remote sensing from space c5646. course layout lectures practicals assessment

Remote Sensing from Remote Sensing from SpaceSpace

C5646C5646

Course Layout

Lectures Practicals Assessment

Lectures

Week 1Introduction, course layout Week 2 The electromagnetic energy, energy source, wave theory, particle theory, Week 3The electromagnetic spectrum Week 4Radiation and the atmosphere, spectral signature

Lectures

Week 5Image display, sensors and platforms Week 6Spectral Resolution, spatial resolution, temporal resolution Week 7Test No. 1Remotely sensed images, multispectral images, type of images Week 8Passive sensors, active sensors

Lectures

Week 9Image Interpretation and analysis, visual interpretation, element of

visual interpretation Week 10Digital image processing, preprocessing, image enhancement Week 11 Image transformation, image classification and analysis Week 12Image classification, information and spectral classes

Lectures

Week 13

Supervised classification, unsupervised classification

Week 14

Test No. 2

Radar, basic principles, radar system in remote sensing

Week 15

Range resolution, radar geometry, radar images

Practicals

Digital Image ProcessingPrint : intro_e.pdf

exerc_e.pdfHands-on assignments to be handed in before week 14

Project Proposal Assigmentsee AssignX.pdfDate Due : week 8

Assesment

Test 2x 30% Coursework (2) 20% Final Exam 50%

Total 100%

Remote SensingRemote Sensing

Remote SensingRemote Sensing is the acquisition and measurement is the acquisition and measurement of data/information on some property(ies) of a of data/information on some property(ies) of a phenomenon, object, or material by a recording phenomenon, object, or material by a recording device not in physical, intimate contact with the device not in physical, intimate contact with the feature(s) under surveillance; feature(s) under surveillance;

Techniques involve amassing knowledge pertinent to Techniques involve amassing knowledge pertinent to environments by measuring force fields, environments by measuring force fields, electromagnetic radiation, or acoustic energy electromagnetic radiation, or acoustic energy employing cameras, lasers, radio frequency receivers, employing cameras, lasers, radio frequency receivers, radar systems, sonar, thermal devices, and other radar systems, sonar, thermal devices, and other instruments.instruments.

Remote SensingRemote Sensing

• Remote Sensing:Remote Sensing: The techniques The techniques for collecting information about an for collecting information about an object and its surroundings from a object and its surroundings from a distance without contactdistance without contact

• Components of Remote Sensing:Components of Remote Sensing:– the source, the sensor, interaction with the source, the sensor, interaction with

the Earth’s surface, interaction with the the Earth’s surface, interaction with the atmosphereatmosphere

Faculty of Geoinformation Science and EngineeringUniversiti Teknologi Malaysia81310 UTM Skudai. Johor Bahruhttp://www.fksg.utm.my

Mechanisms


Remote Sensing Principle

Some Basic TermsSome Basic Terms

• Spectral responseSpectral response is a characteristic is a characteristic used to identify individual objects present used to identify individual objects present on an image or photographon an image or photograph

• ResolutionResolution describes the number of describes the number of pixels you can display on a screen devicepixels you can display on a screen device

• Spatial resolutionSpatial resolution is a measure of the is a measure of the smallest separation between two objects smallest separation between two objects that can be resolved by the sensorthat can be resolved by the sensor

The First Application of The First Application of Remote SensingRemote Sensing

A Brief Chronology of Remote Sensing

1826 - The invention of photography 1960’s - The satellite era, and the space race between the USA and USSR.

1960’s - The setting up of NASA.

1960’s - First operational meteorological satellites

1960’s - The setting up of National Space Agencies


1970’s - Launching of the first generation of earth resource satellites

1970’s - Setting up of International Remote Sensing Bodies

1980’s - Setting up of Specific Remote Sensing Journals - Continued deployment of Earth

Resource satellites by NASA

1990’s - Launching of earth resource satellites by national space agencies and commercial companies


Satellite remote sensing first received operational status in 1966 in the study of meteorology.

At this stage a series of orbiting and geo-stationary American satellites were inaugurated, with the intention that they would yield information to any suitably equipped and relatively modestly priced receiver anywhere in the world.

Wave Theory

Electromagnetic radiation consists of an electrical field (E) which varies in magnitude in a direction perpendicular to the direction in which the radiation is travelling, and a magnetic field (M) oriented at right angles to the electrical field.

Both these fields travel at the speed of light (c)

Wavelength and Frequency

Wavelength is measured in metres (m) or some factor of metres such as: • nanometers (nm, 10-9 metres), • micrometers (m, 10-6 metres) or • centimetres (cm, 10-2 metres).

Frequency refers to the number of cycles of a wave passing a fixed point per unit of time. Frequency is normally measured in hertz (Hz), equivalent to one

cycle per second, and various multiples of hertz.

Wave Theory

From basic physics, waves obey the general equation:

c = v Since c is essentially a constant (3 x 108 m/sec), frequency v and wavelength for any given wave are related inversely, and either term can be used to characterise a wave into a particular form.

Particle Theory

Particle (Quantum) theory suggests that EM radiation is composed of many discrete units called photons or quanta. The energy of a quantum is given as:

Q = h.vwhere:

Q = energy of a quantum (Joules - J)

h = Planks constant, (6.626 x 10-34 J/sec)

v = frequency

Particle Theory

We can combine the Wave and Particle theories for EM radiation by substituting v = c/ in the above equation. This gives us:

Q = h.c

From this we can see that the energy of a quantum is inversely proportional to its wavelength. Thus, the longer the wavelength of EM radiation, the lower its energy content.

Particle Theory

This has important implications for remote sensing from the standpoint that:

Naturally emitted long wavelength radiation (e.g. microwaves) from terrain features, is more difficult to sense than radiation of shorter wavelengths, such as emitted thermal IR.

Therefore, systems operating at long wavelengths must “view” large areas of the earth at any given time in order to obtain a detectable energy signal

Electromagnetic Spectrum

The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x-rays) to the longer wavelengths (including microwaves and broadcast radio waves).

There are several regions of the electromagnetic spectrum which are useful for remote sensing.

Visible Spectrum

The light which our eyes - our "remote sensors" - can detect is part of the visible spectrum.

It is important to recognise how small the visible portion is relative to the rest of the spectrum.

There is a lot of radiation around us which is "invisible" to our eyes, but can be detected by other remote sensing instruments and used to our advantage.

Visible Spectrum

The visible wavelengths cover a range from approximately 0.4 to 0.7 m.

The longest visible wavelength is red and the shortest is violet.

It is important to note that this is the only portion of the EM spectrum we can associate with the concept of colours.

VIOLET: mBLUE: mGREENm YELLOW:mORANGE:mRED:m

Visible Spectrum

Blue, green, and red are the primary colours or wavelengths of the visible spectrum.

They are defined as such because no single primary colour can be created from the other two, but all other colours can be formed by combining blue, green, and red in various proportions.

Although we see sunlight as a uniform or homogeneous colour, it is actually composed of various wavelengths.

The visible portion of this radiation can be shown when sunlight is passed through a prism,

Infrared(IR)Region

The IR Region covers the wavelength range from approximately 0.7 m to 100 m - more than 100 times as wide as the visible portion!

The infrared region can be divided into two categories based on their radiation properties - the reflected IR, and the emitted or thermal IR.

Reflected and Thermal IR

Radiation in the reflected IR region is used for remote sensing purposes in ways very similar to radiation in the visible portion. The reflected IR covers wavelengths from approximately 0.7 m to 3.0 m.

The thermal IR region is quite different than the visible and reflected IR portions, as this energy is essentially the radiation that is emitted from the Earth's surface in the form of heat. The thermal IR covers wavelengths from approximately 3.0 m to 100 m.

Microwave Region

The portion of the spectrum of more recent interest to remote sensing is the microwave region from about 1 mm to 1 m.

This covers the longest wavelengths used for remote sensing.

The shorter wavelengths have properties similar to the thermal infrared region while the longer wavelengths approach the wavelengths used for radio broadcasts.

Emission of Radiation from Energy Sources

Each energy/radiation source, or radiator, emits a characteristic array of radiation waves.

A useful concept, widely used by physicists in the study of radiation, is that of a blackbody.

A blackbody is defined as an object or substance that absorbs all of the energy incident upon it, and emits the maximum amount of radiation at all wavelengths.

A series of laws relate to the comparison of natural surfaces/radiators to those of a black-body:

Stefan-Boltzmann Law

All matter at temperatures above absolute zero (-273 oC) continually emit EM radiation. As well as the sun, terrestrial objects are also sources of radiation, though of a different magnitude and spectral composition than that of the sun.

The amount of energy than an object radiates can be expressed as follows:

M = T4

M = total radiant exitance from the surface of a material (watts m-2) = Stefan-Boltzmann constant, (5.6697 x 10-8 W m-2 K-4)T = absolute temperature (K) of the emitting material

Stefan-Boltzmann Law

It is important to note that the total energy emitted from an object varies as T4 and therefore increases rapidly with increases in temperature.

Also, this law is expressed for an energy source that behaves like a blackbody, i.e. as a hypothetical radiator that totally absorbs and re-emits all energy that is incident upon it…….actual objects only approach this ideal.

Kirchoffs law

Since no real body is a perfect emitter, its exitance is less than that of a black-body.

Obviously it is important to know how the real exitance (M) compares with the black-body exitance (Mb)

This may be established by looking at the ratio of M/Mb, which gives the emissivity (e) of the real body.

M = eMb

Thus a black-body = 1, and a white-body = 0

Weins Displacement law

Just as total energy varies with temperature, the spectral distribution of energy varies also.

The dominant wavelength at which a blackbody radiation curve reached a maximum, is related to temperature by Weins Law:

m = A T

m = wavelength of maximum spectral radiant exitance, mA = 2898 m, KT = Temperature, K

Upon Striking an Object the Irradiance Will Upon Striking an Object the Irradiance Will Have the Following Response:Have the Following Response:– TransmittanceTransmittance - some radiation will penetrate - some radiation will penetrate

into certain surface media such as water into certain surface media such as water

– AbsorptanceAbsorptance - some radiation will be absorbed - some radiation will be absorbed through electron or molecular reactions within through electron or molecular reactions within the medium encounteredthe medium encountered

– ReflectanceReflectance - some radiation will, in effect, be - some radiation will, in effect, be reflected (and scattered) away from the target reflected (and scattered) away from the target at different angles at different angles

Some Basic TermsSome Basic Terms

Reflected Light Remote Sensing

Light Interaction with Surfaces

The Brightness of Surfaces - What Controls This?

(1) Reflectance

(2) Roughness and the BRDF

Effect of Different Types of Scattering/Reflection

(3) The Effect of Topography

On the shaded hill slopes, the sun's illumination is spread over a larger area than on the sunny slopes. So the amount of energy per unit area is less. This means that there is less light available for reflection, and the shaded hill slopes are darker.

The Effect of the Atmosphere on Spectral Data

Path Radiance (Lp)

Atmospheric Transmissivity (T)

Energy Interaction with the Atmosphere

Irrespective of source, all radiation detected by remote sensors passes through some distance (path length) of atmosphere.

The net effect of the atmosphere varies with:

• Differences in path length• Magnitude of the energy signal that is being

sensed• Atmospheric conditions present• The wavelengths involved.

The Process

A. Energy Source – An energy source generates electromagnetic radiation (EMR) that illuminates objects it encounters.

B. Radiation and the Atmosphere – As the EMR encounters the atmosphere, only a fraction of it passes through to the ground.

C. Radiation and the Surface – EMR is absorbed, transmitted, or reflected by objects on the Earth’s surface.

The Process

D. Sensor records Radiation – EMR that is reflected is then recorded by a sensor (via a satellite or other platform).

E. Transmitting Sensor Data – EMR data from the sensor is then transferred to a receiving center where it is transformed into an image.

F. Data Analysis – The data is analyzed and pertinent information is extracted.

G. Remote Sensing Application – The data is used to increase understanding about a particular locale or issue.

B. Radiation and the Atmosphere

When Electromagnetic Radiation(EMR) interacts with the atmosphere, one or more of the following three processes may occur:

Scattering

Refraction

Absorption

Scattering

Upon reaching the atmosphere, EMR encounters large molecules or particles that cause scattering. Water vapor and dust particles are examples of substances that contribute to scattering.

Shorter wavelengths scatter more often than longer wavelengths.

Since blue wavelengths are shorter than red or green wavelengths, they are scattered more easily, causing the sky to appear blue.

Scattering

Atmospheric scattering is the unpredictable diffusion of radiation by particles in the atmosphere.

Three types of scattering can be distinguished, depending on the relationship between the diameter of the scattering particle (a) and the wavelength of the radiation ().

Scattering of EM energy by the atmosphere

Rayleigh Scatter

a < Rayleigh scatter is common when radiation interacts with

atmospheric molecules (gas molecules) and other tiny particles (aerosols) that are much smaller in diameter that the wavelength of the interacting radiation.

The effect of Rayleigh scatter is inversely proportional to the fourth power of the wavelength. As a result, short wavelengths are more likely to be scattered than long wavelengths.

Rayleigh scatter is one of the principal causes of haze in imagery. Visually haze diminishes the crispness or contrast of an image.

Relationship between path length of EM radiation and the level of atmospheric scatter

Mie Scatter

a <=> Mie scatter exists when the atmospheric particle

diameter is essentially equal to the energy wavelengths being sensed.

Water vapour and dust particles are major causes of Mie scatter. This type of scatter tends to influence longer wavelengths than Rayleigh scatter.

Although Rayleigh scatter tends to dominate under most atmospheric conditions, Mie scatter is significant in slightly overcast ones.

Non-selective scatter

a > Non-selective scatter is more of a problem, and occurs

when the diameter of the particles causing scatter are much larger than the wavelengths being sensed.

Water droplets, that commonly have diameters of between 5 and 100m, can cause such scatter, and can affect all visible and near - to - mid-IR wavelengths equally.

Consequently, this scattering is “non-selective” with respect to wavelength. In the visible wavelengths, equal quantities of blue green and red light are scattered.

Non-Selective scatter of EM radiation by a cloud

Absorption

In contrast to scatter, atmospheric absorption results in the effective loss of energy to atmospheric constituents.

This normally involves absorption of energy at a given wavelength.

The most efficient absorbers of solar radiation in this regard are:

• Water Vapour• Carbon Dioxide• Ozone

Absorption of EM energy by the atmosphere

C. Radiation and the Surface

Electromagnetic radiation that passes through the atmosphere interacts with the surface in three ways:

Reflection

Absorption

Transmission1. Reflection – EMR that is reflected off

of the surface

2. Absorption – EMR that is absorbed by the surface

3. Transmission – EMR that moves through a surface

Reflection

In remote sensing, reflection is a very significant factor for recording the Earth’s surface.

There are two important types of reflection:

1. Specular

2. DiffuseA surface’s reflectance is generally a combination of specular and diffuse reflection.

Reflection

Specular reflection (1) occurs on smooth surfaces and is often called mirror reflection. Specular reflection causes light to be reflected in a single direction at an angle equal to the angle of incidence.

Diffuse reflection (2) occurs on rough surfaces and causes light to be reflected in several directions.

Specular reflection

Diffuse reflection

Reflectance of Surfaces

Most earth surface features lie somewhere between perfectly specular or perfectly diffuse reflectors.

Whether a particular target reflects specularly or diffusely, or somewhere in between, depends on the surface roughness of the feature in comparison to the wavelength of the incoming radiation.

If the wavelengths are much smaller than the surface variations

or the particle sizes, diffuse reflection will dominate.

The relationship between these three energy interactions :

E i () = E r () + E a () + E t ()

E i = Incident energy

E r = Reflected energy

E a = Absorbed energy

E t = Transmitted energy

Atmospheric Windows

Because these gases absorb electromagnetic energy in specific wavebands, they strongly influence “where we look” spectrally with any given remote sensing system.

The wavelength ranges in which the atmosphere is particularly ‘Transmissive’ are referred to as “atmospheric windows”

Atmospheric Windows

Some sensors, especially those on meteorological satellites, seek to directly measure absorption phenomena such as those associated with CO2 and other gaseous molecules.

Note that the atmosphere is nearly opaque to EM radiation in the mid and far IR

In the microwave region, by contrast, most of the EM radiation moves through unimpeded - so that radar at commonly used wavelengths will nearly all reach the Earth surface unimpeded - although specific wavelengths are scattered by raindrops.


Remote Sensing Principle: Cont…

Energy Source or Illumination (A) - the first requirement for remote sensing is to have an energy source which illuminates or provides electromagnetic energy to the target of interest.

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.

Interaction with the Target (C) - once the energy makes its way to the target through the atmosphere, it interacts with the target depending on the properties of both the target and the radiation.

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.

Transmission, 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).

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.


The Remote Sensing Process

Steps involved in the Process1. Identifying the problem2. Collection of data3. Analyze data4. Information output

The Answer

The most obvious source of electromagnetic energy and radiation is the sun. The sun provides the initial energy source for much of the remote sensing of the Earth surface. The remote sensing device that we humans use to detect radiation from the sun is our eyes. Yes, they can be considered remote sensors - and very good ones - as they detect the visible light from the sun, which allows us to see.

How much have you learned?

Assume the speed of light to be 3x108 m/s. If the frequency of an electromagnetic wave is 500,000 GHz (GHz = gigahertz = 109 m/s), what is the wavelength of that radiation? Express your answer in micrometres (mm).

The Answer

Using the equation for the relationship between wavelength and frequency, let's calculate the wavelength of radiation of a frequency of

500,000 GHz.

Since micrometres (mm) are equal to 10-6 m, we divide this by

1x10-6 to get 0.6 mm as the answer. This happens to correspond to the wavelength of light that we see as the colour orange.

remote sensing from space c5646. course layout lectures practicals assessment

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