Earth and Space Science - Essay Example

?Earth and Space Science Remote sensing of the atmosphere is very essential for the risk-free navigation of airways and weather forecasting of a region over a particular span of time. The process of remote sensing works on the principle of emission and reflection of electromagnetic radiations through the changing medium of gases present in the atmosphere. Instruments connected to aircrafts and space based platforms of satellite devises perform the function of remote sensing with the analysis of the electronic data recorded during the emission of such radiation for the establishment of forecast ideas. This is a process involving the transmission of radio waves of different frequency through different zones of the atmosphere, some of whom are absorbents of the radiation with the presence of atmospheric gases such as water vapor, carbon dioxide and ozone (Remote sensing, n.d.). Therefore the areas of electromagnetic spectrum where these gases are present are known as absorption bands. Absorption bands are represented by a low transmission value associated with specific ranges of wavelengths. On the other hand, the electromagnetic spectrum of the atmosphere with little or no absorption of the radiation due to the absence of atmospheric gases is called atmospheric windows. They are transparent to radiation and allow the transmission of specific wavelengths to the earth’s surface. The instrumentation of new devices is of great effect with the aviation and weather forecasting as they collect data from the reflections of sunlight from a line-of-sight with an object as well as record the frequency modulations on the basis of presence of carbon dioxide and other gases. The variant ability of the wave lengths to intercept the absorption bands is the primary concept in assuming the transparency of opaqueness of atmospheric zones and therefore is the parameters of setting different band zones (ibid). 2. Atmospheric variations are ascertained by meteorologists with implementation of various techniques of remote sensing which involves a large area of classification of features of data collected through sensor devices such as radars. The photo data thus collected varies in their pixel depth and is separately considered for different spectral classes for the requirement of quantitative analysis. The essential purpose of this classification is meant for the optimum use of all the brightness levels available in the data. The photo integrated wavelength data are classified into two categories; supervised classification and unsupervised classification. The former is used for extracting quantitative information from remotely sensed photo data in order to separately allocate the available data into different known pixels to produce agent parameters for separate classes of interest. Most scientists use the MLC (maximum likelihood classification) classification with advantage of the mean vectors and multivariate spreads of each class. The effectiveness of supervised classification under MLC depends largely on the reasonable levels of accurate estimation of the mean vector m and the covariance matrix for arriving at each spectral data. The problem posed by this classification tool is that the accuracy of the estimation depletes when the classes are of a multimodal distribution (Liu, n.d.). The other classification model is the unsupervised classification. The basic feature of this classification is its independence to human interface by using some clustering algorithm to classify the image data. This classification model is essential for the identification of the number and location of the unimodal spectral classes on the basis of the image data. MMC or migrated means clustering classifier is the tools used in this model for labeling each pixel to unknown cluster centers with intend to move the pixel form one cluster center to another for accurate analysis of the image (ibid). 3. The radiation used for image analysis of the remote sensing function falls subject to the interaction between electromagnetic radiation and the ground elements such as, soil, water and vegetation. It is estimated that half of the radiation from the sun light is expected to be absorbed by the earth’s atmosphere and the remaining half is either reflected, transmitted or absorbed by the surface variations of the interaction media like water, soil or vegetation. Reflection is experienced when the radiation reaches the non-transparent surface of the medium, mostly, the soil. When it touches the smooth surface a complete reflection is the effect. However, diffuse reflection is caused when the surface is Lambertian or rough and the radiation is distributed equally into all directions. The radiation reaching the non-reflecting surface is either transmitted or absorbed with a variation resulting from the difference in wave lengths. Since the absorption is wavelength specific and as result, more energy is absorbed at some wavelengths than at others. High temperature results in immediate transmission and sudden weather changes; likewise, the lower the temperature, the longer the wavelength and delayed is the heat emission. Electromagnetic radiation reaching the surface of the earth is largely reflected in a single direction at an angle equal to the angle of incidence and the resultant radiation comprises infra red waves of longer length. However, rougher surfaces cause scattering in all directions. Thus, the variations in wavelengths observed in the absorption process results in forming spectral signatures of spectral reflectance. These spectral signatures are the electronic representation of the reflectance curves differently marked at different regions of the impact areas of the interaction media through which the image is finally formed (Smith, 2006). In most contexts, these image data significantly changes with the influence of factors like temperature, time of the day and the specification of the medium surface. 4. Remote sensing programmes for mapping of land areas are meant essentially for aviation and forest exploration for scientific reasons. Thematic maps used in the navigation of land areas in the earlier days are still used as an input for global information system (GIS) for satellite imagery of landscapes over wide areas of the earth’s surface. The land mapping imagery is classified into vegetation maps covering six categories such as conifer forest, hardwood forest, brush, meadow, water and barren land or dry grassland. The area mapping and location identification is done on the basis of the sample photo of a region with its matching tendencies to the regions with similar models obtained from satellite imagery. Usually, in assessing the accuracy, the classification model of MLC (maximum likelihood classification) is used to ascertain the spectral classes on the basis of which aerial photos and satellite imageries are analysed for the classification of the vegetation and estimation of its area. Military forces and relate research wings operate more technically sound systems of observation comprising polarisation radars in order to interpret the data collected from the geographic area that are not attainable with any single spectrum sensors. There are certain systems of software designed for the absolute accuracy of the analytical data by defense and meteorology departments of different nations. The Forest Inventory and Monitoring Environmetrics of RMRS (The Rocky Mountain Research Station) has designed a software with the title ‘ACAS’ (Accuracy Assessment), composed of inventory satellite imagery of all the sample spectral models including various complex data sampling designs, cluster plots and stratification for improved efficiency of monitoring (Sheoran, Haack & Sawaya, 2009). 5. Spectral resolution refers to the specific wavelength intervals I the electromagnetic spectrum that a sensor can record. For example, band-1 of the Landsat-TM sensor records energy between 0.45 and 0.52µm. Wide intervals in the electromagnetic spectrum are referred to as coarse spectral resolution and narrow intervals are referred to as fine spectral resolution. Landsat’s multispectral scanner (MSS) helps collect large-area inventory and monitoring data but it was criticized that the resolution was too coarse for some applications (Hazarika, n.d.). Presently, with help of thematic mapper (TM) sensors applied in Landsats 4 and 5 and with France’s SPOT, considerably finer resolution data are offered for monitoring than previous times. However, coarse spectral resolutions are still helpful for exploring the details of a large area of landscape taken under a single pixel unit for satellite imagery. The scientific development in satellite technology for spectral resolution monitoring system has cut down the cost of operation significantly during the recent years. Another branch of resolution, Spatial Resolution refers to the fineness of detail viable in an image. In remote sensing spatial resolution corresponds to ground pixel size. For example, the instantaneous field of view (IFOV) of the Landsat-TM sensor “sees” 30mx30m area on the ground (ibid). In other words, spatial resolution is the measure of how closely lines can be resolved in an image considering the system administered for creating the picture. Another kind of resolution is the radiometric resolution which refers to the dynamic range or numbers of possible data file values in each band. For example, a 6-bit the digital file value of resolution as per the imagery of IRS Pan ranges from 0 to 63 and an 8-bit resolution of a Landsat image ranges up to 255 from zero (ibid). In some sensors, the bit depths 7, 9, 10 and 13 are taken to the next highest digit, 8bit, 11 bit etc. As a whole, it describes how clearly a system can distinguish intensity differences among various pictures taken from different intensities. The last of the four kinds is the temporal resolution which refers to frequency of obtaining an imagery of a particular area. Various satellites have been identified as observing temporal resolutions differently. For example, SPOT takes 26 days of time to reappear to face the same image, Landsat (TM) takes 16 days while NOAA and Terra/Aqua obtains the same picture every day (Hazarika, n.d.). 6. Electromagnetic radiation (EMR) or energy interaction with earth’s atmosphere plays a very important role in the remote sensing for weather forecasting and landscape mapping. As s result of the variations in EMR impacts of the channels of radiation, Spectral windows are ascertained for this purpose. The parameters set for interpreting the reflection properties at various resolutions bring easier identification of remotely sensed images. Energy incident in the form of radiation on any given surface three fundamental energy interactions are formed; various factor s of the energy or radiation are reflected, absorbed and transmitted and a new equation of energy conservation can be framed {as- EI(?) = ER(?) + EA (?) + ET(?)} where EI denotes the incident energy, ER denotes the reflected energy , EA denotes the absorbed energy and ET denotes the transmitted energy, with all energy components being a function of wavelength ? (Energy interactions, n.d.). The impact of energy incident is variable with the nature of surface thereby the amount of conservation differs. This methodology of remote sensing the atmosphere of the temperate region of Britain requires the aide of RSDAS at Plymouth Marine Laboratory to produce higher level, geo-referenced physical or biological, near real-time high spatial resolution products for the assessment of sea-surface temperature and temperate volcanic zone of the land surface. They use the marine based technical support for much of this actions as the land temperature is proportionate to the variables of oceanic surface temperature zones. On the contrary, more potent South Australian weather forecasting zones are identified along the south sea coasts which experience a temperature fluctuation more frequent than Britain as an impact of the presence of the land surface existing higher above the sea level than Britain. Theses variations are the resultant factor of impact variable of energy incidents and the conversion happens to the radiation on the surface of land and water differently and as a result of the impact of variations in the breaking winds and temperature. 7. Uninterrupted waves of electromagnetic radiation reach the surface of the earth through earth’s atmosphere and interact with different materials found on the surface. The surface materials thus are subject to incident energy interaction in various ways like absorption, transmission and reflection. Absorption occurs as a result of the obstruction posed by the material on the way of radiation while transmission happens when the energy passes through it. A variation occurred in the direction of the radiation as a result of its interaction with surface of the medium is called reflection. The amount of energy thus absorbed, transmitted or reflected by a material depends upon the wavelength of the energy, material constituting the surface and the condition of the feature. Radiation reflected from the surface is assessed as of many ways; if the surface is smooth, the resultant effect will be Specular Refection that gives rise to images. On the other hand, the roughness of the surface offers a Diffuse Reflection that denies imagery. Thus the ability of the material to reflect perfectly or diffusively is a comparative element to the wavelength of the radiation while forming assessments on the image. In case of radiation on vegetation, the chlorophyll present in the leaves absorbs radiation in the red and blue wavelengths while it reflects green. The nature of the material- the leaf, changes according to seasons and the effect of absorption varies; as a result, the leaves appear dark green in summer and slightly yellowish in autumn, because of the variations in the amount of chlorophyll present in the medium. Internal structure of healthy leaves create diffuse reflectors of near infrared and a bright picture of the tree is visible to the sensing camera. Application of Infra Red wavelength reflection monitoring is the most popular remote sensing methodology used by scientist for determining the health level of the vegetation over a particular region such as plantations, forests etc. Water, however absorbs longer wavelength radiations such as infrared more than shorter wavelengths; therefore, water looks blue-green due to its reflectance at these shorter wavelengths and darker when viewed at red or near infrared wavelengths. However, the excessive presence of algae on the surface of water causes a green image in the visuals. 8. Scattering is the process in which energy is removed from a beam of electromagnetic radiation and reemitted with a change in direction, phase or wavelength. All EM radiation scatters according to the nature of the medium it passes through. It is a known fact that accelerated electric charges can radiate energy and that electromagnetic radiation consists of fields that accelerate charged particles. The extreme waves of scattered light energy, infrared and ultraviolet zones primarily interact with the electrons in all the material observed as the medium of obstruction of the radiation. Essentially, incident beam is the source of energy for the acceleration of electrons with electric charge. Scattering of light energy was taken for developmental physics by expert scientists to consider the features of elasticity and non-elasticity of the scattered light beam. CV Raman found that the light was inelastically scattered and its energy was shifted by an amount equal to the vibrational energy of a molecule or a crystal. Scattering of light beam is the top most of all factors that contribute to the visibility of an object. Appearance of a white field of vision is largely the result of inhomogenieties in the absorption or multiple scattering. For instance, transparent microscopic crystals make transparent boundaries and as a result, the appearance becomes white. Spectral absorption of some wavelengths of the scattered light results in the appearance of the surface of the object in that particular shade. Models designed for scattering of electromagnetic waves are used in the diverse area of science such as measurements in optics, geophysics, communications and remote sensing of the earth. References ‘Energy interactions with atmosphere and earth surface’, n.d, Viewed 24 Aug 2011, Hazarika, M (n.d), ‘Introduction to remote sensing’, Introduction & Basic Principles of RS (2), pp. 1-35, Viewed 24 Aug 2011 Liu, X (n.d), ‘Supervised classification and unsupervised classification’, Class Report, pp. 1-12, Viewed 24 Aug 2011, ‘Remote sensing: Absorption bands and atmospheric windows’, n.d, Earth Observatory, Viewed 24 Aug 2011, Smith, RB 2006, ‘Introduction to remote sensing of environment (RSE)’, pp. 1-31, Viewed 24 Aug 2011, Sheoran, A, Haack, B & Sawaya, S 2009, ‘Land cover/use classification using optical and quad polarization radar imagery’, ASPRS 2009 Annual Conference, George Mason University, Viewed 24 Aug 2011, Read More