نوع مقاله : مقاله پژوهشی

نویسندگان

• محمد کاظمی قراجه ¹
• خلیل ولی زاده کامران ²

¹ کارشناس ارشد سنجش از دور و سیستم اطلاعات جغرافیایی، دانشکده برنامه ریزی و علوم محیطی، دانشگاه تبریز

² دانشیار گروه سنجش از دور و سیستم اطلاعات جغرافیایی، دانشکده برنامه ریزی و علوم محیطی، دانشگاه تبریز

چکیده

اندازه ‌گیری پارامترهای فیزیکی آب از جمله دمای سطح آب و عمق آب با استفاده از روش ‌های معمولی نیازمند صرف هزینه و زمان زیادی می‌باشد.  در سال ‌های اخیر، فناوری سنجش ‌از دور به ‌عنوان یکی از مهم ‌ترین ابزارهای محاسبه دمای سطح آب و عمق آب، روند رو به رشدی در مطالعات مربوط به دریاها داشته است.  از این ‌رو، هدف پژوهش حاضر محاسبه دمای سطح آب و عمق آب و بررسی ارتباط بین این دو در دریاچه ارومیه واقع در کشور ایران و وان واقع در کشور ترکیه می ‌باشد.  بدین منظور، در ابتدا تصاویر ماهواره لندست 8 سال 2018 برای مناطق مورد مطالعه تهیه شدند.  تصحیح اتمسفری با استفاده از روش فلش (FLAASH)بر روی تصاویر اعمال شد.  سپس دمای سطح زمین با استفاده از روش الگو‌ریتم پنجره مجزاء برای هر دو منطقه مورد مطالعه محاسبه شد.  در نهایت با اعمال ضریب گسیل ‌مندی آب(0.98)برروی دمای سطح زمین، دمای سطح آب به ‌‌دست آمد.  برای محاسبه عمق نسبی آب نیز روش استامپ مورد استفاده قرار گرفت.  نتایج حاصل از محاسبات مربوط به ارزیابی صحت نتایج بیانگر مقادیر      1.2 ،1.2،1.1 RMSE  برای محاسبه دمای سطح آب به ‌ترتیب برای ایستگاه‌ های قالقاچی، مالک‌اشتر و اشکوهمچنین مقادیر 1.5،1.6   و 1.67  برای محاسبه عمق آب به ‌ترتیب برای ایستگاه ‌های قالقاچی، مالک ‌اشتر و اشکو می ‌باشد.  همچنین نتایج حاصل از بررسی ضریب همبستگی به ‌دست آمده بین دمای سطح آب با عمق نسبی آب (0.24- برای دریاچه ارومیه) و( 0.52- برای دریاچه وان) نشانگر وجود رابطه معکوس بین عمق آب و دمای سطح آب است، به ‌طوری که با افزایش عمق، دمای سطح آب کاهش یافته و کاهش عمق آب، افزایش  دمای سطح آب و در نتیجه افزایش تبخیر و تعرق را در پی دارد.

کلیدواژه‌ها

• دمای سطح آب
• عمق نسبی آب
• ماهواره لندست
• دریاچه وان
• دریاچه ارومیه

20.1001.1.25883860.1400.30.117.4.1

عنوان مقاله [English]

Measuring sea surface temperature and water depth using Landsat 8 satellite imagery and estimating the relationship between them Case study: Urmia and Van Lakes

نویسندگان [English]

• Mohammad Kazemi Garaje ¹
• Khalil Valizadeh Kamran ²

¹ Master of remote sensing and geographic information systems, Faculty of planning and environmental sciences, Tabriz University

² Associate professor and department manager, Department of remote sensing and geographic information systems, Faculty of planning and environmental sciences, Tabriz University

چکیده [English]

1- Introduction
Direct measurement of physical parameters of water, such as sea surface temperature and water depth through traditional methods is very time-consuming and costly. Thus, new cost-effective methods, such as remote sensing technology, have always been of interest to experts, managers and decision-makers. Satellite imagery is used to estimate sea surface temperature and water depth. Therefore, the present study seeks to calculate sea surface temperature and water depth and investigate their relation using satellite imagery.
 
2- Materials and Methods
In the present study, Landsat 8 satellite images of Urmia and Van Lake were retrieved from USGS website for August 16th, and August 23rd, 2018. Information about water temperature and water depth of 3 meteorological stations in the study area were also obtained from the Artemia Research Center and the Meteorological Organization of West Azerbaijan Province for a period of three months.
In the next step, geometric and atmospheric corrections were performed on the images using ENVI5.3 software. In thermal remote sensing, thermal bandwidth of satellite imagery cannot reflect black-body radiation. Moreover, electromagnetic spectrum of radiation used in the Boltzmann relationship covers a range of 3 to 300 micrometers. This is while the thermal spectrum range of thermal sensors is generally between 10.5 to 12.5 micrometers.Thus, the split-window algorithm was used to calculate the land surface temperature.
Water emission coefficient equals 0.98. Multiplying the amount of water emission by the amount of land surface temperature (LST) and subtracting the results from zero Kelvins (-273), we can obtain sea surface temperature in Celsius degrees.
 
2-1- Calculating relative depth of water
As one of the dynamic characteristics of water, water depth has an important role in the management and optimal use of marine resources. Water depth measurement refers to the underwater study of oceans, lakes and rivers. Therefore, Stump Method was used to calculate water depthin the present study.
 
2-2- Accuracy assessment
In order to estimate the accuracy, information about water surface temperature and relative water depth in three stations in Lake Urmia, namely Qalqachi, MalekAshtar and Ashk stations, were collected from the Artemia Research Center and the Meteorological Organization of West Azerbaijan Province.
 
3- Results
Results indicate high accuracy of remote sensing methods in sea surface temperature and water depth measurements. The lowest RMSE of sea surface temperature measurement is related to MalekAshtar station (1/1). This station also has the lowest amount of RMSE (1/5) obtained in water depthmeasurement. According to the results, a negative correlation coefficient is observed between the values of sea surface temperature and water depthvariables. The correlation between sea surface temperature and water depth in Lake Van equals -0.52, while this correlation equals -0.24in Lake Urmia.
 
4- Discussion
Despite their relatively high accuracy, usinginformation collected from meteorological stations to calculate physical parameters of water,such as water surface temperature and water depth, has some limitations. However, new technologies such as remote sensing can overcome the limitations of traditional methods. Remote sensing technology has made estimating the physical parameters of water on a regional to a global scale possible. Results of the present study indicate high accuracy of remote sensing technology in measuring physical parameters of water such as surface temperature and depth. In this regard, shallow water bodies have the highest surface temperature and deeper water show lower temperatures. The results also indicate that fluctuations in the water surface temperature and water depth can increase or decrease the correlation coefficient between these two variables. Thus, higher correlation coefficient between water surface temperature and water depth in Lake Van compared to Lake Urmia is due to its greater depth of water.
 
5- Conclusion
Results indicate that the upstream of Lake Urmia is deeper than itsdownstream and also has a higher level of salinity which reduce evapotranspiration in the upstream of the lake. Thus, theupstreamof Lake Urmia has not been as severely affected by the drought. The correlation coefficient between water surface temperature and water depth of Lake Van also shows that this lake has a relatively lower water surface temperature compared to Lake Urmia due to its greater depth. Therefore, the rate of evapotranspiration in this lake is less than Lake Urmia and the drying process is negligible. Due to the fact that Lake Urmia and Van are in the same climate, the high temperature of the water level of Lake Urmia due to its shallower depth can be one of the causes of Lake Urmiadrying. The amount of water in the lake can be increased by increasing the volume of water entering the lake.This can be achieved by destroying a number of dams built on the rivers flowing into the lake or by water transfer from adjacent water bodies. Therefore, increasingwater depth and reducingwater surface temperature can be considered as one of the main solutions to prevent the drying of Lake Urmia. 

کلیدواژه‌ها [English]

• Sea surface temperature
• Relative water depth
• Landsat satellite
• Lake Van
• Lake Urmia