Chapter 3 sensors and platforms part 1 Flashcards
Platforms refer to
the structures or vehicles on which remote sensing instruments are mounted.
The platform on which a particular sensor is housed determines a number of attributes, which may dictate
the use of particular sensors
The platform on which a particular sensor is housed determines a number of attributes, which may dictate the use of particular sensors. These attributes include:
distance the sensor is from the object of interest, periodicity of image acquisition, timing of image acquisition, and location and extent of coverage.
There are three broad categories of remote sensing platforms:
ground based, airborne, and satellite.
A represents
Spaceborne:
satellite
shuttle
B represent
Airborne:
Aeroplane
Helicopter
Hot air ballon
Air ship
Tethered balloon
C represent
Ground-based:
hand-held
Raised platform
A wide variety of ground based platforms are used in remote sensing. Some of the more common ones are
are hand held devices, tripods, towers and cranes
Instruments that are ground-based are often used to
to measure the quantity and quality of light coming from the sun or for close range characterization of objects.
used to measure the quantity and quality of light coming from the sun or for close range characterization of objects. For example, to
to study properties of a single plant or a small patch of grass, it would make sense to use a ground based instrument.
Laboratory instruments are used
almost exclusively for research, sensor calibration, and quality control.
Laboratory instruments are used almost exclusively for research, sensor calibration, and quality control. Much of what is learned from laboratory work is used to
understand how remote sensing can be better utilized to identify different materials.
Much of what is learned from laboratory work is used to understand how remote sensing can be better utilized to identify different materials. This contributes to
to the development of new sensors that improve on existing technologies.
Field instruments are largely used for
research purposes
Field instruments are also largely used for research purposes. This type of remote sensing instrument is often
hand-held or mounted on a tripod or other similar support
Field instruments are also largely used for research purposes. This type of remote sensing instrument is often hand-held or mounted on a tripod or other similar support. An example for field remote sensing instruments used in meteorology is
Doppler on Wheels (or DOW)
DOW
DOW is a fleet of radar trucks maintained by the Center for Severe Weather Research (CSWR) in Boulder, Colorado.
: Mobile ozone and aerosol lidar for field campaigns. Profiles ozone and aerosol between 100m‒4 km.
Permanent ground platforms are typically used for
monitoring atmospheric phenomenon
Permanent ground platforms are typically used for monitoring atmospheric phenomenon, although they are also used for
long-term monitoring of terrestrial features
Towers and cranes are often used to support research projects where
a reasonably stable, long-term platform is necessary.
Towers can be built
on site and can be tall enough to project through a forest canopy so that a range of measurements can be taken from the forest floor, through the canopy and from above the canopy
Weather radars are the best examples for
the permanent ground platforms that are typically used for monitoring atmospheric phenomenon.
Doppler radar
Airborne platforms were
the sole non-ground-based platforms for early remote sensing work.
Balloons are rarely used today because
they are not very stable and the course of flight is not always predictable
Balloons are rarely used today because they are not very stable and the course of flight is not always predictable, although small balloons carrying expendable probes
are still used for some meteorological research.
At present, airplanes are
the most common airborne platform
Nearly the ______________________________are used for remote sensing applications.
whole spectrum of civilian and military aircraft
Nearly the whole spectrum of civilian and military aircraft are used for remote sensing applications. When
altitude and stability requirements for a sensor are not too demanding, simple, low-cost aircraft can be used as platforms.
When altitude and stability requirements for a sensor are not too demanding, simple, low-cost aircraft can be used as platforms. However, as_______________________________, more sophisticated aircraft must be used.
requirements for greater instrument stability or higher altitudes become necessary
aircraft are divided into
three categories (low, mid, and high)
aircraft are divided into three categories (low, mid, and high) based on their
altitude restrictions
In general, the higher an aircraft can fly, the
more stable a platform it is, but correspondingly more costly to operate and maintain.
Low altitude aircraft typically fly
below altitudes where supplemental oxygen or pressurization are needed (12,500 feet above sea level)
Low altitude aircraft are good for
acquiring high spatial resolution data limited to a relatively small area.
Low altitude aircraft:
such as the Cessna 172 or 182, and Piper Cherokee. This class of aircraft is
inexpensive to fly and can be found throughout the world
This class of aircraft is inexpensive to fly and can be found throughout the world. Some of these airplanes are specially outfitted for
mounting remote sensing instruments in the underside of the plane
Some of these airplanes are specially outfitted for mounting remote sensing instruments in the underside of the plane, however, many times instruments are simply
hung out the door using simple mounts
Helicopters are usually used for
low altitude applications
Helicopters are usually used for low altitude applications where
the ability to hover is required.
Helicopters are quite _____________to operate
expensive
Helicopters are quite expensive to operate and they are typically used
only when needed
Ultralight aircraft are
a class of aircraft that is gaining popularity
The Federal Aviation Authority (FAA) defines an ultralight as a
single seat powered flying machine that weighs less than 254 pounds, has a top speed of 55 knots (63 mph), stalls at 24 knots (28 mph) or less and carries no more than 5 gal. of fuel.
(ultralight) These small, often portable, aircraft are_________________ and are able to
inexpensive
take off and land where larger aircraft cannot
(ultralight)
They are limited to flying at
lower elevations and at slow speeds.
If the demands of the remote sensing requirement are not too strict,
ultralight aircraft may be a reasonable alternative to larger aircraft.
Mid-altitude aircraft have an altitude limit
under 30,000 feet above sea level
Mid-altitude aircraft have an altitude limit under 30,000 feet above sea level. This includes a
number of turbo-prop aircraft
. Often at higher altitudes, there is less
turbulence so stability is better
(midlatitude)
. This class of airplane is used when
stability is more important and when it is necessary or desired to acquire imagery from a greater distance than available from low altitude aircraft.
(mid latitude aircrafts)
These aircraft can obtain
greater areal coverage more quickly than low altitude platforms.
High altitude aircraft can fly at altitudes
greater than 30,000 feet above sea level
High altitude aircraft can fly at altitudes greater than 30,000 feet above sea level. This class of airplane is usually powered by
jet engines
High altitude aircraft can fly at altitudes greater than 30,000 feet above sea level. This class of airplane is usually powered by jet engines and is used for
specialized tasks, such as atmospheric studies, research to simulate satellite platforms, and other applications where a high altitude platform is required.
High altitude aircraft are good for acquiring
large areal coverage with typically lower spatial resolutions.
Another class of aircraft that has been in use for many years is
is remote control aircraft, or drones
Remotely controlled aircraft are often used for conditions when
it may be too hazardous to fly.
Remotely controlled aircraft are often used for conditions when it may be too hazardous to fly. They have been used extensively by
the military
The most stable platform aloft is
a satellite
The most stable platform aloft is a satellite, which is
spaceborne
The first remote sensing satellite was launched in 1960 for meteorology purposes. Now, over a
a hundred remote sensing satellites have been launched and more are being launched every year.
Satellites can be classified by their
orbital geometry and timing
Three orbits commonly used for remote sensing satellites are
geostationary, equatorial and Sun synchronous
A geostationary satellite has a period of rotation equal to that of
Earth (24 hours)
A geostationary satellite has a period of rotation equal to that of Earth (24 hours) so the satellite
always stays over the same location on Earth.
Communications and weather satellites often use
geostationary orbits with many of them located over the equator.
In an equatorial orbit, a satellite circles Earth at a
low inclination (the angle between the orbital plane and the equatorial plane).
A represents
Polar orbit
B represents
geostationary orbit
Sun synchronous satellites have orbits with
high inclination angles, passing nearly over the poles
Orbits are timed so that the satellite
always passes over the equator at the same local sun time.
. Orbits are timed so that the satellite always passes over the equator at the same local sun time. In this way the satellites maintain
the same relative position with the sun for all of its orbits.
Many remote sensing satellites are
Sun synchronous
Many remote sensing satellites are Sun synchronous which ensures
repeatable sun illumination conditions during specific seasons.
. Because a Sun synchronous orbit does not pass directly over the poles, it is
not always possible to acquire data for the extreme polar regions.
The frequency at which a satellite sensor can acquire data of the entire Earth depends on
sensor and orbital characteristics.
For most remote sensing satellites the total coverage frequency ranges from
twice a day to once every 16 days
The frequency at which a satellite sensor can acquire data of the entire Earth depends on sensor and orbital characteristics. For most remote sensing satellites the total coverage frequency ranges from twice a day to once every 16 days.
Another orbital characteristic is
altitude
Low Earth orbit (LEO)
geocentric orbits with altitudes from up to 2,000 km.
Medium Earth orbit (MEO):
geocentric orbits ranging in altitude from 2,000 km (1,240 miles) to just below geosynchronous orbit at 35,786 kilometers (22,236 mi). Also known as an intermediate circular orbit.
Both geosynchronous orbit (GSO) and geostationary orbit (GEO) are
orbits around Earth matching Earth’s sidereal rotation period.
All geosynchronous and geostationary orbits have a
semi-major axis of 42,164 km (26,199 mi).
All geostationary orbits are
also geosynchronous, but not all geosynchronous orbits are geostationary.
A geostationary orbit stays
exactly above the equator
A geostationary orbit stays exactly above the equator, whereas a geosynchronous orbit
may swing north and south to cover more of the Earth’s surface.
A geostationary orbit stays exactly above the equator, whereas a geosynchronous orbit may swing north and south to cover more of the Earth’s surface. Both complete
one full orbit of Earth per sidereal day (relative to the stars, not the Sun).
High Earth orbit
geocentric orbits above the altitude of geosynchronous orbit 35,786 km (22,240 miles).
A Represents
LEO= Low earth orbit (100 - 1500 km)
B represents
MEO= medium earth orbit (5,000 - 10,000 km)
C Represents
GEO= Geostationary Orbit (36,000 km)
D Represents
HEO = Highly eliptical orbit
Most remote sensing satellites have been designed to
transmit data to ground receiving stations located throughout the world.
To receive data directly from a satellite, the receiving station must
have a line of sight to the satellite.
If there are not sufficient designated receiving stations around the world, any given satellite may
not readily get a direct view to a station, leading to potential problems of data discontinuity.
. If there are not sufficient designated receiving stations around the world, any given satellite may not readily get a direct view to a station, leading to potential problems of data discontinuity. To work around this problem,
data can be temporarily stored onboard the satellite and then later downloaded upon acquiring contact with the receiving station. Another alternative is to relay data through TDRSS (Tracking and Data Relay Satellite System), a network of geosynchronous (geostationary) communications satellites deployed to relay data from satellites to ground stations.
