317
able, enabling a mapping of the distribution of plant species in mixed grassland
communities using close-range imaging spectroscopy (Lopatin et al. 2017). The
special value of both fixed and mobile towers or simple close-range RS platforms is
that vegetation diversity can be monitored more frequently and with a higher spatial
resolution. Table 13.1 lists the advantages and disadvantages of close-range EO
approaches to monitor and assess vegetation diversity.
13.2.2 Air- and Spaceborne RS Platforms and Sensors
13.2.2.1 Unmanned Aerial Systems (UAS)
In recent years, UAS has become an important RS technology in spatial ecology.
Nowadays a plethora of platforms, including fixed-wing and rotor-based systems,
can carry multispectral, hyperspectral, thermal, LiDAR, and radar sensors and can
navigate autonomously on predefined routes using global navigation satellite system (GNSS). With the increased availability and simplicity, such platforms are
being used more and more in ecological research and monitoring (Anderson and
Gaston 2013). In this context two essential characteristics of UAS are relevant:
(i) High flexibility and low cost of operation: UASs offer high flexibility in terms
of payloads, flight time, and flight specifications such as altitude, time of day,
and weather condition. When compared with manned aircraft or satellites, it is
much easier to plan and conduct an image acquisition campaign once a UAS
and a trained pilot are available. Due to low fixed costs, UAS can be cheaper
than manned planes and helicopters.
(ii) High spatial and temporal resolutions: Within the technical and legal limitations, flight heights of UAS can be freely set and typically range from a couple
of meters to hundreds of meters. Depending on the sensor system, images with
very high spatial resolution (<5 cm) can be acquired when flown at low altitudes. The high flexibility of operation and the low image acquisition costs
enable users to efficiently create multitemporal image series.
In the context of biodiversity monitoring, UASs are used in vegetated ecosystems to
obtain optical images with high spatial and spectral resolution and 3-D point clouds
of the Earth’s surface and vegetation structures.
In grassland ecosystems, high-resolution UAS images are used to map habitat
types (Cruzan et al. 2016) or single target species such as weeds (Hardin and Jackson
2005). In recent studies, proximal RS using scaffolds has been used to link species
and functional diversity to spectral traits (Schweiger et al. 2018). Here the high
spatial resolution is of utmost importance because grassland plants are typically
small and highly mixed (Lu et al. 2016). Very high spatial resolution imagery offers
the potential for both community- and plant-based analysis (Lopatin et al. 2017).
However, even with spatial resolutions <1 cm, species identification of individuals
is challenging and might only work under favorable conditions such as low structural
13 A Range of Earth Observation Techniques for Assessing Plant Diversity
able, enabling a mapping of the distribution of plant species in mixed grassland
communities using close-range imaging spectroscopy (Lopatin et al. 2017). The
special value of both fixed and mobile towers or simple close-range RS platforms is
that vegetation diversity can be monitored more frequently and with a higher spatial
resolution. Table 13.1 lists the advantages and disadvantages of close-range EO
approaches to monitor and assess vegetation diversity.
13.2.2 Air- and Spaceborne RS Platforms and Sensors
13.2.2.1 Unmanned Aerial Systems (UAS)
In recent years, UAS has become an important RS technology in spatial ecology.
Nowadays a plethora of platforms, including fixed-wing and rotor-based systems,
can carry multispectral, hyperspectral, thermal, LiDAR, and radar sensors and can
navigate autonomously on predefined routes using global navigation satellite system (GNSS). With the increased availability and simplicity, such platforms are
being used more and more in ecological research and monitoring (Anderson and
Gaston 2013). In this context two essential characteristics of UAS are relevant:
(i) High flexibility and low cost of operation: UASs offer high flexibility in terms
of payloads, flight time, and flight specifications such as altitude, time of day,
and weather condition. When compared with manned aircraft or satellites, it is
much easier to plan and conduct an image acquisition campaign once a UAS
and a trained pilot are available. Due to low fixed costs, UAS can be cheaper
than manned planes and helicopters.
(ii) High spatial and temporal resolutions: Within the technical and legal limitations, flight heights of UAS can be freely set and typically range from a couple
of meters to hundreds of meters. Depending on the sensor system, images with
very high spatial resolution (<5 cm) can be acquired when flown at low altitudes. The high flexibility of operation and the low image acquisition costs
enable users to efficiently create multitemporal image series.
In the context of biodiversity monitoring, UASs are used in vegetated ecosystems to
obtain optical images with high spatial and spectral resolution and 3-D point clouds
of the Earth’s surface and vegetation structures.
In grassland ecosystems, high-resolution UAS images are used to map habitat
types (Cruzan et al. 2016) or single target species such as weeds (Hardin and Jackson
2005). In recent studies, proximal RS using scaffolds has been used to link species
and functional diversity to spectral traits (Schweiger et al. 2018). Here the high
spatial resolution is of utmost importance because grassland plants are typically
small and highly mixed (Lu et al. 2016). Very high spatial resolution imagery offers
the potential for both community- and plant-based analysis (Lopatin et al. 2017).
However, even with spatial resolutions <1 cm, species identification of individuals
is challenging and might only work under favorable conditions such as low structural
13 A Range of Earth Observation Techniques for Assessing Plant Diversity