chapter 3 sensors and platforms part 2 Flashcards
There are several broad categories of basic sensor system types such as
passive vs. active, and imaging vs. nonimaging
Passive vs. active refers to
the illumination source of the system
imaging vs. nonimaging refers to
the form of the data
A variety of different sensors fit in these categories, which are
not mutually exclusive.
Passive sensors measure
light reflected or emitted naturally from surfaces and objects
Passive sensors measure light reflected or emitted naturally from surfaces and objects. Such instruments
merely observe
Passive sensors measure light reflected or emitted naturally from surfaces and objects. Such instruments merely observe, and depend primarily on
solar energy
Passive sensors measure light reflected or emitted naturally from surfaces and objects. Such instruments merely observe, and depend primarily on solar energy as the
ultimate radiation source
Passive sensors measure light reflected or emitted naturally from surfaces and objects. Such instruments merely observe, and depend primarily on solar energy as the ultimate radiation source illuminating
surfaces and object
Active sensors (such as ……………)
radar and lidar systems
Active sensors (such as radar and lidar systems) first
emit energy (supplied by their own energy source) and then measure the return of that energy after it has interacted with a surface.
Use of data collected by passive sensors often requires
accurate measurements of solar radiation reaching the surface at the time the observations were made
Active sensors :
Use of data collected by passive sensors often requires accurate measurements of solar radiation reaching the surface at the time the observations were made. This information allows for the
correction of “atmospheric effects”
Use of data collected by passive sensors often requires accurate measurements of solar radiation reaching the surface at the time the observations were made. This information allows for the correction of “atmospheric effects” and results in
data or images that are more representative of actual surface characteristics.
Remote sensing data are the recorded representation of
radiation reflected or emitted from an area or object
When measuring the reflected or emitted energy, ………………… can be used
either imaging or nonimaging sensors
Data from imaging sensors can be processed to produce
an image of an area, within which smaller parts of the sensor’s whole view are resolved visually
Nonimaging sensors usually are
hand held devices
Nonimaging sensors usually are hand held devices that
register only a single response value, with no finer resolution than the whole area viewed by the sensor
Nonimaging sensors usually are hand held devices that register only a single response value, with no finer resolution than the whole area viewed by the sensor, and therefore
no image can be made from the data
Nonimaging sensors usually are hand held devices that register only a single response value, with no finer resolution than the whole area viewed by the sensor, and therefore no image can be made from the data. These single values can be referred to as
a type of “point” data
These single values can be referred to as a type of “point” data, however some small area is typically involved depending on
the sensor’s spatial resolution
Image and nonimage data each have particular uses. Nonimage data give information for
one specific (usually small) area or surface cover type
Nonimage data give information for one specific (usually small) area or surface cover type, and can be used to
characterize the reflectance of various materials occurring in a larger scene and to learn more about the interactions of electromagnetic energy and objects.
Image data provide an opportunity to look at
spatial relationships, object shapes, and to estimate physical sizes
Image data provide an opportunity to look at spatial relationships, object shapes, and to estimate physical sizes based on
the data’s spatial resolution and sampling
Image data are desirable when ……………………….. (such as …………..) is needed
spatial information (mapped output)
Image data provide an opportunity to look at spatial relationships, object shapes, and to estimate physical sizes based on the data’s spatial resolution and sampling. Image data are desirable when spatial information (such as mapped output) is needed. This text refers primarily to
imaging sensors and data.
Images produced from remote sensing data can be either
analog (such as a photograph) or digital (a multidimensional array or grid of numbers)
Digital data can be analyzed by
studying the values using calculations performed on a computer
Digital data can be analyzed by studying the values using calculations performed on a computer, or processed to produce
an image for visual interpretation
Image interpretation is used to
decipher information in a scene
In the past, image interpretation was done largely using
subjective visual techniques
In the past, image interpretation was done largely using subjective visual techniques, but with the development and ongoing advancement of
computer technology, numeric or digital processing
In the past, image interpretation was done largely using subjective visual techniques, but with the development and ongoing advancement of computer technology, numeric or digital processing has become
a powerful and common interpretation tool.
In many cases, image interpretation involves the combination of both
visual and digital techniques
In many cases, image interpretation involves the combination of both visual and digital techniques. These techniques
utilize a number of image features
In many cases, image interpretation involves the combination of both visual and digital techniques. These techniques utilize a number of image features including
tone and color, texture, shape, size, patterns, and associations of objects
The human eye and brain are generally thought to more easily process the ………………… of an image
spatial charactaristics
The human eye and brain are generally thought to more easily process the spatial characteristics of an image, such as
shape, patterns and how objects are associated with one another
Computers usually are better suited for
rapid analysis of the spectral elements of an image
Computers usually are better suited for rapid analysis of the spectral elements of an image such as
tone and color
Sophisticated computer software that can perform like the human eye and brain may be
more commonly available in the future.
Passive sensors are the most common sensor type for
vegetation related remote sensing
This is not only because passive sensor systems are generally
simpler in design (built only to receive energy)
Passive sensors are the most common sensor type for vegetation related remote sensing. This is not only because passive sensor systems are generally simpler in design (built only to receive energy) but also because
portions of the solar spectrum provide very useful information for monitoring plant and canopy properties.
A major limitation of passive systems is that in most cases they require
sunlight in order for valid and useful data to be acquired.
A major limitation of passive systems is that in most cases they require sunlight in order for valid and useful data to be acquired. Consequently,
deployment of or data acquisition by passive sensors is very dependent on lighting (time of day, time of year, latitude) and weather conditions,
A major limitation of passive systems is that in most cases they require sunlight in order for valid and useful data to be acquired. Consequently, deployment of or data acquisition by passive sensors is very dependent on lighting (time of day, time of year, latitude) and weather conditions, since cloud cover can
interfere with the path of solar radiation from the sun to the surface and then to the sensor.
The signals detected by passive sensors can be ……………….. due to ….
greatly altered due to atmospheric effects
The signals detected by passive sensors can be greatly altered due to atmospheric effects, especially in the
shorter wavelengths of the solar spectrum
The signals detected by passive sensors can be greatly altered due to atmospheric effects, especially in the shorter wavelengths of the solar spectrum that are
strongly scattered by the atmosphere
The signals detected by passive sensors can be greatly altered due to atmospheric effects, especially in the shorter wavelengths of the solar spectrum that are strongly scattered by the atmosphere. These effects can be
minimized (but not eliminated)
The signals detected by passive sensors can be greatly altered due to atmospheric effects, especially in the shorter wavelengths of the solar spectrum that are strongly scattered by the atmosphere. These effects can be minimized (but not eliminated) by
collecting data only under very clear and dry atmospheric conditions
Sophisticated atmospheric correction routines now exist to
remove atmospheric effects from data acquired by passive sensors
The most common sensor system is the
photographic camera
The most common sensor system is the photographic camera – a
simple passive sensor
Many of the historic developments in remote sensing were directly related to the development of
photographic systems
Camera systems are similar in design to
the human eye
Camera systems are similar in design to the human eye. Both have
a lens at one end of an enclosed chamber and a light-sensitive material (film for a camera and the retina for an eye) at the other
In both systems, an iris is used to
control the amount of light that can strike the film/retina
In a camera, a shutter is placed
between the lens and film to control how long the light can strike the film
Filters can be attached
in front of a lens
Filters can be attached in front of a lens to
restrict the wavelength of light permitted to strike the film
A radiometer is
an instrument designed to measure the intensity of electromagnetic radiation in a set of wavebands ranging from the ultraviolet to microwave wavelengths.
A radiometer is an instrument designed to measure the intensity of electromagnetic radiation in a set of wavebands ranging from the ultraviolet to microwave wavelengths. The radiometers discussed here are called
electro-optic sensors
The radiometers discussed here are called electro-optic sensors because they
measure electromagnetic energy using optical techniques and electronic detectors
The radiometers discussed here are called electro-optic sensors because they measure electromagnetic energy using optical techniques and electronic detectors. Though they are only capable of
recording a single data value for their view area, if they are mounted in a scanner device images can be produced.
Radiometers are similar in design to a
camera
Radiometers are similar in design to a camera in that they have
an opening for the light to enter, lenses and mirrors for the light to pass through
Radiometers are similar in design to a camera in that they have an opening for the light to enter, lenses and mirrors for the light to pass through, but instead of film, they have
an electronic detector
Radiometers are similar in design to a camera in that they have an opening for the light to enter, lenses and mirrors for the light to pass through, but instead of film, they have an electronic detector to
record the intensity of electromagnetic energy
As energy hits the detector, a signal proportional to the incoming irradiance is processed to either a
digital or analog output that can be recorded.
Detectors for radiometers have been devised to measure
wavelengths from 0.4 to 14 micrometers.
Detectors for radiometers have been devised to measure wavelengths from 0.4 to 14 micrometers. Although some radiometers can detect this entire range of wavelengths, most only measure
selected wavebands in this range
Radiometers that measure more than one waveband are called
multispectral radiometers
Radiometers that measure more than one waveband are called multispectral radiometers. For this type of radiometer, the light
must be separated into discrete wavebands
Radiometers that measure more than one waveband are called multispectral radiometers. For this type of radiometer, the light must be separated into discrete wavebands so that
multiple waveband or multichannel readings can be taken
For this type of radiometer, the light must be separated into discrete wavebands so that multiple waveband or multichannel readings can be taken. This separation can be done using
filters, prisms or other sophisticated techniques
Non-imaging radiometers are commonly used as
research tools to better understand how light interacts with objects
Non-imaging radiometers are commonly used as research tools to better understand how light interacts with objects, for
spectral characterization of a variety of surfaces, and for atmospheric measurements.
Non-imaging radiometers are commonly used as research tools to better understand how light interacts with objects, for spectral characterization of a variety of surfaces, and for atmospheric measurements. Another common use is to
measure the quantity and quality of solar energy
Another common use is to measure the quantity and quality of solar energy. These measurements can in turn be used to
correct other imaging and nonimaging measurements for atmospheric effects.
