با گسترش محدوده شهرها برخی زمینهایی که پیشازاین سالها با کاربری باغ مورداستفاده قرار میگرفتند درون حریم شهرها واقع شدهاند. اختلاف ارزش زمین با کاربری باغ نسبت به کاربری شهری نظیر مسکونی و تجاری صاحبان باغها را به سمت تغییر کاربری ترغیب میکند. متولیان امور شهری با اعمال قوانین سختگیرانه سعی دارند مانع از تغییر کاربری شوند. بررسی میزان موفقیت اینگونه برنامهریزیها، نیازمند بررسی تغییر کاربری زمینهای قرار گرفته در محدوده شهر در یک بازه زمانی بلندمدت است. در این تحقیق هدف اصلی آشکارسازی باغهای شهری متروکه با استفاده از تصاویر چند زمانه ماهواره لندست است. هدف دوم تعیین میزان تغییرات باغهای شهری منطقه موردمطالعه طی 30 سال گذشته است. در این تحقیق بر پایه تصاویر ماهواره لندست در سالهای 2018 و 1988 برای دامنه شمالی کوهستان الوند در استان همدان و محدوده شهر همدان شاخص تفاضلی نرمال شده پوشش گیاهی (NDVI) در کنار دمای سطحی زمین (LST) در 9 مقطع زمانی در هر سال استخراج شد. بهطورکلی نتایج تحقیق افزایش دمای سطحی 4/75 سانتی گراد برای منطقه طی 30 سال را نشان میدهد، همچنین رابطه معکوس دمای سطحی با شاخص تفاضلی نرمال شده پوشش گیاهی مورد تأیید است. بر مبنای تفکیک باغهای شهری یک مقایسه بین سالهای 2018 و 1988 صورت پذیرفت که نتایج حاکی از کاهش 175 هکتاری باغهای شهری در منطقه موردمطالعه که معادل کاهش 49 درصدی باغهای شهری است. در بخش اصلی تحقیق بر مبنای رفتارسنجی باغهای شهری در این دو ویژگی یک شاخص تفکیک برای باغهای فعال از متروکه ارائه شده است که پس از بررسی نتایج بر مبنای دادههای واقعیت زمینی شامل 25 باغ فعال و 25 باغ متروکه، روش پیشنهادی دارای دقت کلی %82 و ضریب کاپا 0/64 است.
عنوان مقاله [English]
Feasibility study of abandoned urban gardens detection using the Landsat Satellite images, Case Study of Hamedan City
With the expansion of the urban limits, some of the lands that were used for gardening years ago have been located within the urban limits. The difference between the value of garden land use and urban land use, such as residential and commercial, encourages gardeners to change their land use. Urban managers try to prevent this change of use by enforcing strict rules.Assessing the success of such plans requires examining land-use change in the urban over a long periodof time. The main purpose of this study is to detect abandoned urban gardens using Landsat satellite imagery. The second goal is to determine the extent of changes in urban gardens in the study area over the past 30 years. In this study, based on Landsat satellite images in 2018 and 1988 for the northern slope of Alvand Mountain in Hamadan province and the city of Hamadan, the normalized differential index of vegetation (NDVI) along with land surface temperature (LST) in 9 time periods per year was extracted. The results indicated a 4/75 ° C increase in LSTfor the region over 30 years. Also, the inverse relationship of LST with NDVI is confirmed. Based on the separation of urban gardens, a comparison was made between 2018 and 1988, which showed a decrease of 175 hectares of urban gardens in the study area, which is equivalent to a 49% reduction in urban gardens. In the main part of the research, based on the behavioral evaluation of urban gardens, in these two characteristics, a differentiation index for active and abandoned gardens is presented. Examination of the results based on ground truth data including 25 active gardens and 25 abandoned gardens suggested that the proposed method had an overall accuracy of 82% and a Kappa coefficient of 0/64.
Materials & Methods
The study area includes a part of the northern slope of Alvand Mountain, which is limited to the southern part of Hamedan and has a latitude of 34 degrees and 45 minutes to 34 degrees and 48 minutes north and a longitude of 48 degrees and 27 minutes to 48 degrees and 31 minutes east. Ground truth data including 25 active gardens and 25 abandoned gardens were collected as field visits using a Garmin GPSMAP 62s handheld navigator so that coordinates were collected by attending the location of abandoned and active gardens. The satellite data used in this study concern the time series data of Landsat 8 satellite OLI and TIRS sensors for 2018 and Landsat 5 satellite TM sensor for 1988.
To achieve the first objective and separate active and abandoned gardens in 2018, the land surface temperature (LST) and the normalized difference vegetation index (NDVI) are calculated and the behavior pattern of these two components is examined during the year for active and abandoned gardens in nine periods according to the proposed method, a final index for separating active and abandoned gardens is presented based on the NDVI behavior pattern throughout the year. The time series of NDVI for each year is evaluated in 9 periods and garden maps are extracted in 1988 and 2018 to achieve the second objective and prepare the maps of 30-year changes in active gardens in the study area. The rate of change of area and the percentage of changes in the class of gardens are obtained by comparing the maps.
Results & Discussion
Since this study is conducted mainly to identify abandoned gardens in urban space, two criteria for assessing user accuracy and errors of commission in the abandoned garden class are very important. In other words, in this problem, the number of gardens that are properly divided into the abandoned garden class is important, and the proposed method provides an accuracy of 86%. The most important issue is the number of abandoned gardens that the proposed method has mistakenly labeled as active gardens, which is 14% in this method. Both accuracies provided are evaluated as acceptable. The overall accuracy of the proposed method is estimated at 82%, which is acceptable, indicating the efficiency of the proposed method.
One of the problems facing human societies today is the reduction of forests and gardens. Given the important role that trees play in improving the quality of human life, protecting them is one of the inherent duties of rulers. Various factors cause the destruction of trees, one of which is the development of urban areas in the vicinity of forests and gardens. Traditional methods of conserving natural resources and monitoring their changes have failed in practice. For example, in the study area, 49% of the tree-covered areas have declined over the past 30 years. However, the ban on construction in the area has always been emphasized by city managers in the years under study, and the inefficiency of the methods used has been proven by the statistics provided. New methods of monitoring changes based on satellite image processing can be alternatives to traditional methods due to their high accuracy and speed and significant cost reduction. The proposed index is recommended to be evaluated to separate active and abandoned gardens in other areas facing this problem using images with higher spatial resolution. In different cases of threshold limit, the overall accuracy of the proposed method is examined based on the ground truth data of the evaluator. At best, the separation of active and abandoned gardens is associated with an overall accuracy of 82%.