بررسی و تحلیل امکان آشکارسازی عوارض زیرسطحی از طریق رادار زمین نفوذ بر اساس شبیه‌سازی امواج الکترومغناطیسی

در این تحقیق امکان‌سنجی رادار زمین نفوذ (gpr) برای آشکارسازی و تعیین موقعیت عوارض زیرسطحی در شرایط مختلف بر اساس داده های شبیه‌سازی‌شده مورد بررسی قرار گرفته است. به این منظور، عملکرد امواج رادار در آشکارسازی اهداف با جنس‌های متفاوت، در شرایط محیطی با رسانایی الکتریکی مختلف بررسی شده است. معیار مورد بررسی عملکرد gpr در این مطالعه قدرت تفکیک امواج در استفاده از امواج رادار با فرکانس‌های مرکزی مختلف است. نتایج شبیه‌سازی نشان می‌دهد که انتخاب فرکانس مرکزی در روش gpr تاثیر بسیار زیادی بر اندازه ابعاد هدف در شناسایی با تصویر‌سازی قابل‌قبول را دارد و اهداف با اندازه تقریبی قطر کمتر از 3، 6، 12، 25 و 125 سانتیمتر در آنتن‌های رادار نفوذی زمین با فرکانس‌های مرکزی به ترتیب 2 گیگاهرتز، 1 گیگاهرتز، 500، 250 و 50 مگاهرتز قابلیت مشخص شدن را نخواهند داشت. نتایج به‌دست‌آمده برای محیطی با سرعت 0.15 متر بر نانوثانیه (به‌عنوان‌مثال آبرفت با دانه بندی متوسط و یا ماسه خشک) صادق است. نتایج حاصل از شبیه‌سازی شرایط مختلف بر اساس مشخصه‌های k (گذردهی نسبی)، δ (رسانندگی هر لایه) و d (ضخامت لایه‌های خاک) نشان می‌دهد که رسانایی الکتریکی بیش‌ترین تاثیر را نسبت به دیگر پارامترها در نتایج روش gpr را دارد و لایه هایی با رسانایی الکتریکی بیش از کمتر از 0.1 اهممتر به‌شدت دامنه موج گسیل‌شده در این روش را تضعیف می‌کند و امکان نفوذ برای شناسایی هدف را با مشکل مواجه می‌سازد.

Analysis of Ground Penetrating Radar Method in Detecting Subsurface Targets Based on Simulating Electromagnetic Waves

In this study, the feasibilityof using the Ground Penetrating Radar (GPR) method to detect and locate subsurface utilities in various conditions has been investigated. To do this end, the performance of radar waves in detecting different material types in environmental conditions with different electrical conductivity has been studied. The GPR’s performance criterion in this study is the resolution of the reflected waves in using radar systems with different central frequencies. The results indicate that the central frequency has a great influence on the size of the target with proper imaging. Moreover, the simulation results show that for central frequencies of 50, 250, 500 MHz, 1 GHz and 2 GHz, targets with sizes 125, 25, 6 and 3 cm cannot be detected, respectively. Estimated results on resolution are related to the radar wave propagation velocity in the media severely. Also, the estimated resolution values are valid for a medium with a wave propagation velocity equal to 0.15 m/ns (For example, alluvium with moderate grains or dry sand). Simulation results on martial type based on relative electromagnetic permittivity (Ɛ), sublayer conductivity (δ) and layers thickness (D), show that the electrical conductivity had a higher effect on the GPR results with respect to the other parameters and layers with an electrical conductivity of less than 0.1 ohmmeter strongly weaken the amplitude of the transmitted wave and made it difficult to identify the target. Results show that with changing the central frequency in the GPR system, transmitted and reflected radar waves have different frequency content and pulse width in both frequency and time domain. As it is presented in the paper, short pulse width in time domain led to a broad band in frequency domain. Simulation results on substance type which is simulated by relative electromagnetic permittivity (Ɛ) parameter show that high relative permittivity led to receiving a reflected signal with high frequency content in frequency domain and recording strong amplitude in time domain. The simulation results show that soil conductivity attenuated electromagnetic waves severely. Based on simulated data for a target located in 1 m depth and a GPR system with dominant frequency equal to 500 MHz media with electrical resistivity more than 20 ohm.m does not affect the signal quality in radar waves. However, decreasing electrical resistivity by less than 2 ohm.m caused lack of penetration and without receiving any reflection from the target. The simulation results concluded that, using a GPR system in normal condition such as soil with 100 ohm.m, target and media relative permittivity respectively equal to 80 and 4 and target depth located in effective depth, reflected electromagnetic waves are recorded in different resolution. As results for 50, 250 500 and 2000 MHz central frequency 125, 25, 6 and 3 cm resolution is calculated respectively. Estimated results on resolution is related to radar wave propagation velocity in the media severely. Estimated resolution are valid wave propagation velocity equal to 0.15 m/ns. In the second part oof this study 2D simulation is performed. 2D simulation conducted for four different conditions. In all conditions 3 layers and 3 target is simulated. Ground penetrating radar data is simulated based on central frequency 50 MHz.  Finally, 2D simulation, synthetic crosssections indicated that high conductivity of soils cause the less penetration and lowresolution results. In addition, attenuation parameter investigations show that value of high attenuation in silt and clay soils by two and four cause the very lowresolution data in ground penetrating radar method.