Seminar Nasional Penginderaan Jauh ke-6 Tahun 2019 Kapabilitas Citra Sentinel 1 (SAR) dan Sentinel 2 (MSI) dalam Pendeteksian Tumpahan Minyak di Teluk Balikpapan Sentinel 1 (SAR) and Sentinel 2 (MSI) Imagery Capabilities for Oil Spill Detection in Balikpapan Bay Muhamad Iqbal Januadi Putra1*), Martha Megah Anugerah1, dan Aulia Akbar1 1Department of Geography, Universitas Indonesia *)E-mail: [email protected] ABSTRAK - Teluk Balikpapan merupakan salah satu area yang memiliki sumberdaya migas yang besar di Pulau Kalimantan namun kasus tumpahan minyak di wilayah tersebut telah menarik banyak perhatian dan dianggap sebagai permasalahan lingkungan yang sangat serius. Penelitian ini bertujuan untuk mendeteksi area tumpahan minyak yang terjadi di Teluk Balikpapan akibat kegiatan industri minyak dan gas dengan menggunakan citra satelit. Citra Sentinel 1 (SAR) dan Sentinel 2 (MSI) digunakan untuk mendeteksi area tumpahan minyak di perairan Teluk Balikpapan. Penggunaan kedua citra ini akan menghasilkan informasi sebaran wilayah tumpahan minyak berdasarkan nilai backscatter gelombang dari citra Sentinel 1 dan nilai reflektan spektrum gelombang dari citra Sentinel 2 dengan menggunakan nilai anomali threshold. Hasil dari penelitian ini menunjukkan perbedaan kapabilitas dan kemampuan citra Sentinel 1 dan citra Sentinel 2 dalam mendeteksi wilayah tumpahan minyak di Teluk Balikpapan. Kata kunci: sentinel 1, sentinel 2, nilai anomali threshold, tumpahan minyak ABSTRACT - Balikpapan Bay is one of the areas that rich in petroleum resources in Borneo Island. However, the case of oil spills in this area has attracted people due to consideration as a serious environmental problem. This study aims to detect the oil spill area that occurred in Balikpapan Bay due to oil and gas operational activities with satellite imagery. Sentinel 1 and Sentinel 2 imageries are used to detect oil spill phenomena occurring in Balikpapan Bay waters. The utilization of these two images resulted in information on the oil spill distribution based on backscatter characteristics that resulted from Sentinel 1 imagery and spectral characteristics of each wavelength spectrum by threshold anomaly value method that resulted from Sentinel 2. The results of this study show the difference capability of Sentinel 1 and Sentinel 2 imageries in detecting oil pollution hotspots in Balikpapan Bay. Keywords: oil spill, sentinel 1, sentinel 2, threshold anomaly value 1. INTRODUCTION Balikpapan Bay is one of the areas that rich in petroleum resources in Borneo Island, and the case of an oil spill within this area has attracted many people due to consideration as a serious environmental problem. Therefore, having an oil pollution monitoring system is crucial for the preservation of the coastal ecosystem (Hammound et al., 2018). An approach directed towards an improvement in oil spill detection/identification in the sea with the use of satellite images as the primary source of information has been developed (Eljabri and Gallagher, 2012). Remote sensing has proven capable of assessing oil contamination (Mou et al., 2017). The satellite synoptic view is an attractive option to distinguish the oil slick type that can lead to considerable scientific advances (Carvalho et al., 2017). Response personnel can use this location 321 Sentinel 1 (SAR) and Sentinel 2 (MSI) Imagery Capability for Oil Spill Detection in Balikpapan Bay (Putra, M. I. J., et. al) information to implement countermeasures to minimize the effect of pollution (Fingas and Brown, 2018). With the knowledge of slick locations and movement, response personnel can more effectively plan countermeasures to lessen the effects of the pollution (Fingas and Brown, 2014). Remote sensing can detect the oil spill area because of the spectral and backscatter characteristic of its spill in the water. Although it has been considered that the satellite-borne SAR sensors have been broadly used for oil spill monitoring, have provided excellent data (Harasheh, 2016), and plays a vital role in oil spill detection for its all-day-and-night sensing capability (Prastyani and Basith, 2018), the utilization of optical imagery still be used to understand the capability of both imageries in detecting the oil spill. Satellite imageries, both active (radar) and passive (optical) sensors are frequently used to detect, map, and monitor the oil spill (Bayramov et al., 2018). Thus, in this study, Sentinel 1 (Synthetic-Aperture Radar/SAR) and Sentinel 2 (Multispectral Sensor Imager/MSI) are used for oil spill detection in Balikpapan Bay because of its temporal and spatial availability covering its area. The objective of this research was to examine the capability of both imageries for detecting the oil spill in the ocean. To be precise, this research is striving to analyze the capability of Sentinel 1 (SAR) and Sentinel 2 (MSI) for the mapping oil spill in Balikpapan Bay. 2. METHOD 2.1 Study Area The research was conducted in Balikpapan Bay, East Kalimantan, which had faced a severe case of oil leakage on 31st March 2018. This phenomenon was occurred because of the cracked underwater pipeline when transported crude oil and considered as the biggest oil spill disaster in the past ten years in Indonesia. It also affected the marine and coastal environment around Balikpapan Bay, including mangrove wetlands and the community of human life. Figure 1. Study Area (Source: Data processing) 2.2 Data Processing This research used Sentinel 1 (SAR) and Sentinel 2 (MSI) imagery that downloaded from the Scihub Copernicus ESA website. Sentinel 1 imagery that used in this research was recorded on 1st April – 2018, while Sentinel 2 imagery was recorded on 3rd April, 2018. Sentinel 1 (SAR) image with the VV polarization type was corrected using SNAP 5.0 software. The utilization of cross-polarization (HV or VH) for mapping the oil spill will not gain any results because of the effect of little multiple reflections of the signal by these polarizations (Brekke and Solberg, 2005) so that the use of VV polarization will obtain a better result. Studies about oil spills proved that X-band radar performs better than other bands radar (e.g., C or L) as well as vertical (VV) polarization is better than horizontal (HH) or cross-polarization (HV) (Nezhad et al., 2018). 322 Seminar Nasional Penginderaan Jauh ke-6 Tahun 2019 The processes that include in Sentinel 1 imagery processing are image ellipsoid, speckle correction, and transforming the backscatter image value to dB value conducted by using SNAP 5.0 software. In addition, this software also was used to classify images to determine the area of the oil spill in Balikpapan Bay by applied the threshold anomaly value. Meanwhile, QGIS software was used to process Sentinel 2 imagery. The semi-automatic classification was first applied to change the digital number (DN) value to reflectance value. This method also was applied to conduct atmospheric correction to reduce the appearance of images from black/dark objects (DOS). Meanwhile, image processing to detect oil spill areas will be carried out using the threshold anomaly value method. It will calculate the anomaly value of an index, which will refer to the identification of an object. The calculation of anomaly value begins by identifying the area of the oil spill using the oil spill index (Kolokoussis and Karathanassi, 2018) with Equation 1. The formula uses the standard deviation value of Band 2 in Sentinel 2 and the result of the band ratio of Band 2 with Band 11. The results of oil spill index processing will produce an index value that can be base for determining the anomaly value with Equation 2. Figure 2 shows the entire process to gain oil spill information either by Sentinel 1 (SAR) and by Sentinel 2 (MSI) imagery. The results from both imageries processing will be compared to identify each capability of imagery in mapping the oil spill in Balikpapan Bay. 푂푖푙푆푝푖푙푙퐼푛푑푒푥 = 푆푡퐷푒푣 퐵2 ∗ 퐵2/퐵11 .......................................................................................... (1) 푇ℎ푟푒푠ℎ표푙푑 퐴푛표푚푎푙푦 푉푎푙푢푒 = 푀푒푎푛 + (2 ∗ 푆푡푎푛푑푎푟푑 퐷푒푣푖푎푡푖표푛) ........................................... (2) Figure 2. Schematic Flowchart (Source: Data processing) 3. RESULTS AND DISCUSSION Speckle correction that applied toward Sentinel 1 (SAR) can reduce the appearance of the backscatter value of an oil spill object because of a white stain effect. The whole process was conducted after the imagery was clipped. After that, the result was converted into dB value to enhance the contrast appearance of imagery, especially to separate the visual of the oil spill and other objects. Sentinel 1 image processing results are presented in Figure 3. Visual separation of the oil spill can be understood through the dB value. Generally, the oil spill object has a low dB value from the surrounding object because the backscatter reflection value is low. Oil films can be detected as dark patches relative to the surrounding water as they dampen the wind-generated short surface waves (Ivanov & Zatyagalova, 2008). The water that 323 Sentinel 1 (SAR) and Sentinel 2 (MSI) Imagery Capability for Oil Spill Detection in Balikpapan Bay (Putra, M. I. J., et. al) has been polluted by the oil spill would have a lower pixel value/dB value (Prastyani and Basith, 2018). Based on the results of the histogram analysis of the oil spill object, the histogram value is ranged from 14.5- 16.5 dB (Figure 4). Nevertheless, the dB value outside the range of 14.5-16.5 can be considered as a non-oil spill object in Balikpapan Bay. Figure