Hyperspectral Sensors and Applications
27
therefore more suitable for use in regional to global studies. Hyperion has
a nominal altitude of 705 km giving a narrow (7.5 km) swath width, whilst
CHRIS has a nominal 600 km orbit and images the Earth with a 14 km swath
(with a spatial resolution of 18 m). This coverage generally limits use to local
or landscape-scale studies.
1.3.2.3
Temporal Resolution
Repeat observations with spaceborne sensors, can be achieved to yield a significant advantage for many applications, particularly vegetation mapping and
monitoring. The Hyperion sensor acquires data over the same area (albeit approximately 1 minute after) as the LANDSAT - 7 ETM+ and the Argentinean
SAC-C as part of the AM Constellation and therefore has a similar repeat period
of 16 days. CHRIS also has a repeat period of 16 days. MODIS and MERIS with
repeat periods of 1-2 days and 3 days respectively are more suited for various
land applications with a regional or global context. Although long time-series
of hyper spectral data have not been adequately constructed, the potential benefits of these archives for land applications is enormous, particularly in the
context of vegetation species/community discrimination and understanding
the seasonal variability in biophysical and biochemical attributes.
1.4
Ground Spectroscopy
Data acquired by airborne or spaceborne sensors cannot be considered in
isolation since effective data interpretation requires a detailed understanding
of the processes and interactions occurring at the Earth's surface. In this respect, a fundamental component of understanding hyperspectral sensors is
the laboratory and field measurement of the spectral reflectance of different
surfaces. A number of portable field and laboratory spectroradiometers have
been developed for this purpose, ranging from the Milton spectroradiometer
to the more advanced spectroradiometers that include the Analytical Spectral
Devices (ASD) Fieldspec Pro FR and the IRIS spectroradiometer developed by
GER (Table 1.4).
Technological advances in a number of areas have led to improvements in
the field of spectroscopy. Advances in spectroradiometer technology, specifically with respect to the electro-optical systems, have resulted in an increase
in sensor sensitivity and a decrease in scan times, permitting greater data
collection in a shorter period of time. This has enabled researchers to acquire
high quality reflectance data rapidly, both in the field and under laboratory
conditions. A second advancement has been the increase in the processing
sophistication of computer technology and the reduction in the cost of data
storage. These technological improvements have also reduced the overall costs
so that a greater number of users are able to acquire portable spectrometers,
particularly for use in the field.
27
therefore more suitable for use in regional to global studies. Hyperion has
a nominal altitude of 705 km giving a narrow (7.5 km) swath width, whilst
CHRIS has a nominal 600 km orbit and images the Earth with a 14 km swath
(with a spatial resolution of 18 m). This coverage generally limits use to local
or landscape-scale studies.
1.3.2.3
Temporal Resolution
Repeat observations with spaceborne sensors, can be achieved to yield a significant advantage for many applications, particularly vegetation mapping and
monitoring. The Hyperion sensor acquires data over the same area (albeit approximately 1 minute after) as the LANDSAT - 7 ETM+ and the Argentinean
SAC-C as part of the AM Constellation and therefore has a similar repeat period
of 16 days. CHRIS also has a repeat period of 16 days. MODIS and MERIS with
repeat periods of 1-2 days and 3 days respectively are more suited for various
land applications with a regional or global context. Although long time-series
of hyper spectral data have not been adequately constructed, the potential benefits of these archives for land applications is enormous, particularly in the
context of vegetation species/community discrimination and understanding
the seasonal variability in biophysical and biochemical attributes.
1.4
Ground Spectroscopy
Data acquired by airborne or spaceborne sensors cannot be considered in
isolation since effective data interpretation requires a detailed understanding
of the processes and interactions occurring at the Earth's surface. In this respect, a fundamental component of understanding hyperspectral sensors is
the laboratory and field measurement of the spectral reflectance of different
surfaces. A number of portable field and laboratory spectroradiometers have
been developed for this purpose, ranging from the Milton spectroradiometer
to the more advanced spectroradiometers that include the Analytical Spectral
Devices (ASD) Fieldspec Pro FR and the IRIS spectroradiometer developed by
GER (Table 1.4).
Technological advances in a number of areas have led to improvements in
the field of spectroscopy. Advances in spectroradiometer technology, specifically with respect to the electro-optical systems, have resulted in an increase
in sensor sensitivity and a decrease in scan times, permitting greater data
collection in a shorter period of time. This has enabled researchers to acquire
high quality reflectance data rapidly, both in the field and under laboratory
conditions. A second advancement has been the increase in the processing
sophistication of computer technology and the reduction in the cost of data
storage. These technological improvements have also reduced the overall costs
so that a greater number of users are able to acquire portable spectrometers,
particularly for use in the field.