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Spectral correction Resampling to a true wavelength array; spectral calibration.
Spectral centroid The center point of a spectrum or many spectra, sometimes as
viewed in multidimensional space.
Spectral characteristics Characteristic properties or features related to spectra
collected from a target of interest (e.g., vegetation).
Spectral database (or spectral library) An Internet-based (generally) repository
of spectra tied to metadata including measurement techniques and—for plants—
species identity and/or concurrent trait measurements. For plant spectral databases, entries include leaf- and canopy-level spectra or image- derived spectra
and have specific metadata standards (e.g., EcoSIS.org).
Spectral diversity Variation in spectra, typically measured as reflectance spectra
in the optical range (VIS-SWIR), among a group of plant species, functionally
distinct vegetation types (e.g., grassland vs. forest), or among pixels in a spectroscopic image. See also optical diversity.
Spectral diversity hypothesis The hypothesis that the diversity of spectral profiles predicts some aspect or dimension of biodiversity (e.g., species richness, or
functional diversity). See also optical diversity.
Spectral distance The distance in multidimensional spectral space between spectra. Also a measure of dissimilarity for two or more species or functional types
based on spectral reflectance.
Spectral distortion Systematic inaccuracies in spectra, possibly arising from several sources (e.g., atmosphere or stray light in an instrument).
Spectral domain referring to spectral properties across specific portions of the
electromagnetic spectrum, involving information such as wavelength or spectral
bandwidth.
Spectral feature Pattern in a spectrum due to absorption or scattering characteristics of a material, often involving only a few adjacent wavelengths.
Spectral fingerprint See spectral signature.
Spectral heterogeneity The heterogeneity in spectral characteristics; expected to
be positively related to environmental heterogeneity and also to certain metrics
of biodiversity, but also often a consequence of canopy or landscape variability.
Spectral imaging See imaging spectroscopy.
Spectral index (plural: spectral indices) A mathematical expression, often a
ratio or normalized difference, of measured reflectance or radiance from two or
more spectral bands, with or without a constant or scaling factor, that highlights
a particular feature in the spectral signal.
Spectral laboratory A laboratory using spectrometers, indoors or outdoors,
mobile or stationary.
Spectral mixture analysis A mathematical procedure for estimating the fraction
of subpixel elements in mixed pixels, based on distinct spectral signatures, also
called “endmembers.” The analysis treats pixels as mixtures of these endmembers, which are resolved by calculating the best fitting fractional composition
of all endmembers. Mathematically the fraction of each endmember is multiplied by the endmember’s spectrum, and all fractions are added linearly until
the mixed spectrum is approximated sufficiently, or this process is inverted to
identify relative contributions of each endmember to the mixture. Can be used to
Glossary
Spectral correction Resampling to a true wavelength array; spectral calibration.
Spectral centroid The center point of a spectrum or many spectra, sometimes as
viewed in multidimensional space.
Spectral characteristics Characteristic properties or features related to spectra
collected from a target of interest (e.g., vegetation).
Spectral database (or spectral library) An Internet-based (generally) repository
of spectra tied to metadata including measurement techniques and—for plants—
species identity and/or concurrent trait measurements. For plant spectral databases, entries include leaf- and canopy-level spectra or image- derived spectra
and have specific metadata standards (e.g., EcoSIS.org).
Spectral diversity Variation in spectra, typically measured as reflectance spectra
in the optical range (VIS-SWIR), among a group of plant species, functionally
distinct vegetation types (e.g., grassland vs. forest), or among pixels in a spectroscopic image. See also optical diversity.
Spectral diversity hypothesis The hypothesis that the diversity of spectral profiles predicts some aspect or dimension of biodiversity (e.g., species richness, or
functional diversity). See also optical diversity.
Spectral distance The distance in multidimensional spectral space between spectra. Also a measure of dissimilarity for two or more species or functional types
based on spectral reflectance.
Spectral distortion Systematic inaccuracies in spectra, possibly arising from several sources (e.g., atmosphere or stray light in an instrument).
Spectral domain referring to spectral properties across specific portions of the
electromagnetic spectrum, involving information such as wavelength or spectral
bandwidth.
Spectral feature Pattern in a spectrum due to absorption or scattering characteristics of a material, often involving only a few adjacent wavelengths.
Spectral fingerprint See spectral signature.
Spectral heterogeneity The heterogeneity in spectral characteristics; expected to
be positively related to environmental heterogeneity and also to certain metrics
of biodiversity, but also often a consequence of canopy or landscape variability.
Spectral imaging See imaging spectroscopy.
Spectral index (plural: spectral indices) A mathematical expression, often a
ratio or normalized difference, of measured reflectance or radiance from two or
more spectral bands, with or without a constant or scaling factor, that highlights
a particular feature in the spectral signal.
Spectral laboratory A laboratory using spectrometers, indoors or outdoors,
mobile or stationary.
Spectral mixture analysis A mathematical procedure for estimating the fraction
of subpixel elements in mixed pixels, based on distinct spectral signatures, also
called “endmembers.” The analysis treats pixels as mixtures of these endmembers, which are resolved by calculating the best fitting fractional composition
of all endmembers. Mathematically the fraction of each endmember is multiplied by the endmember’s spectrum, and all fractions are added linearly until
the mixed spectrum is approximated sufficiently, or this process is inverted to
identify relative contributions of each endmember to the mixture. Can be used to
Glossary