پايش نوسانهاي سطح آب درياچه اروميه با پردازش تصاوير ماهواره اي چند سنجنده اي و چند زمانه اي

Monitoring of Urmia Lake Water Surface Fluctuations by Processing of Multi- Sensors and Multi-Temporal Imageries

بررسي نوسانهاي سطح آب درياچه ها به منظور حفاظت آنها به لحاظ اهميت، ماهيت و موقعيت اين مجموعه هاي آبي و به عنوان يك ميراث طبيعي در سالهاي اخيردر بين كشورها در سطح ملي و منطقه اي جايگاه ويژه اي پيدا كرده است. درياچه اروميه با وسعتي بين 4500 - 6000 كيلومتر مربع به عنوان بزرگترين درياچه داخلي ايران و بيستمين درياچه جهان از اهميت ويژه اي برخوردار است. هدف اصلي تحقيق جاري بررسي تغييرات سطح آب درياچه اروميه با استفاده از تصاوير ماهوره اي و سيستم اطلاعات جغرافيايي مي باشد، براي رسيدن به اين هدف تصاوير ماهواره اي چند طيفي ماهواره لندست (شامل تصاوير سنجنده هاي MSS، TM ، (ETM+، MODIS و IRS از سال 1976م. الي 2005 م. مورد استفاده و پردازش قرار گرفت و نوسانهاي سطح آب درياچه در دوره هاي زماني مختلف استخراج شد. مدلهاي نهايي نشان دهنده نوسانهاي گسترده دوره اي و تغييرات چشمگير فصلي در پارامترهاي هندسي درياچه اروميه، به ويژه در طول دهه گذشته مي باشد. بيشترين تغييرات به دليل كاهش ارتفاع آب درياچه بويژه در جنوب شرق و سواحل شرقي درياچه اروميه شده است. ظهور چنين نوسانهاي معناداري باعث كاهش 23 درصدي از سطوح آب درياچه در طي دوره مطالعه شده شده است كه خود باعث تسريع روند تبديل اراضي آبي به زمينهاي لم يزرع و رسوب املاح نمكي در امتداد خطوط ساحلي شده است.

Urmia lake is located in the north-west of Iran and is recognized in the world as a largest habitat for Artemia. The last decade drought episodes and recent dam construction programs have simultaneously caused more evaporation of the lake water and thus considerable variations of water surface levels. The main aim of the present study was to map of Urmia lake water surface changes on a seasonal, periodical and over long-term scales. For this purpose, some different types of multi-scanner, spectral and temporal images (MSS, TM, ETM+, IRS-1C, MODIS and TOPEX/Jason data observing from 1976 to 2005) were processed to generate most of the thematic models in spatial and temporal contexts. First, to choose a number of referred images captured, some ground-based observation data and the obtained information from TOPEX/Jason satellites were analyzed. Then based on the available archived imageries, all the multi-date satellite data were chosen and progressively geo-referenced and then geo-rectified by ERDAS Imagine software package based on the reference ground control points. Subsequently, all the time series images were analyzed to derive some pre-defined segmented Classes such as water surface categories and shorelines changes. The revealed models demonstrated several seasonal persuaded fluctuations and considerable periodical change on the Urmia Lake coastlines particulaarly during the last decade. These great variations have occurred as the result of 3.5 meters decrease in the height of water in the lake and about 23 percent decreasing of water surface during the past 30 years. This has successively caused a diminishing of shorelines particularly on the southeast and east coasts of the Urmia Lake, changing landcover and landuse types by depletion of significant wetlands. Implementation of such significant changes illustrated that the majority of local biotic and biotic components all over the surrounding areas and inner islands, would be in crucial threat in the near future.