Remote Sensing from Space C5646 Introduction 4/12/2017 Remote Sensing from Space C5646 Mohamad Abdul Rahman

Course Layout Lectures Practicals Assessment

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

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

Lectures Week 9 Image Interpretation and analysis, visual interpretation, element of visual interpretation   Week 10 Digital image processing, preprocessing, image enhancement Week 11 Image transformation, image classification and analysis Week 12 Image 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 Processing Print : intro_e.pdf exerc_e.pdf Hands-on assignments to be handed in before week 14 Project Proposal Assigment see AssignX.pdf Date Due : week 8

Practicals Digital Image Processing Print : intro_e.pdf exerc_e.pdf Hands-on assignments to be handed in before week 14 Project Proposal Assigment see AssignX.pdf Date Due : week 8

Assesment Test 2x 30% Coursework (2) 20% Final Exam 50% Total 100%

Remote Sensing Remote Sensing is the acquisition and measurement of data/information on some property(ies) of a phenomenon, object, or material by a recording device not in physical, intimate contact with the feature(s) under surveillance; Techniques involve amassing knowledge pertinent to environments by measuring force fields, electromagnetic radiation, or acoustic energy employing cameras, lasers, radio frequency receivers, radar systems, sonar, thermal devices, and other instruments.

Remote Sensing Remote Sensing: The techniques for collecting information about an object and its surroundings from a distance without contact Components of Remote Sensing: the source, the sensor, interaction with the Earth’s surface, interaction with the atmosphere

Mechanisms

Remote Sensing Principle

Some Basic Terms Spectral response is a characteristic used to identify individual objects present on an image or photograph Resolution describes the number of pixels you can display on a screen device Spatial resolution is a measure of the smallest separation between two objects that can be resolved by the sensor

The First Application of Remote 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

A Brief Chronology of Remote Sensing 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

A Brief Chronology of Remote Sensing 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 l Since c is essentially a constant (3 x 108 m/sec), frequency v and wavelength l 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.v where: 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/l in the above equation. This gives us: Q = h.c l 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

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:. 400 - 0. 446 mm BLUE:. 446 - 0. 500 mm GREEN:. 500 - 0 VIOLET: 0.400 - 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

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 mm - 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 mm to 3.0 mm. 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 mm to 100 mm.

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.

Radiation Emission

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 M = s T4 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 = s T4 M = total radiant exitance from the surface of a material (watts m-2) s = 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: l m = A T lm = wavelength of maximum spectral radiant exitance, mm A = 2898 mm, K T = Temperature, K

Some Basic Terms Upon Striking an Object the Irradiance Will Have the Following Response: Transmittance - some radiation will penetrate into certain surface media such as water Absorptance - some radiation will be absorbed through electron or molecular reactions within the medium encountered Reflectance - some radiation will, in effect, be reflected (and scattered) away from the target at different angles

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 Interactions with the Atmpsphere

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.

C5646 Introduction 4/12/2017 The Process Energy Source – An energy source generates electromagnetic radiation (EMR) that illuminates objects it encounters. Radiation and the Atmosphere – As the EMR encounters the atmosphere, only a fraction of it passes through to the ground. Radiation and the Surface – EMR is absorbed, transmitted, or reflected by objects on the Earth’s surface. Mohamad Abdul Rahman

The Process Sensor records Radiation – EMR that is reflected is then recorded by a sensor (via a satellite or other platform). Transmitting Sensor Data – EMR data from the sensor is then transferred to a receiving center where it is transformed into an image. Data Analysis – The data is analyzed and pertinent information is extracted. 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 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 100mm, 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 Water Vapour Carbon Dioxide Ozone 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 Transmission Reflection – EMR that is reflected off of the surface Absorption – EMR that is absorbed by the surface 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: Specular Diffuse A 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 (l) = E r (l) + E a (l) + E t (l) 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.

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 Process Identifying the problem Collection of data Analyze data 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.

TAMAT