chapter one introduction to remote sensing.pptx

remote sensing technology

1. Remote Sensing Seng3192 By Haile Akelok ( MSC in Geomatics )

2. 1. Concepts of Remote Sensing Remotes sensing Definition Electromagnetic Spectrum (UV, Visible, MIR, NIR) Energy Interaction with Atmosphere Scattering, Absorption Energy Interaction with Earth Surface Feature Absorbance, Transmittance, Interaction with Vegetation, soil and water

3. Brian storm question 1. What come in your mind about remote sensing? 2 . Dose we human beings have a power of sensing remotely? 3 . Which sense organ can help us to conduct any RS activities by our self? 4 . What is RS as a science? And why?

4. 1. Concepts of Remote Sensing, Remotes sensing Definition Remote sensing has been variously defined but basically it is the art or science of telling something about an object without touching it. (Fischer et al., 1976) Remote sensing is the acquisition of physical data of an object without touch or contact ( Lintz and Simonett , 1976) Remote sensing is the observation of a target by a device separated from it by some distance. (Barrett and Curtis, 1976) The term “remote sensing ” in its broadest sense merely means “reconnaissance at a distance.” (Colwell, 1966) Remote sensing, though not precisely defined, includes all methods of obtaining pictures or other forms of electromagnetic records of the Earth’s surface .

5. Cont.…. In Generally 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 ; or it is the art and science of recording, measuring, and analyzing information about a phenomenon from a distance without direct contact to the objects. The human visual system is an example of a remote sensing system in the general sense. Humans with the aid of their eyes, noses, and ears are constantly seeing, smelling, and hearing things from a distance as they move through an environment. Humans are naturally designed to be remote sensors

6. Cont.…. Remote sensors are a device that detects EM energy usually records it in analogue or digital way . the process involves an interaction between incident radiation and the targets of interest .

7. Remote sensing Basic advantages To acquire Timely data To provide digital data To covered large area Rapid data acquiring Cost effective To image difficult area Updating information 3D perspective of objects Historical records of land use Qualitative data analysis: eg . delineation of the area of interest Quantitative analysis: eg . Area difference for change detection (Raghunath, 2006 ). Limitation of Remote sensing Cloud and atmospheric interference Not imaging sample Require geo-referencing Difficult to detect fine objects Similar features detected may be difficult to differentiate

8. Certainly, in much of remote sensing, the process involves an interaction between incident radiation and the targets of interest .

9. Essential Components of RS Element of Remote Sensing 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.

10. Essential Components of RS 4. 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. 5. 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). 6. Interpretation and Analysis (F) - the processed image is interpreted, visually and/or digitally or electronically, to extract information about the target which was illuminated. 7. 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.

11. Essential Components of RS Generally remote sensing involves the detection and measurement of the radiations of different wavelengths reflected or emitted from distant objects or materials, which helps in their identification and categorization. When we generalize remote sensing has four main principles/components / : The energy source The transmission path The target The satellite sensor

12. In principle, there are two main categories of spatial data acquisition: I . Ground-based methods such as making field observations, taking in situ measurements and performing land surveying. The principle of a ground-based method: measurements and observations are performed in the real world II . Remote sensing methods, which are based on the use of image data acquired by a sensor such as aerial cameras, scanners or radar. Taking a remote sensing approach means that information is derived from the image data, which form a (limited) representation of the real world However , that the increasingly remote sensing devices are used in the field that can acquire data in a fashion similar to air or space borne sensors. Thus , the strict division between ground based and remote sensing methods is blurring.

13. Electromagnetic energy source and radiation The first requirement for remote sensing is to have an energy source to illuminate the target (unless the sensed energy is being emitted by the target ). This energy is in the form of Electromagnetic Radiation . The main source of electromagnetic energy is the sun. Electromagnetic energy is radiant energy that travels in waves at the speed of light. It can also be described as radiant energy , electromagnetic radiation , electromagnetic waves , light , or the movement of radiation.

14. Electromagnetic energy source and radiation EMR consists Electrical field (E) which varies in magnitude in a direction perpendicular to the direction in which the radiation is traveling, and Magnetic field (M) oriented at right angles to the electrical field. Both these fields travel at the speed of light ((c) 299792458 m/s or 3*108 m/s).

15. Two characteristics of electromagnetic radiation are particularly important for understanding remote sensing. These are Wavelength and Frequency. Wavelength is the length of one wave cycle , which can be measured as the distance between successive wave crests . It represented by the Greek letter lambda (λ). Wavelength is measured in meters (m) or some factor of meters such as nanometers (nm, 10-9 meters), micrometers (µm, 10-6 meters) (µm, 10-6 meters) or centimeters (cm, 10-2 meters). 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. Electromagnetic energy source and radiation

16. Wavelength and frequency are related by the following formula: Shorter the wavelength , the higher the frequency, the longer the wavelength ; the lower the frequency; Understanding the characteristics of electromagnetic radiation in terms of their wavelength and frequency is crucial to understanding the information to be extracted from remote sensing data.  

17. Electromagnetic Spectrum (UV, Visible, MIR, NIR) The total range of wavelengths is commonly referred to as the electromagnetic spectrum. Electromagnetic spectrum is a continuous sequence of electromagnetic energy arranged according to wavelength or frequency . It is the range of all types of EM radiation This continuum is commonly divided into the following ranges, called spectral bands , the boundaries between them being gradational. The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x rays) to the longer wavelengths (including microwaves and broadcast radio waves). Remote sensing involves the measurement of energy in many parts of the electromagnetic (EM) spectrum. The major regions of interest in satellite sensing are visible light , reflected and emitted infrared , and the microwave regions . The measurement of this radiation takes place in what are known as spectral bands.

18. The types of electromagnetic radiation are broadly classified into the following classes (regions, bands or types ) Gamma radiation X-ray radiation Ultraviolet radiation Visible light Infrared radiation Microwave radiation Radio waves

19. The electromagnetic spectrum… Major Divisions of the Electromagnetic Spectrum Gamma rays < 0.03 nm…absorbed in atmosphere X-rays 0.03–300 nm…..absorbed in atmosphere Ultraviolet radiation 0.30–0.38 μ m…partially used to Remote sensing Visible light 0.38–0.72 μ m… used to Remote sensing Infrared radiation… … used to Remote sensing Near infrared 0.72–1.30 μ m Mid infrared 1.30–3.00 μ m Far infrared 7.0–1,000 μ m (1 mm)(thermal) Microwave radiation 1 mm–30 cm … used to Remote sensing Radio ≥ 30 cm….Not used to Remote sensing

20. Electromagnetic Spectrum (UV, Visible, MIR, NIR) There are several regions of the electromagnetic spectrum which are useful for remote sensing. 1. Ultraviolet (UV) Portion: For most purposes, the Ultraviolet (UV) Portion of the spectrum has the shortest wavelengths which are practical for remote sensing. This radiation is just beyond the violet portion of the visible wavelengths, hence its name. Some Earth surface materials, primarily rocks and minerals, fluoresce or emit visible light when illuminated by UV radiation The human eye can only detect only a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an x-ray machine uses yet another portion. 

21. Visible portion :- known as visible light The visible wavelengths cover a range from approximately 0.4 to 0.7 μm . The longest visible wavelength is red and the shortest is violet . It is important to recognize how small the visible portion is relative to the rest of the spectrum . Blue, green , and red are the primary colors or wavelengths of the visible spectrum . Yellow: 0.578 - 0.592 μm Orange: 0.592 - 0.620 μm Red: 0.620 - 0.7 μm Electromagnetic Spectrum (UV, Visible, MIR, NIR) Violet: 0.4 - 0.446 μm Blue: 0.446 - 0.500 μm Green: 0.500 - 0.578 μm

22. Colour Wavelength ( nm ) Frequency ( THz ) Photon energy ( eV )     violet 380–450 670–790 2.75–3.26     blue 450–485 620–670 2.56–2.75     cyan 485–500 600–620 2.48–2.56     green 500–565 530–600 2.19–2.48     yellow 565–590 510–530 2.10–2.19     orange 590–625 480–510 1.98–2.10     red 625–750 400–480 1.65–1.98

23. Infrared (IR) region It covers the wavelength range from approximately 0.7 μm to 100 μm - more than 100 times as wide as the visible portion! The infrared region can be divided into two categories based on their radiation properties Reflected IR covers wavelengths from approximately 0.7 μm to 3.0 μm . It used for remote sensing purposes in ways very similar to radiation in the visible portion. Emitted or Thermal IR covers wavelengths from approximately 3.0 μm to 100 μm . Essentially the radiation that is emitted from the Earth's surface in the form of heat. Radiation in the reflected IR region is used for remote sensing purposes in ways very similar to radiation in the visible portion. Electromagnetic Spectrum (UV, Visible, MIR, NIR)

24. Microwave region Microwave s are defined as electromagnetic radiations with a frequency ranging between 300 MHz to 300 GHz and Wavelength ranges from about 1 mm to 1 m. in some extent 1 mm to around 30 cm. They fall between infrared radiation and radio waves in the electromagnetic spectrum. The shorter wavelengths have properties similar to the thermal infrared region while the longer wavelengths approach the wavelengths used for radio broadcasts. Electromagnetic Spectrum (UV, Visible, MIR, NIR)

25. 1) Gamma Rays <0.30 nm: This range is completely absorbed by the upper atmosphere and not available for remote sensing. 2) X-Rays 0.03 - 30.0 nm: This range is completely absorbed by the atmosphere and not employed in remote sensing. 3 ) Ultraviolet (0.03 - 0.40 μm ) i ) Hard UV 0.03 - 0.3 μm : This range is completely absorbed by the atmosphere and not employed in remote sensing. ii) Photographic UV 0.30—0.40 μm : This range is not absorbed by the atmosphere and detectable with film and photo detectors but with severe atmospheric scattering. 4) Visible Light : This narrow band of electromagnetic radiation extends from about 400 nm (violet) to about 700 nm (red). It‘s Available for remote sensing the Earth, can be imaged with photographic film . Electromagnetic Spectrum (UV, Visible, MIR, NIR)

26. 5) Infrared: 0.7 to 300 μm wavelength. This region is sensitive to plant water content, which is a useful measure in studies of vegetation health. This band is also used for distinguishing clouds, snow, and ice, mapping geologic formations and soil boundaries. It is also responsive to plant and soil moisture content. This region is further divided into the following bands:7 a) Near Infrared (NIR): 0.7 to 1.5 μm . b) Short Wavelength Infrared (SWIR): 1.5 to 3 μm . c) Mid Wavelength Infrared (MWIR): 3 to 8 μm . d) Long Wavelength Infrared (LWIR): 8 to 15 μm . e) Far Infrared (FIR): longer than 15 μm . The NIR and SWIR are also known as the Reflected Infrared, referring to the main infrared component of the solar radiation reflected from the earth's surface. The MWIR and LWIR are the thermal Infrared. 6) Microwaves ( RadSar ) 1 mm to 1 m wavelength. Microwaves can penetrate clouds, fog, and rain. Images can be acquired in the active or passive mode. Radar is the active form of microwave remote sensing. Radar images are acquired at various wavelength bands. 7 ) Radio and TV Waves ( 10 cm to 10 km) wavelength which is longest wavelength portion of the electromagnetic spectrum. Electromagnetic Spectrum (UV, Visible, MIR, NIR)

27. All this energy is inherently similar and radiates in accordance with basic wave theory. The theory describes electromagnetic energy as traveling in a harmonic, sinusoidal fashion at the " velocity of light". The distance from one wave peak to the next is the wavelength, and the number of peaks passing a fixed point in space per unit time is the wave frequency. In remote sensing, it is most common to categorize electromagnetic waves by their wavelength location within the electromagnetic spectrum. " ultraviolet" and "microwave ") are generally assigned to regions of the electromagnetic spectrum for convenience, there is no clear-cut dividing line between one nominal spectral region and the next. Electromagnetic Spectrum (UV, Visible, MIR, NIR)

28. Electromagnetic Energy Interaction With the exception of objects at absolute zero, all objects emit electromagnetic radiation . Objects also reflect radiation that has been emitted by other objects. By recording emitted or reflected radiation, and applying a knowledge of its behaviors as it passes through the earth’s atmosphere and interacts with objects , Remote sensing analysts develop a knowledge of the character of features such as vegetation, water bodies etc on the earth surface. Interpretation of remote sensing imagery depends on a sound understanding of electromagnetic radiation and its interaction with the earth’s surface and the atmosphere

29. Remote sensing requires that electromagnetic radiation travel some distance through the Earth’s atmosphere from the source to the sensor. Radiation from the sun or an active sensor will initially travel through the atmosphere, strike the ground target , and pass through the atmosphere a second time before it reaches a sensor. The total distance the radiation travel in the atmosphere is called the path length. As radiation passes through the atmosphere, it is greatly affected by the atmospheric particles and gases it encounters. Energy Interaction with Atmosphere

30. Particles and gases in the atmosphere can affect the incoming light and radiation. These effects are caused by the mechanisms of scattering and absorption. As a result , three fundamental interactions in the atmosphere are possible: Absorption, Transmission Scattering . The change the radiation experiences is a function of the atmospheric conditions, path length, composition of the particle, the wavelength measurement relative to the diameter of the particle

31. Atmospheric scattering Atmospheric 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, Abundance of particles or gases, and Distance the radiation travels through the atmosphere. There are three (3) types of scattering which take place: Rayleigh scattering Mie scattering and Non-selective scattering

32. 1. Raleigh scattering:- Rayleigh scattering is also known as selective scattering or molecular scattering It occurs when particles are very small compared to the wavelength of the radiation . the dominant scattering mechanism in the upper atmosphere. These could be particles such as small specks of dust or nitrogen (NO 2) and oxygen (O 2) molecules. The effect of Rayleigh scattering is inversely proportional to the 4th power of the wavelength: Causes shorter wavelengths of energy to be scattered much more than longer wavelengths .

33. 2. Mie scattering Mie scattering occurs when atmospheric 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 It occurs mostly in the lower portions of the atmosphere where larger particles are more abundant, and dominates when cloud conditions are overcast. This type of scattering explains the reddish hues of the sky following a forest fire or volcanic eruption

34. Non-selective scattering It occurs when the particles are much larger than the wavelength of the radiation. It can cause Water droplets and large dust particles Gets its name from the fact that all wavelengths are scattered about equally. causes fog and clouds to appear white to our eyes because blue, green, and red light are all scattered in approximately equal quantities (blue + green + red light = white light). Optical remote sensing cannot penetrate clouds. Clouds also have a secondary effect: shadowed regions on the Earth’s surface.

35. Atsmospheric Absorption : Cause in the molecules in the atmosphere to absorb energy at various wavelengths which Ozone (O3 ), carbon dioxide (CO2 ), and water vapor (H2 O ) are the three main atmospheric constituents which absorb radiation. Each gas absorbs radiation at particular wavelength. Ozone serves to absorb the harmful (to most living things) ultraviolet radiation from the sun. 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 in the atmosphere absorbs much of the incoming longwave infrared and shortwave microwave radiation (between 22μm and 1m ). The presence of water vapor in the lower atmosphere varies greatly from location to location and at different times of the year

36. The areas of the spectrum that are not severely influenced by atmospheric absorption and thus, are useful to remote sensors are called atmospheric windows and include: A window in the visible and reflected infrared region , between 0.4-2μm. This is the window where the optical remote sensors operate . Three windows in the thermal infrared region , namely two narrow windows around 3 and 5 μm , and a third , relatively broad , window extending from approximately 8 to 14 μm .

37. ✓ visible portion of the spectrum to which our eyes are most sensitive, corresponds to both an atmospheric window and the peak energy level of the sun. ✓ Energy emitted by the earth corresponds to a window around 10 micrometer in the thermal IR portion of the spectrum. ✓ The large window at wavelength beyond 1 mm is associated with the microwave region. Parts of the spectrum which are not severely influenced by atmospheric absorption are useful to remote sensors, are called atmospheric window.

38. By comparing the characteristics of the two most common energy/radiation sources (the sun and the earth) with the atmospheric windows available to us, we can define those wavelengths that we can use most effectively for remote sensing. 3. Transmission Transmission of radiation occurs when radiation passes through a substance without significant attenuation. For a given thickness, or depth of a substance, the ability of a medium to transmit energy is measured as transmittance .  

39. Energy Interactions with the Earth’s Surface Radiation that is not absorbed or scattered in the atmosphere can reach and interact with the Earth's surface. There are three forms of interaction that can take place when energy strikes, or is incident (I) upon the surface Absorption (A); Transmission (T); Reflection (R ). The total incident energy will interact with the surface in one or more of these three ways. The proportions of each will depend on the wavelength of the energy and the material and condition of the feature. Absorption , transmission, and reflection are related to one another by: Where : EI = incident energy striking an object EA = absorbed radiation ET = transmitted energy ER = reflected energy. Absorption (A) radiation (energy) is absorbed into the target Transmission (T) occurs when radiation passes through a target. Reflection (R) occurs when radiation "bounces" off the target and is redirected. In remote sensing , we are most interested in measuring the radiation reflected from targe ts . ER= EI-EA+ ET.  

40. The proportions of each will depend on Wavelength of the energy ; reflection is proportion to energy of wave length. low wavelength high energy; high wavelength low energy Geometry of surface (smooth and rough Component of material Condition of the feature .

41. The reflected energy is equal to the energy incident on a given feature reduced by the energy that is either absorbed or transmitted by that feature. The geometric manner in which an object reflects energy is also an important consideration. In this regard, there are two types of reflection, which represent the two extreme ends of the way in which energy is reflected from a target: Specular reflection and diffuse reflection Specular reflection , or mirror-like reflection, typically occurs when a surface is smooth and all (or almost all) of the energy is directed away from the surface in a single direction. 2. Diffuse reflection occurs when the surface is rough and the energy is reflected almost uniformly in all directions.

42. Interaction with Vegetation, soil and water 1. Interaction with Vegetation The reflectance characteristics of vegetation depend on the properties of the leaves, including the orientation the structure of the leaf canopy. The proportion of the radiation reflected in the different parts of the spectrum depends on leaf pigmentation, leaf thickness and composition (cell structure), the amount of water in the leaf tissue . Reflectance of green vegetation is low in the visible portion of the spectrum owing to chlorophyll absorption for photosynthesis, high in the near Infrared due to the cell structure of the plant lower again in the short wave Infrared due to water in the cells . very high reflectance in the near infrared region is due to the physical structure of a plant leaf and The spongy mesophyll of the leaf scatters a high amount of near infrared radiation relatively low visible red reflectance

43. Visible portion of the spectrum there is a local reflectance peak in the green (0.55μm) between the blue (0.45μm) and red (0.68μm) chlorophyll absorption valleys (often called the chlorophyll absorption bands ). there is less absorption and proportionately more reflection of the red wavelengths, making the leaves appear red or yellow (yellow is a combination of red and green wavelengths). Leaves : A chemical compound in leaves called chlorophyll strongly absorbs radiation in the red and blue wavelengths but reflects green wavelengths . Leaves appear "greenest" to us in the summer, when chlorophyll content is at its maximum. In autumn, there is less chlorophyll in the leaves, so there is less absorption and proportionately more reflection of the red wavelengths, making the leaves appear red or yellow (yellow is a combination of red and green wavelengths ) The internal structure of healthy leaves act as excellent diffuse reflectors of near-infrared wavelengths

44. 2. Interaction with Water : Spectral reflectance of clear water is low in all portion of the spectrum. Longer wavelength visible and near infrared radiation is absorbed more by water than shorter visible wavelengths. Thus water typically looks blue or blue-green due to stronger reflectance at these shorter wavelengths, and darker if viewed at red or near infrared wavelengths. If there is suspended sediment present in the upper layers of the water body, then this will allow better reflectivity and a brighter appearance of the water . The apparent color of the water will show a slight shift to longer wavelengths Chlorophyll in algae absorbs more of the blue wavelengths and reflects the green, making the water appear more green in colour when algae is present. The topography of the water surface (rough, smooth, floating materials, etc.) can also lead to complications for water-related interpretation due to potential problems of specular reflection and other influences on colour and brightness.

45. End chapter one Chapter Summary question Define remote sensing Discussed essential element or component of remote sensing process What are the relationship between electro magnetic radiation and electromagnetic spectrum Discussed EMR are interact with atmosphere, earth surface Discussed atmospheric scattering and absorption in remote sensing Thank yours Attention