Principles of Remote sensing PDF

Department of Geography M.Sc. in Applied Geography and Geoinformatics Semester-I Principles of Remote Sensing (PAGTA11101) DR. SWAGATA GHOSH  Department of Geography Introductor...

Department of Geography M.Sc. in Applied Geography and Geoinformatics Semester-I Principles of Remote Sensing (PAGTA11101) DR. SWAGATA GHOSH  Department of Geography Introductory Session 2  Department of Geography Course Objectives: The course gives an insight into the theoretical aspects of remote sensing. After the course students will be able to understand the information content of remotely sensed data and how to retrieve the information. Students will be able to decide which remote sensing techniques suite specific needs. Student Learning Outcomes: Analyses Remote Sensing data for finding the problems and develop appropriate methods for studying and/or solving the problems using remote sensing techniques. Develop a technical skills for data interpretation and analysis and generate a integrate results for solution findings. Formulate and carry out independent research in the general field of remote sensing, possibly as part of a multi- disciplinary research and development project. 3  Department of Geography Credit structure of the Course T P Total 4 0 4 4  Department of Geography Assessment Scheme of the Course IA ES Total 40 60 100 5  Department of Geography Time slots allotted Day 10.00-11.00 11.00-12.00 12.05-1.05 2.30-3.30 3.35-4.35 4.35-5.35 Mon  Tue  Wed  Thu Fri 6  Department of Geography Unit I: Introduction to Remote Sensing: Concepts Definition, Components, History Development, Electro Magnetic Radiation, Electro Magnetic Spectrum, Theories of EMR: Wave and Particle Theory. Types of Remote Sensing: Based on Energy source and Electro Magnetic Spectrum. Energy Interaction with Earth’s atmosphere: Scattering: Rayleigh, Mie and Non selective; Absorption, and Refraction, Atmospheric Windows, Energy Interaction with Earth Surface: Reflection, Absorption Transmission. Unit II: Spectral Signature: Interaction with soil, water and vegetation and other features, Platforms, Sensors, Orbits: Types of platforms: Ground Based, Airborne and Space borne Types of sensors: Active and Passive, Resolution and its types: Spatial, Spectral, Radiometric and Temporal, False color composite, Elements of Visual Image Interpretation, Satellite Data Products: Landsat, MODIS, IRS, CartoSat, Spot and others Products. Unit III: Basics and Image Rectification: Image, Digital Image, Single Layer Digital Image, Multispectral Digital Image; Image Rectification: Radiometric Correction and Geometric Correction, Image Enhancement Techniques: Contrast, Contrast Enhancement – Linear and Non-linear, Histogram Equalization, Density Slicing, Spatial Filtering – Low and High frequency Filtering, Edge Enhancement, Band Rationing, Band Combination. Unit IV: Image Classification: Unsupervised Classification, Advantages and Disadvantages of Unsupervised Classification, Supervised Classification – Steps of Supervised Classification, Algorithms of Classification – Parallelepiped, Minimum Distance to Mean and Maximum Likelihood, Accuracy Assessment.  Department of Geography References ▪ Basudeb Bhatta: Remote Sensing & GIS (2nd Edition) ▪ M. ANJI REDDY Remote Sensing and Geographical Information Systems ▪ Siddiqui (2011). Concepts And Techniques Of Geoinformatics ▪ Lillisand,T., Keifer, Ralph W., Chipman, J. 2011. Remote Sensing and Image Interpretation. John Wiley Pub., New York. ▪ Campbell, J.B. 1996(2nd edition). Introduction to Remote Sensing. Taylor and Francis, London. ▪ Curran, P. 1985. Principles of Remote Sensing. Longman, London. ▪ Sabins, J.F.F. 1997. Remote Sensing: Principles and Interpretation. W.H. Freeman & Co., New York. ▪ Jensen, J.R. 2013. Remote Sensing and Environment. Pearson India ▪ Kumar, S. 2005. Basics of Remote Sensing and GIS. Laxmi Pub. ▪ Joseph, G. 2005: Fundamentals of Remote Sensing, United Press India. ▪ Jensen J. R., 2004: Introductory Digital Image Processing: A Remote Sensing Perspective, Prentice Hall. ▪ Richards, John A.. Remote Sensing Digital Image Analysis: An Introduction. Germany, Springer Berlin Heidelberg, 2013. ▪ Kumar, S.. Basics of Remote Sensing and GIS. India, Laxmi Publications, 2005. ▪ Liu, Jian Guo, and Mason, Philippa J.. Image Processing and GIS for Remote Sensing: Techniques and Applications. Germany, Wiley, 2016. ▪ Jain, Anil K.. Fundamentals of digital image processing. India, Prentice Hall, 1989. ▪ Annadurai, 8 S.. Fundamentals of Digital Image Processing. India, Pearson, 2007  Department of Geography What is the meaning of remote sensing? What we measure using remote sensor? What kind of data is generated through remote sensing?  Department of Geography What is Remote Sensing?  Department of Geography Remote – away from or at a distance. Sensing – detecting data on property or characteristic of a thing/object. Remote Sensing means acquiring data on thing/object from a distance 11  Department of Geography Of our senses we use three as remote sensor: Watching football match from stadium (sense of sight) Smell freshly cooked curry in the oven (sense of smell) Here a mobile phone ring (sense of hearing) Other two senses can not be used remotely: ❑Try to feel smoothness of a surface (sense of touch) ❑Eat a fresh mango and check the sweetness(sense of taste) In the last two cases, we actually touch the object by our organs (sensors)  Department of Geography Human Eye is common examples of remote sensors Light from a source like the Sun or any other source, falls on the object. That light is reflected by the object in all possible directions. The reflected light from the object reaches on the retina of our eyes. Our brain receives the information from the eyes and identify the object. 13  Department of Geography Definitions of Remote Sensing Definition given by Canada Centre for Remote Sensing (CCRS): Remote sensing is the science (and to some extent, art) of acquiring information about the earth’s surface without actually being in contact with it. This is done by sensing and recording reflected and emitted energy and processing, analyzing and applying that information. Definition given by American Society for Photogrammetry and Remote Sensing): Remote sensing is defined as the measurement of acquisition of information of some property of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object or phenomenon, under study. Definition given by India’s National Remote Sensing Agencey (NRSA), now renamed as National Remote Sensing Centre (NRSC) : Remote Sensing is the technique of deriving information about objects on the surface of the earth without physically coming into contact with them. 14  Department of Geography What we measure using remote sensor?  Department of Geography Now, we need to know using remote sensing, What is measured? What kind of output will be generated  Department of Geography When sunlight hits any surface then…..  Department of Geography Source: NPTEL Online Courses  Department of Geography What kind of data is generated through remote sensing?  Department of Geography A representation of external form of person or things or area is called image. Department of Geography Department of Geography Source: Google Image Department of Geography Source: Google Image Department of Geography Source: Google Image  Department of Geography Source: Sunil Kumar, Kousik Midya, Swagata Ghosh & Sultan Singh (2022) Pixel based vs. object-based anthropogenic impervious surface detection: driver for urban-rural thermal disparity in Faridabad, Haryana, India, Geocarto International, 37:25, 8543-8566, DOI: 10.1080/10106049.2021.2002429  Department of Geography Different modes of acquiring images  Department of Geography In the geospatial world, remote sensing is used for earth observation, i.e. observation and collection of data of earth with some instrument from high above the surface without going to the site for which the data is being collected. Instruments are generally placed on aeroplanes and satellites.  Department of Geography Source: Google Images  Department of Geography Remote Sensing Data v/s In Situ Data In Situ Data ▪One form of in situ data collection involves the scientists going out in the field and questioning the phenomena of interest. ▪Other form is, a scientist may elect to use in situ measurement device at the study site to make measurements. For eg. Thermometer to measure temperature of the air, soil, water. Spectrometer to measure spectral reflectance. Anemometer to measure the speed of the wind. To collect in situ data by using some instruments which are not in direct contact with the object, but essentially scientists have to go to the study site. Therefore, it is not remote sensing (for the earth 29 observation)  Department of Geography Remote Sensing Data ▪It is also possible, to collect information about an object or geographic area using specialized instruments without direct contact with the object or area of interest and also without going to the study site. ▪Without direct contact, some means of transferring information (accomplished by the use of Electromagnetic Radiation) are being utilized to serve various purposes. ▪The remote sensing data collection was performed by aerial camera on photographic films. ▪The remote sensing data collection was nowadays performed by electronic sensor mounted in satellite 30  Department of Geography Recording of Energy by the Sensor 31  Department of Geography Spectroradiometer  Department of Geography Particulate Monitor Hand-held GPS PM1025 Department of Geography  Department of Geography Remote Sensing Basic Processes Data Acquisition Data Analysis 35  Department of Geography Data Acquisition i. Energy sources: The first requirement for remote sensing is to have an energy source which illuminates or provides electromagnetic energy to the target of interest. ii. Propagation of energy through the atmosphere: As the energy travels from its source to the target, it will come in contact with and interact with the atmosphere it passes through. iii.Energy interaction with the target (earth surface feature): 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 iv.Retransmission of energy through the atmosphere: As the energy travels from the target to the sensor, it will come in contact with and interact with the atmosphere it passes through, a second time. v. Recording of Energy by the Sensor (Airborne and/or Space borne ): After the energy has been reflected (or emitted) by the target, we require a sensor (remote - not in contact with the target) to collect and record the reflected energy. Energy is converted to electrical signal. Electrical signal is converted to digital form vi.Transmission, Reception, and Processing: Digital signal has to be transmitted, to a receiving and processing station where the data are processed into an pictorial and/or digital format and organized to a storage device or link and distributed to the user.  Department of Geography Data Analysis i. Interpretation and Analysis: Examining the pictorial data and digital data using various viewing and interpretation devices and extracts information about the resources over which the sensor data were collected. ii. Application: The final element of the remote sensing process is achieved when we compile the information which extracted from the imagery about the target in the form of hard copy maps, tables and digital files and merged with other “layers” of information using GIS, in order to better understand it, reveal some new information, or assist in solving a particular problem and utilize them in the decision making for resource management. These elements comprise the remote sensing process from beginning to end.  Sensor Department of Geography Sun Radiance Application Irradiance Atmosphere Reception & Processing Interpretation & Target Analysis 38 Remote Sensing Process Components  Department of Geography Ideal remote sensing system ▪The source of electromagnetic energy provides a high level energy over all wavelengths at a known constant intensity. ▪This energy passes through a non interfering atmosphere where there is no loss of energy and it falls on a target. ▪Depending upon the characteristics of the target, the incident energy interacts with the target and generates unique and uniform reflected and/or emitted energy in all the wavelengths. ▪The super sensor having the capability to record the reflected and/or emitted energy from the target in all the wavelengths, records the information in spectral form. ▪The information recorded by the super sensor is transmitted to a real time data handling system on the ground where it is processed instantaneously in an interpretable form to make possible the identification of all the features uniquely characterized by their physical, chemical and biological properties. ▪The interpretable data becomes available to a user who is supposed to have an in depth knowledge of making use of these data in their respective fields. 39  Department of Geography Real remote sensing system However in reality, the picture is much more different then what the ideal system portrays. ▪First of all, there is no energy source that emits uniform energy both spatially and temporally. Since, the sun is the source of electromagnetic energy, we all know that there are variations in the sun activity which takes place and this leads to a variation in the transmitted energy which is coming from the sun’s surface. ▪Further, while the energy traverses through the earth’s atmosphere which consists of gases and water vapour molecules and dust particles, it interacts with the energy leading to modification of the strength and spectral distribution. The same matter under different conditions may have different spectral response. Also, different matters may have similar spectral response. ▪In reality, there is no ideal super sensor which can accommodate all wavelengths of the electromagnetic spectrum. ▪Due to some practical limitations, sometimes data transmission and interpretation are not in real time. The transmitted data may also not be in the form which a user may desire and thus again, the user may not be receiving the data in desired form in real time. ▪All the users may not have sufficient knowledge of the data acquisition analysis and interpretation of the remote sensing data. So, we can see the deviation of the real remote sensing system in comparison to an ideal remote sensing system. 40  Department of Geography Now we will discuss different components and processes in real remote sensing 41  Department of Geography Source of Energy As you noted earlier in remote sensing basic processes (Refer earlier slides), the first requirement is to have an energy source to illuminate the target,. Just as our eyes need to be objects to be illuminated by the light, so that we can see them, sensors also need a source of energy to illuminate the earth’ surface. The sun is the natural source of energy. The energy is radiated in the form of EMR. 42  Department of Geography Concept of Energy Energy is the ability to do work. In the process of doing work, energy is transferred from one body to another and/or from one place to another. Basic Ways of Energy Transfer Conduction Convection Radiation 43  Department of Geography How is Energy Transferred? a.Conduction: occurs b.Convection: the c.Radiation: when one body (molecule or energy of bodies is transferred the energy transfer by radiation is the atom) transfers its energy to the from one place to another by primary interest of remote sensing, other which is in direct contact physically moving the bodies. because it is the only form of energy with it. Eg. Metal pan heated by Eg. Heating of the air near the transfer that can take place in the stove or burner ground vacuum, such as the region between the sun and the earth 44  Department of Geography Electromagnetic Radiation (EMR) EMR is a form of energy that reveals its presence by the observable effects it produces when it strikes the matter. 45  Department of Geography Characteristics of EMR EMR is an electromagnetic energy or wave that travels through the space at the speed of light (3×108 m/s) Velocity (c): EM waves travel at the speed of light (3×108 m/s) Wavelength (λ): distance between consecutive maximums (or minimums) of a periodic pattern. Frequency (ϑ): number of wavelengths that pass a point per unit time. 46  Department of Geography ϑ= Frequency (number of cycles passing a fixed point per unit time) Crest Distance λ= Wavelength (distance between consecutive maximums (or C Velocity of light minimums) of a periodic pattern ) Trough 47  Department of Geography The relationship between wavelength and frequency of EMR is based on the following formula: c=λ y Frequency is inversely proportional to wavelength. The longer the wavelength, the lower the frequency, and vice-versa. 48  Department of Geography Numerical: If the wavelength of light is about 620nm, what will be the frequency of that light ? =620 nm=620x10-9 m We know, Wavelength x frequency=speed of light =c 620 x10-9 x =3x108 =(3 x 108)/(620 x 10-9)=(3/620)x1017=483.8 x 1012 Hz=483.8 THz  Department of Geography Electromagnetic radiation is a stream flow of particles called Photons. Quantum theory of EMR states that Electromagnetic radiation is composed of discrete units called quanta or Photons A single photon possess a certain quantity of energy. Some other photon can have different energy value Photons show a wide range of discrete energies. The amount of energy charaterizing a photon is determined by Planck’s general equation: Q=hy=hc/λ where Q= energy of a quantum measured in jouls (j) h= Planck’s constant y= frequency of radiation 50  Department of Geography Electromagnetic Spectrum (EMS) EMR extends a wide range of wavelengths EMS: a spectrum of all types of EM radiation in which each type of radiation is ordered according to its wavelength. Each region of radiation is commonly known as bands or channels. EMS extends From: Gamma rays (short wavelength, high frequency and high energy content) To: Radio waves (long wavelength, low frequencies, and low energy content). 51  Department of Geography SUN 1mm 1µm 1nm 1m 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 radio microwave IR UV X rays Gamma rays visible IR Red Green Blue UV 0.7 0.6 0.5 0.4 (µm) The EM Spectrum Different wavelengths of light can be grouped together into different types 52 A narrow range of EMR (0.4 to 0.7 µm), is detected by human eye is known as the visible region.  Department of Geography Portions of EMS (different bands) used in Remote Sensing Ultraviolet (0.3-0.4µm): Wavelength of UV rays are very small and highly affected by the atmosphere. These layers are also absorbed by the ozone layer of the atmosphere. Therefore this band is not suitable for remote sensing. Visible (0.4-0.7µm): The light which our eyes-our remote sensors can detect is part of the visible spectrum. It is important to recognize 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 instrument and used to our advantage. The visible wavelengths cover a range from approximately 0.4 to 0.7 µm. The longest visible wavelengths is red and the shortest wavelengths is violet. Common wavelengths of what we perceive as particular colours from the visible portion of the spectrum are listed below. It is important to note that this is the only portion of the spectrum we can associate with colours. 53  Department of Geography Infrared (IR) (0.7-1.0mm): This region has two sub-regions - Reflective IR and Thermal IR Reflective (or optical) IR (0.7-3.0µm): EMR within this region is reflected from the object. It has two sub-regions. Near IR (NIR) (0.7-1.3µm) Shortwave IR (SWIR) /Middle IR (MIR) (1.3-3.0µm) Thermal IR (3.0µm-1.0mm): This area is also known as Far Infrared. Energy in this region can not be reflected from an object, rather it is emitted by the object. Microwave: This region is subdivided into various regions. 54  Department of Geography Energy Interaction With Atmosphere ▪Once EMR is generated, first it propagated through the vacuum ▪Before radiation (used for remote sensing) reaches the Earth's surface, it has to travel through some distance of the Earth's atmosphere. ▪Particles and gases in the atmosphere can affect the incoming light and radiation. ▪These effects are caused by the mechanisms of scattering and absorption.. 55  Department of Geography Scattering 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 Rayleigh scattering : occurs when particles are very small compared to the wavelength of the radiation. These could be particles such as small specks of dust or nitrogen and oxygen molecules. Rayleigh scattering causes shorter wavelengths of energy to be scattered much more than longer wavelengths. Rayleigh scattering is the dominant scattering mechanism in the upper atmosphere. The fact that the sky appears "blue" during the day is because of this phenomenon. According to Rayleigh's scattering law, the amount of scattering of the light is inversely proportional to the fourth power of the wavelength. 56  Department of Geography 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. Non-selective 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. 57  Department of Geography Absorption Absorption is the process by which radiant energy is absorbed and converted into other forms of energy. An absorption band is a range of wavelengths (or frequencies) in the electromagnetic spectrum within which radiant energy is absorbed by substances such as water carbon dioxide (CO2), oxygen (O2), ozone (O3), and nitrous oxide (N2O). Ozone, carbon dioxide, and water vapor are the three main atmospheric constituents which absorb radiation. Ozone: Ozone serves to absorb the harmful (to most living things) ultraviolet radiation from the sun. Without this protective layer in the atmosphere our skin would burn when exposed to sunlight. Carbon dioxide: Carbon dioxide referred to as a greenhouse gas. This is because it tends to absorb radiation strongly in the far infrared portion of the spectrum - that area associated with thermal heating – which serves to trap this heat inside the atmosphere. Water vapor: Water vapor in the atmosphere absorbs much of the incoming long wave infrared and shortwave microwave radiation (between 22 m and 1m ). The presence of water vapor in the lower atmosphere varies greatly from location to location and at different times of the year. For example, the air mass above a desert would have very little water vapor to absorb energy, while the tropics would have high concentrations of water vapor. 58  Department of Geography Atmospheric Windows The atmospheric gases absorb EMR in different specific regions of the spectrum, they influence where (in the spectrum) we can "look" for remote sensing purposes. Those areas of the spectrum which are not severely influenced by atmospheric absorption and thus, are useful to remote sensors are called atmospheric windows. All spectral regions are affected to some extent by absorption in the atmosphere but some regions are less affected and nearly transparent. These regions are called atmospheric window and thus useful for remote sensing. Figure in the next slide is a generalized diagram showing relative atmospheric transmission of different wavelength. Grey zones marked in the figure show the minimal passage of incoming and outgoing radiation, whereas, white areas denote atmospheric windows, in which the radiation does not interact much with the air molecules and hence is not absorbed. Most remote sensing instruments (aerial or satellite) operate in one or more of these windows by making their measurements with detectors turned to specific wavelength that pass through the atmosphere. 59  Department of Geography 60  Department of Geography Energy Interaction With Earth Surface Electromagnetic energy is incident on any earth Surface feature Three fundamental energy interactions with the feature are possible REFLECTED ABSORBED ENERGY ENERGY TRANSMITTED 61 ENERGY  Department of Geography transmission (T) occurs when radiation passes through a target Absorption (A) occurs when radiation (energy) is absorbed into the Reflection (R) occurs when radiation target The portion of the EM energy which is absorbed by the Earth’s "bounces" off the target and is redirected surface is available for emission and as thermal radiation at longer after hitting the target wavelengths 62  Department of Geography ER(λ) EA(λ) ET(λ) EI(λ) INCIDENT ENERGY (EI) REFLECTED ENERGY (ER) WATER SURFACE ABSORBED ENERGY (EA) TRANSMITTED ENERGY (ET) BASIC INTERACTIONS BETWEEN ELECTROMAGNETIC ENERGY AND AN EARTH SURFACE FEATURE ( WATER BODY ) 63  Department of Geography Wavelength of the energy Proportion of the energy is absorbed, transmitted or reflected by a material will depend upon Material Condition of constituting the feature. the surface PERMIT TO DISTINGUISH DIFFERENT FEATURES ON AN IMAGE 64  Department of Geography IN REMOTE SENSING, WE ARE MOST INTERESTED IN MEASURING THE RADIATION REFLECTED FROM TARGETS. Reflection from surfaces occurs in two ways: DIFFUSE SPECULAR REFLECTION REFLECTION The geometric manner in which an object reflects energy is also an important consideration. This factor is primarily a function of the surface roughness of the object. 65  Department of Geography SPECULAR REFLECTORS gives the mirror-like reflection of light (or of other kinds of wave) from a surface. the angle of incidence equals the angle of reflection (θi = θr in the figure), File:Tso Kiagar Lake Ladakh.jpg File:Reflection angles.svg Reflections on still water are an example 66 of specular reflection  Department of Geography DIFFUSE REFLECTORS gives the reflection of light from a rough surface that reflect incident energy on it, uniformly in all directions 67  Department of Geography The specular or diffusive characteristic of any surface is determined by the roughness of the surface in comparison to the wavelength of the incoming radiation. If the wavelengths of the incident energy are much smaller than the surface variations or the particle sizes, diffuse reflection will dominate. In the visible portion of the spectrum, even a material such as fine sand appears rough while it appears fairly smooth to long wavelength microwaves. Long wave- Appear smooth length to Incident radio energy Sandy range beach Visible portion Appear rough of to incident 68 spectru energy m  Department of Geography SPECTRAL REFLECTANCE (Rλ) ❖ reflected energy from earth surface is measured as function of wavelength The reflectance characteristics of earth surface features may be quantified by measuring the portion of incident energy that is reflected. This is measured as a function of wavelength, and is called SPECTRAL REFLECTANCE, Rλ. It is mathematically defined as ER(λ) Rλ = EI(λ) = Energy of wavelength λ reflected from the object x 100 Energy of wavelength λ incident upon the object 69  Department of Geography PROPORTION OF REFLECTED , ABSORBED & TRANSMITTED ENERGY WILL VARY AT DIFFERENT WAVELENGTH SPECTRAL VARIATION RESULT IN VISUAL EFFECT CALLED “ COLOR” BLUE OBJECT GREEN OBJECT RED OBJECT Reflect more Reflect more Reflect more highly in BLUE highly in GREEN highly in RED portion of the portion of the portion of the spectrum spectrum spectrum 70  Department of Geography Spectral Signatures of three basic types of earth features-Healthy green vegetation, Dry bare soil and Clear lake water The energy that is reflected by features on the earth's surface over a variety of different wavelengths will give their spectral responses/ spectral signature. The graphical representation of the spectral response of an object over different wavelengths of the electromagnetic spectrum is termed as spectral reflectance curve. These curves give an insight into the spectral characteristics of different objects, hence used in the selection of a particular wavelength band for remote sensing data acquisition. 71  Department of Geography 72  Department of Geography Clear water: Clear water has a low spectral reflectance (< 10%) in the visible region At wavelengths longer than 0.75 µm, water absorbs almost all the incoming energy the reflectance from a water body can stem from an interaction with the water's surface (specular reflection), with material suspended in the water, or with the bottom of the water body. Even with deep water where bottom effects are negligible. waters containing large quantities of suspended sediments resulting from soil erosion normally have much higher visible reflectance than other "clear" waters in the same geographical area. Likewise, the reflectance of water changes with the chlorophyll concentration involved. Increases in chlorophyll concentration tend to decrease water reflectance in blue wavelengths and increase it in the green wavelengths. These changes have been used to monitor the presence and estimate the concentration of algae via remote sensing data. 73  Department of Geography Vegetation : generally has three reflectance valleys. one at the red spectral wavelength region (0.65 µm) is caused by high absorptance of energy by chlorophyll in the leaves. other two at 1.45-1.55 µm and 1.90-1.95 µm are caused by high absorptance of energy by water in the leaves our eyes perceive healthy vegetation as green in colour because of the very high reflection of green energy. If a plant is subject to some form of stress that interrupts its normal growth and productivity, it may decrease or cease chlorophyll production. The result is less chlorophyll absorption in the blue and red bands. Often the red reflectance increases to the point that we see the plant turn 74 yellow (combination of green and red).  Department of Geography As we go from the visible to the reflected infrared portion of the spectrum at about 0.7 µm, the reflectance of healthy vegetation increases dramatically. In the range from about 0.7 to 1.3µm, a plant leaf reflects about 50 percent of spectral region is minimal. Plant reflectance in the 0.7 to 1.3 µm range results primarily from the internal structure of plant leaves. Because this structure is highly variable between plant species, reflectance measurements in this range often permit us to discriminate between species, even if they look the same in visible wavelengths. Likewise, many plant stresses alter the reflectance in this region and sensors operating in this range are often used for vegetation stress detection. Beyond 1.3 µm, energy incident upon vegetation is essentially absorbed or reflected, with little to no transmittance o f energy. Dips in reflectance occur at 1.4, 1.9, and 2.7 µm because water in the leaf absorbs strongly at these wavelengths. Accordingly, wavelengths in these spectral regions are referred to as water absorption bands. 75  Department of Geography Dry soil : The soil curve is relatively flat reflectance curve. It shows considerably less peak-and-valley variation in reflectance i.e., the factors that influence soil reflectance act over less specific spectral bands. Some of the factors affecting soil reflectance are moisture content, soil texture, surface roughness etc. These factors are complex, variable, and interrelated. For example, the presence of moisture in soil will decrease its reflectance. As with vegetation, this effect is greatest in the water absorption bands at about 1.4, 1.9, and 2.7 µm. Soil moisture content is strongly related to the soil texture: coarse, sandy soils are usually well drained, resulting in low moisture content and relatively high reflectance; poorly drained fine textured soils will generally have lower reflectance. 76  Department of Geography Multi-concept of Remote Sensing Remote sensing involves a multifarious activities and multifarious forms of data collection. This has been called as the multi concept of remote sensing. Multi- station images involves successive overlapping pictures along a flight line using an aircraft or a spacecraft for better perception of 3D features. Multi band images which exploit the fact that each type of feature tends to exhibit a unique type of tonal signature. Thus, when brightness values seen in a series of images taken in different wavelength bands are suitably combined, it is possible to unambiguously identify special terrestrial features. Multi date images that involve a comparative analysis of the images taken at on a series of preplanned dates can provide an additional handle for identifying the signature, since many features exhibit dynamic characteristics. 77  Department of Geography Multi enhancement images involves the combination of multi date, multi band and multi polarized images to suitably generate composite images. Multi disciplinary analysis involves analyzing the data by two or more analyst from different disciplines to obtain a more accurate. and complete information about the total earth resource of an area. The results of such multi disciplinary analysis are usually presented in a set of multi thematic information. 78  Department of Geography What is Digital Image? A digital image consists of an array of digital numbers (DN) representing the reflectance values (RV) or emittance values (EV) of corresponding pixel. Digital number of column 5, row 4 at band 2 is expressed as BV5,4,2 = 105.  Department of Geography Characteristics of Digital Image It is quantized numeric representation of a scene. The scene is spatially partitioned into a regular array of numbers whose values represent the radiance or brightness of that area in one or more spectral bands. Entire scene is divided into small equal sized units (pixel) The number associated with pixel is DN value The variation of radiance occurs due to the variation of physical, chemical and biological composition of each features. The lowest DN value represents black shade whereas highest DN value represents white The range of lowest and highest DN value depends upon the radiometric resolution of the image.  Department of Geography Few Glimpses of Satellite Images Department of Geography Department of Geography Department of Geography Department of Geography Department of Geography Department of Geography Department of Geography  Department of Geography Resolutions Image resolution is called sensor resolution. It is the ability of a sensor to discriminate neighbouring features within a scene Related to ground Spatial space Resolution Related to Spectral wavelength space Related to revisit Temporal period Related to signal Radiometric strength  Department of Geography Spatial Resolution High vs. Low Spatial Resolution Spatial Resolution refers ability of the sensor to distinguish between closely spaced objects. The earth surface area covered by a pixel of an image is known as spatial resolution. Large area covered by a pixel means low spatial resolution and vice versa. Each sensing element has an instantaneous field of view (IFOV) that determines the spatial resolution of the sensor. Better spatial resolution allows for discriminating smaller objects in the image  Department of Geography Spatial Resolution of selective Sensors High spatial resolution: 0.6 - 4 m WorldView-2 WorldView-1 QuickBird IKONOS CARTOSAT-1 Medium spatial resolution: 4 - 30 m ASTER TM Low spatial resolution: 30 - > 1000 m MODIS GOES  Department of Geography Spectral Resolution ▪ Is the ability of a sensor to separate nearby features in wavelength space which means the ability of a sensor to define fine wavelength interval. ▪ More number of bands in a specified bandwidth means higher spectral resolution and vice versa. ▪ It has got two components i. No. of bands in a sensor ii. Wavelength interval or band width of different bands  Department of Geography Broad classes, such as water and vegetation, can usually be separated using very broad wavelength ranges – the visible and near Infrared Other more specific classes, such as different rock types, may not be easily distinguishable using either of these broad wavelength ranges and would require comparison at much finer wavelength ranges to separate them. Thus, we would require a sensor with higher spectral resolution. 93 Department of Geography  Department of Geography Spectral Resolution of selective Sensors Multispectral (4-7 bands 20 bands) Hyperspectral (> 200 bands) 95  Department of Geography Temporal Resolution ▪ It refers to the frequency of obtaining data over a given area. ▪ Number of days after which the satellite revisits any location on ground. ▪ Temporal Resolution of a remote sensing system to obtain image of the exact same area with same viewing angle for a second time is equal to its revisit periods. ▪ Temporal resolution or revisit time of Landsat 1-3 was 18 days, and for Landsat 4-5 was 16 days. together Landsat 9 and Landsat 8 will provide a temporal resolution of 8 days 96  Department of Geography Source: Dr. R.R. Navalgund, former directr SAC  Department of Geography ▪ Geostationary satellite systems differ from polar orbiting satellites in that they do not orbit and acquire images of the whole globe. Instead, they observe the same section of the surface of the Earth while staying in the same place. That way, they can acquire images of the same area at short intervals of only a few minutes. Therefore geostationary satellite images have high temporal resolution. ▪ We need images with a high temporal resolution for the observation of weather phenomena. In this case use geostationary satellite images should be used. Satellite data with a high temporal resolution can be used in order to observe phenomena such as the tide.  Department of Geography Radiometric Resolution ▪ It describes its ability of an imaging system to discriminate very slight differences in signal strength. ▪ It defines discriminable signal levels and thus grey-scale values while acquiring an image. ▪ A bit stands for the number of grey-scale values a spectral sensor can tell apart. Radiometric Resolution is expressed as 2n where n denotes the bit. ▪ The greater the bit number, the greater the number of grey-scale values a spectral sensor can distinguish. ▪ A 4-bit image indicates there are 16 digital values available ranging from 0 to 15. A 16-bit resolution image indicates there are 65,536 potential digital numbers between 0 to 65,535 for that sensor to record 99  Department of Geography 111 1111 1110 110 1101 1100 101 1011 1010 100 1001 011 1000 0111 0110 010 0101 0100 001 0011 0010 000 0001 0000 100 Department of Geography  Department of Geography FUNDAMENTALS OF VISUAL INTERPRETATION Introduction Aerial photographs as well as imagery, obtained by remote sensing using aircraft or spacecraft as platforms, have applicability in various fields. By studying the qualitative as well as quantitative aspects of various images, like aerial photographs, multi-band photographs, satellite data including thermal and radar imagery, an interpreter well experienced his field can derive lot of information. 102  Department of Geography Image Interpretation is defined as the examination of images for the purpose of identifying objects and judging their significance by studying remotely sensed data through logical process. Image interpretation depicts, identifies, measures and evaluates the significance of environmental and cultural objects, patterns and spatial relationships. It is an information extraction process. 103  Department of Geography 104  Department of Geography Image reading is an elemental form of image interpretation. It corresponds to simple identification of objects using such elements as shape, size, pattern, tone, texture, color, shadow and other associated relationships. Image reading is usually implemented with interpretation keys with respect to each object. Image measurement is the extraction of physical quantities, such as length, location, height, density, temperature and so on, by using reference data or calibration data deductively or inductively. Extracted information will be finally represented in a map form called an interpretation map or thematic map. 105  Department of Geography Remotely sensed images are examined by analyst in a systematic manner with the help of supporting informations collected from ❑ Maps ❑ Field visit report ❑ Previously interpreted images of the same area Interpretation based on physical characteristics of the object appearing on the image. Success of image interpretation depends on ❑ Experience of the analyst ❑ Type of object being interpreted ❑ Resolution of the image 106  Department of Geography Elements of Image Interpretation The characteristics which help in the logical and systematic approach for carrying out image interpretation is called Elements of Image Interpretation. 107  Department of Geography Tone Band of EM spectrum recorded by RS system may be displayed in shades of grey ranging from black to white Tone refers to the relative brightness or colour of an area in imagery. It is a qualitative characteristics. For example in black and white near infrared photographs, water is black and healthy vegetation white to light grey. 108  Department of Geography Agricultural land without crop Agricultural land partially covered with crop Patch of trees (closely space) 109  Department of Geography Size Size of objects in an image is a function of scale. Proper photo scale selected depending on the purpose of interpretation Along with the absolute size of the target, it is important to study the size of the target relative to the size of the neighbouring objects in the scene. Most commonly measured parameters:- length, width, perimeter, area. Example: In an area with a number of buildings, large building represents factories or other commercial properties and small building represents residential area. 110  Department of Geography Large structure 111  Department of Geography Shape It is very important clue for interpretation Shape of an object is described the general form or outline of the image Regular shapes are signs of man-made objects. Such man-made features have defined edges leading to regular shape. Example: Roads, Buildings etc. Irregular shapes with no distinct geometrical pattern are signs of a natural environment. Example : forest area, waterbodies etc. 112  Department of Geography Streams Road Area used for horse Streams racing 113  Department of Geography Texture Refers to the frequency of tonal changes on an image Texture is produced by aggregation of unit features that may be too small to be discerned individually, such as tree leaves It is produced of their individual shape, size, pattern, shadow and tone. It determines overall visual “smoothness” and “roughness” of image features Example: area covered with dry sand appear as smooth texture as the variation of tone for long stretches is not present Forest area having variety of tree species having variety of canopy size, shape and density will appear as rough texture as tone changes rapidly. 114  Department of Geography 115  Department of Geography Pattern Refers to spatial arrangement of visually discernible features The repetition of similar tones and textures produces a distinctive and recognizable pattern. Example: the ordered spatial arrangement of trees in orchards is in distinct contrast to that of forest tree stands. 116  Department of Geography 117  Department of Geography Shadow Shadows are important in two opposing respects: Shape or outline of a shadow affords a impression of the profile of the object (which helps in interpretation) Features within shadow reflect little light therefore difficult to identify. 118  Department of Geography 119  Department of Geography Association Refers to the occurrence of certain features in relation to others. Example: Schools often associated with athletic fields. 120  Department of Geography Yacht Wharf area Major Road 121  Department of Geography Site Refers to topographic or geographic location It is important aid in the identification of vegetation types. Certain tree species occur on well drained upland sites whereas other tree species occur on poorly drained lowland sites Sewage treatment facilities at the lowest feasible topographic position. Power plants located adjacent to water for cooling 122  Department of Geography Image Interpretation Strategies An image interpretation strategy can be defined as disciplined procedure that enables the interpreter to relate geographic patterns to their appearance on the image. 123  Department of Geography Different Image Interpretation Strategies Field Observation ▪required when ground conditions depicted in image is complex. ▪Interpreter forced to go to field visit to correlate ground condition and image information Direct Recognition ▪Using experience, skill and judgment Interpreter associate image pattern with information class Interpretation by Inference ▪Based on relationship, deriving invisible information from the visible information on the image Probabilistic Interpretations ▪non-image information (collateral information) is to be used for deriving the information class in image Deterministic Interpretation ▪Most precise method ▪Based upon quantitative relationship that tie image characteristics to ground condition. 124  Department of Geography Land use/ Land cover mapping Land Cover” (the natural condition of the land, e.g. forest , waterbodies) and “Land use” (the modified state of the land after anthropogenic interference to employ the land and its resources, e.g. residential/ commercial area) both have huge significance in relation to Land, the most vital and fundamental resource pertaining to the urban development  Department of Geography Land use/ Land cover mapping Reference: Technical Manual National Land Use Land Cover Mapping using Multi- temporal Satellite Data (PDF provided)  Department of Geography IMAGE CHACTERISTICS FOR IDENTIFICATION OF LAND USE/LAND COVER FROM SATELLITE IMAGERY Built-up land ▪These are the land surfaces of man-made constructions due to non-agricultural use including buildings, transportation network, communication, industrial, commercial complexes, utilities and services in association with water, vegetation and vacant lands. Collectively, cities, towns and habitations are included under this category. ▪Built-up land comprises of developed areas like buildings, industrial structures, transportation network etc. The physical size or built –up sprawl with transport network can a surrogate to classify a settlement as urban or rural.  Department of Geography ▪It is identifiable on the imagery by its dark bluish green to bluish tone, definite size, shape and texture. Often, built-up land with high density of buildings etc appear in dark tone at the center and lighter on peripheries because of being less dense and less developed. ▪The pattern is contiguous to non contiguous (punctuated by vacant lands and vegetation), clustered or scattered. It occurs on all types of terrain amidst agricultural lands, forests, wastelands, in association with road, rail and canal networks and other artifacts. ▪Transport network appear in shades of dark bluish green to light yellow (unmettled or kwacha roads) to red (wherever vegetation occurs along the road). Department of Geography Department of Geography Department of Geography  Department of Geography Agricultural land: These are the land primarily used for farming, production of food, fiber, other commercial and horticultural crops. It includes land under crops (irrigated and unirrigated), fallow, plantations, etc. Crop- Land ▪It includes those lands with standing crops as on the date of the satellite data acquisition. ▪The tonal contrast of crop land vary from bright red to red which may signify greenness of foliage different stages of crop growth phenological condition (healthy or infected) besides the nature of soil (moist or dry), type of terrain etc. ▪Its spatial extent varies in size and shape with smooth texture (when the crop is in full matured state) to coarse or mottled (at the early stages of planting and growth). ▪It is contiguous under irrigated (canal, tank or well etc.) areas and non-contiguous in unirrigated or rain-fed drylands. ▪Very often contiguity of crop lands is punctuated by harvested fields or fallow lands.  Department of Geography Fallow land ▪The agricultural land which is taken up for cultivation but is temporarily allowed to rest, uncropped for one more season, but less than one year. These are particularly devoid of crops at the time; when the imagery is taken. It appears yellow to greenish blue in tone depending on the topography, nature of soil and moisture content on ground. It appears light in tone in sandy red soils and in coastal soils, and dark in tone in alluvial black cotton (Deccan – trap areas) and in soils rich in clay. In irrigated lands fallow lands appear small in size, often with regular field boundaries and non – contiguous. In un-irrigated or dry (farming) lands they appear large in size, contiguous and with limited patch of crop and. Regular openings amidst crop land also suggest occurrence of fallow lands. The texture is medium to cosarse due to surface irregularities and absence of vegetation cover. Identification of fallow lands in drought prone districts as found in parts of Andhra Pradesh, Gujarat, Tamilnadu, Karnataka, Maharastra etc. require the use of multidate imagery, lest to avoid misinterpretation of wastelands etc.  Department of Geography Plantations (Agriculture) ▪These are agricultural land with tree plantation or fruit orchards; planned by adopting certain agricultural management techniques. ▪These appear dark red to red intone, small in size with regular shapes and sharp and smooth edges. ▪The difference in tone may signify different types of plantations or same plantation in different stages of growth or foliage cover or due to seasons. ▪These occur on uplands, foot hills and occasionally in river plains. ▪Some plantations like Tea, Coffee, Rubber, and Arecanut occur amidst notified forest and outside the notified forest areas. ▪These can be identified throughout the year from January to December.  Department of Geography Forest: It is an area (within the notified forest boundary) bearing an association predominantly of trees, other vegetation types capable of producing timber and other forest products. Evergreen /Semi –evergreen forests ▪These appear bright red to dark red in tone in all the months of the year because of their green foliage, very dense canopy cover associated with moisture all round the year. ▪ They vary in size and shape, are smooth in texture and contiguous due to forest clearings. ▪These occur on the higher reaches of hill-slopes coinciding with the zones of very high rainfall. E.g. Western Ghats, West Bengal, Assam, North Eastern States (Broad leaved forests), UP hills, Himachal Pradesh, Sikkim, Arunachal Pradesh etc.  Department of Geography Deciduous forests ▪It is observed dark red to red in tone (during maximum greenness period) except during the month of leaf fall in dry season/autumn when tonal changes occur. ▪Their areal spread is contiguous and non- contiguous wherever the forest clearing occurs. ▪They vary in size with irregular and discontinuous boundaries and smooth texture wherever the canopy covers is uniform. ▪Deciduous forest occurs on the mountain/hill slopes of Western Ghats, Eastern Ghats, Siwaliks, and North-Eastern States. Lower Himalayas, etc. ▪Deciduous forests are associated with other forest types and sub-types and occur within the notified forest areas.  Department of Geography Degraded or Scrub land ▪Scrub forest is associated with barren rocky/stony waste due to inadequate and erratic rainfall conditions that brings drought and extreme heat in summer season which preclude hardly in any profitable forest ▪It appears light red to dark brown in tone subject to the amount of foliage cover and season. ▪The areal spread, vary in size with irregular dis-continuous shapes. The coarse to mottled texture is due to thin tree/vegetation cover and exposure of terrain underneath. ▪It is contiguous to limited extent but mostly non-contiguous tonal patterns due to openings (thinning of vegetation by natural degradation) and tree felling for timber, agricultural practices etc. ▪Degraded forest occur on mountain/hill slopes, isolated hills, uplands in association with different forest types and sub types within the notified forest areas. ▪Scrub occurs on foot slopes, associated with thin soil cover, small in size, mottled texture, non-contiguous and within the notified forest areas. ▪Images from January to April would be useful for delineation. ▪While interpreting the degraded forest, there is a possibility if misinterpretation of degraded forest with uplands having scrubs  Department of Geography Forest Blank ▪Forest blank appear distinctly on the imagery in light yellow to light brown tone, small in size, with regular to irregular shapes, coarse to mottled texture dispersed and scattered amidst forests of all types and sub-types. ▪These occur on forests hill slopes and hill tops in association with areas accessible for tree felling (for timber for cultivation) etc., around inhabited areas, near dam sites etc. These can be identified on images from January to April months. Forest Plantations It is described as an area of trees with species of forestry and its importance raised on notified forest lands. These are artificially planted areas with tree cover, either in the open spaces or by clearing the existing forests for economically inferior species. The common indigenous and exotic trees of forest plantations are Teak, Sal, Chir-pine, Deodar etc. ▪It appears light red to red in tone depending upon the foliage cover, stage of growth and season etc. ▪The plantations vary in size with regular to irregular shapes, smooth to medium texture (depends on the thickness of the canopy cover) contiguous to non- contiguous (subject to tree felling). ▪It occurs on uplands, foot slopes, coastal plains in associations with forest trees and other vegetation, within the notified forest boundaries, which are clearly identifiable on the imagery. ▪Any forest plantation outside the notified areas is to be shown separately in other plantations. ▪These can be identified on images from January to December months.  Department of Geography Wastelands: These are degraded lands which can be brought under vegetative cover with reasonable effort. These are currently under utilized and deteriorating due to lack of appropriate water & soil management or on account of natural causes. Sandy area (coastal and desert) These appear in bright white to yellow with bluish to reddish tone (subject to surface moisture and spots of vegetation), vary in size with regular (sand dunes, beaches, channel islands) to irregular shapes, smooth to mottled texture (subject to vegetation cover), contiguous and linear in pattern. It occurs in deserts, river-beds, coastal plain in association with shifting sand dunes, coastal beach sands, sand dunes, river sand and natural leaves. Sand dunes and inter-dune areas in Rajasthan desert are easily identifiable.  Department of Geography Barren rocky / Stony waste /Sheet rock area These are the lands characterized by exposed massive rocks, sheet rocks, stony pavements or land with excessive surface, accumulation of stones that render them unsuitable for production of any green biomass. This appears in greenish blue to yellow to brownish tone ( subject to varying rock type) vary in size with irregular and discontinuous shapes very coarse to coarse to medium texture, linear to contiguous and dispersed in pattern. It occurs as steep hill slopes crest, isolated hillocks plateau and eroded plains in association with barren and exposed rock/stony/waste. E.g. Laterite castors, boulders, quarried sites and mine areas.  Department of Geography Water bodies: This class comprises areas of surface water, either impounded in the form of ponds, lakes and reservoirs or flowing as streams, rivers, canal, etc. These are clearly observed on standard FCC in different shades of blackish blue to light blue color depending on the depth of waterbodies. Rivers / Streams River/Streams appear in light blue to dark blue to dark blue tone ( subject to shallow surface water spread, deep and more volume of water, turbidity etc), long and narrow to wide in size with irregular and sinuous shape, smooth to medium in texture ( in case of high turbidity), contiguous, non-linear to dendritic / sub-dendritic in pattern. It occurs as natural rivers/streams (perennial and non-perennial), in association with all types of terrain and slopes, having good rainfall and surface flow of water as runoff.  Department of Geography Lake/ Reservoir/ Tank/ Canal These water bodies appear in light blue to dark blue tone (subject to shallow surface water spread, volume of water, turbidity etc.). The presence of weed/vegetation contributes to patches of red tone amidst them. They are small/medium to large with regular to irregular shapes, smooth to mottled in texture (subject to vegetation cover) non-contiguous and dispersed in pattern, except canals which show a linear pattern. Tanks and lakes occur in lowlands/depressions of plains, uplands and valleys, reservoirs occur surrounded by mountains/hills and canals occur in inland plains, desert plains along the contour and gently sloping grounds. These are associated with agricultural lands, dams-sites, built-up areas as a source of irrigation, power and supply of water for domestic and industrial consumption etc.  Department of Geography Snow covered and /or Glacial areas These appear as bright white tones subject to moisture, age of snow (fresh snow appears brighter than snow formed earlier) and thickness of deposition/precipitation. It is large and extensive in size with irregular and discontinuous shape smooth texture and contiguous pattern. It occurs on mountain peaks and slopes in association with high relief and glaciers. Separation of snow and cloud (appearing together) is difficult to separate on IRS imagery. However, they can be separated on band –5 (1.55-2.35 microns) of landsat TM imagery. Accumulation of snow starts from December to March (subsequently melting starts) and the imagery from December to March would be ideal for its identification