507
acteristics have also improved with time, leading to instruments that are better and
better suited for ecological applications (Asner et al. 2012).
A diversity of airborne instruments exist today. In addition, several spaceborne
imaging spectrometers are likely to fly in the next decade (see below), including
NASA’s Earth Surface Mineral Dust Source Investigation (EMIT), aimed at studying atmospheric dust; the Hyperspectral Imager Suite (HISUI) from Japan (Ogawa
et al. 2017), a general purpose instrument deployed to the International Space
Station (ISS) in 2019; and EnMAP from Germany. Nevertheless, the SBG instrument is needed to meet rigorous and community-determined objectives to quantify
plant functional traits globally. SBG will be aimed at studying plant functional
diversity, along with aspects of geology and hydrology, and will be paired with a
thermal imager designed to study hydrological and geological processes as well as
thermal drivers of ecosystem processes, such as evapotranspiration. The following
discussion covers only those aspects of the instrument that directly address plant
functional diversity. SBG’s objectives for observing plant functional diversity are
summarized in Table 19.2, excerpted from the National Academies (2018) document.
The Science and Applications Traceability Matrix (SATM) for the plant functional trait designated observable of SBG (Table 19.2) allows us to see the shape of
the mission likely to fly in the mid-2020s. An SATM links science of a mission to
the measurements necessary for the mission’s objectives, as well as providing metrics for assessment of instrument performance for those measurements. What will
the data from this mission look like? The matrix defines a number of key parameters, and those parameters allow us to see the opportunities and challenges this
instrument will raise, once flown.
The data, radiance measurements of reflected sunlight, should cover the spectral
region from 400 to 2500 nm, with approximately 10 nm spectral discretization,
leading to an instrument with >200 spectral channels, meaning the data volume
from this instrument will be very high. The information content would likewise be
high, as work by Thompson et al. (2017) and Asner et al. (2012) shows that data like
these collected over vegetated surfaces have as many as 30 significant principal
components, meaning that pixels can be described in 30-dimensional space, while
by contrast LANDSAT has 3 dimensions (Schimel et al. 2013).
The National Academies report calls for SBG’s pixels to be of order 30–45 m,
meaning each pixel is about 900–2000 m
2
, collected nominally at least every 16,
which could be halved if paired with the CHIME mission. The terrestrial Earth surface is about 2/3 covered with clouds at any given time, though that varies geographically and with time of day and season, so not every acquisition succeeds in
capturing the land surface. A nominal 16-day revisit means most sites will be
imaged, on the average, about once a month, but in some very cloudy regions and
ecosystems—for example, humid tropical ecosystems—a 16-day revisit might
mean one acquisition every few years. In the National Academies (2018) report,
more frequent but less spectral resolved measurements are suggested as a complement to SGB-type measurements, providing less functional information though
more phenological or time series information.
Signal-to-noise ratio is one of several spectroscopic parameters that determine
the information content of IS data. Gross features of plant composition emerge with
19 Prospects and Pitfalls for Spectroscopic Remote Sensing of Biodiversity…
acteristics have also improved with time, leading to instruments that are better and
better suited for ecological applications (Asner et al. 2012).
A diversity of airborne instruments exist today. In addition, several spaceborne
imaging spectrometers are likely to fly in the next decade (see below), including
NASA’s Earth Surface Mineral Dust Source Investigation (EMIT), aimed at studying atmospheric dust; the Hyperspectral Imager Suite (HISUI) from Japan (Ogawa
et al. 2017), a general purpose instrument deployed to the International Space
Station (ISS) in 2019; and EnMAP from Germany. Nevertheless, the SBG instrument is needed to meet rigorous and community-determined objectives to quantify
plant functional traits globally. SBG will be aimed at studying plant functional
diversity, along with aspects of geology and hydrology, and will be paired with a
thermal imager designed to study hydrological and geological processes as well as
thermal drivers of ecosystem processes, such as evapotranspiration. The following
discussion covers only those aspects of the instrument that directly address plant
functional diversity. SBG’s objectives for observing plant functional diversity are
summarized in Table 19.2, excerpted from the National Academies (2018) document.
The Science and Applications Traceability Matrix (SATM) for the plant functional trait designated observable of SBG (Table 19.2) allows us to see the shape of
the mission likely to fly in the mid-2020s. An SATM links science of a mission to
the measurements necessary for the mission’s objectives, as well as providing metrics for assessment of instrument performance for those measurements. What will
the data from this mission look like? The matrix defines a number of key parameters, and those parameters allow us to see the opportunities and challenges this
instrument will raise, once flown.
The data, radiance measurements of reflected sunlight, should cover the spectral
region from 400 to 2500 nm, with approximately 10 nm spectral discretization,
leading to an instrument with >200 spectral channels, meaning the data volume
from this instrument will be very high. The information content would likewise be
high, as work by Thompson et al. (2017) and Asner et al. (2012) shows that data like
these collected over vegetated surfaces have as many as 30 significant principal
components, meaning that pixels can be described in 30-dimensional space, while
by contrast LANDSAT has 3 dimensions (Schimel et al. 2013).
The National Academies report calls for SBG’s pixels to be of order 30–45 m,
meaning each pixel is about 900–2000 m
2
, collected nominally at least every 16,
which could be halved if paired with the CHIME mission. The terrestrial Earth surface is about 2/3 covered with clouds at any given time, though that varies geographically and with time of day and season, so not every acquisition succeeds in
capturing the land surface. A nominal 16-day revisit means most sites will be
imaged, on the average, about once a month, but in some very cloudy regions and
ecosystems—for example, humid tropical ecosystems—a 16-day revisit might
mean one acquisition every few years. In the National Academies (2018) report,
more frequent but less spectral resolved measurements are suggested as a complement to SGB-type measurements, providing less functional information though
more phenological or time series information.
Signal-to-noise ratio is one of several spectroscopic parameters that determine
the information content of IS data. Gross features of plant composition emerge with
19 Prospects and Pitfalls for Spectroscopic Remote Sensing of Biodiversity…