1. A Presentation On Data Acquisition
By Microwave Band
By-
Anamika Debbarma (DC2011BTE0127)
Jorali Longmailai (DC2011BTE0208)

2. INTRODUCTION TO MICROWAVE
REMOTE SENSING
 Electromagnetic radiation in the microwave wavelength region
is used in remote sensing to provide useful information about
the Earth's atmosphere, land and ocean.
 Valuable environmental and resource information can be
derived from sensors that operate in the microwave portion of
the electromagnetic spectrum.
 It ranges from wavelength of 1mm to 1m. The longest are
about 25,00000 times longer than the shortest waves.

3. CHARACTERISTICS OF
MICROWAVE ENERGY
 Microwaves are capable of penetrating the atmosphere under
virtually all conditions. Depending on the wavelengths
involved, microwave energy can “see through” haze, light rain
and snow, clouds, and smoke.
 Microwave reflections or emissions from earth materials bear
no direct relationship to their counterparts in the visible or
thermal portion of the spectrum. For example, surfaces that
appear “rough” in the visible portion of the spectrum may be
“smooth” as seen by microwaves .

4. MICROWAVE SENSORS
The sensors operating in the microwave region, can be
broadly classified as active & passive sensors.
The microwave sensors can operate during day and night.
Depending on the wavelength, the atmosphere is more
transparent to microwaves than to optical rays, thus providing
an all-weather monitoring capability

5. Active Microwave Sensors:
 Active sensors can carry their own source of electromagnetic radiation to illuminate
the target.
 The sensors sends short microwave pulses and measures the backscattered energy
and the time taken for the round trip travel.
 The time measurement gives the distance of the target from the sensor and hence
gives the location of the target and the amount of energy backscattered depends on
the target properties and hence gives the measure of some of the target
characteristics.
 Two types of sensors are there depending on the radar source-receiver configuration
and analysis techniques namely bistatic radar and monostatic radar.
 Separate antennas are used for transmitting and receiving in bistatic radars. On the
other hand, same antenna is used for transmitting and receiving in monostatic
radars.
 Some of the active microwave sensors are Side Looking Airborne Radar (SLAR) &
Synthetic Aperture Radar( SAR).
Passive Microwave Sensors:
 Passive sensors detect the natural radition emanating from the earth.
 Passive microwave sensors are generally known as microwave radiometers. The
emission could be either from the surface of earth-land ,ocean,ice etc. ,-or from
atmospheric constituents ,ie ,the emission of the atmosphere known as atmospheric
sounding.

6. RADAR OPERATION
Imaging radar systems in typical use for remote sensing are
pulsed- the energy that they transmit from their antenna is
confined to a very short interval of time. This outgoing
packet of energy eventually interacts with the landscape and
some of it may be backscattered to return toward the antenna.
In order to keep track of the outgoing and incoming energy
packets, the system uses a pulse repetition frequency which
provides sufficient time for any backscatter from the far
range portion of the scene to return to the antenna before the
next transmitted pulse occurs.

7. The pulse duration, the time interval during which the
antenna is energized during the transmit phase ,controls the
range –width of the outgoing energy packet.

8. Single Pulse Time- Space Diagram

9. Synthetic Aperture Radar
The SAR makes use of the radar principle to form an image by utilizing the
time delay of the backscattered signals. Synthetic aperture radar (SAR)
imaging, microwave pulses are transmitted by an antenna towards the earth
surface. The microwave energy scattered back to the spacecraft.
A radar pulse is transmitted
from the antenna to the ground
The radar pulse is scattered by the
ground targets back to the antenna

10. In real aperture radar imaging, the ground resolution is limited by the size of the
microwave beam sent out from the antenna. Finer details on the ground can be
resolved by using a narrower beam. The beam width is inversely proportional to
the size of the antenna, i.e. the longer the antenna, the narrower the beam.
The microwave beam sent
out by the antenna
illuminates an area on the
ground (known as the
antenna's "footprint"). In
radar imaging, the recorded
signal strength depends on
the microwave energy
backscattered from the
ground targets inside this
footprint. Increasing the
length of the antenna will
decrease the width of the
footprint.

11. It is not feasible for a spacecraft to carry a very long antenna which is required for
high resolution imaging of the earth surface. To overcome this limitation, SAR
capitalises on the motion of the space craft to emulate a large antenna .
Imaging geometry for a typical strip-mapping synthetic aperture radar imaging
system. The antenna's footprint sweeps out a strip parallel to the direction of the
satellite's ground track.

12. SLAR( Side-Looking Airborne Radar)
SLAR imagery is acquired by an antenna array aimed to the
side of the aircraft, so that it forms an image of a strip of land
parallel to, and at some distance from the ground track of the
aircraft.
One of SLAR’s most unique and useful characteristics is its
ability to function during the inclement weather.
SLAR systems are independent of solar illumination,
missions, using SLAR can be schedule at night or during early
morning or evening hours when solar illumination might be
unsatisfactory for acquiring aerial photographs.

13. GEOMETRY OF THE RADAR IMAGE

14. The aircraft is viewed head-on, with the radar beam
represented in vertical cross section as the fan-shaped figure at
the side of the aircraft.
The upper edge of the beam forms an angle with a horizontal
line extended from the aircraft; this angle is designated as the
depression angle of the far edge of the image.
The smallest depression angle forms the far –range side of
the image.
The near range region is the edge nearest to the aircraft.
Intermediate regions between the two edges are sometimes
referred to as mid range portions of the image.

15. RADAR BANDS AND DESIGNATIONS

16. TRANSMISSION CHARACTERISTICS
OF RADAR SIGNALS
The wavelength and the polarization of the energy pulse used
influences the transmission characteristics of the signal of a radar
system.
The letter codes for the various bands were originally selected
arbitrarily to ensure military security.
The wavelength of a radar signal determines the extent to which it is
attenuated and/or dispersed by the atmosphere.
For example-Rain and clouds can affect radar signal returns when the
radar wavelength is 2cm or less. At the same time, the effect of rain is
minimal with wavelengths of operation greater than 4cm. With K- and
X- band radar, rain may attenuate or scatter radar signals significantly.

17. X Band

18. POLARIZATION
Electromagnetic energy has two components-electrical and magnetic –
which are planar fields of oscillation that are orthogonal to each other.
Polarization refers to the spatial orientation of the electrical oscillation
plane— it is oriented vertically, horizontally, or at some other angle.
Because radar is an active remote sensing device, the orientation of the
electromagnetic energy that is transmitted can be controlled. Although all
angles are possible, only vertical or horizontal orientations are used. The
orientation of the backscatter which will be received can also be controlled.
This gives four possibilities for a radar system.
HH horizontal transmit and receive(like –polarized or parallel polarized)
VV vertical transmit and receive(like –polarized or parallel polarized)
HV horizontal transmit, vertical receive(cross-polarized )
VH vertical transmit, horizontal receive(cross-polarized)

20. REFERENCE
Remote Sensing and Image Interpretation-by Lillesand, Kiefer
and Chipman.
Fundamentals of Remote Sensing –by George Joseph.
The Sage Handbook of Remote Sensing-by M Duane
Introduction to Remote Sensing-by James B Campbell

21. THANK YOU