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Abstract: Radio astronomical observatory site selection in Malaysia is a complex attempt due to the increase of man-made Radio Frequency interferences (RFIs) that can contaminate the observations outcomes. If these signals are continuously present, the avoiding of high RFI location is desirable in order to find the most potential site. In this paper Geography Information Systems (GIS) is integrated to solve radio astronomical site selection problem and to develop a ranking of the potential areas based on a variety of criteria. A proper radio astronomical observatory base is a function of many parameters including population, population density, topology, road network and transmitters' locations. Therefore, by considering almost all of the effective spatial factors simultaneously, two stages of multicriteria evaluation are presented. In order to find the suitable sites, GIS digital map overlay and buffer techniques are used. The resulting residual sites are then evaluated through an internal and external weighting of each parameter. Field observation for targeted sites is conducted where RFI observation setup is carried out in wideband and narrowband analyses. Eventually, the optimum site will be evaluated based on the observations upshot. The results of the experiment will support to the development of the first radio telescope in Malaysia.
Keywords: GIS, RFI, Radio Astronomy
Radio astronomy is the study of celestial objects serve in emitting radio frequency portion of the electromagnetic spectrum. By the means of radio astronomy techniques, Cosmic Microwave Background Radiation can be observed that aided in discovering of an invisible universe. Radio astronomy deals with radio waves in space sequentially to obtain data and information about particular regions in the universe. In addition, radio astronomy techniques are utilized by scientists in observing astronomical phenomena that cannot be seen in visible light with the radio spectrum ranges from approximately one millimeter to hundreds of meters. In comparison, the visible part of the spectrum lies in the study of optical astronomy with the wavelengths of approximately 400 nm (purple) to 700 nm (red) . The development of radio astronomy was started early 1937 at Wheaton Illinois by Grote Reber. Alleviation of man-made RFI is a growing crisis of the importance for radio astronomy. Indeed, numerous satellite services of all kinds create lots of electromagnetic signals of the radio spectrum that most likely to disturb the radio astronomical observations. In order to set up a radio astronomical observation site in Malaysia, it is important to identify and avoid the RFIs disturbance in the targeted areas. To achieve this objective, GIS technology as a computer-based tool for mapping is needed in analyzing and integrating database operations. A GIS-based approach could provide an effective means for graphically conveying complex information related with site targeting, recognizing and identifying the intense sources of interference from terrestrial transmitters.
Generally, RFIs can be classified into two major types. One is the narrowband which arises from licensed transmission and the other is known as wideband which deals with electronic interferences. Licensed transmission refers to telecommunication services such as Global System for Mobile Communications (GSM) networks, radio and TV stations, pager transmitters, cell phones, etc. Conversely, electronic interferences specify on radio broadcast emissions, analog and digital television broadcast emissions, aeronautical communications that are as an indirect result of the operation of electrical equipment. The RFI can be generated locally, through unwanted emissions from the numerous items of equipment at the observatory site, or from off-site, through licensed or unlicensed terrestrial and space-borne transmitters. These sources may produce signals, related harmonics, and other out-of-band emissions, that may fall within the protected radio astronomy bands . Therefore, the man-made interference (RFI) can be easily masked by the weak cosmic radio sources.
The man-made RFIs act as a major threat to the radio astronomy by masking the extremely weak radio signals arriving on Earth. These signals may be very much weaker than the signals used by communication systems . Henceforth, interfering signals could contaminate data collected by radio telescopes which are potentially lead to faulty interpretation. Beyond the RFI factor in sites selection, the consideration of other aspects had give rise to the attempt to study the population, accessibility (road network), population density, topology, and transmitters' location in Malaysia. Population was selected as a parameter due to the man-made RFIs which are likely caused by human. However, population density indicates urban or non-urban area that reflects the level of RFI in a particular location. The selection of the transmitter's location act as a major source of RFI in terms of emitting signals from transmitter towers. Consequently, road network serve as an important factor since it covers the construction of radio telescope in the selected site that correlate with accessibility. Nevertheless, topology is used as an indicator due to the beneficial of land use. Thus, in justifying the finest potential site for radio astronomy observation, information about these aspects are required to illustrate the actual surroundings of the targeted areas using GIS. Hence, the integration of a GIS-based multicriteria decision analysis in estimating the changes of the landscape is facilitated in the selection of potential site for radio astronomy observatory base.
GIS for RFI site selection
According to Malaysian Communications and Multimedia Commission (MCMC) all radiocommunication transmissions shall be capable of being identified by identification signals or by other means. For a radiocommunication station that is opened to the international public correspondence and capable of causing harmful interference beyond its national boundary as in the case of the Amateur Radio Service. Nowadays, as the spectrum is more and more crowded, and interference is becoming difficult to avoid completely. In return, these signals eventually cease the possibility of having an area which is free from RFI. As far as the sensitivity of the new radio telescopes improves the harder becomes the effort to find suitable sites. Zero or least RFI exposure site would be the choice for setting up a radio astronomy observatory base. As regards, a proper selection for radio astronomy observatory base has a vital task in providing spatial data information by means of GIS -spatial data. Appropriate site selections of these potential areas should have minimal RFI exposure and population density with excellent accessibility in addition to suitable topology. Geographic information systems (GIS) are capable of managing large amounts of spatially related information, providing the ability to integrate multiple layers of information and to derive additional information. Site selection technique in GIS implemented a geospatial database relation. This include the spatial features on the Earth's surface as map features and attribute data of each parameter used in this study. In geographical analysis, selection of potential sites was made based on a set of criteria - accessibility, transmitter's location, population, population, and topology. These criteria perform as RFI indicators with the intention to help in determining the best possible site for radio astronomy base. Yet, the answers to question on the suitability of the selected site are provided from network analysis. Using the criteria GIS processes such as buffering, union, erase, dissolve and intersect narrow down the number of possible sites. Result of the geographic and network analyses were then ranked accordingly.
The following variables are undertaken:
RFI are essentially caused by the human being seeing that man-made RF energy had developed into a major contribution of RF energy exposure. With the vast increase of terrestrial and satellite broadcasting and communications, and the enormous number of mobile phones now in use, urban areas are irradiated by a vast number of electromagnetic signals. As usage increases, there is pressure for the use of more frequencies. Therefore, great population site of an area has higher chances of exposing to the RF energy. For that reason, population had become an indicator to RFI in this study.
Distribution of the population densities:
Increase of population density indicates the process of urbanization. As urbanization continue to grow drastically with the increase numbers of population, people tends to bond and demand for more supplies of new technologies. Sequentially, to meet the demand of users for more frequency, more RF energy is needed to facilitate with the development process of urbanization. Thus, population densities turn out to be an important factor in detecting the sources and the strength of RFI level at various locations in Peninsular Malaysia.
Depiction road network:
Most major radio observatories require encompassing good road accessibility that varies from usable to reachable. This parameter is important to reach the selected site regarding to the concept of accessibility. It covers the construction of radio telescope in the selected site. In addition, if no roads exist or the site is quite far from the existing road network, additional costs would have to be incurred to build an access road linking the existing road system. Marketing costs, of which transportation cost, will be a major component that can affect the construction of radio astronomy observatory base.
The existing numbers of frequency bands allocated in radio astronomy prohibit the sensitive receiving equipment of radio astronomers to transmit in the radio astronomy bands. In addition, transmitters using frequencies approximate to radio astronomy can cause interference to radio telescopes. This occurs when the transmitter's output is unduly "broad," spilling over into the radio astronomy frequencies, or when the transmitter emits frequencies outside its intended range [?]. Thus, the avoiding of these transmitters' location is desirable in order to find the most suitable site by means of low RFI level.
The topology is used as one of the parameter in order to determine the site that has the beneficial of land use which refers to a site that should not be restricted from any collaborating institution. On top of that, radio astronomy observatory installations cover a large area with high transmitting power. Due to Malaysia topography, radio telescope should install at elevated locations for clearer observation, and this means that, there are usually no residential buildings in the immediate vicinity. In contrast, non-mountainous areas are the constriction to the astronomy site.
The Study Area
Malaysia is seen as a prospective land in constructing the very first radio astronomy observatory base due to the geographical suitability in terms of climate, topology, existing infrastructure and source availability. The geographical position of the study area which is Peninsular Malaysia with the area of 131600 km2 is located at the south of Thailand in Asia continent of Southeast Asia region. Peninsular Malaysia involved a total of 11 states and the interconnected of 82 districts in Malaysia. It is situated between longitude 100o 19' 0" E to 104o 10' 0" E and latitude 1o 25' 43" N to 6o 39' 56" N. Sequentially, this study area is selected through topological characteristics as well as geographical position of a population of 27million. There are many factors which should be considered in locating a radio astronomy observatory base. In general, a site for an astronomical project should be excellent in terms of atmosphere and geography, as well as other non-technical conditions. The atmospheric factors include atmospheric transparency, seeing, meteorological conditions and sky brightness or interference. While geographical and geological conditions consist of local topography, seismicity, properties of rocks and soils, and source availability. And as for the non-technical issues such as existing infrastructure, accessibility, status of the host country, and construction cost may play major roles in determination of the site. Eventually in this study, only geospatial factors are accessible to be taken into account in justifying the study area in terms of geospatial relation. These factors mainly consist of population, population density, topology, road network and transmitters' location and RFI of exposure. Thus, by integrating all the geographical information through geospatial analysis, the best possible site to build the first radio telescope in Malaysia can be attained. Figure 1 shows the research area for radio astronomical observation selection site.
Figure1: Research area for radio astronomical observation selection site.
Site Selection Process and Database Development
The study of GIS-based multicriteria decision analysis for radio astronomy is apparently one of the first attempts that utilize GIS in determining the alternative sites that best satisfy the multiplicity of selected parameters value. Based on the parameter tested, data were gathered from government agencies. The government agencies that involved in providing secondary spatial and attribute data are the Department of Statistics Malaysia, Department of Meteorological Malaysia, Malaysia Communication and Multimedia Commission (MCMC) and Department of Maps and Measurements of Malaysia. After all data requirements are set, a "base map" scale 1:1,205, 000 can be established. The various thematic maps of the Peninsular Malaysia prepared by GIS are given below:
Fig 2: State boundaries map in Peninsular Malaysia
Fig 3: Road Network map in Peninsular Malaysia
Fig 4: Transmitter location in Peninsular Malaysia
Lowest Population site
Fig 5: Lowest population site in Peninsular Malaysia
Lowest population density
Fig 6: Lowest population density site in Peninsular Malaysia
The spatial model has been developed by implementing these criteria and related conditions under GIS environment. In general, various criteria adopted for selecting the sites using GIS include:
1) Site should be far from human activities
2) Site should be at low population density
3) Site should have good road accessibility
4) Site should not be within 20 km radius from the transmitter signals.
By considering the study area size and the diversity of parameters, site selection analysis is demonstrated in two main steps.
Exclusion of areas unsuitable for radio astronomy observation
Exclusion areas are areas incompatible for setting up a radio astronomy base due to the existence of RFI disturbance to the radio telescope. Data regarding to the parameters are gathered in digital form followed by the process of compilation where data compilation involves assembling all of the spatial and attribute data that are stored in a computerized format within the GIS. In this case, digitizing is required. During this stage, the data are in vector format and geo-processing techniques such as buffer and overlay are used to create the exclusion areas. Buffer range distance of transmitter signal within 20km is determined in order to assist the system in data preparation. The exclusion areas indicate an area which has high population density and transmitter signal with poor accessibility. Most of the non-hilly, non-mountainous part is restricted for radio observation construction due to the extremely weak radio signals received from outer space and long observing times. In other words, the exclusion method essentially eliminates the non-potential areas from any further consideration within the model.
Weighting of residual areas
After comprehensive study of selection parameters, all required spatial features are defined and categorized into three main classes of physical, environmental and socio economic features. The classification is presented in table 1. The weighting process is done through an internal and external weighting of each parameter. Essentially the internal weighting is relied on interference-free operation. As for the external weighting, it would be based on the technical, implementation, safety, environmental, economical and other factors. The residual areas are those remaining after the exclusion areas have been eliminated. These lands are then regarded as suitable sites for setting up a radio astronomy observatory base. After identifying the residual areas, a 24 hours wideband and narrowband observations at frequency 1MHz-2000MHz and 1419MHz-1421 MHz are performed in selecting the most potential sites.
Table 1: The classification of important features
GIS is utilized to identify the most appropriate site by comparing alternative sites on the basis of the non-spatial attributes. Each feature is represented in different layers in ArcGIS. From these layers, a final compilation map is generated according to the essence of the related factor and its effect on the suitability of the site in Peninsular Malaysia. The framework of site selection is shown in figure 7.
The GIS analysis approach is used to selectively delineate the residual areas on the map. Simultaneously, it directs to any features that are conscientious not to match a certain criteria were excluded from the map; the resulting map is then displayed only the criteria that are significant for the analysis. Once all of the criteria defined above had been entered into the GIS, the areas that fulfilled all of the conditions set is depicted by the computer. A few radio astronomy observation sites are selected in a priorities manner. By adopting different parameters and criteria, three levels (level I, II, and III) of preferences have been chosen for selecting the radio astronomy site locations.
The final maps (figure 8) clearly illustrate by defining specific criteria that have to be met or factors that have to be excluded during the choice of a suitable area, the optimal sites that fulfill all of the criteria are quickly depicted using the GIS system. The main conditions that the area meets can be summarised as being areas that are:
Close to relatively low population dense areas
Close to both main roads and railways (accessibility)
Sufficiently far from villages, specific urban communities
Exclude from transmitter signal (outside of 20km radius of transmitters)
Crater earth surface that shield the observatory base from RFI
The spatial model has been developed by implementing these criteria and related conditions under GIS environment. The land suitability maps for radio astronomy sitting at a scale of 1:1,205, 000 have been prepared from a background base of GIS application (figure 8). Due to their greater capacity and detail, these maps are likely to give complete and precise information about site selection application. The information is presented in table 2. From the result, three potential sites that fulfill all the conditions above are identified. Each site is then evaluated using ranking method. The ranking outcomes are as follow:
Kg Sekayu (latitude: 04o57.967' N, longitude: 102o57.332' E)
Kg Bertam ( latitude: 05o09.991' N, Longitude: 102o02.764' E)
Jelebu (latitude: 03o 03.108' N, longitude: 102o 03.912' E)
Table 2: Characteristics of the proposed sites
Average signal (dBW/m2Hz)
Field observation for the three targeted sites is conducted later on where RFI observation setup is carried out in two methods which are the wideband and narrowband analyses. In return, the results for both wideband and narrowband analyses have proven that Sekayu, Terengganu encompassed the lowest RFI site in Peninsular Malaysia with average signals -152.32 dBW/m2Hz in wideband and -153.93 dBW/m2Hz in narrowband. Besides having the lowest transmitter signals, Sekayu also perfectly fit all the criteria as mentioned above (table 2). Hence, Sekayu is proposed to be the most suitable area for radio astronomical observation site in Peninsular Malaysia. In order to visualize the merged map effectively, colours were assigned to different parameters. The capabilities of ArcView and GIS-based maps made the task of selecting these areas much easier. Figure 8 shows the compilation map of RFI indicators for the purpose of radio astronomical site selection.
Fig 8: The compilation map of RFI indicators and the targeted sites in Peninsular Malaysia map.
The use of GIS for evaluation of future radio astronomical observatory base has shown to save time when there is need for fast evaluation. Weighing against others, the result of wideband and narrowband analyses with other indicators show that the most appropriate area to build a radio astronomical observatory base is in Sekayu, Terengganu. In this project maps are developed for potential zones based on site selection criteria. The main advantage found in the use of GIS is the great flexibility with which the data can be manipulated as well as the easy access to the given geographical maps that provide information about RFI indicators and site selection parameters for all states in Peninsular Malaysia. This approach would increase trend in using proper tools, which have the ability to integrate a lot of spatial data simultaneously. These maps may be used by local government agencies to anticipate suitable locations for radio astronomy observatory systems. The most important results of using this method meant for radio astronomy selection is visualization, where GIS offers powerful in presenting spatial information to the level of spatial factors and in conducting multicriteria modeling. It determines geographical distribution and variation of parameters. In studying the surveillance of radio astronomy site selection indicators in Peninsular Malaysia, it is important to note which spatial factor is significant. GIS generated thematic- maps, ranged colour maps or proportional symbol maps to represent the most suitable site that meets the expected criteria. In comparison with tables and charts, maps developed by GIS are more effective means for communicating messages. For the time being, GIS also permits dynamic link between databases system and maps with the intention that data updates are automatically reflected on the maps. Finally, the development of technology in radio astronomy GIS model, in hand represent a step in a more specific decision making for astronomy observatory site selection in Malaysia. However, there is an urgent need, in line with government policy, to reduce economical, social and political constrains which at the same time, boost up the collaborations among agencies. Henceforth, time and major commitment are most needed in contributing to the success of setting up the very first radio astronomical observatory in Sekayu, Terengganu.