The first civilian radar system to operate from space was mounted in a Space Shuttle. Seasat was an experimental L-Band radar whose primary mission was to measure ocean surfaces. However, it produce very informative images of the land surface, including this scene that includes Death Valley, one of the prime test sites for determining the capabilities of various sensors.
Among systems now operational
are the Canadian Radarsat, ERS-1 and ERS-2 managed by the European Space Agency,
and JERS-1 and JERS-2 under the aegis of the National Space Development Agency
of Japan, NASDA. As an example, here is the first image acquired by Radarsat,
showing part of Cape Breton in Nova Scotia, and the surrounding waters.
The European Space Agency,
ESA, also has flown radar on its ERS-1 and ERS-2 satellites. Here is an image
in black and white showing the San Francisco, California, metropolitan area and
the peninsula to its south, as well as Oakland, California, the East Bay, and
beyond.
I-26:
Look at the above two radar images, especially the one showing
San Francisco. State two characteristics of the radar images that seem to differ
from those of Landsat. ANSWER
The ERS satellites had
other sensors, as was indicated in the Overview. One in wide use is ATSR (Along
Track Scanning Radiometer). Here is an image of the English Channel made by
that instrument:
NASA, through its Jet Propulsion
Laboratory (JPL) in Pasadena, California, has flown three radar missions on
the Space Shuttle. The SIR (Shuttle Imaging Radar) series has used different
wavebands and look conditions, with many excellent images over much of the globe
having been acquired. Appearing below is a SIR-C image obtained on October 3,
1994 during a flight of the Space Shuttle. This is a false color composite made
by assigning the L-Band HV, L-Band HH, and C-Band images to red, green, and
blue respectively (see page
8-7). The area shown is that part of Israel containing disputed West Bank
territory that includes Jerusalem (yellowish patterns on left) and the top of
the Dead Sea.
Remote sensors that cover
two thermal intervals - the 3-5 µm and 8-14 µm broad bands (corresponding to
two atmospheric windows) allowing sensing of thermal emissions from the land,
water, ice and the atmosphere - have been flown on airplanes for several decades.
Many of the meteorological satellites (see next page) include at least one thermal
channel. A thermal band is included on the Landsat Thematic Mapper. The principles behind thermal
remote sensing are treated in some detail in Section 9. For now, let us look
at two representative samples of the types of thermal images that indicate the
kinds of information resulting from operation of thermal sensors on moving platforms
above the Earth's surface. This next image was made
from a satellite dedicated to sensing one thermal property - thermal inertia
(defined on page 9-3).
The Heat Capacity Mapping Mission (HCMM) was launched in 1978 and is described
on page 9-8. This image covers
about 700 km (435 miles) on a side and was taken at night (daytime thermal images
were also generated) on July 16, 1978 over southern Europe using a sensor that
integrates thermal emissions within the wavelengths from 10.5 to 12.5 µm. The
darker area in the upper left portrays lowlands in eastern France and southwestern
Germany. The Alps form a broad arc crossing the image. The blackish pattern
within the Alps corresponds to the cold higher elevations (with some snow).
The lighter-toned land below the Alps is the Piedmont and western plains of
Italy's Po Valley. The light tones near the image bottom are the waters of the
Mediterranean Sea, which at night are warmer (heat sink) than most land surfaces.
Thermal data, especially from
the 8-14 µm region become more valuable in singling out (classifying) different
materials when this spectral interval is subdivided into bands, giving multispectral
capability. NASA's JPL has developed an airborne multiband instrument called TIMS
(Thermal IR Multispectral Scanner) that is a prototype for a system eventually
to be placed in space. The images it produces are notably striking in their color
richness, as evident in this scene that includes a desert landscape around Lunar
Lake in eastern California.
The image pair below covers
a part of the White Tank Mountains of Arizona. The left image is made from 3
TIMS bands; the right is a false color composite formed from visible band data
on another multispectral scanner onboard the aircraft that gathered TIMS emitted
radiation.
While these color patterns
make some sense when interpreted through geologic maps, aerial photos, field
visits (ground truth), etc., it is hard to envision what they mean just from
this image pair. Perhaps a better insight and context will result from the view
below, which is an oblique or perspective "photo" showing the full extent of
the White Tank Mountains (a fault block range) and surrounding desert and agricultural
farms, about 40 km (25 miles) west of Phoenix. But, this is really a "trick
picture", in that it is made from Landsat TM bands (1,2,3) that have been registered
to Digital Elevation Model (DEM) data (see page 11-5) that contain
heights above sea level, from which a 3-dimensional representation is constructed.
Other such examples will appear in several Sections of this Tutorial.
