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پژوهش های ژئوفیزیک کاربردی - سال سوم شماره 1 (پیاپی 5، بهار و تابستان 1396)

نشریه پژوهش های ژئوفیزیک کاربردی
سال سوم شماره 1 (پیاپی 5، بهار و تابستان 1396)

  • تاریخ انتشار: 1396/04/15
  • تعداد عناوین: 10
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  • بهزاد سرلک، حمید آقاجانی *، علی نجاتی کلاته صفحات 1-14
    استفاده از روش های ژئوفیزیکی در کاوش های باستانی، قبل از حفاری، جهت تعیین مرز بی هنجاری ها می تواند مفید و موثر باشد. در این میان، به دلیل نداشتن اثرات مخرب محیطی، روش مغناطیس سنجی یکی از روش های پرکاربرد است. در محوطه های باستانی تغییر مغناطیدگی در محیط به دلایل طبیعی و فعالیت های بشری صورت می گیرد. به کمک روش مغناطیس سنجی، تباین خودپذیری مغناطیسی محیط پیرامون به طورکلی با اقلام فلزی، مصالح ساختمانی مورداستفاده و حفره های پرشده با مواد متنوع که دارای خاصیت مغناطیسی هستند، موردمطالعه قرار می گیرد. در این مقاله از داده های مغناطیس مصنوعی، واقعی و فیلترهای فازی به منظور بررسی ساختارهای زیرسطحی در محوطه باستانی تپه حصار دامغان استفاده شده است. در این راستا از فیلترهای زاویه تمایل، نقشه تتا، لاپلاسین و تانژانت هایپرپولیک استفاده شد. همچنین در این مقاله یک فیلتر توانمند جدید که یک زاویه از نسبت مشتق های افقی است و در راستای محور قائم نرمالیزه شده، معرفی شد. این فیلتر روی لبه ها بیشینه می شود و به خوبی مرزها را آشکار می کند. نتایج حاصل از بررسی داده های مغناطیسی تپه حصار با نتایج حفاری های انجام شده انطباق بالایی دارد.
    کلیدواژگان: مغناطیس سنجی، باستان شناسی، آشکارسازی لبه، فیلترهای فازی، محوطه باستانی تپه حصار
  • سید حسین سید آقامیری*، علی غلامی صفحات 15-27
    موجک منتشر شده در زمین که از لایه های مختلف بازتاب می شود، ناپایا است و با انتشار در درون زمین به خاطر جذب و پدیده های دیگر تغییر می کند. واهمامیخت لرزه ای ابزاری برای استخراج سری ضرایب بازتاب زمین از ردلرزه ثبت شده و یا به عبارتی حذف اثر موجک از ردلرزه است. در تئوری واهمامیخت پایا فرض می شود که موجک منتشر شده پایا بوده و تغییر نمی کند؛ پس نمی تواند راه حل خوبی برای یک ردلرزه ناپایا باشد. روش واهمامیخت گابور یک مسئله ناپایا را به چند زیر مسئله تقسیم کرده و فرض می کند که هرکدام پایا باشد و با استفاده از واهمامیخت پایا، سری ضرایب بازتاب هر بخش را تخمین زده و در نهایت با تصویر کردن آن ها تقریبی از سری ضرایب بازتاب زمین ایجاد می کند. واهمامیخت گابور به دلیل خطاهای سیستماتیک ناپایدار است و از طرفی چون مسئله وارون برای هر زیر مسئله جداگانه حل می شود؛ منظم سازی مسئله وارون بسیار وقت گیر است و اعمال قید مناسب و اطلاعات اولیه در حل مسئله وارون دشوار است. روش واهمامیخت گابور تصویر شده با جابجایی ترتیب انجام واهمامیخت پایا و عملگر تصویر کردن، علاوه بر این که باعث کاهش خطای سیستماتیک و در نتیجه پایداری بهتر مسئله وارون می شود؛ کاهش چشم گیری در زمان انجام محاسبات به همراه دارد؛ زیرا نیاز است تنها یک مسئله وارون حل شود. همچنین می توان قیدهای مورد نظر یا اطلاعات اولیه را به راحتی وارد مسئله وارون کرد. در این مقاله راه حلی برای واهمامیخت ناپایا در حضور نوفه گوسی و اسپایکی بر مبنای روش گابور تصویر شده ارائه می شود. نتایج اعمال این روش بر مثال های مصنوعی و داده های واقعی نشان می دهد که واهمامیخت گابور تصویر شده جواب دقیق تر و پایدارتری نسبت به واهمامیخت گابور دارد.
    کلیدواژگان: واهمامیخت ناپایا، واهمامیخت گابور، واهمامیخت گابور تصویر شده، جذب، مدل Q ثابت، تخمین موجک ناپایا
  • سیامک ابوالحسنی*، نوید امینی، حمیدرضا سیاه کوهی صفحات 29-42
    یک مسئله کلیدی در پردازش داده های لرزه ای و تصویرسازی با استفاده از این داده ها، تخمین درست سرعت انتشار امواج لرزه ای است. وارون سازی شکل موج کامل، یک روش نوین جهت تخمین پارامترهای زیرسطحی مانند سرعت، چگالی و فاکتور کیفیت است. این روش، یک مسئله وارون در ژئوفیزیک محسوب می شود؛ که در آن به دنبال پارامترهایی می باشند که شکل موج های ثبت شده (لرزه نگاشت ها) را توصیف نمایند. فرآیند وارون سازی شکل موج کامل در قالب یک مسئله بهینه سازی از طریق تعریف یک تابع هزینه به صورت اختلاف بین شکل موج های مشاهده ای (ثبت شده) و شکل موج های محاسبه ای بیان می شود. در تصویرسازی دوبعدی و سه بعدی، اندازه فضای پارامترهای مدل و همچنین پیچیدگی های محاسباتی مدل سازی مستقیم اجازه ی استفاده از روش های بهینه سازی سراسری را نخواهد داد و باید تابع هزینه از طریق روش های بهینه سازی محلی، کمینه شود. مسئله حداقل سازی در این روش اغلب به صورت یک فرآیند تکراری از طریق روش های گرادیانی که بر پایه مشتقات مرتبه اول و دوم تابع هزینه عمل می کنند، انجام می شود. در این مقاله به مقایسه عملکرد دو الگوریتم بهینه سازی، الگوریتم گاوس-نیوتن با حضور قطر اصلی شبه هشین و الگوریتم شبه نیوتنی L-BFGS پرداخته می شود. الگوریتم گاوس-نیوتن با حضور قطر اصلی شبه هشین، یک الگوریتم استاندارد گاوس-نیوتن به شمار می رود؛ که با اصلاحاتی بر محاسبه ی صریح ماتریس هشین جهت کاهش بار محاسباتی همراه شده است و الگوریتم L-BFGS، یک الگوریتم شبه نیوتنی است که در آن نیازی به محاسبه صریح ماتریس هشین ندارد. در این مقاله، عملکرد و کارایی این دو الگوریتم بهینه سازی از لحاظ کیفی و کمی روی یک مدل سرعت مصنوعی بررسی می شود. مطابق نتایج ملاحظه خواهد شد که هر دو روش موفق شده اند مدل صحیح را به لحاظ کیفی به خوبی بازسازی نمایند. همچنین با بررسی کمی عدم تطابق بین مدل صحیح و مدل وارون شده برای هر دو الگوریتم، این جمع بندی به دست می آید که عملکرد الگوریتم گاوس-نیوتن با حضور قطر اصلی شبه هشین، در 40 تکرار صورت گرفته در این مطالعه، عملکرد نسبتا بهتری داشته است.
    کلیدواژگان: تصویرسازی لرزه ای، وارون سازی شکل موج کامل آکوستیک، بهینه سازی غیرخطی، روش بهینه سازی گاوس، نیوتن، روش بهینه سازی شبه نیوتنی، Limited، Memory BFGS، شبه هشین
  • بهنام بابایی، مهدی فلاحی پور، حمیدرضا باغزندانی* صفحات 43-49
    گرانی سنجی یکی از روش های ژئوفیزیکی است که به کمک دیگر روش های ژئوفیزیکی در حل بعضی از مسائل و مشکلات موجود در تفسیر ساختارهای زمین شناسی کمک می کند. هرچند به منظور دست یابی به یک تفسیر جامع می توان از مدل سازی داده های ژئوفیزیکی بهره برد. یکی از این روش ها، مدل سازی وارون داده ها است. مدل سازی وارون به منظور تعیین پارامترهای مدل از داده ها به کار می رود. در وارون سازی داده های ژئوفیزیکی، پارامترهای مدل دو دسته اند: 1) فیزیکی 2) هندسی. بر همین مبنا دو روش وارون سازی داده های میدان پتانسیل وجود دارد، در روش اول پارامترهای هندسی ثابت و پارامترهای فیزیکی به عنوان مجهولات مسئله در نظر گرفته می شود و در روش دوم پارامترهای فیزیکی مدل ثابت فرض شده و پارامترهای هندسی مانند عمق در روند وارون سازی تخمین زده می شود. در این تحقیق با برداشت 380 داده گرانی سنجی در منطقه محلات و انجام تصحیحات لازم، پردازش داده ها و اعمال فیلترینگ مناسب جهت تشخیص روندهای سطحی و تلفیق داده ها با اطلاعات زمین شناسی موجود، سعی گردید روندهای سطحی و عمقی تاثیرگذار بر روی چشمه های آبگرم موجود در منطقه تعیین شده و مخازن احتمالی موجود در منطقه با استفاده از آن شناسایی گردد.
    کلیدواژگان: گرانی سنجی، مدل سازی معکوس، مخازن زمین گرمایی
  • مریم شیبی*، پروین مجیدی صفحات 51-63
    توده گرانیتوئیدی چالو، در جنوب شرق شهرستان دامغان و در شمالی ترین بخش پهنه ساختاری ایران مرکزی واقع شده است. تزریق این توده نفوذی به درون سنگ های آتش فشانی و آتش فشانی- رسوبی و سیال های گرمابی حاصل از آن ها، باعث ایجاد فرایندهای دگرسانی و کانه زایی شده است. در مجموع دو فاز دگرسانی پروپیلیتی و آرژیلیکی در این توده قابل شناسایی است. قابلیت پذیرفتاری مغناطیسی (Km) در نمونه های سالم و انواع دگرسان شده توده گرانیتوئیدی چالو با استفاده از روش فابریک مغناطیسی اندازه گیری شده است. پذیرفتاری مغناطیسی میانگین
    اندازه گیری شده برای مونزودیوریت ها و کوارتز دیوریت های سالم، به ترتیب SIμ3410 ± 28872 SIμ3916 ±21487 است. گردش سیالات گرمابی از میان توده نفوذی باعث ایجاد تغییرات مهم کانی شناسی شده و خواص مغناطیسی اصلی توده را تغییر داده است؛ به گونه ای که میانگین پذیرفتاری مغناطیسی (Km) در نمونه های دارای دگرسانی پروپیلیتی و آرژیلیتی در دو واحد سنگی سازنده این توده به ترتیب SIμ988 ± 25117 و SIμ 1577 ± 6262 کاهش یافته است. ماهیت انواع کانی های کدر موجود در این توده نفوذی نیز بر اساس منحنی های ترمومغناطیسی (تغییرات پذیرفتاری مغناطیسی با دما) تعیین شده است. این یافته ها نشان می دهند که چگونه میزان بزرگای پذیرفتاری مغناطیسی، همگام با پیشرفت مراحل مختلف دگرسانی گرمابی به علت حذف یا کاهش در اندازه منیتیت و یا تبدیل آن به کانی های مغناطیسی دیگر نظیر هماتیت (فرومغناطیس) و یا پیریت (پارامغناطیس) کاهش می یابد؛ بنابراین به نظر می رسد روش ناهمسانگردی قابلیت پذیرفتاری مغناطیسی (AMS) علاوه بر آشکارسازی الگوی درونی توده های نفوذی و پی بردن به ساز و کار جای گیری آن ها می تواند موجب به کمیت در آوردن شدت و نوع دگرسانی های مختلف در داخل آن ها شده و الگوی مناسبی برای اکتشاف و شناسایی مسیر سیالات گرمابی شود.
    کلیدواژگان: قابلیت پذیرفتاری مغناطیسی، دگرسانی گرمابی، گرانیتوئید، چالو، دامغان
  • عطا اسحق زاده*، ناهید سادات مرتضوی صفحات 65-86
    در این مقاله با استفاده از یک روش وارون سازی غیرخطی داده های گرانی، پارامترهای عمق، شعاع، ضریب دامنه و عامل شکل چشمه بی هنجاری محاسبه می شود. با تعیین مقدار گرانی در مبدا مختصات و نیز دو مقدار دیگر گرانی در روی پروفیل برداشت، عمق چشمه بی هنجاری با حل معادله غیرخطی f(z)=0 تخمین زده می شود. از آنجایی که در طبیعت، چشمه های بی هنجاری گرانی ناهمگن بوده و دارای شکل هندسی نامنظم می باشند؛ داده های گرانی پروفیلی معمولا نسبت به نقطه مبدا -که دارای مقدار گرانی بیشینه، بدون توجه به علامت مثبت و منفی آن، است و معرف مرکز چشمه بی هنجاری است- نامتقارن است و منحنی تغییرات میدان گرانی در راستای پروفیل ناهموار است.
    به همین دلیل در عمل از چندین داده در طول یک پروفیل برای تخمین پارامترهای عمق، ضریب دامنه و عامل شکل استفاده می شود. با دانستن مقدار عمق، سه پارامتر شعاع، ضریب دامنه و عامل شکل قابل محاسبه می باشند. روش پیشنهادی، برای چشمه هایی با شکل های هندسی استوانه عمودی، استوانه قائم و کروی مورد بررسی قرار می گیرد. کارایی روش مذکور با افزودن نوفه تصادفی به میدان گرانی محاسبه شده برای مدل های مصنوعی نیز تحلیل می شود. همچنین تاثیر عمق و اختلاف فاصله در تعیین نقطه مبدا چشمه بی هنجاری گرانی بررسی خواهد شد. از روش وارون سازی غیرخطی برای تخمین عمق، شعاع و نیز تعیین شکل حدودی یک گنبد نمکی استفاده می شود. در این مطالعه گنبد نمکی آجی چای بررسی شده و طی آن عمق گنبد مذکور در حدود 63/64 متر زمین و شعاع آن 8/34 متر برآورد شده است. همچنین شکل هندسی این گنبد نمکی بر اساس عامل شکل که 43/1 محاسبه شده است، به کره قابل تشبیه است.
    کلیدواژگان: ضریب دامنه، عامل شکل، گرانی، گنبد نمکی، وارون سازی غیرخطی
  • منصوره خالقی یله گنبدی*، وحید ابراهیم زاده اردستانی صفحات 87-97
    در این مقاله وارون سازی سه بعدی داده های گرانی برای تعیین توده زیرسطحی به روش زمین آماری کوکریجینگ بررسی شده است. سطح زیرین در ناحیه برداشت داده های گرانی، به تعداد زیادی مکعب با ابعاد و موقعیت معلوم تقسیم شده است. تباین چگالی مجهول هر یک از این مکعب ها (به عنوان پارامتری که باید تخمین زده شود)، در نظر گرفته شده است. از آنجا که این نوع وارون سازی از نوع تصادفی به شمار می آید؛ تابع هدف شامل ماتریس کواریانس گرانی و ماتریس کواریانس چگالی برای در نظر گرفتن عدم قطعیت به ترتیب در داده ها و پارامترهاست. علاوه بر آن از ماتریس وزن دهی عمقی به منظور جلوگیری از انقباض توده به سمت سطح نیز استفاده شده است. برای وارون سازی رابطه وارون از روش گرادیان مزدوج پیش شرط (PCG) استفاده شده است. برنامه کامپیوتری به زبان متلب نوشته شده است و این برنامه روی یک مدل مکعبی به عنوان مدل مصنوعی آزمایش شده است. نتایج از نظر چگالی و موقعیت در تطابق خوبی با مدل مکعبی است. در انتها داده های گرانی برداشت شده روی معدن منگنز صفو واقع در شمال غرب ایران با استفاده از برنامه وارون سازی مذکور برگردان و مدل سازی شده اند. نتایج وارون سازی توزیع ماده معدنی توده ای با گسترش عمقی 5 تا حدود 35 متری را نشان می دهد؛ که با نتایج حاصل از حفاری انطباق دارد.
    کلیدواژگان: گرانی سنجی، وارون سازی سه بعدی، کوکریجینگ، زمین آمار، واریوگرام، معدن صفو
  • محمدفهیم آویش، حجت الله رنجبر*، آزاده حجت، سعید کریمی نسب، ایمان معصومی صفحات 99-118
    استان کرمان به دلیل قرارگیری در زون های ساختاری مختلف و تکتونیک فعال آن، می تواند دارای مناطق با پتانسیل بالای ژئوترمال باشد. در این پژوهش، با استفاده از تصاویر سنجنده های مودیس، ETM+ و استر و داده های مغناطیسی هوابرد و زمینی، به بررسی نشانه های وجود پتانسیل منابع ژئوترمال در منطقه سیرچ-گلباف استان کرمان پرداخته شد. دمای سطح زمین با استفاده از بررسی های سنجش از دور و روش های الگوریتم پنجره مجزا تعمیم یافته، نرمال سازی گسیلندگی و روش تخمین دمای سطح زمین سنجنده ETM+، جهت شناسایی بی هنجاری های حرارتی منطقه و تخمین اینرسی حرارتی ظاهری که در ارتباط با منابع ژئوترمال سطحی بوده، محاسبه شد. نتایج نشان می دهد یک بی هنجاری حرارتی در بخش جنوب شرقی منطقه و یک بی هنجاری حرارتی دیگر در محدوده شمالی وجود دارد. از داده های مغناطیسی به منظور تعیین محل توده های نفوذی به عنوان نشانه ای از وجود منبع ژئوترمال و ردیابی گسل ها استفاده شد. با استفاده از فیلترهای ادامه فراسو، مشتق قائم و سیگنال تحلیلی روی داده های مغناطیسی هوابرد، بی هنجاری هایی در محدوده مورد مطالعه تشخیص داده شدند؛ که با توجه به ارتباط چشمه های آب گرم و توده های نفوذی، این بی هنجاری ها می توانند مرتبط با توده های نفوذی و نیز بی هنجاری های حرارتی آشکار شده از روش دورسنجی حرارتی باشند. از طرفی، بی هنجاری های حرارتی و بی هنجاری مغناطیسی تشخیص داده شده با روش های دورسنجی و مغناطیس زمینی، با بی هنجاری های مغناطیسی آشکار شده به روش داده های مغناطیسی هوابرد مطابقت می کنند.
    کلیدواژگان: مودیس، لندست ETM+، استر، دمای سطح زمین، اینرسی حرارتی ظاهری، مغناطیس سنجی هوابرد، مغناطیس سنجی زمینی
  • حسام حسین نیا، امین روشندل کاهو*، بهزاد تخم چی صفحات 119-130
    داده های لرزه ای بازتابی اغلب آلوده به نوفه های همدوس می باشند که بازتاب های مورد نیاز برای استخراج یک تصویر دقیق زیرسطحی را می پوشانند. یکی از مهم ترین نوفه های لرزه ای همدوس نوفه زمین غلت است که دارای محدوده فرکانسی پایین، دامنه بالا و سرعت پایینی است و در سراسر و نزدیک سطح زمین گسترش پیدا می کند. این نوفه اغلب بازتاب های کم عمق را در دورافت های نزدیک و بازتاب های عمیق را در دورافت های دور می پوشاند و اطلاعات مفید حاصل از اکتشافات لرزه ای را پنهان می کند. از این رو نوفه زمین غلت یک مشکل همیشگی در تصویرسازی لرزه ای است و تضعیف این دسته از نوفه ها یک مرحله ضروری در پردازش داده های لرزه ای خشکی به حساب می آید. روش های زیادی برای تضعیف این نوفه ها معرفی شده است. در این مقاله، به منظور تضعیف نوفه همدوس از تبدیل موجک در حوزه ردلرزه شعاعی استفاده شده است. این روش بر اساس کاربرد مشترک تبدیل موجک گسسته دو بعدی و تبدیل ردلرزه شعاعی برای تضعیف نوفه همدوس و به طور خاص نوفه زمین غلت است. چون تبدیل ردلرزه شعاعی، رخدادهای خطی در حوزه دورافت-زمان (x-t) را به رخدادهای عمودی در حوزه سرعت ظاهری-زمان (r-t) تبدیل می کند، لذا یک محیط کار مطلوب برای تبدیل موجک گسسته دو بعدی فراهم می کند. نتایج به دست آمده از داده های واقعی به خوبی بهتر بودن روش پیشنهادی را نسبت به فیلتر f-k اثبات می کند. همچنین، نتایج نشان داد که الگوریتم در مقابل تغییرات اندک مبدا مختصات تبدیل ردلرزه شعاعی و نوع موجک تبدیل موجک گسسته دوبعدی پایدار بوده و تغییر چشم گیری در نتایج ایجاد نشده و خروجی تقریبا یکسانی تولید می کند.
    کلیدواژگان: تبدیل موجک گسسته دو بعدی، تبدیل ردلرزه شعاعی، نوفه زمین غلت، تضعیف نوفه همدوس
  • فریدون شریفی، صفا خزایی* صفحات 131-143
    پاک سازی میادین مین و مناطق آلوده به مواد منفجره عمل نکرده یکی از مسائلی است که در کشورهای جنگ زده و از جمله کشور ما، با وجود گذشت ده ها سال از زمان جنگ، نیازمند توجه جدی است. روش های مختلف ژئوفیزیکی از جمله روش GPR نقش بسیار مهمی در آشکارسازی محل این آثار مخرب باقیمانده از جنگ دارند. روش GPR هوابرد به دلیل قابلیت ها و برتری های خاصی که نسبت به روش برداشت زمینی دارد، توجه ویژه متخصصان امر را به استفاده از آن در آشکارسازی UXO معطوف داشته است. در این تحقیق به منظور امکان سنجی کاربرد روش GPR هوابرد در آشکارسازی UXO، به شبیه سازی عددی و تجزیه و تحلیل سیگنال های برگشتی از یک مین فلزی ضد نفر مدفون در عمق 10 سانتیمتری خاک با استفاده از این روش پرداخته شده است. برای این منظور دو مدل مصنوعی، شامل یک لایه هوا و یک لایه خاک، طراحی شده است که در یکی از آن ها مدل عاری از مین (Model A) و دیگری مدل حاوی یک مین فلزی ضد نفر مدفون در عمق 10 سانتی متری خاک و در موقعیت x=0.25m (Model B) در مرکز مدل، می باشند. در ادامه ردها و نگاشت های راداری در ارتفاع های پرواز (0 تا 10 متر) و در بازه فرکانسی 100 تا 1500 مگاهرتز و منطبق با مرکز دو مدل فوق الذکر، در مجموع تعداد 638 حالت مختلف، با استفاده از روش تفاضل محدود در حوزه زمان (FDTD) شبیه سازی شده اند. تجزیه و تحلیل داده ها شامل بررسی انرژی سیگنال، تبدیل موجک برای انتقال داده ها به حوزه فرکانس و حذف نوفه و در نهایت انتقال داده ها به حوزه زمان- فرکانس در محیط نرم افزار MATLAB انجام پذیرفته است. با توجه به نتایج هر سه روش پردازش سیگنال مورد استفاده، قابلیت آشکارسازی مین با روش GPR هوابرد تا حداکثر ارتفاع پرواز 10 متر و در بازه فرکانسی 550 تا 1500 مگاهرتز تایید شد.
    کلیدواژگان: GPR هوابرد، شبیه سازی عددی، انرژی سیگنال، تبدیل موجک، تحلیل زمان، فرکانس، آشکارسازی UXO
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  • Behzad Sarlak, Hamid Aghajani*, Ali Nejati Kalateh Pages 1-14
    Summary: Geophysical methods are effective tools in archaeological investigations. Sensitive magnetometers have been used for many years to locate and characterize archaeological sites. Magnetometry is one of the most widely geophysical methods in this application as it contains no harmful environmental effects. Magnetization contrast in ancient sites is created by natural causes and human activities. Studies have shown that topsoil has generally a higher magnetic susceptibility than most bedrocks and sub-soils. Vegetation fires and fermentation effects increase background magnetic susceptibility, and oxidation-reduction cycles associated with alternate wetting and drying of the soil; all of these tend to convert the iron compounds to strongly magnetic oxide maghaemite. In this paper, subsurface structures have been investigated in the Tepe-Hissar ancient area of Damghan. In this regard, synthetic and real magnetic data and fuzzy filters have been used to investigate these subsurface structures. Moreover, normalized derivatives respect to vertical derivative (NAVD or NA) filter has been introduced that enhance edges in potential field methods.
    Introduction
    Magnetization contrast has been examined between metal items, building materials, ditches, pits, and their surrounding environment. This magnetization can be either remanent magnetization, induced magnetization, or both, that creates a contrast in magnetization between the interested features and the surrounding environment. Remanent magnetization can be locked into archaeological materials such as kilns, ovens and floors that are baked (Clark et al., 1988). Induced magnetization also plays a large part in the ability to detect archaeological features. Fire has long been known to increase the magnetic susceptibility of soil. Weakly magnetic iron oxides in the clay and silt particles are transformed into highly magnetic oxides through burning. When the organic matter in a soil burns at 200 0C, it produces a reducing atmosphere, which can change hematite to magnetite, and probably maghaemite on reoxidation as the burn ceases (Aspinall et al. 2008). For better interpretation, noise must be removed. After necessary corrections, the total magnetic intensity map is seen to be dominated by long wavelength magnetic anomalies. The anomaly appears to be about 100nT that represents the amount of magnetization of the area.
    Methodology and Approaches: Local phase filters provide an approach to detect the edges of the anomalies but conventional phase functions need to be unwrapped to remove phase ambiguity (Fitzgerald et al., 1997). Therefore, detection of the boundary of chambers or walls and the location of sources can be obtained from derivative based filters such as the horizontal gradient magnitude, tilt-angle, theta-map, Laplacian and tangent hyperbolic filters, however, these filters typically fail for archaeological investigations due to the high noise content of the acquired data. In this paper, similarly to prospect an area, a synthetic model is prepared which combines structures and the lane or rooms that have been filled with alluvium and soil. One of the conventional phase filter that is used for edge detection is the tilt angle (Miller and Singh, 1994). The tilt angle is effective in balancing the amplitudes of different anomalies, but it is not primarily an edge-detection filter. The theta map uses the analytic signal amplitude to normalize the total horizontal derivative (Wijns et al. 2005). The amplitude of the response of this filter from the deeper and shallow source bodies is similar, although the response from the deeper bodies is rather different. The hyperbolic tilt angle (HTA) filter uses of the real part of the hyperbolic tangent function in the tilt angle. Using this filter, better delineation of the edges of the anomalous body than the other filters is achieved. The maximum value of the HTA gives location of the body edges (Cooper and Cowan, 2006). Edge enhancement in potential field methods helps to make proper geological and archaeological interpretation. There are many methods for enhancing edges, most of which are high-pass filters based on the horizontal or vertical derivatives of the field. Normalized angle respect to vertical derivative (NAVD) filter, which is a new edge detection filter, is based on ratios of the horizontal derivatives of the field. The NAVD filter has been demonstrated on synthetic and real magnetic data from the archaeological site of Tepe-Hissar. Compared with other filters, the NAVD filter detects edges very well.
    Results and
    Conclusions
    Results of this research work indicate that the obtained information from magnetometry is compatible with the subsurface information before excavations in the area. The results of magnetic surveys in the archaeological site of Teppe-Hissar show that the site has an irregular construction with meandering lanes. The main lane in this archaeological site appears to be along northeast-southwest direction. This fact is clearly understood from the magnetic images of the site.
    Keywords: Magnetometry, Archaeology, Edge Detection, Fuzzy Filters, NAVD Filter, Teppe-Hissar
  • Seyed Hossein Seyed Aghamiry*, Ali Gholami Pages 15-27
    Summary: Deconvolution is considered as a successful tool in seismic exploration for increasing the temporal resolution of the data. Gabor deconvolution is proposed to treat the non-stationarity issue of the problem by breaking it into several stationary sub-problems via a Gaussian window, solving them independently, and then, recombining/projecting the sub-solutions into an approximate solution to the original nonstationary problem. The projected Gabor deconvolution has recently been proposed by the second author as an improvement over Gabor deconvolution. In the projected Gabor deconvolution, the sub-problems are projected to a unified problem in time domain, and then, the resulting problem is solved. This modification brings useful advantages over the Gabor deconvolution including an improved convergence property, more efficiency for sparse deconvolution, more flexibility for incorporating prior information in the presence of noise, and more reflectivity structure via a least-squares method. In this paper, we propose a method for sparse and non-sparse deconvolution of non stationary seismic signals in the presence of Gaussian and spike-like random noises. Numerical tests using simulated and field data are presented to show high performance of the proposed method for generating accurate and stable reflectivity models from nonstationary seismograms.
    Introduction
    According to the convolutional model of the Earth, a seismic signal can be modeled as convolution of the source generated wavelet with the Earth impulse response. The Earth impulse response contains the reflectivity information of the layer boundaries and the elasticity effects of the medium such as attenuation, absorption, etc. The aim of nonstationary seismic deconvolution is the recovery of the reflectivity series from such non-stationary signals. Gabor deconvolution, as an extension of stationary deconvolution, breaks the original problem into several stationary subproblems, then solves each sub-problem independently, and finally, recombines/projects the sub solutions into an approximate solution to the original non-stationary problem. A main property of the method is the treatment of the problem somehow in a blind fashion without requiring the attenuation model of the Earth as a priori. Projected Gabor deconvolution has been proposed as an alternative non-stationary deconvolution method. The projected Gabor deconvolution, compared to the Gabor deconvolution, shows an improved convergence property, and is more stable in the presence of noise, more efficient for non-linear optimizations like sparse recovery, and can better handle non- Gaussian noises in the data. The focus of this paper is on the latter property. Based on the projected Gabor deconvolution, we propose a method for non-stationary deconvolution of non-stationary seismic signals in the presence of spike-like noise.
    Methodology and Approaches: Gabor deconvolution approximates a non stationary seismic deconvolution by several stationary sub-problems to be solved via stationary processes in the Gabor time-frequency domain. For random reflectivity sequences, it enables us to approximately determine the non-stationary operator via the Gabor time-frequency transform of the recorded trace. However, the inherent instability of the problem due to the approximations prevents the algorithm from converging to the solution. Furthermore, solving the Gabor deconvolution by nonlinear optimizations is rather time consuming. In the Gabor deconvolution, first an inverse operator is applied to each sub-problem, and then, the obtained sub-solutions are projected into the time domain to form a solution to the original problem. The projected Gabor deconvolution is similar to the Gabor deconvolution with the difference that the inverse operator is performed after the projection operator. There are many ways to estimate the Gabor and projected Gabor deconvolution operator. Among the many possibilities, we estimate the effect of attenuation with smoothing along hyperbolic trajectories in the time-frequency plane, and also, we estimate seismic wavelet with smoothing along the frequency axis. Thus, we can estimate the non-stationary deconvolution operator by these two procedures in an iterative manner. If we take inverse Fourier transform from columns of it and smooth it along main diagonal, we estimate the projected Gabor deconvolution operator. The projected Gabor deconvolution provides a solution to non-stationary deconvolution problem, which can be obtained by any regularization method that depends on the noise and reflectivity type.
    Results and
    Conclusions
    We have proposed a method, based on the projected Gabor deconvolution, for non stationary deconvolution of seismic signals in the presence of Gaussian and spike-like noises, and then, we have compared the results with those of the Gabor deconvolution method. Numerical examples from simulated and field data have confirmed that the projected Gabor deconvolution, compared to the Gabor deconvolution, has a better convergence property, generates more accurate results, and is more efficient to be solved via sparse optimizations.
    Keywords: Non-Stationary Deconvolution, Gabor Deconvolution, Projected Gabor Deconvolution, Seismic Attenuation, Q-Constant Model, Non-Stationary Wavelet, Estimation
  • Siamak Abolhassani*, Navid Amini, Hamid Reza Siahkoohi Pages 29-42
    Summary: Today, the significance of the velocity model estimation in seismic migration as well as time to depth conversion of seismic sections is very clear to every geophysicist. From a practical point of view, approaches such as well logging techniques or direct observations cannot provide a reliable description of regional scale physical properties of the earth. Seismic imaging is a tool to describe the earth physical properties. Today, one of the imaging techniques, which is highly welcomed by geoscientists is the full waveform inversion (FWI). The full waveform inversion - an efficient method in seismic imaging - uses all available information in the seismograms, including the amplitude, phase, and the first arrival time so as to judge the physical properties of the earth. In fact, FWI is represented as an optimization problem by defining a misfit function, which measures differences between the observed waveforms and the computed waveforms. In FWI, the size of the model space parameters will not allow us using global minimization algorithms. Therefore, we minimize the misfit function by local optimization methods. A waveform inversion problem is usually solved repetitively by the gradient-based solutions. In this paper, we have compared two gradient optimization algorithms of Gauss-Newton algorithm based on the main diagonal of the pseudo Hessian matrix (GN-DPH) and the limited memory-BFGS (LBFGS). Although the L-BFGS does not need the computation of Hessian matrix, but according to the numerical tests on synthetic models, we have found that GN-DPH algorithm results are more accurate than L-BFGS after 40 iterations.
    Introduction
    From a general point of view, in oil and gas exploration, approaches for delineating physical properties of the earth can be divided into direct solutions and indirect solutions. In large scale seismic problems, we have to focus on indirect solutions. Consequently, we use imaging techniques to extract desired parameters of the earth. There are various approaches for the imaging and estimations of the earth elastic parameters. FWI is one of efficient imaging techniques, which has become popular recently in seismic communities.
    Methodology and Approaches: We have compared one of Newton-based methods, namely Gauss-Newton based on the main diagonal of the pseudo Hessian Matrix (GN-DPH), and the limited memory-BFGS (L-BFGS). For the forward modeling, we have solved 2D acoustic wave equation using finite-difference approximation equipped with a second order absorbing boundary condition in the frequency domain. To estimate the gradient vector efficiently, the adjoint-state method (Plesseix, 2006) has been used. In the GN-DPH algorithm, a method developed by Shin et al. (2006) has been applied in order to compute the Hessian matrix, and in the L-BFGS algorithm, we have followed a preconditioned L-BFGS approach developed by Nocedal (1980). In the numerical example, the performance of the aforementioned algorithms has been examined.
    Results and
    Conclusions
    By comparison of the two reviewed optimization methods in terms of the gradient pre conditioners, we found that both methods succeeded to estimate the true velocity model. Analyzing the model estimation error revealed that the GN-DPH method was more efficient than the L-BFGS during the first 40 iterations performed in the study. Decreasing the normalized misfit function values showed the advantage of GN-DPH algorithm over the L BFGS. There is two justifications for this fact: First, the convergence rate for the GN-DPH is of a second order, whereas that of the L-BFGS is super-linear. Second reason is valuable information, which exists on the main diagonal of the linear part of the Hessian matrix that acts as pre-conditioner in the GN-DPH algorithm. On the other hand, it should be noted that by increasing the number of iterations, better results can be expected due to the fact that the Hessian matrix includes both linear and nonlinear parts and is more accurate than the other investigated method. It is also interesting to note that by increasing the complexity of a true model, we will definitely encounter a more nonlinear misfit function, which needs a more efficient Hessian for preconditioning the gradient vector where the importance of L BFGS algorithm will be highlighted there.
    Keywords: GNSeismic, Imaging, Acoustic Full Waveform Inversion, Nonlinear Optimization, Gauss-Newton Optimization, Quasi-Newton Optimization, Limited Memory-BFGS, Pseudo Hessian
  • Behnam Babaei, Mahdi Falahipour, Hamid Reza Baghzendani* Pages 43-49
    Summary: Gravimetric survey, together with other geophysical methods, could be used for analysis and interpretation of geological structures. For a more comprehensive interpretation, we could employ geophysical data modeling methods. One of these methods is the method of data inverse modeling, which is used to determine the model parameters from the obtained data. In this method, we consider two types of model parameters, namely, physical and geometrical parameters. Consequently, there are two types of inverse modeling for interpretation of potential field data. In the first type, the geometrical parameters are considered to be constants and physical parameters are considered to be variables which need to be determined, while in the second type, physical parameters are constants and geometrical parameters, such as depth, should be calculated. In the present study, gravity data were measured in 380 points in Mahallat area, and then, necessary corrections and appropriate filtering and processing, were applied on the acquired data to determine surface trends. After combining the gravity data with the existing geological information, an attempt was made to find out the effective surface and deep trends on local hot springs, and hence, to determine the possible presence of geothermal reservoirs in the area.
    Introduction
    In this paper, after reviewing various geophysical methods in studying geothermal areas of different countries, the geothermal reservoir in the study area is modeled and the depth of the reservoir is estimated using combination of gravity data and geological field observations, and also, determination of tectonic patterns, especially fault zones and fractures in the study area.
    Methodology and Approaches: After processing the obtained gravity data, the Bouguer anomaly map of the area weas obtained. Considering the geological information of the area, the anomalous zones of the area were obtained using the trend analysis of the Bouguer anomaly map. The gradient filters derived in vertical and horizontal modes were also applied on the gravity data. Finally, the geothermal potential areas were determined as a result of the modeling and interpretation of the gravity data.
    Results and
    Conclusions
    The presence of geothermal resources in the study area is evident considering hot springs, geological and tectonic observations in the area such as formation of travertine rocks due to possible geothermal reservoirs and outcrops of an intrusive body in the northeast of the area that is very likely larger in depth. Processing, modeling and interpretation of the acquired gravity data, combined with the geological and tectonic information of the study area have led to determination of the geothermal potential zones in the area.
    Keywords: Gravimetry, Inverse Modeling, Geothermal Reservoirs
  • Maryam Sheibi*, Parvin Majidi Pages 51-63
    Summary: Challu granitoid pluton is located in southeast of Damghan and northern part of central Iranian structural zone. Intrusion of the pluton into volcanic and volcanic-sedimentary rocks and the resultant hydrothermal fluids has caused alteration and Fe mineralization. Generally, two different phases of propylitic and argillic alterations are identified in the studied pluton. Magnetic susceptibility of fresh and altered rocks at the Challu granitoidic pluton is measured by magnetic fabric technique. The average measured magnetic susceptibility has been obtained about 28872±3410 μSI for monzodiorite and 21487 ±3916 μSI for quartzdiorite. Circulation ofhydrothermal fluids throughout the intrusive body has caused the main mineral compositions variation and changed the magnetic properties of minerals as the average measured magnetic susceptibility for the above rocks has, respectively, been reduced to 25117±988 μSI and 6262±1577 μSI, due to propylitic and argillic alteration. Differentkinds of opaque minerals in thepluton have also been identifined by thermomagnetic curves as magnetic susceptibility changes with temperature. These results show how magnitude of magnetic susceptibility decreases during alteration due to removal or reducing in the size of magnetite or its convertion to hematite.
    Introduction
    This research investigates changes in the magnetic fabrics of the samples taken from the Challu granitoidic pluton that have been affected by hydrothermal alteration during iron mineralization. Magnetic nature of different kinds of opaque minerals in the pluton has also been investigated via thermomagnetic curves as magnetic susceptibility changes with temperature.
    Methodology and Approaches: Three oriented hand samples were collected at each of the 32 sites located on a 0.5-1 kilometer grid pattern with good coverage across the Challu granitoidic pluton.The specimens were measured for their magnetic fabric using a Kappabridge MFK1-FA susceptometer (AGICO) at the Geomagnetic Laboratory, Shahrood University of Technology, Iran. The instrument is operated at low field (4 × 10−4T; 920 Hz) during measurements. The orientations and magnitudes of the three principal axes of the AMS ellipsoids (K1 ≥ K2 ≥ K3) were obtained for each sampling station through the tensor average of four individual AMS measurements. Moreover, 32 thin sections were prepared, and then, they were petrographically studied. Basic magnetic mineralogy, aimed at identifying the minerals responsible for the magnetic susceptibility of the samples, was performed using the CS-2 furnace (AGICO) coupled to a KLY-2 susceptometer, located at the Paleomagnetism laboratory of Geological Survey of Iran. As a result, the variation of the susceptibility with temperature from 20°C to 700°C was obtained.
    Results and
    Conclusions
    Investigation of magnetic fabric results in relation with the alteration and mineralogy of the rock samples taken from the Challu intrusive body reveal the following
    Conclusions
    1) The rocks belongs to the I-type granite and have high magnetic susceptibility (Km> 400μSI). 2) Regular variations of magnetic fabric on fresh and altered rocks of Challu granitoid show how behavior and character of minerals and rocks changes progressively with alteration. In fact, the magnitude of magnetic susceptibility is controlled by concentration of magnetic minerals (like magnetite), removal or re-deposition of it during the alteration of the intrusive body. 3) magnetic fabric studies can help us for finding internal fabric and emplacement mechanism of the intrusive body as well as identifing alteration zones and suitable pattern for exploration of mineralization passage. 4) Investigation of magnetic susceptibility changes with temperature in the mentioned granite indicates exact evidences of opaque mineral chemistry and magnetic carriers phases. The most important results of present research is that magnetic fabric changes of intrusive bodies not only provide precise information on internal structural and magnetic mineralogical nature, but also indicate geochemical variations and processes such as crystal fractionation and alteration in granites. Consequently, it seems that the AMS method not only can help us for finding internal fabric and emplacement mechanism of intrusive bodies but also for quantifying alteration types and intensity, and providing convenient model for exploration and hydrothermal fluid passages.
    Keywords: Magnetic Susceptibility, Hydrothermal Alteration, Granitoid, Challu, Damghan
  • Ata Eshaghzadeh*, Nahid Sadat Mortezavi Pages 65-86
    Summary: A nonlinear inversion technique using a fast method is developed to estimate successively the depth, shape factor and amplitude coefficient of a buried structure using residual gravity anomalies along a survey line. By defining the anomaly value at the origin and the anomaly value at different points on the survey line, the problem of depth estimation is transformed into a problem of solving a nonlinear equation of the form f (z) = 0. Knowing the depth of the anomaly source, we can estimate the shape factor, and finally, the amplitude coefficient of the anomaly. Using the amplitude coefficient, we can also compute the radius of the anomaly. This technique is applicable for a class of geometrically simple anomalous bodies, including semi-infinite vertical cylinder, infinitely long horizontal cylinder, and sphere. The efficiency of this technique is demonstrated using the gravity anomaly due to a theoretical model with and without random errors. Finally, the applicability of the technique is illustrated using the residual gravity anomaly of a salt dome, situated near Miyaneh, northeast of Iran. The interpreted depth and other model parameters are in good agreement with the known actual values of the parameters. The estimated depth, radius, shape factor and the amplitude coefficient values of the salt dome are 64.63 m, 34.8 m, 1.43 and -472 mGal, respectively.
    Introduction
    Gravity data interpretation is always subject to ambiguity. Different geometrical distributions of the subsurface mass can yield the same gravity field at the surface (Skeels, 1947). However, Roy (1962) describes how a mathematically unique solution can be achieved directly from gravity data when the density contrast is constant and the bounding surface of the body is known. Simple geometrically shaped models can be very useful in quantitative interpretation of gravity data acquired in a small area over the buried structures. The models may not be geologically realistic, but usually approximate equivalence is sufficient to determine whether the form and magnitude of the calculated gravity effects are close enough to the observed gravity data to make the geological postulate reasonable. In this paper, an inversion technique based on nonlinear equation z = f (z) is applied to analyze gravity anomalies due to simple structures. The inversion technique simultaneously estimates the depth (z), nature of the source (shape factor (q)), amplitude coefficient (A) and radius (R) of the buried structures. The accuracy of the results obtained by this procedure depends on the accuracy to which the residual anomaly can be separated from the Bouguer anomaly. Moreover, the accuracy of the results of the present method depends on the extent to which the source body conforms to one of the assumed geometries.
    Methodology and Approaches: The general vertical component of the gravity anomaly expression produced by a sphere 3D), an infinite long horizontal cylinder (2D), and a semi-infinite vertical cylinder (3D) is given in Abdelrahman et al (1989). The depth of the anomaly is determined by solving a nonlinear equation for z using standard methods. Iteration form of the solution can be expressed as ( ) f j z  f z , where zj is the initial depth and zf is the revised depth; zf will be used as the zj for the next iteration. The iteration stops when |zf −zj| ≤ e, where e is a small predetermined real number close to zero. Any initial guess for z works well because there is always one global minimum. Theoretically, two different values of N and M are enough to determine the depth. In practice, more than two values of N and M are preferable because of the presence of noise in the data (xi = ± N and xi = ± M where N = 1, 2, 3, . . . and M = , , 3, . . ., and xi is the position coordinate). For each value of N and M, we compute the values of the model parameters (i.e., z, q, A and R).
    Results and
    Conclusions
    A simple and rapid inversion approach was formulated to use the anomaly values at the origin and two pairs of measured data points (±N and ±M). The results of the synthetic and real 2D gravity data analysis showed the proficiency the proposed method. The computed depth of the salt dome was obtained as 64.63 m and the salt dome shape was obtained as sphere approximately.
    Keywords: Amplitude Coefficient, Shape Factor, Gravity, Salt Dome, Nonlinear Inversion
  • Mansoureh Khaleghi Yalegonbadi*, Vahid Ebrahimzadeh Ardestani Pages 87-97
    Summary: In this paper, 3D inversion of gravity data for determination of subsurface density distribution is made using geostatistical co-kriging method. Co-kriging is a mathematical interpolation and extrapolation tool. It uses the spatial correlation between the secondary variables and a primary variable to improve the estimation of the primary variable at un-sampled locations. The Co-kriging method gives weights to the data so as to minimize the estimation variance (the co-kriging variance). In this paper, the primary variable is density, (estimated by ρ*) and the secondary variable is gravity g. For determination of kernel matrix, the subsurface area is divided into large number of rectangular blocks of known sizes and positions. The unknown density contrast of each prism is the parameter that should be estimated. In addition, the weighting matrix has also been used in order to improve the depth resolution. Preconditioned conjugate gradient method has been used for inversion. The computer program has been written in MATLAB and tested on synthetic gravity of a rectangular prism model. The results indicate that the geometry and density of the reconstructed model are close to those of the original model. The gravity data acquired in an area, which includes concealed manganese ore bodies (Safoo mine site), in northwest of Iran. The results show a density distribution in the subsurface from the depth of about 5 to 35-40 m. These results are in good agreement with the results of the borehole drilled in the site.
    Introduction
    We may encounter two problems in gravity data inversion: non-uniqueness and non stability of solutions. The first one occurs for two reasons: The first reason is known as the theoretical ambiguity of the unknown nature of potential theory. The second reason is known as algebraic uncertainty, which is considered when the number of parameters is greater than the number of observations. The second problem may occur because of bad condition (ill-condition) of the kernel matrix and the presence of noise in the data. For finding a unique and stable solution, constraints should be considered in the objective function, and then, the new objective function, which is replaced the initial objective function, should be minimized.
    Methodology and Approaches: For determination of kernel matrix, the subsurface of the survey area is divided into a large number of rectangular prisms of known sizes and positions. The unknown density contrast of each prism is the parameter to be estimated. This kind of parameterization is flexible for the reconstruction of the subsurface model, but generates more unknown model parameters than observations (here N Results and
    Conclusions
    By applying co-kriging stochastic algorithm on synthetic data in states of without and with random noise, good results for the density and depth of the model have been achieved. By applying the method on actual data from Safoo manganese mine site, the results obtained for the depth and density of the subsurface ore body are in good agreement with the results of drilling implemented in the mine site. Furthermore, as a result of applying the method on the data, general shape of the subsurface ore body was well determined.
    Keywords: Gravimetry, 3D Inversion, Co-Kriging, Geostatistics, Variogram, Safoo Mine
  • Mohammad Fahim Avish, Hojjatollah Ranjbar*, Azadeh Hojat, Saeed Karimi Nasab, Iman Masoumi Pages 99-118
    Summary: In this study, satellite images, and aeromagnetic and ground magnetic data were analyzed to explore the geothermal potential in Sirch-Golbaf area in Kerman province. Thermal anomalies and apparent thermal inertia images were studied using MODIS, Landsat and ASTER images. As a result, two thermal anomalies were obtained; one in the southeastern part of the study area and the other one in Jooshan location. Magnetic investigations also detected two anomalies; a deep magnetic anomaly in the southern part of the area and another magnetic anomaly near Jooshan hot spring in the northeastern part. These magnetic anomalies were correlated with thermal anomalies.
    Introduction
    Remote sensing techniques are helpful reconnaissance tools for detecting surface temperature anomalies and identifying geothermal indicators (Calvin et al., 2005). Lu et al. (2008) used Landsat ETM thermal images to detect thermal anomalies strongly correlated with faults in certain scales in the Jiangshan-Shaoxing fault in the Zhejiang Province, China. They defined thermal anomalies as areas having temperatures higher than the temperature of the spatial background. In a geothermal resource exploration in Akita and Iwate prefectures, northern Japan, Noorollahi et al. (2007) showed that 95% of the production wells were located in a zone within 6000 m to the active faults and 4000 m to hot springs. Magnetic measurements are also generally used in geothermal exploration programs to locate hidden intrusive bodies and possibly estimate their depths. Moreover, they can be used to trace buried dykes and faults, and also to detect areas of reduced magnetization due to thermal activity (Georgeson, 2009). A variety of magnetic studies in geothermal exploration projects having different objectives can be found in the literature (e.g. Hojat et al., 2016; Gailler et al., 2014; Georgsson, 2009; Hunt, 1989; Palmason, 1975). The aim of this study is to analyze remote sensing and magnetic data (airborne and ground measurements) for evaluating the geothermal potential zones in an area east of Kerman Province.
    Methodology and Approaches: The input data in this research include MODIS, MOD11_L2 005 (day and night) reflectance and LST products, for the year 2015, ASTER L1T night-time image on November 10, 2015, Landsat ETM day-time image on November 14, 2015, aeromagnetic data collected by Houston Texas Co., USA, in 1975-1977, and geomagnetic total intensity contour map of Gowk area having 1:50000 scale, which surveyed by Atomic Energy Organization of Iran. Ground magnetic survey is also carried out in an area around Joshan hot spring. A comparison of the day-time and night-time images can reveal surface thermal differences for detecting geothermal anomalies. Land surface temperature was calculated using generalized split-window algorithm for MODIS sensor (Wan and Dozier, 1996), emissivity normalization method for ASTER (Coll et al., 2007; Banerjee et al., 2014), and LST calculation method for Landsat sensor (Barsi et al., 2003; Barsi et al., 2005; Coll et al., 2010). Apparent thermal inertia of the three sensors was calculated using albedo and LST difference of day and night (Sabol et al., 2006; Scheidt et al., 2010; Chang et al., 2012; Qin et al., 2013). After removal of noise from the observed magnetic data, processing steps including main field removal using IGRF model of the proper period, reduction to the pole, and upward continuation were applied on the magnetic data. The processed magnetic data were finally interpreted in order to locate the hidden intrusive bodies and faults.
    Results and
    Conclusions
    Two thermal anomalies were detected on the maps and charts obtained for the average temperature difference (day and night) and apparent thermal inertia. One anomaly was located in the Jooshan area and the other one was situated in the western part of Gowk fault and continues along it to the southeastern side. Gowk fault is an active fault with Jooshan (45 C) hot spring, and most earthquakes larger than magnitude 5 have occurred in this part. These might be evidences of a thermal anomaly. The results of magnetic interpretations confirmed thermal anomalies showing a deep magnetic anomaly in the southern part of the study area and another magnetic anomaly in the Jooshan hot spring.
    Keywords: MODIS, Landsat ETM+, ASTER, LST, Apparent Thermal Inertia, Aeromagnetic Data, Ground Magnetic Data
  • Hessam Hoseinnia, Amin Roshandel Kahoo*, Behzad Tokhmchi Pages 119-130
    Summary: Reflection seismic data is often contaminated by a variety of coherent and incoherent noises that influence the reliability of the seismic data to provide a better understanding of the hydrocarbon reservoir characteristics. The groundroll noise is characterized by dispersive wave, low frequency, high amplitude that propagates along and near the surface of the earth and will often obscures the seismic reflection data. Removal of this type of noise is an essential part of land seismic data processing. Most of ground-roll noise removal or attenuation methods are based on transforms. Radial trace transform and wavelet transform are two of the most important and common transforms, which are used to attenuate ground-roll noise. Various methods have been introduced by different authors to attenuate the ground-roll noise. In this paper, we have used the wavelet transform on radial basis to attenuate the ground-roll noise. The method is based on the joint application of the two-dimensional discrete wavelet and radial transforms in order to eliminate the coherent noise, especially ground-roll noise. Since the radial trace transform reassign the linear events in the x-t domain into vertical events in the r-t domain, it provides a pleasant framework for two-dimensional (2D) discrete wavelet transform. The de-noised signal can be obtained by suppressing the vertical band of one-level, 2D discrete wavelet transform of the radial transformed seismic gather followed by transforming back the filtered radial-wavelet transform into the x-t domain. To evaluate the efficiency of the proposed method to eliminate the ground-roll noise, we have tested the method on a real reflection seismic gather from an oilfield in southwest of Iran. We have also compared the obtained results with those from the f – k filtering for ground-roll noise suppression from seismic data. The results obtained from applying the proposed method on the real data test prove that the proposed method for ground-roll noise attenuation is as good as, or better than, those produced using f –k filtering.
    Introduction
    Ground-roll noise is the main type of coherent seismic noise and is characterized by dispersive wave, low frequency, high amplitude relative to other events of interest in land seismic surveys that propagates along and near the surface of the earth and obscures useful information seismic exploration. There has been much research about eliminating groundroll noise published in the literature, and many authors have introduced various methods for handling the ground-roll noise problem. A most straightforward and commonly used method for suppressing the ground-roll noise is band-pass filtering. In the case of the frequency overlap of primary reflections and ground-roll, the band-pass frequency filter either fail to attenuate all the ground-roll noise or remove much useful reflection energy. Dip filtering, also known as f-k filtering, which is based on the 2D Fourier transform, is another commonly used technique to attenuate ground-roll noise. In 2D Fourier transform of a seismic prestack gather, there is no a clear separation border between signal and noise region, consequently it leads to signal distortion. Another widely used method to remove ground-roll noise from seismic data is singular value decomposition (SVD)-based methods. Nevertheless, all of the above-mentioned approaches disagree with natural behavior of seismic data because of stationary seismic signal assumptions. Several methods have been introduced that consider the non-stationary nature for seismic data. The time-frequency de-noising algorithm is an effective method for handling noise problems. In this paper, we explain this method in detail, and analyze the influencing factors on the result of the method. Finally, the obtained results are compared with the results of the conventional f-k method.
    Methodology and Approaches: We used a method, introduced by Almeida et al. (2015) based on the joint application of the radial and wavelet transforms in order to attain effective ground-roll noise attenuation. Since the radial trace transform reassign the linear events in the x-t domain into vertical events in the r-t domain, it provides a pleasant framework for 2D discrete wavelet transform. At the first, we perform the forward radial transform to remap of the seismic common shot gather to ensure efficient event separation by the wavelet transform. Next, the one-level, 2D discrete wavelet transform is applied on the output of the first stage. Due to the described inherent property of the four sub-bands of the 2D discrete wavelet transform and ground-roll characteristics, the ground-roll noise will appear mainly in the vertical (HL) band. The denoised signal can be obtained by suppressing the vertical band of one-level, 2D discrete wavelet transform and transform back the radial-wavelet transform into the x-t domain.
    Results and
    Conclusions
    The data set that we use to validate the efficiency of the proposed method is a common shot gather from demo data set of seismic data processing software VISTA. The obtained results show that, the proposed method is not sensitive to the type of mother wavelet and the geometric configuration of the origin of the radial trace transform. Hence, it can be an excellent alternative technique to ground-roll noise attenuation.
    Keywords: 2D Discrete Wavelet Transform, Radial Trace Transform, Ground-Roll Noise, Coherent Noise Attenuation
  • Fereydoun Sharifi, Safa Khazaei* Pages 131-143
    Summary: Cleaning of contaminated lands containing unexploded ordnance (UXO) and mine fields demands special consideration in the war-torn countries. Some geophysical methods have been used for detecting these destructive remnants of war. Nowadays, airborne GPR has been considered as a fast and effective tool for UXO detection. In this study, the feasibility of airborne GPR for detection of anti-personal metallic landmines has been investigated by numerical simulation of back scattered GPR waves from two artificial physical models A and B. Model A is a column of a two-layer model comprising of a layer of soil under a layer of air. In model B, an anti-personal metallic landmine has been buried in the center of model A at a depth of 10 cm beneath the soil. By using the numerical finite-difference time-domain (FDTD) method, the radargram and central traces of back scattered GPR waves from both physical models A and B have been simulated in various altitudes (0-10 meters) and operating frequencies of the transmitted GPR wave (100-1500 MHz). To do this, MATLAB and REFLEXW software packages have been employed. Moreover, several signal processing techniques including signal energy analysis, multi resolution wavelet transform, and time-frequency analysis have been performed instead of using the noise removal and trace extraction, which are related to the target. As a result, detection of intended mine becomes possible by applying airborne GPR up to altitude of 10 m and using operation frequency of transmitted GPR wave of 550 MHz to over 1000 MHz.
    Introduction
    Landmines are a humanitarian challenge because they indiscriminately kill and maim people and they remain active for decades. As a result, most of the victims of mines are innocent men, women and children. Hence, cleaning of contaminated lands containing UXO and mine fields requires special consideration in the war-torn countries. In situations of dealing with dangerous landmine targets and a wide-area coverage requirement, tactical forces are highly desirable. This requirement could be attained by applying airborne GPR method. Therefore, in this study, the feasibility of detection anti-personal metallic landmines using airborne GPR method has been considered. For this purpose, the backscattered GPR waves from two artificial models have been simulated by applying numerical FDTD method in various altitudes and operational frequencies.
    Methodology and Approaches: In this study, the ability of airborne GPR data simulation for detecting anti-personal metallic landmines has been evaluated by applying numerical FDTD method using MATLAB and REFLEXW software packages. Then, travel time signals have been analyzed using signal energy analysis, wavelet transform, and time frequency analysis techniques.
    Results and
    Conclusions
    Based on the numerical simulation and signal processing conducted in this study, the results show that detection of the landmine target under test is possible up to the altitude of 10 m using the operation frequency of 550 MHz to over 1000MHz. Furthermore, the results show that the detection of the target using airborne GPR operation in high frequencies of the transmitted GPR wave and in low altitudes is feasible.
    Keywords: Airborne GPR, Numerical Simulation, Signal Energy, Wavelet Transform, Time-Frequency Analysis, Unexploded Ordnance (UXO), Detection