504
similar ecosystems (e.g., tropical rainforests in South America vs. Africa vs. SE
Asia), species and functional diversity can vary widely, and differential responses of
those ecosystems to change depend on their functional composition and diversity.
Current ecosystem models do not have access to data representing functional diversity and need better spatially explicit and temporally resolved measurements to
more accurately characterize responses to change than can be obtained from groundbased and airborne observations.
Space-based measurements add a unique dimension to biodiversity studies. No
single measurement can fully characterize biodiversity, and any single measurement
only captures one or a subset of the dimensions of the diversity of life on Earth.
Species diversity can be captured by taxonomic identification quantified by richness
and turnover, while genetic analyses can capture additional levels of variation,
including within-species variation. Traits are often used to characterize diversity of
function, which may or may not parallel either species or within-species diversity.
Remote sensing (RS) has long been used to characterize controls or correlates of
diversity such as land use, fragmentation, productivity, habitat, and habitat structure. More recently, RS has been used to measure functional diversity (Schneider
et al. 2017) and spectral diversity that predicts species diversity (Gholizadeh et al.
2019) and to characterize species diversity itself (Féret and Asner 2014). RS observations are indirect in the sense that inference must be made from the interaction of
electromagnetic radiation with matter, but they provide far more sampling in time
and space than most in-situ techniques and so are a valuable complement for inherently variable and even ephemeral aspects of the distribution and abundance of
organisms (Saatchi et al. 2015).
For decades, scientists have proposed spaceborne imaging spectrometers as a
means of obtaining information about vegetation in more detail than provided by
multispectral sensors (Ustin et al. 1991), but only limited actual deployments have
occurred (Pearlman et al. 2003) so ecologists have had access primarily to data collected from aircraft, over relatively limited areas. While global access is valuable
(i.e., the ability to sample over all or most of the world while only collecting data
over particular places), global coverage has proved enormously valuable for other
measurements such as greenness, and global spectroscopy will enable studies of
global biogeography, biogeochemical cycles, and biodiversity. As of 2020, this
capability is in planning, and global assessment of plant functional diversity is
likely to become a reality by the latter part of the 2020s. This paper will serve as an
introduction to the likely system so ecologists can become aware of the general
characteristics of the data that are likely to become available.
In 2018, the US National Research Council released the second Decadal Survey
for the Earth Sciences (National Academies of Sciences, Engineering, and Medicine
2018). This document, following the first such survey, released in 2007 (National
Research Council 2007), presented a clear vision for the role of RS in addressing
some of the many dimensions of biodiversity. That report notes that “[k]ey fluxes
within ecosystems are mediated by the composition and functional traits of the
organisms present. Imaging spectroscopy is a tool for determining global terrestrial
and marine plant functional traits, functional types and in some cases, provides
D. Schimel et al.
similar ecosystems (e.g., tropical rainforests in South America vs. Africa vs. SE
Asia), species and functional diversity can vary widely, and differential responses of
those ecosystems to change depend on their functional composition and diversity.
Current ecosystem models do not have access to data representing functional diversity and need better spatially explicit and temporally resolved measurements to
more accurately characterize responses to change than can be obtained from groundbased and airborne observations.
Space-based measurements add a unique dimension to biodiversity studies. No
single measurement can fully characterize biodiversity, and any single measurement
only captures one or a subset of the dimensions of the diversity of life on Earth.
Species diversity can be captured by taxonomic identification quantified by richness
and turnover, while genetic analyses can capture additional levels of variation,
including within-species variation. Traits are often used to characterize diversity of
function, which may or may not parallel either species or within-species diversity.
Remote sensing (RS) has long been used to characterize controls or correlates of
diversity such as land use, fragmentation, productivity, habitat, and habitat structure. More recently, RS has been used to measure functional diversity (Schneider
et al. 2017) and spectral diversity that predicts species diversity (Gholizadeh et al.
2019) and to characterize species diversity itself (Féret and Asner 2014). RS observations are indirect in the sense that inference must be made from the interaction of
electromagnetic radiation with matter, but they provide far more sampling in time
and space than most in-situ techniques and so are a valuable complement for inherently variable and even ephemeral aspects of the distribution and abundance of
organisms (Saatchi et al. 2015).
For decades, scientists have proposed spaceborne imaging spectrometers as a
means of obtaining information about vegetation in more detail than provided by
multispectral sensors (Ustin et al. 1991), but only limited actual deployments have
occurred (Pearlman et al. 2003) so ecologists have had access primarily to data collected from aircraft, over relatively limited areas. While global access is valuable
(i.e., the ability to sample over all or most of the world while only collecting data
over particular places), global coverage has proved enormously valuable for other
measurements such as greenness, and global spectroscopy will enable studies of
global biogeography, biogeochemical cycles, and biodiversity. As of 2020, this
capability is in planning, and global assessment of plant functional diversity is
likely to become a reality by the latter part of the 2020s. This paper will serve as an
introduction to the likely system so ecologists can become aware of the general
characteristics of the data that are likely to become available.
In 2018, the US National Research Council released the second Decadal Survey
for the Earth Sciences (National Academies of Sciences, Engineering, and Medicine
2018). This document, following the first such survey, released in 2007 (National
Research Council 2007), presented a clear vision for the role of RS in addressing
some of the many dimensions of biodiversity. That report notes that “[k]ey fluxes
within ecosystems are mediated by the composition and functional traits of the
organisms present. Imaging spectroscopy is a tool for determining global terrestrial
and marine plant functional traits, functional types and in some cases, provides
D. Schimel et al.