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نوع مقاله : مقالات پژوهشی

نویسنده

دانشکده محیط زیست، سازمان حفاظت محیط زیست، کرج

چکیده

مقدار قطعات سنگی و سنگریزه‌ها به عنوان پوشش محافظ خاک در کنترل فرسایش بادی نقش بسیار قابل ملاحظه‌ای دارد از اینرو اطلاع از تغییرات این پارامتر در چشم‌انداز به تحلیل رویدادها در سیمای سرزمین کمک می‌نماید. فوتوگرامتری برد کوتاه به عنوان ابزار دقیق اندازه‌گیری براساس تحلیل عکس در سالیان اخیر به سرعت پیشرفت نموده و به طور گسترده استفاده از آن در برآوردهای محیطی رو به افزایش است. در این پژوهش سعی شده است به بخش‌های بنیادی علم فوتوگرامتری برد کوتاه ورود شود و توان آن در برآورد درصد قطعات سنگی و سنگریزه بستر سنجیده شود. بدین منظور یک پلات1×1 متر مختص فوتوگرامتری برد کوتاه طراحی و ساخته شد و ابزارها و شیوه عکسبرداری مناسب این مطالعه مشخص گردید. به منظور تهیه نقشه درصد قطعات سنگی و سنگریزه به کمک داده سنجنده OLI یک طرح نمونه‌برداری بر روی دشت تهران-کرج پیاده سازی شد و عکسبرداری صورت پذیرفت. عکس‌ها به کمک نرم‌افزار تحلیل عکس PhotoScan پردازش و عکس عمودی شده پلات و مدل رقومی ارتفاعی زمین از هر پلات بدست آمد. نتایج نشان داد نرم افزار فوتوگرامتری برد کوتاه Photoscan به خوبی قادر است اعوجاج‌های موجود در عکسها را از بین ببرد. توجیه داخلی و خارجی عکس‌ها به خوبی توسط این نرم افزار صورت می‌پذیرد و مدل رقومی سطح با قدرت تفکیک مکانی بالا و عکس‌های عمودی‌شده خروجی با کیفیت توسط این نرم افزار فراهم می‌گردد. عکس‌ها به دو روش 1- طبقه‌بندی به کمک مدل رقومی ارتفاعی یا مدل رقومی سطح زمین به روش درخت تصمیم‌سازی و 2- طبقه‌بندی شئ‌گرا به کمک تصویر عمودی شده و مدل رقومی ارتفاعی طبقه‌بندی شدند تا مقدار قطعات سنگی و سنگریزه در هر پلات مشخص شود. طبقه بندی به کمک درخت تصمیم‌سازی در نرم‌افزار ERDAS IMAGINE 2015 با استفاده از روش درونیابی چندجمله‌ای درجه اول و یا دوم به کمک مدل رقومی سطح زمین صورت پذیرفت. نتایج نشان داد این روش سرعت بالا و دقت متوسط دارد، ولی امکان خودکارسازی استخراج اطلاعات مربوط به قطعات سنگی و سنگریزه در این روش فراهم است. طبقه‌بندی شئ‌گرا در نرم‌افزارeCognition Developer 9 با استفاده از تصاویر عمودی‌شده و مدل رقومی سطح زمین انجام شد. نتایج نشان داد این روش دقت بالا و سرعت کمتر دارد و امکان خودکارسازی فرآیند استخراج اطلاعات مربوط به سنگ و سنگریزه وجود ندارد. در نهایت بر اساس روش ارزیابی صحت طبقه‌بندی و خروجی ماتریس خطا (شاخص کاپا و دقت کلی) در هر پلات مقدار قطعات سنگی و سنگریزه به روش مناسب‌تر بدست آمد و به عنوان متغیر وابسته در مدلسازی بکار رفت. به منظور تخمین درصد قطعات سنگی و سنگریزه ابتدا داده سنجنده OLI تصحیح هندسی و رادیومتری شد تا مقادیر بازتابندگی از آن استخراج شود و با اعمال شاخص‌های طیفی بارزسازی گردید. خروجی این شاخص‌ها و بازتابندگی باندها وارد مدلسازی خودکار خطی شدند تا مقدار قطعات سنگی و سنگریزه تخمین زده شود. بر این اساس یک مدل خطی با ضریب تعیین بیش از 9/0 بدست آمد که توان فن فوتوگرامتری برد کوتاه را در استخراج درصد تخته‌سنگ، قلوه‌سنگ و سنگریزه به خوبی نشان می‌دهد.

کلیدواژه‌ها

عنوان مقاله [English]

Gravel, cobbles and boulders Percentage mapping using Close-Range Photogrammetry (Case Study: The Tehran-Karaj Plain)

نویسنده [English]

  • Behzad Rayegani

College of Environment, Department of Environment, Karaj

چکیده [English]

Introduction: Gravel, cobbles and boulders as erodible parameters play significant role to control wind erosion. Therefore, our understandings of gravel, cobbles and boulders percentage variations help to analyze events in the landscape. Close-range photogrammetry as an accurate measurement tool based on photos analysis has been extraordinary improved in recent years and its usage is rapidly growing in environmental analyses. It seems that close range photogrammetry in mapping and measuring the shapes and surfaces have a great potential. Currently close range photogrammetry is mostly used for preparation of Digital Elevation Model (DEM) and Digital Terrain Model (DTM). Now, high resolution DEMS only can be created using 3D Laser Scanner and close range photogrammetry. Despite having a considerable potential, close range photogrammetry has been rarely used in quantitative natural resource studies. In the current assessment, we examined the ability of close range photogrammetry for a quantitative parameter (i.e. percentage of gravel, cobbles and boulder).
Materials and Methods: In this study, we tried to used the close range photogrammetry and assess its performance to estimate the percentage of gravel, cobbles and boulders. For this purpose, a specific quadrat was designed for close range photogrammetry and the required photography tools and techniques were determined. In order to prepare the mapping of gravel, cobbles and boulders percentage, a sampling plan using OLI data was designed for the plain of Tehran-Karaj and photography was performed accordingly. Photos were processed using the PhotoScan software and Orthophotos and Digital Terrain Models were then created. The photos were classified by two methods: 1- Decision Tree Analysis using Digital Terrain Models that it was done using the ERDAS IMAGINE 2015 software; 2- Object-based Classification using Orthophotos and Digital Terrain Models that the eCognition Developer 9 software was used. Gravel, cobbles and boulders percentage of each quadrat was estimated based on more accurate method and used as the dependent variable for modeling process. To model gravel, cobbles and boulders percentage, OLI data was firstly preprocessed to extract reflectance of the bands and then spectral indices were used. Geometric correction and radiometric correction using ATCOR3 were carried out in preprocessing phase and spectral indices of soil characterize were used to enhance the image. Finally, the reflectance of the bands and the spectral indices were used to create a multiple regression model using IBM SPSS Statistics 22 software.
Results and Discussion: The results showed that the Close Range Photogrammetry software (PhotoScan) is able to fix the distortion in photos well. One-dimensional relief displacement error was removed by PhotoScan. Interior and exterior orientation was done very well using the software and measurements which were calibrated by it. High quality Ortho-Photos and high resolution Digital Terrain Models were created using PhotoScan.
Classification by Decision Tree Analysis using Digital Terrain Models was done by the ERDAS IMAGINE 2015 software. First-order and Second-order polynomial interpolation was applied to Digital Terrain Models and the uniform surfaces were created. Two surfaces (original one created by PhotoScan and Interpolated Surface) were then compared and the gravel, cobbles and boulders parts were separated using some thresholds. The results indicated that this method can create the gravel, cobbles and boulders map rapidly but the accuracy is moderate.
Comparing with Decision Tree Analysis, Object-based Classification by the eCognition Developer 9 software which uses Orthophotos and Digital Terrain Models was more accurate. However, the latter was time-consuming as it is needed to be done manually in many different steps and there were many options to be created for final layer.
Automatic linear modeling in IBM SPSS Statistics 22 software was used to create multiple regression model and Iron Oxide and Inferred indices and reflectance of the bands 1, 2, 3 and 7 of OLI Sensor were selected by the software. The coefficient of determination of the model was more than 0.9 showing the good potential of the close-range photogrammetry. This model was used to create maps of percentage and the final map was in full compliance with the field observations.
Conclusions: Our results showed that the Close Range Photogrammetry has a vast potential and it can be an important tool in the environmental studies in the future.

کلیدواژه‌ها [English]

  • eCognition
  • Specific Quadrat for Photogrammetry
  • Decision Tree Analysis
  • Object-based Classification
  • PhotoScan
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