OPTICS, EDM, ERRORS AND

INTERFEROMETRIC BASELINE MEASUREMENT

Prepared and Presented

By

Surv. R.O. OYINLOYE PhD fnis

rooyinloye@yahoo.com
DEPARTMENT OF SURVEYING AND GEOINFORMATICS
FACULTY OF ENVIRONMENTAL DESIGN AND MANAGEMENT (EDM)

Obafemi Awolowo University (OAU), Ile-Ife, Nigeria

 OPTICS
RECALL:
1. A wave allows energy to be transferred from one point to
another some distance away without particles of the medium
travelling between the two points

2. A wave which is propagated by vibrations perpendicular to the

direction of travel of the wave is called a Transverse Wave

3. A Longitudinal Wave is one in which the vibrations occur in the

same direction as the direction of travel of the wave

4. A plane wave is a constant-frequency wave whose wavefronts

(surfaces of constant phase) are infinite parallel planes of constant
peak-to-peak amplitude normal to the phase velocity vector
• A standing wave – Is a wave that appears stationary,
meaning it remains in a constant position

In a string, a standing wave is a type of transverse wave

where the movement of the particles of the medium is
perpendicular to the direction of the propagation of the
wave

A standing wave can occur when two identical waves

moving in different directions along the string interfere
• Standing wave occurs due to the interference
when transverse waves in strings are reflected
and the incident and reflected waves meet

Standing Wave
 SPHERICAL WAVE
Spherical waves – Are emitted from a single point
source in a spherical shape
Spherical waves come from point source in a spherical
pattern

Every point that a luminous disturbance touches

becomes itself a source of a spherical wave
The sum of these secondary waves determines the
form of the wave at any subsequent time
Spherical Wave
Spherical Wave
• Recall that waves interact with each other
• They interfere either constructively or
destructively
• Constructive interference occurs when waves are
completely in phase with each other and amplifies
the waves
• Destructive interference occurs when waves are
exactly out of phase with either other, and if
waves are perfectly out of phase with each other,
the wave will be cancelled out completely
 DIFFRACTION
Diffraction – Is the slight bending of light as it passes
around the edge of an object

The amount of bending depends on the relative size

of the wavelength of light to the size of the opening

If the opening is much larger than the light's

wavelength, the bending will be almost unnoticeable
Refraction is the change in direction of waves that
occurs when waves travel from one medium to
another

Refraction is always accompanied by a wavelength

and speed change

Diffraction is the bending of waves around obstacles

and openings
When the gap size is larger than the wavelength, the
wave passes through the gap and does not spread out
much on the other side

When the gap size is equal to the wavelength,

maximum diffraction occurs and the waves spread
out greatly - the wavefronts are almost semi-circular
Diffraction – Large Opening (Slit)
Diffraction – Narrow Opening (Slit)
The diffraction of light has many important
applications

For example, a device known as the diffraction grating

is used to break white light apart into its colour
components

Diffraction grating – Is a large number of close

parallel equidistant slits, ruled on glass or metal
It provides a very valuable means of studying spectra
 THIN FILM
A thin film – Is a layer of material ranging from
fractions of a nanometer (monolayer) to several
micrometers in thickness

Thin Film Deposition – Is the technology of applying a

very thin film of material (between a few nanometers
to about 100 micrometers, or the thickness of a few
atoms) onto a “substrate” surface to be coated, or
onto a previously deposited coating to form layers
The controlled synthesis of materials as thin films (a
process referred to as deposition) is a fundamental
step in many applications

An anti-reflection coating eliminates reflected light

and maximizes transmitted light in an optical system

A film is designed such that reflected light produces

destructive interference and transmitted light
produces constructive interference for a given
wavelength of light
 CRYSTAL DIFFRACTION
X-ray crystallography – Is a technique used for
determining the atomic and molecular structure
of a crystal, in which the crystalline atoms cause
a beam of incident X-rays to diffract into many
specific directions
x-ray Crystallography
 X-ray Diffraction Analysis
X-ray Powder Diffraction (XRD) – Is a rapid analytical
technique primarily used for phase identification of
a crystalline material and can provide information on
unit cell dimensions

X-Ray Diffraction (XRD) is a laboratory-based

technique commonly used for identification of
crystalline materials and analysis of unit cell
dimensions
 What Does X-Ray Diffraction Measure?
X-ray crystallography is a technique used for
determining the atomic and molecular structure of a
crystal, in which the crystalline atoms cause a beam
of incident X-rays to diffract into many specific
directions.

In a single-crystal X-ray diffraction measurement, a

crystal is mounted on a goniometer

The analyzed material is finely ground, homogenized,

and average bulk composition is determined.
 HOLOGRAPHY
Holography – Is the science and practice of
making holograms.
Typically, a hologram is a photographic recording of
a light field, rather than of an image formed by a lens,
and it is used to display a fully three-dimensional
image of the holographed subject, which is seen
without the aid of special glasses or other
intermediate optics
The hologram itself is not an image and it is usually
unintelligible when viewed under diffuse ambient
light

It is an encoding of the light field as an interference

pattern of seemingly random variations in the
opacity, density, or surface profile of the
photographic medium
Two Photographs of a Single Hologram taken from Different Viewpoints
In its pure form, holography requires the use
of laser light for illuminating the subject and for
viewing the finished hologram

In a side-by-side comparison under optimal

conditions, a holographic image is visually
indistinguishable from the actual subject, if the
hologram and the subject are lit just as they
were at the time of recording
 DISPERSION
Dispersion – Is the separation of white light into colours or of
any radiation according to wavelength

Dispersion in optics is the separation of white light into a

colour spectrum by a prism

These colours are often observed as light passes through a

triangular prism

Upon passage through the prism, the white light is separated

into its component colours - red, orange, yellow, green, blue
and violet

The separation of visible light into its different colours is

known as dispersion.
In fluid dynamics, dispersion of water waves
generally refers to frequency dispersion, which
means that waves of different wavelengths travel at
different phase speeds

Water waves, in this context,

are waves propagating on the water surface, with
gravity and surface tension as the restoring forces
Because white light is made up of ALL visible
wavelengths, its colours can be separated
(dispersed) by this difference in behaviour

When light passes through glass, it encounters TWO

interfaces: one entering and the other leaving

It slows down at the first interface and speeds up

back at the second interface
Acoustic dispersion – Is the phenomenon of a sound
wave separating into its component frequencies as it
passes through a material

The phase velocity of the sound wave is viewed as a

function of frequency
 SCATTERING
Scattering, in physics – Is a change in the direction of
motion of a particle because of a collision with
another particle

As defined in physics, a collision can occur between

particles that repel one another, such as two positive
(or negative) ions, and need not involve direct
physical contact of the particles
Light scattering – Is a form of scattering in
which light, in the form of propagating energy,
is scattered

Light scattering can be thought of as the deflection

of a ray from a straight path, for example by
irregularities in the propagation medium, particles,
or in the interface between two media
Scattering – Is the process by which small particles
suspended in a medium of a different index of
refraction diffuse a portion of the incident radiation
in all directions

Scattering theory is a framework for studying and

understanding the scattering of waves and particles

Wave scattering corresponds to the collision and

scattering of a wave with some material object, for
instance, sunlight scattered by rain drops to form a
rainbow
There are three different types of scattering:
• Rayleigh scattering,
• Mie scattering, and
• non-selective scattering

Rayleigh scattering mainly consists of scattering

from atmospheric gases

This occurs when the particles causing the scattering

are smaller in size than the wavelengths of radiation
in contact with them (i.e., when the wavelength is
greater than the size of the particle)
Large particles in the atmosphere are able to scatter
to all wavelengths of white light equally. when all
wavelengths of white light are scattered equally,
then Mie scattering is occurring (i.e., when the
wavelength is comparable (equal or about equal to
the size of the particle)

Non-selective scattering – Is the scattering of all

wavelengths of electromagnetic radiation equally in
the atmosphere, usually caused by particles which
are much larger than the energy wavelengths (i.e.,
when the wavelength is smaller than the size of the
particle)
 Scattering in Remote Sensing
When electromagnetic radiation travels through
the atmosphere, it may be absorbed or
scattered by the constituent particles of the
atmosphere. Molecular absorption converts the
radiation energy into excitation energy of the
molecules. The overall effect is the removal of
energy from the incident radiation
 ELECTROMAGNETIC DISTANCE
MEASUREMENT (EDM)
Electromagnetic Distance Measurement (EDM) – Is the
measurement of the total distance from the instrument
to the reflector and back to the instrument

EDM is the electronic distance measuring device which

measures the distance from the instrument to its target

The EDM device sends out a laser or infrared beam which

is reflected back to it, and it uses velocity measurement
to calculate the distance travelled by the beam
 PRINCIPLE OF EDM
The principle of the measuring device in EDM,
which is currently used in a total station and
used along with electronic/optical theodolites,
is that it calculates the distance by counting
the total number of complete wavelengths and
measuring the phase shift during the radiated
electromagnetic wave (such as an infrared
light)
An EDM uses electromagnetic (EM) energy to
determine the length of a line

In Electrical Engineering:
Electrical Discharge Machining (EDM) is a controlled
metal-removal process that is used to remove metal
by means of electric spark erosion. In this process an
electric spark is used as the cutting tool to cut
(erode) the workpiece to produce the finished part
to the desired shape.
 CLASSIFICATION OF EDM DEVICES
EDM instruments are classified according to the
type of carrier wave employed:

• Instruments using light or IR waves are

classified as electro-optical instruments

• Instruments based on radio waves are

generally called microwave instruments
 ERRORS: INSTRUMENTAL AND
ATMOSPHERIC
Observational error (or measurement error) is the
difference between a measured value of a quantity
and its “true” value

In Statistics, an error is not a "mistake" but a mistake

in SVG is referred to as Gross Error

Variability is an inherent part of the results

of measurements and of the measurement process
Instrument error refers to the combined accuracy
and precision of a measuring instrument, or the
difference between the actual value and the value
indicated by the instrument (error)

Thus the need for instrument calibration

Measuring instruments are usually calibrated on

some regular frequency against a standard
1. Static error, 2. Dynamic error

1. Static error of a measuring instrument is the

numerical difference between the “true” value
and the value of the quantity by measurement
2. Dynamic error of a measuring instrument is the
difference between the “true” value and the value
of the quantity of repeated measurements of the
same quantity in a dynamic or kinematic mode
Random errors are statistical fluctuations (in either
direction) in the measured data due to the precision
limitations of the measurement device

Random errors usually result from the Observer’s

inability to take the same measurement in exactly
the same way to get exact the same value
Gross errors are caused by Observer’s carelessness
or equipment failure. These "outliers" are so far
above or below the “true” value that they are usually
discarded when assessing data

The "Q-Test" is a systematic way to determine if a

data point should be discarded
Another type of error that comes into play because
of faulty procedure adopted by the Observer is
called "PERSONAL ERROR“

Personal error comes into existence due to making

an error in reading a scale, a tape or a figure

It is due to faulty procedure adopted by the person

making measurement
Systematic Error is a type of error that is in-built or
inherent in the measuring device, e.g., graduation error,
incorrect pointing of the needle on the scale, etc.

An environmental error is an error in calculations or

observations due to environment or location on the
globe

Any experiment performed anywhere in the universe has

its surroundings, from which we cannot eliminate our
system
Definition of Bias. Systematic error is also
known as bias. It is any systematic process in the
conduct of a study that results in the incorrect
estimate of a measure of disease occurrence or
measure of association
To reduce the systematic error of a data set, you
must identify the source of the error and remove it
through calibration

Unfortunately, even when calibration is carried out,

systematic error will never reduce by taking more
measurements
Zero Error – Any indication that a measuring system
gives a false reading when the true value of a
measured quantity is zero, e.g., the needle on an
ammeter failing to return to zero when no current
flows

A zero error may result in a systematic error or

uncertainty
 PRECISION AND ACCURACY
Precision refers to the closeness of two or more (i.e.,
repeated) measurements to each other or one another. It
is a measure of dispersion of repeated measurements

For example, if a given substance is weighed five times

and we get 3.2 kg each time, then the measurement is
very precise but may not be accurate

Precision is independent of accuracy

To determine if a value is precise, find the average of the

measured data, then subtract each measurement from it
Percent Error – As the measured values can be
anything, a concept called percent error has been
developed

Find the difference (subtract) between the accepted

value (MPV) and the experimental (measured) value,
then divide by the accepted value and multiply the
result by 100
Accuracy and precision are used in context of
measurement

Accuracy refers to the degree of conformity and

correctness of something when compared to a “true”
or “absolute” value

While precision refers to a state how consistently

something is when repeated several times
 INTERFROMETRIC METHODS OF
BASELINE MEASUREMENTS
Interferometry is a family of techniques in which
waves, usually electromagnetic waves, are
superimposed causing the phenomenon of
interference in order to extract information

In surveying, a baseline is a line between two points

on the earth's surface and the direction and
distance between them. In a triangulation network,
at least one baseline needs to be measured to
calculate the size of the triangles by trigonometry
In geometric measurements, length is the most
extended dimension of an object

In the International System of Quantities, length is

any quantity with dimension distance

In other contexts "length" is the measured dimension

of an object
Interferometers are investigative tools used in many
fields of science and engineering

They are called interferometers because they work

by merging two or more sources of light to create an
interference pattern, which can be measured and
analyzed; hence "Interfere-ometer"
Interferometry is a measurement method using the
phenomenon of interference of waves (usually light,
radio or sound waves)

In addition, interferometry is used to describe the

techniques that use light waves for the study of
changes in displacement
In Traditional Surveying, length is the
measurement of distance

There are many tools such as vernier calliper, gauge,

tapes, metric rulers which are used to measure
length

Depending upon what we intend to measure,

tool varies. Vernier calliper is used to measure the
length of rod, length and diameter of a wire
Very-long-baseline interferometry (VLBI) is a type of
astronomical interferometry used in radio
astronomy. In VLBI, a signal from an astronomical
radio source, such as a quasar, is collected at
multiple radio telescopes on Earth

The Very Long Baseline Array (VLBA) is an

interferometer consisting of 10 identical antennae
on trans-continental baselines up to 8000km

Each VLBA station consists of a 25m diameter

antenna and an adjacent control building
In triangulation, the base line is of prime importance

It is the only horizontal distance to be measured

It should be measured very accurately since the

accuracy of the computed sides of triangulation
system depends on it

Length of a base line varies from a fraction of 10km to

a fraction of 16 – 25km or more
In selecting site for a base line, the following
requirements should be considered:
• The site should be fairly level or uniformly sloping or
gently undulating
• It should be free from obstructions throughout the
entire length
• The ground of the two stations should be firm and
smooth
• The site should be such that the whole length can be
laid out; the extremities of the line being intervisible
at ground level
• The site should be such that well shaped triangle can
be obtained by connecting the end stations of the
base line to the main triangulation stations
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