Ch: Introduction to Maps, Map Scale, Latitude; Longitude and Time, Map Projections, Topographical Maps, Introduction To Aerial Photographs, Introduction To. PRACTICAL WORK in Geography. PART II. TEXTBOOK This book is sold subject to the condition that it shall not, by way of trade, be lent, re-sold, hired out or. Practical Work in Geography: Class 11th. Table of Contents. CHAPTER 1. Introduction to Maps; CHAPTER 2. Map Scale; CHAPTER 3. Latitude, Longitude and.
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Rate Product. Have doubts regarding this product? Post your question. Safe and Secure Payments. Easy returns. Back to top. The topographical maps in India are prepared in two series, i.
India and Adjacent Countries Series: Henceforth, the preparation of maps for the adjoining 49 countries was abandoned and the Survey of India confined itself to prepare and publish the topographical maps for India as per the specifications laid down for the International Map Series of the World.
Imaginary lines joining all the points of equal elevation or altitude above mean sea level. Interval between two successive contours. It is also known as vertical interval, usually written as V. Generally, it is constant for a given map. A side view of the ground cut vertically along a straight line.
It is also known as a section or profile. Small straight lines drawn on the map along the direction of maximum slope, running across the contours. They given an idea about the differences in the slope of the ground. Topographic Map: A map of a small area drawn on a large scale depicting detailed surface features both natural and man made.
Relief in this map is shown by contours. The topographical maps of India are prepared on 1: The numbering system of each one of these topographical maps is shown in Fig.
International Map Series of the World: Topographical Maps under International Map Series of the World are designed to produce standardised maps for the entire World on a scale of 1: Reading of Topographical Maps: The study of topographical maps is simple.
It requires the reader to get acquainted with the legend, conventional sign and the colours shown on the sheets. The conventional sign and symbols depicted on the topographical sheets are shown in Fig. The map showing these features is called a relief map. Figure 5. These methods include hachure, hill shading, layer tints, benchmarks and spot heights and contours.
However, contours and spot heights are predominantly used to depict the relief of an area on all topographical maps. Contours are imaginary lines joining places having the same elevation above mean sea level. A map showing the landform of an area by contours is called a contour map.
The method of showing relief features through contour is very useful and versatile. The contour lines on a map provide a useful insight into the topography of an area. Earlier, ground surveys and levelling methods were used to draw contours on topographical maps.
However, the invention of photography and subsequent use of aerial photography have replaced the conventional methods of surveying, levelling and mapping. Henceforth, these photographs are used in topographical mapping. Contours are drawn at different vertical intervals VI , like 20, 50, metres above the mean sea level. It is known as contour interval. It is usually constant on a given map. It is generally expressed in metres.
While the vertical interval between the two successive contour lines remains constant, the horizontal distance varies from place to place depending upon the nature of slope.
The horizontal distance, also known as the horizontal equivalent HE , is large when the slope is gentler and decreases with increasing slope gradient. Drawing of Contours and Their Cross Sections We know that all the topographical features show varying degrees of slopes.
For example, a flat plain exhibits gentler slopes and the cliffs and 53 gorges are associated with the steep slopes. Similarly, valleys and mountain ranges are also characterised by the varying degree of slopes, i. Hence, the spacing of contours is significant since it indicates the slope. Types of slope The slopes can broadly be classified into gentle, steep, concave, convex and irregular or undulating. The contours of different types of slopes 54 show a distinct spacing pattern.
Gentle Slope Steep Slope When the degree or angle of When the degree or angle of slope of a feature is very low, the slope of a feature is high and slope will be gentle. The the contours are closely spaced, contours representing this type they inddicate steep slope. Concave Slope Convex Slope A slope with a gentle gradient in Unlike concave slope, the the lower parts of a relief feature convex slope is fairly gentle in and steep in its upper parts is the upper part and steep in the called the concave slope.
As a result, the Contours in this type of slope are contours are widely spaced in widely spaced in the lower parts the upper parts and are closely and are closely spaced in the spaced in the lower parts. Plateau 56 A widely stretched flat—topped high Conical Hill land, with relatively steeper slopes, It rises almost uniformly from rising above the adjoining plain or the surrounding land.
A conical sea is called a plateau. The contour hill with uniform slope and lines representing a plateau are narrow top is represented by normally close spaced at the margins concentric contours spaced with the innermost contour showing almost at regular intervals. VALLEY A geomorphic feature lying between two hills or ridges and formed as a result of the lateral erosion by a river or a glacier is called a valley.
A V-shaped A U—shaped valley is formed by strong valley occurs in mountainous areas. The lowermost part of the between its two sides and the lowest U—shaped valley is shown by the value of the contour is assigned to it. The contour uniform intervals for all other contour value increases with uniform intervals lines outward.
Gorge Spur In high altitudes, gorges form in the A tongue of land, projecting from. It is also represented by V- lateral erosion. They are deep and shaped contours but in the reverse narrow river valleys with very steep manner. The arms of the V point to sides. Sometimes, a waterfall succeeds or precedes with a cascading stream forming rapids CLIFF upstream or downstream of a It is a very steep or almost waterfall. The contours representing perpendicular face of landform.
On a a waterfall merge into one another map, a cliff may be identified by the while crossing a river stream and the way the contours run very close to one rapids are shown by relatively distant another, ultimately merging into one. Steps for Drawing a Cross-section The following steps may be followed to draw cross-sections of various relief features from their contours: Draw a straight line cutting across the contours on the map and mark it as AB.
Take a strip of white paper or graph and place its edge along the AB line. Mark the position and value of every contour that cuts the line AB. The number of such lines should be equal or more than the total contour lines. Mark the appropriate values corresponding to the contour values along the vertical of the cross-section. The numbering may be started with the lowest value represented by the contours.
Now place the edge of the marked paper along the horizontal line at the bottom line of the cross-section in such a way that AB of the paper corresponds to the AB of the map and mark the contour points. Draw perpendiculars from AB line, intersecting contour lines, to the corresponding line at the cross-section base.
Smoothly join all the points marked on different lines at the cross- section base. The location and pattern of distribution of different features help in understanding the area shown on the map.
Distribution Of Settlements It can be seen in the map through its site, location pattern, alignment and density. The nature and causes of various settlement patterns may be clearly understood by comparing the settlement map with the contour map. Four types of rural settlements may be identified on the map a Compact b Scattered c Linear d Circular Similarly, urban centres may also be distinguished as a Cross-road town b Nodal point c Market centre d Hill station e Coastal resort centre f Port g Manufacturing centre with suburban villages or satellite towns h Capital town i Religious centre Various factors determine the site of settlements like a Source of water b Provision of food c Nature of relief d Nature and character of occupation e Defence Site of settlements should be closely examined with reference to the contour and drainage map.
Density of settlement is directly related to food supply. Sometimes, village settlements form alignments, i. In the case of an urban settlement, a cross-road town assumes a fan-shaped pattern, the houses being arranged along the roadside and the crossing being at the heart of the town and the main market place. In a nodal town, the roads radiate in all directions. Transport And Communication Pattern Relief, population, size and resource development pattern of an area directly influence the means of transport and communication and their 61 density.
These are depicted through conventional signs and symbols. Means of transport and communication provide useful information about the area shown on the map. Knowledge of map language and sense of direction are essential in reading 62 and interpreting topo-sheets. You must first look for the northline and the scale of the map and orient yourself accordingly. All topo-sheets contain a table showing conventional signs and symbols used in the map Figure 5. Conventional signs and symbols are internationally accepted; so, anyone can read any map anywhere in the world without knowing the language of that particular country.
A topographic sheet is usually interpreted under the following heads: Marginal Information: It includes the topographical sheet number, its location, grid references, its extent in degrees and minutes, scale, the districts covered, etc. Relief of the Area: The general topography of the area is studied to identify the plains, plateaus, hills or mountains along with peaks, ridges, spur and the general direction of the slope.
These features are studied under the following heads: With concave, convex, steep or gentle slope and shape. Whether it is broad , narrow, flat, undulating or dissected. Its types, i. General elevation, peak, passes, etc. Drainage of the Area: The important rivers and their tributaries and the type and extent of valleys formed by them, the types of drainage pattern, i.
Land Use: It includes the use of land under different categories like: Transport and Communication: The means of transportation include national or state highways, district roads, cart tracks, camel tracks, footpaths, railways, waterways, major communication lines, post offices, etc.
Settlements are studied under the following heads: The types and patterns of rural settlements, i. Type of urban settlements and their functions, i. The general occupation of the people of the area may be identified with the help of land use and the type of settlement. For example, in rural areas the main occupation of majority of the people is agriculture; in tribal regions, lumbering and primitive agriculture dominates and in coastal areas, fishing is practised.
Similarly, in cities and towns, services and business appear to be the major occupations of the people. For example, the distribution of natural vegetation and cultivated land can be better understood against the background of landform and drainage. Likewise, the distribution of settlements can be examined in association with the levels of transport network system and the nature of topography.
The following steps will help in map interpretation: This would give an idea of the general characteristics of the major and minor physiographic divisions of the area. Note the scale of the map and the contour interval, which will give the extent and general landform of the area. For example, if a contour map is superimposed over a land use map, it provides the relationship between the degree of slope and the type of the land used.
Aerial photographs and satellite imageries of the same area and of the same scale can also be compared with the topographical map to update the information. If you are interpreting the cultural features from a topographical sheet, what information would you like to seek and how would you derive this information?
Discuss with the help of suitable examples. Exercise A Study the contour pattern and answer the following questions. Name the geographical feature formed by contours. Find out the contour interval in the map. Find out the map distance between E and F and convert it into ground distance.
Find out the direction of E, D and F from G. Exercise B Study the extract from the topographical sheet No. Convert 1: Name the major settlements of the area.
What is the direction of flow of the river Ganga? At which one of the banks of river Ganga, Bhatauli is located? What is the pattern of rural settlements along the right bank of river Ganga?
What does the yellow colour in the area refer to? What means of transportation is used to cross the river by the people of Bhatauli village? Give the height of the highest point on the map. River Jamtihwa Nadi is flowing through which quarter of the map? Which is the major settlement located in the east of the Kuardari Nala?
What type of settlement does the area have? Name the geographical feature represented by white patches in the middle of Sipu Nadi. Name the two types of vegetation shown on part of the topographical sheet. What is the direction of the flow of the Kuardari? In which part of the sheet area is Lower Khajuri Dam located? Introduction To Aerial Photographs We are familiar with photographs taken with normal cameras.
These photographs provide us with a view of the object similar to the way we see them with our own eyes. In other words, we get a horizontal perspective of the objects photographed.
For example, a photograph of a part of settlement will provide us a perspective the way it appears to us when we look at it Fig. Suppose we want to take a Figure 6. When we do so and look down, we get a very different perspective.
This perspective, which we get in aerial photographs, is 69 termed as aerial perspective Fig. The photographs taken from an aircraft or helicopter using a precision Figure 6. The photographs so obtained have been found to be indispensable tools in the topographical mapping and interpretation of the images of the objects.
Aerial Camera: A precision camera specifically designed for use in aircrafts. Aerial Film: A roll film with high sensitivity, high intrinsic resolution power and dimensionally stable emulsion support.
Aerial Photography: Art, science and technology of taking aerial photographs from an air-borne platform. Aerial Photograph: A photograph taken from an air-borne platform using a precision camera.
Fiducial Marks: Index marks, rigidly connected at the central or corner edges of the camera body. When the film is exposed, these marks appear on the film negative.
Forward Overlap: The common area on two successive photographs in the flight direction. It is usually expressed in per cent. Image Interpretation: An act of identifying the images of the objects and judging their relative significance.
Nadir Point: The foot of the perpendicular drawn from the camera lens centre on the ground plane. Principal Point: The foot of the perpendicular drawn from the camera lens centre on the photo plane. Principal Distance: The perpendicular distance from the perspective centre to the plane of the photograph. Perspective Centre: The point of origin perspective centre of the bundle of light rays. The science and technology of taking reliable measurements from aerial photographs. Aerial photographs are used in topographical mapping and interpretation.
It refers to the science and technology of making reliable measurements from aerial photographs. Hence, they are used as the data source for creating and updating topographic maps. The development of aerial photography in India is briefly given in Box 6. Aerial photography in India goes back to when large-scale aerial photographs of Agra city were obtained.
Subsequently, Air Survey Party of the Survey of India took up aerial survey of Irrawaddy Delta forests, which was completed during — Subsequently, several similar surveys were carried out and advanced methods of mapping from aerial photographs were used. Today, aerial photography in India is carried out for the entire country under the overall supervision of the Directorate of Air Survey Survey of India New Delhi.
Three flying agencies, i. Puram, New Delhi. It is an art of identifying images of objects and judging their relative significance. A trained interpreter can thus utilise aerial photographs to analyse the land-use changes.
The basic advantages that aerial photographs offer over ground based observation are: Improved vantage point: Time freezing ability: An aerial photograph is a record of the surface features at an instance of exposure.
It can, therefore, be used as a historical record. Broadened Sensitivity: The sensitivity of the film used in taking aerial photographs is relatively more than the sensitivity of the human eyes.
Our eyes perceive only in the visible region of the electromagnetic 72 spectrum, i. Three Dimensional Perspective: Aerial photographs are normally taken with uniform exposure interval that enables us in obtaining stereo pair of photographs.
Such a pair of photographs helps us in getting a three-dimensional view of the surface photographed. The types of the aerial photographs based on the position of optical axis and the scale are given below:. On the basis of the position of the camera axis, aerial photographs are classified into the following types: While taking aerial photographs, two distinct axes are formed from the camera lens centre, one towards the ground plane and the other towards the photo plane.
When the photo plane is kept parallel to the ground plane, the two axes also coincide with each other. The photograph so obtained is known as vertical aerial photograph Figures 6. However, it is normally very difficult to achieve perfect parallelism between the two planes due to the fact that the aircraft flies over the curved surface of the earth.
The photographic axis, therefore, deviates from the vertical axis. If such a deviation is within the range of plus or minus 3o, the near-vertical aerial photographs are obtained. Any photography with an unintentional deviation of more than 3o in the optical axis from the vertical axis is known as a tilted photograph. Introduction To Aerial Photographs.
Figure 6. This kind of photograph is often used in reconnaissance surveys. Such photography is useful in reconnaissance surveys. Table 6. Characteristics Horizon does not Horizon does Horizon appear.
The aerial photographs may also be classified on the basis of the scale of photograph into three types. When the scale of an aerial photograph is 1: The aerial photographs with a scale ranging between 1: The photographs with the scale being smaller than 1: To understand the geometry of an aerial photograph, it is important to appreciate the orientation of the photograph with respect to the ground, i.
The following three examples of such projection would be useful in understanding the problem.
Parallel Projection: In this projection, the projecting rays are parallel but not necessarily perpendicular. Orthogonal Projection: This is a special case of parallel projections. Maps are orthogonal projections of the ground. The advantage of this projection is that the distances, angles or areas on the plane are independent of the elevation differences of the objects.
Central Projection: The projecting rays Aa, Bb and Cc pass through a common point O, which is called the perspective Centre. The image projected by a lens is treated like a central projection. An aerial photograph, as discussed earlier is a central projection. In an absolutely vertical flat terrain the aerial photograph will be geometrically the same as the corresponding map of the area.
However, because of the tilt of the photograph and relief variations of the ground photographed, an Figure 6. As shown in Figure 6. The bundle of light rays coming from the ground plane converge at this point and diverge from there towards the negative photo plane to form images of the objects. Thus, the central projection is characterised by the fact that all straight lines joining corresponding points, i.
If we draw a perpendicular from S following the 77 camera axis onto the negative plane, the point where this perpendicular meets the negative is known as the principal point P in Fig. Similarly, if we draw a vertical line plumb line as indicated by the direction of gravity through S, it will meet the photo negative at a point known as the nadir point and 78 on the ground as the ground nadir point. Observe from figures 6.
Thus in case of a vertical photograph, the principal and the nadir points also coincide with one another. For an oblique photograph, the angle between the camera axis and the plumb line is the tilt angle. The geometry of the positive and the negative planes are identical.
It needs to be understood here that SP, i. On the other hand, SPG, i. A map cannot be directly traced out of an aerial photograph. The reason is that there is a basic difference in the planimetry projection and perspective of a map and an aerial photograph. The difference is given in Table 6. An aerial photograph is A map is a geometrically correct geometrically incorrect.
The representation of the part of the earth distortion in the geometry is projected. The scale of the photograph is The scale of the map is uniform not uniform. Aerial photography holds good for The mapping of inaccessible and inaccessible and inhospitable areas. Even vertical aerial photographs do not have a consistent scale unless they have been taken of a flat terrain. Aerial photographs need to be transformed from perspective view to the planimetric view before they can be used as map substitute.
Such transformed photographs are known 79 as orthophotos. You are already familiar with the concept of a map scale See Chapter 2.
Scale is the ratio of a distance on an aerial photograph the distance between the same two places on the ground in the real world. Scale determines what objects would be visible, the accuracy of estimates and how certain features will appear. When conducting an analysis that is based on air photos, it will sometimes be necessary to make estimates regarding the number of objects, the area covered by a certain amount of material or it may be possible to identify certain features based on their length.
To determine this dimension during air photo interpretation, it will be necessary to make estimates of lengths and areas, which require knowledge of the photo scale. There are three methods to compute the scale of an aerial photograph using different sets of information. Method 1: If additional information like ground distances of two identifiable points in an aerial photograph is available, it is fairly simple to work out the scale of a vertical photograph.
Provided that the corresponding ground distances Dg are known for which the distances on an aerial photograph Dp are measured. In such cases, the scale of an aerial photograph will be measured as a ratio of the two, i. Problem 6. The known distance between the same two points on the ground is 1 km. Compute the scale of the aerial photograph Sp. Method 2: As we know, the distances between different points on the ground are not always known.
However, if a reliable map is available for the area shown on an aerial photograph, it can be used to determine the photo scale. In other words, the distances between two points identifiable both on a map and the aerial photograph enable us to compute the scale of the aerial photograph Sp. The relationship between the two distances may be expressed as under: Photo scale: Map distance Dm x Map scale factor msf Problem 6.
The corresponding distance on an aerial photograph is 10 cm. Calculate the scale of the photograph when the scale of the map is 1: Method 3: The photo scale Figure 6.
The focal length of the camera f and the flying height of the aircraft H are provided as marginal information on 82 most of the vertical photographs Box 6.
The Fig. Focal Length f: Ground distance Dg Problem 6. Fiducial Marks. B is the Flying Agency that carried out the present photography In India three flying agencies are officially permitted to carry out aerial photography. In which of the following aerial photographs the horizon appears?
Vertical b. Near-vertical c. Low-oblique d. In which of the following aerial photographs the Nadir and the principle points coincide? Which type of the following projections is used in aerial photographs? Parallel b. Orthogonal c. Central d. None of the above. State any three advantages that an aerial photograph offers over ground based observations. Answer the following questions in about words: If you have carefully gone through its contents, you would have appreciated that it is an extension of the observation and recording capabilities of the human eyes.
The term remote sensing was first used in the early s. Later, it was defined as the total processes used to acquire and measure the information of some property of objects and phenomena by a recording device sensor that is not in physical contact with the objects and phenomena in study.
It can be noted from the above definition of remote sensing that it primarily involves an object surface, the recording device and the information carrying energy waves Fig 7. The ratio of the radiant energy absorbed by a substance to the energy it receives. Digital image: An array of digital numbers DN arranged in rows and columns, having the property of an intensity value and their locations.
Digital Image Processing: The numerical manipulation of DN values for the purpose of extracting information about the phenomena of the surface they represent. Electromagnetic Radiation EMR: The Energy propagated through a space or a medium at a speed of light.
Electromagnetic Spectrum: The continuum of EMR that ranges from short wave high frequency cosmic radiations to long wavelength low frequency radio waves. An artificially generated colour image in which blue, green and red colours are assigned to the wavelength regions to which they do not belong in nature. For example, in standard a False Colour Composite blue is assigned to green radiations 0. Gray scale: A medium to calibrate the variations in the brightness of an image that ranges from black to white with intermediate grey values.
The permanent record of a scene comprising of natural and man-made features and activities, produced by photographic and non—photographic means. Any imaging or non—imaging device that receives EMR and converts it into a signal that can be recorded and displayed as photographic or digital image.
The ratio of the radiant energy reflected by a substance to the energy it receives. Spectral Band: The range of the wavelengths in the continuous spectrum such as 85 the green band ranges from 0. Figure 7. These basic processes that help in the collection of information about the properties of the objects and phenomena of the earth surface are as follows: Source of Energy: Sun is the most important source of energy used in remote sensing.
The energy may also be artificially generated and used to collect information about the objects and phenomena such as flashguns or energy beams used in radar radio detection and ranging. Transmission of Energy from the Source to the Surface of the Earth: The energy waves vary in size and frequency.
The plotting of such variations is known as the Electromagnetic Spectrum Fig. On the basis of the size of the waves and frequency, the energy waves are grouped into Gamma, X— rays, Ultraviolet rays, Visible rays, Infrared rays , Microwaves and Radio waves.
Each one of these broad regions of spectrum is used in different applications. However, the visible, infrared and microwave regions of energy are used in remote sensing. The propagating energy finally interacts with the objects of the surface of the earth.
This leads to absorption, transmission, reflection or emission of energy from the objects. We all know that all objects vary in their composition, appearance forms and other properties.
Besides, one particular object also responds differently to the energy it receives in different regions of the spectrum Fig. You may be aware of the fact that atmosphere comprises of gases, water molecules and dust particles. The energy reflected from the objects comes in contact with the atmospheric constituents and the properties of the original energy get modified.
Whereas the Carbon dioxide CO2 , the Hydrogen H , and the water molecules absorb energy in the middle infrared region, the dust particles scatter the blue energy. Hence, the energy that is either absorbed or scattered by the atmospheric constituents never reaches to sensor placed onboard a satellite and the properties of the objects carried by such energy waves are left unrecorded.
Introduction To Remote Sensing. The sensors recording the energy that they receive are placed in a near— polar sun synchronous orbit at an altitude of — km. These satellites are known as remote sensing satellites e. Indian Remote Sensing Series. As against these satellites, the weather monitoring and telecommunication satellites are placed in a Geostationary position the satellite is always positioned over its orbit that synchronises with the direction of the rotation of the earth and revolves around the earth coinciding with the direction of the movement of the earth over its axis at an altitude of nearly 36, km e.
INSAT series of satellites. A comparison between the remote sensing and weather monitoring satellites is given in Box 7. Remote sensing satellites are deployed with sensors which are capable of collecting the EMR reflected by the objects. However, the sensors used in remote sensing satellites possess a mechanism that is different from photographic camera in collecting and 90 recording the information. The images so acquired by space-borne sensors are in digital format as against the photographic format obtained through a camera-based system.
The radiations received by the sensor are electronically converted into a digital image. It comprises digital numbers that are arranged in rows and columns. These numbers may also be converted into an analogue picture form of data product. The sensor onboard an earth-orbiting satellite electronically transmits the collected image data to an Earth Receiving Station located in different parts of the world.
In India, one such station is located at Shadnagar near Hyderabad. Extraction of Infor mation Contents from Data Products: After the image data is received at the earth station, it is processed for elimination of errors caused during image data collection. Once the image is corrected, information extraction is carried out from digital images using digital image processing techniques and from analogue form of data products by applying visual interpretation methods.
The interpreted information is finally delineated and converted into different layers of thematic maps. Besides, quantitative measures are also taken to generate a tabular data.
SENSORS A sensor is a device that gathers electromagnetic radiations, converts it into a signal and presents it in a form suitable for obtaining information about the objects under investigation. Based upon the form of the data output, the sensors are classified into photographic analogue and non— photographic digital sensors.
A photographic sensor camera records the images of the objects at an instance of exposure. On the other hand, a non—photographic sensor obtains the images of the objects in bit-by-bit form.
These sensors are known as scanners. In the present chapter, we will confine ourselves to describe the non—photographic sensors that are used in satellite remote sensing. Multispectral Scanners: These sensors are designed to obtain images of the objects while sweeping across the field of view. A scanner is usually made up of a reception system consisting of a mirror and detectors.
A scanning sensor constructs the scene by recording a series of scan lines. While doing so, the motor device oscillates the scanning mirror through the angular field of view of the sensor, which determines the length of scan lines and is called swath. It is because of such reasons that the mode of collection of images by scanners is referred bit—by—bit. Each scene is composed of cells that determine the spatial resolution of an image.
The oscillation of the scanning mirror across the scene directs the received energy to the detectors, where it is converted into electrical signals. These signals are further converted into numerical values called Digital Number DN Values for recording on a magnetic tape. The Multi-Spectral Scanners are divided into the following types: The whiskbroom scanners are made up of a rotating mirror and a single detector.
The mirror is so oriented that when it completes a rotation, the detector sweeps across the field of view. The pushbroom scanners consist of a number of detectors which are equivalent to the number obtained by dividing the swath of the sensor by the size of the spatial resolution Fig. In satellite remote sensing, the sun-synchronous polar orbit enables the collection of images after a pre-determined periodical interval referred to as the temporal resolution or the revisit time of the satellite over the same area of the earth surface.
In another example, Fig. The image acquired in June clearly shows the undisturbed topography of Banda Aceh in Indonesia, whereas the post tsunami image acquired immediately after tsunami reveals the damages that were caused by the tsunami. The red patches in May image refer to Coniferous vegetation.
In November 93 image the additional red patches refer to Deciduous plants and the light red colour is related to the crops. Remote sensors are characterised by spatial, spectral and radiometric resolutions that enable the extraction of useful information pertaining to different terrain conditions.
You must have seen some people using spectacles while reading a book or newspaper. Have you ever thought as to why they do so. It is simply because of the fact that resolving power of their eyes to differentiate two closed spaced letters in a word is unable to identify them as two different letters.
By using positive spectacles they try to improve their vision as well as the resolving power. In remote sensing, the spatial resolution of the sensors refers to the same phenomena.
It is the capability of the sensor to distinguish two closed spaced object surfaces as two different object surfaces. As a rule, with an increasing resolution the identification of even smaller object surfaces become possible. It refers to the sensing and recording power of the sensor in different bands of EMR Electromagnetic radiation. Multispectral images are acquired by using a device that disperses the radiation received by the sensor and recording it by deploying detectors sensitive to specific spectral ranges.
The images obtained in different bands show objects response differently as discussed in Para 3 of the stages in remote sensing data acquisition. It is the capability of the sensor to discriminate between two targets. Higher the radiometric resolution, smaller the radiance differences that can be detected between two targets. The spatial, spectral, and radiometric resolutions of some of the remote 95 sensing satellites of the world are shown in Table 7.
Table 7. You must have seen the rainbow. It is formed through a natural process of dispersion of light rays through PRISM water molecules present in the Artificial Dispersion of Light atmosphere. The same phenomena may be experimented by putting a beam of light at one side of a prism.
At the other side of the prism you may notice the dispersion of energy into seven colours that form white light. We have seen that the electromagnetic energy may be detected either 98 photographically or electronically.
The photographic process uses light sensitive film to detect and record energy variations Refer Chapter 6. On the other hand, a scanning device obtains images in digital mode.
It is important to distinguish between the terms — images and photographs. An image refers to pictorial representation, regardless of what regions of energy have been used to detect and record it. A photograph refers specifically to images that have been recorded on photographic film. Hence, it can be said that all photographs are images, but all images are not photographs.
Based upon the mechanism used in detecting and recording, the remotely sensed data products may be broadly classified into two types: Photographic Images: Photographs are acquired in the optical regions of electromagnetic spectrum, i. Four different types of light sensitive film emulsion bases are used to obtain photographs. These are black and white, colour, black and white infrared and colour infrared.
However, in aerial photography black and white film is normally used. Photographs may be enlarged to any extent without loosing information contents or the contrast. Digital Images: A digital image consists of discrete picture elements called pixels. Each one of the pixels in an image has an intensity value and an address in two-dimensional image space. A digital number DN represents the average intensity value of a pixel. It is dependent upon the electromagnetic energy received by the sensor and the intensity levels used to describe its range.
In a digital image, the reproduction of the details pertaining to the images of the objects is affected by the size of the pixel. A smaller size pixel is generally useful in the preservation of the scene details and digital representation.
However, zooming of the digital image beyond certain extent produces loss of information and the appearance of pixels only. Using a digital image processing algorithms, the digital numbers representing their intensity level in an image may be displayed Fig. We have seen that different sensors obtain photographic and digital data products. Hence, the extraction of both qualitative and quantitative properties of such features could be carried out using either visual interpretation methods or digital image processing techniques.
The visual interpretation is a manual exercise. It involves reading of the images of objects for the purpose of their identification.
On the other hand, digital images require a combination of hardware and software to 99 extract the desired information. It would not be possible to deliberate upon the digital image processing techniques under the constraints of time, equipments and accessories. Hence, only visual interpretation methods would be discussed. Elements of Visual Interpretation Whether we are conscious of it or not we use the form, size, location of the objects and their relationships with the surrounding objects to identify them in our day-to-day life.
These characteristics of objects are termed as elements of visual interpretation. We can further group the characteristics of the objects into two broad categories, i. The image characteristics include tone or colour in which objects appear, their shape, size, pattern, texture and the shadow they cast. On the other hand, location and the association of different objects with their surrounding objects constitute the terrain characteristics.
Tone or Colour: We know that all objects receive energy in all regions of spectrum. The interaction of EMR with the object surface leads to the absorption, transmittance and reflection of energy. It is the reflected amount of the energy that is received and recorded by the sensor in tones of grey, or hues of colour in black and white, and colour images respectively. The variations in the tone or the colour depend upon the orientation of incoming radiations, surface properties and the composition of the objects.
In other words, smooth and dry object surfaces reflect more energy in comparison to the rough and moist surfaces. For example, healthy vegetation reflects strongly in the infrared region because of the multiple-layered leaf structure and appears in a light tone or bright red. Similarly, a fresh water body absorbs much of the radiations received by it and appears in dark tone or black colour, whereas the turbid water body appears in light tone or light bluish colour in FCC due to mixed response shown by the water molecules as well as suspended sand particles Figures 7.
Waterbody Clear water Dark blue to black Turbid waterbody Light blue. Built — up area High density Dark blue to bluish green Low density Light blue. The texture refers to the minor variations in tones of grey or hues of colour. These variations are primarily caused by an aggregation of smaller unit features that fail to be discerned individually such as high density and low density residential areas; slums and squatter settlements; garbage and other forms of solid waste; and different types of crops and plants.
The textural differences in the images of certain objects vary from smooth to coarse textures Fig. For example, dense residential areas in a large city form fine texture due to the concentration of the houses in a smaller area and the low-density residential areas produce a coarse texture.
Similarly, in high resolution images the sugarcane or millet plants produce coarse texture in comparison to the fine texture of rice or wheat plants. One can also notice the coarse texture in the images of scrubbed lands if compared with the fine texture of lush green evergreen forests. The size of an object as discerned from the resolution or scale of an image is another important characteristic of individual objects. It helps in distinctively identifying the industrial and industrial complexes with residential dwellings Fig.
The general form and configuration or an outline of an individual object provides important clues in the interpretation of remote sensing images. The shape of some of the objects is so distinctive that make them easy to identify. For example, the shape of the Sansad Bhawan is typically distinct from many other built-up features.
Similarly, a railway line can be readily distinguished from a road due to its long continuous linearity in shape with gradual change in its course Figure 7. The shape of some of the objects is so typical that they could not be identified without finding out the length of the shadow they cast. For example, the Qutub Minar located in Delhi, minarets of mosques, overhead water tanks, electric or telephone lines, and similar features can only be identified using their shadow.
Shadow also adversely affects the identifiability of the objects in city centres as it produces a dark tone, which dominates the original tone or colour of the features lying under the shadow of tall buildings. It may , however, be noted that the shadow as an element of image interpretation is of less use in satellite images. However, it serves a useful purpose in large-scale aerial photography. The spatial arrangements of many from Sharp Bending natural and man—made features show repetitive Roads.
The arrangements can easily be identified from the images through the utilisation of the pattern they form. For example, planned residential areas with the same size and layout plan of the dwelling units in an urban area can easily be identified if their pattern is followed Figure 7.
Similarly, orchards and plantations produce arrangements of the same type of plants with uniform inter — plant distances. A distinction can also be made between various types of drainage or settlements if their pattern is properly studied and recognised. The association refers to the relationship between the objects and their surroundings along with their geographical location. For example, an educational institution always finds its association with its location in or near a residential area as well as the location of a playground within the same premises.
Similarly, stadium, race course and golf course holds good for a large city, industrial sites along highway at the periphery of a growing city, and slums along drains and railway lines. Choose the right answer from the four alternatives given below i Remote sensing of objects can be done through various means such as A. Which of the following represents the true order of their evolution.
Answer the following questions in about 30 words. Answer the following questions in about words. Explain how it is different from pushbroom scanner. Draw clues from the description of the elements of image interpretation discussed and the colours in which various objects appear on a standard alse Colour Composite.
Weather Instruments, Maps and Charts. Weather Instruments, Maps and Charts Weather denotes the atmospheric conditions of weather elements at a particular place and time.
The weather elements include temperature, pressure, wind, humidity and cloudiness. Each day weather maps are prepared for that day by the Meteorological Department from the data obtained from observations made at various weather stations across the world. In India, weather-related information is collected and published under the auspices of the Indian Meteorological Department, New Delhi, which is also responsible for weather forecasting.
Weather forecasts help in taking safety measures in advance in case of the likelihood of bad weather. Predicting weather a few days in advance may prove very useful to farmers and to the crew of ships, pilots, fishermen, defence personnel, etc. The condition of the atmosphere at a given place and time with respect to atmospheric pressure, temperature, humidity, precipitation, cloudiness and wind.
These factors are known as weather elements. Weather Forecast: Prediction with a reasonable amount of certainty about the conditions of weather that would prevail in the coming 12 to 48 hours in a certain area. Globally, meteorological observations are recorded at three levels, viz. A typical surface observatory has instruments for measuring and recording weather elements like temperature maximum and minimum , air pressure, humidity, clouds, wind and rainfall. Specialised observatories also record elements like radiation, ozone atmospheric trace gases, pollution and atmospheric electricity.
These observations are taken all over the globe at fixed times of the day as decided by the WMO and the use of instruments are made conforming to international standards, thus making observations globally compatible. In India, meteorological observations are normally classified into five categories depending upon their instruments and the number of daily observations taken. The highest category is Class-I. Typical instrumental facility available in a Class-I observatory consists of the following: However, for logistic reasons, some of the observatories take limited number of daily observations upper air observation during daytime only.
Weather satellites make comprehensive and large-scale observations of different meteorological elements at the ground level as well in the upper layers of the atmosphere. The geo-stationary satellites provide space-based observations about weather conditions refer to Chapter 7. Various instruments are used for measuring different weather phenomena. Some of the common but important weather instruments are listed below. Thermometer Thermometer is used to measure air temperature.
Most thermometers are in the form of a narrow closed glass tube with an expanded bulb at one end. The bulb and the lower part of the tube are filled with liquid such as mercury or alcohol. Before the other end is sealed off, the air in the tube is released by heating it.