برآورد غلظت كل مواد جامد محلول و كدورت آب سدهاي كرخه و دز و رودخانه كارون بزرگ با استفاده از تصاوير ماهواره Sentinel-2

Estimation Total Dissolved Solids and Turbidity Concentration in Karkheh and Dez Dam and Great Karun River by Using Sentinel-2 Satellite Images

سنجش از دور ازجمله فناوري‌هاي نويني است كه مي‌تواند با صرف هزينه اندك، اطلاعات پيوسته‌اي ازنظر زمان و مكان تغييرات پارامترهاي كيفيت آب در منابع آب سطحي برآورد نمايد، بنابراين اين مطالعه با هدف برآورد غلظت پارامترهاي كيفيت آب TDS و Turbidity در سدهاي كرخه و دز و رودخانه كارون بزرگ با استفاده از تصاوير برداشت‌شده به‌وسيله ماهواره سنتينل-2 انجام گرفت. ابتدا با انجام پردازش‌هاي اوليه بر روي تصاوير ماهواره مذكور، شاخص‌هاي طيفي مناسبي از آن‌ها استخراج گرديد و سپس با به‌كارگيري مدل شبكه عصبي، روابطي بهينه‌ ميان آن‌ها و مقادير هركدام از پارامترهاي TDS و Turbidity برقرار شد. جهت ارزيابي دقت مدل‌سازي‌هاي انجام‌شده شاخص‌هاي RMSE و خطاي نسبي استفاده گرديد و مقادير هركدام از آن‌ها براي مدل‌سازي ميان تصاوير ماهواره‌اي و پارامتر TDS به ترتيب برابر با (ppm) 48/105 و 088/0 و براي مدل‌سازي ميان تصاوير ماهواره‌اي و پارامتر Turbidity برابر با (N.T.U) 1/3 و 110/0 به دست آمد. در نهايت با اعمال مدل‌هاي تهيه‌شده بر روي تصاوير ماهواره‌اي سنتينل-2 كه در سال‌هاي 1394 تا 1395 برداشت‌شده بودند، نقشه پراكندگي پارامترهاي كيفيت آب ذكر شده در چهار زمان براي سدهاي كرخه و دز و رودخانه كارون بزرگ در مقطع ملاثاني تا ايستگاه‌ هيدرومتري فارسيات در جنوب اهواز تهيه گرديد.

1-Introduction Considering the importance of rivers as part of freshwater resources and their role in meeting the needs of agriculture, industry, urban populations, etc., monitoring and predicting the quality of these water resources is essential. These water sources are affected by numerous factors due to their different geological and environmental conditions and their qualitative status also undergoes dramatic changes. However, the quality monitoring of these abundant water resources on the planet's surface is not feasible and requires the use of advanced and powerful tools (Bagherian Marzouni et al., 2014). Due to its capabilities, satellite remote sensing can be used as one of these tools in monitoring water quality and will accurately detect the spatial and temporal changes of these water sources (Bonansea et al., 2015). So far, in many studies, the capabilities of remote sensing satellites to estimate surface water quality parameters has been evaluated, and in most of them, acceptable results have been obtained indicating the ability of this technology in the issue as mentioned above. Among these studies, we can mention laili et al. (2015), in which in a small section of Indonesian waters, have figured out a new regression algorithm between Landsat 8 and groundwater quality parameters. Toming et al. (2016) in a study using satellite images of Sentinel-2 on the water quality of the lakes in Estonia, could find a good correlation between the satellite band proportions and ground. The purpose of this research is to establish a relation between satellite images of Sentinel-2 A and two quality water parameters with a suitable model along the Karun and Dez River. For this purpose, firstly suitable spectral indices were extracted from them by applying the necessary processing on satellite images. In the next step, optimal relationships between extracted indices and water quality parameters are established using different models. Finally, using models with higher accuracy in terms of modeling, the dispersion map of each parameter in the length of the Karun River is provided.The purpose of this research is to establish a relation between satellite images of Sentinel-2 A and 2 quality water parameters with a suitable model along the Karun and Dez River. For this purpose, firstly suitable spectral indices were extracted from them by applying the necessary processing on satellite images. In the next step, optimal relationships between extracted indices and water quality parameters are established using different models. Finally, using models with higher accuracy in terms of modeling, the dispersion map of each parameter in the length of the Karun River is provided. 2-Methodology This study presented in eight steps as below: Step 1: Preparation of ground data and satellite imagery:The ground data used in this study is the measured data at the water quality sampling stations. The data included information on these quality parameters that were used from 2015 to early 2017 in ten stations. Step 2: Recording the value of the reflection bands at the ground measurement stations:In order to implement this research, satellite images of sentinel-2 and groundwater quality parameters were collected and measured at the same time from the study area. In this step, the values of measured water quality parameters were also sorted by date and sampling stations were prepared in separate files. Step 3: Analyze the initial sensitivity and determine the bands that have a stronger connection with each water quality parameter