Paper No: 6 Remote Sensing & GIS Applications in Environmental Sciences Module: 1 Concept of space and time; Types of Satellites Development Team Principal Investigator Prof. R.K. Kohli & Prof. V.K. Garg & Prof. Ashok Dhawan Co- Principal Investigator Central University of Punjab, Bathinda Dr. Puneeta Pandey Assistant Professor Paper Coordinator Centre for Environmental Sciences and Technology Central University of Punjab, Bathinda Dr. Puneeta Pandey Content Writer Central University of Punjab, Bathinda Content Reviewer Dr. Yogalakshmi K.N. Central University of Punjab, Bathinda Anchor Institute Central University of Punjab 1 Remote Sensing & GIS Applications in Environmental Sciences Environmental Sciences Concept of space and time; Types of Satellites Description of Module Subject Name Environmental Sciences Paper Name Remote Sensing & GIS Applications in Environmental Sciences Module Name/Title Concept of space and time; Types of Satellites Module Id EVS/RSGIS-EVS/1 Pre-requisites Basic knowledge of computers To study the concept of space and time. Objectives To provide an overview of the types of satellites based on their applications. Keywords Space, Time, Resolution, Scale, Satellites 2 Remote Sensing & GIS Applications in Environmental Sciences Environmental Sciences Concept of space and time; Types of Satellites Module 1: Concept of space and time; Types of Satellites CONTENTS 1. Learning Objectives 2. Concept of space and time 3. Properties of space 4. Models 5. Types of Satellites 6. Conclusions 7. References 1. Learning Objectives The present module will help us understand the concept of space and time and the role that GIS plays in various domains of space and time. Further, this module would also provide an overview of the types of satellites based on their applications. On completion of this chapter, we would have got an overview on the spatial and temporal framework to receive solutions for spatially related questions. We would also be able to appreciate the fact that spatial dimensions help us in getting better solutions to a problem. 2. Concept of space and time The concept of space can be related to the concept of ‘geo’ in ‘geography’ - geographical entities (physical features) and phenomena (processes). The geographical entities vary over scale, ranging from a small house to the entire planet itself. The phenomena occurs at varied spatial scales and changes over a period of time. Thus, geographical phenomenon encompasses the concept of both ‘space’ and ‘time’. Real world is the physical environment around us that we perceive according to the five senses- sight, touch, taste, smell or hearing. Real world phenomenon may be natural or man-made. Any process that takes place without any human intervention is a natural phenomenon, such as topography, weather, natural disasters; while, those which require human intervention are man-made processes, e.g., construction activities, industrial processes etc. Everything in the world has a spatial dimension or pattern, for example, location of ATM in a city, telephone directories, maps, location of civic amenities, travel route to work place, picnic destinations 3 Remote Sensing & GIS Applications in Environmental Sciences Environmental Sciences Concept of space and time; Types of Satellites and so on. The perception of the world around us falls in the domain of spatial cognition; a field that explores the spatial properties of the world and its changes over time. 3. Properties of space The concept of space broadly encompasses the following properties: 3.1 Location – Every object in a space can be characterized by its location. Location exemplifies ‘spatial’ data, implying that it is in some way referenced to locations on the earth. This location may be represented by Cartesian geometry (x,y plane) or geographical coordinates (latitude, longitude). The location of an object can provide answers to the questions ‘where’, ‘next to what’, ‘close to .... or how far...... from another object’ and may be answered in terms of latitude/longitude, precise address or in relation to other object. The precise location based on latitude and longitude is called as ‘absolute location’; while, a location defined on the basis of a frame of reference or on the basis of a place whose absolute location is known is called as ‘relative location’. 3.2 Size – Size refers to the geometric dimensions of any object in space. Further, size also involves the concept of relative size rather than absolute size; thus, emphasizing the concept of scale. Any object on large scale will provide higher details about the object or area under investigation; while that in a small scale will provide lesser details but larger area. 3.2.1 Scale Scale refers to the ratio of distance on the map to the actual distance on the ground. This has a direct bearing on the details that can be observed on the data; for example, if the scale is fine, higher details can be observed and vice-versa. Spatial scale involves the concept of grain and extent. Grain represents the size of the pixel which is the smallest resolvable unit; while extent represents the size of the study area and is thus, the largest resolvable unit. 4 Remote Sensing & GIS Applications in Environmental Sciences Environmental Sciences Concept of space and time; Types of Satellites Figure 1: Wetland representing bigger grain sizes (http://gif.berkeley.edu/documents/Scale_in_GIS.pdf) The series of pictures in Figure 1 shows a section of wetland at progressively bigger grain sizes. It can be observed clearly that for better details; higher computational power is required. An example of scale is given in Table 1; which provides an overview of different scales employed at various levels of planning. Table 1 gives the information at various scales and levels of planning. Table 1. Information Contents at Various Levels and Scales of Planning (http://www.isprs.org/proceedings/XXXIII/congress/part7/127_XXXIII-part7s.pdf) Level of Planning Range of Scale of Maps Information Contents on the Base Map and Exercise Thematic Maps Regional Planning 1:50,000 NationaL boundaries, Roads ; Railway Lines – Boundaries – 1:100,000 Bridges – Railway, River, Canal, Water 1:250,000 1:1,000,000 Bodies, Topography, Natural hazard prone areas, Environmentally and ecologically sensitive areas, Waste lands. Perspective Planning 1:50,000 1:100,000 Metropolitan Boundaries, Roads, Railway 1:250,000 Lines, Bridges, River, Canal, Lakes, Marshy Lands, Ponds, Embankments, Low lying areas, Religious Places, Places of archeological and historical interests, City forests and parks, Green belts, Cantonment areas, Floodable areas, Sanitary land filling sites, Environmentally and ecologically sensitive areas. 5 Remote Sensing & GIS Applications in Environmental Sciences Environmental Sciences Concept of space and time; Types of Satellites Development Planning 1:10,000 1:25,000 All information contents as in Perspective 1:50,000 Planning above; Ward wise population and density distribution; Water supply and sewage disposal works, Gas and electric supply works and lines, Parking sites, Slums and squatter areas; Areas limiting the development Annual Planning 1:5,000 1:10,000 All information contents as in Development 1:25,000 Planning above Projects/ Schemes/ Site 1:500 1:1,000 1:2,500 All vegetation (trees, bushes, arboriculture, Planning 1:5,000 etc.), Water bodies; High Tension/ Overhead electric and telephone lines, Water supply lines, Sewer lines including manholes, Drainage channels. 3.2.2 Resolution: It refers to the size of the smallest possible feature that can be detected. Most remote sensing images are composed of a matrix of picture elements, or pixels, which are the smallest units of an image. 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. Many posters of satellite images of the Earth have their pixels averaged to represent larger areas, although the original spatial resolution of the sensor that collected the imagery remains the same. Types of Resolution 3.2.2.1 Spatial 3.2.2.2 Spectral 3.2.2.3 Radiometric 3.2.2.4 Temporal 3.2.2.1 Spatial Resolution It is the measure of smallest angular or linear separation between two objects that can be resolved. Spatial resolution of sensors depends on their Instantaneous Field of View (IFOV); which is defined as the angle in the form of cone from sensor to the ground at a given altitude at any instant of time. The dimensions of the area viewed on the ground is determined by multiplying the IFOV by the distance from the ground to the sensor.- 6 Remote Sensing & GIS Applications in Environmental Sciences Environmental Sciences Concept of space and time; Types of Satellites Figure 2: Spectral Resolution and IFOV In images that have coarse or low resolution, such as various commercial satellites, larger details are not available in the image. However, in fine or high resolution images, very minute objects can be detected. Examples include sensors deployed for military purpose. Figure 3: Coarse vs Fine Spatial Resolution (http://gis.humboldt.edu/club/Images/Documents/lecture7.pdf) 7 Remote Sensing & GIS Applications in Environmental Sciences Environmental Sciences Concept of space and time; Types of Satellites 3.2.2.2. Spectral Resolution- It considers number and width of wavelength intervals (spectral bands). It is believed that different features in an image respond differently to different wavelengths. For example, water and vegetation can be distinguished by visible and near infrared wavelengths. However, it would be difficult to distinguish different rock types (Figure 4) based on wide wavelength ranges; rather it requires narrow wavelength bands, implying the sensor should have high resolution.