The document discusses topics related to surveying terrain for microwave transmissions, including: 1. It describes map representations and how to determine geographic coordinates and altitude from maps. 2. It explains concepts of line-of-sight propagation and how terrain profiles are used to determine signal propagation and clearance between points. 3. Factors that influence microwave signals traversing the atmosphere like refraction, reflection, and diffraction are outlined. 4. Guidelines for ensuring sufficient clearance of transmission paths based on the Fresnel zone are provided.

1. Geography of Microwave Survey
FIELD TELECOMMUNICATION SURVEY
www.huawei.com

2. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 2

3. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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

4. TOPOGRAPHY
M ap representation
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 m
1/50 000 1 mm = 50 m
1/24 000 1 mm = 24 m1
1/10 000 1 mm = 10 m
1/ 5 000 1 mm = 5 m
Page 4

5. TOPOGRAPHY
M ap representation
• 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 (Gé rard Kremer alias)
– LAMBERT
Page 5

6. TOPOGRAPHY
M ap representation
• Cylindrical projection.
• The projection surface is a cylinder which is tangential or secant
to the earth's model.
Transverse cylindrical projection
Direct cylindrical projection Oblique cylindrical projection
• Example: UTM projection is divided of 60 zones of 6° in
longitude
– France is on 3 zones: zone 31 30 32
Page 6

7. TOPOGRAPHY
M ap representation
• Conical projection.
• The projection surface is a cone tangent or secant to the earth's
model.
Tangent conic presentation Secant conic presentation
• Example: LAMBERT projection is divided into 4 zones
– LAMBERT I - II - III - IV or LAMBERT II extended which covers all
the country.
Page 7

8. TOPOGRAPHY
M ap representation
• 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)
Page 8

9. TOPOGRAPHY
M ap representation
• Date of creation and update
• Ellipsoid
Earth surface
Ellipsoid
Geoid
Page 9

10. TOPOGRAPHY
M ap representation
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
Page 10

11. TOPOGRAPHY
M ap representation
Magnetic variation
Magnetic North Geographic North • 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'
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'.
Page 11

12. TOPOGRAPHY
M ap representation
MN
Magnetic variation GN
7°
237°/MN
230°/GN
Page 12

13. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 13

14. TOPOGRAPHY
Geographical coordinates
Latitude 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.
Page 14

15. TOPOGRAPHY
Geographical coordinates
Latitude and longitude
112m
100
m
50m
Each index contour line is accentuated Contour intervals: 10m
Page 15

16. TOPOGRAPHY
Geographical coordinates
Latitude and longitude
• Enable to calculate geographic coordinates of any point
on earth thanks to abscissa and ordinate report
• Earth circumference ≈ 40000 km
40000 km / 360° = 111.111 km = 1°
1° = 60' => 1.852km = 1' = 1 mile
1' = 60" => 31 m = 1"
AT EQUATOR LEVEL
Page 16

17. TOPOGRAPHY
Geographical coordinates
GREENWICH MERIDIAN OR MERIDIAN 0 (zero)
N
Latitude and longitude
LONG W
LONG E
LAT N
LAT N
W or
uat
Eq
LONG W LONG E
LAT S LAT S E
Origin of any map
S
Page 17

18. TOPOGRAPHY
Geographical coordinates
• Site pointing
1cm
5mm
Cross with soft lead pencil
Pointing with hard pencil
Page 18

19. TOPOGRAPHY
Geographical coordinates
Latitude and longitude °degrees, ' minutes, " seconds
• 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
Page 19

20. TOPOGRAPHY
Geographical coordinates
48°05'
ymm
Latitude
y'mm
48°00
Origin
2°05'
2°00' X'mm
longitude
xmm
Page 20

21. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 21

22. TOPOGRAPHY
Altimetry
• ALTITUDE MEASUREMENT
hpa (hectopascal) = Meteorology
mmhg (millimeter of mercury) = Medical unit
mbar (millibar) = Old unit
bar = Industrial pressure
unit
Altitude Pressure
===>
Page 22

23. TOPOGRAPHY
Altimetry
• The altimeter is a barometer
1 NEWTON
1 pa = = 1N / m²
1m²
Page 23

24. TOPOGRAPHY
Altimetry
• Normal atmospheric pressure measured at standard point
Altitude m Pressure hpa Temp °C
7000 410 -30.5°
6000 472 -24°
5000 540 -17.5°
4000 616 -11°
3000 701 -4.5°
2000 795 2°
1000 899 8.5°
0 1013 15°
Page 24

25. TOPOGRAPHY
Altimetry
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
Page 25

26. TOPOGRAPHY
Altimetry
• 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
Page 26

27. TOPOGRAPHY
Altimetry
• It is thus necessary to apply the so-called double measurement
procedure
2 altimeters are required
Mark a point on the map
Calibrate both altimeters on it
Reference altitude will be ckecked out at regular time slots,
every 10' for example
• Altitude measurements will be performed during that time with
the 2 nd altimeter, indicating each time the measurement time.
Altitudes will be compared and correction applied
Page 27

28. TOPOGRAPHY
Altimetry
Can be 333 A geodetic point with hub
132 An altimetry point
Alt A Alt B
Reference Measurement
Page 28

29. TOPOGRAPHY
Altimetry
Reference
Alt A Alt B
Reference Measurement
Report variations Measure the points
every 10' or more and report measurement
Fill in a sheet times
Page 29

30. TOPOGRAPHY
Altimetry Alt A Alt B
Reference Origin 8:20
235m. 8:30
200m.
- 8:00 333 SITE A
∆ = +1 SITE B
- 8:10 333 8:40
- 8:20 334 SITE A = 234m. 185m.
∆ = +2
- 8:30 335 SITE B = 198m. SITE C
∆ = +3
- 8:40 336 SITE C = 182m.
∆ = +4
- 8:50 337 SITE D = 206m.
- 9:00 338
- 9:10 338
- 9:20 339 Correction SITE D 8:50
- 9:30 340
210m.
Area limited to 10 to 15km around the point with altitude deviation <500m
Page 30

31. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 31

32. TERRAIN PROFILES
Propagation
• 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.
Page 32

33. TERRAIN PROFILES
Propagation E R
A B
(A) antenna supplied by P power (transmitted power) will create in the
whole
space an E magnetic field and (B) antenna introduced in this space
will
collect a part of E field (Received power).
Page 33

34. TERRAIN PROFILES
Propagation
• 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
Page 34

35. TERRAIN PROFILES
Propagation
• Radio waves are related to 3 phenomena
Diffraction
Refraction
Reflection
Page 35

36. TERRAIN PROFILES
Propagation
Let's examine the following diagram: it seems there is no diffraction
P
B
E R
Page 36

37. TERRAIN PROFILES
Propagation
• 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
Page 37

38. TERRAIN PROFILES
Propagation
• 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)
4π d (m)
AdB =20log
λ ( m)
Page 38

39. TERRAIN PROFILES
Propagation
• Definition of CLEARANCE
C = 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
Page 39

40. TERRAIN PROFILES
Propagation
Climate-Terrain Factor c
Band <2 (good to >2 (moderate to
average) 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 40

41. TERRAIN PROFILES
Propagation
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
Page 41

42. TERRAIN PROFILES
Propagation
DESCARTES SNELL's refraction law
Incident ray Reflected ray
θ1 θi
n2
n1
n1 sin i1 = n2 sin i2
Refracted ray
n6
θ2 n5
n4
n1 and n2 indexes are linked to the environment n3
n2
n1
n0
n0 sin io = n1 sin i1 = n2 sin i2 ............... = etc
Page 42

43. TERRAIN PROFILES
Propagation
• Propagation of a radius in an
atmosphere
of which index depends on the altitude
Ro is the Earth's radius, that is to say
6400 km
L
ϕ1 ϕ1
nm
K ϕ'k
ni hk h1
ϕk
nk Earth
Ro • With fundamental relation that
rules
propagation in this kind of
atmosphere
n (Ro+h) cos ϕ = Cte
0
Page 43

44. TERRAIN PROFILES
Propagation
• 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 considered
N refractivity = one million times the amount by which the
refractive index n exceeds unity
Spheric atmosphere with constant vertical gradient of
dn
= − 40 N / per km
dh
Page 44

45. TERRAIN PROFILES
Propagation
• Empirical formula for N
77.6 e
N= ( p + 4810. )
T T
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
dn
= − 40 N / per km
dh
Page 45

46. TERRAIN PROFILES
Propagation
Let's use the formula (Ro+h) cos ϕ = Cte
With successive deviation, we have a relative curvature of
rays compared with Earth's surface
dn 1
σ = +
dh Ro
We suppose that the index is approximatively a linear
function of the height, therefore:
dn
= constant
dh
Page 46

47. TERRAIN PROFILES
Propagation
• 3 cases:
dn
Case 1 = 0
dh
ray path is straight
dn
Case 2 > 0
dh
highly positive
ray path is downtilted: there is a subrefraction
dn
Case 3 < 0
dh
highly negative
ray path is uptilted: there is a superrefraction
Page 47

48. TERRAIN PROFILES
Propagation
• 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.
Page 48

49. TERRAIN PROFILES
Propagation
Let's use a fictive earth enabling wave propagation to be in straight
line
dn
=0
that is to say dh
1 1 dno
= =
R Ro dh
The fictive earth's radius is given by:
1
k=
1 + Ro( dno / dh)
using a k coefficient, we have
R 8500
k= = = 4 / 3 = 1.33
Ro 6400
written:
Page 49

50. TERRAIN PROFILES
Propagation
• 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
Page 50

51. TERRAIN PROFILES
Propagation
• 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 2
Case number 2 is important for project definition
A 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.
Page 51

52. TERRAIN PROFILES
Propagation 1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
10 20 30 40 50 60 70 80 90 100 200
Path length (km)
Figure 2 - ke value exceeded during about 99.9% of the worse month
(continental temperate climate)
Page 52

53. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 53

54. TERRAIN PROFILES
Profiles
• 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 54

55. TERRAIN PROFILES
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
Page 55

56. TERRAIN PROFILES
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.
Page 56

57. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 57

58. TERRAIN PROFILES
Reflection
Reflection point
Ground reflections
A B
Reflective surface
• This figure shows a typical signal reflection. The more
conductive the ground, the stronger the reflection is.
Page 58

59. TERRAIN PROFILES
Reflection
• 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.
Page 59

60. TERRAIN PROFILES
Reflection
• The received signal is the combination of the direct signal and
the reflected signal.
Page 60

61. TERRAIN PROFILES
Reflection
• 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
Height
Optimum
Antenna
Separation
Field strength
Page 61

62. TERRAIN PROFILES
Reflection
• 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
Page 62

63. TERRAIN PROFILES
Reflection
• 1 Geometrical method
A 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.
Tangent
Page 63

64. TERRAIN PROFILES
Reflection
• 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.
Page 64

65. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 65

66. LIST OF TOOLS USED DURING THE
SURVEY
The various types of GPS
• Models used by Harris MCD
Garmin …GPS 12XL
Garmin …GPSMAP 76S (WAAS)
Garmin …GPS III / III Plus
Page 66

67. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 67

68. GPS
GPS user's guide
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
Page 68

69. GPS
GPS user's guide
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
Page 69

70. GPS
GPS user's guide
Navstar satellite constellation
24 Sat
6 planes
20.200 km Orbit
Page 70

71. GPS
GPS user's guide
Space 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
Page 71

72. GPS
GPS user's guide
Satellite-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
Page 72

73. GPS
GPS user's guide
Satellite-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)
Page 73

74. GPS
GPS user's guide
GPS segments
SPACE SEGMENT
CONTROL
STATIONS
MASTER
CONTROL SEGMENT
USER SEGMENT
Page 74

75. GPS
GPS user's guide
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
Page 75

76. GPS
GPS user's guide
How does GPS work ? Once GPS knows distance,
GPS measures distance
3
To measure the distance
GPS needs good clocks 4 it needs to know satellite's
2 position
from the satellites and a fourth SV
using speed of light.
Then correct for
5 ionospheric and
tropospheric delays.
GPS receiver
Trilateration from satellites
1 is basis of system
Page 76

77. GPS
GPS user's guide
1 trilateration from satellites
• By measuring distance from several satellites you can calculate
your position thru mathematics
Page 77

78. GPS
GPS user's guide
Trilateration
• One measurement narrows down our position to the surface of a
sphere
11,000 miles
• We're somewhere on the
surface of this sphere.
Page 78

79. GPS
GPS user's guide
Trilateration
• Second measurement narrows it down to intersection of two
spheres
11,000 Miles
12,000 Miles
Intersection of two
spheres is a circle
Page 79

80. GPS
GPS user's guide
Trilateration
• Third measurement narrows to just two points
Intersection of three
spheres is only two
points.
Page 80

81. GPS
GPS user's guide
Trilateration
• Fourth measurement will decide between two points.
Fourth measurement
will only go through
one of the two points.
Page 81

82. GPS
GPS user's guide
Trilateration
• 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)
Page 82

83. GPS
GPS user's guide
2 satellite ranging
Measuring the distance to a satellite
• Done by measuring travel time of radio signals
Page 83

84. GPS
GPS user's guide
Speed-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
Page 84

85. GPS
GPS user's guide
GPS community base station
GPS Antenna
Mounting Pole*
Antenna Cable
Data/Power
Cable
GPS Receiver PC*
120VAC to
12VDC
Power Supply
120V Uninterruptible Power
Supply *
* Supplied by Customer
Page 85

86. GPS
GPS user's guide
Why we use satellites for mapping
Line of sight
TRIMBLE NAVIGATION
Page 86

87. GPS
GPS user's guide
PDOP
PDOP BAD PDOP Good
Page 87

88. GPS
GPS user's guide
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
Page 88

89. GPS
GPS user's guide
Altitude 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
HAE
MSL
Earths Surface
Ellipsoid
Geoid
Page 89

90. GPS
GPS user's guide
Datum
• 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.
Ellipsoid
fitting
Eur North
rth ope
No erica America
Ellipsoid Am
fitting
Europe
Geoid
Page 90

91. GPS
GPS user's guide
Datum
• 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)
Page 91

92. GPS
GPS user's guide
Datum (WGS 84)
Page 92

93. GPS
GPS user's guide
Datum (NAD 27)
Page 93

94. GPS
GPS user's guide
Datum
• One point can have different sets of coordinates depending on
the datum used.
X
Page 94

95. GPS
GPS user's guide
Projection types
Re fe re nc e to WGS 72
De s ig natio n Ellips o id Diame te r 1/f Zo ne
∆ y ∆x ∆z
WGS 72 6378135 298.26 0 0 0 World
Euro p 50.ED Ma yford 1924 6378388 297 103 84 127 Europe
NAD27 Cla rke 1866 6378206 294.98 -157 22 -176 US A
IGN (NTF) Cla rke 1880 6378249 293.47 66 170 -311 Fra nce – North
Africa
Wake -Eniwe to k Hough 6378270 297 -68 -112 44 Kwa ja le in
1960 -62 -121 22 Wa ke
-62 -144 38 Ennwe tok
Guam 1963 Cla rke 1866 6378206 94.98 235 89 -254 Ile s Ma ria ne s
Arc 1950 (CAPE) Cla rke 1880 6378249 293.465 131 129 292 S outh Africa
Adindan Cla rke 1880 6378249 293.47 26 152 -212 Egypt
Page 95

96. GPS
GPS user's guide
2d 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)
Page 96

97. GPS
GPS user's guide
2d versus 3d data (Contd.)
Inputting a poor elevation will give a poor horizontal position.
Line of position
Page 97

98. GPS
GPS user's guide
2d versus 3d data
Inputting the correct elevation will result in the correct position.
Line of position
Correct Elev.
Correct Latitude
Page 98

99. GPS
GPS user's guide
2d versus 3d data (Contd.)
Inputing the wrong elevation will result in the wrong position.
Line of position
Wrong Elev.
Wrong Latitude
Page 99

100. FIELD TELECOMMUNICATION SURVEY
Contents
1) Topography
- M ap 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 100

101. GROUNDING SYSTEM
• Roles of the grounding system
What 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 / lightning
2) technical quality
Page 101

102. GROUNDING SYSTEM
• 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.
Page 102

103. GROUNDING SYSTEM
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
leakage
PHASE
Conductor current doesn't flow into the ground
Unavoidable leakage currents are looped by
230V
NEUTRAL neutral's grounding conductor
Ground conductor
Page 103

104. GROUNDING SYSTEM
Equipment leakage current
• A leakage current of some ten ampè res 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
Page 104

105. GROUNDING SYSTEM
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 Rising sand
i=xya
R<10k Ω
Page 105

106. GROUNDING SYSTEM
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
Page 106

107. GROUNDING SYSTEM
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
Page 107

108. GROUNDING SYSTEM
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.
Page 108

109. GROUNDING SYSTEM
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.
STORY
Automatic 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
Page 109

110. GROUNDING SYSTEM
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.
Page 110

111. GROUNDING SYSTEM
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
Page 111

112. GROUNDING SYSTEM
Implementation of a ground network
Building
man-hole
min.
2m
Ground post
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
Page 112

113. GROUNDING SYSTEM
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
Page 113

114. GROUNDING SYSTEM
Example of meshing
Bridle Bridle
Raft foundation
10m
Bridle Bridle
Manhole bond
Page 114

115. GROUNDING SYSTEM
• 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
Page 115

116. Thank you