JED - August 2016 - 42

EW 101

Space EW - Part 3

Satellite Geometry
By Dave Adamy

I

n this, and the next couple of columns, we will discuss some general
geometrical issues with satellites
and their orbits - relative to EW
problems. The exercise this month
is to show how to determine the
range from the satellite to a point on
the Earth's surface. This is, of course, so
we can calculate the link loss - a key
element in the effectiveness of jamming
or intercept from space.

Satellite

North
Pole

Longitude
of sub-vehicle point
Greenwich
Meridian
Center of
Earth

Sub-vehicle
point

42
The Journal of Electronic Defense | August 2016

SUB-VEHICLE POINT
The point on the Earth's surface that
is right below the satellite is called the
sub-vehicle point (SVP). As shown in
Figure 1, this point is the intersection
of the line from the center of the Earth
to the satellite with the surface of the
Earth. The latitude of the SVP is the geocentric angle from the equator up to the
SVP. The longitude of the SVP is the angle between the longitude line running
through the SVP and the longitude line
running through Greenwich England.
Figure 1 also shows the definitions of
Longitude and Latitude. Longitude lines
are great circle segments - that is, each
is on a plane that cuts through the center of the Earth. Latitude lines are not
great circles, but the latitude is defined
as the angle north or south of the equator to the latitude line.

AN EARTH SURFACE LOCATION
To simplify the discussion, we will
assume that there is a transmitter
on the satellite and a receiver on the
Earth's surface. Figure 2 shows the SVP
and the receiver location on the Earth.

Latitude
of sub-vehicle point

Equator

Figure 1: The sub-vehicle point is the intersection of a line from the center of the Earth to the
satellite with the Earth's surface.

North
Figure 1: The sub-vehicle
point isLongitude
the intersection of a line from the
Center of the Earth
's surface.
Poleto the satellite with the Earth
Receiver
location
Sub-vehicle
point
Latitude
of sub-vehicle
point
Center
of Earth

Latitude
of receiver
A
b

c
a
B

Figure 2: A spherical triangle is formed between the North Pole, the sub-vehicle point and the
receiver location.

Figure 2:A spherical triangle is formed between the North pole, the sub-vehicle
point and the receiver location.

C



JED - August 2016

Table of Contents for the Digital Edition of JED - August 2016

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
Cyber Blitz: US Army Gains New Insight for EW/Cyber Operational Integration
Technology Survey: Solid State Power Amplifiers for EW, Radar and Communications Applications
EW 101
Threat Monitor
AOC Election
Index of Advertisers
JED Quick Look
JED - August 2016 - cover1
JED - August 2016 - cover2
JED - August 2016 - 3
JED - August 2016 - 4
JED - August 2016 - 5
JED - August 2016 - The View From Here
JED - August 2016 - 7
JED - August 2016 - insert1
JED - August 2016 - insert2
JED - August 2016 - Conferences Calendar
JED - August 2016 - 9
JED - August 2016 - Courses Calendar
JED - August 2016 - 11
JED - August 2016 - From the President
JED - August 2016 - 13
JED - August 2016 - 14
JED - August 2016 - The Monitor
JED - August 2016 - 16
JED - August 2016 - 17
JED - August 2016 - 18
JED - August 2016 - 19
JED - August 2016 - 20
JED - August 2016 - 21
JED - August 2016 - World Report
JED - August 2016 - 23
JED - August 2016 - Cyber Blitz: US Army Gains New Insight for EW/Cyber Operational Integration
JED - August 2016 - 25
JED - August 2016 - 26
JED - August 2016 - 27
JED - August 2016 - 28
JED - August 2016 - 29
JED - August 2016 - 30
JED - August 2016 - 31
JED - August 2016 - 32
JED - August 2016 - 33
JED - August 2016 - 34
JED - August 2016 - Technology Survey: Solid State Power Amplifiers for EW, Radar and Communications Applications
JED - August 2016 - 36
JED - August 2016 - 37
JED - August 2016 - 38
JED - August 2016 - 39
JED - August 2016 - 40
JED - August 2016 - 41
JED - August 2016 - EW 101
JED - August 2016 - 43
JED - August 2016 - Threat Monitor
JED - August 2016 - 45
JED - August 2016 - 46
JED - August 2016 - AOC Election
JED - August 2016 - 48
JED - August 2016 - Index of Advertisers
JED - August 2016 - JED Quick Look
JED - August 2016 - cover3
JED - August 2016 - cover4
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