Hyperspectral Sensors and Applications
13
and two in the NIR respectively. The successors of the MSS, the LANDSAT
Thematic Mapper (TM on board LANDSAT 4-5) and Enhanced Thematic
Mapper (ETM + on board LANDSAT 7) provided additional measurements in
the shortwave infrared (SWIR) region centred on 1600 nm and 2100 nm and
at a finer (30 m) spatial resolution and level of quantization. The provision
of a 15 m panchromatic band on the LANDSAT ETM+ also facilitated greater
resolving of ground features and opportunities for data fusion. The SPOTseries of sensors, developed in France, were first launched in 1986. Initially,
the SPOT 1-3 High Resolution Visible (HRV) recorded reflectance (at 20 m
spatial resolution) in three visible and NIR (VNIR) channels, although the
subsequent High Resolution Visible InfraRed (HRVIR; SPOT 4) supported
a SWIR waveband. The launch of SPOT-S, in 2003, heralded a new era in
fine spatial resolution remote sensing, with the panchromatic (PAN) sensor
increasing in spatial resolution from 10m to 5 m, with potential to obtain 2.5 m
spatial resolution data through simultaneous observation. The resolution of
the SPOT -5 multispectral (XS) sensor also increased to 10 m (maintaining 20 m
in the SWIR region). The IRS series of spacecraft, which were first launched by
India in 1988, complemented the Landsat and SPOT-series, as several sensors
were in orbit, observing in four VNIR bands and at spatial resolutions of
approximately 23.5-36.25 min XS (70 min SWIR) and 6 m in PAN mode.
With time, these sensors have provided consistent historical data with which
to observe and quantify intra-annual, inter-annual or decadal changes occurring on the Earth's surface. The addition of other sensors (e.g., IKONOS and
Quickbird) observing at a variety of spatial and temporal resolutions and also
band configurations and quantizations has served to extend the time-series and
to provide additional information on Earth surface processes and dynamics.
The continuation and development of these Earth observing programs is testament to the important role that data from these sensors play in understanding
the longer-term dynamics of both natural and anthropogenic change. This also
indicates the commitment of national and international organisations to Earth
observation for environmental monitoring.
A fundamental limitation of these multispectral sensors, however, is that
data are acquired in a few broad (typically 100-200 nm in width) irregularly
space spectral bands (van der Meer and de Jong 2001). As such, narrow spectral
features may not be readily discriminated and tend to be either averaged across
the spectral sampling range or masked by stronger proximal features (Kumar
et al. 2001), thereby resulting in a reduction or loss in the environmentally
relevant information that can potentially be extracted. This deficiency in the
spectral, radiometric, and spatial resolution of many multispectral systems,
therefore render them unsuitable for identifying many surface materials and
features, particularly minerals (Goetz 1995).
13
and two in the NIR respectively. The successors of the MSS, the LANDSAT
Thematic Mapper (TM on board LANDSAT 4-5) and Enhanced Thematic
Mapper (ETM + on board LANDSAT 7) provided additional measurements in
the shortwave infrared (SWIR) region centred on 1600 nm and 2100 nm and
at a finer (30 m) spatial resolution and level of quantization. The provision
of a 15 m panchromatic band on the LANDSAT ETM+ also facilitated greater
resolving of ground features and opportunities for data fusion. The SPOTseries of sensors, developed in France, were first launched in 1986. Initially,
the SPOT 1-3 High Resolution Visible (HRV) recorded reflectance (at 20 m
spatial resolution) in three visible and NIR (VNIR) channels, although the
subsequent High Resolution Visible InfraRed (HRVIR; SPOT 4) supported
a SWIR waveband. The launch of SPOT-S, in 2003, heralded a new era in
fine spatial resolution remote sensing, with the panchromatic (PAN) sensor
increasing in spatial resolution from 10m to 5 m, with potential to obtain 2.5 m
spatial resolution data through simultaneous observation. The resolution of
the SPOT -5 multispectral (XS) sensor also increased to 10 m (maintaining 20 m
in the SWIR region). The IRS series of spacecraft, which were first launched by
India in 1988, complemented the Landsat and SPOT-series, as several sensors
were in orbit, observing in four VNIR bands and at spatial resolutions of
approximately 23.5-36.25 min XS (70 min SWIR) and 6 m in PAN mode.
With time, these sensors have provided consistent historical data with which
to observe and quantify intra-annual, inter-annual or decadal changes occurring on the Earth's surface. The addition of other sensors (e.g., IKONOS and
Quickbird) observing at a variety of spatial and temporal resolutions and also
band configurations and quantizations has served to extend the time-series and
to provide additional information on Earth surface processes and dynamics.
The continuation and development of these Earth observing programs is testament to the important role that data from these sensors play in understanding
the longer-term dynamics of both natural and anthropogenic change. This also
indicates the commitment of national and international organisations to Earth
observation for environmental monitoring.
A fundamental limitation of these multispectral sensors, however, is that
data are acquired in a few broad (typically 100-200 nm in width) irregularly
space spectral bands (van der Meer and de Jong 2001). As such, narrow spectral
features may not be readily discriminated and tend to be either averaged across
the spectral sampling range or masked by stronger proximal features (Kumar
et al. 2001), thereby resulting in a reduction or loss in the environmentally
relevant information that can potentially be extracted. This deficiency in the
spectral, radiometric, and spatial resolution of many multispectral systems,
therefore render them unsuitable for identifying many surface materials and
features, particularly minerals (Goetz 1995).