Introduction
Surveies have shown that merely few landscape on Earth surface remain unchanged or in their natural province and is due to plunge demographic force per unit area and anthropogenetic activities ( Zubair, 2006 ) . Competition between species and human existences has been the taking cause of land screen alteration in the universe. This factor is well verified by the transition of forest land to other utilizations like farming areas for agribusiness, industry urban development, substructure, diversion and others. ( Brown, 2004 )
Forest plays an of import function in the overall stableness of C in the atmosphere mitigating or worsening the effects of planetary heating. Therefore, Forest C segregation can assist to understate the rise of nursery gases in the ambiance, ( Juan and Louis, 2009 )
It is hence of import to observe that woods are counted among the universe ‘s main C sinks subscribers. They store more than 289 giga metric tons ( Gt ) of C in their litter, deadwoods and dirt and these are more than the C found in the ambiance. Globally, there was lessening in C stocks of forest biomes of 0.5 Gt a twelvemonth between 2000 – 2010 and was chiefly due to deforestation, ( FAO, 2010 )
“Globally, about 13 million hectares of woods were changed to other utilizations an some were lost through natural causes each twelvemonth, that is between 2000 and 2010 as when compared to about 16 million hectares per twelvemonth during the 1990s” ( FAO, 2010 ) . The biggest losingss or the highest net one-year loss of woods from 2000 to 2010, are in South America and Africa with four and 3.4 million hectares severally.
On the other manus, a recent survey by the Food and Agriculture Organisation ( FAO, 2010 ) reveal that by and large, the devastation of tropical wood for agricultural activities has decreased over the last 10 old ages, but the rate of deforestation for other activities continues to increase at an dismaying high rate.
The tropical rain woods are important constituent of the clime system and play an of import function in the entire carbon-dioxide exchange balance of the Earth ‘s works screen. McGuffie et Al. ( 1995 ) suggested that the being of tropical rain wood has a great influence on regional clime and as such tropical deforestation has been seen to impact the clime of different parts of the universe.
Tropical woods make up the most diversified ecosystems in the universe with the highest biomass per square meter particularly in the lowland rain wood ( McGuffie et al. 1995 ) . But much of the forest countries have been subjected to uninterrupted depletion as a consequence of artificial or natural factors. The one-year rate of devastation to the rain wood seems to be increasing and could duplicate in the following few decennary ( Myers, 1992 ) .
The tropical rain forest in Nigeria is besides undergoing terrible development as a consequence of population growing, urban enlargements, misdirection and socio-economic development. The procedure of deforestation is chiefly caused by glade of forest land for agricultural activities, logging, fuel wood, excavation and industrialisation etc. Like most tropical parts of the universe, deforestation remain a cardinal issue on environmental, ecological and socio-economic challenge in Nigeria ( Uneke and Ibeh, 2009 )
Nigeria has the highest deforestation rate of primary woods from the revised deforestation figures obtained from Food and Agriculture Organisation of the United Nations ( FAO ) . Between 2000 and 2005 the state lost 55.5 % of its primary woods and contributes 3.3 % in the universe therefore ranked the universe highest rate deforested state. Since 1990 the state has lost a sum of 6.1 million hectares or 35.7 % of its forest screens and this has consequence in the doomed of its primary or old wood at a faster rate. Since 2000 study have shown that Nigeria is losing at an norm of 11 % of this primary wood and which has double the rate of 1990s. Furthermore, the Nigeria First National Biodiversity Report-NFNBR ( 2001 ) estimates the rate of deforestation at approximately 5 % yearly compared with 0.6 % globally.
The major causes of deforestation in Nigeria include corruptness, overpopulation, urbanisation, population growing, unjust distribution of wealth, and poorness ( Ayodele, 2010 ) .The United Nations Framework Convention on Climate Change has stated that the overpowering cause of deforestation is agriculture. It stated that subsistence agribusiness histories for 48 % of deforestation, while 32 % of deforestation consequences from commercial agribusiness. Wood-fuel is said to account for 5 % .
Forest biomass has remained the most common beginning of family energy in Nigeria, run intoing 80 % of domestic energy demands. In 1992, entirely, forest wood and wood coal merchandises were estimated at 55 million dozenss, proposing that much forest forests are been used for domestic intents.
Harmonizing to Choji ( 2005 ) , more than half of 9.6 million hour angle of rain woods in the South of Nigeria have been used to run into the demand for fuel wood in rural and urban vicinities. Compared with the costs of crude oil merchandise, fuel wood is cheaper than any commercial fuel replacement and this has, over the old ages, increased forest depletion. He farther noted that this appears to hold propounded consequence on the environment and the sustainability of the wood.
Similarly, ( Uyigue and Agho,2007 ) besides noted Logging, urbanisation, oil development, subsistence agribusiness, and the aggregation of fuel-wood among all are noted as first causes of deforestation in Nigeria.
Therefore an effort will be made in this survey to map out the position of alterations in the forest countries of Niger Delta Region of Nigeria between 1987 and 2002 utilizing both distant detection and GIS.
Research Question: Is at that place alteration in forest screen in Niger Delta Region of Nigeria between 1987 and 2002?
Purpose: To place and map out alterations in forest screen of Niger Delta Region Nigeria and follow suited methods in observing such alterations utilizing distant feeling informations and GIS techniques
Aims:
* To analyse the Spatio-Temporal alteration in wood screen utilizing categorization methods
* To use different alteration sensing techniques and place alterations in wood screen
* To map out countries of alterations
* To analyse the effects of land screen alteration in the part and to propose some recommendations.
THE STUDY AREA
The survey country is located in the Atlantic coastline of southern Nigeria 5°30N 6°30s. Niger Delta part falls within the tropical rain forest zone of the universe. It ‘s named as the 2nd largest delta in the universe busying about 450 kilometers crossing coastline. The part is describes as largest wetland in Africa and screens over 2000 square kilometres that chiefly consists of lakes, rivers and brook. Ecosystem is diverse and extremely supportive to legion species both aquatic and tellurian and human life, ( Uyigue and Agho, 2007 ) .
The part is vegetation screen is chiefly swamp forest which can be farther divided into two categories ; the Mangrove and the fresh H2O wood. The Mangrove crossing around 1900 square kilometers and the largest in Africa, ( Uyigue and Agho,2007 ) . The chief characteristics of its geographics include utmost blocks of elaborate high wood that occur in the part. It has the largest ply-wood and veneer workss in West Africa and has known as a Centre for proverb milling. The country consist of three types of forest strata of tree tall ( 120m high ) , moderate ( 50m – 100m ) and those below 50m.Some common trees found in the country are obeche, abura, sepele and mahogany. hypertext transfer protocol: //www.britannica.com/EBchecked/topic/523642/Sapele
States found around the part include Niger Delta, Port Harcourt to south western provinces Oyo, Osun and Lagos province. The part has heavy precipitation of between 1824 millimeters and over 4000 millimeters along the seashore. Rainfall falls throughout the twelvemonth with a shorter interruption in August and longer one from December to January. Trade air currents originated from Atlantic Ocean of the southern portion of the state is responsible for Nigerian rainy seasons Nigeria. The part has an equatorial monsoon clime ; temperature ranges between 28°C ( 82.4°F ) and 26°C ( 78.8°F ) ( Wikipedia ) .
Map demoing the location of the survey country
LITERATURE REVIEW
Landsat is an of import constituent in the clime system, and plays a cardinal function in supervising planetary alteration and is primary beginning of medium spacial declaration Earth observation used in determination devising ( Gyanesh Chandera et al. , 2009 ) . Remote sensed imagination provides accurate apprehension and comprehensive manner of modeling and projecting land alteration ( Elvidge et al. , 2004 )
With the debut of landSat5 1984 and landSat7 ETM+ 2002, this has marked a important progress in distant feeling through obtaining more sophisticated progress detector ; better acquisition and transmittal of informations and more rapid processing at a extremely processing installation ( Gyanesh Chandera et al. , 2009 ) .
Change Detection is one of the chief applications of remote sensed informations. A considerable sum of literatures has been published by the research workers in seeking to quantify and assess land screen alteration sensing
Change sensing is the procedure of placing differences in the province on an object or phenomena by detecting it at different times, over a certain period of clip. ( Singh, 1989 ) cited in ( Lu et. al. , 2004 )
A quite figure of alteration sensing techniques have been summarised by many writers in an effort to happen out land screen alterations over clip. Lu et al. , ( 2004 ) categorizes these techniques into seven categories runing from simple algebra ‘s to more complex and progress 1s viz. ; Algebra which include image rationing, image differencing flora index differencing, Change vector analysis, others in the class includes transmutations, categorizations, Advance theoretical accounts, Biophysical parametric quantity methods and those that involve the combination of both GIS and remote feeling informations for analysis
Change sensing have gained broad scope of application in the field land usage land screen alteration ; Peiju et al. , ( 2010 ) , reported to hold used multi- temporal remote feeling Landsat TM to supervise urban land screen and flora alteration in Xuzhon metropolis between 1987 – 2007, the consequence of the statistical analysis show that build up countries have evidently increase while farming area have seen in a uninterrupted loss due to urban growing and human activities. Zubair ( 2006 ) detects alterations in land usage land screen in Kwara province Nigeria between 1972 1nd 2001 utilizing alteration sensing techniques of GIS and remote feeling informations, the consequence of the analysis show that there was rapid growing in the built up countries and was a consequence of population force per unit area. He noted that there was steady decrease in forest screen in the survey country and farther predicts continues loss in subsequent old ages. Chen, 2002, noted the usage of GIS and remote feeling techniques and proctors alterations along the coastline zone of Korea, the consequence of the survey show that both human and natural factors are responsible for the alteration and this has on the other manus impacted the sustainable development of the part. Janifer et al. , 2010, proctors forest alteration in the landscapes country of Chile between 1975 and 2008, the consequence of the survey show an mean rate Deforestation was -1.7 % and bush land -0.7 % , nevertheless agribusiness and timber plantations increased at one-year rate of 1.1 % and 3.3 % severally. The survey concludes there is progressive doomed of forest screen in the part.
Furthermore, in the field of Urban and environmental alteration ; George et al. , ( 2009 ) , used Landsat imagination alteration sensing methods in updating the 2001 national land screen database land screen categorization to 2006, conservative thresholds based on Anderson degree 1 categories were used to segregate the alteration vectors and determine countries of alteration and no alteration. An truth of 83.225 % of the five selected countries achieved. Woodcock et al. , ( 2001 ) noted Landsat in observing environmental alteration over clip, the survey makes usage of generalisation method in supervising big countries for wood alteration and conclude that method is state-of-the Earth as other methods and consumes less clip as other conventional methods
Change sensing in the field of forest or flora alteration includes the work of Chengquan et al. , ( 2009 ) , in the appraisal of Paraguay ‘s forest screen alteration utilizing Landsat observation of high declaration image showed that Atlantic forest ecosystem experienced the most loss with the 73.4 % forest screen in the 1970 ‘s diminishing sharply down to 40.4 % by the 1990s and farther down to 24.9 % by the twelvemonth 2000. Rasuly et al. , 2010, noted the advantage of utilizing GIS and remote feeling techniques to supervise the rate of forest changes in the Arasbaran protected country utilizing assorted methods, the consequence of the survey show that about 6146.9 hectares of the country has being deforested over the past 18 old ages, in collaborating with the GIS besides show that the doomed was due to physiographic factors and they suggest to distant colonies from the protected country. Similarly Li et al. , 2011, noted the advantage of Landsat Lider merger for patterning the tallness of immature forest. Schlerf and Atzberger ( 2005 ) , estimates the structural canopy variables utilizing hyper spectral remote feeling informations INFORM “Invertible forest Coefficient of reflection Model” . Main advantage of this method is that it does non necessitate old standardization.
Olthot EL al. , ( 2004 ) map out deciduous wood of ice storm harm utilizing Landsat and environmental informations in the E of Ontario, the survey demo a restriction in the trouble of both distant detection and environmental informations to know apart many degrees of the deciduous ice harm, nevertheless it can be consider as a utile technique in distinguishing countries of low to medium harm from the terrible harm. An overall truth of 69 % was achieved. Mapedza et al. , 2003, look into s land screen alteration of the forest modesty country of Mafungautsi Zimbabwe, the survey show that whilst forest screen within the modesty remain the same, but nevertheless there is steadily decline outs its boundaries as a consequence of agricultural enlargements, the aggregation of fuel wood and edifice stuffs demand
3.0 METHODOLOGY
Pair of multi- temporal cloud free Landsat images was selected to sort the survey country ; 1987 and 2002, the image of image 1987 was Landsat 5 TM and the other Landsat 7 ETM+ . The images were downloaded from GLCF web sites in different beds and will be layer stack together utilizing ERDAS Imagery 9.2. A subset will be collected and image sweetening is to use utilizing Histogram equalised to envisioned characteristics more clearly. The images were geo-reference to Universal transverse Mercator ( WGS84 – zone 32 ) , and a common geo-link window covering the same geographical co-ordinates were so extracted from each image
3.1.1IMAGE Processing Technique:
Digital image processing is classified into three categories which includes ; pre-processing stage, treating stage and the post-processing stage. The pre-processing stage is the first phase in the processing technique, it involves rectification of informations through assorted agencies and techniques, different types of mistakes that are associated with any satellite images includes ; geometrical mistake, atmospheric mistake and radiometric mistake. Geometric rectification is a technique used to rectify mistakes that are normally induced by detector screening, geometry and terrain fluctuations, it involves rectifying spacial deformation in an image due to earth curvature, atmosphere etc and therefore giving it a existent universe co-ordinate system.
The two images to be used in this survey will non undergo the pre-processing stage because the two images obtained are ortho-rectified. The processing phases involve use of images through the spacial sweetening and the spectral sweetening techniques.
Image Enhancement ; the process is applied in order to expose efficaciously the tonic differentiations within assorted characteristics display in the image. It usually involves techniques for increasing the ocular differentiations between characteristics to aids in ocular reading and analysis. ( lillesand et al. , 2008 p482 )
Histogram -equalised stretch is traveling to use to spread out the DN values and besides heighten the quality of the characteristics in the image so that radiometric item is enhanced. ( Lillesandet al. ,2008 )
3.1.1 CLASSIFICATION ANALYSIS
Supervised categorization, utilizing maximal likeliness algorithm is traveling to be used, supervised categorization requires choice of sufficient preparation sample which are later used to delegate image pels to the preparation samples that best fits the corresponding informations, it individually classifies multi-temporal images, pel by pel. Supervised categorization requires an huge sum of clip and know-how in making classified merchandises. Furthermore, the concluding truth depends upon on the value of the classified image of each day of the month. Yueling and Xu ( 2010 ) , reported to hold used supervised categorization technique in monitoring and driving force analysis of urban enlargement in Guangzau City China and the consequence of the result shows an one-year 19.7 % growing rate.
Post-classification comparing ( PCC ) , is another of import method that is recognized as the most effectual and accurate method of observing alterations in mages with different day of the months and register, the algorithm is capable of comparing the classified images pixel by pel. The usage of PCC is therefore reduces the environmental and atmospheric effects associated with the temporal images and therefore Provide a complete alteration matrix( Lu et Al. ,2004 ) .
Accuracy appraisal is the overall truth of the work done ; it shows the proportion of land trying points that are right classified. The user truth shows the proportion of classified pels in harmonizing with the existent land types as taken from the land truth proving informations. Accuracy assessment allows you to measure a classified image file ( Thematic raster bed ) .
3.1.2 CHANGE DETECTION TECHNIQUES:
Change sensing techniques is utile in a broad assortment of applications such as ; land usage alteration analysis, supervising switching cultivation, appraisal of deforestation etc. alteration sensing techniques to be used for this surveies will include ; alter vector analysis, image ratios and image differencing. These techniques have the ability to cipher country alteration, alteration rate every bit good as the spacial distribution alterations. These techniques will affect calculating the country covered by each of the two supervised classified images from the two informations beginnings independently and compare between the two images for addition or lessening in alterations that have occurred in footings of forest alteration screen ( Lu et al. , 2004 ) .
Change vector analysis is a technique that generates two end products, the first end product produced is on spectral alteration from the first to the 2nd image and the 2nd end product will bring forth the entire alteration magnitude per pel, Change vector analysis is computed by finding the Euclidian distance between terminal points through n-dimensional alteration infinite ( Lu et al. , 2004 ) . Its chief advantage in footings of analysing alteration sensing is its ability to treat any figure of spectral sets desired by the analyst and capable of bring forthing in elaborate of alteration sensing information as it defines threshold and identify alteration flights which is a good manner to cipher per centum rate of alteration that has occurred in a peculiar surveies. Furthermore the way of the spectral alteration is frequently relates to that type of alteration that had occurred ( Lillesand et al. , 2008 ) . Method was used by Allen and Kupfer ( 2000 ) in conifer wood alteration sensing.
Image differencing is a alteration sensing technique that will be used in this research to pull out more information sing the alterations that have occurred in the survey country ; image differencing subtracts the first day of the month image from the 2nd day of the month image, pel by pel to demo the alterations within the two dated images, it identifies suited image sets and thresholds. Image differencing normally yields a better consequences when carried out on the strength sets generated by transforming the RGB information sets into IHS colour infinite. Singh ( 1986 ) applied this method in tropical wood alteration, likewise ( Jha and Unni 1994 ) in forest preservation alteration sensing.
Image ratio is traveling to be applied because it is a simple manner of seeking to pull out utile information from TM imagination. With image ratio technique, strengths of reflected energy recorded in one set for the pel of a orbiter images are divided by strengths in the same set for the other rectified images. Image ratios depict the colour of an object, although the colour merely corresponds to human perceptual experience when the three seeable sets of ruddy, green and blue are considered. Image ratio is prepared by spliting the digital figure in one set by the corresponding digital figure in another set for each pel, therefore stretching the ensuing values, and plotting the new values as an image rationing is an effectual manner of visualising different types of dirts because the chief spectral differences in the seeable and close infrared spectral parts are found in the incline of the coefficient of reflection curves. It calculates the related measure of registered images of different two day of the months pixel by pel. Ratios for changed countries have higher values or lower ratio values whereas an country of no alteration tends to travel towards one ( 1 ) . An of import advantage of this method is it tends s to normalise the impact of Sun angle and shadow which has been caused as a consequence of external factors. ( Lillesand et al. , 2008 p596 ) Method has being used in land usage function and alteration sensing by Prakash and Gupta ( 1998 )
Finally, sheathing operations would be made to see the alterations that occur in the part. And Data is exported to GIS informations base for map production.
The above figure show a alteration sensing process for the Landsat Images would undergo during the analysis.
