جستجوی مقالات مرتبط با کلیدواژه « threshold » در نشریات گروه « جغرافیا »

Today, climate change and its obvious negative effects on ecosystems have caused concern. This research seeks to test whether vegetation changes are sensitive to climate shocks and also how the ecosystem recovery process is through this index. In this regard, by using the GEE platform, Java coding, GIS and statistical analysis, vegetation and Palmer indices were calculated and based on time series climate data, vegetation and climate changes were presented. The results of Palmer's drought index show that during the statistical period (1985-2020) the study area is facing drought or is moving towards drought. Also, the results indicate the longest period of drought in the region from 2013 to 2020. Totaly from 420 evaluated months, the NDVI index is below the change threshold in 70 months. Among these, 31 months of the study period is below the acceptable threshold in green and non-reservoir seasons, which is ecologically worrying. The distribution of the vegetation index based on hexagons in 1985 and 2005 had a normal and almost normal distribution; But in 2020, the graph deviated from the normal state and skewed towards the vegetation cover index under stress or even thin covers. According to the analysis of the indicators, it is predicted that the Gorgan region is on the border of such ecological developments and the historical ecosystem of the region is moving towards new ecosystems or being in a new equilibrium state with climatic conditions and human disturbances

The weather fronts are  known for their large vorticity, dense, moisture, and statical Stability gradients,   and their longitudinal scale is one unit greater than their width. The width of the front is known as the baroclinical zone, in which the front lines have a very large temperature gradient, which is determined by the angle between pressure and temperature lines. Position of a front is located in warm side of the extreme temperature gradient, inside the heat transfer zone and  intensity of the front is determined by the size of the horizontal or quasi-horizontal temperature gradient.Even the numerous expert synopticians disagree with each other in the position of the fronts, their types and intensity, in the manual drawing method of the fronts. So their drawn  fronts are very different While objective front is based on numerical methods and its purpose is to avoid applying people''s tastes in their manual method. The advantages of objective front metod in comparison with subjective front method are high speed front detection, the possibility of determining front frequeny, moving, and feedback of fronts with land side effects. So far, various methods have been developed for objective front method. They performed objective front method using numerical methods and the first and second derivatives of the temperature parameter on a regular grid points with a relatively low resolution of about 100 km. Inside the country, there has been no study about automatic and numerical front methods. On the other hand more than 90 percent of heavy rainfall in the tropics is associated with the fronts. Therefore, considering Iran''s location in the middle latitudes, it is very necessary to study and identify the fronts. So the climatological study of the manual front detectin is very time consuming, expensive and practically impossible. Therefore, in this research, the, automatic and numerical front detection have been discussed for the first time in the country.

In this study, grid point data  from the European Center for Medium-range Weather Forecasting (ECMWF) of type (ERA - Interim) is used with gaussian grid points. In this centre, different types of data are classified into different formats and in different time intervals and different grid resolution. In order to study  of the fronts, isobaric level data with 6 hour intervals and resolution of 0.75 × 0.75 degrees with grib format is used. This grid resolution is set in a regular 61×61 matrix with a grid distance of 83 km. Different quantities can be used to select the appropriate parameter to detection of fronts such as temperature, humidity, wind direction and wind speed, vorticity, thickness and thickness changes ,and temperature is on of  the most important of them. On the other hand, detection of the exact location of the extreme temperature gradient, which is accompanied by the effects of heating on the warm convergence belt in the warm side of the front leads to warm weather, can be identified only by using the equivalent potential temperature.

The main idea for identifying frontal areas is to use a temperature parameter in two-dimensional horizontal coordinates. The line representing the front in these areas is identified using a frontal identification function. In order to identify the front, the masking conditions are applied once or several times. In other words, in this equation, the horizontal gradients of the equivalent potential temperature are used, which should not be less than the value of the K-threshold value. >K  . Several indicators are considered to identify the front. The first of them is that the front must be at a turning point in the curvature of the temperature lines which is along the temperature gradient. The second indicator is the location of the maximum values of temperature gradient,and the third criterion is the point where the second derivative of the temperature gradient is zero. Various experiments have shown that the smaller the temperature derivative of the front temperature parameter, the less error there will be (J. Jenkner, 2009). Thus, the Front Termal Parameter (TFP), invented by Renard & Clarke (1965), was used as the main method of frontal reconnaissance. TFP = In this equation, second derivative of the temperature parameter has been used, which has converted the temperature gradient, which is a vector quantity, to a scalar quantity.

Examination of the results of objective fronts showed that the detection of fronts near the ground due to the interaction between the boundary layer and the fronts is very erroneous and the fronts are practically indistinguishable. On the other hand, at higher levels, shallow fronts at numerical output are not detected. Therefore, the appropriate level for automatic identification of fronts in the study area, 700 hPa level was selected. Examining the results, it is inferred that cold and warm fronts are often found at the bottom of the ridge and above the ridge of the upper surfaces, and these fronts, during the formation stage, are often discontinuous and gradually evolve during the developmental stages. Strengthening the front will take a more integrated form. Studies have shown that cold fronts produce stronger frontogenesis than warm fronts. Also, the output of objective fronts showed that TFP is a good parameter for detecting the front in this region and with the results of previous studies such as Hewson (1998: 49), Jenkener et al. (2010: 9), they show a good match. The results of this study can be used in the discussion of climatology and forecasting of fronts and can be helpful in the discussion of flood management due to heavy rainfall on the front.

The watershed is a geomorphologic unit suitable for managing natural resources and achieving sustainable development. The drainage network of the catchment area is a series of streams and rivers that guide and drain the surface water flow. These spatial data play an important role in physiographic studies, hydrology, erosion and sedimentation of a catchment area. The network of canals can be considered as a system that is dynamic in a state of equilibrium, in which dependent variables such as form; the slope and horizontal projection of the river or the amount of data and the coincidence that whenever there is a change in the data, This system reacts quickly with the coordination of their morphological characteristics with the new situation. The drainage network pattern is one of the most prominent landforms of the earth's surface. The order and distribution of hydrographic networks are different. The purpose of this study is to identify the factors of balance and imbalance of the right and left side of the research area and which part of the research area has severe asthma and chaos. The basis of this research is the method analysis order matrix of basin Ramhormoz at the beginning of the study. The exact coordinates of basin Ramhormoz boundary from Global Mapper.20 software were taken in Arc GIS 10.5 software using the Dem area of the study; for Draw curves, lane lines and line basin s, slope direction, fracture of streams and formations. Arc GIS software has been used to evaluate the Ramhormoz river basins using the Order Matrix method. To set the categories in matrix form. orders 1 to 1, 2 to 2, 3 to 3, and to the last. order that is the main. order, are placed in tables in the two views (right and left) in the array view. In the following, the. order 1, which joins the large. orders r, is calculated separately and the rest of the orders are calculated in this way (order 2 to 3, 4, 5, ... 3rd to 4th, 5th And other orders). In the study, the split density and drainage density are used. In this study, the number of waterways in the upper reaches of the two sides of the study area with a very significant difference indicates the imbalance in the research area. Erosion, slope changes, channel displacement, channel redirection, tectonic activity of these factors in causing significant differences and effective imbalances on both sides of the research area as well as the manner, extent and stages of changes in the form of the canals affected by time as a The main variable is to create the threshold, and the reason that the canals tend to trigger the chaos process, and even show a slight change, causing them to balance and imbalance. on both sides of the research area, the most balanced average of the lengths of the waterways, the order of waterway 1 falls to the 7th (right 819.2 km and the left is 819.1km). Due to changes in the geomorphological parameters of the basin, due to changes in the parameters of the basin, resulting in no change in their form during the period. The correlation coefficient between the longitudinal lengths of the two sides of the research with the coefficient of determination (0.9932), due to the slope and elevation variations, shortage of the path and length of the branches of the canals, which are located on both sides of the research area, in the right side of the study, correlation relationship Between the length and length of the waterways with the coefficient of determination (0.929), the left side of the study area, the length and length of the waterways with a coefficient of determination (0.8821) indicating the presence of the threshold and the chaos on both sides of the research area and these factors Due to the effects of erosion that indicate tectonic activity, side erosion, floor, grooves, and fault systems, especially in the left-hand region of the research, these factors (other than erosion) are more severe. The imbalance and the threshold on the left of the research area are more intense. The right side of the study area, with a branching ratio of 3.34 and drainage density of 7.87, the left side of the research area with a split ratio of 3.50 and a drainage density of 4.06, due to the split ratio of the two river research areas, has a moderate construction turbulence. The drainage density is correlated with the amount of erosion. In the right zone of the study, the moderate drainage density is equal to the rate of high erosion, which is due to the high percentage of Aghajari Formation in this research area and the greater proportion of branching in the left side of the research area to the right of the research is due to the Bakhtiari Formation.

The most evolution of the waterways of both parts of the research, especially the left, is the tectonic research, erosion, and formations, Bakhtiari, Gachsaran and Aghajari formations are more than the Mishan Formation and the terraces and Low level alluvial fan and valley terrace deposits in the creation of chaos, Threshold and erosion. Lateral erosion in the right side of the research is more and less erosion of the floor, while the left side erosion of the research is less and the erosion of the floor is greater, these factors are due to imbalance in the two areas of research. Tectonic activity, albeit moderately, interfered with changing the state of the trenches, eroding, shortening the length of the waterways, and varying the number of waterways. Keywords: Ramhormoz River, Fluvial Geomorphology, Matrix, Order Matrix Model, Threshold.

With the advent of remote sensing technology, huge volume of remotely sensed data is now availablein different areas. As the fastest and the most cost-efficient method, satellite data is available for both researchers and responsible authorities seeking to produce land use (LU) maps. Compared to traditional methods, object based image analysis (OBIA) techniques use more comprehensive datasets,including geometric information (shape and placement of phenomena), digital elevation models, andvarious spectralindicesfor LU classification.Therefore, different OBIA methods have been widely used forclassification of satellite imageriesin different regions. Despite large amount of researches performed in this area, little attention has been paid to the systematic comparison ofdifferent object-based methods. Therefore, examining different techniques used for object-based processing of satellite imageries in diffrent situations can be considered as an appropriate research field for researchers.  The present studyexamines some powerful OBIA classification techniques such as threshold, nearest neighbor algorithm and fuzzy object based classification to determine the most suitable OBIA algorithm for classification of Ikonos satellite images.  

An Ikonos satellite imagery was used in this studywhich included red, green, blue and near-infrared bandswith spatial resolution of 4 m and a1 m resolutionpanchromatic band.Object based classification can be implemented in three general phases: segmentation, classification, and accuracy assessment.The present study has appliedmulti-resolution segmentation method in the segmentation phase. Three techniques ofthreshold, nearest neighbor algorithm and fuzzy based OBIA were also used for classification. 

The present study takes advantage of various features to extract land use classesfrom Ikonos satellite imageswith high level of accuracy.Textual information (Grey Level Co-occurrenceMatrix), mean of the imagery’s spectral bands, geometry (shape, density and asymmetry), and normalized difference vegetation index (NDVI)were among these features.Compared to threshold method,nearest neighbor algorithm withoverall accuracy of 92% and kappacoefficient of 0.9hada higher level of accuracy.Also, FOS algorithm was used to optimize the nearest neighbor technique. This algorithm optimizes intervals between the training samples using secondary information provided by the user.The eighteenth dimension, which contains the mean of spectral bands3 and 4, vegetation index, brightness, length to width ratio, indices of shape, compactness, asymmetry, texture information (homogeneityand contrast), were determined by FOS algorithmas the best dimension for extracting each LU classes. Finally,featuresproposed by FOS algorithm were used for image classification in nearest neighbor method.This optimizing process is considered to be one of the main reasons for superior performance ofnearest neighbor technique compared to threshold method.  

In this research, three OBIA methods including threshold technique, nearest neighbor algorithm and fuzzy based OBIA algorithm were compared based on their capability in producing land use map from Ikonos satellite image. Identical ground control pointsof the study areawere used to classify and compare the results of these three OBIA classification methods.Finally, the best classification algorithmwas determinedbased on thevalues of accuracy assessment metrics including overall accuracy and kappa coefficient. Results indicate thatwith overall accuracy of 97%, and kappa coefficient of 0.95, fuzzy based OBIA classification algorithm has thehighest accuracy as compared to nearest neighbor algorithm and threshold method. Generally, the accuracy of fuzzy based OBIA classification method largely depends on the selection of appropriateclassification parameters and suitablealgorithm to obtain membership degrees.Investigating membership degree of effective parameters in the classification and using parameters with maximum degree of membership are considered to be two main reasons for achieving this high accuracy. Results of the present study indicate that fuzzy based OBIA techniqueis the best algorithm for classification ofIKONOS satellite images in the study area, andareas with similar conditions. This findingcanguide researchers and organizations producingLU map from IKONOS satellite imagery. Finally, investigating different techniques using satellite imageries (imageries with different spatial resolution, and received from areas with different land uses) is considered to be an appropriate area of study for OBIA researches.

  Air inversion is a climatic phenomenon causing increasing in the aggregation of pollutants in highly populated and industrial cities, such that crossing from the air quality threshold would have extensive problems for the citizens. Attention of managers to this problem is mainly referred to polluting factors such as traffic. However, it should be seen that in case this phenomenon exists during all the seasons and if the polluting factors have no great changes during the year, what factor can lead in crossing the air quality index from the threshold value, and, will there be an approach for reducing the continuity of this situation, if continuity of the inversion leads to such a condition?
The main problem in this study is whether there is the possibility of managing Esfahan air pollution in such a way for the atmosphere pollution density not to tend towards the critical threshold. In case the answer is positive, how can a model be presented for controlling the air pollution crisis threshold by relying on the climatic management? The research method in this paper is mainly relying on an analytical method and depends on the principles of interpreting climatic and atmospheric pollutants data. The subject of air pollution critical thresholds is considered for approaching the research aims. Thus, the used data were related to a 30-year data (1985-2015) from Meteorological Organization and balloon data including pressure, temperature, speed, wind direction, and rains, and the air pollution data were from 14 pollution measurement stations belonging to Esfahan Environmental Organization. The analyses in various levels enabled us to find out about the inversion conditions in different levels. Hence, only the 1670, 1680, and 1860 m levels were selected due to formation of pressure and temperature closed cells among one hundred produced weather maps. Then, the cellular excitation index (C.E.=f/k) was calculated, where k= D/(Δt,p) and “f” is the Newton mass, and the temperature and cellular pressure differences were calculated by using this formula. The two indices showed the conditions and possibility of excitation of temperature and pressure closed cells for reducing the continuity of inversion time. Regarding the documentation data and extracted results, the inversion in the city of Esfahan was analyzed, and the intensity, continuity, and altitude of the inversion in various high levels were determined. Thus, the temperature and pressure inversion conditions were investigated for different levels with regards to the balloon data, and inversion analysis for different levels became possible according to temperature and pressure closed cells. The analyses included 100 maps from different altitudes that according to the analysis, the two 1670 m and 1680 m were for the temperature and the 1860 m level was for the pressure in the closed cells. In fact, the above altitudes were the levels having temperature and pressure closed cells with specific differences, providing the possibility of excitation. Afterwards, the excitation conditions were calculated by calculating the cellular excitation index. Statistical analysis of the obtained information from the balloons and atmospheric profile indicate that the inversion phenomenon in Esfahan region occurs in different days of the year, and the considered point regarding the research questions is the continuity of inversion time. In other words, inversion phenomenon may not be considered as the main factor in emergence of pollution crisis, but the continuity of this of this condition is the factor for increasing the density of atmospheric pollutants and crossing from critical threshold (AQI 150). Hence, it can be stated that continuity of inversion condition leads to exceeding of the pollutants density from the permissible range.
It can be concluded from the statement that occurrence of atmospheric pollution condition can be prevented by two different Reducing inversion continuity
Management of urban pollutants
Thus, the following statements can be considered as the achievements of this study:In the most intensive dominating days of air inversion, pressure and temperature cellular nuclei provide the possibility to manage the continuity duration of air inversion by exciting the cells
Regarding the intensity of inversion phenomenon exceeding quality index from the permissible range can be avoided in November and December by controlling the inter-city traffic control, and in January by controlling the industrial pollutants
Threshold control models for November, December, and January in multiple basis are as follows: - General model for November includes:A.P.C*isf.Nov = (C.M**) V (U.M***)
A.P.Cisf.Nov = (C.E****) V (C.CO or C.SO2)
A.P.Cisf.Nov = (C.E) V (C.NO2 or C.O3) *Air Pollution Control
** Climatic Management
*** Urban Management
**** Cell Excitability - General model for December includes:A.P.Cisf.Dec = (C.M) V (U.M)
A.P.Cisf.Dec = (C.E) V (C.CO or C.SO2)
A.P.Cisf.Dec = (C.E) V (C.NO2 or C.O3) - General model for January includes:A.P.Cisf.Jan = (C.M) V (U.M)
A.P.Cisf.Jan = (C.E) V (C.CO or C.SO2)
A.P.Cisf.Jan = (C.E) V (C.NO2 or C.O3)

Introduction Gully erosion is a major problem for natural resource management, leading to land degradation and economic losses worldwide. Determining the threshold for research on Geomorphology and natural ecosystems is important for many scholars. Land managers and specialists knowledge about factors affecting the growth of gully enables them to control them and predict their growth rate under similar conditions in other ecosystems. In the study area, this type of erosion has caused many lands to be destroyed, and with runoff and flood runoff, there is a significant amount of sediment that leads to unutilized land. It seems that examining these factors and determining their thresholds will help determine control strategies and more successful implementation of water and soil conservation projects. The purpose of this study was to determine the threshold of effective factors in the longitudinal growth of gullies using data mining techniques in Sanganeh Kalat watershed in the northern part of Khorasan Razavi province.
Methodology Initially, the location of 23 gullies was recorded using the Global Positioning System (Garmin 76CSX) and the distribution map of the gullies in the study area. Then, the Soil gravel, bare soil, cover, litter in heads of the selected gully were measured.
For this purpose, 15 plots were placed in one square meter and their means and the previously mentioned parameters were determined. In order to measure the physical and chemical properties of the soil, a soil sample was taken from a point at the head of each gully. After they were transferred to the erosion and sedimentation laboratory, the electrical conductivity (ECe), PH, OM, SAR, Clay, Silt and the Sand were measured. Also, the permeability at the top site of head of each gully was calculated using double cylinders. In addition, the amount of water penetration of the soil was calculated. Finally, using the data mining technique (K-Means Clustering and CART Decision Tree), the threshold of the factors influencing the longitudinal growth of gully in the study area was determined.
Discussion Of the total of 23 gullies studied in this study, the accuracy of the estimation based on the parameters influencing the longitudinal extension of the gullies in the final model were measured and were respectively 100% and 85% for the educational and experimental data sets. The interpretation of the rules extracted from the decision tree of the CART, based on the clustering of the length of the gullies, is as follows: - The results of the analysis of the CART decision tree algorithm show that when the width of the gullies is 275.32, the SAR is 0.147, the gullies headcuts slope is 1.39, and the percentage of silt would increase from 37.12, long-length gullies (cluster 1) are created.
- In the formation of mid-range gullies, when the ratio of girder width is greater than 198.84, the SAR is less than or equal to 0.174, and the gradient of the gully headcuts slope is less than 0.73, the average length gullies (cluster 2) are created.
- When the width of the gullies is from 108.77 m, the SAR is less than or equal to 0.174, and the gullies headcuts slope is smaller or equal to 0.481, gullies of low length (101.35 to 163.23 m) are created.
Conclusion The results of the decision tree of CART based on the length of gullies clustering showed that the most important factors affecting the longitudinal expansion of gullies in the study area were gully width, SAR, gully headcuts slope and silt percentage.As a result, the main factor in the longitudinal expansion of gullies is the surface runoff. The second factor is the soil erosion sensitivity in the study area. The main reason for this is the poor vegetation and low soil permeability. In addition, the texture of the soil is another factor that overwhelms the longitudinal extension of the gullies. The prevalence of the amount of silt in the soil texture is due to the lack of adhesion, waste, and the transfer of more sediment, resulting in the longitudinal extension of the gullies.

The threshold word that entered the field of geomorphology studies by Schumm and Fabric in 1980 represents the time that a system reacts to an external factor such as climate change (Vitek&Giardino, 1993). The main difference between the internal and external types of thresholds is that internal alters donot change the structure of the system, but the outer threshold that is affected by external factors, changes and transforms it into a geomorphic system (Elverfeldt, 2011).A geomorphic system is confronted only with changes in external variables with external thresholds.Such as the reaction of alluvialfan systems, rivers, glaciers, etc., to climate or tectonic changes that make the geomorphic system more adaptable and adapt to new conditions(Huggett, 2011).One of the basic subjects in geomorphic studies is how to check the process of changes in the levels of the earth. Nowadays, the essence of geomorphic studies includes the analysis of form and geomorphic process on the level of the earth. In systematic view, geomorphic analysis is based on the form and process. Since geomorphic thresholds show the border conditions in making changes and in order to understand time changing, it is one of the basic concepts in systematic theory, it has a high value. GhezelOzanRiver and its branches in the Quaternary period have constantly been redirected to geological adaptation.As a result of these displacements, the process of alluvial to fluvial or fluvial to alluvial has changed in the opposite direction.These displacements are still ongoing and cause the river to stay away from the geomorphic equilibrium.The study of alluvial, fluvial and equivalent levels with the help of geomorphic thresholds is the main purpose of this paper. The GhezelOwzan river system is located in the North West of Iran and it pours in the Caspian Sea. This river finds its source in mountain of Kurdistan and length of over 550 km after crossing the provinces of Zanjan, East Azarbaijan, Ardebil and receiving multiple branches along your route anymore confluence with the river in Gilan province into the dam Sefidrud. Basin area is of nearly 49400 sq2. The river is located between the provinces of Kurdistan, Zanjan, East Azerbaijan, Ardebil, Hamedan and small part of Qazvin, West Azerbaijan and Gilanprovinces. The study area is located between 46.45°– 49.33°E and 34.92°– 37.92°N.
Material and This survey, which is based on library studies in the provinces, areas and balance on the way to systematic analysis, tries to study its threshold and categories in GhezelOwzan Basin. So, according to this analysis they are studied in three different areas, internal, external, synthetic samples of measurement curves of lithology, bondage and deviance, erosion_ ditch, gradient, geomorphology and geoneron to understand the subject better.Analyzing virtual form and processes basin have been carried out with the help of topographic, lithology, slope, drought maps (with the help of SPI and Moran index), geonerons (with the help of isotherm and isohyet maps, and using Justin), track ancient lake and erosional surfaces, geomorphological evidences captivity and diversion.
Rivers and captivity deviations can be detected in several ways: 1- Redirect with angles of 90 degrees or more along the rivers. Over time, rivers achieve a balance in their basin in terms of their topographical, hydrological and drainage condition.The bed of streams that are lithologically homogeneous there is no maze created by redirection. 2- Elementary and middle part of the river that is the source of the water, sediment and the coastal route (sometimes in the water), the sediments is of record. Alluvial deposits are not at the sources.The presence of alluvial deposits at the origin of GhezelOzan, either due to a redirection of the river, or due to the construction of the source ofGhezelOzan Plains 3- Over time a basin is almost symmetric, itmeans that the left and right banks of it become the same in size and is symmetrical over the time. It is the result of tectonic disturbance of fetal status or captivity and diversion of rivers; the main factor in much of GhezelOwzan, was to change the course of rivers. Shorter duration of waterways on one side than the other side of the river in GhezelOwzan, indicates the redirection of the river.4- The height difference is an inevitable phenomenon in the coastal watershed,but presencea difference in elevation along with less drainage length and diagenetic alluvial deposits in the dividing line, indicate the 90 degrees redirection of the river, relative to the previous track.The side of the river, which has a lower altitude, shows the length of the river's previous course. Such effects are very prominent in the direction of river redirection.Contour lines with deep pulses or deep sinuses between and below the contour lines of smooth to simple sinuses are a reason for river redirection.The prolongation of the equilibrium leads to a smooth contour lines, and the collapse of the equilibrium leads to the overcoming of recoil erosion and generates deep pulses in the contour lines.
The results showed that in the southern part of the zone a kind of geomorphic balance has yielded and the reason is the slow deplete of Bijar and its erosion surface configuration. By depleting these surfaces, the main rivers like Angoranchae and Sojasrood changetheir path and through a deviated path in present situation enter another place in GhezelOwzan Basin. The study of the zone geonerons also showed that Zanjanrood’s ford and Myane were absorbed; the amount of water which is less than the amount emerged it and if the rivers such as Angoranchae and Qaranghochae werenot joining on the path, so the river dried. In this case, the major sub rivers of the zone (Source and ford) are part of the reinforces and this occasion caused the GhezelOwzan River to be survived because of material and energy from sub rivers and to be away from their geomorphic equilibrium.

Increasing more injection of substances (precipitation) and decreasing the evaporation process in water basins has led to formation of Abarkooh hole in cold periods and also Abarkooh lake; a lake around which several social communities have been created due to this feature and in warm periods, it has turned into desert as the result of disturbing the proportion of its input and outputs. These climatic fluctuations and changes and environmental responses to them have produced many changes in the local hydrologic system and accessible water sources and have also endangered the sustainability of the area because of the external disorder factors such as drought. The danger which certainly threats the social communities and if no special management practices have been employed , will lead to the destruction of human communities and demolish of its natural ecosystems. This study which is derived from a research plan in Isfahan University has been conducted by the aim of studying how the weather changes affect the evolution path of Abarkooh basin. Moreover, it has examined the basin status and icings reduction rate and therefore the basin input rate, by relying on the Allometry procedure and evaluating 6 synoptic stations in analyzing the annual changes process of climatic parameters such as mean temperature, maximum temperature, minimum temperature, current and past precipitation of the lake and also by using the evapotranspiration method. Results obtained from the research suggest that changing the current environmental parameters ratio to the colder periods have all exceeded from the stability thresholds and the general state of the environmental systems is about to collapse.

The change detection using satellite images is one of the main fields of remote sensing researches. Numerous errors in the images are one problem with the use of satellite imagery. Errors caused by surface illumination, are the main problems in the process of change detection. Therefore, in this study, in order to reduce errors in the results of the detection of changes using change vector analysis, a simple, yet effective method to reduce errors caused by topography is proposed. After applying Tasseled Cap Transform on images, the proposed method compare the angle between direction of change vector with the direction of vector of the pixel in the base image using spectral space, and then calculates the angular threshold. The area under the ROC curve, the Probability Detection and False alarm of proposed method are 0.970, 0.97 and 0.32 respectively.

Edge detection is a fundamental concept of image processing in remote sensing which aims at detecting points of the image at which the brightness changes sharply. Sharp changes in the image properties usually represent important events and changes in environmental factors. This kind of detection method can be useful in different image processing applications such as satellite image segmentation. Many classical mathematical algorithms for the edge detection, such as Gradient operators, Laplacian and Laplacian of Gaussian operators,are based on the derivative of the original image pixels. In the remote-sensing imagery, because of the high rate of changes, these edge detection operators perform weakly in correct diagnosis of the feature boundaries and in keeping their consistency. In order to solve these problems, this research presents a knowledge-based system to detect the feature edges based on the properties of remote-sensing images. In this method, the threshold is firstly determined piecewisely in different regions of the image using a knowledge-based system, and then the area boundaries are extracted using the Shannon entropy, which safeguards the continuity of the edges. The advantage of this approach is simultaneous evaluation of the image features in both partial and general cases. In addition, the system is flexible in terms of the type of user needs and the intended details and applications. Eventually, to evaluate the method, the results are compared with Sobel, Perwitts and LOG standard algorithms. It is observed that the proposed technique can efficientlydetect the edges for different digital images.

The Central Place Theory of Walter Christaller, a well-known German geographer, was first proposed in his 1933 book "Central Places in South Germany". The term central point or place is used to refer to a location that supplies goods and services to its surrounding areas, and is thus central to several areas and the source of their needs. In fact, this theory is designed to respond to the spatial distribution of cities and the systems of hierarchy among them, and the centrality of a site increases and decreases with corresponding increase and decrease in the level of service received by that location. In this paper, first the hypotheses and principles of the theory of Christaller are presented based on whose assumptions it can be said that in this theory all phenomena are placed in their ideal state, something that can be rarely found in reality. After assumptions, the urban hierarchy has been examined; according to his observations on central locations in southern Germany, Christaller found that there is a hierarchical system in the economic and administrative system of these central locations. His belief in the existence of a hierarchy among the central locations of the southern regions of Germany led him to classify them according to their population and degree of centrality. According to the Central Place Theory, the spatial distribution of central places takes shape in a regular geometric space that is displayed in the form of conventional and overlapping polygons (hexagons). After urban hierarchy, the concept of threshold and the concept of the sphere of influence of goods and services in the Central Location Theory, the factors affecting the return of consumers to the central location, the assessment of economic activities in a hierarchical system and the application of central places in regional planning are examined, and after reviewing these cases, Christaller’s theory has been evaluated, and finally a conclusion has been made.