Unit - 5

Remote Sensing

• Remote sensing is taking the pictures of any area, by a camera, without touching it i.e., taking the pictures remotely. The first remote sensing technique is the Aerial photography. These photographs are taken from the air, by using Aero planes. These Aerial maps are taken from various heights depending upon the purpose.
• The Aerial photography has many applications e.g., for Military purpose, for geological surveys, urban planning Disaster planning like floods, landslides, forest fires, for exploration of oil or minerals etc.
• The success of Arial photographs, using the visible portion of the electromagnetic spectrum also triggered the experiments to use other wave length regions of the electromagnetic spectrum.
• From 1960 onwards, many technological experiments were made to make it possible to get the images, in other wavelength regions like.
• Thermal infrared (IR) and microwave of the electromagnetic spectrum etc. So, it started a way back in the beginning of 20th century to get Aerial photograph by Aero- plains at a lower height.
• Now we have started using the manned and also unmanned satellites for taking the images of the earth from the space.

• Remote sensing is a method of collecting and interpreting information about terrain and other objects from a distance without being in physical contact with the objects.
• Remote sensing involves the use of electromagnetic energy for the characteristic’s determination of the object.
• In remote sensing, the imagery is obtained with a sensor. Special techniques are used in remote sensing to process and interpret remote sensing imagery to obtain conventional maps, resource surveys etc.
• It collects information about geology, geography, forestry agriculture etc. and has a vast application in exploration of natural resources.
• Remote sensing has application in the study of natural hazards such as earth quakes, landslides and land subsidence.

1. The term Remote sensing is referred as a "Bird's Eye view" Le looking from above. It gives a synoptic overview of the earth surface. So, it has a lot of advantages for understanding the situation and for planning e.g., floods over a large region, or the forest fire can be located from above and rescue planning can be immediately arranged. So Remote sensing is very good technique for the initial study and for understanding the situation on the field like the areas affected by Tsunamis.
2. The data generated by Remove sensing technique, is multi spectral and have Repetitive coverage. Same feature can be observed in different seasons or with a given interval e.g., the process of desertification can be studied by taking images with regular intervals.
3. The inaccessible areas like volcanic explosion, breaking of a river dam, causing floods, or the forest fire regions etc. For the actual ground survey can be covered by remote sensing techniques, which can collect the images and explain the intensity of the disaster and its aerial expansion.
4. This technique can help to collect the information in a little period of times the timely help can be given to the areas facing the disaster. So, it provides accurate and immediate information about the area under study.
5. The data generated by this remote sensing techniques can be used by multi-disciplines e.g., land use planning, for forest development, geological surveys, urban planning, disaster management etc.

• The aerial photographs and the satellite images, do not have the facilities of identification of the areas by naming them (what the maps have) So it is difficult to the correlate an aerial photograph with the grovel.

• It is a very advanced technology and so it needs a skilled person the collect to analyse and to map the data. So, besides the data collection, the Remote Sensing Analysis also includes data processing to extract information for the direct input to Geographic Information System (G.I.S.).

• The range of all possible frequencies of electromagnetic radiation is called as electromagnetic spectrum.

• The electromagnetic spectrum of an object is defined as the characteristics distribution of electromagnetic radiation emitted or absorbed by the object.

• The electromagnetic spectrum is used for modern radio to gamma radiation at the short-wavelength end. The electromagnetic spectrum covers the wavelength from thousands of kilometres down to a fraction of the size of an atom. The long wavelength limit is the size of the universe itself.

• Some radiations are marked as N but some waves penetrate the atmosphere although it is minimum as compared to the other radiations.

• Although visible light is the most obvious manifestation of electromagnetic radiation, its other forms also exist. The electromagnetic spectrum is the continuum of energy which has range starting from meter to nano-meter in wave length travels at the speed of light and propagates through a vacuum i.e., outer space.

• In general, the wave lengths and frequencies varies from shorter wavelength (i.e., high frequency cosmic waves) to long wave length (i.e., low frequency radio waves)

• Remote sensing deals with energy in visible, thermal, microwave and infrared regions but since earth atmosphere absorbs energy in gamma ray, X-ray and ultra-violet region, these regions are not more advantageous for remote sensing Regions are split up into bands such as green, blue, red, mid infrared, near infrared, microwave and thermal. Thermal infrared remote sensing is carried out at longer wave length.

• Electromagnetic waves are typically described by any of the physical properties like frequency (f), wavelength (A) or photo energy (E). Frequencies ranges from 2.4 x 1023 Hz to 1 Hz.

• Whenever electromagnetic waves exist in a medium with matter then wave length is decreased.
• Generally electromagnetic radiation is classified into radio wave, microwave, infrared and visible region. The behavior of EM radiation depends on its wavelength.

• Spectroscopy can detect a much wider region of the EM spectrum than the visible range of 400 mm to 700 mm.

• When electromagnetic radiation travels through the atmosphere, then radiation can be absorbed or scattered by the constituent particles of the atmosphere.
• When there is radiation absorption then molecular absorption converts the radiation energy into the excitation energy of the molecules.
• When there is scattering of radiation, the scattering redistributes the energy of the incident beam to all direction. The overall effect is the removal of energy from the incident radiation.
• Various effects of absorption and scattering are briefly explained as follows:
• The energy can change only in discrete amount called as transitional energy. A photon of electromagnetic radiation can be absorbed by a molecule when its frequency matches one of the available transitional energies.
• Scattering of electromagnetic radiation is caused by the interaction of radiation with matter. Scattering effectively removes energy from the incident beam. Here energy is not lost as like by absorption; but it is redistributed to other direction.

• Electromagnetic strength can be detected both photographically or electronically. The photographic technique makes use of chemical reactions at the floor of light-touchy movie to come across and file strength variations. It is vital to differentiate among the phrase’s pictures and pix in far off sensing.
• A photo refers to any pictorial representation, no matter what wavelengths or far off sensing tool has been used to come across and file the electromagnetic strength. An image refers especially to pictures which have been detected in addition to recorded on photographic movie. The black and white picture graph to the left, of a part of the town of Ottawa, Canada changed into taken withinside the seen a part of the spectrum. Photos are generally recorded over the wavelength variety from 0.three µm to 0.nine µm - the seen and meditated infrared.
• Based on those definitions, we are able to say that everyone pix are pictures, however now no longer all pictures are pix. Therefore, until we're speak me especially approximately a photo recorded photographically, we use the time period photo.
• An image can also be represented and displayed in a virtual layout via way of means of subdividing the photo into small equal-sized and fashioned areas, known as image factors or pixels, and representing the brightness of every place with a numeric fee or virtual range.
• Indeed, this is precisely what has been accomplished to the picture graph to the left. In fact, the usage of the definitions we've got simply discussed, that is genuinely a virtual photo of the authentic image! The image changed into scanned and subdivided into pixels with every pixel assigned a virtual range representing its relative brightness.
• The laptop shows every virtual fee as distinct brightness stages. Sensors that file electromagnetic strength, electronically file the strength as an array of numbers in virtual layout proper from the start.
• These distinct approaches of representing and showing far off sensing records, both pictorially or digitally, are interchangeable as they bring about the identical records (despite the fact that a few elements can be misplaced whilst changing returned and forth).
• In preceding sections, we defined the seen part of the spectrum and the idea of colorings. We see coloration due to the fact our eyes come across the complete seen variety of wavelengths and our brains technique the records into separate colorings. Can you believe what the arena might appear to be if we ought to simplest see very slim degrees of wavelengths or colorings? That is what number of sensors work.
• The records from a slim wavelength variety is accumulated and saved in a channel, additionally every so often known as a band. We can integrate and show channels of records digitally the usage of the 3 number one colorings (blue, green, and red). The records from every channel is represented as one of the number one colorings and, relying at the relative brightness (i.e., the virtual fee) of every pixel in every channel, the number one colorings integrate in distinct proportions to symbolize distinct colorings.
• When we use this technique to show an unmarried channel or variety of wavelengths, we're genuinely showing that channel thru all 3 number one colorings. Because the brightness stage of every pixel is the identical for every number one coloration, they integrate to shape a black and white photo, displaying diverse sun sunglasses of grey from black to white.
• When we show a couple of channels every as a distinct number one coloration, then the brightness stages can be distinct for every channel/number one coloration aggregate and they'll integrate to shape a coloration photo.

1. A uniform energy source
2. A super sensor
3. A non-interfering atmosphere
4. Multiple data users
5. A real-time data handling system

• The source which provides energy over all wavelengths at a constant high level of output irrespective of place and time is a uniform energy source.

• Super sensor is simple and reliable and it do not need virtually no power or space and it is accurate and economical to operate. This super sensor is highly sensitive to all wavelength providing spatially detailed data on the absolute brightness from a scene throughout the spectrum.

• It is the atmosphere which do not change or modify or conserve the energy from the source any how towards the earth surface or from the earth surface itself.

• The users have knowledge of both their respective areas and of remote sensing data acquisition and analysis techniques. The same set of data have various types of information for different users.

• This is such system in which the instant radiance versus wavelength response over a terrain element is produced. Its further process into an interpretable format and recognize as a unique for the particular terrain element from which it receives. This processing provides timely information.

• Digital image processing consists of the various procedures such as formatting and correcting of the data, digital enhancement for the purpose of better visual interpretation or even automated classification of targets and features completely done by computer.
• In the digital processing of remote sensing imagery, the data should be recorded in digital format so as to store it in computer disk. Hence computer system is main requirement for digital image processing. The various process which are done by a computer system called as an image analysis system consisting of the hardware and software so as to process the data. For the purpose of remote sensing image processing, the special software is commercially developed.
• Methods of Digital Image Processing:
• The main image processing functions available in image analysis system are classified into four group viz.

1. Preprocessing
2. Image enhancement
3. Image transformation
4. Image classification and analysis
5. Data Integration and Analysis
6. Remote Sensing by Satellites

• The meaningful information from the imagery should be extracted so as to obtain the required result from remote sensed data. Therefore, image interpretation techniques are important.
• Interpretation technique of remote sensing imagery consist of the identification and measurement of various targets in an image so as to extract the useful and required information of the targets in an image.
• In remote sensing, the target image can be any object or feature which can be seen and observed in an image and target may be a point, line, surface of the features or area of the features like a tower, a bridge or roadway, large water body or a field.
• A target should be distinguishable indicating the important factor of the target and the target also should contrast with the features around it in the image.
• In remote sensing imagery, the interpretation and identification of targets is performed manually, but in many cases, it can be performed by using imagery displayed in photograph format or a pictorial type of format, not dependent of the type of sensor used to collect the data.
• Remote sensing images can also be shown in a computer as arrays of pixels in which each pixel represent the brightness level in the image but data should be in a digital format visual interpretation can also be done by examining the digital imagery displayed on a computer screen.
• Analogue and also digital imagery can be displayed as black and white images or monochrome images or color images of various wave lengths.
• Digital processing and analysis can be used for visual interpretation by using computer, if remote sensing data is available in digital format.
• Digital processing and analysis are done automatically so as to locate and identify the targets and extract information without any human interpreter. But the digital processing and analysis is not complete replacement at a place of human interpretation because it is rarely carried out.
• Digital processing and analysis are more advance and recent techniques. Note that both manual techniques and digital techniques have their respective advantages and disadvantages for the purpose of interpretation of remote sensing use of specialized equipments are rather less in case of manual interpretation but specialized equipments and expensive equipments are required in case of digital interpretation and analysis.
• Manual interpretation has some limitations because if analyze only a single image at a time but it cannot analyze the multi-images at a time.
• Manual interpretation is a subjective process in which the results will vary with different interpreters and digital analysis is more objective in which the results are more consistent, but determining the accuracy and validity of the required results with the help of digital processing may be difficult.
• In most cases, for analyzing imagery, both visual and digital techniques and methods is used so as to obtain proper image interpretation.

• For visual interpretation and understanding of imagery, the image enhancements are used. The manipulation of the digital pixel values in an image can be done by the digital imagery. This is one of the advantages of digital imagery. Before the distribution of data to the user, radiometric corrections for illumination, atmospheric influences and sensor characteristics can be done but the image will still not be optimized for visual interpretation.
• Some of the remote sensing devices are operated from satellite platforms, should be designed so as to bring to the levels of target or background energy. If there are large variations in spectral response from a diverse range of targets like forest, deserts, water, snowfields etc, then generic radiometric correction cannot give the optimum brightness range, for display and contrast for all targets. Hence a custom adjustment of the range and distribution of brightness values is more essential and necessary for each application and each image.
• Contrast enhancement consists of the changing the original values, therefore the more of the available range can be used. Due to this, the contrast between the targets and their backgrounds can be increased. Understanding the concepts of an image histogram is the key to understand the contrast enhancement. Histogram gives the graphical representation of the brightness values for an image. The brightness values are on x-axis of the graph; whereas the frequency of occurrence of each value in the image is on y-axis and hence it is possible to apply the various enhancements to the data by manipulating the range of digital values in an image with the help of histogram.

• For identification the homogeneous groups of pixels, a human analyst uses the elements of visual interpretation. A human analyst also uses the elements of visual interpretation so as to classify features in an image.
• Spectral information in one or more spectral bands is used by digital image classification and digital image classification attempts to classify each individual pixel based on the spectral information represented by the digital numbers. All pixels in the image to particular classes or themes like water, wheat, corn, coniferous forest, deciduous forest can be assigned.
• In the information classes, the analyst is actually trying to identify in the imagery like rock types, different geologic units, tree species, different kinds of crops, different forest types. Spectral classes consist of group of pixels which are uniform with respect to their brightness values in the various spectral channels of the data. Matching the spectral classes in the data to the information classes of interest is the main purpose or objective.
• A broad information class may consist of a number of spectral sub-classes with unique spectral variations. The analysts do the job to decide on the utility of the different spectral classes and useful information classes.

• Remote sensing statistics could be very essential in terms of infrastructure control. It facilitates you are making choices on a way to upgrade, construct or set up your work. Constructing with right control offers higher outcomes in comparison to building with none leads. Furthermore, far flung sensing offers you a clean image of what your challenge will appearance like. It makes positive which you recognize your needs, mitigate environmental impacts, and additionally to decrease expenses and problems. All the strategies enhance while you operate GIS because the number one device for statistics control and visualization. You may even use them if you have much less time to modernize your strategies with the aid of using mapping and visualization

• The protection and safety of the homes are each the obligations of the engineers. With far flung sensing, securing infrastructure has come to be a clean task. It facilitates to perceive weaknesses in any challenge to make modifications on time. Furthermore, it gives equipment used for combining statistics from elevation and evacuation routes to investigate structural specs and outcomes. The statistics is typically stored in a geodatabase that without problems presentations statistics on a web-primarily based totally map in real-time

• GIS quick includes and analyzes numerous varieties of statistics and pix for web website online analysis. It provides correct outcomes that civil engineers use to engage and hook up with customers without problems thru an easy map. The base map consists of environmental safety areas, aerial photos, and topographic maps. Besides civil engineers use far flung sensing strategies to expect destiny essentials.

• GIS and far-flung sensing era assist in decreasing the price of control. Engineers that employ far flung sensing and GIS not want costly gadgets consisting of printers. Besides, they don’t even want to spend a variety of time the use of technical pens and papers. Before a variety of time and assets had been ate up with the aid of using doing such activities. However, nowadays they handiest want to factor an area and all of the cloth that they want is listed. That manner that there are advanced communications which makes control clean and much less costly.

• The organization that advanced GIS, ESRI assures you that you could get statistics approximately any area. Besides, it affords different essential statistics consisting of the date and get right of entry to logs. Furthermore, GIS facilitates in inspecting and reading statistics therefore making creation simpler for civil engineers.

• Towns are rising in nearly each nook of the world. Proper making plans facilitates in having an easy and handy town. Remote sensing and GIS perform a totally essential position in making sure that its miles achieved. GIS is chargeable for positioning assets in right locations. Remote sensing, on the opposite hand, facilitates to music matters consisting of strength traces and drainage.

• Almost each of us is dealing with rampant urbanization inflicting issues which includes sanitation and housing. Other issues because of urbanization encompass disposal of effluents, water supply, and environmental pollution. However, the use of the proper far off sensing strategies civil engineers could make right city developments.

• Remote sensing and GIS strategies have proved to be impactful in relation to water sources engineering. Constructing dams or different reservoirs calls for quite a few records to permit right sharing. Furthermore, it improves go with the drift controls. Civil engineers can assemble infrastructures that permit human beings to get entry to water sources.

• When aligning highways civil engineers use far off sensing to identify the most inexpensive path. Without far off sensing, avenue creation might be a completely luxurious task. For example, satellite tv for pc records may be used to the spotless hilly path which is straightforward to assemble an avenue or rail. Furthermore, satellite tv for pc pics offer correct facts as a result making plans turns into easy.

• Terrain mapping and evaluation may be very crucial specifically in relation to civil engineering. Terrain mapping enables civil engineers to assemble fine roads. Furthermore, it enables them to keep away from risky regions or spot the exceptional terrains. Without far off sensing strategies, avenue and rail creation may be a completely tough task.

• Civil engineers may be cap in a position to research landslides or different herbal failures the use of far-off sensing strategies. That permits them to construct systems which includes bridges, roads, and rails in secure places. Landslides can reason large harm to infrastructure as a result main to large losses. All this is prevented via way of means of integrating GIS and far off sensing in civil engineering.

• Construction necessities want to be correct for the method to run smoothly. GIS and far off sensing offer logistics, visitors management, and different substances tracking. Furthermore, all facts furnished via way of means of GIS is continually correct as it entails using gadgets which includes satellites. One such example of the facts furnished is the space among points.

• Planners use GIS and far off sensing records to increase and put into effect local plans. Additionally, it presents them with the important gear which includes maps to layout towns, cities, and neighborhoods. Planners have monetary understanding, political survey and technical skill ability to increase areas the use of far-off sensing and GIS.

• Civil engineering is all approximately records coping with. The GIS software program utilized in those fields can keep reference records which includes traces polygons and points. Furthermore, it enables in modeling and simulation as a result engineers could make fine creation the use of fewer sources. Data coping with is a completely touchy discipline that calls for correct figures. Otherwise, mistakes could make the sphere of civil engineering very tough. With far off sensing and GIS, civil engineers could make fine infrastructure.