2. AERIAL CAMERA:
A Camera is a device used for taking photographs by letting light from an
image fall briefly onto sensitized film, usually by means of a lens-and-shutter
mechanism.
PARTS OF AN AERIAL CAMERA:
An aerial camera consists of three basic parts: a body, a cone, and a magazine.
(See the figure)
The body has following constituent parts:
Filter
Front lens
Shutter
Diaphragm
Rear lens
The magazine has three constituents:
Supply reel/ spool
Take up reel/spool
Platen
The cone is intermediate part of the camera which keeps the camera body and
magazine at a definite distance apart from each other.
3. FUNCTIONING:
When the camera is focused at infinity, the lens gathers
light rays reflected from the objects and transmits them in
an orderly fashion to the light-sensitive areas known as the
film. The shutter serves to regulate the amount and
duration of light reaching the film when making an
exposure and it has a millimeter opening which overcomes
the jerks and blurring caused by the moving aircraft and to
capture the whole picture. In addition to a fast and effective
shutter, the camera should have a high-grade lens which
should admit sufficient light at the required shutter speed
and must be adaptable to the particular camera design and
the film used and should have low distortion characteristics.
5. The growing need for geo-data everywhere is driving customers to demand
shorter turnaround rates and higher levels of detail. These needs can be met by
aerial imagery directly captured in digital format onboard an aircraft. In tandem
with the new product survey on Digital Aerial Cameras .
Medium-format
From the application point of view, the larger and heavier a camera, the
more stable it will remain under aircraft vibration and other motion, and
the more suited it will be for accurate bulk topographic and cadastral
mapping of larger areas. However, companies such as Intergraph and Leica,
traditionally involved in manufacturing high-end cameras for demanding
mapping applications, recognise that remote-sensing professionals,
engineers and construction people are looking for cost-effective solutions
when carrying out smaller projects. To fill this gap, Intergraph has brought
out a medium-format digital camera called RMK D.
6. Linear Array
Leica’s ADS family focuses on accurate mapping, as well as remote-sensing
applications. The multispectral sensor collects RGB and NIR imagery
simultaneously, in this way satisfying multiple applications. Both the ADS40 and
ADS80 have three panchromatic linear arrays at differing viewing angles, enabling
creation of reliable DEMs (Figure ). The CCD linear array of the ADS40 contains
12,000 elements for both the panchromatic and multispectral lines. In the new
ADS80, one pair of panchromatic lines are staggered by half a pixel, doubling the
number of sensor elements to 24,000 and making it possible to fly at twice the
height without compromising Ground Sample Distance (GSD). This, in addition to
the digital workflow, enables the ADS family to acquire and process imagery over
large areas in limited time.
7. Objects around us give off heat to some degree, and that heat is made up of long
wavelength infrared radiation that the human eye cannot see. Thermal imaging
uses a sensor to convert the radiation into a visible light picture. Not only does this
picture help us identify objects in total darkness, or through dense smoke, but the
sensor information can be used to measure temperature differences as well.
Thermal imaging cannot be used in applications where the materials absorb long
wavelength radiation. Thermal imaging cannot look through common materials
such as water or glass. There are two types of infrared detectors: photon detectors
and thermal detectors. Photon detectors usually offer better sensitivity and
response times than thermal detectors. However, photon detectors require that
the detector be cooled by liquid nitrogen or other means, therefore they are
larger, more expensive, and less reliable. Thermal detectors have become the unit
of choice in the law enforcement community.
Thermal Imaging Technology
8. There are many thermal detection processes available, but the two
most common are resistive bolometers and pyroelectric sensors.
Resistive bolometers are much like complementary metal oxide
semiconductor (CMOS) solid state cameras. They have no moving
parts, but must periodically recalibrate themselves because they
constantly respond to the radiation being produced by an object.
Pyroelectric sensors, on the other hand, respond to changes in the
radiation of an object. Therefore, they must use a rotating motorized
"chopper" wheel to modulate the radiation.
9. Multispectral remote sensing involves the acquisition of visible, near infrared, and
short-wave infrared images in several broad wavelength bands. Different materials
reflect and absorb differently at different wavelengths. As such, it is possible to
differentiate among materials by their spectral reflectance signatures as observed
in these remotely sensed images, whereas direct identification is usually not
possible.
Hyperspectral vs Multispectral Imaging
Hyperspectral imaging systems acquire images in over one hundred contiguous
spectral bands. While multispectral imagery is useful to discriminate land surface
features and landscape patterns, hyperspectral imagery allows for identification
and characterization of materials. In addition to mapping distribution of materials,
assessment of individual pixels is often useful for detecting unique objects in the
scene.
Hyperspectral sensors pose an advantage over multispectral sensors in their ability
to identify and quantify molecular absorption. The high spectral resolution of a
hyperspectral imager allows for detection, identification and quantification of
surface materials, as well as inferring biological and chemical processes.
10. Microwave radiometer
A microwave radiometer (MWR) is a
radiometer that measures energy emitted at
millimetre-to-centimetre wavelengths
(frequencies of 1–1000 GHz) known as
microwaves. Microwave radiometers are very
sensitive receivers designed to measure
thermally-emitted electromagnetic radiation.
They are usually equipped with multiple
receiving channels in order to derive the
characteristic emission spectrum of planetary
atmospheres, surfaces or extraterrestrial
objects. Microwave radiometers are utilized in
a variety of environmental and engineering
applications, including remote sensing,
weather forecasting, climate monitoring,
radio astronomy and radio propagation
studies.
12. A microwave radiometer consists of an antenna system, microwave radio-
frequency components (front-end) and a back-end for signal processing at
intermediate frequencies. The atmospheric signal is very weak and the
signal needs to be amplified by around 80 dB. Therefore, heterodyne
techniques are often used to convert the signal down to lower
frequencies that allow the use of commercial amplifiers and signal
processing. Increasingly low noise amplifiers are becoming available at
higher frequencies, i.e. up to 100 GHz, making heterodyne techniques
obsolete. Thermal stabilization is highly important to avoid receiver drifts.
Usually ground-based radiometers are also equipped with environmental
sensors (rain, temperature, humidity) and GPS receivers (time and
location reference). The antenna itself often measures through a window
made of foam which is transparent in the microwave spectrum in order to
keep the antenna clean of dust, liquid water and ice. Often, also a heated
blower system is attached the radiometer which helps to keep the window
free of liquid drops or dew (strong emitters in the MW) but also free of ice
and snow.
13. Laser scanning
Laser scanning is the controlled deflection of laser beams, visible or invisible.
[1]
Scanned laser beams are used in some 3-D printers, in rapid prototyping,
in machines for material processing, in laser engraving machines, in
ophthalmological laser systems for the treatment of presbyopia, in confocal
microscopy, in laser printers, in laser shows, in Laser TV, and in
barcode scanners.
14. Most laser scanners use moveable mirrors to steer the laser beam. The
steering of the beam can be one-dimensional, as inside a laser printer,
or two-dimensional, as in a laser show system. Additionally, the mirrors
can lead to a periodic motion - like the rotating polygon mirrror in a
barcode scanner or so-called resonant galvanometer scanners - or to
a freely addressable motion, as in servo-controlled galvanometer
scanners. One also uses the terms raster scanning and vector scanning to
distinguish the two situations. To control the scanning motion, scanners
need a rotary encoder and control electronics that provide, for a desired
angle or phase, the suitable electric current to the motor (for a polygon
mirror) or galvanometer (also called galvos). A software system usually
controls the scanning motion and, if 3D scanning is implemented, also
the collection of the measured data.
Scanning mirrors
Laser
scanning
module
with two
galvanome
ters, from
Scanlab
AG. The
red arrow
shows the
path of the
laser
beam.
15. In order to position a laser beam in two dimensions, it is possible either to rotate one
mirror along two axes - used mainly for slow scanning systems - or to reflect the laser
beam onto two closely spaced mirrors that are mounted on orthogonal axes. Each of
the two flat or polygon (polygonal) mirrors is then driven by a galvanometer or by an
electric motor respectively. Two-dimensional systems are essential for most
applications in material processing, confocal microscopy, and medical science. Some
applications require positioning the focus of a laser beam in three dimensions. This is
achieved by a servo-controlled lens system, usually called a 'focus shifter' or 'z-
shifter'. Many laser scanners further allow changing the laser intensity.
In laser projectors for laser TV or laser displays, the three fundamental colors - red,
blue, and green - are combined in a single beam and then reflected together with two
mirrors.
The most common way to move mirrors is, as mentioned, the use of an electric motor
or of a galvanometer. However, piezoelectric actuators or magnetostrictive actuators
are alternative options. They offer higher achievable angular speeds, but often at the
expense of smaller achievable maximum angles. There are also microscanners, which
are MEMS devices containing a small (millimeter) mirror that has controllable tilt in
one or two dimensions; these are used in pico projectors.
16. Radar altimeter (Radio Altimeters)
A radar altimeter (RA), also called a radio
altimeter (RALT), electronic
altimeter, reflection altimeter, or low-range
radio altimeter (LRRA), measures altitude
above the terrain presently beneath an aircraft
or spacecraft by timing how long it takes a
beam of radio waves to travel to ground,
reflect, and return to the craft. This type of
altimeter provides the distance between the
antenna and the ground directly below it, in
contrast to a barometric altimeter which
provides the distance above a defined
vertical datum, usually mean sea level.
17. The underlying concept of the radar altimeter was developed
independent of the wider radar field, and originates in a study of
long-distance telephony at Bell Labs. During the 1910s,
Bell Telephone was struggling with the reflection of signals caused by
changes in impedance in telephone lines, typically where equipment
connected to the wires. This was especially significant at repeater
stations, where poorly matched impedances would reflect large
amounts of the signal and made long-distance telephony difficult.[5]
Engineers noticed that the reflections appeared to have a "humpy"
pattern to them; for any given signal frequency, the problem would
only be significant if the devices were located at specific points in the
line. This led to the idea of sending a test signal into the line and then
changing its frequency until significant echos were seen, and then
determining the distance to that device so it could be identified and
fixed.[5]
Lloyd Espenschied was working at Bell Labs when he conceived using
this same phenomenon to measure distances in a wire. One of his
first developments in this field was a 1919 patent (granted 1924)[6]
on
the idea of sending a signal into railway tracks and measuring the
distance to discontinuities. These could be used to detect broken
tracks, or if the distance was changing more rapidly than the speed of
the train, other trains on the same line.[5]
![Laser scanning
Laser scanning is the controlled deflection of laser beams, visible or invisible.
[1]
Scanned laser beams are used in some 3-D printers, in rapid prototyping,
in machines for material processing, in laser engraving machines, in
ophthalmological laser systems for the treatment of presbyopia, in confocal
microscopy, in laser printers, in laser shows, in Laser TV, and in
barcode scanners.](https://image.slidesharecdn.com/unit2cameras-250811045222-10d4099d/85/unit-2-camerasfor-remotesending-data-uni-13-320.jpg)
![The underlying concept of the radar altimeter was developed
independent of the wider radar field, and originates in a study of
long-distance telephony at Bell Labs. During the 1910s,
Bell Telephone was struggling with the reflection of signals caused by
changes in impedance in telephone lines, typically where equipment
connected to the wires. This was especially significant at repeater
stations, where poorly matched impedances would reflect large
amounts of the signal and made long-distance telephony difficult.[5]
Engineers noticed that the reflections appeared to have a "humpy"
pattern to them; for any given signal frequency, the problem would
only be significant if the devices were located at specific points in the
line. This led to the idea of sending a test signal into the line and then
changing its frequency until significant echos were seen, and then
determining the distance to that device so it could be identified and
fixed.[5]
Lloyd Espenschied was working at Bell Labs when he conceived using
this same phenomenon to measure distances in a wire. One of his
first developments in this field was a 1919 patent (granted 1924)[6]
on
the idea of sending a signal into railway tracks and measuring the
distance to discontinuities. These could be used to detect broken
tracks, or if the distance was changing more rapidly than the speed of
the train, other trains on the same line.[5]](https://image.slidesharecdn.com/unit2cameras-250811045222-10d4099d/85/unit-2-camerasfor-remotesending-data-uni-17-320.jpg)