The document explains radar technology, distinguishing between imaging and non-imaging radar, and describes how radar measures various physical quantities such as range, speed, and temperature. It also defines sensors as devices that convert physical quantities into readable signals and discusses their applications in everyday technology and remote sensing. Additionally, it outlines the types of remote sensing platforms, including spaceborne, airborne, and ground-based systems, along with the advantages and disadvantages of each.

1. What is RADAR?

2. Imaging Radar - General
• RADAR (Radio Detection And Ranging) is a way to
detect and study far off targets by transmitting a
radio pulse in the direction of the target and
observing the reflection of the wave.
• It’s basically radio echo
• Wavelengths used in imaging radar range between 1
mm and 1 m
• Longer wavelengths are used for communication and
navigation.

3. Non-Imaging Radar
• Police radar, which detects the speed
of passing vehicles and displays that
speed on a screen, operates on the
principle of the Doppler effect. The
Doppler effect is the change in
frequency (number per unit time) of
sound or light waves emitted from a
moving source. The Doppler effect
was explained by Austrian physicist
Christian Doppler (1803-1853) in
1842. According to Doppler, waves
bunch up as they approach their
target and spread out as they move
away from their target.
Radar (an acronym for "radio
detection and ranging") is a device
that emits and receives radio waves.
The waves bounce off the targeted
vehicle and are received by a
recorder. The recorder compares the
difference between the sent and
received waves, and translates the
information into miles per hour.

4. Non-Imaging Radar
To provide a polar-coordinate map-
like display of targets, the radar PLAN-
POSITION INDICATOR (PPI)-the well-
known radar scope with the round
face and the sweeping hand-
between 1939 and 1940. The PPI is
now universally used by military and
commercial interests around the
world for the display of radar
information for such functions as air
and surface detection, navigation, air
traffic control, air intercept, and
object identification

5. RADAR
RAdio Detection And Ranging
Radar observables:
• Target range
• Target angles (azimuth & elevation)
• Target size (radar cross section)
• Target speed (Doppler)
• Target features (imaging)
Antenna
Transmitted
Pulse
Target
Cross
Section
Propagation
Reflected
Pulse
(“echo”)

6. The Range
• Distance from the radar
• Measured from time
delay between
transmitted pulse and
returned signal received

7. Radar
• The range and the direction of the target
determine its location, which is what is
needed for many radar applications such as air
traffic control.

8. Radar Can Measure Pressure
• The strength of the echo received from the
ionosphere measures the number of electrons
able to scatter radio waves or what we call
electron pressure

9. Radar Can Measure Temperature
• Some electrons are moving
due to heat - In this case
the echo is scattered
• The echo will contain a
range of frequencies close
to the transmitter
frequency
• As the temperature
increases, the electrons
move faster
• So radar can act like a
thermometer and measure
the temperature of the
ionosphere

10. Radar Can Measure Wind Speed
• When an electron is
removed from an atom, the
remaining charged atom is
called an ion
• The ion gas can have a
different temperature from
the electron gas
• The electron/ion mixture is
known as a plasma and is
usually in motion (like our
wind)
• So incoherent scatter radar
can also measure wind
speed

11. What is SENSORS?

12. Sensors
• A sensor (also called detector) is a converter
that measures a physical quantity and
converts it into a signal which can be read by
an observer or by an (today mostly electronic)
instrument. For example, a mercury-in-glass
thermometer converts the measured
temperature into expansion and contraction
of a liquid which can be read on a calibrated
glass tube.

13. Sensors
• A sensor is a device which receives and
responds to a signal.
• A sensor's sensitivity indicates how much the
sensor's output changes when the measured
quantity changes. For instance, if the mercury
in a thermometer moves 1 cm when the
temperature changes by 1 °C, the sensitivity is
1 cm/°C (it is basically the slope Dy/Dx
assuming a linear characteristic).

14. Sensors
• Sensors that measure very small changes must
have very high sensitivities. Sensors also have
an impact on what they measure; for instance,
a room temperature thermometer inserted
into a hot cup of liquid cools the liquid while
the liquid heats the thermometer.

15. Sensors Uses
• Sensors are used in everyday objects such as
touch-sensitive elevator buttons and lamps
which dim or brighten by touching the base.
There are also innumerable applications for
sensors of which most people are never
aware. Applications include cars, machines,
aerospace, medicine, manufacturing and
robotics.

16.  There are meaningful distinctions between remote sensing ‘platforms’,
‘sensors’ and ‘images’
 Platform
 The craft on which a sensing device
is mounted
 Sensor
 The sensing device or instrument
itself
 Image
 The image data acquired by the
sensing device
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Platforms, sensors and images

17.  There are three main categories of remote sensing
platforms
Spaceborne
- Satellite
- Shuttle
Ground-based
- Hand-held
- Raised platform
Airborne
- Aeroplane
- Helicopter
- Hot air balloon
- Air ship
- Tethered balloon
Commonest
platforms
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Remote sensing platforms

18. Satellite
path
Field of
view
Ground track
(imaged area)
Advantages
Continuous data acquisition
 Permanent orbit
High geometric accuracy
 Stable orbit (no atmosphere)
Wide area of coverage
 High vantage point
Low data cost?
Disadvantages
Geometric distortion
 Earth curvature
High operation cost
 Launch, etc.
Low spatial detail?
 High vantage point
Cloud cover?
High data cost?
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Satellite platforms

19.  Generally, remote sensing satellites
are in low Earth orbits (LEOs), at
altitudes of several hundreds of
kilometres
 These satellites orbit the Earth
approximately every hour
 Most remote sensing satellites follow
a ‘polar’ orbital path (approximately
north-south)
 Polar orbits maximise the area of data
acquisition, exploiting the Earth’s
rotation
Satellite orbit
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.

20.  As the Earth rotates eastwards, the
satellite passes North-South (or
South-North) acquiring a ‘swath’ of
imagery
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Polar orbit

21.  As the Earth rotates eastwards, the
satellite passes North-South (or
South-North) acquiring a ‘swath’ of
imagery
 As the Earth continues to rotate,
another image swath is acquired
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Polar orbit

22.  As the Earth rotates eastwards, the
satellite passes North-South (or
South-North) acquiring a ‘swath’ of
imagery
 As the Earth continues to rotate,
another image swath is acquired
 And again…
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Polar orbit

23.  Some remote sensing satellites follow
a ‘geostationary’ orbital path
 This means they constantly view the
‘same’ area of coverage
 By orbiting in coincidence with
the Earth’s rotation
 All geostationary satellites orbit
around the Earth’s equator
 A common example is meteorological
satellites
 Other non-remote sensing satellites
also use geostationary orbits
 E.g., communications
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Geostationary orbit

24. Advantages
High spatial detail
 Low vantage point
On-demand acquisition
 Requested flights
Low operation cost?
Avoid cloud cover?
Low data cost?
Disadvantages
Narrow area of coverage?
 Low vantage point
Sporadic acquisition
 Occasional flights
Low geometric accuracy
 Yaw, pitch, roll
High data cost?
Field of
view
Ground track
(imaged area)
Flight
path
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Aeroplane platforms

25.  There are various types of sensors or instruments
 Any type of sensor can be operated from any remote sensing platform
 Satellite, aircraftor ground-based
Digital
- Sensor
- Camera
- Video
- Radar
- LiDAR
Analogue
- Camera

Described
in lecture
4th ISPRS Student Consortium and WG VI/5 Summer School, Warsaw 13-19 July 2009.
Sensors