3 Lectures Week 1 Introduction, course layout Week 2 Week 2The electromagnetic energy, energy source, wave theory,particle theory,Week 3The electromagnetic spectrumWeek 4Radiation and the atmosphere, spectral signature
4 Lectures Week 5 Image display, sensors and platforms Week 6 Week 6Spectral Resolution, spatial resolution, temporal resolutionWeek 7Test No. 1Remotely sensed images, multispectral images, type of imagesWeek 8Passive sensors, active sensors
5 LecturesWeek 9Image Interpretation and analysis, visual interpretation, element of visual interpretationWeek 10Digital image processing, preprocessing, image enhancementWeek 11Image transformation, image classification and analysisWeek 12Image classification, information and spectral classes
10 Remote SensingRemote 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.
11 Remote SensingRemote Sensing: The techniques for collecting information about an object and its surroundings from a distance without contactComponents of Remote Sensing:the source, the sensor, interaction with the Earth’s surface, interaction with the atmosphere
14 Some Basic TermsSpectral response is a characteristic used to identify individual objects present on an image or photographResolution describes the number of pixels you can display on a screen deviceSpatial resolution is a measure of the smallest separation between two objects that can be resolved by the sensor
16 A Brief Chronology of Remote Sensing The invention of photography1960’s - The satellite era, and the space racebetween the USA and USSR.1960’s - The setting up of NASA.1960’s - First operational meteorologicalsatellites1960’s - The setting up of NationalSpace Agencies
17 A Brief Chronology of Remote Sensing 1970’s - Launching of the first generation of earth resource satellites1970’s - Setting up of International Remote Sensing Bodies1980’s - Setting up of Specific Remote Sensing Journals- Continued deployment of EarthResource satellites by NASA1990’s - Launching of earth resource satellites by national space agencies and commercial companies
18 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.
19 Wave TheoryElectromagnetic 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)
21 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) orcentimetres (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.
23 Wave TheoryFrom basic physics, waves obey the general equation:c = v lSince 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.
24 Particle TheoryParticle (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 J/sec)v = frequency
25 Particle TheoryWe can combine the Wave and Particle theories for EM radiation by substituting v = c/l in the above equation. This gives us:Q = h.clFrom 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.
26 Particle TheoryThis 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
28 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.
30 Visible SpectrumThe 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.
32 Visible SpectrumThe 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.
34 VIOLET:. 400 - 0. 446 mm BLUE:. 446 - 0. 500 mm GREEN:. 500 - 0 VIOLET: mm BLUE: mm GREEN: mm YELLOW: mm ORANGE: mm RED: mm
35 Visible SpectrumBlue, 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,
37 Infrared(IR)RegionThe IR Region covers the wavelength range from approximately 0.7 m to 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.
39 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 mm to 100 mm.
40 Microwave RegionThe 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.
43 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:
44 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 T4M = total radiant exitance from the surface of a material (watts m-2)s = Stefan-Boltzmann constant, ( x 10-8 W m-2 K-4)T = absolute temperature (K) of the emitting material
45 Stefan-Boltzmann LawIt 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.
46 Kirchoffs lawSince 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 = eMbThus a black-body = 1, and a white-body = 0
47 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 = ATlm = wavelength of maximum spectral radiant exitance, mmA = 2898 mm, KT = Temperature, K
50 Some Basic TermsUpon Striking an Object the Irradiance Will Have the Following Response:Transmittance - some radiation will penetrate into certain surface media such as waterAbsorptance - some radiation will be absorbed through electron or molecular reactions within the medium encounteredReflectance - some radiation will, in effect, be reflected (and scattered) away from the target at different angles
53 The Brightness of Surfaces - What Controls This? (1) Reflectance(2) Roughness and the BRDF
54 Effect of Different Types of Scattering/Reflection
55 (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.
56 The Effect of the Atmosphere on Spectral Data Path Radiance (Lp)Atmospheric Transmissivity (T)
58 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 lengthMagnitude of the energy signal that is being sensedAtmospheric conditions presentThe wavelengths involved.
59 C5646 Introduction4/12/2017The ProcessEnergy 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
60 The ProcessSensor 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.
61 B. Radiation and the Atmosphere When Electromagnetic Radiation(EMR) interacts with theatmosphere, one or more of thefollowing three processes mayoccur:ScatteringRefractionAbsorption
62 ScatteringUpon 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.
63 ScatteringAtmospheric 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 ().
65 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.
66 Relationship between path length of EM radiation and the level of atmospheric scatter
68 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.
69 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.
70 Non-Selective scatter of EM radiation by a cloud
71 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 VapourCarbon DioxideOzone
73 C. Radiation and the Surface Electromagnetic radiation that passes through the atmosphere interacts with the surface in three ways:ReflectionAbsorptionTransmissionReflection – EMR that is reflected off of the surfaceAbsorption – EMR that is absorbed by the surfaceTransmission – EMR that moves through a surface
74 ReflectionIn remote sensing, reflection is a very significant factor for recording the Earth’s surface. There are two important types of reflection:SpecularDiffuseA surface’s reflectance is generally a combination of specular and diffuse reflection.
75 ReflectionSpecular 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.
78 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.
79 The relationship between these three energy interactions : E i (l) = E r (l) + E a (l) + E t (l)E i = Incident energyE r = Reflected energyE a = Absorbed energyE t = Transmitted energy
80 Atmospheric WindowsBecause 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”
81 Atmospheric WindowsSome 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 IRIn 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.
82 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.
83 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.
84 The Remote Sensing Process Steps involved in the ProcessIdentifying the problemCollection of dataAnalyze dataInformation output
85 The AnswerThe 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.
86 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).
87 The AnswerUsing 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 by1x10-6 to get 0.6 mm as the answer. This happens to correspondto the wavelength of light that we see as the colour orange.