Glossary

A-B-C-D- E-F-G-H- I-J-K-L- M-N-O-P- Q-R-S-T- U-V-W-X- Y-Z

A

Absorptivity

With respect to the monochromatic radiation incindent upon a layer, the absorvity is the ratio between the radiation absorbed by a layer and the intensity of the radiation incindent upon that layer.(Peixoto and Oort,"Physics of Climate" 1992)


Atmospheric windows

Are regions of the electromagnetic spectrum where radiation suffers little attenuation by the atmosphere (that is, atmospheric transmissivity is high and absortivity is low). It is through those windows that satellites observe Earth surface on the visible and/or infrared regions of the electromagnetic spectrum


B

Black Body

Is by definition a perfect absorber. It also emits the maximum possible amount of energy at a given temperature (Peixoto and Oort,"Physics of Climate" 1992)


Bidirectional Reflectance Distribution Functions (BRDF)

Describes the reflection behavior for all possible combinations of sun-viewing geometries. The characteristics of the BRDF will determine what "type" of material the viewer thinks the displayed object is composed of.

Biomass

The total amount of living matter in a given population or community. (Kimball's Biology Pages http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/)


Biome

A large, distinctive complex of plant communities created and maintained by climate. (Kimball's Biology Pages http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/)


Body

A coherent mass of material which can be regarded as having uniform temperature and composition (Wallace and Hobbs, 1977)


C

Cellulose

The basic structural component of plant cell walls, comprises about 33 percent of all vegetable matter (90 percent of cotton and 50 percent of wood are cellulose) and is the most abundant of all naturally occurring organic compounds. Nondigestible by man, cellulose is a food for herbivorous animals. (Encyclopaedia Britannica www.britannica.com/Biology/cellulose/)


Chloroplasts

Organelles located within a green plant cell in which photosynthesis occurs. (Encyclopaedia Britannica www.britannica.com/Biology/chloroplast/)


D

Dry Matter Productivity (DMP)

Is the increase in dry matter biomass.


Diffusion

The light in the atmosphere is diverted or scattered from its direction of propagation when it encounters particles or inhomogeneities. When those particles are sufficiently large the dispersion of radiation approaches a 1/λ dependence we have diffuse reflection or diffusion.


E

Electromagnetic spectrum

Is the full range of frequencies (or wavelenghts) that characterize light, from the highest frequencies (short wavelengths) to the lowest frequencies (long wavelengths). It ranges from gamma (<10-8cm) and x-rays (10-9cm-10-7cm), through ultraviolet, visible and infrared radiation, to microwaves and radiowaves (>10m).


F

Fraction of Photosynthetically Active Radiation (fAPAR)

Represents the fraction of incoming solar radiation in the photosynthetically active radiation (PAR) spectral range (0.4μm - 0.7μm) that is absorbed by the green parts of the canopy.


Fraction Vegetation Cover (FVC)

Amount of vegetation distributed on a flat background: FVC = covered by vegetation / (uncovered by vegetation + covered by vegetation)


G

Geostationary orbit

A geostationary (GEO=earth) orbit is one in which the satellite is always in the same position with respect to the rotating Earth. The satellite orbits at an elevation of approximately 35,790 km because that produces an orbital period (time for one orbit) equal to the period of rotation of the Earth (23 hrs, 56 mins, 4.09 secs). By orbiting at the same rate, in the same direction as Earth, the satellite appears stationary (synchronous with respect to the rotation of the Earth).


H

HDF5

Hierarchical Data Format 5, is a data format suitable to handle large data collections.The HDF5 files in Land SAF system have the following structure:(i) a common set of attributes for all kind of data, containing general information about the data; (ii) a dataset for the parameter values; (iii) additional datasets for metadata (e.g., quality flags, error field).


I

Isotropic reflectance

Reflectance values directionally normalised to reference illumination and observation.


J


K

Kernel functions

A kernel is a non-negative real-valued integrable function K satisfying the following two requirements:
-∞+∞K(u)du = 1;
and
K(-u) = K(u); for all values of u.
Kernel functions are used in BRDFs (please consult Bidirectional Reflectance Distribution Functions), to estimate vegetation parameters. In the model proposed by Roujean et al. (1992) the Kernel functions, F1 and F2, only depend on the angular configuration of aquisition; the sun zenith angle; the satellite zenith angle and the relative azimuth angle between sun and satellite.


L

Leaf Area Index (LAI)

is geometrically defined as the total one-sided area of photosynthetic tissue per unit of ground surface area. It represents the amount of leaf material in ecosystems and controls the links between biosphere and atmosphere through various processes such as photosynthesis, respiration, transpiration and rain interception.

Leaf structure

A cross section through the blade of a typical leaf reveals 4 distinct tissue.(1) Upper epidermis

This is a single layer of cells containing few or no chloroplasts. The cells are quite transparent and permit most of the light that strikes them to pass through to the underlying cells. The upper surface is covered with a waxy, waterproof cuticle, which serves to reduce water loss from the leaf. (2)Palisade layer

This consists of one or more layers of cylindrical cells oriented with their long axis perpendicular to the plane of the leaf. The cells are filled with chloroplasts (usually several dozen of them) and carry on most of the photosynthesis in the leaf. (3)Spongy layer

Lying beneath the palisade layer, its cells are irregular in shape and loosely packed. Although they contain a few chloroplasts, their main function seems to be the temporary storage of sugars and amino acids synthesized in the palisade layer. They also aid in the exchange of gases between the leaf and the environment. During the day, these cells give off oxygen and water vapor to the air spaces that surround them. They also pick up carbon dioxide from the air spaces. The air spaces are interconnected and eventually open to the outside through pores called stomata (sing., stoma). (4) Lower epidermis

Typically. most of the stomata (thousands per square centimeter) are located in the lower epidermis. Although most of the cells of the lower epidermis resemble those of the upper epidermis, each stoma is flanked by two sausage-shaped cells called guard cells. These differ from the other cells of the lower epidermis not only in their shape but also in having chloroplasts. The guard cells regulate the opening and closing of the stomata. Thus they control the exchange of gases between the leaf and the surrounding atmosphere (Kimball's Biology Pages http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/)

LEO

Low Earth Orbit, the same as Polar orbit (please consult Polar orbit).


Lingnin

A polymer in the secondary cell wall of woody plant cells that helps to strengthen and stiffen the wall.


Long rain season

In equatorial East Africa, two wet and two dry seasons are common, reflecting the dual passage of the ITCZ. (Trewartha, G. T. and L.H. Horn, "An Introduction to Climate" 5th edition McGraw-Hill). In Kenya, the rain season with longer time duration and therefore called long rain season, extends from March to May and reflects the passage of the ITCZ from the southern position at the Southern Hemisphere in January to the northern position at the Northern Hemisphere in July.


M

Mesophyll cells

Are cells specialized for photosynthesis filled with chloroplasts. This photosynthesis specialized cells are of two types: the palisade mesophyll located in the palissade layer, that consists of columnar cells and the spongy mesophyll that consists of spherical cells and are located in the spongy layer.


MSG

Meteosat Second Generation consists of a series of four geostationary meteorological satellites, along with ground-based infrastructure, that will operate consecutively untill 2018. The first MSG satellite to be launched was Meteosat-8, in 2002. The second satellite followed up in December 2005.(more information in http://www.eumetsat.int/Home/Main/What_We_Do/Satellites/Meteosat_Second_Generation/)


N

NDVI

Normalized Difference Vegetation Index, it consists of a normalized ratio of the NIR and red bands
NDVI = ( ρNIR - ρred ) / ( ρNIR + ρred )
Where:
ρNIR and ρred - are the surface bidirectional reflectance factors for their respective sensor bands.


O

Orbit

- the path followed by a moon, planet or artificial satellite as it travels around another body in space.


P

Palisade layer

Consists of one or more layers of cylindrical cells oriented with their long axis perpendicular to the plane of the leaf. The cells are filled with chloroplasts (usually several dozen of them) and carry on most of the photosynthesis in the leaf. (please consult Leaf structure)


Pigment

Any substance that absorbs light.


Polar Orbit

LEO or Helio-synchronous (HELIOS=sun) orbit. These satellites operate in a sun-synchronous orbit. The satellite passes the equator and each latitude at the same local solar time each day, meaning the satellite passes overhead at essentially the same solar time throughout all seasons of the year. This feature enables regular data collection at consistent times as well as long-term comparisons. The orbital plane of a sun-synchronous orbit must also rotate approximately one degree per day to keep pace with the Earth's surface.


Q


R

Reflectivity

with respect to the monochromatic radiation incindent upon a layer, the reflectivity (or albedo at a given wavelength) is the ratio between the radiation reflected by a layer and the intensity of the radiation incindent upon that layer.(Peixoto and Oort,"Physics of Climate" 1992)


Red edge

The abrupt transition between the strong absorption in the visible red and the strong reflectance in the NIR domain is an optical property common to all healthy green vegetation.


S

SAFs

Satellite Application Facilities are dedicated centres for processing satellite data and form an integral part of the distributed EUMETSAT Application Ground Segment. Each SAF is led by the National Meteorological Service (NMS) of a EUMETSAT Member State in association with a consortium of EUMETSAT Member States and Cooperating States, government bodies and research institutes. The lead NMS is responsible for the management of each complete SAF project. The research, data and services provided by the SAFs complement the standard meteorological products delivered by EUMETSAT’s central facilities. There are currently seven SAFs providing products and services on an operational basis:

  • SAF on Support to Nowcasting and Very Short Range Forecasting
  • Ocean and Sea Ice SAF
  • Climate Monitoring SAF
  • Numerical Weather Prediction SAF
  • Land Surface Analysis SAF
  • Ozone and Atmospheric Chemistry Monitoring SAF
  • GRAS Meteorology SAF

One SAF is under development:

  • Support to Operational Hydrology and Water Management

more information can be found at http://www.eumetsat.int/Home/Main/What_We_Do/SAFs/)

Satellite zenith angle

The angle between the local zenith and the line of sight to the satellite.(please consult http://asd-www.larc.nasa.gov/SCOOL/)

Senescence

Physiological decline or aging of a plant.

Short rain season

In equatorial East Africa, two wet and two dry seasons are common, reflecting the dual passage of the ITCZ. (Trewartha, G. T. and L.H. Horn, "An Introduction to Climate" 5th edition McGraw-Hill). In Kenya, the rain season with shorter time duration and therefore called short rain season, extends from October to December and reflects the passage of the ITCZ from the northern position at the Northern Hemisphere in July to the southern position at the Southern Hemisphere in January.

SOS

Start Of Season, starting time of the plants growing season for a region.

Spectral Mixture Analysis (SMA)

The signal from a single pixel (surface reflectance) is assumed to be the contribution of different vegetation and bare soil components within the scene.

Sun zenith angle

The angle between the local zenith and the line of sight to the sun.(please consult http://asd-www.larc.nasa.gov/SCOOL/)


T

Transmissivity

With respect to the monochromatic radiation incindent upon a layer, the transmissivity is the ratio between the radiation transmitted by a layer and the intensity of the radiation incindent upon that layer.(Peixoto and Oort,"Physics of Climate" 1992)


U


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W


X


Y


Z