1. Multiple choice question ; AR- 7251 M. Sc. (Rural Technology) II Semester Fundamental of Remote Sensing Model Paper 1. Chlorophyll strongly absorbs radition of : (b) Red and Blue wavelength (ii) Which are the primary colour in visible spectrum: (b) Red, Blue, Green (iii) Who wrote the word " Photogrammetry" at first time : (c) A. Maidenbar (iv) In the spectrum, inrared (IR) region covers the wavelength range from: (c) 0.7-100 Um (v) The component of thermal radition in comparision of reflected solar radition in the thermal infrared region is : (c) Small (vi) Ultraviolet and microwave are generally assigned to regions of the : (c) Electromagnetic spectrum (vii) Longest wavelength used for remote sensing is : ((b) Microwave (viii) Hoe many camera unit are used in the convergent photography : (c) Two Camera (ix) India SAR Satellite is : (b) RISAT-1 (x) In GIS environment, cities will be represented with : ( c) Polygon Short Answer Question : How EMR absorption differ in various feature of earth surface. Answer:- Absorption is the main mechanism at work when electromagnetic radiation interacts with the atmosphere. Ozone, carbon dioxide, and water vapors are the three main atmospheric constituents which absorb radiation. There are three ways in which the total incident energy will interact with earth's surface materials. These are Absorption, Transmission, and Reflection. Absorption (A) occurs when radiation (energy) is absorbed into the target while transmission (T) occurs when radiation passes through a target. Reflection (R) occurs when radiation "bounces" off the target and is redirected. How much of the energy is absorbed, transmitted or reflected by a material will depend upon: Wavelength of the energy Material constituting the surface, and Condition of the feature. 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). Water: 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. 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. Soil: Four main factors influence the soil reflectance in remote sensing images: mineral composition, soil moisture, organic 1
matter content and soil texture (surface). Size and shape of the soil aggregate also influence the reflectance in the images. The mineral composition of soils affect the reflectance spectrum. (2) Discuss the difference between low and high oblique photograph. Answer : Oblique is a term that means neither perpendicular nor parallel. In photography terms a photograph taken from an airplane with the camera directed horizontally or downward. Photographs taken at an angle are called oblique photographs. If they are taken from a low angle earth surface aircraft, they are called low oblique and photographs taken from a high angle are called high or steep oblique. Low Oblique Aerial Photography:- Only covers a relatively small area. The ground features have a familiar view It does not show the horizon. High Oblique Aerial Photography :- It covers a very large area (not all usable). Ground Features vary from the very familiar to unfamiliar, depending on the height. (3) How spatial resolution differ form temporal resolution? Spatial Resolution : The detail discernible in an image is dependent on the spatial resolution of the sensor and refers to the size of the smallest possible feature that can be detected. Spatial resolution of passive sensors depends primarily on their Instantaneous Field of View (IFOV). The IFOV is the angular cone of visibility of the sensor, which determines the area on the Earth's surface which is "seen" from a given altitude at one particular moment in time. The size of the area viewed is determined by multiplying the IFOV by the distance from the ground to the sensor. This area on the ground is called the resolution cell and it determines a sensor's maximum spatial resolution. For a homogeneous feature to be detected, its size generally has to be equal to or larger than the resolution cell. If the feature is smaller than this, it may not be detectable as the average brightness of all features in that resolution cell will be recorded. However, smaller features may sometimes be detectable if their reflectance dominates within a articular resolution cell allowing sub-pixel or resolution cell detection. Image pixels are normally square and represent a certain area on an image. It is important to distinguish between pixel size and spatial resolution - they are not interchangeable. If a sensor has a spatial resolution of 20 metres and an image from that sensor is displayed at full resolution, each pixel represents an area of 20m x 20m on the ground. In this case the pixel size and resolution are the same. However, it is possible to display an image with a pixel size different than the resolution. Commercial satellites provide imagery with resolutions varying from a few meters to several kilometers. Temporal Resolution : The concept of temporal resolution is also important to consider in a remote sensing system. The absolute temporal resolution of a remote sensing system is to image the exact same area, at the same viewing angle with the same time. Thus, the actual temporal resolution of a sensor depends on a variety of factors, including the satellite/sensor capabilities, the swath overlap, and latitude. The ability to collect imagery of the same area of the Earth's surface at different periods of time is one of the most important elements for applying remote sensing data. Spectral characteristics of features may change over time and these changes can be detected by collecting and comparing multi-temporal imagery. For example, during the growing season, most species of vegetation are in a continual state of change and our ability to monitor those subtle changes using remote sensing is dependent on when and how frequently we collect imagery. By imaging on a continuing basis at different times we are able to monitor the changes that take place on the Earth's surface, whether they are naturally occurring or induced by humans (such as urban development or deforestation). The time factor in imaging is important when: persistent clouds offer limited clear views of the Earth's surface, short-lived phenomena (floods, oil slicks, etc.) need to be imaged multi-temporal comparisons are required for the changing appearance of a feature over time can be used to distinguish it from near similar features. (4) Write the importance of microwave remote sensing. 2
Answer : Microwave Remote Sensing : There are some remote sensing satellites which carry passive or active microwave sensors. The active sensors emit pulses of microwave radiation to illuminate the areas to be imaged. A microwave imaging system can produce high resolution image of the Earth is the synthetic aperture radar (SAR). Electromagnetic radiation in the microwave wavelength region is used in remote sensing to provide useful information about the Earth's atmosphere, land and ocean. When microwaves strike a surface, the proportion of energy scattered back to the sensor depends on many factors: (i) Physical factors such as the dielectric constant of the surface materials which also depends strongly on the moisture content; (ii) Geometric factors such as surface roughness, slopes, orientation of the objects relative to the radar beam direction; (iii) The types of landcover (soil, vegetation or man-made objects) and (iv) Microwave frequency, polarisation and incident angle. The performance of sensors operating at microwave frequencies is likely to get affected by ice clouds, water clouds, and rain. These three natural phenomena affect the radio waves differently at different frequencies. The ice clouds are completely transparent to all microwave frequencies whereas these are opaque at optical wavelength. Water clouds strongly affect the frequencies above 30 GHz whereas below 15 GHz, the effect is negligible. showed the effect of clouds on radio transmission from space to ground. The effect of rain is more pronounced above 10 GHz in case of intense rain. The imaging radars operate mostly independent of weather and are not affected by cloud cover or haze. Water clouds significantly affect the radars operating above 15 GHz frequencies and the effect of rain is not important at frequencies below 10 GHz. gives the effect of rain on radio transmission from space to ground. The microwave frequencies, one gets information about the target object even during night. This is not possible using optical sensors. The microwaves can penetrate through vegetation and soil to a limited extent. The longer wavelengths penetrate deeper as compared to shorter wavelengths. Thus, using higher frequencies, one can get information about canopies, and using lower frequencies, one can get information about the soil and also subsoil information. The moisture content and density of vegetation also plays an important role in this phenomenon. (5) Describe the effect of mie scattering in remote sensing. Answer: Atmospheric Scattering is the redirection of EMR by particles suspended in the atmosphere or by large molecules of atmospheric gases. Scattering not only reduces the image contrast but also changes the spectral signature of ground objects as seen by the sensor. The amount of scattering depends upon the size of the particles, their abundance, the wavelength of radiation, depth of the atmosphere through which the energy is traveling and the concentration of the particles. Theoretically scattering can be divided into three categories depending upon the wavelength of radiation being scattered and the size of the particles causing the scattering. Mie scattering occurs when the particles are just about the same size as the wavelength of the radiation. Dust, pollen, smoke and water vapour are common causes of Mie scattering. It tends to affect longer wavelengths than those affected by Rayleigh scattering. Mie scattering occurs mostly in the lower portions of the atmosphere where larger particles are more abundant, and dominates when cloud conditions are overcast. (6)What is real remote sensing. Answer : Real Remote Sensing : The real remote sensing is different from ideal remote sensing. In the real situation the climate, sensor, platform, earth speed affect the remote sensing process. The following elements affect the ideal situation of image gathering through satellite. Energy source: Varies with time, place, and objects in ways that cannot be fully predicted. Calibration is sometimes possible, but the exact nature of available electromagnetic energy is usually not known. Atmosphere: Varies according to latitude, season, time of day, local weather, etc. Strong absorption and scattering are the rule at most times and places. Spectral signatures: All objects have theoretically unique signatures, but in practice these may change and cannot always be distinguished; many objects appear the same. Real sensors: No existing sensing system can operate in all wavelengths of interest. Each system is limited by its optical or electronic nature to certain wavelengths. Multiple users: No single combination of remote sensing data and analysis will satisfy all users. Many users are not 3
knowledgeable about subjects outside their immediate disciplines and thus cannot appreciate the full potential or limitations of remotely sensed data and images. Write long Answer : (1)What is the kind of remote sensing Answer : There are two main types of remote sensings: passive remote sensing and active remote sensing. In the passive remote sensing, the sun act as a very convenient source of energy for remote sensing. The sun's energy is either reflected, as in case of visible wavelengths, or absorbed and then reemitted, as in case of thermal infrared wavelengths. Remote sensing systems which measure energy that is naturally available are called passive sensors. Passive sensors can only be used to detect energy when the naturally occurring energy is available. For all reflected energy, this can only take place during the time when the sun is illuminating the Earth. There is no reflected energy available from the sun at night. Energy that is naturally emitted (such as thermal infrared) can be detected in day or night, as long as the amount of energy is large enough to be recorded. Examples of passive remote sensors include film photography, infrared, charge-coupled devices, and radiometers. In the active remote sensing, sensor provide their own energy source for illumination. The sensor emits radiation which is directed toward the target to be investigated. The radiation reflected from that target is detected and measured by the sensor. Advantages for active sensors include the ability to obtain measurements anytime, regardless of the time of day or season. Active sensors can be used for examining wavelengths that are not sufficiently provided by the sun, such as microwaves, or to better control the way a target is illuminated. However, active systems require the generation of a fairly large amount of energy to adequately illuminate targets. Some examples of active sensors are a laser fluorosensor and a synthetic aperture radar (SAR). Que (ii) Describe the difference between vertical and oblique photograph. Answer : Aerial Photographs :There are two main kinds of aerial photograph; oblique images which are taken specifically to record archaeological sites and vertical photographs which are usually taken for other purposes. Vertical photography : Vertical photographs are taken with the camera pointing straight down to the ground and provide a plan view. The camera is usually fixed to a mount inside the aircraft over an opening in the fuselage. Vertical photographs are taken at a specific nominal scale, for example 1:5,000 (which means that an object in the photographs is 5,000 times smaller than it is on the ground). The photographs are taken at set intervals so that each frame overlaps the next by 60 percent. This ensures that all parts of the ground are covered by at least two photographs taken from slightly different positions. When viewed through a specially designed optical instrument called a stereoscope, these two photographs are combined to form a single three-dimensional image. Using computers accurate plans and measurements can be made from these stereoscopic models. Vertical photographs are not usually taken for archaeological purposes, but for reasons such as military and cartographic reconnaissance and civil engineering projects. Vertical surveys usually provide complete cover of a wide area of landscape. Oblique photography : Oblique photographs (also known as oblique aerial photographs or oblique air photographs) are taken from a high point, which is at an angle neither horizontal (ground level photograph) nor perpendicular (vertical aerial photograph) to the area being photographed. This angle is often referred to as a slope. Not long after the development of the camera in the 19th century, to achieve photographs from a sloping angle, oblique photographs began to be taken from cameras attached to balloons, kites and even carrier pigeons. With the advent of modern technology in more recent times, oblique photographs are now taken from an aeroplane or helicopter. Oblique photographs are usually divided into two main types. A high oblique photograph features the horizon in the image. A low oblique photograph is directed at a lower angle, which means that the horizon is not visible. The uses of oblique photographs are endless. Cartographers use them to construct physical and topographical maps. The property and construction industries also use oblique photographs to record and measure properties, as well as to track the progress of development sites. 4
Advantages and disadvantages Oblique photographs have a number of advantages. They show more of an area than ground level photographs, since their view is not obscured by hills, trees or houses. Oblique photographs can also easily be assessed and understood. The perspective of an oblique photograph is similar to that of a conventional (ground-level) photograph, so the physical and cultural features of the landscape are still recognisable. This is unlike vertical aerial photographs which are presented from a map-like perspective. Another advantage of oblique photographs is that they do not require the aircraft to fly directly overhead the area being photographed. This is particularly useful in the case of photo-reconnaissance by the military. A major disadvantage of an oblique photograph is that scale is inconsistent. This means that while distances can be calculated in the foreground, according to the provided scale, distances which are closer to the horizon would be completely inaccurate if calculated using the same scale. (3)Write the difficulties in obtaining the aerial photograph : Answer : Please elaborate the following point. Flight line and path Camera unit and their tilt Type of films Speed of the airplane Climatically/Seasonal situations Time and duration Speed of wind and their direction Financial situation (4) Describe the feature of CARTOSAT and RESOURCESAT satellite. Answer : The Cartosat series of satellites are a type of earth observation satellites indigenously built by India. Up till now 4 Cartosat satellites have been launched by ISRO. The Cartosat series is a part of the Indian Remote Sensing Programme. They were specifically launched for Earth s resource management and monitoring. Cartosat-1 was launched by PSLV-C6 on 5 May 2005 from Satish Dhawan Space Centre's SLP at Sriharikota. [1] Images from the satellite is available from GeoEye for worldwide distribution. The satellite covers the entire globe in 1867 orbits on a 126 day cycle. It carries two state-of-the-art panchromatic (PAN) cameras that take black and white stereoscopic pictures of the earth in the visible region of the electromagnetic spectrum. The two cameras with 2.5 m spatial resolution, acquire two images simultaneously, one forward looking (FORE) at +26 degrees and one aft of the satellite at -5 degrees for near instantaneous stereo data. The time difference between the acquisitions of the same scene by the two cameras is about 52 seconds. Cartosat-2 was launched by PSLV-C7 on 10 January 2007 from Satish Dhawan Space Centre's FLP at Sriharikota. Cartosat-2 carries a state-of-the-art panchromatic (PAN) camera that take black and white pictures of the earth in the visible region of the electromagnetic spectrum. The swath covered by this high resolution PAN camera is 9.6 km and their spatial resolution is less than 1 meter. The satellite can be steered up to 45 degrees along as well as across the track. Cartosat-2 is an advanced remote sensing satellite capable of providing scene-specific spot imagery. The data from the satellite is used for detailed mapping and other cartographic applications at cad-astral level, urban and rural infrastructure development and management, as well 5
as applications in Land Information System (LIS) and Geographical Information System (GIS). Cartosat-2A was launched by PSLV-C9 on 28 April 2008 from Satish Dhawan Space Centre's SLP at Sriharikota along with 9 other satellites. It is a dedicated satellite for the Indian Armed Forces which is in the process of establishing an Aerospace Command. The satellite carries a panchromatic (PAN) camera capable of taking black-and-white pictures in the visible region ofelectromagnetic spectrum. The highly agile Cartosat-2A can be steered up to 45 degrees along as well as across the direction of its movement to facilitate imaging of any area more frequently. Cartosat-2B was launched by PSLV-C15 on 28 April 2008 from Satish Dhawan Space Centre's FLP at Sriharikota. The satellite carries a panchromatic (PAN) camera capable of taking black-andwhite pictures in the visible region of electromagnetic spectrum. The highly agile CARTOSAT-2B can be steered up to 26 degrees along as well as across the direction of its movement to facilitate imaging of any area more frequently. Cartosat-3 is a much more capable satellite, having a resolution of 25 cm (10"). It uses 1.2 m optics with 60% of weight removal compared to Cartosat-2. Other features include the use of adaptive optics, acousto optical devices, in-orbit focusing using MEMs and large area-light weight mirrors. The satellite is planned to be launched on board PSLV during 2014. Potential uses include weather mapping, cartography, and strategic applications. RESOURCESAT-1 (also known as IRS-P6) is an advanced remote sensing satellite built by Indian Space Research Organization. The tenth satellite of ISRO in IRS series, RESOURCESAT-1 is intended to not only continue the remote sensing data services provided by IRS-1C andirs-1d, both of which have far outlived their designed mission lives, but also vastly enhance the data quality. Resourcesat-2 is a follow on mission to Resourcesat-1 and the eighteenth Remote Sensing satellite built by ISRO.RESOURCESAT-2 is intended to continue the remote sensing data services to global users provided by RESOURCESAT-1, and to provide data with enhanced multispectral and spatial coverage as well. Compared to Resourcesat-1, LISS-4 multispectral swath has been enhanced from 23 km to 70 km based on user needs. Suitable changes including miniaturization in payload electronics have been incorporated in Resourcesat-2. Resourcesat-2 along with Youthsat and X-Sat(Singapore) was launched on PSLV-C16 on 20 April 2011. 6