Bölgesel ölçekte klorofil-a konsantrasyonunun belirlenmesinde sentınel-3 olcı verilerinin kullanım olanaklarının araştırılması

Abstract

Türkiye güneyde Akdeniz, kuzeyde Karadeniz, batıda Ege Denizi ile çevrilidir. Ülke sınırları içinde bulunan Marmara Denizi, Karadeniz'i Ege Denizi ve Akdeniz'e bağlar. Birbiriyle bağlantılı olan bu denizlerin izlenmesi doğal çevrenin sağlığı ve canlılar için önemlidir. Uzaktan algılama çalışmalarıyla yapılan araştırmalar sonucu denizlerdeki problemler tespit edilmektedir. Marmara Denizi birçok ekosistemi etkilemesiyle birlikte insan sağlığı içinde önemli bir iç denizdir. Denizin kirliliği doğrudan ya da dolaylı yollarla bütün canlıların hayatına olumsuz yansıyacaktır. Evsel, ticari, endüstriyel, doğal ve tarımsal gibi birçok nedenle deniz kirliliği artmaktadır. Bu durum Marmara Denizi'nde organik ve inorganik kirleticilerin çoğalmasıyla deniz suyuna ve denizde bulunan ekosisteme ciddi zararlar vermektedir. Bununla birlikte Avrupa'nın en büyük ikinci nehri olan Tuna Nehri'nin sanayinin yoğun olduğu ülkelerden, yerleşim yerlerinden ve tarım alanlarından geçerek Karadeniz'e ulaşması ve Karadeniz'de oluşturduğu kirliliğin Marmara Denizi'ne yansımasıda deniz kirliliğinde büyük bir etkendir. Sentinel-3 OLCI deniz ve yeryüzü hakkında bilgi kaydeden bir uydudur. Çevre ve iklimsel gözlem çalışmalarında da kullanılmaktadır. Sentinel-3A ve Sentinel-3B olmak üzere iki özdeş uyduya sahiptir. Tez kapsamında Sentinel-3 OLCI uydu görüntü verileriyle Karadeniz'in batısında ve Marmara Denizi'ndeki klorofil-a konsantrasyonunun neden olduğu kirlilik incelenmiştir. Veriler Yerüstü Su Kalitesi Yönetmeliğinde belirlenen su kalite sınıflarına göre 9 sınıfa ayrılmış ve makine öğrenme algoritması olan destek vektör makinesi (SVM) kullanılarak kontrollü sınıflandırma yapılmıştır. Destek vektör makinesi iki sınıflı doğrusal verilerin veya çok sınıflı doğrusal olmayan verilerin sınıflandırılması için tasarlanmış bir algoritmadır. Farklı mevsimlerde alınan 2020 yılına ait sınıflandırılmış uydu görüntülerine göre klorofil-a konsantrasyonunun ilkbaharda en yüksek sonbaharda en düşük olduğu belirlenmiştir. Bununla ilişkili olarak alg konsantrasyonunun da ilkbahar aylarında artış göstermesi bu durumu desteklemektedir. Ek olarak Tuna Nehri'nin Karadeniz'de yarattığı kirliliğin Marmara Denizi'ne yansımasıyla deniz kirliliğinin arttığı değerlendirilmiştir. Suda yaşayan algler fotosentez yapan canlılardır. Deniz yüzeyinin kirli olması güneş ışınlarını engellediği için bu canlıların fotosentez yapmasına izin vermemektedir. Deniz yüzeyinin kirliliği sonucu ısı dengesi de bozulmaktadır. Bunların sonucunda algler çoğalarak salgı üretir ve müsilaj (deniz salyası) problemine neden olmaktadır. 2021 yılının bahar mevsimine ait Sentinel-3 OLCI (Ocean and Land Colour Instrument) uydu görüntü verileri incelendiğinde 2020 yılının bahar mevsimine kıyasla Marmara Denizi'ndeki klorofil-a oranında artış görülmüştür. Buna bağlı olarak oluşan müsilaj Marmara Denizi'nde büyük bir soruna neden olmuştur. Müsilaj probleminin kontrol altına alınabilmesi için Marmara Denizi ve Batı Karadeniz'in düzenli olarak izlenmesi gerekmektedir. Sentinel-3 OLCI verileriyle yapılan çalışmalar, yıl içinde mevsimlere bağlı klorofil-a konsantrasyonundaki değişimin takip edilmesi için iyi bir seçenek olabilir. Bunun dışında OLCI için geçmiş yıllara ait verileri bulmak her zaman mümkün olmamaktadır. Bu durumda yapılan çalışmaların farklı uydu görüntüleriyle desteklenmesi çalışmaların sürdürülebilirliğinin sağlanması açısından bir gereklilik olacaktır.

Turkey is surrounded on the south by the Mediterranean Sea, north by the Black Sea, and west by the Aegean Sea. The Sea of Marmara, which lies within the country's borders, connects the Black Sea with the Aegean Sea and the Mediterranean Sea. Monitoring these interconnected seas is important for the health of the natural environment and living creatures. As a result of research conducted through remote sensing studies, problems in the seas are identified. The Sea of Marmara is an important inland sea for human health. Pollution of the sea will have a direct or indirect negative impact on the life of all living beings. Marine pollution is increasing due to various reasons such as domestic, commercial, industrial, natural, and agricultural. This situation causes serious damage to seawater and the marine ecosystem with the increase of organic and inorganic pollutants in the Sea of Marmara. The main pollutants causing pollution in the Marmara Sea are the pollution carried by the Black Sea discharges from the sewage treatment plants in İstanbul, the pollution loads carried into the sea by the rivers that form the surface drainage network of İstanbul, and the pollution caused by maritime traffic and accidents at sea. The basic parameters reflecting seawater quality are dissolved oxygen, suspended solids, total nitrogen, total phosphorus, chlorophyll-a, heavy metals (Pb, Fe, Mn), detergent measurements. The increase in total nitrogen and total phosphorus concentration causes eutrophication. The excessive proliferation of plankton and algae simultaneously damages the marine ecosystem. The balance in the marine ecosystem is disturbed by marine pollution. One of the factors causing this pollution is the high chlorophyll-a concentration formed by mixing nutrients such as nitrogen and phosphorus into the water. As a result, marine and freshwater ecosystems are greatly damaged. The algae that multiply with the increase in the number of nutrients in the water cause eutrophication by consuming oxygen, resulting in a decrease in water quality. This situation, which is generally seen in the spring months, ends in the summer months. However, the increase in chlorophyll-a concentration has been frequent in recent years. If this situation lasts for a long time, it can cause the death of all creatures living in the water with the decrease of oxygen in the ocean. The increase of elements such as nitrogen and phosphorus causes the proliferation of algae by disturbing the ecological balance. Dying algae from lack of oxygen as a result of overgrowth rise to the surface of the water and form a red layer. Living organisms that continue their life with oxygen cannot survive in eutrophic conditions. The algal bloom is called a red tide. Algal blooms are seasonally common, usually in less deep coastal waters, inland seas, gulfs, lakes, and near estuaries. Since the Marmara Sea has a large surface area, it may be affected by atmospheric deposition. There are major industrial areas in the catchment area of the Marmara Sea. Most of them discharge their effluents into this inland sea without decontamination. This leads to excessive pollution of the Marmara Sea. The Sea of Marmara is located between the Mediterranean Sea and the Black Sea and has a continuous current. Due to this current, pollutants can be transported over long distances on the sea. Pollution can occur even in areas with industrialization and low population density. The Sea of Marmara has a large volume and the hydraulic residence time of water is long in this sea. As a result, pollutants can remain in this environment for a long time. This situation over the ecosystem poses serious risks. The Sea of Marmara is replenished by the waters of the undercurrent from the Aegean Sea. Measures should be taken to prevent the North Aegean and Dardanelles Strait from being unaffected by this pollution. In addition, it is of great importance in monitoring pollutants coming from the Black Sea with the upper stream. Water Framework Directive According to European Union (EU), the main directive relating to water quality aims to achieve "good status" in all surface waters in Europe. To achieve this goal, member countries are supposed to establish water quality monitoring systems and they have to determine the ecological and chemical status of water bodies. According to the directive, ecological status is to be determined using the biological quality elements and the physical, chemical, and hydromorphological characteristics of the waters as supporting elements of the biological quality elements. The hydrography of the Sea of Marmara is determined by the change over the straits. The existence and characteristics of the Sea of Marmara are related to the Black Sea which is in direct interaction with the Bosphorus. The Black Sea determines the ecological quality in the upper layer of the sea the most. The Danube, the second largest river in Europe, flows through industrial, residential, and agricultural areas and reaches the Black Sea. It is a major factor in marine pollution in the reflection of the pollution it produces in the Black Sea to the Marmara Sea. Recently, the mucilage problem in the Marmara Sea has caused significant damage to the marine ecosystem. The mucilage is a slimy structure formed by the combination of many biological and chemical conditions, the proliferation of algae with the increase of bacterial activities as a result of high sea temperature and stability. The excess nitrogen and phosphorus pollution in the Marmara Sea, the increase of salinity with temperature has revealed the mucilage problem. Sentinel-3 OLCI is a medium resolution satellite that allows a wide perspective view of the earth's surface. It can be preferred for ocean observations depending on climate change. It is advantageous in terms of detailed measurement of atmosphere composition, with 6 additional bands developed compared to MERIS, designed to provide data continuity with Envisat's MERIS sensor. Sentinel-3 OLCI is a satellite that records information about the ocean's topography, temperature, color, and earth. It is also used for environmental and climate monitoring studies. It has two identical satellites, Sentinel-3A and Sentinel-3B. As part of the thesis, the pollution of the Sea of Marmara was investigated with Sentinel-3 OLCI data. The data were divided into 9 classes according to the water quality classes determined in the Surface Water Quality Regulation. Supervised classification was made using a support vector machine (SVM), a machine learning algorithm. The support vector machine is an algorithm designed for the classification of two-class linear data or multi-class nonlinear data. In the satellite images of the 2020 year were observed that highest in spring and lowest in autumn of the chlorophyll-a density according to the seasons. The increase of algae blooms in spring also supports this situation. Additionally, marine pollution has increased with the reflection to the Sea of Marmara of the pollution caused by the Danube River in the Black Sea. When the data for the spring season of the 2021 year are examined, an increase in the algae population in the Marmara Sea has been observed compared to the spring season of the 2020 year. Therefore mucilage caused a major problem in the Sea of Marmara. In order to control the mucilage problem, the Marmara Sea and the Western Black Sea should be monitored regularly. Studies with Sentinel-3 OLCI data may be a good option to follow the seasonal changes in chlorophyll-a concentration throughout the year. Apart from that, it is not always possible to find data for the past years for OLCI. In this case, it would be good to support the studies with different satellite images.