MOD 5 SVIT NOTES VTU SYLLABUS 2018 SCHEME.pdf

2018 SCHEME SAT COMN NOTES MOD 5

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Remote sensing orbits and Payloads
Remotesensingsatelliteshave
sun-synchronous subrecurrent
orbitsataltitudesof700–900
km,allowingthemtoobserve
thesameareaperiodicallywitha
periodicityoftwotothree
weeks.
orbits
1. Passive sensors
2. Active sensors
Payloads
Apassivesystemgenerally
consistsofanarrayof
sensorsordetectorsthat
recordtheamount of
electromagnetic radiation
reflectedand/oremitted
fromtheEarth’ssurface
Anactivesystem,onthe
other hand, emits
electromagneticradiation
and measures the
intensityofthereturn
signal
Scanningsensors
haveanarrow
fieldofviewand
theyscana
smallareaat
anyparticular
time.
Anon-scanning
sensorviews
theentirefield
inonego.

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SensorParameters
1. Instantaneous field-of-view (IFOV)
Thisisdefinedasthesolidanglefromwhichthe
electromagneticradiationmeasuredbythesensorata
givenpointoftimeemanates
Thiscorrespondstothetotalsizeofthegeographical
areaselectedforobservation
Thisdefinestheminimumpowerlevelrequiredbythe
sensortoidentifyanobjectinthepresenceofnoise
Linearityreferstothesensor’sresponsetothevarying
levelsofradiationintensity
Sensorsemploythreewavelengthbandsforremote
sensingapplications:theopticalband,thethermalband
andthemicrowaveband.
2. Overall field-of-view
3. S/N ratio
4. Linearity
5. Wavelength band

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SensorParameters
Swath width of the sensor is the area on the surface of
the Earth imaged by it.
Thesensor’sdwelltimeisdefinedasthediscreteamount
oftimerequiredbyittogenerateastrongenoughsignal
tobedetectedbythedetectoragainstthenoise
Resolutionisdefinedastheabilityoftheentireremote
sensingsystem(includingthelens,antenna,display,
exposure,processing,etc.)torenderasharplydefined
image
6. Swath width
7. Dwell time
8. Resolution

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Resolution of any remote sensing system is specified in terms of
Thisisdeterminedbythebandwidthofthe
electromagneticradiationusedduringtheprocess.
Thenarrowerthebandwidthused,thehigheristhe
spectralresolutionachieved.
spectral resolution,
radiometric resolution
spatial resolution
temporal resolution
Radiometricresolutionreferstothesmallestchangein
intensitylevelthatcanbedetectedbythesensing
system
Spatialresolutionisdefinedastheminimumdistance
thetwopointfeaturesonthegroundshouldhavein
ordertobedistinguishedasseparateobjects
Itisspecifiedasthenumberofdaysinwhichthe
satelliterevisitsaparticularplaceagain.

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Passive Scanning Sensors
The multispectral scanner (MSS) is the most commonly used passive scanning sensor
These include
optical mechanical scanners Push broom scanners
central perspective scanners

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Passive Scanning Sensors
optical mechanical scanners
TheplatformmovesforwardovertheEarth,successive
scansbuildupatwo-dimensionalimageoftheEarth’s
surface
Afterpassingthroughtheopticalsystemtheincoming
reflectedoremittedradiationisseparatedintovarious
wavelengthbandswiththehelpofgratingprismsorfilters.
Eachoftheseparatedbandsisthenfedtoabankof
internaldetectors,witheachdetectorsensitivetoaspecific
wavelengthband.
Thesedetectorsdetectandconverttheenergyforeach
spectralbandintheformofanelectricalsignal.This
electricalsignalisthenconvertedtodigitaldataand
recordedforsubsequentcomputerprocessing.

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Passive Scanning Sensors
Push Broom Scanners opticalmechanicalscannersoffernarrowerview
anglesandsmallband-to-bandregistration
error.
However,pushbroomscannershavealonger
dwelltimeandthisfeatureallowsmore
energytobedetected,whichimprovesthe
radiometricresolution.
theyarecheaper,lighterandmorereliableas
theydonothaveanymovingpartandalso
requirelesspower

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Central Perspective Scanners
Passive Scanning Sensors
Inthiscase,duringimageformation,thesensing
devicedoesnotactuallymoverelativetotheobject
beingsensed.
Thusallthepixelsareviewedfromthesamecentral
positioninamannersimilartoaphotographic
camera.

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Active Sensors
Active sensor systems
comprisebothatransmitter
aswellasareceiver
The transmitter emits electromagnetic radiation of a
particular wavelength band, depending upon the
intended application
The receiver senses the same electromagnetic radiation
reflected or scattered by the ground.

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Active non-scanning
sensor systems include
microwave altimeters
Microwavealtimetersorradaraltimetersareused
tomeasurethedistancebetweenthesatelliteand
thegroundsurfacebymeasuringthetimedelay
betweenthetransmissionofthemicrowavepulses
andthereceptionofthesignalsscatteredback
fromtheEarth’ssurface
microwave scatterometers
laser distance meters
Microwavescatterometersareusedtomeasure
windspeedanddirectionovertheoceansurface
bysendingoutmicrowavepulsesalongseveral
directionsandrecordingthemagnitudeofthe
signalsbackscatteredfromtheoceansurface
Laserdistancemetersaredeviceshavingthe
sameprincipleofoperationasthatof
microwavealtimetersexceptthattheysend
laserpulsesinthevisibleortheIRregion
insteadofthemicrowavepulses

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Types of Images
the satellite images can be classified
Primary images
secondary images
The raw images taken from the satellite
the primary images are processed so as to enhance
their features for better and precise interpretation
monogenic images polygenic images
Monogenicimage,alsoreferred
toaspanchromaticimage,is
producedfromasingleprimary
imagebyapplyingchangestoit
likeenlargement,reduction,
error correction,contrast
adjustments,etc.
Polygenic secondary
imagesarecomposite
images formed by
combiningtwoorthree
primaryimagesinorder
tomaketheextraction
ofinformationfromthe
imageeasierandmore
meaningful.

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Polygenic images
Multitemporal images,as
mentioned earlier,are
secondaryimagesproducedby
combiningtwo ormore
primaryimagestakenat
differenttimes
multitemporal imagesmultispectral images
Inmultispectralimages,
threeimagestakenin
differentspectralbands
areeachassigneda
separateprimarycolour
natural colour composite images false colour composite images true colour composite images
Inatruecolourcomposite
image,thespectralbands
correspondtothethree
primarycolours(R,GandB)
Ifthespectralbandsintheimage
donotcorrespondtothethree
primarycolours,thentheresulting
imageiscalledafalsecolour
compositeimage
Incaseofsensorsnothavingoneor
moreofthethreevisiblebands,the
opticalimageslackthesevisualbands

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Image Classification
Supervised Classification Unsupervised Classification
Withsupervisedclassification,the
landcovertypesofinterest(referred
toastrainingsitesorinformation
classes)intheimageareidentified.
The image processing software system
is then used to develop a statistical
characterization of the reflectance for
each information class.
Unsupervisedclassificationisamethod
thatexaminesalargenumberof
unknownpixelsanddividesthemintoa
numberofclassesonthebasisof
naturalgroupingspresentintheimage
value

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Image Interpretation
Extraction of useful information from the images is referred to as image interpretation
Interpreting Optical and Thermal Remote Sensing Images
1. Radiometric information
2. Spectral information
3. Textural information
4. Geometric and contextual information
Radiometric information corresponds to the
brightness, intensity and tone of the images
Multispectral or colour composite images are
the main sources of spectral information
The texture of the image may be used to
classify various kinds of vegetation covers or
forest covers
Geometricandcontextualinformationis
providedbyveryhighresolutionimages
andmakestheinterpretationoftheimage
quitestraightforward
Interpreting Microwave Remote Sensing Images
suffer from a lot of noise, referred to as speckle
noise may require special filtering before they can
be used for interpretation and analysis
Thehigherthevalueofthebackscattering
coefficient,therougheristhesurfacebeing
imaged.

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GIS in Remote Sensing
The geographic information system (GIS) is a computer based information system used to digitally
represent and analyze the geographic features present on the Earth’s surface

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Applications of Remote Sensing Satellites
Land Cover Classification
Land Cover Change Detection
Water Quality Monitoring and Management
Flood Monitoring
Urban Monitoring and Development
Measurement of Sea Surface Temperature
Deforestation
Global Monitoring
Predicting Disasters (earthquakes,volcanic eruptions, hurricanes, storms, etc)

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Weatherforecasting,aspeoplecallit,isbothascienceaswellasanart
Itisaboutpredictingtheweather,whichcanbebothlongtermaswellas
shortterm
Generally,shorttermpredictionsarebasedoncurrentobservations
longtermpredictionsaremadeafterunderstandingtheweatherpatterns,on
thebasisofobservationsmadeoveraperiodofseveralyears

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Images from Weather Forecasting Satellites
Weather forecasting satellites take images mainly in the
visible,
the IR and
the microwave bands

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Visible Images
Themostcommonlyusedbandhereis
thevisibleband(0.4to0.9micro
m)
Visibleimagesrepresenttheamount
ofsunlightbeingreflectedbackinto
spacebycloudsortheEarth’ssurface
inthe
visibleband.
These images are mainly used in the
identification of clouds
Anothercommontypeofsatellite
imagerydepictstheradiation
emittedbythecloudsandthe
Earth’ssurfaceintheIRband(10
to12microm).
IRimagesprovideinformationonthe
temperatureoftheunderlying
Earth’ssurfaceorcloudcover.
Thisinformationisusedinproviding
temperatureforecasts,inlocating
areasoffrostandfreezesandin
determiningthedistributionofsea
surfacetemperaturesoffshore
IR images Microwave Images
Weather satellitesalso
utilizethemicrowaveband,
mostly within the
wavelengthregionfrom0.1
to10cm
Measurements inthe
microwavebandalsohelpin
determinationofquantities
suchassnow cover,
precipitation and
thunderstorms

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Weather Forecasting Satellite Orbits
Weather forecasting satellites are placed into either of the two types of orbits
polar sun-synchronous low Earth orbit
geostationary orbit

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Weather Forecasting Satellite Payloads
Radiometer
A Radiometer is an instrument that makes quantitative measurements of
the amount of electromagnetic radiation incident on it from a given area
within a specified wavelength band
The radiometer comprises
optical system,
scanning system,
electronic system
calibration system
Radiometers can operate in one of two modes-imaging mode and the sounding mode
Imagersmeasureandmapsea-surface
temperatures,cloud-toptemperaturesand
land-surfacetemperatures
Sounderisaspecialkindofradiometer,which
measureschangesintheatmospherictemperature
duetochangeinwatervaporcontentofthe
atmospherewithheight

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Active Payloads
Altimeter
Analtimetersendsaverynarrowpulseofmicrowave
radiationwithadurationofafewnanoseconds
verticallytowardsEarth
Thetimetakenbythereflectedsignaltoreachthe
satellitedeterminesthedistanceofthesatellitefrom
Earthwithanaccuracyoftheorderoffew
centimetres
Thishelpsincalculatingthesurfaceroughnessofthe
landsurface,strengthofoceancurrents,wave
heights,windspeedsandothermotionoverthe
oceans

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Scatterometer
scatterometer is a microwave radar sensor used to measure the reflection or scattering
produced while scanning the surface of the Earth using microwave radiation
Itemitsafanshapedmicrowavepulsehavingadurationof
theorderofafewmillisecondsandmeasuresthefrequency
andtheintensityprofileofthescatteredpulse
Aroughoceansurfacereturnsastrongersignalbecausethe
oceanwavesreflectmoreoftheradarenergyback
towardsthescatterometerwhereasasmoothoceansurface
returnsaweakersignalbecauselessenergyisreflectedback
inthiscasehelpstodetermineoceanwavesandhencein
estimatingthewindspeedanddirection.

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Synthetic Aperture Radar (SAR)
Synthetic aperture radar (SAR) is the most commonly used radar on weather forecasting
satellites
SAR is a special type of radar that uses the motion of the spacecraft to emulate a large
antenna from a physically small antenna.
It works on the same principle as that of a conventional radar
It also sends microwave pulses and measures the intensity, time delay and frequency of
the return pulse.

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Lidar
Lidar has the same principle of operation as that of a radar, except that it sends laser pulses
rather than microwave pulses.
Lidar sends a beam of laser light through the atmosphere.
The particles present in the path of the beam scatter it.
A portion of the scattered beam returns to Weather Satellites the receiver.

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Weather Forecasting Satellite Applications
Measurement of Cloud Parameters
Rainfall
Wind Speed and Direction
Ground-level Temperature Measurements
Air Pollution and Haze
Fog
Oceanography
Severe Storm Support
Fisheries
Snow and Ice Studies

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Global Positioning System (GPS)
The GPS comprises of three segments, namely
the space segment
control segment
usersegment

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Space Segment
Thespacesegmentcomprisesofa28satelliteconstellationoutof
which24satellitesareactivesatellitesandtheremainingfour
satellitesareusedasin-orbitspares
The satellites are placed in six orbital planes, with four satellites
in each plane
The satellites orbit in circular medium The satellites orbit in circular
medium
The orbital period of each satellite is around 12 hours (11 hours, 58
mins)
All GPS satellites are equipped with atomic clocks having a very high
accuracy of the order of a few nanoseconds (3 ns in a second).
These satellites transmit signals, synchronized with each other on two
microwave frequencies of 1575.42 MHz (L1) and 1227.60 MHz (L2)

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Control Segment
ThecontrolsegmentoftheGPSsystemcomprisesa
worldwidenetworkoffivemonitorstations,four
groundantennastationsandamastercontrol
station.
The monitor stations are located at
Hawaii and Kwajalein in the Pacific Ocean,
Diego Garcia in the Indian Ocean,
Ascension Island in the Pacific Ocean
and Colorado Springs, Colorado.
Thereisamastercontrolstation(MCS)atSchriever
AirForceBaseinColoradothatcontrolstheoverall
GPSnetwork
ThegroundantennastationsarelocatedatDiego
GarciaintheIndianOcean,KwajaleininthePacific
Ocean,AscensionIslandinthePacificOceanandat
CapeCanaveral,USA

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User Segment
TheusersegmentincludesallmilitaryandcivilGPSreceivers
intendedtoprovideposition,velocityandtimeinformation.
Thesereceiversareeitherhand-heldreceiversorinstalledon
aircraft,ships,tanks,submarines,carsandtrucks
The basic function of these receivers is to detect, decode and
process the GPS satellite signals

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Operation of the GPS navigation system

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Working Principle of the GPS
Theoretically,ifthedistanceofapointisknown
fromoneobject,thenitliesanywhereonasphere
withtheobjectasthecentrehavingaradiusequal
tothedistancebetweenthepointandtheobject

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Working Principle of the GPS
Ifthedistanceofthepointisknownfromtwo
objects,thenitliesonthecircleformedbythe
intersectionoftwosuchspheres

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Working Principle of the GPS
Thedistancefromthethirdobjecthelps
inknowingthatthepointislocatedat
anyofthetwopositionswherethethree
spheresintersect

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In the GPS, the position of any receiver is determined by calculating its distance from four
satellites
This distance is referred to as the ‘Pseudorange
Theinformationfromthreesatellitesissufficientforcalculatingthelongitudeandthelatitude
positions;however,informationfromthefourthsatelliteisnecessaryforaltitudecalculations
Hence,ifthereceiverislocatedonEarth,thenitspositioncanbedeterminedonthebasisof
informationofitsdistancefromthreesatellites

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GPS Signal Structure
The GPS signal contains three different types of information, namely
the pseudorandom code
ephemeris data
almanac data
AlmanacdatatellstheGPSreceiver
whereeachsatelliteshouldbeat
anytimeduringtheday
Italsocontainsinformationon
clockcorrectionsandatmospheric
dataparameters
Thepseudorandomcode(PRN
code)isanID(identity)code
thatidentifieswhichsatelliteis
transmittinginformationandis
used for ‘pseudorange’
calculations
Ephemerisdatacontains
informationabouthealth
ofthesatellite,current
dateandtime
All this information is transmitted at two microwave carrier frequencies, referred to as L1
(1575.42 MHz) and L2 (1227.60 MHz)

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GPSsatellitestransmittwo
typesofcodes,namely
thecoarseacquisition(C/Acode)
andtheprecisioncode(Pcode)
theL1signalismodulatedbyboth
theC/AcodeandthePcodeand
theL2signalbythePcodeonly.
Thecodesaretransmittedusing
theBPSK(binaryphaseshift
keying) digital modulation
technique

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Otherthanthesecodes,thesatellite
signalsalsocontainanavigation
messagecomprisingtheephemerisand
almanacdata
Thisprovidescoordinateinformationof
GPSsatellitesasafunctionoftime,
satellitehealthstatus,satelliteclock
correction,satellitealmanacand
atmosphericdata
Thenavigationmessageistransmitted
atabitrateof50kbpsusingBPSK
technique.

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Pseudorange Measurements
thefundamentalconceptbehindtheGPSisto
make use of simultaneous distance
measurementsfromthree(orfour)satellites
tocomputethepositionofanyreceiver

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Determination of the Receiver Location
Aftercalculatingpseudorangesfromfour
satellites,thereceiverdeterminesthe
position/timesolutionoffourrangingequations
forgenerationofitspositionandtime
information
where,
xn, yn, zn=x, y and z coordinates of the nth satellite
Ux,Uy,Uz=x, y and z coordinates of the user receiver
PRn= pseudorange of the user receiver from the nth
satellite
EC= error correction

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GPS Positioning Services and Positioning Modes
There are two levels of GPS positioning and timing services, namely
precision positioning service (PPS)
standard positioning service (SPS)
ThePPS,asthenamesuggests,
isthemost preciseand
autonomous serviceandis
accessiblebyauthorizedusers
only
SPSislessaccuratethanPPSandis
availabletoallusersworldwide,
authorizedorunauthorized

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GPS Positioning Modes
Positioning with GPS can be performed in either of the following two ways:
1. Point positioning
2.Relative positioning
Pointpositioningemploysone
GPS receivertodothe
measurements.
Herethereceivercalculates
itspositionbydeterminingits
pseudorangesfromthree(or
four)satellitesusingthe
codestransmittedbythe
satellite
GPS relativepositioning,also
referredto as differential
positioning,employstwoGPS
receiverssimultaneouslyfortracking
thesamesatellites
Theyareusedforhighaccuracy
applicationssuchassurveying,
precisionlandingsystemsfor
aircraft,measuringmovementof
theEarth’scrust,mapping
Thecorrectionsarebasedonthe
differencebetweenthetrue
locationofthebasereceiverand
thelocationdeterminedbythe
GPSsystem

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Applications of Satellite Navigation Systems
CivilianApplications Military Applications
Navigation
Tracking.
Bomb and missile guidance
Rescue operations
For mapping and construction.
Saving lives and property
Vehicle tracking and navigation