Remote Sensing Workflow - Essay Example

The Remote Sensing Workflow: The planet-Earth is full of many adventures and natural phenomena, that we are still unfamiliar with, despite our innumerable efforts to proceed in the field of science and technology. To know and comprehend the planet that we live in and study the phenomena occurring within it, both natural and otherwise, there is a dire need to obtain accurate, comprehensive and robust data about the earth. The most efficient and promising way to achieve this is with the help of monitoring the earth through remote observation. (For example space). Morris & Kokhan (2007, p. 239) have defined the remote sensing as a field of science or art that makes use of energy reflected from the Earth that is later processed, evaluated and applied in order to assist one in retrieving information regarding the surface of Earth without physically having to be on it. Sun is the fundamental source of energy for all the creatures on earth. Sun rays falling on earth are partly reflected which are captured by the satellites for generating information. This essay will examine and evaluate the workflow of the remote sensing process and other principals related to it. (CCRS/CCT cited in Canada Centre for Remote Sensing, n.d., p. 5). A) Energy Source: The first condition without which, the process of remote sensing can not take place, is the provision of electromagnetic energy as waves to a specific place or to a study area. Although there are many electromagnetic energy sources, yet the sun is fundamentally the best source of energy. B) Radiation and the Atmosphere: Basically, the energy travels from a source to a target through a medium or vacuum. When it comes to the earth, the energy interacts with the atmosphere, and this interaction gets repeated when the energy is reflected from the study area to the sensor. C) Interaction with the Target: After the electromagnetic waves have passed the atmosphere from some source, they interact with the study area. This interaction depends on the characteristics of the study area and also on the electromagnetic radiation sent to it. D) Recording of Energy by the Sensor: After the electromagnetic waves interact with the study area, part of them is absorbed and the rest is reflected back to the space. Recording and collecting the reflected electromagnetic waves requires a special type of sensor which is familiar with the reflective waves. E) Transmission, Reception, and Processing: The next step is to send the collected electromagnetic waves by the sensor to ground receiving stations and processing stations in an electronic form. F) Interpretation and Analysis: The data is sent to the translation and analysis station where it is converted to graphic form or images that can be seen by eyes so that the decision makers can decide. G) Application: The last step of this operation is to understand, disclose and apply the information that has been retrieved from the study area. The problem can be solved by conducting its comparison with the real information. In 1864, the British physicist Clark Maxell predicted the existence of electromagnetic waves and supposed that the magnetic and electric fields work together to produce radiant energy. In addition to that, he described the visible light to be composed of electromagnetic waves. All types of electromagnetic waves have the same properties and behaviour as those of the visible light; they can be spread, reflected and broken. Electromagnetic radiation consists of electrical field and magnetic field. Each direction of the movement of one field is perpendicular to the other, while they travel at the speed of light. Being the fundamental traits of electromagnetic radiation, a good understanding of wavelength and frequency is vital to ensure correct perception of the remote sensing operation. Harrington (2001, p. 2) has defined wavelength as “the length of one wave cycle, which can be measured as the distance between successive wave crests”. In addition to the definition of wavelength, Harrington (2001) also gave a very precise definition of frequency in his article. Frequency can be defined as “the number of cycles of a wave passing a fixed point per unit of time.” (Harrington, 2001, p. 2). Wavelength is symbolized by a Greek letter lambda (λ). λ may either be measured in meters or any length measurement, including centimeter (10-2 meters), micrometer(10-6 meters) or nanometer (10-9 meters). Frequency was first discovered by the Dutch physicist Heinrich Hertz. It is measured in hertz(Hz) and can be calculated with the help of the formula; c = v λ , where c is the fixed constant referring to the speed of light, and v refers to the frequency of an electromagnetic wave. The satellite spins around to collect and register the reflected electromagnetic waves from the study area forming an orbit. Satellites revolve around the earth in many forms, for example, a satellite may spin in a circular or oval motion. In addition to that, it also revolves at different altitudes, for example, it may operate at 250 Kilometers or 36000 kilometers above the surface of earth. Two factors make satellites stable in their orbits. The first factor is the speed of satellite in straight line, without which, the gravity will drag the satellite and make it return it to the earth. The second factor is the force of attraction between the satellite and the earth, without which, the satellite will fly away in straight line to the space. Although there are generally a huge number of orbits, yet the majority of the satellites revolve around two main orbits which will be illustrated. Geostationary orbits: Satellites that revolve in this orbit revolve with the same spinning direction and the same speed as that of the earth. Therefore, the geostationary satellites appear always in the same place, when observed from the earth. Furthermore, satellites are located almost 36000 Kilometer above the earth and they are useful to collect information over a specific area continuously. Eeather systems and communication satellites are two peculiar examples. Near polar orbits: Satellites that revolve in this orbit revolve between the south and the north. Therefore, they collect a large amount of information as they cover a very large area of the earth. Satellites pass a specific area in the same local sun time and in the same season which provides a consequent lighting condition when collecting information. So there is no need to correct the information if it was formerly collected in good conditions. Existing sensors do not capture all the electromagnetic waves. Their spectral sensitivity and the spatial resolution are also limited. The best way to choose the best sensor for a particular task is by trade off. For example, photographic systems have good spatial resolution, which the non-photographic systems do not. These requirements determine the type of sensors’ platform that has to be used, which may begin with simple platform like a stepladder or helicopter and end with uninhabited aerial vehicles satellites. In addition to that, there are a large number of limitations that make the process of collection of data more expensive that include but are not limited to the time and place limitations. However, it usually gets more complicated when we use modern and innovative ways of collecting the data. For example, the data which is collected by a satellite is limited by the orbit characteristics of the satellite, while the data which is collected by airborne is limited by flight routes. The process of remote sensing is meaningless unless we extract the information and data from the image that is capture by a sensor. The process of extracting the data passes through two main stages. The first stage is pre-process, in which the analyses are usually carried out before the main data analysis and before extracting information from an image. These analyses are grouped as geometric or radiometric corrections and they depend on the platform used and particular sensor. It usually involves correction of data for unwanted sensor or atmospheric noise, so the data represents the reflected waves with more accuracy, correcting radiometric distortions for the data as a result of the differences in geometry of the sensor-earth. Besides, it also involves data conversion to real world coordinates (longitude and latitude). The second stage is “image classification and analysis” which is used in order to identify the pixels and select them digitally. According to (Canada Centre for Remote Sensing, n.d.), the classification “assigns each pixel in an image to a particular class or theme based on statistical characteristics of the pixel brightness values”. There are many ways to approach which are used in reclassification, which are commonly divided into two main groups. The first group is named as “supervised classification”, where the analyst determines the uniform representative samples for the types of cover surface. The second group is the reverse of the supervised classification named as “unsupervised classification”. In this group, by using the clustering algorithm, the analyst determines the number of clusters that are there to be searched in the data, so that the required number of classes may be determined. References: Canada Centre for Remote Sensing (n.d.) Fundamentals OF Remote Sensing. Retrieved from http://www.ccrs.nrcan.gc.ca/resource/tutor/fundam/pdf/fundamentals_e.pdf. Harrington, J. (2001, Nov. 19). Linksys – Antenna Basics. 1-7. Retrieved from http://www- personal.umich.edu/~csev/hng4/chapter-05/antennawhtpaper.pdf. Morris, A., and Kokhan, S. (eds.) (2007). Geographic Uncertainty in Environmental Security. 239-247. NATO Science for Peace and Security Series C:Environmental Security. Doi: 10.1007/978-1-4020-6438-8_14. Read More