geography of microwave survey
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FIELD TELECOMMUNICATION SURVEY
Geography of Microwave Survey
Page 2
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 3
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 4
Map reading
• Collect all the maps available, preferably 1/50 000 (1/24 000 for North America).
• In some circumstances 1/200 000 maps will also be useful.
• Scale
1/200 000 1 mm = 200 m1/50 000 1 mm = 50 m1/24 000 1 mm = 24 m1
1/10 000 1 mm = 10 m1/ 5 000 1 mm = 5 m
TOPOGRAPHYTOPOGRAPHY
Map representationMap representation
Page 5
TOPOGRAPHYTOPOGRAPHY
• Image of the earth surface, watched from particular point of view and projected on to a tangent plane on the earth surface
• Types of projections– MERCATOR (Gérard Kremer alias)– LAMBERT
Map representationMap representation
Page 6
• Cylindrical projection.
• The projection surface is a cylinder which is tangential or secant to the earth's model.
TOPOGRAPHYTOPOGRAPHY
• Example: UTM projection is divided of 60 zones of 6° in longitude– France is on 3 zones: zone 31 30 32
Map representationMap representation
Direct cylindrical projection Oblique cylindrical projection
Transverse cylindrical projection
Page 7
• Conical projection.
• The projection surface is a cone tangent or secant to the earth's model.
TOPOGRAPHYTOPOGRAPHY
• Example: LAMBERT projection is divided into 4 zones– LAMBERT I - II - III - IV or LAMBERT II extended which covers all the
country.
Map representationMap representation
Tangent conic presentation Secant conic presentation
Page 8
TOPOGRAPHYTOPOGRAPHY
• For map representation, the ellipsoid closest to the Geoid of the area to be represented will be used. For France, we'll use clarke 1880 ellipsoid lambert conformal map projection. For Africa we'll use clark 1866 ellipsoid
• Ellipsoid is a mathematical model to define the earth surface
• Geoid is a mathematical model to which coincides with mean sea level extended to all continents.(Geoid conventionnally coincides with altitude zero)
• Datums: NAD 27, NAD 83, Old Hawaiian (for North America)
Map representationMap representation
Page 9
Geoid
Earth surface
Ellipsoid
TOPOGRAPHYTOPOGRAPHY
• Date of creation and update
• Ellipsoid
Map representationMap representation
Page 10
TOPOGRAPHYTOPOGRAPHY
Magnetic variation• Magnetic North is the only one which can be measured (compass).
• Geographic north is the north on the map.
• An angle measured from magnetic north can be reported on a map if the variation is known.
• It’s possible to Check the magnetic variation via the internet:
www.geolab.nrcan.gc.ca/geomag/e_cgrf.html
www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl
Map representationMap representation
Page 11
• When Magnetic variation decreases, it means it's getting closer to geographic North - it varies according to geographic areas on earth - it is more important near the poles.
2°47'
Magnetic North Geographic North
Example of indication on IGN France map
Magnetic variation coincides with the middle of
the sheet on 1st January 1990 it decreases
every year by 8'.
TOPOGRAPHYTOPOGRAPHY
Magnetic variationMagnetic variation
Map representationMap representation
Page 12
MNGN
7°
237°/MN
230°/GN
TOPOGRAPHYTOPOGRAPHY
Magnetic variationMagnetic variation
Map representationMap representation
Page 13
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 14
Latitude and longitudeLatitude and longitude
• On a single map, we can have two different projections.– The projections can be found in the map’s legend.
• Each map provides a legend that must be read.
• Contour lines are essential to draw a profile.
• Systematically check the contour intervals.
TOPOGRAPHYTOPOGRAPHY
Geographical coordinatesGeographical coordinates
Page 15
Each index contour line is accentuated Contour intervals: 10m
112m
100m
50m
TOPOGRAPHYTOPOGRAPHY
Latitude and longitudeLatitude and longitude
Geographical coordinatesGeographical coordinates
Page 16
Latitude and longitude
• Enable to calculate geographic coordinates of any point on earth thanks to abscissa and ordinate report
• Earth circumference 40000 km40000 km / 360° = 111.111 km = 1°
1° = 60' => 1.852km = 1' = 1 mile1' = 60" => 31 m = 1"
AT EQUATOR LEVEL
TOPOGRAPHYTOPOGRAPHY
Geographical coordinatesGeographical coordinates
Page 17
Origin of any map
W
E
LONG ELAT S
LONG WLAT S
LONG ELAT N
LONG WLAT N
GREENWICH MERIDIAN OR MERIDIAN 0 (zero)
N
S
Equator
TOPOGRAPHYTOPOGRAPHY
Latitude and longitudeLatitude and longitude
Geographical coordinatesGeographical coordinates
Page 18
1cm
5mm
Cross with soft lead pencil
Pointing with hard pencil
TOPOGRAPHYTOPOGRAPHY
• Site pointing
Geographical coordinatesGeographical coordinates
Page 19
Latitude and longitude
• Coordinate calculation– 1) Write out the point on the X and Y axes with a square and HARD PENCIL
– 2) Measure the mm. value of 300" and deduce the value of 1 second in xmm longitude and ymm latitude
– 3) Measure the variation between the point written out and the origin selected
– 4) Apply the rule of three
– 5) Add the calculated values to original values
DO NOT HESITATE TO DETAIL YOUR CALCULATIONS
°degrees, ' minutes, " seconds
TOPOGRAPHYTOPOGRAPHY
Geographical coordinatesGeographical coordinates
Page 20
TOPOGRAPHYTOPOGRAPHY
Geographical coordinatesGeographical coordinates
48°05'
ymm
Latitude
y'mm
48°00
Origin
2°00' 2°05'X'mm
longitudexmm
Page 21
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 22
• ALTITUDE MEASUREMENThpa (hectopascal) = Meteorologymmhg (millimeter of mercury) = Medical unitmbar (millibar) = Old unitbar = Industrial pressure
unit
===>Altitude Pressure
TOPOGRAPHYTOPOGRAPHY
AltimetryAltimetry
Page 23
• The altimeter is a barometer
TOPOGRAPHYTOPOGRAPHY
AltimetryAltimetry
²/1²1
11 mN
m
NEWTONpa
Page 24
• Normal atmospheric pressure measured at standard point Altitude m
7000
6000
5000
4000
3000
2000
1000
0
Pressure hpa
410
472
540
616
701
795
899
1013
Temp °C
-30.5°
-24°
-17.5°
-11°
-4.5°
2°
8.5°
15°
TOPOGRAPHYTOPOGRAPHY
AltimetryAltimetry
Page 25
Map information
• Origin of altitudes measured
Altimetry
• The altimeter under forcasts altitude deviations under warm temperatures and overforcats them under cold temperatures.In winter it gives too high altitude and too low in summer
TOPOGRAPHYTOPOGRAPHY
AltimetryAltimetry
Page 26
• Summer– 4000 m measured in a summer day with a temperature of 0°C:
+11°C deviation compared with standard atmosphere– Applicable correction is: +11x4x4m = 176m Real altitude is 4176m
• Winter– 4000m measured in a winter day with a temperature of -20°C: -9°C
deviation compared with standard atmosphere– Applicable correction: -9x4x4m = -144m Real altitude is 3856m
Correction is of 4m per 1000m, and per deviation degree compared with standard temperature at reading altitude with deviation sign
TOPOGRAPHYTOPOGRAPHY
AltimetryAltimetry
Page 27
• It is thus necessary to apply the so-called double measurement procedure2 altimeters are requiredMark a point on the mapCalibrate both altimeters on itReference altitude will be ckecked out at regular time slots, every 10' for example
• Altitude measurements will be performed during that time with the 2nd altimeter, indicating each time the measurement time.Altitudes will be compared and correction applied
TOPOGRAPHYTOPOGRAPHY
AltimetryAltimetry
Page 28
Can be A geodetic point with hub333
132 An altimetry point
Alt A
Reference
Alt B
Measurement
TOPOGRAPHYTOPOGRAPHY
AltimetryAltimetry
Page 29
Alt A
Reference
Alt B
Measurement
Report variationsevery 10' or moreFill in a sheet
Measure the pointsand report measurementtimes
TOPOGRAPHYTOPOGRAPHY
ReferenceReference
AltimetryAltimetry
Page 30
Alt A Alt B
Origin
- 8:00 333- 8:10 333- 8:20 334- 8:30 335- 8:40 336- 8:50 337- 9:00 338- 9:10 338- 9:20 339- 9:30 340
= +1
= +2
= +3
= +4
SITE A = 234m.
SITE B = 198m.
SITE C = 182m.
SITE D = 206m.
SITE ASITE B
SITE C
SITE D
8:20235m. 8:30
200m.
8:40185m.
8:50210m.
Correction
Area limited to 10 to 15km around the point with altitude deviation <500m
TOPOGRAPHYTOPOGRAPHY
ReferenceReference
AltimetryAltimetry
Page 31
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 32
• What is propagation ?– Energy transfer with no physical transportation
• Line of sight propagation– Propagation between 2 points for which the direct ray is sufficiently clear
of obstacles for diffraction to be a negligible effect.
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 33
(A) antenna supplied by P power (transmitted power) will create in the wholespace an E magnetic field and (B) antenna introduced in this space willcollect a part of E field (Received power).
A B
E R
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 34
• Line of sight links– Link in which diffraction effects are minor
• What is diffraction ?– Diffraction is a phenomena which tends to modify radio wave path
nearing on obstruction
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 35
• Radio waves are related to 3 phenomena
Diffraction
Refraction
Reflection
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 36
Let's examine the following diagram: it seems there is no diffraction
E R
B
P
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 37
• Maxwell equations indicate that:
– The field in R point can be calculated with the field created in E in any point of P Plane
– P plane will be separated in concentric rings
– If P plane is moved in parallel to itself, B creates a revolution ellipse harring E and R as centers.
– The main part of the Energy is concentrated along the ER line.The first ellipsoid along this line concentrated along the ER line.The first ellipsoid along this line concentrates the main part of the energy.
– The first ellipsoid is called Fresnel Ellipsoid
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 38
• The ellipsoid shall be cleared from any obstruction. But the energy radiated in E will suffer from attenuation when reaching point R. This attenuation is the ratio of transmitted power to received power. It is called propagation loss (Diffraction loss)
)(
)(4log20
m
mdAdB
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 39
• Definition of CLEARANCEC = 1 means that 100% of Fresnel zone is cleared from any obstruction. Only 60% of the first ellipsoid shall be cleared of obstructions to have a received level equivalent to the level of free space.
• For Microstar (Short High Frequency Hops), 100% of clearance (C = 1) will be required.
• Please, refer to the next page for the Main (Top-to-Top) Path Clearance Rules
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 40
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagationClimate-Terrain Factor c
Band <2 (good to average)
>2 (moderate to very difficult)
Above 3 Ghz 0.6F1 @ k = 1 F1 @ k = 4/3 and 0.3F1 @ k = 2/3*
Below 3 Ghz 0.6F1 @ k = 1 0.6F1 @ k = 1
* If 0.3F1 @ k=2/3 clearance is controlling, diversity protection is usually required
Diversity (Top-to-Bottom) Path Clearance Rule
All bands 0.6F1 @ k = 4/3 0.6F1 @ k= 4/3
« Blackout » Area Main Path Clearance Rule
Above 3 Ghz N/A K = 1 grazing over a 150 ft ABL
Page 41
In reality, atmosphere has an influence. It is not homogeneous.
Instead of being straight, the wave will be bent in relation to the
atmosphere's refraction index.
Air n index is written n=1+N 10-6 and is close to the unity
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 42
n0
n1n2n3n4
n5
n6
n0 sin io = n1 sin i1 = n2 sin i2 ............... = etc
n2
n1
n1 sin i1 = n2 sin i2
1 i
2
Refracted ray
Reflected rayIncident ray
n1 and n2 indexes are linked to the environment
TERRAIN PROFILESTERRAIN PROFILES
DESCARTES SNELL's refraction lawDESCARTES SNELL's refraction law
PropagationPropagation
Page 43
• Propagation of a radius in an atmosphereof which index depends on the altitudeRo is the Earth's radius, that is to say 6400 km
nk
ni
nm
k
K'k
hk
1
L 1
Earth
Ro
0
h1
TERRAIN PROFILESTERRAIN PROFILES
• With fundamental relation that rulespropagation in this kind of atmosphere
n (Ro+h) cos = Cte
PropagationPropagation
Page 44
• A few definitions:– Troposphere: the lower layers of the atmosphere just above the
Earth's surface in which temperature decreases with height. This portion extends from the surface up to 9km at the poles to about 17 km at the equator
– There can be temperature inversion in the troposphere– Refractive index n: ratio between wave speed in vaccuum and wave
speed in the environment consideredN refractivity = one million times the amount by which the refractive index n exceeds unitySpheric atmosphere with constant vertical gradient of
dn
dhN per km 40 /
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 45
• Empirical formula for N
T is the temperature in KELVIN (Degree in celsius + 273.15)p is the air pressure (hpa in mbar)e is water vapor pressure
p, e and t depend on the height, therefore.N depends on the height
NT
peT
77 6
4810.
( . )
dn
dhN per km 40 /
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 46
Let's use the formula (Ro+h) cos = Cte
With successive deviation, we have a relative curvature of
rays compared with Earth's surface
We suppose that the index is approximatively a linear
function of the height, therefore:
dn
dh Ro
1
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
dh
dnconstant
Page 47
• 3 cases:
Casedndh
1 0
Casedn
dh2 0
highly positive
Casedndh
3 0
highly negative
ray path is straight
ray path is downtilted: there is a subrefraction
ray path is uptilted: there is a superrefraction
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 48
• The most frequent case is n°3 rays ondulate further than if their propagation is in straight line they have thus better clearing above the ground.It is difficult to define a project by taking into account the rays' curvature. The important element in calculation being the rays' relative curvature compared with real earth, we'll replace the real earth by a fictive one on condition that the rays' relative curvature remains constant.
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 49
Let's use a fictive earth enabling wave propagation to be in straight line
that is to say
The fictive earth's radius is given by:
using a k coefficient, we have
written:
0dh
dn
1 1
R Ro
dno
dh
kRo dno dh
1
1 ( / )
kR
Ro
8500
64004 3 1 33/ .
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 50
• We replaced real case by equivalent case in which propagation is straight
Fictive earth's radius varies with propagation in compliance with R Law = k Ro
Parameter k being defined, paragraph a) of CCIR 338-5 Rec for profile definition will apply
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 51
• In the case of super-refraction– Fictive ray is highly superior to standard ray k>1 and R>Ro and there will
be visible lowering of obstructions. This is case number 3– In the case of sub-refraction– Fictive ray is highly inferior to standard ray k<1 and R<Ro and there will
be visible raise of obstructions. This is case number 2Case number 2 is important for project definitionA curve defined by BOITHIAS and BATTESTI based on measurements carried out under continental temperate climate shows the values under which coefficient k = R/Ro does not decrease during 10-4 of the time, depending on the hop length.
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation
Page 52
Path length (km)Figure 2 - ke value exceeded during about 99.9% of the worse month
(continental temperate climate)
TERRAIN PROFILESTERRAIN PROFILES
PropagationPropagation1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.310 20 30 40 50 60 70 80 90 100 200
Page 53
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 54
TERRAIN PROFILESTERRAIN PROFILES
ProfilesProfiles
• Terrain profiles are necessary to determine antenna heights.
• The following criteria must be observed to select the various sites of a Telecom network:
• Line of sight between them according to the respect of the clearance rules.
Page 55
TERRAIN PROFILESTERRAIN PROFILES
Path profile
• Example of the path profile, plotted with the application software recommended by Harris MCD:
Fresnel zone Line of sight
Tower 2
Tower 1
Altitude + vegetation
ProfilesProfiles
Page 56
TERRAIN PROFILESTERRAIN PROFILES
Path profile
• This figure shows the path profile with first fresnel zone and terrain
that varies with k value.
The line of sight is drawn as a straight line and the ray bending due to
variation of k value is added to the terrain elevation.
There must be 60% clearance of first Fresnel zone to avoid diffraction
loss in addition to the free space loss.
Earth bulge
• In order to draw the line of sight in a path profile, the ray bending due
to variation of the k value is added to the terrain heights.
ProfilesProfiles
Page 57
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 58
TERRAIN PROFILESTERRAIN PROFILES
Ground reflectionsGround reflections
• This figure shows a typical signal reflection. The more conductive the
ground, the stronger the reflection is.
A B
Reflection point
Reflective surface
ReflectionReflection
Page 59
• Reflections from sea, ponds etc … are more critical than reflections from terrain with vegetation.The reflection coefficient is dependant of the type of terrain.Generally the reflection coefficient decreases with the frequency.On the other hand a larger area is required to reflect a signal at a lower frequency.
• The effective reflection coefficient is also a function of the path's grazing angle and the curvature of the earth (the k value).Generally vertical polarization gives reduced reflection, especially at lower frequencies.
TERRAIN PROFILESTERRAIN PROFILES
ReflectionReflection
Page 60
• The received signal is the combination of the direct signal and the reflected signal.
TERRAIN PROFILESTERRAIN PROFILES
ReflectionReflection
Page 61
• Adding these two signals will give a signal strength that is a function of the height at the receiver site as indicated in the figure below
TERRAIN PROFILESTERRAIN PROFILES
OptimumAntennaSeparation
Field strength
Height
ReflectionReflection
Page 62
• To counteract the effect of ground reflections space diversity arrangements with two receiver antennas with a vertical separation are widely used.The antenna separation should give maximum received signal level at the space antenna when the main antenna is at a minimum and vice versa vice versa.
• The optimum antenna separation may be found using one of 2 different methods.
– 1 Geometrical method using Fresnel zone– 2 Analytical method using services expansions
TERRAIN PROFILESTERRAIN PROFILES
ReflectionReflection
Page 63
• 1 Geometrical methodA geometrical property of the ellipsoid is that the angle of incidence equals the reflection angle at the circumference. This property may be used to find the reflection point.
TERRAIN PROFILESTERRAIN PROFILES
Tangent
ReflectionReflection
Page 64
• When fresnel ellipsoid tangents the reflection plan can be calculated.Consequently the reflection point may be found by increasing the fresnel zone until it touches the terrain. If the ellipse tangent is parallel to the terrain, there is a reflection point.
TERRAIN PROFILESTERRAIN PROFILES
ReflectionReflection
Page 65
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 66
• Models used by Harris MCDThe various types of GPSThe various types of GPS
LIST OF TOOLS USED DURING THE SURVEYLIST OF TOOLS USED DURING THE SURVEY
Garmin …GPS 12XLGarmin …GPSMAP 76S (WAAS)Garmin …GPS III / III Plus
Page 67
FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
Page 68
What is GPS
A super accurate system
• Developed and maintained by Dept. of Defense
• Nuclear subs needed positioning
• Satellite-based
• Sold Congress on the idea that other applications would follow
GPS user's guideGPS user's guide
GPSGPS
Page 69
Status of GPs
• In development since 1973
• First satellite launched in 1978
• All GPS satellites built and tested
• Next generation of satellites (Block IIR) are already on contract
• Managed by the Department of Defense
GPSGPS
GPS user's guideGPS user's guide
Page 70
Navstar satellite constellationNavstar satellite constellation24 Sat6 planes20.200 km Orbit
GPSGPS
GPS user's guideGPS user's guide
Page 71
Space segment descriptionSpace segment description
• 24 satellites in final constellation– 6 planes with 55° rotation– Each plane has 4 satellites
• Very high orbit– 12,600 miles– Approximately 1 revolution in 12 hours– For accuracy– Survivability– Coverage
GPSGPS
GPS user's guideGPS user's guide
Page 72
Satellite-basedSatellite-based
Uses trilateration from satellites
• 24 satellites in final constellation– 21 operational, 3 spares
• Satellites in very high or bit (12,600 miles)– for accuracy– survivability– coverage
• Only possible with today's technology– computers and clocks
GPSGPS
GPS user's guideGPS user's guide
Page 73
Satellite-basedSatellite-based
• Weight when the satellite is lauched- 3855 kg
• Weight in final ORBIT - 816 kg
• Power - 700 w
• 2 frequency bandwiths L and S
• S1 2227,5 MHz
• S2 1783,74 MHz
• L1 (1575 MHz)
• L2 (1227 MHz)
• L1 an L2 are generated by a Ref frequency 10,23 MHz given by a ATOMIC reference clock (cesium)
GPSGPS
GPS user's guideGPS user's guide
Page 74
GPS segmentsGPS segments
MASTER
CONTROL SEGMENT
CONTROLSTATIONS
SPACE SEGMENT
USER SEGMENT
GPSGPS
GPS user's guideGPS user's guide
Page 75
How accurate is it ?How accurate is it ?
That depends:
• Depends on some variables– Time spent on measurements– Design of receiver– Relative positions of satellites
• Sub-centimeter accuracies from survey products
• Fifteen to fifty meters with non-differential GPS
• One to five meters with differential GPS
• Gouvt. can degrade accuracy if they want to
GPSGPS
GPS user's guideGPS user's guide
Page 76
How does GPS work ?How does GPS work ?
2GPS measures distancefrom the satellitesusing speed of light.
3To measure the distanceGPS needs good clocksand a fourth SV
4Once GPS knows distance,it needs to know satellite'sposition
5Then correct forionospheric andtropospheric delays.
1 Trilateration from satellitesis basis of system
GPS receiver
GPSGPS
GPS user's guideGPS user's guide
Page 77
1 trilateration from satellites1 trilateration from satellites
• By measuring distance from several satellites you can calculate your position thru mathematics
GPSGPS
GPS user's guideGPS user's guide
Page 78
TrilaterationTrilateration
• One measurement narrows down our position to the surface of a sphere
11,000 miles• We're somewhere on the surface of this sphere.
GPSGPS
GPS user's guideGPS user's guide
Page 79
TrilaterationTrilateration
• Second measurement narrows it down to intersection of two spheres
11,000 Miles
12,000 Miles
Intersection of twospheres is a circle
GPSGPS
GPS user's guideGPS user's guide
Page 80
TrilaterationTrilateration
• Third measurement narrows to just two points
Intersection of threespheres is only twopoints.
GPSGPS
GPS user's guideGPS user's guide
Page 81
TrilaterationTrilateration
• Fourth measurement will decide between two points.
Fourth measurementwill only go throughone of the two points.
GPSGPS
GPS user's guideGPS user's guide
Page 82
TrilaterationTrilateration
• In practice 3 measurements are enough
• We can discard one point
• One point will be a ridiculous answer– Out in space– Or moving at high speed
• We still need the 4th measurement because there are four dimensions to solve for (X,Y,Z and Time)
GPSGPS
GPS user's guideGPS user's guide
Page 83
2 satellite ranging2 satellite ranging
Measuring the distance to a satellite
• Done by measuring travel time of radio signals
GPSGPS
GPS user's guideGPS user's guide
Page 84
Speed-of-light measurementSpeed-of-light measurement
Measure how long it takes the GPS signal to get to us
• Multiply that time by 186,000 miles/sec– Time (sec) x 186,000 = miles
• If you've got good clocks, all you need to know is exactly when signal left satellite
GPSGPS
GPS user's guideGPS user's guide
Page 85
GPS community base stationGPS community base stationGPS community base stationGPS community base station
Mounting Pole*
PC*
Data/PowerCable
GPS Receiver
120V Uninterruptible PowerSupply *
* Supplied by Customer
120VAC to12VDCPower Supply
GPS Antenna
Antenna Cable
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Line of sight
Why we use satellites for mappingWhy we use satellites for mappingWhy we use satellites for mappingWhy we use satellites for mapping
TRIMBLE NAVIGATION
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PDOPPDOPPDOPPDOP
PDOP BAD PDOP Good
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Dilution of precision (DOP)Dilution of precision (DOP)
Can be expressed in different dimensions
• GDOP - Geometric dilution of precision
• PDOP - Position dilution of precision
• HDOP - Horizontal dilution of precision
• VDOP - Vertical dilution of precision
• EDOP - East dilution of precision
• NDOP - North dilution of precision
• TDOP - Time dilution of precision– GDOP² = PDOP² + TDOP²– PDOP² = HDOP² + VDOP²– HDOP² = EDOP² + NDOP²
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Altitude referenceAltitude reference
• Ellipsoid– A smooth, mathematically defined model of the earth's surface
• Geoid– A surface of equal gravitational pull (equipotential) best fitting the average
sea surface over the whole globe
Geoid
MSLHAE
Earths Surface
Ellipsoid
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DatumDatum
• There are many regional datums that are chosen so that the ellipsoid could conform as closely as possible to the geoid over the region rather than the whole globe.
EllipsoidfittingNorthAmerica
EllipsoidfittingEurope
Geoid
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DatumDatum
• A datum is a specifically oriented reference ellipsoid defined by 8 elements
– Position of the network (3 elements)– Orientation of the network (3 elements)– Parameters of the reference ellipsoid (2 elements)
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Datum (WGS 84)Datum (WGS 84)Datum (WGS 84)Datum (WGS 84)
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Datum (NAD 27)Datum (NAD 27)Datum (NAD 27)Datum (NAD 27)
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DatumDatum
• One point can have different sets of coordinates depending on the datum used.
X
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Projection typesProjection typesProjection typesProjection types
Reference to WGS72Designation Ellipsoid Diameter 1/f
y x zZone
WGS72 6378135 298.26 0 0 0 World
Europ 50.ED Mayford 1924 6378388 297 103 84 127 Europe
NAD27 Clarke 1866 6378206 294.98 -157 22 -176 USA
IGN (NTF) Clarke 1880 6378249 293.47 66 170 -311 France – NorthAfrica
Wake-Eniwetok1960
Hough 6378270 297 -68-62-62
-112-121-144
442238
KwajaleinWakeEnnwetok
Guam 1963 Clarke 1866 6378206 94.98 235 89 -254 Iles Marianes
Arc 1950 (CAPE) Clarke 1880 6378249 293.465 131 129 292 South Africa
Adindan Clarke 1880 6378249 293.47 26 152 -212 Egypt
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2d versus 3d data2d versus 3d data
• 3d needs 4 SV's (X, Y, Z and Time)
• 2d needs 3 SV'S (X, Y, Time and user entered Z)
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2d versus 3d data (Contd.)2d versus 3d data (Contd.)
Inputting a poor elevation will give a poor horizontal position.
Line of position
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2d versus 3d data2d versus 3d data
Inputting the correct elevation will result in the correct position.
Line of position
Correct Latitude
Correct Elev.
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2d versus 3d data (Contd.)2d versus 3d data (Contd.)
Inputing the wrong elevation will result in the wrong position.
Line of position
Wrong Latitude
Wrong Elev.
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FIELD TELECOMMUNICATION SURVEYFIELD TELECOMMUNICATION SURVEY
ContentsContents1) Topography
- Map representation
- Geographical coordinates
- Altimetry
2) Terrain profiles
- Propagation
- Profiles / Clearance criteria guidelines
- Reflection
3) GPS
- The various types of GPS
- GeoExplorer user's guide
4) Grounding system
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• Roles of the grounding systemWhat is it used for ?The only use of a ground system is to handle into the ground
the currents entering or leaving the location in common mode.
A ground system is only a "waste receptacle" but shall be a good quality system.
• It ensures:1) electrical protection / lightning2) technical quality
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• Protective ground– The primary role of a ground connection is to protect people against
electrocutions risks. Electric shock risk depends on the strength of the electric current flowing through the body, and on the part of the human body touched.
– Human body resistance is not linear.1mA current is hardly detected by the hands. 10mA current causes strong shock and a 30mA current can tetanize muscles and cause heart fibrillation.
– Rules for protection against electric shocks can not take into account variable resistance of human body. They reduce contact voltage to conventional protection value in order to prevent fatal shock.
– The concept of protective ground is not standardized. It's important to know that it's the correct ground equipotentiality which protects installation, and not the grounding system.
– Manhole bond around residential housing is more efficient than a single ground post, whatever its resistance.
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Equipment leakage current
• Leakage currents are handled via grounding conductors grounding conductor is conventionally in green/yellow color. It connects equipment chassis to the ground system but current doesn't flow to the ground "fault currents" are closed by connecting neutral conductor to the ground, not in the ground. Grounding is strictly conventional. We may think that the role of a ground connector is to dry off the leakage current but it's no true
GROUNDING SYSTEMGROUNDING SYSTEM
Conductor current doesn't flow into the groundUnavoidable leakage currents are looped byneutral's grounding conductor
leakage
230V
PHASE
NEUTRAL
Ground conductor
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Equipment leakage current
• A leakage current of some ten ampères is normal for large computer rooms
• Since leakage and fault currents are internal currents, they don't flow through the ground. Ground resistance is therefore different
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Equipment leakage current
• Static potential referent– Some moving vehicules isolated from the ground (trucks, planes ...) are
charged compared to the ground (i.e dry dusty wind). Electric charges carried by airborne particles settle on the vehicule of which potential difference compared to the ground can reach tens of kilovolts!During fuel tank filling, a spark may inflame vapors if the vehicule is not discharged first. Only a connector used to discharge a moving vehicule can called "protective ground" without making a mistake
i=xya
R<10k
Rising sand
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Equipment leakage current
• Ground connection is not used as protection it is the equipotentiality between chassis which is taken into account. It does not dry off the leakage currents (except for HV in TT configuration)
• A simple post can discharge an isolated moving vehicule. External currents, including lightning current, are dried off both through the ground and through other external cables.
• Ground resistance is not important in cable protection
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Equipment leakage current
• For people as well as for equipment, the risk lies under too important potential differences between near points. The most important thing is for people the equipotentiality between chassis simultaneously accessible and for equipment, the equipotentiality between interconnected equipment.
• The most important for equipment operation is the location equipotentiality
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Ground resistance measurement
• Ground connection quality is measured by its resistance.
• Ground resistance is applicable only with low frequencies. Beyond several MHz (frequency range in which electronic systems are very sensitive), ground connector impedance can no longer be measured and has physically no sense any more.
• All the ground connectors on a single location shall be interconnected.
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Importance of ground resistance measurement
• When the absolute value of ground resistance is unchanged, it's evolution in time is interesting (if the value falls, it means ground cables are deteriorating). Ground network resetting may be required.
STORYAutomatic switch's ground resistance value = the infinity war bomb had cut off the grounding conductor but no one had noticed it in the system operation for half a century
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Ground resistivity
• Ground resistivity is measured via 4-wire ground current meter. The unit of measurement is the Ohm.meter
Resistivity < 300 is correct Resistivity > 500 is bad
• Contrary to ground network resistivity, ground resistivity is very important– Resistivity of soil layers varies significantly and ground network
conductors should preferably be burried at low resistance depth.– In soils with high resistivity, meshed ground networks should be made of
small size meshes for good horizontal equipotentiality.
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Ground resistivity
• With average ground resistivity and the geometry of underground conductors, it is possible to assess the ground network resistance.
• It is not very important but evaluating the resistance with calculation and validating it with measurement may put the customer's mind at ease
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Vertical post or horizontal cable ?Underground conductor may be rammed in vertically (post) or burried horizontally (manhole bond or bridles)Horizontal conductors are better for the location equipotentiality
man-hole
Ground post
min.2m
Building
Implementation of a ground network
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Implementation of a ground network
• Horizontal conductors should be spaced by at least 20 cm from other metal cables to reduce corrosion rate (use preferably 50 mm² section copper or 35 mm² flat copper cable). Depth of lay: 1m. The trench will be refilled with low resistivity arable soil, but not with crusher - run stones. Underground cable connections should be brazed and welded. Underground network should be meshed
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Raft foundation
10m
Bridle Bridle
Bridle Bridle
Manhole bond
Example of meshing
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• 3 mistakes to be avoided
– Low ground resistance requirement• Only location equipotentiality is important, or at least the equipotentiality of
interconnected equipment (only the ground system of VHV station shall have low impedance rate) let's not spend money in ground resistance reduction
• Separated ground systems• They break the equipotentiality principle
– Star connection of chassis to the ground connector• Meshing is the only solution allowing chassis current division and equipotentiality
improvement
GROUNDING SYSTEMGROUNDING SYSTEM
Thank you