Introduction to Geographic Information system and Remote Sensing (RS)

Introduction to Geographic Information system
(GIS) and Remote Sensing (RS)
Chala Hailu (M.Sc)
Lecturer at Jimma Institutes of Technology
February, 2022

1. INTRODUCTION TO GIS AND RS
Introduction of GIS
Applications of GIS in water resources
management
Introduction of RS
Applications of RS
 Cartography
Coordinate system
 Map projection
 Map projections Classification
 Distortion in a map projection

What GIS?
Geographic Information Systems (GIS)
“G” = Geographic
– Location based, spatial, geo-referenced
“I” = Information
– knowledge about location
– attribute data, spreadsheets
“S” = Systems ,Science ,Studies ,Services
– processes, software/hardware
INTRODUCTION TO GIS AND RS

DEFINITION OF GIS
• A geographic information system (GIS) is a system
designed to capture, store, manipulate, analyze, manage,
and present all types of geographical data
• A spatial system that creates, manages, analyzes, and
maps all types of data.

GIS Data
• GIS data can be described by three data types
–Spatial data
–Attributes data (None spatial data)
–Metadata
• Geospatial data tells you where it is.
• Attributes data tells you what it is.
• Metadata (data about data) describes both
geospatial and attribute data (date created, date
modified, and file size).

Spatial vs None Spatial
 Spatial data?
 Any data that is associated with a specific geographic location
 Describes the absolute and relative location of geographic
features. Where it is?
eg. Soil map, Aerial photography, Remotely sensed imagery, Road
networks, Wetlands delineation, Stream gauges, Dam sites, land
use/land cover map, Etc…
 Non-spatial data?
 Is any data which cannot be explained or associated in terms of
position.
 Describes characteristics of the spatial features. These
characteristics can be quantitative and/or qualitative in nature.
Attribute data is often referred to as tabular data. What it is?
eg. Human resource and financial data of an organization.

QUESTIONS A GIS CAN ANSWER
 ESRI(Environmental system research institute)
(1992) noted that a GIS can answer five generic
types of questions.
 These are (in increasing order of complexity):
 Location Where is it…?
 Condition What is it…?
 Trends What has changed since…?
 PatternHow is it distributed…?
 Modeling What if…?

(1) Where is it…? (LOCATION)
 What exists at a particular location.
 Location name, Post office, Geographic information such
as x and y, Vegetation, habitat, soil type, or hydrologic
conditions exist at the proposed site.
(2) What is it…? (CONDITION). Mode of existence
 Instead of just specific location, you just want to find a
location where certain conditions area are satisfied.
 For example, you may wish to determine which areas are
most suited for supporting a certain wildlife species.
 He or she may wish to produce a map showing areas
with particular vegetation types of a specific size and
greater than a critical distance away from recreation
activities.

(3) What has changed since...? (TRENDS).
For instance, there may be interest in quantifying long-term
changes to vegetation composition.
 Vegetation can be mapped using archived information, such
as aerial photography, and compared in the GIS to more
recent maps of vegetative cover.
 This information can be useful for determining long-term
changes to vegetation that may be caused by different types
of land use.
 For example, overuse of riparian areas by grazing and off-
road vehicles may have caused erosion conditions that
altered downstream vegetation composition. Such changes
may be slow and imperceptible to the observer on the
ground, but they can become very apparent when 10 to 20
years of vegetation change is viewed in a GIS.

(4) What spatial patterns exist? (PATTERNS).
For example, if nest sites of a particular species are of
concern, it may be possible to use the GIS to link these nest
sites to other types of information, such as specific vegetation
types, understory conditions, distance from water, topography,
etc.
(5) What if...? (MODELING).
The most complex use of a GIS involves tying the GIS to a
known set of relationships, scientific laws, etc., to model real-
world phenomena.
Hydrology, soil loss, and habitat quality are all examples of
geographic phenomena often modeled in a GIS environment.
Modeling can be a powerful tool, as it often opens the door for
both trend and predictive analysis, which can prove quite
useful in planning operations.

COMPONENTS OF GIS
GIS is an integration of five basic components
Procedures

COMPONENTS OF GIS
 People
 This is the most important component in a GIS.
People must develop the procedures and define
the tasks of the GIS.
 People can often overcome shortcomings in
other components of the GIS
 Data
The availability and accuracy of data can affect
the results of any query or analysis.

COMPONENTS OF GIS
 Hardware
Hardware capabilities affect processing speed,
ease of use, and the type of output available.
 Software
This includes not only actual GIS software but
also various database, drawing, statistical,
imaging, or other software.
 Procedures
Analysis requires well-defined, consistent
methods to produce accurate, reproducible
results.

GIS FUNCTIONAL COMPONENTS
 GIS mainly consists of four functional
components, which support key GIS functions.
 These are:
Data capture and preparation,
Data storage,
Data analysis (Query and analysis), and
Presentation of spatial data (Data display and
output)

 Is a manifestation of an entity or process of interest that:
 can be named or described;
 can be geo-referenced; and
 can be assigned a time (interval) at which it is/was present.
 For instance, in water management, relevant geographic
phenomena (objects) can be river basins, agroecological units,
measurements of actual evapotranspiration, meteorological
data, groundwater levels, irrigation levels, water budgets and
measurements of total water use.
 Natural phenomena (landscape, weather, natural processes)
 Man-made phenomena (roads, buildings, …)
 The phenomena divided in to two: geographic fields &
objects. 17
GEOGRAPHIC PHENOMENA

A) Geographic Fields
 is a geographic phenomenon that has a value
‘everywhere’ in the study area.
 Fields can be discrete or continuous.
Continuous Fields: the field values along any path
through the study area do not change abruptly, but only
gradually. Good examples of continuous fields are air
temperature, barometric pressure, soil salinity and
elevation.
Discrete: Discrete fields divide the study space in
mutually exclusive, bounded parts, with all locations in
one part having the same field value. Typical examples
are land classifications, for instance, using either
geological classes, soil type, land-use type, crop
type or natural vegetation type.
18

19
Continuous
Filed
Discrete
Filed

B) Geographic objects
• When a geographic phenomenon is not present
everywhere in the study area, but somehow ‘sparsely’
populates it, we look at it as a collection of geographic
objects.
• Such objects are usually easily distinguished and
named, and their position in space is determined by a
combination of one or more of the following
parameters:
• Location (where is it?),
• shape (what form does it have?),
• size (how big is it?) and
• Orientation (in which direction is it facing?).

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DATA TYPES AND VALUES USED FOR GPS
Different types of values that we can use to represent
“phenomena”. Four different data types:
 Nominal data values, Ordinal data values, Interval data
values and Ratio data values
 A value of nominal data: these values establish the group, class,
member, or category with which the geographic object at the position
of the cell is associated.
 These values are qualities, not quantities, with no relation to a fixed
point or a linear scale.
 Coding schemes for land use, soil types, or any other attribute
qualify as a nominal measurement.
N.B Global Positioning Systems (GPS)

Ordinal data
 These measurements show place, such as first, second,
or third, but they do not establish magnitude or relative
proportions.
 You cannot infer a quantitative difference, such as how
much an entity is larger, higher, or denser than the others.
Interval data
 It represents a measurement on a scale such as time of
day, temperature in Fahrenheit degrees, and pH value.
These values are on a calibrated scale but are not
relative to a true zero point.
 You can make relative comparisons between interval
data, but their measure is not meaningful when compared
to the zero point of the scale.

RATIO DATA
 A value of ratio data represents a measure on a scale with
a fixed and meaningful zero point.
 Mathematical operations can be used on these values
with predictable and meaningful results.

APPLICATIONS OF GIS IN
WATER RESOURCES MANAGEMENT
A. Watershed management
B. Flood management
C. Groundwater
D. Water quality

A. WATERSHED MANAGEMENT
 Terrain/ Landscape modeling
 Flow modeling
Terrain modeling
 Creation of DEMs
 Automated watershed extraction from topography
 Flow determination –direction and accumulation
Flow modeling
 Flow direction and accumulation
 Contributing area analysis
 Stream-ordering

B. FLOOD MANAGEMENT
Flood Management
 Flood plain delineation
 Use of satellite imagery
 Assessment/modeling of topography
 Soil
 Hydrology
 Channel characteristics
 Channel cross-section
 Channel length
 Channel shape
 Changes over time
 Channel erosion and depositional features
 Risk modeling and mitigation

CONT…
Infrastructure analysis
• From analysis of inundation models, determine
effects on infrastructure
• Assessment of bridge and other structures that
span river channels
• Assessment of dykes and other mitigation
structures that run parallel to channel
• Effects of these on sedimentation and erosion
processes downstream
• Assessment of road and other critical networks
and facilities with respect to flood hazards

C. GROUNDWATER
• Modeling subsurface flow –rate, advection,
concentration
• Well and spring models

D. WATER QUALITY
Management of surface and subsurface water
• Water quality measurements of oxygen, pH,
bacterial content, etc
F. Permitting Engineer For:
• Agricultural irrigation
• Human consumption
• Transport
• Extraction of resource
• Consider topography and other natural physical
elements, and population/demand centers to
determine means to supply resource from source

Remote Sensing:
• Art, science and technology of observing an object,
scene or phenomenon by instrument-based
techniques without physical contact
• Remote sensing is the observation of
an object from a distance.
• This is done by sensing and recording
reflected or emitted energy and
processing, analyzing, and applying
that information.
• Examples are Aerial Photography
and the use of satellites to observe
the Earth.
INTRODUCTION TO RS

Key Words While defining RS
 Information is collected by a device (sensor) that is
not in contact with the objects being measured.
 Information transfer is accomplished by use of
electromagnetic radiation (EMR).
 Concerned not only with data collection but also
extracting information via different techniques.
 Q#1
 Which humans sense organ is remote sensor and
which is not?
INTRODUCTION: DEFINITION OF RS

RS started when free balloons were used for photography by the
French Gaspard Felix Tournachon to photograph the village of Petil
Becetre near Paris in 1863.
History of Remote Sensing

Earth Observation
is the gathering of information about planet
Earth’s physical, chemical and biological
systems via remote sensing technologies
supplemented by earth surveying techniques,
encompassing the collection, analysis and
presentation of data.
INTRODUCTION REMOTE SENSING

Why Earth Observation (EO) by RS
 Synoptic view- observations that give a broad view of a
subject at a particular time.
 Large areas, dense data
 Synergy (Working together) with in suitable
measurements
 High repeatability (temporal resolution)
 Multiple measurements in invisible spectra
 Global, inaccessible/secure areas
 Multi purpose
 Cost effective (can be)
 Data collection without disturbance
INTRODUCTION REMOTE SENSING

The first requirement for remote sensing is to have an
energy source which illuminates or provides electromagnetic
energy (EME) to the target of interest.
 EMR is a form of energy that reveals (exposes) its
presence by the observable effects it produces when it
strikes the matter.
 The sun is the most obvious source of EMR for remote
sensing,
 Light is Electromagnetic (EM) radiation
 Can be modeled in 2 ways:
 by waves
 by photons (energy bearing particles)
Remote Sensing Process
Energy Source or Illumination (A)

EM Radiation Wave Model
 Electromagnetic radiation
(ER) travels as waves
 Waves are characterized by
2 fields:
 Electric and Magnetic
 The 2 fields oscillate in time
 The 2 fields oscillate in
space perpendicularly to
each
 Waves travel with speed of
light:

Wave length and Cycle

EM-Spectrum is the entire range of wavelengths of
electromagnetic radiation.
The electromagnetic spectrum extends from below the low
frequencies used for modern radio communication to gamma
radiation at the short-wavelength (high-frequency)
Most sensors operate in the visible, infrared, and microwave
regions of the spectrum.
……..Energy Source or Illumination (A)
ELECTROMAGNET SPECTRUM

……. EM-SPECTRUM
Violet: 0.4 00 - 0.446 mm
Blue: 0.446 - 0.500 mm
Green: 0.500 - 0.578 mm
Yellow: 0.578 - 0.592 mm
Orange: 0.592 - 0.620 mm
Red: 0.620 - 0.700 mm

Ultraviolet:
 Has short wavelengths (0.3 to 0.4 μm) and high
frequency.
 Used in geologic and atmospheric science applications
(tracking changes in the ozone layer).
Visible Light
 Radiation detected by human eyes as colors, and
ranges from approximately 0.4 to 0.7μm
 The longest visible wavelength is red and the shortest is
violet.
 Blue, green, and red are the primary colors or
wavelengths of the visible spectrum.
 Applicable in manmade and natural feature identification
and study.
……..EM-SPECTRUM

Infrared
 Ranges from approximately 0.7 to 1000 μm.
 It is 100 times as wide as the visible portion.
Reflected Infrared
 Shares radiation properties exhibited by the visible portion.
 Valuable for delineating healthy verses unhealthy or fallow
vegetation, and
 For distinguishing among vegetation, soil, and rocks.
Thermal Infrared
 Radiation that is emitted from the Earth’s surface in the form of
thermal energy.
 Useful for monitoring temperature variations in land, water and
ice.
…….EM-SPECTRUM

Microwave
 Ranging on the spectrum from 1000μm to 1 m.
 The longest wavelength used for remote sensing.
 Used in the studies of meteorology, hydrology, oceans,
geology, agriculture, forest and ice and for topographic
mapping.
 Microwave emission is influenced by moisture content, it is
useful for mapping soil moisture, sea ice, currents, and
surface winds.
……..EM-SPECTRUM

Solar Spectrum
 The range of electromagnetic energy emitted by the sun is
known as the solar spectrum, and lies mainly in three
regions:
 ultraviolet,
 visible, and
 infrared.
 The solar spectrum extends from about 0.29 µm (or 290
nm) in the longer wavelengths of the ultraviolet region, to
over 3.2 µm (3,200 nm) in the far infrared.
………EM-SPECTRUM

Radiation and the Atmosphere (B) – as the energy travels from
its source to the target, it will come in contact with and interact
with the atmosphere it passes through. This interaction may
take place a second time as the energy travels from the target to
the sensor.
• These effects are caused by the mechanisms of scattering and
absorption
• Scattering occurs when particles or large gas molecules
present in the atmosphere interact with and cause the
electromagnetic radiation to be redirected from its original
path.
• How much scattering takes place depends on several factors
including the wavelength of the radiation, the abundance of
particles or gases, and the distance the radiation travels through
the atmosphere.
Radiation and the Atmosphere (B)

C) EM Interaction with Atmosphere

……Radiation and the Atmosphere (B)
There are three (3) types of scattering which take place
a. Rayleigh (molecular) scattering
 Rayleigh scattering occurs when
particles are very small compared to
the wavelength of the radiation,
e.g. small specks of dust or nitrogen
and oxygen molecules.
 Rayleigh scattering causes shorter
wavelengths of energy to be scattered
much more than longer wavelengths.
This is the dominant scattering
mechanism in the upper atmosphere.

Rayleigh (small particle scattering)
 In visible light, light of shorter wavelength (e.g. blue) wavelength
at 0.4 μm is scattered 5 time as the red wavelength at 0.6 μm.
 This explains why the clear sky appears blue. The scattering
made blue light reach our eyes from all parts of the sky.
….. cont……………

b. Mie (or nonmolecular) scattering
 Mie scattering occurs when the
particles are just about the
same size as the wavelength
of the radiation.
 Dust, pollen, smoke and water
vapor are common causes of
Mie scattering which tends to
affect longer wavelengths than
those affected by Rayleigh
scattering.
 Mie scattering occurs mostly in
the lower portions of the
atmosphere where larger
particles are more abundant
……Radiation and the Atmosphere (B)

…..Radiation and the Atmosphere (B)
c. Nonselective scattering
 This occurs when the particles are much larger than the
wavelength of the radiation.
 Water droplets and large dust particles can cause this type of
scattering.
 Nonselective scattering gets its name from the fact that all
wavelengths are scattered about equally.
 This type of scattering causes fog and clouds to appear white
to our eyes because blue, green, and red light are all
scattered in approximately equal quantities (blue+green+red
light = white light). Moreover, clouds have a further limiting effect
on optical RS

…..Radiation and the Atmosphere (B)
Absorption
 Absorption is the other main
mechanism at work when
electromagnetic radiation
interacts with the atmosphere.
 This phenomenon causes
molecules in the atmosphere to
absorb energy at various
wavelengths. Ozone (O3),
Carbon Dioxide (CO2), and
water vapor (H2O) are
the three main atmospheric
constituents which absorb radiation.

Absorption-Global Warming
……..Radiation and the Atmosphere (B)
• Most of the atmosphere consists of nitrogen (78%) and oxygen
(21%), other gases account for the remaining 1%.
• Water vapor (can vary highly in concentration), carbon dioxide
(0.035%), methane, and nitrous oxide (N2O) are called
greenhouse gases.
• These gases (mainly water vapor and carbon dioxide) have the
ability to absorb long wave radiation emitted by the Earth and
reemit it from much colder levels to the outer space. They are
able to store heat in the atmosphere and keep the Earth warm.
It looks like the Earth is surrounded by a thermal blanket. This
phenomenon is called the greenhouse effect.
• What is negative is the enhanced greenhouse effect. As To atm >
To earth, it leads to the increase in the Earth temperature. The
more the concentration of greenhouse gases, the higher the
temperature of the atmosphere.

EARTH’S ATMOSPHERIC WINDOW
 Those areas of the frequency spectrum which are not severely
influenced by atmospheric absorption and thus, are useful to
remote sensors, are called atmospheric windows.
 The upper atmosphere blocks 100% of the gamma rays, x-
rays, and most ultra-violet light. But visible light freely passes.
Our eyes use this visible light to see features on Earth.
(https://gisgeography.com/atmospheric-window/)


EARTH’S ATMOSPHERIC WINDOW
 The combined effects of atmospheric absorption, scattering, and reflectance
reduce the amount of solar irradiance reaching the Earth’s surface
 The EM radiation (in blue) is what sensors are capable of seeing on
Earth.
 Our eyes can see red, green, and blue which is visible light. Healthy
vegetation (or chlorophyll) reflects more green light. However, it
absorbs more red and blue light. That is why our eyes see plants as
green.
 Measuring and monitoring the near infrared reflectance is one way that
scientists determine how healthy particular vegetation may be.
 Majority of the radiation incident upon water is not reflected but is either
absorbed or transmitted.
 Longer visible wavelengths and near infrared radiation is absorbed
more by water than by the visible wavelengths.
 Thus water looks blue or blue green due to stronger reflectance at
these shorter wavelengths and darker if viewed at red or near
infrared wavelengths.

QUESTION #2
 What is the best atmospheric conditions for remote
sensing in the visible portion of the spectrum?
 Around noon on a sunny, dry day with no clouds and
no pollution would be very good for remote sensing in
the visible wavelengths. At noon the sun would be at its
most directly overhead point, which would reduce the
distance the radiation has to travel and therefore the
effects of scattering, to a minimum. Cloud-free conditions
would ensure that there will be uniform illumination and
that there will be no shadows from clouds. Dry, pollutant-
free conditions would minimize the scattering and
absorption that would take place due to water droplets
and other particles in the atmosphere.

Interaction with the Target (C): Radiation that is not absorbed
or scattered in the atmosphere can reach and interact with the
Earth's surface.
There are three forms of interaction that can take place when
energy strikes, or is incident (I) upon the surface:
Absorption (A), Transmission (T), Reflection (R)
Interaction with the Target (C)

……..Interaction with the Target (C)……
Absorption (A) occurs
when radiation (energy) is
absorbed into the target.
Transmission (T) occurs
when radiation passes
through a target.
Reflection (R) occurs when
radiation "bounces" off the
target and is redirected.

……..Interaction with the Target (C)……
Specular Vs Diffuse
 When a surface is smooth, we get specular or mirror-like
reflection where all (or almost all) of the energy is
directed away from the surface in a single direction.
 Diffuse reflection occurs when the surface is rough and
the energy is reflected almost uniformly in all directions.

Recording of Energy by the Sensor (D)
Recording of Energy by the Sensor (D) - after the energy has
been scattered by, or emitted from the target, we require a
sensor (remote - not in contact with the target) to collect and
record the electromagnetic radiation

Reception, and Processing (E)
Reception, and Processing (E) - the energy recorded by
the sensor has to be transmitted, often in electronic form, to
a receiving and processing station where the data are
processed into an image (hardcopy and/or digital).

…………Remote Sensing Process
Interpretation and Analysis (F) - the processed image is
interpreted, visually and/or digitally or electronically, to
extract information about the target which was illuminated.
Application (G) - the final element of the remote sensing
process is achieved when we apply the information we
have been able to extract from the imagery about the target
in order to better understand it, reveal some new
information, or assist in solving a particular problem.

 Major Components Remote Sensing Technology
 Energy Source
Passive System: sun, irradiance from earth's materials;
Active System: irradiance from artificially generated
energy sources such as radar.
 Platforms: (Vehicle to carry the sensor) (truck, aircraft,
space shuttle, satellite, etc.)
 Sensors: (Device to detect electro-magnetic radiation)
(camera, scanner, etc.)
 Detectors: (Handling signal data) (photographic, digital,
etc.)
 Processing: (Handling Signal data) (photographic,
digital etc.)
 Institutionalisation: (Organisation for execution at all
stages of remote-sensing technology: international and
national organisations, centres, universities, etc.).
REMOTE SENSING COMPONENTS

PLATFORM & SENSORS
PLATFORMS
 In order for a sensor to collect and record energy
or emitted from a target or surface, it must reside on
stable platform away from the target or surface
observed.
 Platform is a Vehicle to carry the sensor.
 Platforms for remote sensors may be situated on the
ground, on an aircraft or balloon (or some other
within the Earth's atmosphere), or on a spacecraft or
satellite outside of the Earth's atmosphere.
Ground Based Sensors (up to 50 m)
 Air borne Platforms (50 m to 50 km)
 Space borne platforms (100 km to 36,000 km)

PLATFORMS
Ground-based platforms (up to 50 m)
 Are used on the surface of the Earth
 Are often used to record detailed information as
compared to aircraft or satellite sensors
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 Have the capability of viewing the
object from different angles & are
mainly used for collecting the
ground truth or for laboratory
simulation studies.
E.g. on ladder, crane, building etc

PLATFORMS
Air borne Platforms (50 m to 50 km)
Placed within the atmosphere of the Earth
Balloons and
Aircrafts
Aircrafts are commonly used as remote-sensing
for obtaining Aerial Photographs.
Affected by atmospheric pressure and gravity.
Have been playing an important role in the development
of space borne remote sensing techniques.
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PLATFORMS
Space borne platforms (100 km to 36,000 km)
 Platforms in space (satellites) outside the influence of
atmospheric pressure and earth’s gravity.
 Move freely in their orbits around the earth.
 The entire earth or any part of the earth can be covered at
specified intervals depending on the orbit of the satellite.
 Provide enormous amount of remote sensing data
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PLATFORMS
Q: What advantages do sensors carried on board satellites have over
those carried on aircraft? Are there any disadvantages that you can
think of?
Sensors on board satellites generally can "see" a much larger area
of the Earth's surface than would be possible from a sensor onboard
an aircraft ( global coverage).
Because they are continually orbiting the Earth, it is relatively easy
to collect imagery on a systematic and repetitive basis in order to
monitor changes over time.
The geometry of orbiting satellites with respect to the Earth can be
calculated quite accurately and facilitates correction of remote
sensing images to their proper geographic orientation & position.
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PLATFORMS
However, aircraft sensors can collect data at any time and
over any portion of the Earth's surface (as long as conditions
allow it) while satellite sensors are restricted to collecting data
over only those areas and during specific times dictated by
their particular orbits.
Air craft sensor provide more detail information
 It is also much more difficult to fix a sensor in space if a
problem or malfunction develops.
High cost for designing and launching satellites 73

PLATFORMS: SATELLITE MISSION
 Platforms carry Sensors
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PLATFORMS: SATELLITE - ORBIT
 Satellite orbit is the path followed by a satellite
 Orbit selection can vary in terms of
 Altitude (their height above the Earth's surface) and
 Their orientation and rotation relative to the Earth
(inclination).
 It influences to a large extent the area that can be viewed
(i.e. the spatial coverage) and the details that can be
observed (the spatial resolution).
 In general, the higher the altitude, the larger the spatial
coverage but the lower the spatial resolution.
75

PLATFORMS :SATELLITE - SWATH
 As a satellite revolves around the Earth, the sensor
“sees” a certain portion of the Earth’s surface. The
area imaged on the surface, is referred to as the
swath.
 Imaging swaths for space borne sensors generally
vary between tens and hundreds of kilometers
wide.
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SENSORS
 A remote sensor is a device that detects EM radiation,
quantifies it and, usually, records it in an analogue or
digital form.
 A remote sensor may also transmit recorded data (to
a receiving station on the ground).
 Consists of detectors which are used for handling signal
data and play an important role in receiving information
from the ground.
 Record different wavelengths bands of EME coming from
the earth’s surface.
 Sensors can be categorized based on different factors
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SENSORS
 Sensor can be classified into two types: Active sensors and
Passive sensors.
Passive sensor:
 Do not have their own source of energy.
 Receive the reflected solar energy from the earth surface
or the emitted electromagnetic energy by the earth surface
itself.
 Can only be used to detect energy when the naturally
occurring energy is available, except thermal sensor.
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SENSORS
Passive sensor:
 The properties of a passive sensor are:
1. relatively simple & does not have high
power requirement.
2. most of them are relatively wide band
systems.
3. It depends upon good weather
conditions.
e.g. Most satellite sensors (Landsat,
SPOT etc)
79

SENSORS
Active Sensor
 Use their own source of energy to illuminate Earth surface.
 A part of this energy is reflected back which is received by the
sensor to gather information about the earth’s surface.
 E.g. photographic camera with flash, Radar and laser
altimeter are active sensors.
 Radar is composed of a transmitter and a receiver.
 The transmitter emits a wave, which strikes objects and is
then reflected or echoed back to the receiver.
80

SENSORS
Sensor Characteristics (Data Resolution)
 Resolution” in RS refers to the ability of a sensor to
distinguish or resolve objects that are physically near or
spectrally similar to other adjacent objects.
 The distance between the target being imaged and the
platform and nature of the sensor determine the image
resolution.
 Fine or high resolution- detail information, capable of
identifying similar &/or closer features & cover smaller
area on the ground.
 Low or Coarse resolution- provide less detail
information/data, less capable of identifying similar
features, large area coverage. 81

GROUND RECEIVING STATIONS
 Data obtained during airborne remote sensing missions
can be retrieved once the aircraft lands.
 Data acquired from satellite platforms need to be
electronically transmitted to Earth, since the satellite
continues to stay in orbit during its operational lifetime.
 Three options for transmitting data acquired by satellites to
the surface.
1. Directly transmitted to Earth if a Ground Receiving
Station (GRS) is in the line of sight of the satellite (A)
2. the data can be recorded on board the satellite (B) for
transmission to a GRS at a later time
83

GROUND RECEIVING STATIONS
3. Data can also be relayed to the GRS through the
Tracking and Data Relay Satellite System (TDRSS), the
data are transmitted from one satellite to another until
they reach the appropriate GRS.
84
• Satellite receiving stations are
positioned throughout the world.
• Each satellite program has its own
fleet of receiving stations with a
limited range from which it can pick
up the satellite signal.
• Satellites can only transmit data
when in range of receiving station.

APPLICATION OF REMOTE SENSING
Urbanization & Transportation
 Urban planning
 Roads network and
transportation planning
 City expansion and control
boundaries by time
 Wetland delineation
Image source: www.ldeo.columbia.edu
Image source: www.geospectra.net

Agriculture
The application of remote
sensing in agriculture include:
- Soil sensing
- Farm classification
- Farm condition assessment
- Agriculture estimation
- Mapping of farm and
agricultural land characteristics
- Mapping of land management
practices
- Compliance monitoring
 Wageningen UR 2002

Natural resource Management
 Forestry: biodiversity, forest, deforestation
 Water source management
 Habitat analysis
 Environmental assessment
 Pest/disease outbreaks
 Impervious surface mapping
 Mineral province
 Geomorphology

HYDROLOGY
Hydrology is inherently related to many other applications of remote
sensing, particularly forestry, agriculture and land cover
 Most hydrological processes are dynamic and require frequent
observation.
 Remote Sensing offers a synoptic view of the spatial distribution and
dynamics of hydrological phenomena, often unattainable by traditional
ground surveys
Flood delineation and mapping
 Remote sensing techniques are used to measure and monitor the real
extent of the flooded areas to efficiently target rescue efforts and to
provide quantifiable estimates of the amount of land affected.
 Incorporating remotely sensed data into a GIS allows for quick
calculation and assessment of water levels, damage, and areas facing
potential flood danger

GROUND WATER
 Remote Sensing based groundwater prospect zone map
serve as a base for further exploration using
hydrogeological and geophysical methods to locate well
sites.
 If remote sensing data are used at first level to delineate
prospective zones and further follow up by
hydrogeological and geophysical surveys, higher success
could be achieved besides saving in terms of cost, time
and work.
 Remote Sensing data helps in identifying suitable areas
for recharging groundwater .

Cartography
• What is a map?
A graphic representation (depiction) of all or part of a
geographic territory (realm) in which the real-world
features have been replaced by symbols in their
correct spatial location at a reduced scale.
Maps are perfect interfaces between geo-
information and human users
 Maps are efficient systems to structure and
order information by spatial component

CONT..
Maps perform two important functions:
–Storage medium for information
–Provides a picture of the world to help understand:
• Spatial patterns
• Spatial relationships
• Environmental complexity
Maps tell us:
–Where it is
–What it is
–When it is (often but not always)
–What is nearby
•How far away
•In which direction
•How do I get there

CONT…
Cartography is about efficient communication
of spatial information to:
answer space-related questions
 support spatial behavior
enable spatial problem solving (reasoning,
planning)
support spatial awareness
by
creation and use of maps anytime, anywhere

Coordinate systems
A coordinate system is a grid used to identify
locations on a page or screen that are equivalent
to grid locations on the globe
The coordinates are (x, y) pairs that are based on
some universal origin point for reference.
The data stored in a GIS, in other words, describe
objects from the real world in terms of their
position with respect to a known coordinate
system.
The most commonly used is latitude and
longitude

Latitude and longitude refer to degree, minutes and seconds of arc
from reference lines that run East-West (latitude; equator) or
North-South (longitude; prime meridian)

Cont….
Coordinate system in GIS can broodily divided in two:
Geographic Coordinate system and projected coordinate system.
a. Geographic Coordinate system
Common working window for all world if the data base is in decimal
degree.
The most commonly used for all world is
WGS_1984 ------GCS_WGS_1984

Cont….
Projected coordinate system
• It is location based and displayed if and only if the coordinated
system is related to the position.
• The Universal Transverse Mercator (UTM) It is widely used
because direction is not distorted and can be used for
navigation.
• Ethiopia location: UTM ----North hemisphere
@WGS_1984_UTM_Zone_37N
• Africa---- Adindan_UTM_Zone_37N

Geographic Coordinate Systems
• Not uniform:
– Distances and measures
are not accurate
• Meridians Converge Near
Poles
• 1° longitude:
– @ Equator= 111 km
– @ 60° lat. = 55.8 km
– @ 90° lat. = 0km
Distance of 60° long at equator
vs.
Distance of 60° long at 40° latitude

Geographic Coordinate Systems
• Use Decimal Degrees (angles), 3 digits or less
• Ethiopia located in North East
• NB:
– @ South West of the Prime Meridian, so Longitude (X) is
negative
– @ North of the Equator, Latitude (Y) is positive
Reference latitude
(y=0)
Reference Longitude (central meridian (x=0)

Converting between degrees, minutes seconds and
decimal degrees
• GIS Software takes Geographic Coordinates in Decimal Degrees,
not degrees, minutes, seconds
• Converting is easy
• Divide each value by the number of minutes or seconds in a
degree.
• Example
37 degrees 36 ' 30"
• Divide 36 minutes by 60:
36/60=.60
• Divide 30 seconds by 3600
30/3600=.00833
• Add up the degrees to get the answer
37 degrees + .60 + .0083 = 37.60833 DD

COORDINATE SYSTEM
 Different kinds of coordinate systems are used to position data in space.
 spatial and planar coordinate systems.
 Spatial (or global) coordinate systems are used to locate data either on
the Earth’s surface in a 3D space or on the Earth’s reference surface
(ellipsoid or sphere) in a 2D space.
 Eg. the geographic coordinates in a 2D or 3D space and the geocentric
coordinates, also known as 3D Cartesian coordinates.
 Planar coordinate systems, on
the other hand, are used to locate
data on the flat surface of a map
in a 2D space.
 Eg. 2D Cartesian coordinates
and the 2D polar coordinates
(Projected Coordinate system)
102

COORDINATE SYSTEM
 2D geographic coordinates
 The most widely used global coordinate system consists of lines of
geographic latitude and longitude (lambda or ).
 Lines of equal latitude are called parallels. They form circles on the
surface of the ellipsoid.
 Lines of equal longitude are called meridians and form ellipses
(meridian ellipses) on the ellipsoid
 They are always given in angular units.
 Eg. Point ‘X’
52o 13’ 26.2’’N;
6o 53’ 32.1’’E
 There are several formats for the angular
units of geographic coordinates. The
Degrees:Minutes:Seconds is the most
common format, another the Decimal
Degrees (49.5000°, -123.5000°),
generally with 4-6 decimal numbers.
103

COORDINATE SYSTEM
 3D geographic coordinates
 3D GC are obtained by introducing the ellipsoidal height ‘h’ into the
system.
 The ellipsoidal height (h) of a point is the vertical distance of the point in
question above the ellipsoid & measured in distance units along the
ellipsoidal normal from the point to the ellipsoid surface. 3D geographic
coordinates can be used to define a position on the surface of the
Earth.
 Lat and lon are always given in angular
units, However, h in meter
 Eg. Point ‘X’
52o 13’ 26.2’’N;
6o 53’ 32.1’’E
1200m
104

COORDINATE SYSTEM
 3D geocentric coordinates
 also known as 3D Cartesian coordinates. The system has its origin at
the mass-centre of the Earth with the X- and Y-axes in the plane of the
equator. The X-axis passes through the meridian of Greenwich, and the
Z-axis coincides with the Earth's axis of rotation. The three axes are
mutually orthogonal and form a right-handed system. Geocentric
coordinates can be used to define a position on the surface of the Earth
 It should be noted that the
rotational axis of the Earth changes
its position over time (referred to
as polar motion). To compensate
for this, the mean position of the
pole in the year 1903 (based on
observations between 1900 and
1905) has been used to define the
so-called 'Conventional
International Origin' (CIO).
105

COORDINATE SYSTEM
 2D Cartesian coordinates
 A flat map has only two dimensions: width (left to right) and length
(bottom to top). Transforming the three dimensional Earth into a two-
dimensional map is subject of map projections and coordinate
transformations
 2D CC system is a system of intersecting perpendicular lines, which
contains two principal axes, called the X- and Y-axis.
 The horizontal axis is usually referred to as the X-axis and the vertical
the Y-axis (note that the X-axis is also sometimes called Easting and
the Y-axis the Northing).
 The plane is marked at intervals by
equally spaced coordinate lines,
called the map grid. Giving two
numerical coordinates x and y for
point P, one can now precisely and
objectively specify any location P on
the map.
106

COORDINATE SYSTEM
 2D polar coordinates
 Another possibility of defining a point in a plane is by polar coordinates
( ,d).
 ‘d’ is a distance from the origin to the point concerned and the angle ‘ ’
between a fixed (or zero) direction and the direction to the point.
 The angle ‘ ’ is called azimuth or bearing and is measured in a
clockwise direction. It is given in angular units while the distance d is
expressed in length units.
 Bearings are always related to a
fixed direction (initial bearing) or a
datum line. In practice three different
directions are widely used: True
North, Grid North and Magnetic
North
107

Map projections
• A map projection is a mathematically described technique of
how to represent the Earth’s curved surface on a flat map.
– To represent parts of the surface of the Earth on a flat paper
map or on a computer screen, the curved horizontal
reference surface must be mapped onto the 2D mapping
plane.
 Mapping onto a 2D mapping
plane means transforming each
point on the reference surface
with geographic
coordinates (f, l) to a set of
Cartesian coordinates (x,y)
representing positions on the
map plane

Cont…
• Equations
– Example
• Map projection equations for the Mercator projection (spherical
assumption)
Forward Equation
Inverse Equation

Cont…
Equations
 Example
 Suppose a point, located at 60oN and 130oW, is projected
on a map that uses the Mercator projection (where the
reference surface is a sphere with a radius of 6371000 m.
and the central meridian (lo) is 0o, equal to the Greenwich
meridian).
 Using the forward mapping equation of the Mercator
projection, the values found for the Cartesian coordinates
are for x = -14,455,340m and for y = 8,390,339m.

Map projections Classification
 Map projections can be described in terms of
their:
 class (cylindrical, conical or azimuthal),
 point of secancy (tangent or secant),
 aspect (normal, transverse or oblique), and
 distortion property (equivalent, equidistant or
conformal).

Map projections
Classification

Map projections classification
Class

Aspect
 Projections can also be described in terms of the direction of the
projection plane's orientation (whether cylinder, plane or cone) with
respect to the globe. This is called the aspect of a map projection.
 The three possible aspects are normal, transverse and oblique.
 In a normal projection, the main orientation of the projection surface
is parallel to the Earth's axis.
 Transverse projection has its main orientation perpendicular to the
Earth's axis.
 Oblique projections are all other, non-parallel and non-
perpendicular, cases.
Normal Projection Transverse Projection Oblique Projection

MAP PROJECTIONS CLASSIFICATION
Conformal cylindrical projection with a transverse
cylinder and secant projection plane.
(e.g. Universal Transverse Mercator)

Conformal conical projection with a normal cone and
tangent projection plane
(e.g. Lambert conformal conic)

Conformal azimuthal projection with a tangent polar
projection Plane
(e.g. Universal Polar Stereographic)

MAP PROJECTIONS SELECTION
The selection of a map projection for a particular area can be made on
the basis of:
 the shape of the area,
 the location (and orientation) of the area, and
 the purpose of the map.
 Normal cylindrical projections are typically used to map the World in
its entirety.
 Conical projections are often used to map the different continents,
 Azimuthal projection may be used to map the polar areas.
 For topographic and large-scale maps, conformality and equidistance
are important properties.
 The Universal Transverse Mercator (UTM)
 Other projections Transverse Mercator (Argentina, Colombia,
Australia, Ghana, S-Africa, Egypt use it) and the Lambert
Conformal Conic (in use for France, Spain, Morocco, Algeria).

MAP PROJECTIONS
Universal Transverse Mercator
International Standard
 Conformal Cylindrical (transverse secant) projection
• The Universal Transverse
Mercator (UTM) projection
uses a transverse cylinder,
secant to the reference
surface.
• It is recommended for
topographic mapping by the
United Nations Cartography
Committee in 1952.

SPATIAL REFERENCING
THE ELLIPSOID
 Grids and Datums of Ethiopia
 Source:
http://coordtrans.com/coordtrans/guide.asp?section=SupportedCountries&platform=winxp
 Ethiopia
 Adindan
 UTM Zone 37N
 UTM Zone 38N
 Massawa
 UTM Zone 37N
 WGS72
 UTM Zone 35N
 UTM Zone 36N
 UTM Zone 37N
 UTM Zone 38N
 WGS84
 UTM Zone 35N
 UTM Zone 36N
 UTM Zone 37N
 UTM Zone 38N

DISTORTION IN A MAP PROJECTION
Converting a sphere to a flat surface results in distortion.
This is the most profound single fact about map
projections
The four spatial properties subject to distortion in a
projection are:·
 Shape
 Area
 Distance
 Direction

DISTORTION IN A MAP PROJECTION
Shape
 If a map preserves shape, then feature outlines (like country
boundaries) look the same on the map as they do on the
earth. A map that preserves shape is conformal.
 Even on a conformal map, shapes are a bit distorted for very
large areas, like continents.
 A conformal map distorts area—most features are depicted
too large or too small.
 The amount of distortion, however, is regular along some
lines in the map.

 For example, it may be constant along any given parallel. This
would mean that features lying on the 20th parallel are equally
distorted, features on the 40th parallel are equally distorted
(but differently from those on the 20th parallel), and so on.
 This category includes:·
 Topographic maps and cadastral (land parcel) maps·
 Navigation charts (for plotting course bearings and wind
direction)·
 Civil engineering maps·
 Military maps·
 Weather maps (for showing the local direction in which
weather systems are moving)

CONT…
 For example, it may be constant along any given parallel. This
would mean that features lying on the 20th parallel are equally
distorted, features on the 40th parallel are equally distorted (but
differently from those on the 20th parallel), and so on.
 This category includes:·
 Topographic maps and cadastral (land parcel) maps·
 Navigation charts (for plotting course bearings and wind
direction)·
 Civil engineering maps·
 Military maps·
 Weather maps (for showing the local direction in which weather
systems are moving)

CONT…
Area
 Maps that preserve area On an equal-area projection, the size of any area
on the map is in true proportion to its size on the earth.
 You should use equal-area projections to show:·
 The density of an attribute with dots (for example, population
density)·
 The spatial extent of a categorical attribute (for example, land use
maps)·
 Quantitative attributes by area (for example, Gross Domestic Product by
country)
 Equal-area maps have also been used as world political maps to correct
popular misconceptions about the relative sizes of countries.
 In an equal-area map, the shapes of most features are distorted. No map
can preserve both shape and area for the whole world, although some
come close over sizeable regions.

CONT…
Distance
 Projection can distort measures of true distance. Accurate
distance is maintained for only certain parallels or
meridians unless the map is very localized.
 Maps are said to be equidistant if distance from the map
projection's center to all points is accurate.

CONT…
Direction
Direction, or azimuth, is measured in degrees of angle from
north. On the earth, this means that the direction from a to b is
the angle between the meridian on which a lies and the great
circle arc connecting a to b.
If the azimuth value from a to b is the
same on a map as on the earth,
then the map preserves direction from
a to b. An azimuthal projection is one
that preserves direction for all
straight lines passing through a single,
specified point. No map has true direction everywhere.

A few projections with different properties

Cont…
On figure above
• The Lambert Conformal Conic preserves shape.
• The Mollweide preserves area.
• The Orthographic projection preserves
direction.
• The Azimuthal Equidistant preserves both
distance and direction.
• The Winkel Tripel is a compromise projection.

Introduction to Geographic Information system and Remote Sensing (RS)

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