Abstract
The study area, which is part of the Sirt sedimentary basin in the north-central part of Libya, is characterized by natural resources of important environmental value that need special attention as they are threatened by many human activities. The focus of this study was mainly on the production of high-resolution maps of oil-contaminated surfaces, and the series time maps of events resulting from oil pollution using multi temporal satellite data and validation of the results. Digital image processing techniques were used on satellite-based sensing, whether optical or radar data, which proved to be a cost-effective way to collect information on the volume of lake water, and to assess the depth and concentration of pollution in the study area rich in lakes taken from different periods (1972 to 2006). The area of the oil-contaminated lake, called produced water, was calculated from the 1972 Landsat MSS digital satellite imagery data and was about 1.8 km2 and then increased to 10.7 km2, during 2006 from Landsat digital image TM data. The size change in this area was due to the increase of the quantities of water production that continued to increase as the oil and gas fields reached maturity. The 2019 Landsat satellite imagery reveals a drastic shrinkage in the area of the lake attributed to the suspension of the produced water pumping as well as the cycle of evaporation that resulted to the water led to a limited volume of water remaining in the lake.
Highlights
Depths of less than two meters which represent shallow areas are located on the edge of the lake and this depth gradually increases as we head to the south-central part of the lake, which appears in dark blue with a depth of more than 8 m
Implement the same method for lake area multiplied by the approximate average depth of 5 m at that time. This decrease is about 32% of the volume of water that covered the lake. This is evident by the interpretation of the Landsat satellite image, through which the following conclusions were reached as shown in Fig. 14: 1. The size of remaining water less polluted by oil, which appears in blue colour is only about 1.663 km[2] whilst the water volume is about 831.5 m3 and the variation in the blue colour difference from very dark (1.1) to light (1.2) is due to the depth and amount of water which mixed slightly with oil
Whilst the surrounding of the lake, which appears in dark brown colour (5) is the remainder of the soil, which is predominantly the concentration of oil pollutants, which occurred by pushing water currents by wind for these pollutants to settle on the edge of the lake. From this standpoint can be used to stop the pumping for certain periods, especially in areas characterized by high temperature, such as the study area, which contributes to the drying of the lake by evaporation of water and remains only solid substances harmful to the environment and can be removed at the final stage
Summary
The main objective of this study is to determine the size and depth of the lake and the amount of concentration of pollutants inside the lake utilizing satellite-based sensing.In addition, satellite data has been used for several dates of oil pollution events using indicators of change with multiple time images over the past decades.The focus of this study was mainly on the production of high-resolution maps of oil-contaminated surfaces, and the series time maps of events resulting from oil pollution using multi temporal satellite data and validation of the results.Through this work, the following procedures were carried out:• Preliminary study of the satellite images and identify areas of possible oil contamination were vectorized in ArcGIS and entering attribute information in the application ArcMap.• Perform reconnaissance of produced water body extension, depth, and locate the data on GIS to produce multi- GIS layers of the available data• Identify latitude, longitude (in terms of x, y coordinates) of the polluting features. • Verify the direction of flow and assess their impact on the surrounding areas. • The satellite imagery contains all bands has been used to classify produced water bodies according to different features: i.e., extension, and depth. • Different time series aerial and satellite imagery have been used as a base for this and used to extract features relevant to this study. • In order to predict the future extension of the disposal lake, topographical map of the study area has been constructed. To achieve this goal the available different dataset such as the SRTM obtained elevation data on a near-global scale to generate the most complete high-resolution digital topographic database of Earth supported by local topographical maps.
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