Browsing by Author "Kassa, Girmay"

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    Gis Based Analysis of Land Use /Land Cover, Land Degradation and Population Changes. (A Study of Boru-Metero Area of South Wello, Amhara Region)
    (Addis Ababa University, 2003-06) Kassa, Girmay; Tegene, Belay (PhD)
    The North-Central high lands of Ethiopia have been exploited over centuries and their present status is alarming. A subsistence rain fed production using obsolete methods characterizes agriculture the predominant economic activity of the area. The study area which cover about 3088ha of South Wello found in Tehuledere Wereda known as Boru-Metero is one of the representative area of the highlands in the region where its land use and land cover has significantly changed due to demographic pressure. Today in many parts of the North-central highlands, cultivated and grazing lands are commonly seen dissected by gullies and gorges of different sizes. Almost all natural forests have been cleared irrespective of slope steepness and are now under cultivation without proper land management. The size of farmland per household is very low due to population growth. Because of these and other factors the rural population of the region and the study area are vulnerable to food shortage every year. The study is designed to address the above interwoven problems in the area related mainly to land use/land cover, land degradation and human population pressure. Accordingly two main objectives were designed: first, establishing the current status and trends in changes of population distribution, land use/land cover changes and identifying areas severely affected by the changes. Second, identifying the causes and consequences of temporal and spatial changes in population distribution, land use/land cover changes and land degradation. In order to fulfill the above objectives, assessment of land use/land cover changes in relation to population growth was done using the available aerial photographs of 1936,1965, 1986 and 1994. An-in-depth investigation of each aerial photographs of the study area was carried out using different raster and vector GIS soft wares such as photogrammetric workstation known as VIRTUOZO, ERDAS Imagine ver.8.3 Map/Info ver.4.1 Arc/view ver.3.2 and others. In order to support those GIS technologies analogue instruments such as Procom-2, pocket Stereoscope, field camera, handheld GPS-45 and others were used. With the help of these technologies and field assessment, land use/land cover changes taking vegetation cover as an indicator was investigated and rural population of the area was also estimated from the stated aerial photos and mapped for each year. The 1936 aerial photographs of the Italians was interpreted for sample area of Borur Sellassie and Gora area and separately compared with the recent 1994 aerial photographs to evaluate land use land cover changes, land degradation and population distribution. While the 1965, 1986 and the 1994 aerial photographs were applied for the whole study area. All the stated year aerial photographs were converted in to digital formats using the above stated soft wares and then geo-referenced, land cover types identified are digitized. The result shows that, cultivated land in Boru-Metero increased from 44.86 percent in 1965 to 49.44 percent and 49.62 percent in 1986 and 1994 respectively. In this respect the change of crop land was not significant because the areas suitable for cropland was already farmed by the 1980’s and since. Conversely, the natural vegetation cover declined from 3.43 percent in 1965 and became 2.74 percent in 1986 and 2.59 percent in 1994. The most significant land cover change found was the increasing of tree farming of Eucalyptus trees. It was only 1.63 percent coverage in 1965 and increased to 4.71 percent in 1986 and 4.63 percent in 1994. This change was the result of the aforestation and enclosure of hill side program done in the 1980’s as well as the increasing of financial income gained from the selling of fuel wood and poles that initiate farmers to plant Eucalyptus trees around their homestead and on their farms. The result of land use/land cover changes investigated on aerial photographs of 1936 in the sample areas of Boru sellassie shows that, cropland which was 50.83 percent coverage in 1936 increased to 64.25 percent in 1994, which was 69.51 additional hectare within 58 years difference. This indicates that there was an expansion of farmland since the 1936 in the area. The analyzed result for Gora area shows that, the cover of natural forest (dominated by Juniperous procera) declined from 18.22 percent in 1936 to 7.70 percent in 1994. The area coverage of natural forest in 1936 shows about 130.9 ha and declined to about 55.1ha in 1994. Therefore, the natural forest cover cleared within 58 years was 57.91 percent of the cover existed in 1936 around Gora area. The investigation of rural population done from the stated aerial photographs show a population of 5404 in 1965, 8050 in 1986 and 9774 in 1994 settled in Boru-Metero. Based on this the population density of the study area shows 175 persons/km2 in 1965, 261 persons /km2 in 1986 and 317 persons /km2 in 1994. Population density regarding the sample area of Boru Sellassie area in 1936 shows 298 persons/km2 and increased into 628 persons/km2 in 1994. On similar trend the population density of Gora area during the 1936 accounted about 44 persons/km2 and increased to about 364 persons/km2
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    Security Improvement for Mobile Ip Communication
    (Addis Ababa University, 2007-08) Kassa, Girmay; Asalefew, Abyot (PhD)
    Route optimization is an enhancement to mobile IP which improves routes for the communication of mobile node with its correspondent nodes. Despite its improvement for the performance of this communication, it brought additional security requirements for the Mobile IP communications since it needs securing the new binding update messages. If the binding update toward the home or correspondent nodes is attacked, future communication between the mobile node and the node to which the binding update was intended to reach will be highly in threat. For this reason the IETF designed solution to secure binding update toward the home agent and the correspondent nodes. The binding update toward the home agent uses the security architecture for Internet protocol and no attacks or flaws have been observed. However the binding update toward correspondent nodes is secured with return routable protocol and there are some flaws that are seen on it which can be analyzed from the design. This thesis presents such flaws on the protocol and describes a solution designed to avoid these security problems. In the solution the return routable protocol is modified to decrease the number of message transfers to send binding update and integrated to work with IPSec for securing it. The design is implemented for simulation using ns-2.29 with C++ and tested for its security and performance. Analysis made from the test results showed that security requirements of binding update to the correspondent nodes in Mobile IP communication system are satisfied as the correspondent node is able to identify false binding updates. In addition the system’s performance is equivalent to the performance of base Mobile IP; the average packet processing time obtained from simulation is 0.75 sec and the average network delay is 12ms.