Environmental Engineering Reference
In-Depth Information
Blackbody at 5800 K
Sun's energy
Blackbody at 1200 K
Blackbody at 600 K
Blackbody at 300 K
Blocking effect of atmosphere
Human eye
Thermal scanners
Radar
Photography
Multispectral scanners
Passive microwave
Gamma ray
Radio
X-ray
Radar
Ultraviolet
Microwave
Near infrared
Infrared
FIGURE 2.4
The electromagnetic spectrum illustrating atmospheric attenuation and general sensor categories. (From Way,
D.S.
Terrain Analysis
, 2nd ed., Dowden, Hutchinson & Ross, Stroudsburg, Pennsylvania, 1978.)
panchromatic mode has a spatial resolution of 5 m. Swath width is 60
60 km.
SPOT is capable of acquiring stereocoptic (overlapping) imagery.
IKONOS, Quick Bird (DigitalGlobe), and OrbView-3 (Orbimage) are recently
launched U.S. satellites that are reported to have a multispectral spatial resolu-
tion of 4 m and a panchromatic spatial resolution of 1 m. Swath width is of the
order of 8
●
8 km.
Other countries including India, Russia, Japan, and China have also launched
satellites.
●
Satellite Imagery (Radar Sensors)
SAR (s
ynthetic aperture radar
) images have been obtained by the European Space
Agency with satellites ERS-1 and ERS-2 since 1992. Since SAR is based on
reflected signals from radio waves, images can be obtained during day or night,
and through cloud cover.
●
InSAR (
interferometric SAR
)
,
is also known as
DifSAR (differential synthetic aper-
ture radar interferometry
). Using two different satellite passes and applying a com-
plex and computer-intensive process, an interferogram is created. Because of
precise, specific geometry, the sources combine to create bright and dark patterns
of interference or “fringes,” which can be converted to ground heights with a
precision reported down to 0.7 cm possible. The images are color-enhanced
using filters to produce color-coded interferograms. They have been used to
record ground subsidence over large areas (see
Section 10.2.2)
(Professional
Surveyor, 1999).
●
Airborne Imagery (Digital Sensors)
Airborne digital imagery
is obtained from aircraft flying at less than 3000 m. Data pro-
●
