فهرست مطالب

فیزیک زمین و فضا - سال چهل و ششم شماره 1 (بهار 1399)

فصلنامه فیزیک زمین و فضا
سال چهل و ششم شماره 1 (بهار 1399)

  • تاریخ انتشار: 1399/03/20
  • تعداد عناوین: 12
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  • علیرضا نیک سجل، ظاهر حسین شمالی* صفحات 1-20
    مجموعه ابزار KIWI (KInematic Waveform Inversion)، یک روش جدید در تعیین سازوکار کانونی و پارامترهای چشمه زمین لرزه های ناحیه ای است که در آن با انجام برگردان در دو حوزه زمان و فرکانس، پارامترهای چشمه نقطه ای و گسترده تعریف شده در مدل چشمه ایکونال (eikonal) طی فرآیندی مرحله ای تعیین می شود. هدف از این مطالعه، تعیین پارامترهای چشمه نقطه ای و گسترده زمین لرزه 5 آوریل 2017 سفیدسنگ (0/6Ml) ضمن تشریح مراحل برگردان در مجموعه ابزار KIWI است. شکل موج های استفاده شده در این تحقیق برگرفته از ایستگاه های دایمی باندپهن پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله (IIEES) و شبکه جهانی IRIS است. به منظور ارزیابی عملکرد مجموعه ابزار KIWI، فرآیند برگردان با استفاده از شش زیرگروه اطلاعاتی مختلف (شامل مدل پوسته IASP91، مدل پوسته میانگین ایران (IRSC) و داده های مذکور) انجام شده که در این بین مجموعه متشکل از مدل سرعتی IRSC و کل داده های موجود به عنوان مجموعه اطلاعاتی بهینه در نظر گرفته شده است. نتایج حاصل از برگردان با استفاده از مجموعه اطلاعاتی بهینه بیانگر جنبش عمدتا معکوس با مولفه راستالغز راست گرد با شیب به سمت شمال شرق است که با مشخصات گسل کشف رود همخوانی دارد. پارامترهای چشمه نقطه ای نظیر عمق مرکزوار و بزرگای گشتاوری زمین لرزه به ترتیب 1/7 کیلومتر و 2/6 به دست آمد. برگردان پارامترهای چشمه گسترده نیز نتایجی چون جهت یافتگی عمدتا یک طرفه به سمت جنوب شرق، مدت زمان شکست 3/9 ثانیه، مساحت شکست 300 کیلومتر مربع و نیز میانگین لغزش 16 سانتی متر را به دست داده است.
    کلیدواژگان: مجموعه ابزار KIWI، برگردان چند مرحله ای در حوزه زمان و فرکانس، پارامترهای چشمه نقطه ای و گسترده، زمین لرزه سفیدسنگ (0، 6 Ml)
  • محمدفهیم آویش، حجت الله رنجبر، آزاده حجت*، سعید کریمی نسب صفحات 21-34

    در این مطالعه از آنالیز طیفی داده های مغناطیسی هوابرد در محدوده ای در شرق استان کرمان جهت شناسایی مناطق دارای شار زمین گرمایی استفاده شد. ابتدا تصحیح مربوط به میدان مغناطیسی مرجع با مدل IGRF انجام و سپس فیلتر برگردان به قطب بر روی داده ها اعمال شد. سپس به منظور حذف اثرات ناشی از توپوگرافی، خصوصیات زمین شناسی و میدان های مغناطیسی هسته، از فیلتر میان گذر استفاده شد. پس از بلوک بندی محدوده و انتقال داده ها به فاز فوریه، طیف توان هر بلوک محاسبه شد. عمق بالایی و عمق مرکزی هر بلوک از منحنی های لگاریتمی طیف توان به دست آمدند. عمق کف منابع مغناطیسی که به عنوان عمق کوری در نظر گرفته می شود از رابطه  محاسبه و برای تخمین گرادیان زمین گرمایی و شار زمین گرمایی منطقه استفاده شد. نتایج نشان داد کمترین عمق کوری (5/9-5/8 کیلومتر) با بیشترین گرادیان دما و شار زمین گرمایی در جنوب کویر لوت (جنوب شرق محدوده) و جنوب غرب گلباف در محدوده راین با واحدهای آذرین متنوع و بیشترین عمق کوری در کویر لوت و واحدهای رسوبی شمال منطقه قرار دارد.

    کلیدواژگان: داده های مغناطیسی هوابرد، عمق نقطه کوری، زمین گرمایی، کرمان، طیف توان
  • معصومه الهی سرشت، مهدی رضاپور* صفحات 35-49
    پدیده های الکترومغناطیسی ازجمله اختلال در سیگنال های رادیویی (VLF, Very Low Frequency) برای پیش بینی کوتاه مدت زمین لرزه از چند سال پیش در دنیا مورداستفاده قرارگرفته اند. سیگنال های VLF از مرز پایینی یونوسفر بازتاب می یابند بنابراین هر تغییری در منطقه D یونوسفر شرایط بازتاب امواج VLF را تغییر می دهد. احتمالا یکی از عواملی که پارامترهای مختلف یونوسفر را تحت تاثیر قرار می دهد، فرآیندهای اطراف کانون زمین لرزه قبل از وقوع آن است. تاکنون چند فرضیه برای مکانیسم نفوذ انرژی از کانون زمین لرزه های با عمق کمتر از 40 کیلومتر به یونوسفر به صورت تیوری پیشنهاد شده است. یکی از مناسب ترین فرضیه ها نقش امواج گرانشی جوی در این رابطه است با این حال مدارک مشاهده ای زیادی وجود ندارد. در این تحقیق تغییرات مشاهده شده در سیگنال های VLF دریافت شده در گیرنده موسسه ژیوفیزیک دانشگاه تهران (TEH)، به عنوان پیش نشانگر قبل از وقوع رخداد لرزه ای مورد بررسی قرار گرفته است. در بازه زمانی و مسیر های مورد مطالعه تنها زمین لرزه نسبتا بزرگ، زمین لرزه 5.8 Mn سیرچ کرمان در تاریخ 22/07/2018 می باشد. نتایج نشان می دهد که اختلالات واضحی چند روز قبل از وقوع زمین لرزه سیرچ کرمان مشاهده می شود که پس از بررسی عوامل مختلف موثر بر سیگنال می توان آن را به عنوان یک پیش نشانگر برای این زمین لرزه در نظر گرفت. همچنین تحلیل طیفی سیگنال های VLF فرستنده VTX3 در جنوب هند که در گیرنده تهران دریافت شده اند، بررسی شده است و نتایج آن نقش نوسانات گرانشی جوی را به عنوان مکانیسم اتصال لیتوسفر- یونوسفر به صورت مشاهده ای تایید می کند.
    کلیدواژگان: پیش نشانگر زمین لرزه، یونوسفر، امواج گرانشی جوی، سیگنال های فرکانس خیلی پایین، زمین لرزه سیرچ کرمان
  • میررضا غفاری رزین*، مهدی محسنی صفحات 51-66

    در این مقاله از سیستم استنتاج فازی (FIS) جهت مدل سازی میدان جابه جایی سطحی پوسته زمین در منطقه ایران استفاده شده است. سیستم استنتاج فازی سیستمی است که از پایگاه قواعد اگر-آنگاه فازی برای شناخت ویژگی های پدیده مورد نظر استفاده می کند. با توجه به اینکه این سیستم قابلیت مدل سازی پدیده های غیرخطی را داراست، در نتیجه در این مقاله از این روش جهت مدل سازی تغییرات سطحی پوسته زمین در فلات ایران استفاده شده است. همچنین برای ارزیابی بهتر و دقیق تر، نتایج حاصل از سیستم استنتاج فازی با نتایج مشاهدات میدان سرعت حاصل از ایستگاه های GPS و همچنین نتایج حاصل از شبکه عصبی مصنوعی (ANNs) مورد مقایسه قرار گرفته است. برای انجام این کار پنج ایستگاه آزمون درنظر گرفته شده و مشاهدات مربوط به این پنج ایستگاه در آموزش های شبکه فازی و شبکه عصبی مورد استفاده قرار نگرفته است. براساس آنالیزهای انجام گرفته، بیشینه مقدار خطای نسبی محاسبه شده در پنج ایستگاه آزمون برای شبکه فازی و شبکه عصبی در مولفه شرقی (Ve) به ترتیب برابر با 02/20 درصد و 74/29 درصد محاسبه شده است. همچنین برای مولفه شمالی (Vn) میدان سرعت، بیشینه مقدار خطا برای هر دو روش به ترتیب برابر با 80/18 درصد و 05/27 درصد تعیین شده است. نتایج بیانگر این موضوع است که شبکه فازی از دقت و صحت بیشتری نسبت به شبکه عصبی مصنوعی در مدل سازی میدان سرعت برخوردار است.

    کلیدواژگان: منطق فازی، شبکه عصبی، میدان جابه جایی، GPS، ایران
  • شایان خوشگواری، یزدان عامریان*، هانی محبوبی صفحات 67-80
    مدل سازی پارامترهای چگالی الکترونی یونسفر (IED) و محتوای الکترونی کلی (TEC) در تعیین موقعیت ماهواره ای با گیرنده های تک فرکانسه، مطالعات فیزیک فضا، عملکرد سیستم های راداری و ارتباطات مخابراتی ضروری است. مدل های مرجع بین المللی یونسفر (IRI) و نقشه های جهانی یونسفر (GIMs) منابع اطلاعاتی هستند که TEC را در مقیاس جهانی در اختیار کاربران قرار می دهند. این مدل ها از منابع داده های جهانی به دست آمده اند که در منطقه ایران دارای تراکم مناسبی نیستند، بنابراین دقت آنها در این ناحیه کم است. لذا مطالعه و مدل سازی محلی TEC در منطقه ایران دارای اهمیت است. در این مطالعه مدل سازی TEC برحسب توابع پایه شعاعی کروی (SRBF) و با استفاده از مشاهدات شبکه دایم GPS ایران انجام شده است. در این مطالعه مدل سازی TEC در روز 124ام سال 2016 در کل منطقه ایران که داده ها دارای تراکم یکنواخت نیستند و همچنین در محدوده شمال غرب ایران که داده ها دارای تراکم یکنواخت تری هستند، صورت گرفته است. نتایج مدل سازی نشان می دهند که مدل ارایه شده از GIMs دقیق تر است و همچنین دقت مدل سازی در منطقه شمال غرب ایران که توزیع مشاهدات یکنواخت تر است، بیشتر می باشد. در کل منطقه ایران دقت مدل سازی VTEC با روش مقاله برای بازه زمانی 0 تا 1 و 10 تا 11 ساعت جهانی به میزان 04/1 و 67/0 در مقیاس TECU نسبت به GIMs بهبود می یابد. همچنین محدود کردن ناحیه مدل سازی به شمال غرب ایران و افزایش تراکم توزیع داده ها، موجب بهبود دقت به میزان 54/1 و 86/0 TECU نسبت به GIMs می شود.
    کلیدواژگان: مدل سازی منطقه ای یونسفر، مجموع محتوای الکترونی، نقشه های جهانی یونسفر، توابع پایه شعاعی کروی، پایدارسازی تیخونوف
  • ایمان صمدی، معصومه کردی*، مهرداد سلیمانی منفرد، امیر احمدی صفحات 81-96
    شناسایی و مطالعه گسل ها در مخازن هیدروکربنی، اهمیت ویژه ای در مراحل ازدیاد برداشت و توسعه میدان دارد. در بررسی ساختارهای با زمین شناسی پیچیده، تفسیر گسل ها با عدم قطعیت بالایی همراه خواهد بود. روش های متعارف تفسیر و مدل سازی گسل ها در داده های لرزه ای علاوه بر نیاز به دانش زمین شناسی مفسر که خود می تواند به عنوان منشا عدم قطعیت باشد، فرآیندی بسیار دشوار و وقت گیر است. بدین منظور در این مطالعه یک استراتژی خودکار و ترکیبی به منظور افزایش دقت و سرعت مدل سازی گسل ها و شکستگی ها در داده لرزه ای معرفی می شود. گسل ها به طور معمول با استفاده از نشانگرهای لرزه ای تفسیر می شوند. به منظور تفسیر گسل های میدان مورد نظر در این تحقیق، ابتدا نشانگرهای آشفتگی، واریانس، انحنا و الگوریتم ردیابی مورچه از داده های لرزه ای استخراج شد. از بین نشانگرهای موجود، نشانگرهای آشفتگی، واریانس و انحنا به طور واضح گسل های بزرگ مقیاس را مشخص کردند. گسل های کوچک مقیاس که شناسایی آنها در داده های لرزه ای دشوار است، به کمک الگوریتم ردیابی مورچه مدل سازی شدند. به کارگیری روش های بیان شده در تفسیر ساختاری مخزن در کنار مدل سازی قطعی گسل ها به روش ترکیبی بر روی داده های لرزه ای، نشان دهنده شناسایی و تفسیر بهتر گسل ها با استفاده از استراتژی پیشنهادی و رویکرد ترکیب روش های موجود بود. نتایج حاصل از تفسیر چند نشانگری و همچنین مدل سازی گسل ها در میدان مورد مطالعه، انطباق خوبی با اطلاعات زمین شناسی نشان داد. لذا می توان پیشنهاد داد استراتژی به کار گرفته شده در مدل سازی و استفاده از یافته های مطالعات چند نشانگری می توانند به منظور افزایش دقت در مطالعات ساختاری مخزن، مورد استفاده قرار گیرند.
    کلیدواژگان: مدل سازی چند مقیاسی، نشانگر لرزه ای، انحنا، آشفتگی، الگوریتم ردیابی مورچه
  • سید ساسان بابایی، مسعود مشهدی حسینعلی*، سمیع سمیعی اصفهانی صفحات 97-115

    در دهه های اخیر فناوری تداخل سنجی راداری ابزاری کارا را برای اندازه گیری کمی تغییرشکل زمین، تحت تاثیر عوامل طبیعی و انسانی نظیر فرونشست، زلزله، زمین لغزش، برداشت بی رویه از سفره های آب زیرزمینی و معدن کاری فراهم کرده است. با این وجود ماهیت اندازه گیری جابه جایی در راستای خط دید ماهواره در این فناوری، امکان استخراج میدان جابه جایی سه بعدی سطح زمین مخصوصا در مطالعه بسیاری از پدیده های زمین ساختی که نیازمند درک جامعی از مولفه های جابه جایی سه بعدی شان است را با چالش مواجه می کند، لذا همواره حداقل سه هندسه مستقل راداری نیاز است تا حل مساله بازیابی میدان جابه جایی سه بعدی امکان پذیر شود. با این حال هندسه قطبی تصویربرداری ماهواره های راداری به نحوی است که سهم جابه جایی و تاثیر نویز مشاهدات بر پارامترهای مجهول (مولفه های سه بعدی) متفاوت می شود و حتی در برخی از موارد مساله ناپایدار خواهد شد. لذا در این تحقیق حساسیت به نویز مساله بازیابی میدان جابه جایی سه بعدی در هندسه های مستقل و متفاوت راداری بررسی و همچنین براساس روش همپوشانی بین مدارها در ماهواره راداری سنتینل، با استفاده از داده های شبیه سازی شده و واقعی میدان جابه جایی سه بعدی زلزله های به ترتیب 16 فروردین و 21 آبان سال 1396 سفیدسنگ و ازگله بازیابی می شود و کارایی این روش مورد ارزیابی قرار می گیرد.

    کلیدواژگان: تداخل سنجی راداری، جابه جایی در راستای خط دید ماهواره، مولفه های جابه جایی سه بعدی، آنالیز حساسیت به نویز، زلزله سفیدسنگ، زلزله ازگله کرمانشاه
  • وحید محمدنژاد آروق* صفحات 117-128

    در مقاله حاضر به بررسی و مقایسه نتایج حاصل از استخراج پهنه های مرطوب و آبی جنوب دریاچه ارومیه با استفاده از تصاویر خام و تصحیح جوی شده ماهواره سنتینل 2 پرداخته شده است. بدین منظور تصویر ماهواره سنتینل 2 مربوط به بهار سال 2019 دریافت شد. با توجه به اینکه هدف مقایسه اثر تصحیحات جوی روی تصاویر است، تصویر مورد نظر با استفاده از روش تفریق شیء تیره در قالب نرم افزار QGIS تصحیح شد. سپس به منظور استخراج پهنه های مرطوب و آبی از دو تصویر خام و تصحیح شده، چهار شاخص NDWI2، MNDWI، NDTI و شاخص SAVI با استفاده از نرم افزار SNAP تهیه و مورد مقایسه قرار گرفت و هشت نقشه مختلف تهیه شد. این چهار شاخص به منظور استخراج پهنه های مرطوب، آبی و پوشش گیاهی طراحی و توسعه پیدا کرده اند. به منظور مقایسه دقت خروجی ها نیز از ضرایب کاپا و دقت تولیدکننده و دقت کاربر استفاده شد. نتایج نشان می دهد که در بین این چهار شاخص، شاخص های MNDWI و NDTI، با ضرایب کاپای بالا بهترین عملکرد را دارند. همچنین شاخص NDWI2 با ضریب کاپای 79/0 برای تصویر خام و 83/0 برای تصویر تصحیح شده کمترین دقت را دارد. همچنین مساحت پهنه های مرطوب و آبی استخراج شده از چهار شاخص با مقادیر واقعی مقایسه شد. مساحت های مستخرج از تصاویر خام و تصحیح شده و مقایسه آن با مساحت واقعی پهنه های مرطوب نشان می دهد که تصاویر تصحیح شده از دقت بالایی برخوردار است.

    کلیدواژگان: تصاویر ماهواره ای، تصحیحات جوی، تفریق شیء تیره، سنتینل 2، دریاچه ارومیه
  • منا ضرغامی پور، حسین ملکوتی* صفحات 129-147
    نظر به اهمیت الگوی باد بر فعالیت های متعدد در جزایر و همچنین تاثیر آن بر سایر پارامترهای هواشناسی، رفتار زمانی و مکانی بلند مدت میدان باد تراز پایین مشاهداتی روی جزیره قشم مطالعه شد. به منظور حساسیت سنجی شبیه سازی های عددی باد تراز پایین به وسیله مدل WRF، پارامترسازی لایه مرزی و لایه سطحی روی جزیره قشم، در ماه منتخب از فصل گرم (جولای) و ماه منتخب از فصل سرد (ژانویه) برای سال 2015 بررسی شده است. نتایج شبیه سازی ها در پنج پیکربندی مختلف با سرعت باد مشاهداتی ایستگاه قشم فرودگاهی و قشم دریایی اعتبار سنجی شده است و نتایج نشان می دهد که در هر دو ماه طرحواره لایه مرزی ACM2 به علت این که اختلاط قایم را هم به صورت محلی و هم غیرمحلی در نظر می گیرد و در فصل گرم همرفت را بهتر از دیگر طرحواره ها لحاظ می کند در ترکیب با طرحواره لایه سطحی Pleim-Xio و پارامترسازی سطح زمین Noah شبیه سازی بهتری از سرعت و جهت باد تراز پایین ارایه می کند. پس از انتخاب پیکربندی مناسب، شبیه سازی میدان باد به مدت یک سال (2015) به منظور بررسی الگوی باد جزیره قشم، ساختار قایم باد لایه مرزی و تاثیر جزیره بر روی میدان باد لایه مرزی منطقه به انجام رسید. نتایج بیانگر آن است که سرعت باد در فصول بهار و تابستان از مقادیر بالاتری برخوردار است و زبری و پسای جزیره باعث کاهش سرعت باد، رخداد همگرایی و چرخش میدان باد بر روی تنگه هرمز می شود. نسیم دریا و زبری سطح در مناطق ساحلی باعث تقویت رودباد تراز پایین در حین روز و در ارتفاع های 180 تا 200 متر شده است.
    کلیدواژگان: پارامتری سازی، شبیه سازی عددی، سرعت باد، لایه مرزی، رودباد تراز پایین، جزیره قشم
  • محمد جغتایی*، نیلوفر جوینده، محمدحسین معماریان صفحات 149-157

    لایه یون سپهر از لایه های مهم جو زمین است که در اثر جذب تابش ماوراءبنفش و ایکس خورشیدی و برخورد ذرات باردار با اتم ها و مولکول های جو زمین و برهمکنش فوتوشیمیایی بین ترکیبات آن تشکیل می شود. الکترون های آزاد در این لایه بر مسیر امواج رادیویی تاثیر می گذارد و هرگونه اختلال احتمالی در این لایه، تاثیر جدی در ارتباطات ماهواره ای، ارتباطات دقیق ناوبری و ارتباطات دوربرد می گذارد. پس شناخت مقادیر میانگین و توزیع نصف النهاری مقادیر الکترون های آزاد کمک شایانی به شناخت پریشیدگی و اختلال های احتمالی آن می کند. یک روش پذیرفته شده در تحقیق ساختار زمانی و فضایی و تغییرپذیری الکترون های آزاد یون سپهر، برآورد محتوای کلی الکترون (TEC) است. TEC مجموع الکترون های موجود در استوانه ای با سطح مقطع یک متر مربع است که در مسیر ماهواره تا گیرنده زمینی محاسبه می شود. در این پژوهش برای بررسی پریشیدگی های یون سپهری از داده های جهانی و شبکه بندی شده ایستگاهی GNSS، برای بازه زمانی 1999 تا 2017 استفاده شده است. از داده ها میانگین سالانه و ماهانه برای 19 سال گرفته شده است. همچنین برای فعالیت خورشیدی از شاخص F10.7 استفاده شده است که تابش خورشید در طول موج cm 7/10 است. در پژوهش انجام شده، روند تغییرات TEC، وابستگی زیادی به تغییرات چرخه خورشیدی دارد. با بررسی مقادیر TEC مشاهده شد که مقدار TEC در ماه های آوریل و مارس واکتبر بیشینه است در حالی که در ماه های جولای و جون کمینه مقادیر را دارد. به بیان دیگر مقادیر TEC در اعتدالین بیشتر و در انقلاب تابستانی کمترین مقدار را داراست.

    کلیدواژگان: یون سپهر، TEC، GNSS، چرخه خورشیدی، F10، 7
  • فاطمه جان نار فریدون، سمیه نهاوندیان اصفهانی*، نعمت الله محمودی صفحات 159-174
    در این تحقیق تغییرات فصلی و مکانی عمق لایه آمیخته و ساختار قایم دما و شوری در آب های نزدیک به ساحل دریای خزر در منطقه بابلسر و رامسر در سه فصل بهار، تابستان و پاییز سال 1391 با استفاده از اندازه گیری های CTD مورد بررسی قرارگرفت. با وجود مشابهت محدوده تغییرات دما و شوری در دو منطقه اندازه گیری، نوسانات شوری در بابلسر بالاتر از رامسر و در فصل بهار شوری در لایه سطحی در رامسر به شکل قابل توجهی کمتر از بابلسر است. هالوکلاین تقریبا هم عمق ترموکلاین قرار داشته و به شکل نوسانات شدید شوری خود را نشان می دهد. برای تخمین عمق لایه آمیخته از روش آستانه و با آستانه های (C) 05/0، (C) 5/0، (C) 1 و (C) 25/1 استفاده شد. بدون در نظرگرفتن تفکیک فصلی مقدار آستانه (C) 25/1 عمق لایه آمیخته را بهتر از مقادیر دیگر آستانه تخمین زد. در نهایت الگوریتم ترکیبی به تفکیک فصل، با آستانه (C) 25/1 در بهار، 1 (C) در تابستان و مقدار آستانه (C) 5/0 در فصل پاییز برای تخمین عمق لایه آمیخته مورد استفاده قرار گرفت. کمینه و بیشینه عمق لایه آمیخته به ترتیب در بهار و پاییز مشاهده شد و طبق نتایج به دست آمده، ساختار قایم لایه آمیخته را می توان به سه نوع، کلاسیک در پاییز، شیب دار در بهار و پله ای در تابستان تقسیم کرد.
    کلیدواژگان: دریای خزر، بابلسر، رامسر، لایه آمیخته، عمق لایه آمیخته
  • محمد مرادی*، عباس رنجبر سعادت آبادی، پرویز رضازاده صفحات 175-189

    این مقاله به پتانسیل آلایندگی در بوشهر به کمک مدل پخش گاوس پرداخته است. در این پژوهش انحراف معیار قایم مدل به سبب نبود داده های سرعت اصطکاکی و طول مونیون-ابکوف، از روابط هاسکر-اسمیت، ارتفاع خیزش پلوم از روش بریگز و ارتفاع لایه آمیخته از روش هیفتر به دست آمد. برای تعیین کلاس های پایداری، از داده های تابش خورشیدی و گرادیان قایم دما و برای اجرای مدل، از داده های برج هواشناسی بوشهر در سال 2016 استفاده شده است.   نتایج حاصل از اجرای مدل نشان داد که در موقعیت برج هواشناسی بوشهر در فصل زمستان، آلاینده های فرضی از شمال به سوی جنوب برج پخش می شود در حالی که نحوه پخش آنها در تابستان از شمال غرب به جنوب شرق و همچنین از جنوب به سوی شمال است. این تفاوت می تواند به سبب قوی بودن نسیم دریا به خشکی در تابستان و ضعیف بودن آن در زمستان باشد. قسمتی از آلاینده فرضی نیز به دلیل وجود مولفه جنوبی باد سالانه، به سوی شمال پخش می شود. در فصل های بهار و پاییز نیز نحوه پخش آلاینده ها متفاوت است. در فصل بهار که باد غالب در ارتفاع 100 متری برج هواشناسی بوشهر شمال غربی است، آلاینده ها بیشتر به سوی جنوب شرق پخش می شوند در حالی که در فصل پاییز فراوانی باد شمالی بیشتر است و آلاینده های فرضی بیشتر به سوی جنوب پخش می شوند. همچنین بررسی روش های برآورد ضرایب مدل گوس نشان داد که روابط هاسکر-اسمیت با در نظرگرفتن طول زبری سطح برای منابع نقطه ای که فاقد داده های سرعت باد اصطکاکی و طول مونیون-ابکوف هستند، روش مناسبی است.

    کلیدواژگان: برج هواشناسی، مدل پخش گاوس، فرمول هاسکر-اسمیت، الگوریتم هیفتر
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  • Alireza Niksejel, Zaher Hossein Shomali * Pages 1-20
    KIWI (KInematic Waveform Inversion) is a recently developed multi-step inversion tools at the Institute of Geophysics of University of Hamburg. The main aim of developing this method is to perform moment tensor inversion retrieving the point and extended source parameters in regional distances. In KIWI tools, point and kinematic source parameters are retrieved in a sequential process in three inversion steps in time and frequency domains using different inversion methods, parts of waveforms and so on. After the point source inversion done, the method retrieves the radiation pattern, including fault plain parameters, Scalar moment and centroid depth. Also, for large enough earthquakes (Mw>5.5), extended source inversion retrieves finite source parameters such as rupture directivity, rupture area and velocity, rise and rupture time, average slip and nucleation point regarding to the point source centroid location. KIWI tools uses pre-calculated Greens functions, hence, the inversion process is quite fast. Due to the same reason, this method is rendered for automatic real-time retrieval of point and extended source parameters. In general, we can highlight the most important characteristics and applications of KIWI tools as follows: ability of easy implementation for real-time retrieval of source parameters, stability of inversion, rapid directivity detection, no requirements of aftershocks and foreshocks, no limitation in depth and magnitude and ability of retrieving reliable results even in absence of accurate velocity model used to build the Green’s functions and large stations azimuthal gap. In this research, we introduce the KIWI tools and use its applications to study of the April 5, 2017 (Ml 6.0) Sefidsang-Fariman earthquake. The data used in this research were recorded by permanent broadband stations of International Institute of Earthquake Engineering and Seismology (IIEES) and some global broadband stations from IRIS network at a minimum epicenteral distance of 200 kilometers. To have a better evaluation of KIWI tools functionality, we made inversion of source parameters using six different set of information (including IASP91 and IRSC velocity models and the mentioned set of data). Then, the information set including IRSC velocity model and all available data considered as the optimum one. Comparing the obtained results using the optimum set of information and the remaining sets, Maximum difference in centroid depth, Latitude and Longitude is 1.9 kilometer, 0.23 and 0.5 degree related to information sets including only IRIS network data, while there is a good consistency in retrieved focal mechanisms. After all, it is tried to run a sensitivity test using the optimum information set to have a better assessment on KIWI tools stability in source parameters analysis. Based on the achieved results, the erroneous input parameters (e.g. Latitude, Longitude and Depth) had a low influence on our optimum results. The final results in this research represents the centroid of earthquake in a shallow depth (7.1 km) with a magnitude slightly larger than those published by other institutions like USGS (Mw 6.2). Retrieved focal mechanism shows mainly reverse faulting with small dextral strike-slip component dipping north-east which is in a good accordance with the Kashafrood fault characteristics as the closest active fault to the epicenter. Also, extended source inversion revealed mostly unilateral source directivity toward SE with a rupture area, rupture time and approximate average sleep of 300 km2, 9.3 seconds and 16 cm.
    Keywords: KIWI tools, multistep inversion in time, frequency domains, point, extended source parameters, Sefidsang earthquake (Ml 6.0)
  • MohammadFahim Avish, Hojjatollah Ranjbar, Azadeh Hojat *, Saeed Karimi Nasab Pages 21-34

    In the recent decade, there has been an increasing interest in developing various resources of renewable energy as an alternative to fossil fuels in Iran. Geothermal energy is one of the promising reservoirs and exploration of geothermal favorability has become one of the main research interests in most parts of the country. Some reconnaissance studies have shown that the Kerman Province can be one of the geothermal potential regions in Iran. Different studies are being performed to prepare the geothermal favorability map for Kerman Province. The aim of this study is to estimate the Curie point depth (CPD), heat flow and geothermal gradient from spectral analysis of aeromagnetic data for reconnaissance exploration of geothermal resources in the east of Kerman Province, southeast of Iran. This area is selected because it is characterized by thermal manifestations such as several hot springs with temperatures between 20–73°C, faults, and igneous rocks in the southern and southwestern parts. Aeromagnetic data were first processed for removing the geomagnetic main field (using the International Geomagnetic Reference Field (IGRF)), reduced to pole (RTP) and band-pass filter. Then, we used spectral analysis technique to estimate the top and bottom boundaries of the magnetized crust. Comparison of magnetic map with geologic map shows a good correlation between the exposed geological units and magnetic signatures. Strong variations in magnetic intensity suggest a variety of magnetic properties. Bandpass filtered data were produced from the RTP aeromagnetic anomalies to isolate near surface and undesired deep effects. Then, the map was divided into thirty blocks, each having 50% of overlap with the adjacent block. A first-order trend was removed from each block, and grids were expanded by 10% using the maximum entropy method to make the edges continuous. Then, each block was analyzed using the spectral centroid method to obtain the depths to the top, centroid and bottom of magnetic sources. First, we calculated the radially averaged log power spectrum of each block. To compute the spectrum of the data, the magnetic anomaly of the area was transformed by 2D Fourier to obtain the average Curie depth. From the slope of the very long wavelength part of the spectrum, the centroid depth (Z0) was estimated, while the average depth to the top (Zt) was estimated from the second longest wavelength part of the spectrum. Using the values obtained for Z0 and Zt, the depth to the bottom (Zb) was calculated for each block using the equation Zb=2Z0−Zt. The depths obtained for the bottom of the magnetized crust are assumed to correspond to Curie point depths where the magnetization of the layer disappears. Variations of the Curie isotherm level can correlate to some indices of geothermal activity (e.g., geothermal gradient and near-surface heat flow) in the study area. The results showed that Curie point depth in the study area varies from 8.5km to 18.2km, and accordingly, the geothermal gradient ranges between 31-67°C/km. The heat flow was estimated in the range 139-294mW/m2 in the study area. The results showed the shallowest Curie depths occurring in the southern part of the area. This is the zone which mainly hosts volcanic rocks and hot springs.

    Keywords: Aeromagnetic data, Curie point depth, Geothermal, Kerman, power spectrum
  • Masoumeh Elahiseresht, Mehdi Rezapour * Pages 35-49
    Electromagnetic phenomena such as disturbance of VLF (very low frequency) radio signals, have been used for prediction of short-term earthquakes in the world from some years ago. VLF signals are reflected from the lower bound of the ionosphere, so any change in the ionosphere D region leads to changes in the conditions of the VLF wave propagation. One of the factors that influences the various parameters of the ionosphere is the processes surrounding the earthquake center before it occurs. So far, several hypotheses have been proposed for the mechanism of energy penetration from the earthquake to the ionosphere in theory. One of the most appropriate hypotheses is the role of atmospheric gravitational waves in this regard. However, there are not many observational evidence. In this study, after a review of variations in VLF signals received at the receiver of Tehran University's Institute of Geophysics (TEH), significant disturbances were observed several days prior to the onset of the Mn 5.8 Sirch earthquake that occurred on 22 July, 2018, in Kerman province, southeastern Iran. These abnormalities appeared as decreasing in the night range and increasing in the amplitude of the day and were only in the VTX3-TEH pathway, so they did not have any relation to the disorder in the transmitter or receiver. The association of these abnormalities with the factors affecting the ionosphere, including Solar flares, Lightning, Meteorological and geomagnetic activities was also studied and risk associated with these factors were rejected. These abnormalities began about four days before the earthquake and continued until the day of the earthquake; therefore, they are probably related to the precursor effects of the Sirch Kerman earthquake. Spectral analysis of signals was also performed and a 20 minutes harmonic was found in the spectrum of days before the earthquake. This period is not observed in the quiet days. This result, in addition to denying the probability of a geomagnetic effect on the signal, shows the effect of atmospheric gravitational waves in the lithosphere-atmospheric-ionospheric coupling mechanism for this earthquake. Based on these observations, the radio anomaly under study can be considered as a precursor of the Sirch earthquake in Kerman. The 22 July 2018 Mn 5.8 Sirch earthquake disturbances in Kerman provide another evidence of radio frequency disturbances at the VLF frequency before the earthquake. However, for more accurate monitoring of these signals, regular monitoring of long-term data as well as the number of more receivers in the country is required. In this case three important features, an earthquake pre-indicator, the time, location and magnitude of the earthquake in VLF/LF anomalies, occur from about a week to a maximum of 10 days before the earthquakes (Biagi, 2009) and are suitable for short-term forecasting, but still the exact time of earthquake is not clear. The disturbances do not appear for earthquakes with magnitude less than 5.5 and for earthquakes between 5-6 disturbances are less severe than earthquakes larger than 6, so this method may estimate the magnitude of the earthquake. Also, using an appropriate network coverage of the VLF/LF receivers and the use of appropriate processing methods, it is possible to locate somewhat an earthquake. Finally, it can be said that this new field of science is considered as a promising candidate for short-term earthquake prediction to reduce earthquake damage in active area such as Iran.
    Keywords: Earthquake Precursor, Ionosphere, Atmospheric Gravitational Waves, VLF Signals, Kerman-Sirch earthquake
  • MirReza Ghaffari Razin *, Mehdi Mohseni Pages 51-66

    Today, by the expansion of geodetic networks and the creation of base points for geodetic applications, the study of the motion of the earth's crust and the study of the activity of faults are the most important tasks of geodesic. With the establishment of satellite positioning systems, the creation of base points in geodetic networks has been substantial. The basic point in creating base points is the estimation and obtaining the velocity field and the displacement of these points in a reference framework. Determining velocity field with the high precision and the displacement of the base points in geodetic networks is of great importance. With the availability of information on the velocity of GPS stations in a geodetic network, one can model the kinematics and dynamics of the earth's crust in that area. In this regard, extensive research on these problems has been conducted around the world. The main objective of this paper is the use of Fuzzy Inference System (FIS) for modeling the surface displacement field in Iran. The concept and study of fuzzy logic began in 1920, but the fuzzy logic was first used by Lotfizadeh (1921-2017) in 1965 at Berkeley University. FIS can formulate the behavior of a phenomenon in terms of the use of descriptive and empirical rules without the need for an accurate analytical model. The fuzzy inference system is the tool for formulating a process with the help of rules as if-then. The set of these fuzzy rules is called the fuzzy rules base. Argumentation is done using a fuzzy inference system. The fuzzy inference system is generally made up of the following components: 1. Fuzzy, 2. Base rules, 3. Fuzzy Inference Engine, 4. Diffusion. The process of converting explicit variables into linguistic variables is called fuziation. The inference engine evaluates and deduces the rules using inference algorithms, and after the rules are combined, the output is converted by the divisible unit into an explicit or numerical value. The most common type of fuzzy inference system is the Tacagi-Sugeno fuzzy system. In this paper, the FIS is used to model the surface displacement field of the Earth's crust in Iran. A fuzzy inference system is a system that uses the rules of the if-then-fuzzy rules to recognize the properties of the phenomenon. Since this system is capable of modeling nonlinear phenomena, in this paper it is used to model the surface variations. For better and more accurate evaluation, the results of the fuzzy inference system were compared with the results of GPS velocity field observations as well as the results of the artificial neural network (ANNs). To do this, 5 test stations have been considered and observations of these 5 stations have not been used in fuzzy network and neural network training. Based on the analysis, the maximum relative error calculated at the 5 test stations for the fuzzy network and the neural network in the eastern component were calculated to be 20.02% and 29.74%, respectively. The results indicate that the fuzzy network has more accuracy than the artificial neural network in speed field modeling.

    Keywords: Fuzzy logic, Artificial Neural Network, displacement field, GPS, Iran
  • Shayan Khoshgovari, Yazdan Amerian *, Hany Mahbuby Pages 67-80
    Satellite positioning using single frequency receivers and space technologies such as radar and communication systems all demand a precise knowledge of the ionosphere. Ionosphere is the upper layer of atmosphere which is ionized and affects the transmission of electromagnetic waves depending on their frequencies. Parameters that characterize this layer of the atmosphere are the Ionospheric Electron Density (IED) and the Total Electron Content (TEC). Hence, modeling and understanding of TEC in a precise way is an undeniable necessity. International Reference Ionosphere (IRI) and Global Ionospheric Maps (GIMs) are the sources of information that provide TEC values globally for all users. It could be expected that the accuracy of such global models in some regions like Iran are not suitable since these models are obtained from the global data sources which they lack a good density in Iran plateau. Thus, regional TEC modeling over Iran needs more attention. In this study, the total electron content obtained from the permanent dual-frequency GPS receivers are utilized in regional TEC modeling. Estimation of TEC requires satellites and receivers Differential Code Biases (DCB) to be known. DCB values for satellites and the International GNSS Service (IGS) receivers can be observed from IGS analysis centers e.g. the Center for Orbit Determination in Europe (CODE). However, for local dual frequency receivers to be used for the purpose of TEC monitoring, their DCB should be estimated. In this research, the DCB value of each station is computed from observations which their corresponding elevation angles are more than 60 degrees. The DCB computation process consists of 3 steps. First, Vertical Total Electron Content (VTEC) is obtained from the spatial and temporal interpolation of (IGS-IONEX) files. Second, each interpolated VTEC is multiplied by a mapping function. After that, the difference of the observed pseudo-range of the two frequencies is denoised via a moving average filter. Eventually utilizing the interpolated VTEC and smoothed difference of the observed pseudo-ranges and the mapping function, DCB values of all stations are estimated. Thereafter, a parameterization of the estimated VTEC over the study area is implemented. For this purpose, the Spherical Radial Basis Function (SRBF) method is used. These functions are compact support and more practical for interpolation of observations on a regional scale. It is necessary to mention that the optimization of the depth of SRBFs plays an important role in increasing the accuracy of the regression. The coefficients of the expansion are computed by least squares estimation, and the Tikhonov regularization method is used in which the regularization parameter is obtained from L-curve. Some of the observations are excluded from the dataset as check points for evaluation of the constructed model. In this research, once the modeling process is conducted over Iran and also the north-western region of Iran which has a more proper distribution of data, is parameterized on the 124th day of 2016. The height of the ionosphere layer is assumed 450 km above the earth's surface. Then aregular grid of point-mass functions that has the simplest form of SRBFs is constructed. Then, by changing the depth of the grid, an optimal depth is estimated at which the best accuracy is obtained at the check points. The results reveal that the parameterization of TEC with a regular grid of SRBFs in which the number of grid points are approximately 10% of the number of data, leads to the construction of a model whose accuracy in the check points is significantly enhanced comparing to GIMs. In addition, the accuracy of the modeling is better in areas where data density and distribution are more appropriate. The results of this research show that the accuracy of VTEC modeling in the whole region of Iran in 0 to 1 Universal Time (UT) and 10 to 11 UT are 0.87 and 1.30 TECU respectively. According to the GIMs VTEC accuracy of 1.91 and 1.97 TECU in the same periods of time, it is concluded that the accuracy of VTEC modeling in this research is improved by 1.04 and 0.67 TECU with respect to GIM. In addition, with increasing the density of data distribution and limiting the study region to the north west of Iran, the accuracy of the proposed model is equal to 0.33 and 1.66 TECU. With respect to the GIMs accuracy this is equal to 1.87 and 1.92 TECU, the proposed method has an improvement of about 1.54 and 0.86 TECU comparing to the GIMs model.
    Keywords: Local ionosphere modeling, Total electron content (TEC), Global Ionospheric Maps (GIMs), Spherical Radial Basis Functions (SRBF), Tikhonov regularization
  • Iman Samadi, Masoumeh Kordi *, Mehrdad Soleimani Monfared, Amir Ahmadi Pages 81-96
    Fault and fracture modelling is an important step in reservoir engineering which is required for any reservoir characterization and production management. There are various types of methods and strategies for building such models, however, each has its own advantages and drawbacks. The most important issue that should be considered is the ability to model both large- and small-scale faults, simultaneously. It is important, as large faults define geological frameworks of the reservoir, while small faults influence fluid movement in the reservoir. In this study, we introduce an integrated strategy for modelling small- and large-scale faults by seismic data, using multi-attributes. Large faults are defined by hand picking from seismic data using attributes, and small faults are modelled by an automatic ant tracking algorithm. Then, two separated models are integrated to build a unique, but multi-scale fault model. Result of each step of modelling is evaluated by well data. The methodology is applied on a hydrocarbon reservoir from the Persian Gulf. Results show that the multi scale fault model is accurate when evaluated by well data. Integrated modelling of faults of fractures to obtain a unique multi-scale model is an interesting topic in reservoir engineering. Normally fractured reservoirs are divided into several production zones based on division made by large faults, while fluid movement in each zone is controlled by small fracturs and faults. Thus, obtaining a unique model which contain information of faults in several scale is under investigation. However, conventional methods use separate sources of information for modelling faults in various scales. Large scale faults are normally modelled by seismic data while well data are used for modelling small faults. Ozkaya (2019) stated that modelling of faults both with seismic and well data would reduce uncertainty in reservoir fracture modelling. Cao et al. (2019) introduced an integrated strategy for modeling faults with two scales in 2D seismic data, but using seismic and well data. Kurison et al. (2019) have modelled faults and fractures in reservoir with 3D seismic data and well data, but in separate manners. But their final interpretation has shown that using both types of model would result in better reservoir modelling. Xu et al. (2019) introduced an integrated strategy for modelling faults and fractures in two scales simultaneously using seismic and well data. In this study, we introduce an integrated strategy for multi-scale fault modelling using only seismic data, which could be used in reservoirs which lack of well data. The proposed strategy introduced here, initiates with a geological model building. Subsequently, large faults can be defined on seismic data and related attributes. Simultaneously, small scale faults can be modelled by an ant tracking algorithm in an automatic manner, then it would be refined by interpreter to remove other lineaments than fault that was modelled by the algorithm. Each model then would be evaluated by well data and in case of any error in the model, they would be removed by more ant tracking parameter optimizations and also deeper investigation by the interpreter. In the final step, both fault model would be integrated to build a unique informative multi-scale fault model which contains information of all faults in various sizes. Other characteristics of faults in the integrated model would be investigated for further analysis. Large scale fault model showed major faults with northwest-southeast trending acting in the center of the reservoir, which has a dome shaped structure, and some minor faults with various trending around the major one. Through this modeling curvature, chaos and variance attributes were used for better fault detection. Small faults obtained by ant tracking distributed around the center of the field. Ant tracking algorithm parameter were optimized through sensitivity analysis prior to application. Afterwards, fault model was refined to remove non-fault lineament. Both models were evaluated by a fullbore formation microimager (FMI) log which proved fractures and faults that were obtained by seismic data. One fault that was detected by the proposed strategy were also captured by well. Then both fault models were integrated to a unique model and faults were modeled by deterministic method. The integrated fault model obtained by the proposed strategy revealed the importance of a multi-scale fault model in reservoir engineering. Large faults of the study reservoir showed different zones of fractures in the formation reservoir, while small faults in the same model built a discrete network of fractures which provides canals for fluid movement. The integrated model shows that large faults in the study field are mostly in the center of the reservoir, while small faults are distributed through the edges of the formation reservoir, which could be used for further investigation of locating for production and/or injection wells.
    Keywords: multiscale modelling, seismic attributes, curvatures, Chaos, Ant tracking algorithm
  • Seyed Sasan Babaee, Masoud Mashhadi Hossainali *, Sami Samie Esfahany Pages 97-115

    In recent decades, Interferometric Synthetic Aperture Radar (InSAR) technology has been an efficient tool in quantitatively measuring of the earth's deformation, influenced by natural and human factors, such as the overexploitation of water from underground aquifers, mining, subsidence, earthquake, and landslide. However, in the nature of the displacement measurement in the satellite's line of sight (LOS) in this technology, the possibility of extracting a three-dimensional displacement field has faced challenges. Especially in the study of many tectonic phenomena requiring a comprehensive understanding of the three-dimensional displacement components. Therefore, at least three independent radar geometries or InSAR-derived LOS displacements are always needed to solve the problem of retrieval of the three-dimensional (3D) displacement field. However, the polar geometry of imaging radar satellites is such that the contribution of the displacement and effect of the noise of the observations on the estimated parameters (Three-dimensional components) will be different, even in some cases, the problem will be unstable. Therefore, in this research, the noise sensitivity of the three-dimensional displacement field retrieval problem in independent and differential radar geometries is investigated and also based on the orbit overlapping method in the Sentinel radar satellite, using simulated and real data, the three-dimensional displacement of the Sefidsang and Ezgeleh earthquakes of 21 March and 12 November 2017 respectively is retrieved and the efficiency of this method is evaluated. In fact, in this study, considering the importance of knowing and measuring the components of the 3D surface displacement field, the problem of three-dimensional displacement field retrieval was investigated using a combination of independent radar geometries. Then, according to the variance-covariance matrix structure of the problem and the principal component analysis (PCA) method, the sensitivity of recovering each component of the displacement field to the input data noise by taking measurements of three independent radar geometries was discussed. The results show that the north-south displacement component has the highest sensitivity to the input data noise and has the least contribution of displacement along with the satellite LOS. Then the east-west and up-down components have approximately the same sensitivity to noise, although, for some specific incidence angles, the sensitivity to noise for the up-down component will be increased. Also, the condition number of the design matrix in the 3D field retrieval problem show that in most cases (except when the incidence angles of the two geometries are equal or have very slight differences), it is a well-established and stable problem and there is no need to solve it with regularization method. In the second part of the paper, remembering that in the Sentinel radar satellite, each sub-swath is imaged at different angles (with a difference of about 10 degrees), so the concept of overlap between the orbits (at least three different geometries) can be used to retrieve the 3D displacement field in most regions. The feasibility and efficiency of this method were evaluated with real and simulated data. The results showed that in the absence of noise components, the orbit overlap interferometry (OOI) method could be well used in 3D field reconstruction.

    Keywords: radar interferometric, line of sight (LOS), three-dimensional displacement components, noise sensitivity analysis, Sefidsang earthquake, Ezgeleh earthquake
  • Vahid Mohammadnejad Arooq * Pages 117-128

    Wetlands comprise roughly 6–9 percent of the Earth’s surface. The role of wetlands in maintaining environmental quality includes the storage of global terrestrial carbon. In addition, they influence many aspects of ecology, economy and human welfare. Furthermore, wetlands act as an oasis in an urban area which is important in the reduction of surrounding surface air temperature. Changes in the spatial distribution of wetlands (croplands, forests, water bodies and rivers), either by natural factors or anthropogenic activities could significantly affect the ecosystem. Satellite imagery enables us to monitor short-and long-term changes in wetlands and its vegetation density. Due to the fact that the electromagnetic waves reaching the satellites pass through the Earth's atmosphere, the reflections recorded by the sensor of these satellites do not really reflect the phenomena of the Earth's surface. By applying some corrections on the images, it is possible to convert them to Top Of Atmosphere reflectance values (TOA) and the Earth's surface reflections (BOA) ones. In this paper, we have reviewed and compared the results of extraction of wetlands and water body using raw and atmospheric corrected images of Sentinel 2 in south of Lake Urmia. The study area includes wetland and agricultural lands of southern Urmia Lake. Due to the existence of two large Zarrineh and Simineh rivers in the region as well as its very fertile soil, agriculture has expanded rapidly. The main data of this study is satellite images of Sentinel 2 (spring 2019). The dark object subtraction (DOS) is one of the methods of atmospheric correction of satellite images, which with a partial fraction of the dark object's reflection of the whole image, it makes an atmospheric correction of the satellite image. In this paper, this method has been used for atmospheric correction. In fact, a copy of the raw satellite image of the study area was made and the atmospheric corrections were applied. Then the results were compared with the raw images. In order to compare two raw and corrected images, it was attempted to separate the wetlands (rivers, ponds, wetlands) from non-moisturizing lands, so that the effect of atmospheric correction on the ground reflection could be observed. For this purpose, NDWI2 MNDWI, NDTI and SAVI indexes have been used in this paper. To compare the effect of atmospheric correction on Sentinel satellite images, the image of the study area was first provided and entered into the QGIS software for atmospheric correction. Then, using a combination of short infrared, near-infrared and green bands, the extraction and classification of wetlands, water bodies and vegetation cover density was made by SNAP software. Due to the lack of ground control points, the images were sampled by the ArcMap software and verified by using google earth images. Three precision coefficients were used to check and compare the accuracy of raw data with the atmospheric corrected data. In order to compare the accuracy of the outputs, Kappa coefficients, users’ accuracy and producers’ accuracy were calculated using the ArcMap software. The MNDWI and NDTI indices are the best indicators for raw images and for corrected images, to extract wetlands and water bodies. Kappa values of these indicators are above 0.9 and also users’ accuracy and producers’ accuracy are above 96%. Among the four above-mentioned indicators, the NDWI2 index has the lowest accuracy as well as the minimum Kappa coefficient. The results show that corrected images have high accuracy in extracting and displaying wetlands and water bodies. The area of the wetlands and water bodies to be redirected from corrected images is closer to actual areas. The actual area in the SAVI index is 25.15 square kilometers and the redistributed area of raw and corrected images are 25.71 and 25.38 km2, respectively. The actual area in the NDWI2 index is 180 km2, with a corrected area of 178.93 square kilometers. For other indicators, NDTI and MNDWI, the actual areas are 10.37 and 29.5 km2, respectively. In general, it can be concluded that atmospheric corrected images using the DOS method show better results in showing wetlands and water bodies areas. The results of this paper show that the application of atmospheric corrections to the Sentinel 2 images can increase the accuracy of the extraction of wetlands and water bodies areas and even other landcovers. Considering the four indicators and extracting the zones from raw and atmospheric corrected images, it was determined that, firstly, MNDWI and NDTI indices are the best indicators for extracting wetlands and water bodies in the south of Lake Urmia. Secondly, among these two indicators, the data from the corrected atmospheric images have high precision coefficients than raw images. Therefore, it can be said that in estimating the wetlands and water bodies using Sentinel images 2, these images must be corrected using different methods to minimize their error of representations.

    Keywords: Satellite image, Atmospheric correction, Dark object subtraction, Sentinel 2, Lake Urmia
  • Mona Zarghamipour, Hossein Malakooti * Pages 129-147
    Since the wind pattern on various activities in islands as well as its effect on other meteorological parameters is important long – term temporal and spatial variations of the wind field are studied. Here, the warmest month (July) and the coldest month (January) 2015, are selected in order to test the sensitivity of low-level wind simulations of the Weather Research and Forecasting (WRF) model to the parameterizations of the boundary layer (PBL), the surface layer (SL) and the land surface (LSM) over Qeshm Island. As this work was focused on the simulation of near-surface and vertical wind profiles, the physical options related to the parameterizations of boundary layer processes (SL, PBL and LSM) that have significance influence for this purpose are validated. Although more physical options are available in the model (for cumulus convection, short and long wave radiation, microphysics and etc.), it is not feasible or necessary to include all the model configuration options in the sensitivity analysis to obtain an efficient model configuration optimization. The model grid comprised of four nested domains at horizontal resolutions of 45, 15, 5 and 1 km respectively. The innermost domain (D4) with 1 km spatial resolution covered the chosen area to simulate PBL wind field over Qeshm island region. The results of the simulations under five different configurations are validated with the observational wind speed data of Qeshm Airport and Marine Qeshm Stations. The results demonstrate that in both episodes, the ACM2 boundary layer scheme has presented the best performance in combination with the Pleim - Xio surface layer and the Noah land surface schemes because it considers vertical mixing both local and non-local in simulation of planetary boundary layer wind structure. The simulations of WRF are sensitive to warm and cold seasons as well as selected parameterizations. After selecting the appropriate configuration, the simulation of the wind field for one year was carried out to investigate the low level wind field, the vertical structure of the boundary layer wind and the impact of the land mask distribution on and around the Qeshm Island. These simulations indicate higher wind speed in spring and summer and the roughness of the island causes a low level wind convergence, then turn to the left on the Strait of Hormuz with decreasing wind speed. Monthly average of the wind direction during the daytime of reference month of each season are generally simulated to be southwesterly (January, April, July, October) and during the nights of January and July it is southerly to southeast and in April and October it is simulated southwesterly. The direction of the wind has significant variations at sunrise and sunset due to changes in regional scale forcing and baroclinicity behavior between the sea and the coast. Surface roughness in coastal areas, strait narrowing and sea breeze, enhance the low-level jet during summer and spring middays at altitudes of about 180 to 200 meters. In other words, we can say these low-level jet (Shamal winds) during summer and spring occurs as a result of the interaction of two pressure systems; the heat low pressure cell (low level cyclone) over Iran and a semi-permanent high over northwestern Saudi Arabia and it acquires some convergence because of the these factors.
    Keywords: Parameterization, Numerical simulation, wind speed, boundary layer, Low-level jet, Qeshm Island
  • Mohammad Joghataei *, Niloofar Jooyande, MohammadHossein Memarian Pages 149-157

    The Earth’s ionosphere is one of the important layers of the atmosphere, starting from 60 kilometers extending up to about 1000 kilometers. Even though the layer contains less than 1% of the total mass o f the atmosphere; however, it has very important effects on the solar radiation and transmission of radio waves. The ionosphere is formed under effect of solar extreme ultraviolet (EUV), solar X-ray radiation, and electron precipitation of solar winds. The lower atmosphere also contributes to the variability of the ionosphere. In other words, ionosphere is under effects of both lower atmosphere dynamics from below and solar radiation from above boundary. Therefore, the amount of changes of particles in the ionosphere depend largely on many parameters such as time, radiation pattern, Sun-Earth geometry, ion chemistry, and solar activity. Sun’s variability is most important origin of the ionosphere long term change, so that the amount of change in the ionosphere layers depends largely on the time and mode of radiation, the Earth-Sun status, and the solar activity. Variety of periodic and nonperiodic variations should be considered in the ionosphere, which makes serious impacts on satellite and ground communication, precise navigation and radio broadcasting. In this research, the relationship between solar activity and total electron content (TEC) is investigate with gridded global TEC data. Total electron content (TEC) data are important ionosphere parameter that can be derived from time delay of radio wave transmitted from satellite to ground base station. The maps of TEC are given with the resolution of 5o in longitude and with the resolution of 2.5o in latitude, 12 times every day (one map in every two hours at UTC time). In the other word, each IONEX file includes 13 maps in which one map has overlap with next day. Longitude ranges from -180 to 180 degrees that includes 73 points resolution. Latitude ranges from -87.5 to 87.5 degrees that indicates 71 points with the resolution of 2.5o. We use F10.7 index for determination of solar activity. This parameter is indicative of radio emittion of sun in 10.7 cm radio wave. This index has a good correlation with sun spot number and nowadays it is used in many research as solar activity parameter. In this investigation, we used 19-years data IONEX for the period 1999 – 2017 for both 23 and 24 solar cycles. At first, we calculated zonal mean of data (in all longitudes, for every latitude) every day, then for every month and finally for every year. We had the mean data of TEC for every day, month and year of these 19 years. In the 23 solar cycle that began in August 1996 and continued to December 2008, minimum amount of TEC was 14 TECU in 2008, and maximum amount was about 57 TECU in 2000 and 2002. In this solar cycle, the time gap between minimum and maximum was 6 to 8 years. In the current solar cycle, solar cycle 24, with minimum amount of TEC was 14 TECU in 2009 and with maximum 44 TECU in 2014. The time gap between both extremes was about 5 years. In all years, maximum amount of TEC was in low and middle latitude, and minimum was in high latitude. Results indicated that maximum TEC was in southern hemisphere in December, January and February. In June, July and August, maximum TEC is located in northern hemisphere. Maximum amount of TEC was in March, April and October, and minimum was in June, July and August. It seems that maximum position and value depend on solar declination, Earth-Sun position and geometry.

    Keywords: Ionosphere, TEC, GNSS, Solar Cycle, F10.7
  • Fatemeh Jannar Fereidouni, Somayeh Nahavandian Esfahani *, Nematollah Mahmoudi Pages 159-174
    The physical processes play an important role on the biochemical phenomenal in the seas and oceans. The Mixed layer is the surface layer in which due to the air-sea exchange, the physical parameters such as temperature, salinity and density are almost constant. The layer beneath the mixed layer where the gradient of the physical parameters is large, is called thermocline, halocline and pycnocline, respectively in the temperature, salinity and density profiles. The deep part is the deepest layer where the physical parameters are nearly constant. Because the mixed layer acts as an interface between the atmosphere and deeper layers of the sea, its depth is not only influenced by weather but also strongly impacts the climate change. The mixed layer depth (MLD) has an important role in biochemical processes, gas exchanges, transferring heat, mass and momentum between the atmosphere and the sea. In this study seasonal and spatial variations of the MLD as well as the temperature and the salinity profiles are investigated in the Southern Caspian Sea in the Babolsar and Ramsar regions based on the Conductivity-Temperature-Depth (CTD) measurements conducted during fall, spring and summer 2012. According to the observations, despite the fact that the range of variations of the temperature and the salinity in the Babolsar and Ramsar is comparable, during the spring the salinity fluctuation inside the halocline is larger in Babolsar. It is worth to mention that the salinity fluctuates highly inside the halocline, contrary to the classic definition that the salinity increases with depth inside the halocline. The MLD has been estimated using the threshold method with four different threshold values (0.05, 0.5, 1 and 1.25 (°C)). In order to avoid erroneous estimation of MLD (very extreme values), each temperature profile is also carefully examined by visual investigation. Then visual inspection and statistical analysis approaches have been employed to assess the most appropriate threshold value. To this end, calculated MLDs using different threshold values have been plotted against visual MLDs. Large number of points away from line of 45° shows that the calculated MLDs using related threshold value is biased against visual MLDs. While the largest number of points around 45° line demonstrates that the MLDs estimated by both methods are similar to each other and the considered threshold value is an appropriate one. The results reveal that the seasonal hybrid algorithm with threshold values of 0.5 (°C) for fall, 1 (°C) for summer, and 1.25 (°C) for spring gives the best estimation for the MLDs. The calculated MLDs show that the MLD is maximum in the fall and minimum in the spring which is in agreement with Jamshidi et al. (2010). The reason for a deeper MLD in the summer compared to the spring can be related to the high evaporation during this season, which leads to salinity increase at the surface and augmentation of the convection. Spatial comparison of the MLDs in Babolsar and Ramsar regions shows that the MLD is slightly deeper in Ramsar and the gradient of the temperature just below the mixed layer in Ramsar is larger compared with that in Babolsar. The vertical structure of the mixed layer can be sub-divided into three principle types: the classical, stepwise and inclined types. The classical and stepwise type profiles are similar to the results reported by Tai et al. (2017) conducted in the principle northern South China Sea. The classical type has quasi isothermal mixed layer followed by a steep thermocline which is the most observed in the fall. In the stepwise type, the temperature decreases inside the mixed layer with one or more small steps before drastical decrease in the seasonal thermocline. The stepwise type has been observed more often during the summer. Finally in the inclined type which is occurred in the spring, the MLD’s temperature gently decreases with depth followed by an abrupt decrease of the temperature in the thermocline.
    Keywords: Caspian Sea, Babolsar, Ramsar, Mixed layer, Mixed layer depth
  • Mohammad Moradi *, Abbas Ranjbar Saadat Abadi, Parviz Rezazadeh Pages 175-189

    A serious problem which threatens life in metropolises is air pollution released in boundary layers in local and regional scales due to human activities. Pollutants accumulate in specific meteorology conditions in cities. Air stagnation, temperature inversion, cold air damming, topography, mountain and valley winds, urban buildings wakes and atmospheric stability are metrological factors. These conditions are recorded in most air pollution episodes in the world. Many researchers have used Gaussian distribution model for analyzing the manner of pollutants distribution in long term. In these works not only Gaussian model for distribution and deposition has been analyzed but the meteorological conditions for running the model and estimation of coefficients of model have also been analyzed. In this article the potential air pollution in Bushehr city is studied by the Gaussian diffusion model to calculate the horizontal and vertical standard deviations of the model outputs, using the Hosker-Smith formula. The plume rise height is calculated by Briggs method and the height of the mixed layer by the Heffter algorithm. For the model run we used 2016 archived data from the 100m height Bushehr meteorology tower. In this research for winter the months of December of 2015, January and February of 2016 are considered, for spring, March, April and May, for summer June, July and August and for fall, September, October and November are considered. The annual covers from January to December of 2016. Regarding the presented conditions, Gaussian distribution model run for a hypothetical point source in open rural area. The process is as following: 1- Data of direction and speed of wind in height of 10 to 100 meters are analyzed in different days of 2016 and December of 2015 and after omitting doubtful data, the average values of daily, monthly, seasonal and annual wind field are extracted. 2- These data were used in calculation of average value of multiplying classified wind speed by normalized coefficient instability classes. 3- Data of radiation and temperature in different levels of meteorology tower are analyzed and after omitting the noises and attaining adequate accuracy, vertical gradient of temperature was calculated and regarding the wind speed, the stability classes for day and night were calculated. 4- Vertical and horizontal standard deviations were calculated based on Hosker-Smith equations. 5- Height of plume rise was calculated for estimating effective height by using chimney inner diameter, gas discharging velocity and its temperature in different stability classes according to Briggs method. 6- Mean length of mixed layer was calculated by using long term data of nearest upper air station to Bushehr meteorology tower. Analysis of wind field at the height of 100 meters of Bushehr meteorology tower showed that in spring the abundance of northwesterly wind is 19.5%, north wind 11.4% and northeasterly wind is 10.4%. In summer abundance of north- northwesterly wind is 15.6% and northwesterly wind is 15.3%. In fall the abundance of northerly wind is 17.4%, northwesterly 14.5%, north- northwesterly 14.5% and north-northeasterly wind is 12.3%. In winter abundance of northerly wind is 31.6%, north- northwesterly 17.2% and north-northeasterly is 15.6%. The annual abundance in 2016 of northerly wind is 18.3% and north-northeasterly wind is 11%. The vertical and horizontal standard deviations are estimated in different stability and instability classes. Calculating the horizontal standard deviation by different methods in all classes, does not make significant difference is. Calculation of vertical standard deviation by Hosker-Smith method has a significant difference in all classes. It is very similar to Briggs method in very severe instability classes and by increasing the distant from pollutant source, its quantity slightly increases. In stability classes, this method gives higher values in comparison with the others.     The model results show that hypothetical pollutants distribute in winter toward south, in spring southeast and Southwest, in summer to southeast and north and in fall to southeast, south and southwest. The annual distribution is toward south and southeast. The maximum values of this quantity in spring, summer and fall spread up to 2km along the mentioned directions but the maxima in summer spreads up to 3km from the source. Annual maxima do not extend more than 2 km from the source. Analyzing the results and adjusting them with the results of 100-meter meteorological tower seasonal wind rose, results show that, how perfectly simplified Gaussian model depicts the manner of pollutants distribution. The model results indicate that the hypothetical pollution dispersion in winter time around the Bushehr meteorology tower is toward south, while in summer the dominant dispersion is toward southeast and north. The difference in dispersion direction between summer and winter is due to stronger sea breeze in summer. Some northward emission may exist due to southerly winds in the annual wind regime.

    Keywords: Bushehr meteorological tower, Gaussian diffusion model, Hosker-Smith formula, Heffter algorithm