Image Processing Reference
In-Depth Information
spatial, radiometric, spectral, and temporal resolutions discussed below refer
primarily to the imaging sensor characteristics.
While the emphasis in this section is on the resolution or precision of remotely
sensed measurements, the reader should be aware that the extent, duration, or loca-
tion of the measurement in space, time, and spectral or energy intervals may be
equally important. For instance, the spatial extent of coverage, range of energy
sensed, position of wavebands throughout the spectrum, or temporal record length
of archived imagery are also important factors when selecting imagery to match a
particular urban application.
7.2.1
Spatial Resolution
The spatial resolution of remote sensing instruments is a
function of the altitude of the platform relative to the earth
surface and the resolving power of the sensor, and is often
expressed as the ground sampling distance (GSD) of the
sensor at nadir. High spatial resolution imagery provide a
closer view of smaller objects while low spatial resolution
imagery provide a farther view of larger objects.
Moderate to high spatial resolution imagery have been used for urban remote
sensing applications. Imagery at 80 m spatial resolution have been available from
the Landsat Multispectral Scanner (MSS) archive since 1972, and at 30 m since the
mid-1980s, from the Landsat Thematic Mapper (TM) sensor. In the late 1980s, the
French Centre National d'Etudes Spatiales (CNES) launched the SPOT mission
with the first four satellites carrying the High Resolution Visible (HRV) payload
acquiring images of 10 m resolution in panchromatic mode and 20 m resolution in
visible/near infrared (V/NIR) mode. On May 4, 2002 SPOT 5 was launched with
two different payloads, the High Resolution Geometric (HRG) panchromatic
instrument and the High Resolution Stereoscopic (HRS) multispectral sensor with
spatial resolutions of 2.5 and 10 m, respectively. In addition to the higher spatial
resolution than the HRV, the HRS includes a shortwave infrared (SWIR) band. The
Indian Department of Space launched a series of IRS satellites equipped with high
and moderate spatial resolution versions of the Linear Imaging Spectral Scanner
(LISS). The latest IRS RESOURCESAT-1 satellite was launched on October 17,
2003 and provides imagery from three spaceborne sensors, the high resolution
LISS sensor (LISS-IV), the medium resolution LISS sensor (LISS-III), and the
Advanced Wide Field Sensor (AWiFS) with spatial resolutions of 6, 24, and 60 m,
respectively (Rao and Cook
2004
). RESOURCESAT-2 is planned for launch in
2006 and will carry the high spatial resolution version of the LISS payload.
Since 1999 the urban remote sensing community has had access to imagery from
very high spatial resolution sensors such as the digital imaging payloads onboard
IKONOS and DigitalGlobe's QuickBird satellite systems. Although IKONOS 1
and QuickBird 1 both experienced launch failures, the second missions launched in
spatial resolution
is expressed in
terms of the
ground sampling
distance of the
sensor at nadir
