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Spectral variation hypothesis (SVH) A hypothesis that states that the spatial
variability in the remotely sensed signal, i.e., the spectral heterogeneity, is
expected to be positively related to environmental heterogeneity, or to variation
in plant traits, and could therefore be used as a proxy of biodiversity.
Spectral vegetation index A mathematical combination of reflectance from
wavelength regions that together are relevant to vegetation properties or processes (see spectral index).
Spectranomics Term introduced by Asner and Martin (2008) to describe an
approach to link plants, canopies, and community as well as their functional
traits to their spectral properties with the objective of providing time- varying,
scalable methods for remote sensing of ecosystems and biodiversity.
Spectrophotometer An instrument for measuring the spectral transmittance of
light to infer the spectral absorbance. Spectrometers are typically used for determining absorbance in a solution to quantify the concentration of particular compounds. See also spectrometer.
Spectrometer A device that is designed to measure electromagnetic radiation as
a function of wavelength; not necessarily radiometrically calibrated (c.f. spectroradiometer). See also spectrophotometer and spectroradiometer.
Spectrometry Measurement with a spectrometer.
Spectroradiometer A device that is designed to measure electromagnetic radiation across a range of wavelengths; a radiometrically calibrated spectrometer
(c.f. spectrometer).
Spectroscopy An area of study focused on the interactions between electromagnetic radiation and matter. For imaging spectroscopy of plant biodiversity, the
term is used to describe the measurement of electromagnetic radiation in a pixel
of an image to study the properties of leaves, canopies, ecosystems, and landscapes and their variation in time and space.
Spectrum A depiction of the intensity or distribution of electromagnetic radiation, typically the emittance, radiance, reflectance, absorptance, or transmittance
over the wavelength interval measured and expressed in digital numbers, radiance (watts per steradian per square meter, W·sr
−1
·m
−2
), or as a fraction or percentage of outgoing to incoming radiance (reflectance) or emissivity. Can also
be used to express absorbance, fluorescence, or emittance as a function of wavelength. Plural: spectra.
Specular A type of electromagnetic reflection that is scattered away from a very
smooth, mirror-like surface. When light is specularly reflected from a surface, it
is reflected at the same angle as the incident ray but on the opposite side of the
plane normal to the surface (c.f. Lambertian or isotropic).
Spongy mesophyll Photosynthetic parenchyma tissue in plant leaves where the
cells are loosely arranged. Typically located on the abaxial side (normally the
lower surface) of the leaf and specialized to facilitate the transport and exchange
of CO 2 , H 2 O, and O 2 .
Stationarity Equality or constancy of parameter values or statistical descriptors
(e.g., mean, variance) of equidistant points in space or time.
Stomata The turgor-controlled valves, comprised of specialized epidermal cells
(guard cells), typically located on the abaxial (lower) side of the leaf, that open
Glossary
Spectral variation hypothesis (SVH) A hypothesis that states that the spatial
variability in the remotely sensed signal, i.e., the spectral heterogeneity, is
expected to be positively related to environmental heterogeneity, or to variation
in plant traits, and could therefore be used as a proxy of biodiversity.
Spectral vegetation index A mathematical combination of reflectance from
wavelength regions that together are relevant to vegetation properties or processes (see spectral index).
Spectranomics Term introduced by Asner and Martin (2008) to describe an
approach to link plants, canopies, and community as well as their functional
traits to their spectral properties with the objective of providing time- varying,
scalable methods for remote sensing of ecosystems and biodiversity.
Spectrophotometer An instrument for measuring the spectral transmittance of
light to infer the spectral absorbance. Spectrometers are typically used for determining absorbance in a solution to quantify the concentration of particular compounds. See also spectrometer.
Spectrometer A device that is designed to measure electromagnetic radiation as
a function of wavelength; not necessarily radiometrically calibrated (c.f. spectroradiometer). See also spectrophotometer and spectroradiometer.
Spectrometry Measurement with a spectrometer.
Spectroradiometer A device that is designed to measure electromagnetic radiation across a range of wavelengths; a radiometrically calibrated spectrometer
(c.f. spectrometer).
Spectroscopy An area of study focused on the interactions between electromagnetic radiation and matter. For imaging spectroscopy of plant biodiversity, the
term is used to describe the measurement of electromagnetic radiation in a pixel
of an image to study the properties of leaves, canopies, ecosystems, and landscapes and their variation in time and space.
Spectrum A depiction of the intensity or distribution of electromagnetic radiation, typically the emittance, radiance, reflectance, absorptance, or transmittance
over the wavelength interval measured and expressed in digital numbers, radiance (watts per steradian per square meter, W·sr
−1
·m
−2
), or as a fraction or percentage of outgoing to incoming radiance (reflectance) or emissivity. Can also
be used to express absorbance, fluorescence, or emittance as a function of wavelength. Plural: spectra.
Specular A type of electromagnetic reflection that is scattered away from a very
smooth, mirror-like surface. When light is specularly reflected from a surface, it
is reflected at the same angle as the incident ray but on the opposite side of the
plane normal to the surface (c.f. Lambertian or isotropic).
Spongy mesophyll Photosynthetic parenchyma tissue in plant leaves where the
cells are loosely arranged. Typically located on the abaxial side (normally the
lower surface) of the leaf and specialized to facilitate the transport and exchange
of CO 2 , H 2 O, and O 2 .
Stationarity Equality or constancy of parameter values or statistical descriptors
(e.g., mean, variance) of equidistant points in space or time.
Stomata The turgor-controlled valves, comprised of specialized epidermal cells
(guard cells), typically located on the abaxial (lower) side of the leaf, that open
Glossary