Transcript Satellite-based Sensors

Satellite-based Sensors
Chapter 7
Low Spatial-Resolution
• Mostly geostationary satellites used for
meteorology
– GOES
• Also those that gather complete earth
image over 1 or 2 days
– AVHRR, MODIS, SeaWiFS
• satellites placed in geosynchronous orbit
afforded nearly instantaneous coverage of nearhemispheres of the Earth
– rapidly update views of cloud decks and circulation
patterns over almost any part of the world.
– Ironically, the very thing that compromises
observations of the land and open ocean, namely
clouds, is the prime target of meteorological satellites
(Metsats).
• As more versatile sensors evolved, they quantitatively
monitored various other atmospheric or oceanographic
properties, such as the stratosphere, tropospheric
temperatures, Earth radiation budget, air chemistry (e.g.,
ozone, CO2, sulphur compounds, and aerosols), wind and
sea current movements, sea-ice, and marine biotic nutrients.
ATS-1
GOES
Sun-synchronous
• Defense Meteorological Satellite Program
(DMSP)
– Primarily for weather and navigation
conditions
– 0.4-1.10 μm and 8-13 μm bands
– 3,000 km swath
• Used for night-lights
AVHRR crop monitoring
Landsat
Landsat
SPOT
The viewing angle of the sensors can be
adjusted to look to either side of the
satellite's vertical (nadir) track, allowing offnadir viewing which increases the satellite's
revisit capability. This ability to point the
sensors up to 27° from nadir, allows SPOT
to view within a 950 km swath and to revisit
any location several times per week.
By pointing both HRV sensors to cover
adjacent ground swaths at nadir, a
swath of 117 km (3 km overlap between
the two swaths) can be imaged.
Ocean Color
CZCS
SeaWiFS
• Five sensors on Terra are:
• CERES - Clouds and the Earth's Radiant Energy
System
• MOPITT - Measurements of Pollution in the
Troposphere (Canada)
• MISR - Multi-angle Imaging Spectroradiometer
• ASTER - Advanced Spaceborne Thermal
Emission and Reflection Radiometer (Japan)
Part of a MODIS image set that includes the Mississippi Delta and the Gulf of Mexico
MODIS data allow calculation of the "NDVI" parameter (Normalized Difference
Vegetation Index, obtained by dividing a Near IR minus Red radiance by a Near IR +
Red value) and sea surface temperatures, as displayed here.
Other wavelengths on MODIS aid in picking up the atmospheric appearance of
aerosols, much being the result of pollution.
MODIS can pick out water vapor, even when heavy clouds are absent or
dispersed, as shown in this image.
MODIS can also use its short wavelength bands to measure the fluorescent properties
of the ocean, which relate to plankton content. Light not used in photosynthesis is reemitted as fluorescence and heat, so that higher levels of fluorescence indicate lower
photosynthetic activity. This is evidenced in this image (red is highest amount) that
includes Africa, Saudi Arabia, Iran, India and Pakistan, and parts of the Indian Ocean
and the Bay of Bengal:
Other MODIS wavebands in the visible are suited to picking out chlorophyll
content (similar approach as SeaWIFS), with reds being high and blues low
concentrations.
The versatile MODIS also has thermal bands (for surface temperatures from 3.6 to 4.1
µm). The image below shows the entire Iberian Peninsula (Spain and Portugal) during
one of the hottest heat waves ever recorded in that region. On July 1, 2004, one locality
reached a ground (not air) temperature of 59°C (138°F). The only cool area in the scene
are the Pyrennees Mountain chain dividing Spain from France (in greenish-blue).
MISR
To illustrate the benefit of looking simultaneously at an area from multiple angles,
consider these four views of part of the Appalachians; because of the more oblique look
angle the image farthest to the right shows an aerosol haze that is absent from the nadir
and close-in images.
MISR is well-adapted to
determining the extent of
drought conditions by
measuring over time the albedo
changes of vegetation.
To the left are two MISR
natural color images of the
Black Hills and surrounding
plains that are largely grass
covered. The rise in albedo
from 2000 to 2004 indicates
higher reflectance in these
lands as vegetation is
diminished and turns into
more reflective brown
shades:
ASTER
Ocean Color
• CZCS
• SeaWiFS
• ATSR and AATSR
– Along-track scanning radiometer, and advanced
• MERIS – MEdium Resolution Imaging
Spectrometer
• IRS-P4 – has Ocean Color Monitor and
Multifrequency Scanning Microwave Radiometer
• Terra and Aqua carry MODIS Moderate
Resolution Imaging Spectrometer
Medium Spatial Scale
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Medium scale roughly means 5-250 m GSD
Beginning with Landsat 1 in 1972
SPOT
IKONOS
IRS-1C – have LISS-III Linear Imaging SelfScanning sensor and a WiFS Wide Field Sensor
• JERS
• ADEOS
High Spatial Resolution
• Befroe 1999 only military had < 1m
resolution
• IKONOS
• Quickbird
• EROS-A1
• OrbView-3
• 10 x 10 km image about $2,500 uncorrected
Suitability
• A number of factors need to be considered
– Spatial resolution
– Interpretability – atmospheric problems
– Availability and alternative imagery
– Availability of equipment and personnel to
analyze
– Time frame
– Level of geometric accuracy
• Mapping vs feature ID
• Scale required