Hyperspectral Sensors and Applications
19
A significant advancement in hyperspectral remote sensing occurred when
the Airborne VisiblelInfrared Imaging Spectrometer (AVIRIS) was proposed to
NASA in 1983 (Vane et al. 1993). This sensor was the first to acquire image data
in continuous narrow bands simultaneously in the visible to SWIR wavelength
regions. Following approval in 1984, the first engineering flights occurred
in early 1987 with data provided to scientific investigators shortly after. The
AVIRIS was modified subsequently and flown throughout North America and
Eurasia in the following 4 years and, since this period, this sensor has continued
to be improved and is still providing some of the highest quality data to the
scientific community today.
Parallel to NASA's development of the AVIRIS sensor have been a number
of commercial ventures where hyperspectral sensors have been designed and
deployed. Since 1978, the Canadian company ITRES has paved the way for
airborne hyperspectral remote sensing through the development of the Compact Airborne Spectrographic Imager (CASI), which was based on the earlier
FLI (Hollinger et al. 1987). This sensor has been in operation since 1989 and
was used not only for commercial operations in the private sector but also
for research projects. The CASI-2 and CASI-3 instruments were replacements,
with the latter released in 2002. The particular advantage of the CASI-3 is that
the swath width (i. e., width of an individual scene) was increased by a factor of 2. 9. However, all CASI instruments observe only in the VNIR and, as
such, have been found to be of reduced value in many terrestrial applications.
In response to this limitation, ITRES also developed the SASI (Shortwave Infrared Airborne Spectrographic Imager) which, when coupled with the CASI,
extended the spectral range to the SWIR.
A number of sensors were also developed to provide bidirectional viewing
capability. For example, the Advanced Solid-State Array Spectroradiometer
(ASAS) has been maintained and operated by the NASA Goddard Space Flight
Centre (GSFC) since 1984, although evolved from technology developed in
the early 1970s. This sensor provides directional viewing capability (from 70°
forward to 55° aft along the direction of flight) in the VNIR regions (Irons et
al. 1991; Dabney et al. 1994; Ranson et al. 1994).
In 1994, the first HyMap series of hyper spectral sensors was commissioned
by De Beers and the sensor has been in operation since 1996. The HyMap
series of airborne hyperspectral sensors have been deployed internationally,
undertaking remote sensing surveys to support an extremely disparate range
of applications, including mineral exploration, defense research and forest
inventory. In many ways, the Australian-based HyMap systems have set the
benchmark for commercially available hyperspectral sensors in terms of their
SNR, image quality, stability, adaptability and ease of use.
1.3.1.1
Spectral Regions, Resolutions and Bidirectional Capability
Although hyperspectral remote sensing implies observation across the full
spectral region (i. e. 400-2500 nm), many sensors operate only within the
VNIR regions. As examples, the ASAS and CAS I record reflectance in the
19
A significant advancement in hyperspectral remote sensing occurred when
the Airborne VisiblelInfrared Imaging Spectrometer (AVIRIS) was proposed to
NASA in 1983 (Vane et al. 1993). This sensor was the first to acquire image data
in continuous narrow bands simultaneously in the visible to SWIR wavelength
regions. Following approval in 1984, the first engineering flights occurred
in early 1987 with data provided to scientific investigators shortly after. The
AVIRIS was modified subsequently and flown throughout North America and
Eurasia in the following 4 years and, since this period, this sensor has continued
to be improved and is still providing some of the highest quality data to the
scientific community today.
Parallel to NASA's development of the AVIRIS sensor have been a number
of commercial ventures where hyperspectral sensors have been designed and
deployed. Since 1978, the Canadian company ITRES has paved the way for
airborne hyperspectral remote sensing through the development of the Compact Airborne Spectrographic Imager (CASI), which was based on the earlier
FLI (Hollinger et al. 1987). This sensor has been in operation since 1989 and
was used not only for commercial operations in the private sector but also
for research projects. The CASI-2 and CASI-3 instruments were replacements,
with the latter released in 2002. The particular advantage of the CASI-3 is that
the swath width (i. e., width of an individual scene) was increased by a factor of 2. 9. However, all CASI instruments observe only in the VNIR and, as
such, have been found to be of reduced value in many terrestrial applications.
In response to this limitation, ITRES also developed the SASI (Shortwave Infrared Airborne Spectrographic Imager) which, when coupled with the CASI,
extended the spectral range to the SWIR.
A number of sensors were also developed to provide bidirectional viewing
capability. For example, the Advanced Solid-State Array Spectroradiometer
(ASAS) has been maintained and operated by the NASA Goddard Space Flight
Centre (GSFC) since 1984, although evolved from technology developed in
the early 1970s. This sensor provides directional viewing capability (from 70°
forward to 55° aft along the direction of flight) in the VNIR regions (Irons et
al. 1991; Dabney et al. 1994; Ranson et al. 1994).
In 1994, the first HyMap series of hyper spectral sensors was commissioned
by De Beers and the sensor has been in operation since 1996. The HyMap
series of airborne hyperspectral sensors have been deployed internationally,
undertaking remote sensing surveys to support an extremely disparate range
of applications, including mineral exploration, defense research and forest
inventory. In many ways, the Australian-based HyMap systems have set the
benchmark for commercially available hyperspectral sensors in terms of their
SNR, image quality, stability, adaptability and ease of use.
1.3.1.1
Spectral Regions, Resolutions and Bidirectional Capability
Although hyperspectral remote sensing implies observation across the full
spectral region (i. e. 400-2500 nm), many sensors operate only within the
VNIR regions. As examples, the ASAS and CAS I record reflectance in the