Hyperspectral Imagers
Description
Hyperspectral imagers simultaneously acquire
radiance measurements in many narrow,
contiguous spectral bands, and the field is
often referred to as ‘imaging spectroscopy’.
Whereas multispectral scanners measure
radiance in a small number of relatively
broad wavelength bands (typically less than
ten), hyperspectral imagers collect
measurements in a much larger number of
bands (up to hundreds) focused on adjacent,
narrowly defined regions (typically less
than 10 nm) in the electromagnetic
spectrum.
Hyperspectral imagery is a relatively new
type of Earth observation data and its
utility is still being assessed in many
application areas. It has the potential to
allow greater understanding of vegetation
dynamics and physiology and will also help
to determine the most discriminating
spectral bands for particular target
materials and/or conditions. To date,
space-based hyperspectral imagers have
focused on the visible- to shortwave
infrared range; however - useful
applications may also be possible in the
thermal infrared range.
Information from the first generation of
space-based hyperspectral imagers is also
valuable for designing future sensors,
correcting atmospheric and illumination
effects in other imagery, determining
optimum timing (in the diurnal and/or
seasonal cycle) for target discrimination,
and/or calibrating data from other Earth
observation sensors. Typical spatial
resolution for hyperspectral imagers is 30
m, and the intensive spectral sampling
required generates significant data volumes,
which introduces significant strains on
downlink and the data handling and
processing infrastructure.
While a gradual move from multispectral to
hyperspectral imagery could be envisaged,
significant developmental and scientific
challenges remain to unlock the significant
potential of this technology.
Mineral mapping by AVIRIS airborne
hyperspectral imager.
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Current & planned
instruments
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HISUI
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Hyperion
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HSI
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Visible imaging spectrometer
(HyspIRI)
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HYC
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Representation of a typical hyperspectral
‘data cube’.
Applications
The highly resolved image radiance
measurements collected by hyperspectral
imagers allow continuous spectra to be derived
for target features. The resulting spectra can
then be compared with field and/or laboratory
spectra to identify surface materials. This
has proven particularly valuable for mapping
minerals and soils, vegetation species,
composition and health, shallow coastal and
coral reef habitats, and water quality.
Hyperspectral imagery is typically used to
acquire intensive measurements over research
sites that are subsequently extrapolated to
larger areas using other datasets, though some
applications do use regional or broader
coverage, and repeat imagery is often required
to monitor changes.
For some application areas, the value of
hyperspectral imagery is focused on specific
spectral regions, such as:
− Thermal infrared for soil moisture
research;
− Visible to shortwave infrared for vegetation
mapping;
− Middle infrared plus thermal infrared for
mapping minerals and soils; and
− Visible to near infrared for shallow coastal
and coral reef bathymetry, and benthic cover
mapping.
The fusion of hyperspectral imagery with
imaging microwave radar (SAR) data is valued
for defence applications, and for improving
the separation of fractional cover components
in evergreen vegetation.
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