509
SNRs of 100–200, but modern airborne IS instruments have SNRs of >1000:1,
depending on the fraction of incoming sunlight reflected. The brighter the surface,
the more light is reflected and the more light is incident on the instrument’s detector,
increasing SNR. This is also true spectrally, so even over a particular location, parts
of the spectrum will have higher or lower SNR, depending on the spectral reflectance of the surface. With modern instruments (Mouroulis et al. 2011), SNR is not
expected to be limiting for plant functional trait estimates.
Several other objectives for an SBG mission may be inferred from the wording
of the SATM but require additional discussion to fully quantify. For example, the
defining question for the plant functional trait designated observable asks why traits
are changing in time and space. This implies broad coverage, ideally global, to
observe spatial changes (e.g., along environmental gradients) and a long-enough
time series to see at least some timescales of change.
While in many ecosystems, an SBG instrument would observe phenological
change, several years or more on orbit would be required to see other types of change,
such as successional change or change after disturbance. The report discusses three
types of disturbance that could cause change, each with a different timescale. Wildfire
causes extremely rapid change but may require decades or longer for full recovery.
Pine beetle infestations, such as those have occurred in the Western United States and
Canada, emerge more slowly, over several years, but may likewise trigger decades of
recovery. Permafrost thaw is the slowest disturbance to emerge of the three considered; it does not lead to recovery but rather may initiate a long-term cascade of change
to a new state. A global imaging spectroscopy mission would see some aspects of these
disturbance processes as expressed through changing plant functional traits, but likely
only a sequence of missions could see the slower aspects of recovery and change.
The formal mission study for SBG began in 2018. Some changes from the above
description could occur between the National Academies (2018) definition of the
observables and objectives identified for construction, so the above descriptions
should be considered provisional.
19.3 EMIT, HISUI, and EnMAP
Several other imaging spectrometers with global access, although more limited coverage, are likely to fly before SBG. All will prove valuable in gathering imaging
spectroscopy data in previously unsampled or inaccessible regions to serve as baselines for change in areas surveyed later by SBG (Schimel et al. 2013). While several
other imaging spectrometers may fly, the three described below are most likely to
provide data of interest to ecologists.
EMIT is a NASA Earth Venture Instrument investigation selected competitively
and planned for flight on the ISS in 2021. It will be an advanced spectrometer, spanning 380–2500 nm, with 30 m pixels and a swath of ~40 km, aimed at studying the
arid, dust source regions of the world to better understand the interaction of dust
with the climate system. EMIT has a specific disciplinary focus in geology but will
provide significant information about vegetation, especially in arid lands.
19 Prospects and Pitfalls for Spectroscopic Remote Sensing of Biodiversity…
SNRs of 100–200, but modern airborne IS instruments have SNRs of >1000:1,
depending on the fraction of incoming sunlight reflected. The brighter the surface,
the more light is reflected and the more light is incident on the instrument’s detector,
increasing SNR. This is also true spectrally, so even over a particular location, parts
of the spectrum will have higher or lower SNR, depending on the spectral reflectance of the surface. With modern instruments (Mouroulis et al. 2011), SNR is not
expected to be limiting for plant functional trait estimates.
Several other objectives for an SBG mission may be inferred from the wording
of the SATM but require additional discussion to fully quantify. For example, the
defining question for the plant functional trait designated observable asks why traits
are changing in time and space. This implies broad coverage, ideally global, to
observe spatial changes (e.g., along environmental gradients) and a long-enough
time series to see at least some timescales of change.
While in many ecosystems, an SBG instrument would observe phenological
change, several years or more on orbit would be required to see other types of change,
such as successional change or change after disturbance. The report discusses three
types of disturbance that could cause change, each with a different timescale. Wildfire
causes extremely rapid change but may require decades or longer for full recovery.
Pine beetle infestations, such as those have occurred in the Western United States and
Canada, emerge more slowly, over several years, but may likewise trigger decades of
recovery. Permafrost thaw is the slowest disturbance to emerge of the three considered; it does not lead to recovery but rather may initiate a long-term cascade of change
to a new state. A global imaging spectroscopy mission would see some aspects of these
disturbance processes as expressed through changing plant functional traits, but likely
only a sequence of missions could see the slower aspects of recovery and change.
The formal mission study for SBG began in 2018. Some changes from the above
description could occur between the National Academies (2018) definition of the
observables and objectives identified for construction, so the above descriptions
should be considered provisional.
19.3 EMIT, HISUI, and EnMAP
Several other imaging spectrometers with global access, although more limited coverage, are likely to fly before SBG. All will prove valuable in gathering imaging
spectroscopy data in previously unsampled or inaccessible regions to serve as baselines for change in areas surveyed later by SBG (Schimel et al. 2013). While several
other imaging spectrometers may fly, the three described below are most likely to
provide data of interest to ecologists.
EMIT is a NASA Earth Venture Instrument investigation selected competitively
and planned for flight on the ISS in 2021. It will be an advanced spectrometer, spanning 380–2500 nm, with 30 m pixels and a swath of ~40 km, aimed at studying the
arid, dust source regions of the world to better understand the interaction of dust
with the climate system. EMIT has a specific disciplinary focus in geology but will
provide significant information about vegetation, especially in arid lands.
19 Prospects and Pitfalls for Spectroscopic Remote Sensing of Biodiversity…