satellite & radar presentation

8/3/2019 Satellite & Radar Presentation

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Introduction

Global Navigation Satellite Systems is a set of

satellites that allow users on earth to determine

there position.

Several NSS are used in the world like, GPS,

GLONASS, Galileo; all together form the GNSS.

NSS accuracy has improved, and made it possible

to find your way through a city, based only onthe data gathered by your receiver from space.


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Transit

Developed by the American NAVY in 1959.Also

known as NAVY Navigation Satellite System.

Only one satellite is required for positioning. A position can be calculated as soon as the

satellite passes overhead.

It can guarantee a successful measurement in110 min at the equator.


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Configuration

Satellites are configured in uniform orbitalprecession, in six polar orbits.

Six satellites.

Six polar orbits.

altitude: 960 km

period: 106 min

inclination: 90

Three ground-based monitor stations.


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Concept

theory of relationship between satellites and receiver:

1. a satellite sends its exact position and time overfrequency fo.

2. a receiver searches for signal over a certain frequencyrange above fo.

3. if the signal can be found on a certain frequency f, thereceiver will continue to track this frequency as itcontinues to drop.

4. when fo = f, then the satellite is somewhereoverhead.

5. at this point, a calculation can be performed, and thereceiver can stop listening.


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Disadvantages

The calculations narrow the receivers positionto two possible locations.

For anything but maritime expeditions, thiswould render the system useless unless thealtitude is known.

Other disadvantages include bad coverage,

poor accuracy and the requirement thatreceiver physically has to wait until a satellitepasses overhead.


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GPS

Global Positioning System was developed by

the US Department of defense.

A measurement requires data from fourdifferent satellites.

A successful measurement is done within 36

seconds.

Each satellite must know the exact time, with

an accuracy of at least 10 nanoseconds.


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Configuration

the configuration for the GPS that provide globalcoverage:

21 active satellites

3 spare satellites six orbital planes (in MEO orbit)

altitude: 20,200 km

period: 11h 58m

inclination: 53 degree

four satellites per plane

five monitor stations.


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Concept

Basic relationship between the satellite and receiver:

1. A receiver receives a signal from a GPS satellite.

2. It determines the difference between the current

time and the time submitted over the frequency.3. It calculates the distance of the satellite from thereceiver, knowing that the signal was sent at thespeed of light.

4. The receiver receives a signal from another two

satellites, and again calculates the distance fromthem.

5. Knowing its distance from three known locations, thereceiver triangulates its position.


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Disadvantages

GPS coverage is relatively poor.

especially in places where there are many

large obstructions in the receiver's horizon. microwave frequencies are very sensitive.

signals may bounce, or be blocked entirely.


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Galileo

A European GNSS developed in 2004.

Satellites have a relatively lightweight of 625kg.

Satellites broadcast over a wider spectrum of

frequencies than GPS. Services:

1. Open service

2. Safety of life service

3. Commercial service4. Public regulated service

5. Search and rescue service.


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Configuration

the major difference from other systems is that itsconfiguration uses only three planes instead of six

27 active satellites

3 spare satellites

three orbital planes (in MEO orbit)

altitude: 23,616km

period: 14h 4minclination: 56 degree

10 satellites per plane


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Concept

Has the same relationship between satellite andreceiver an GPS.

Design advantages:

1. Increased power output with Lithium-Ionbatteries.

2. Lightweight and compact.

3. Laser retro-reflector allows pinging from earthby laser.

4. Upgradeability with extra payloads.


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5. Communication amongst satellites by Inter-

Satellite Link (ISL).

6.C

an be injected directly into the correct orbitby the launcher.

7. Launchers can accommodate two to eight

satellite vehicles.


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Meteorogical Satellites

They observe and transmit information to the

stations located on the earths surface.

They serve as collector of global visible andinfrared cloud data and other specialized

meteorological, oceanographic and solar-

geophysical data.

The are of two types, Polar orbiting and

Geostationary.


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Satellite Sensor System

Most sensors are designed to measure

photons.

A negatively charged detector (light-sensitivematerial) is subjected to the beam of photon.

Electrons are emitted at the contact of

photons with the detector.

The electrons can then be made to flow from

the plate, collected, and counted as a signal.


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Information Classification

a) Spatial information: obtaining the requiredinformation over a 2-dimantional plane.

b) Spectral information: for certain applications,

the spectral details of an electromagnetic signalare of crucial importance (ex. Atmosphericlayers).

c) Intensity information: the measure the intensity

of the EM radiation reflected from the object toknow the dielectric properties and theroughness of the object.


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Principle of satellite remote sensing

All objects emit electromagnetic radiation. Thehotter the source, the greater is the intensity ofemission. Substances which absorb all theradiation falling on them at every wavelength arecalled black bodies. The coefficient ofabsorption is then unity.

Most substances, however, are not perfect blackbodies. Their emissivity is less than unity.

Unlike solids and liquids, gases are not blackbodies. They only absorb or emit strongly atcertain wavelengths.


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Satellite Imagery:

a) Visible (VIS) - imagery derived from reflectedsunlight at visible and near infrared wavelength(0.4 - 1.1 m).

b) Infrared (IR) imagery derived from emissions bythe earth and its atmosphere at thermal infraredwavelengths (10-12 m).

c) Water Vapor (WV) imagery derived from watervapor emissions (6-7m).

d) Images from microwave radiometer such asSpecial Sensor Microwave Imager (SSM/I), andTRMM Microwave Imagers.


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RADAR

RADAR is an acronym for Radio Detection And

Ranging.

RADAR is an object detection system thatuses EM waves to identify the range, altitude,

direction or speed of both moving and fixed

objects such as aircrafts, ships, weather

formations and terrain.


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Principle of operation

Reflection of electromagnetic waves.

Measurement of running time of transmittedpulses.

RADAR observables:

Target range

Target angle(azimuth & elevation)

Target size

Target speed (Doppler)

Target features (imaging)


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Components of RADAR system

Synchronizer

Transmitter

Antenna

Duplexer

Receiver

Display unit Power supply


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Radio Waves

Type of EM radiation

Travel with speed of light

Wavelength 100 meters to 30cm

Frequency 3MHz to 1000MHz

Naturally occurring

Artificially generated


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Applications of RADAR

Search RADAR scans a large area

Targeting RADAR scans a small area

Navigational RADAR used on commercial ships

and aircrafts

Mapping RADAR remote sensing andgeographic applications

Weather RADAR locate precipitation, itsmotion and future

Air traffic control.


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conclusion

RADAR is a way to detect and study far off

objects by transmitting a radio pulse in the

direction of the target and observing the

reflection of the wave.


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references

[1] European Space Agency. Why Europe needs Galileo.

http://www.esa.int/esaNA/GGG0H750NDC index 0.html.

[2] Stuart at Random Useless Info. GPS Stuff.

http://www.randomuseless.info/gps/.

[3] Robert J. Danchik and L. Lee Pryor.The legacy of transit. Johns Hopkins APL Technical

Digest, 11(1,2), 1990

http://www.globalsecurity.org/space/systems/transit.htm.

[4] European Commission Directorate-General Energy and Transport. Galileo: European

Satellite Navigation System.

http://europa.eu.int/comm/dgs/energy transport/galileo/index en.htm.

[5] William H. Guier and George C. Weiffenbach. The Early Days of Sputnik.

http://sd-www.jhuapl.edu/Transit/sputnik.html.

[6] PerkinElmer Inc. Rubidium Frequency Standard Model RFS-IIF. http://optoelectronics.perkinelmer.com/content/Datasheets/rfs2f.pdf.

[7] US Army Space Institute. Army Space Reference Text.

http://fas.org/spp/military/docops/army/ref text/.

[8] Laurence Nardon. Galileo and GPS: Cooperation or Competition?

http://www.brookings.edu/fp/cusf/analysis/nardon.pdf.

[9] University ofCalifornia Berkeley. Earth Sciences & Map Library.

http://www.lib.berkeley.edu/EART/.

[10] Delft University ofTechnology. Eurofix: PRN codes.

http://www.eurofix.tudelft.nl/prncode.htm.

[11] Hans Herman of the European Space Agency. Galileo: The European Initiative in Satellite

Navigation.

http://tcmc.tugraz.at/PDF/tcmc2001/pdf/1 1/Fromm.pdf.

[12] Mobilecomms Technology. Galileo Satellite Radio Navigation System.

http://www.mobilecomms-technology.com/projects/galileo/.

[13] Department of Geography University ofColorado Boulder. Global Positioning System

Overview.

http://www.colorado.edu/geography/gcraft/notes/gps/gps.html.

[14] Steve M. Yionoulis. The transit satellite geodesy program. Johns Hopkins APL Technical

Digest, 19(1):3638, 1998

http://techdigest.jhuapl.edu/td1901/yionoulis.pdf.

Kidder, S.Q. and Vonder Haar, T.H. 1995. Satellite Meteorology : An Introduction. Academic Press.

Krishna Rao, P. 2000. Weather Satellites System Data and Environmental Application. American Meteorological Society, London.

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