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Dated :14/10/14 Lecture# 1 P-II Subject Database Management System & Applications of Remote sensing and GIS Topic Concept of Remote Sensing Consult Lectures 1,2 & 3 of Part-I for this topic Presented by Rehana Jamal 1 14/10/14 What is Remote sensing? Remote sensing is a technique of collecting information from a distance OR Remotely sensed data The data collected from a distance 2 14/10/14 Definitions of Remote Sensing “Remote Sensing (RS) is the science and art of acquiring information about material objects, area, or phenomenon, without coming into physical contact with the objects, areas, or phenomenon under investigation “ OR “Remote sensing is the science and art of obtaining information about an object ,area or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area or phenomenon under investigation” 14/10/14 3 Characteristics of Electromagnetic radiation Electromagnetic Energy can be modelled in two ways i. By waves ii. By Photons(Energy bearing particles) Electromagnetic waves consist of a combination of oscillating electrical and magnetic fields, perpendicular to each other. 4 14/10/14 Characteristics of Electromagnetic radiation It can travel through empty space. The speed of light is constant in space. A wavelength: Distance between crests or troughs through visible light Velocity: 186,000 miles per second or300,000 kilometers per second or 299,790,000m/s or 3*108 m/s Amplitude: The amplitude of electromagnetic waves relates to its intensity or brightness(as in the case of visible light) Frequency: •The number of crests of the waves that pass by a point per second. •Measured in units of hertz(Hz) •1 hertz = 1 wave crest/second 5 14/10/14 / Crest Velocity of light, c 6 14/10/14 Relation between the speed of light (c), wavelength ( ), and frequency (f or V ): f or V = c/ Thus, there is an inverse relationship between wavelength and frequency 7 14/10/14 Relation between the speed of light (c), wavelength ( ), and frequency (f or V ): Thus (frequency [f/V] * wavelength[lambda]) is equal to a constant (c) 8 14/10/14 9 Sources of electromagnetic radiation Sources of long wavelengths Sources of visible light Sources of short wavelength Detectors of electromagnetic radiation 14/10/14 10 Note the trends: bluer light has shorter wavelength, higher frequency, and more energy. Redder light has longer wavelength, lower frequency, and less energy. 14/10/14 11 The unit of length chosen to describe a particular wavelength is typically dependent on the type of electromagnetic radiation Unit Symbol Length (m) Type of Radiation Angstrom Å 10-10 X-ray Nanometer nm 10-9 UV, visible Micrometer µm 10-6 Infrared Millimeter mm 10-3 Infrared Centimeter cm 10-2 Microwave Meter m 1 TV, radio 14/10/14 Types of Energy Resources In respect to the type of Energy Resources: Passive Remote Sensing: Makes use of sensors that detect the reflected or emitted electro-magnetic radiation from natural sources. Active remote Sensing: Makes use of sensors that detect reflected responses from objects that are irradiated from artificially-generated energy sources, such as radar. In respect to Wavelength Regions: Visible and Reflective Infrared Remote Sensing. Thermal Infrared Remote Sensing. Microwave Remote Sensing. 12 14/10/14 In respect to the type of Energy Resources Passive Remote Sensing 13 14/10/14 In respect to the type of Energy Resources Passive Remote Sensing 14 14/10/14 In respect to the type of Energy Resources: Active Passive remote Sensing 15 14/10/14 Wavelength regions of electro-magnetic radiation Electro-Magnetic Spectrum (EMS) Remote Sensing Technology makes use of the wide range of Electro-Magnetic Spectrum (EMS) from a very short wave "Gamma Ray" to a very long 'Radio Wave'. Wavelength regions of electro-magnetic radiation have different names ranging from Gamma ray, X-ray, Ultraviolet (UV), Visible light, Infrared (IR) to Radio Wave, in order from the shorter wavelengths to the longer wavelengths. 16 14/10/14 17 Electromagnetic spectrum Definition: “The range of wavelengths for electromagnetic waves--from the very long to the very short--is called the Electromagnetic Spectrum”. It includes following wavelengths bands: •Radio and TV waves are the longest usable waves, having a wavelength of 1 mile (1.5 kilometer) or more. •Microwaves are used in telecommunication as well as for cooking food. •Infrared waves are barely visible. They are the deep red rays you get from a heat lamp. •Visible light waves are the radiation you can see with your eyes. Their wavelengths are in the range of 1/1000 centimeter. •Ultraviolet rays are what give you sunburn and are used in "black lights" that make object glow. •X-rays go through the body and are used for medical purposes. •Gamma rays are dangerous rays coming from nuclear reactors and atomic bombs. They have the shortest wavelength in the electromagnetic spectrum of about 1/10,000,000 centimeter. 14/10/14 Name Wavelength(mm) Optical wavelength Reflective portion (i) Visible (ii) Near IR (iii) Middle IR Far IR (Thermal, Emissive) 0.30-15.0 0.38-3.00 0.38-0.72 0.72-1.30 1.30-3.00 7.00-15.0 18 14/10/14 In respect to Wavelength Regions Visible and Reflective Infrared Remote Sensing Thermal Infrared Remote Sensing Microwave Remote Sensing 19 14/10/14 (1mm) 20 14/10/14 21 Summary 14/10/14 Energy interactions in the atmosphere Fundamental interactions in the atmosphere Source of energy Sun Absorption Transmission Scattering 22 Fig.1 Absorbed Incoming solar radiation 100% Total atmospheric absorption 17 % Scattered/Reflected Total scattering/reflection 30% (albedo) 14 % By atmospheric components 5% By dust 25% By clouds 47% 3% By clouds Clouds Clouds Direct radiation 31% 22% Diffuse radiation Earth’s surface Fig. 2 Energy interactions in the atmosphere 23 Clouds Energy interactions in the atmosphere & on the land 24 Fig.3 Efficient absorbers of solar radiation in the atmosphere Ozone(O3) Water vapour(H2O) Carbon dioxide(CO2) Electromagnetic spectrum between 0-22um is useless for remote sensing Only Wavelength regions out side the main absorption bands of the atmospheric gases are useful for remote & these regions are called “atmospheric transmission windows” 25 “Atmospheric transmission windows” Fig.5 26 Fig.6 27 “Atmospheric transmission windows” A window in the visible & reflected infrared region(0.4-2um) Three windows in the thermal infrared region (Two narrow windows around 3 & 5um & Third relatively broad window from 8 to 14 um) Frequency(Hz) ELECTROMAGNETIC SPECTRUM Fig.4 28 AM Radar Far IR Thermal IR Near IR Wavelength Atmospheric Scattering Amount of scattering depends on following factors: wavelength of the radiation the amount of particles & gases radiation distance Types of scattering Rayleigh scattering (Particle size < wavelength) Mie scattering ( Particle size = wavelength) Non-selective scattering 29 (Particle size > wavelength) Energy interactions with the Earth’s surface In remote sensing applications, Land & Water have different surface characteristics Energy interactions: When electro-magnetic energy is incident on any given earth surface feature, three fundamental energy interactions with the features are possible:1.Reflection , 2.Absorption , 3.Transmission Fig.7 30 Two types of Reflection Specular reflection (mirror like reflection from smooth surface) Diffuse reflection (reflection from rough surface) Fig.8 31 Fig.9 Fig.10 32 Irradiance & radiance Sun Energy reaching the surface is called irradiance. Earth’s surface Energy reflected by the surface is called radiance Earth’s surface The density of radiation incident on a given surface usually expressed in watts per square centimeter or square meter. 33 Summary Remote sensing is a technique of collecting information from a distance Characteristics of Electromagnetic radiation A wavelength Velocity Amplitude Frequency Electromagnetic Spectrum 34 14/10/14 Summary Interactions between Matter & Electromagnetic radiation Energy interactions in the atmosphere: Absorption, Transmission, Scattering Atmospheric absorption Direct radiance Reflected and scattered by cloud Reflected and scattered by dust 17% 31 % 47 % 5% Efficient absorbers of solar radiation in the atmosphere Ozone(O3), Water vapour(H2O), Carbon dioxide(CO2 Types of scattering Rayleigh scattering (Particle size < wavelength) Mie scattering ( Particle size = wavelength) Non-selective scattering (Particle size > wavelength Types of Reflection Specular reflection, Diffuse reflection Percentage of spectral reflectance Vegetation: Soil : Water: 50% 30-40% 10% 35 References • www.google.com • www.wikipedia.com • Principles of Remote sensing • edited by Lucas L.E. Janssen • Remote sensing and image interpretation by Thomas M.Lillesand • University Practical Geography by M. Iftikhar Akram Ch. • http://www.answers.com/topic/specular/-reflection • http://hyperphysics.phyastr.gsu.edu/hbase/mod3.html • http://hosting.soonet.ca/eliris/remotesensing/bl130lec3.html • http://www.cps-amu.org/sf/notes/m1r-1-8.htm 36 14/10/14 Possible Exam Questions Q1. Define the following: Visible spectram Infrared wavelength region Optical wavelength range Radio wave band Q2.Differentiate the Passive remote sensing and Active remote sensing. 5 Marks Q3.Define Electromagnetic spectrum. Describe in detail the all wavelength regions of electromagnetic spectrum. 15 Marks Q5.Write a not on EM spectrum. 37 5 Marks 14/10/14