de un bosque de Polylepis reticulata ubicado en un ecosistema de páramo

La Granja ◽  
2021 ◽  
Vol 34 (2) ◽  
pp. 63-79
Author(s):  
Amanda Suqui ◽  
Rolando Célleri ◽  
Patricio Crespo ◽  
Galo Carrillo-Rojas
Keyword(s):  
Plant Canopy

La medición de la cobertura vegetal es fundamental para conocer qué porcentaje de la precipitación queda interceptada sobre la misma. Las técnicas más utilizadas para medir la cobertura in situ son el índice de área foliar (IAF) y la densidad del dosel (DD). Sin embargo, no se ha puesto atención en las diferencias registradas en el uso de las dos técnicas ni cómo estas variables influyen sobre el balance hidrológico particularmente sobre la precipitación efectiva (PE). Por tal motivo, el objetivo del estudio es evaluar la relación entre las mediciones de la cobertura vegetal realizadas por los métodos de IAF y DD e identificar cómo se relacionan con la PE, importante para aplicaciones hidrológicas. El estudio se desarrolló en un bosque de Polylepis reticulata de 15633 m2, ubicado en el Observatorio Ecohidrológico Zhurucay, sur de Ecuador, en un rango altitudinal de 3765 a 3809 m s.n.m. El IAF se midió con el equipo CI-110 Plant Canopy Imager y la DD con un densiómetro esférico, cubriendo un amplio rango de valores de cobertura de dosel. Para medir la PE se instrumentó el sitio de estudio con 9 pluviógrafos. Los resultados indican que el IAF y DD son en promedio 2,43 m2 m-2 y 88%, respectivamente; cuya relación resulta ser significativa (R2= 0,913; p<0,05). La PE media anual es de 773,2 mm, que tiende a disminuir con el incremento del IAF y DD; aunque su relación resulta estadísticamente no significativa (valores p>0,05). Este estudio muestra la importancia de caracterizar la cobertura vegetal para entender la interacción con la PE.

A Comparison of Two Photographic Techniques for Estimating Foliage Angle Distribution

1977 ◽  
Vol 25 (5) ◽  
pp. 545 ◽  
Author(s):  
JA Smith ◽  
RE Oliver ◽  
JK Berry
Keyword(s):  
Integral Equation ◽  
Solar Radiation ◽  
Ground Level ◽  
Theoretical Models ◽  
Angle Distribution ◽  
Plant Canopy ◽  
Agropyron Smithii ◽  
In Situ Method ◽  
Vegetation Canopies

There is an increasing interest in theoretical models which describe the interaction of solar radiation with vegetation canopies. Common to these models is a need to describe mathematically the geometric structure of the plant canopy. The amount of radiation reflected or absorbed by the canopy is primarily determined by the distribution of gaps in the foliage with respect to the radiation source. A measure of canopy geometry related to gap frequency at various view angles is the distribution of leaf angles. Two methods for measuring the distribution of leaf angles are discussed. The first method is to project orthogonally and photograph individual plants and relate the measured leaf angles in the projections to the canopy distribution of angles. The second method is a rapid in situ method based on ground level multiple view angle photography. A Fredholm integral equation relating foliage angles to the proportion of gap in the canopy as a function of view angle is then solved. Comparisons of the results using the two methods are made for a canopy of Western wheat grass (Agropyron smithii).

3D forest model-assisted validation of the Sentinel-2 SNAP fAPAR product

2020 ◽  
Author(s):  
Niall Origo ◽  
Joanne Nightingale ◽  
Kim Calders ◽  
Mathias Disney
Keyword(s):  
Energy Balance ◽  
Carbon Cycle ◽  
Global Climate ◽  
Data Uncertainty ◽  
Plant Canopy ◽  
Validation Data ◽  
Uncertainty Estimates ◽  
The Impact ◽  
Sentinel 2

&lt;p&gt;fAPAR is a radiometric quantity describing the fraction of photosynthetically active radiation (PAR) absorbed by a plant canopy. It is an important component of carbon cycle and energy balance models and has been named as one of the 50 Global Climate Observing System (GCOS) essential climate variables (ECVs). Space agencies such as the ESA and NASA produce satellite fAPAR products in order to address the need for spatially explicit global data to address environmental and climate change issues. Given the derived nature of satellite fAPAR products it is essential to independently verify the results they produce. In order to do this, validation sites (or networks of sites) are needed that directly correspond to the measurands. Further to this, in order to understand divergences between product and validation data, uncertainty information should be provided with all measurement results.&lt;/p&gt;&lt;p&gt;The canopy radiative transfer models which are used in satellite-derived fAPAR products implement simplistic assumptions about the state of the plant canopy and illumination conditions in order to retrieve an fAPAR estimate in a computationally feasible time. This contribution assesses the impact of the assumptions made by the Sentinel-2 SNAP-derived fAPAR and includes it in a validation of the product over a field site (Wytham Woods, UK), which also has concurrent fAPAR measurements. This is achieved using a 3D model of Wytham Woods which is used to simulate biases associated with specific assumption types. These are used to convert the in situ measurements to the same quantity assumed by the satellite product. The measurement network which provides the fAPAR data is also traceable to SI through sensor calibrations and has associated uncertainty estimates. To our knowledge, these latter points have not been implemented in the biophysical product validation literature, which may explain some of the large discrepancies seen between validation and satellite-derived fAPAR data.&lt;/p&gt;&lt;p&gt;The ultimate aim of this work is to demonstrate a validation framework for derived biophysical variables such as fAPAR which properly considers the quantity estimated by the satellite and that measured by the in situ sensors, whilst providing metrologically derived uncertainties on the in situ data. This will help to properly inform users as to the quality of the data and determine whether the GCOS requirements set for fAPAR are attainable, ultimately improving carbon cycle and energy balance estimates.&lt;/p&gt;

Rendez vous with Saturn's rings

1984 ◽  
Vol 75 ◽  
pp. 743-759 ◽  
Author(s):  
Kerry T. Nock
Keyword(s):  
Solar Energy ◽  
Electric Propulsion ◽  
Power Source ◽  
Propulsion System ◽  
Low Thrust ◽  
Ring Plane ◽  
The Earth ◽  
Total Impulse ◽  
Saturn's Rings

ABSTRACTA mission to rendezvous with the rings of Saturn is studied with regard to science rationale and instrumentation and engineering feasibility and design. Future detailedin situexploration of the rings of Saturn will require spacecraft systems with enormous propulsive capability. NASA is currently studying the critical technologies for just such a system, called Nuclear Electric Propulsion (NEP). Electric propulsion is the only technology which can effectively provide the required total impulse for this demanding mission. Furthermore, the power source must be nuclear because the solar energy reaching Saturn is only 1% of that at the Earth. An important aspect of this mission is the ability of the low thrust propulsion system to continuously boost the spacecraft above the ring plane as it spirals in toward Saturn, thus enabling scientific measurements of ring particles from only a few kilometers.

The Use of Advanced Analytical Techniques for Characterization of the Chemical, Physical, and Crystallographic Nature of a Surface

1973 ◽  
Vol 31 ◽  
pp. 132-133 ◽  
Author(s):  
R. E. Herfert
Keyword(s):  
Surface Characterization ◽  
Analytical Techniques ◽  
X Ray Diffraction ◽  
Depth Of Penetration ◽  
X Ray ◽  
The Past ◽  
Transmission Electron ◽  
Scanning Electron

Studies of the nature of a surface, either metallic or nonmetallic, in the past, have been limited to the instrumentation available for these measurements. In the past, optical microscopy, replica transmission electron microscopy, electron or X-ray diffraction and optical or X-ray spectroscopy have provided the means of surface characterization. Actually, some of these techniques are not purely surface; the depth of penetration may be a few thousands of an inch. Within the last five years, instrumentation has been made available which now makes it practical for use to study the outer few 100A of layers and characterize it completely from a chemical, physical, and crystallographic standpoint. The scanning electron microscope (SEM) provides a means of viewing the surface of a material in situ to magnifications as high as 250,000X.

Structural Studies on Mitotic Spindle Fibres

1978 ◽  
Vol 36 (3) ◽  
pp. 615-626
Author(s):  
J.R. Mcintosh
Keyword(s):  
Chemical Composition ◽  
Mitotic Spindle ◽  
Structural Studies ◽  
Mitotic Apparatus ◽  
Chemical Studies ◽  
Medical Interest ◽  
Spindle Fibres

The mitotic apparatus is a structure of obvious biological and medical interest, but it has proved to be a difficult cellular machine to understand. The chemical composition of the spindle is only slightly elucidated, largely because of the difficulties in preparing useful isolates of the structure. Chemical studies of the mitotic spindle have been reviewed elsewhere (Mcintosh, 1977), and will not be discussed further here. One would think that structural studies on the mitotic apparatus (MA) in situ would be straightforward, but even with this approach there is some disagreement in the results obtained with various methods and by different investigators. In this paper I will review briefly the approaches which have been used in structural studies of the MA, pointing out the strengths and problems of each approach. I will summarize the principal findings of the different methods, and identify what seem to be fruitful avenues for further work.

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