Microwave remote sening

1. APPLICATION OF REMOTE SENSING AND
GEOGRAPHICAL INFORMATION SYSTEM IN
CIVIL ENGINEERING
Date:
INSTRUCTOR
DR. MOHSIN SIDDIQUE
ASSIST. PROFESSOR
DEPARTMENT OF CIVIL ENGINEERING

2. Electromagnetic (EM) Spectrum
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3. The portion of the spectrum of
more recent interest to remote
sensing is the microwave region
from about 1mm to 1m.
This covers the longest wavelengths
used for remote sensing.
The shorter wavelengths have
properties similar to the thermal
infrared region while the longer
wavelengths approach the
wavelengths used for radio
broadcasts.
The remote sensing using
microwave spectrum is termed
as microwave sensing
Microwave Spectrum
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4. Microwave remote sensing covers EM spectrum in
the range from approximately 1mm to 1m
Because of their long wavelengths, compared to
the visible and infrared, microwaves have special
properties that are important for remote sensing.
Longer wavelength microwave radiation can
penetrate through cloud cover, haze, dust, and
all but the heaviest rainfall as the longer
wavelengths are not susceptible to atmospheric
scattering which affects shorter optical
wavelengths.
This property allows detection of microwave
energy under almost all weather and
environmental conditions so that data can be
collected at any time
Microwave Remote Sensing
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5. Type of Microwave Remote Sensing
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Passive RS
Natural (EMR from Sun)
RS using reflected solar radiation
RS using emitted terrestrial radiation
Active RS
Technological Assisted
Radiation
RS using senor’s transmitted radiation

6. Passive microwave sensing is similar in concept to thermal remote sensing.
All objects emit microwave energy of some magnitude, but the amounts are
generally very small.
A passive microwave sensor detects the naturally emitted microwave energy
within its field of view. This emitted energy is related to the temperature and
moisture properties of the emitting object or surface.
Because the wavelengths are so long, the energy available is quite small
compared to optical wavelengths. Thus, the fields of view must be large to
detect enough energy to record a signal.
Most passive microwave sensors are therefore characterized by low spatial
resolution.
Applications of passive microwave remote sensing include meteorology,
hydrology, and oceanography
Passive microwave sensing
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7. Active microwave sensors provide their
own source of microwave radiation to
illuminate the target
The most common form of imaging active
microwave sensors is RADAR.
RADAR is an acronym for RAdio
Detection And Ranging
RADAR transmits a microwave (radio)
signal towards the target and detects the
backscattered portion of the signal.
The strength of the backscattered signal
is measured to discriminate between
different targets and the time delay
between the transmitted and reflected
signals determines the distance (or range)
to the target
Active microwave sensing
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8. A radar is essentially a ranging or distance
measuring device.
It consists fundamentally of a transmitter, a
receiver, an antenna, and an electronics system to
process and record the data.
The transmitter generates successive short bursts (or
pulses of microwave (A) at regular intervals which
are focused by the antenna into a beam (B). The
radar beam illuminates the surface obliquely at a
right angle to the motion of the platform.
The antenna receives a portion of the transmitted
energy reflected (or backscattered) from various
objects within the illuminated beam (C).
How Radar Works
By measuring the time delay between the transmission of a pulse and the
reception of the backscattered "echo" from different targets, their distance
from the radar and thus their location can be determined
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9. How Radar Works
Pulse radar: The round-trip time for the radar pulse
to get to the target and return is measured. The
distance is proportional to this time.
Continuous wave (CW) radar
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10. Fundamental Radar Equation
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11. Ka, K, and Ku bands: very short
wavelengths used in early airborne radar
systems but uncommon today.
X-band: used extensively on airborne
systems for military reconnaissance and
terrain mapping.
C-band: common on many airborne
research systems, ERS-1 and 2 and
RADARSAT).
S-band: used on board the Russian
ALMAZ satellite.
L-band: used onboard American SEASAT
and Japanese JERS-1 satellites and
NASA airborne system.
P-band: longest radar wavelengths, used
on NASA experimental airborne research
system.
Wavelength ranges or bands of microwave
Ranges and bands were given
code letters during World War II,
and remain to this day.
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12. Wavelength ranges or bands of microwave
Band Designations
(common wavelengths Wavelength (λ) Frequency (υ)
shown in parentheses) in cm in GHz
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Ka (0.86 cm) 0.75 - 1.18 40.0 to 26.5
K 1.18 - 1.67 26.5 to 18.0
Ku 1.67 - 2.4 18.0 to 12.5
X (3.0 and 3.2 cm) 2.4 - 3.8 12.5 - 8.0
C (7.5, 6.0 cm) 3.8 - 7.5 8.0 - 4.0
S (8.0, 9.6, 12.6 cm) 7.5 - 15.0 4.0 - 2.0
L (23.5, 24.0, 25.0 cm) 15.0 - 30.0 2.0 - 1.0
P (68.0 cm) 30.0 - 100 1.0 - 0.3
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13. Types of radar
Nonimaging radar
Traffic police use handheld Doppler radar system determine the speed by
measuring frequency shift between transmitted and return microwave
signal
Plan position indicator (PPI) radars use a rotating antenna to detect targets
over a circular area, such as NEXRDA
Satellite-based radar altimeters (low spatial resolution but high vertical
resolution)
Imaging radar
Usually high spatial resolution,
Consists of a transmitter, a receiver, one or more antennas, GPS, computers
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14. Radar Nomenclature
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15. Azimuth Direction
– direction of travel of aircraft or orbital track of satellite
Range angle
– direction of radar illumination, usually perpendicular to azimuth direction
Depression angle
– angle between horizontal plane and microwave pulse (near range
depression angle > far range depression angle)
Incident angle
– angle between microwave pulse and a line perpendicular to the local
surface slope
Polarization
– linearly polarized microwave energy emitted/received by the sensor
(HH, VV, HV, VH)
Radar Nomenclature
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16. Radar imagery has a different geometry
than that produced by most conventional
remote sensor systems Therefore, one
must be very careful when attempting to
make radargrammetric measurements.
Uncorrected radar imagery is displayed in
what is called slant-range geometry, i.e., it
is based on the actual distance from the
radar to each of the respective features in
the scene.
It is possible to convert the slant-range
display into the true ground-range display
on the x-axis so that features in the scene
are in their proper planimetric (x,y)
position relative to one another in the final
radar image.
Slant Range vs. Ground Range
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17. Radar layover
At near range, the top of a tall
object is closer to the antenna than is
its base. As a result, the echo from
the top of the object reaches the
antenna before the echo from the
base.
Because the radar can measure only
slant-range distances, AB and BC are
projected onto the slant-range
domain, represented by the line bac.
Geometric errors
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18. Radar foreshortening,
It occurs in terrain of modest to high
relief depicted in the mid- to far-
range portion of an image
Here the slant-range representation
depicts ABC in their correct
relationships abc, but the distances
between them are not accurately
shown. Whereas AB = BC in the
ground-range domain, ab < bc when
they are projected into the slant range
Geometric errors
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19. Polarization of the radiation is also important. Polarization refers to the
orientation of the electric field.
Most radars are designed to transmit microwave radiation either horizontally
polarized (H) or vertically polarized (V).
Similarly, the antenna receives either the horizontally or vertically polarized
backscattered energy, and some radars can receive both.
Four combinations of both transmit and receive polarizations as follows:
HH - for horizontal transmit and horizontal receive,
VV - for vertical transmit and vertical receive,
HV - for horizontal transmit and vertical receive, and
VH - for vertical transmit and horizontal receive.
The first two polarization combinations are referred to as like-polarized and
the last two combinations are referred to as cross-polarized
Polarization
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20. The spatial resolution of radar system is
controlled by several parameters
For imaging radar, the size of ground
resolution cell is controlled by the pulse
duration, ground range and beamwidth
Pulse duration and ground range dictate
the spatial resolution (range resolution) in
the direction of energy propagation
referred to as the range resolution
Beam width determines the spatial
resolution in the direction of flight
referred to as azimuthal resolution
Spatial Resolution
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21. Spatial Resolution
Effect of pulse length. (a) Longer pulse length means that the two objects
shown here are illuminated by a single burst of energy, creating a single echo
that cannot reveal the presence of two separate objects.
(b) Shorter pulse length illuminates the two objects with separate pulses,
creating separate echoes for each object. Pulse length determines resolution
in the cross-track dimension of the image.
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22. Spatial Resolution
Azimuth resolution. For real aperture radar, the ability of the system to
acquire fine detail in the along-track axis derives from its ability to focus
the radar beam to illuminate a small area.
Beam width, in relation to range (R), determines detail—region 1 at
range R1 will be imaged in greater detail than region 2 at greater range
R2
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23. SLAR (Side-Looking Airborne Radar)
- develop in the 1950's
- airborne, fixed antenna width, sends one pulse at a time and measures what
gets scattered back
- resolution determined by wavelength and antenna size (narrow antenna
width = higher resolution)
SAR (Synthetic Aperture Radar)
- also developed by those responsible for SLAR, but this configuration is not
dependent on the physical antenna size although to achieve higher resolution
the receiving antenna components and transmitter components need to be
separated.
- "synthesizes" a very broad antenna by sending multiple pulses
Types of Imaging Radar
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24. Synthetic Aperture Radar
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25. Look direction, the direction at which the radar signal strikes the landscape, is
important in both natural and man-made landscapes.
Look angle, the depression angle of the radar, varies across an image, from
relatively steep at the near-range side of the image to relatively shallow at
the far-range side
In natural landscapes, look directions especially important when terrain
features display a preferential alignment.
Look directions perpendicular to topographic alignment will tend to maximize
radar shadow, whereas look directions parallel to topographic orientation will
tend to minimize radar shadow
Radar Shadow
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26. The portion of the outgoing radar
signal that the target redirects
directly back towards the radar
antenna is termed as backscattering
When a radar system transmits a
pulse of energy to the ground (A), it
scatters off the ground in all
directions (C). A portion of the
scattered energy is directed back
toward the radar receiver (B), and
this portion is referred to as
"backscatter".
Backscatter
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27. Speckle
A=Specular Reflection,
B=Diffuse scattering Corner Reflector Volume Scattering
SAR images are subject to fine-textured effects that can create a grainy
salt-and-pepper appearance when viewed in detail called speckle
Speckle is created by radar illumination of separate scatterers that are
too small to be individually resolved
Volume scattering is the scattering of radar energy within a volume or medium, and
usually consists of multiple bounces and reflections from different components within
the volume
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28. The incidence angle is defined as the angle between
the axis of the incident radar signal and a
perpendicular to the surface that the signal strikes
If the surface is homogeneous with respect to its
electrical properties and “smooth” with respect to
the wavelength of the signal, then the reflected
signal will be reflected at an angle equal to the
incidence angle, with most of the energy directed in
a single direction (i.e., specular reflection).
For “rough” surfaces, reflection will not depend as
much on incidence angle, and the signal will be
scattered more or less equally in all directions (i.e.,
diffuse, or isotropic, scattering)
Incident angle and scattering
Incidence
Angle
Local incidence angle
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29. A radar signal that strikes a surface will be reflected in a manner that
depends both on characteristics of the surface and properties of the radar
wave, as determined by the radar system and the conditions under which it is
operated
Surface Roughness
According to Rayleigh roughness
criterion
h = the vertical relief (average
height of surface irregularities)
= the radar wavelength
(measured in cm)
= the depression angle
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30. Surface Roughness
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31. Penetration of Radar signals
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32. Flood mapping, Snow mapping, Oil Slicks
Sea ice type, Crop classification,
Forest biomass / timber estimation, tree height
Soil moisture mapping, soil roughness mapping /
monitoring
Wave height monitoring
Crop yield, crop stress
Flood prediction
Landslide prediction
Applications
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33. Comments….
Questions….
Suggestions….
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I am grateful to all the information sources (regarding
remote sensing and GIS) on internet that I accessed
and utilized for the preparation of present lecture.
Thank you !
Feel free contact

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