THE USE OF ALOS IMAGERY FOR MAPPING COASTAL VULNERABILITY INDEX IN PADANG CITY

Transcription

1 THE USE OF ALOS IMAGERY FOR MAPPING COASTAL VULNERABILITY INDEX IN PADANG CITY Muhammad Ramdhan 2)*), Gunardi Kusumah 1), and Dini Purbani 2) 1) Institute Coastal Vulnerability and Marine Research 2) Center for Research and Development of Marine and Coastal Resources *) Abstract Advanced Land Observing Satellite (ALOS) data has been used in many applications, including for food security, disaster mitigation, and biodiversity conservation. This paper will present the process of making maps of coastal vulnerability index in Padang city. The city was chosen as a study area because it was recorded by BNPB as a high index disaster-prone areas. Other data used in this paper are: Topographical Map Indonesia, Geological Map, Aster-GDEM, and stastistical data from BPS. The coastal vulnerability index map in Padang city shows that 15% of the coastal areas are categorized as an area with both high and very high vulnerability index. The district with the highest vulnerability index area is the West Padang district. Key Words: ALOS Image, Coastal Vulnerability Index, Padang city 1. Introduction ALOS is satellite which was launched by Japan Aerospace Exploration Agency (JAXA) on January 24, The primary mission is to find local problem solution (local issue) such as: food security, the scarecity of water sources, disaster mitigation and biodiversity conservation (Wikantika, 2010). Satellite Alos specifations can be seen in table. Table 1. ALOS satellite specification is as follows IDC (International Designation Code) : A Date of launching : 10:33 (JST), 24 Januari 2006 Date of stopped operation : Mei Launching location : Tanegashima Space Center : Main Part: 6.2 m x 3.5m x4.0 m : Solar Array Paddle: 3.1 m x 22.2 m Dimension : PALSAR Antenna: 8.9m x 3.1 m : Bobot: kg Orbit : Sun-Synchronous; Periode Recurrent/Subrecurrent : 46 hari Height : 700 km Angle of inclination : 98 o The movement controller : High accuracy attitude control orbit determination function : PRISM : 2,5 meter Spatial resolution : AVNIR-2 : 10 meter Swath width : 70 Km Source: ALOS Data Users Handbook, JAXA,2008 During operational, Alos data has been used as supporting data in analizing many kinds of fenomena happened in the earth. In its orginal country of Japan, Alos data has been used to identified problems in coastal areas. This paper is discussing about the usage of Alos data to map vulnerability index in the coastals of Padang city. Padang city is the city of the province of West Sumatera, geographically it is the coastal city located in 00 o o South Longitude, 100 o o East Latitude with 96,46 km coast line. The city has ever suffered earthquake disaster 2007 and The data from the National Disaster Management Agency (BNPB) shows that West Sumatera area especially Padang city is one of the area often attached by natural disaster.

2 Padang City Figure 1.Disaster vulnerability index map on Indonesia (source: Table 1. The statistic of population in Padang city No Regency Land Area Population Density Km 2 Precentage (%) People Precentage Population (%) (People/Km 2 ) 1 Bungus Teluk Kabung 100,78 14, , Lubuk Kilangan 85,99 12, , Lubuk Begalung 30,91 4, , Padang Selatan 10,03 1, , Padang Timur 8,15 1, , Padang Barat 7,00 1, , Padang Utara 8,08 1, , Naggalao 8,07 1, , Kuranji 57,41 8, , Pauh 146,29 21, , Koto Tangah 232,25 33, , TOTAL 694, Source: Padang in Figures Year-2008, BPS Padang According to the National Disasster Management Agency (BNPB), vulnerability is the condition that shows causes disability of individual or social community in facing dangerous threat (Triutomo, 2006). Coastal vulnerability is the condition of coastal area with shows its ability/disability in facing dangreous threat. In this paper the disaster which happens in coastal area is mostly dangreous erosion and sea level rise. The main causes those disasters are: the level population density, land cover, slope area and geology structure. 2. Methodology As mention before the purpose of this paper is to present the process of making map of coastal vulnerability index in Padang city by using Alos data. Coastal area is the convergent of land and sea (Nelson 2010), this area has high level complexity and vulnerability. This paper only discusses the long vulnerability coastal area Padang city. The data were used: Alos image number scene: ALAV2A was acquisition on September , Topografi Map Indonesia, Geological Map, ASTER GDEM-30 and BPS data. Equipment used: PC Desktop with software GIS ARCGIS 9.3 digital image processing ER Mapper 7.0.

3 Figure 2. Alos image, topography map geological map for Padang area Table 2. Geospatial data are used No Data type Spatial Date of Resolution acquisition Source 1 Citra ALOS, September meter AVNIR LAPAN 2 Topographic Map update 1: of Indonesia 2004 BAKOSURTANAL 3 Geological Map 1: Direktorat Geologi - ESDM 4 ASTER -GDEM 30 meter Important information Land Cover, Coast line Administration border Geology structure Slope area Figure 3. Flowchart of vulnerability index map for Padang city area Generally, the method used in this research can be seen in the figure 3.Alos data will be classified visually to differentiate land cover into 5 classification (dense residence, residence, open land, vegetation and dense vegetation). The result will be used as a refine to determine index of land cover.

4 Based on Public Works guidance about the function of the edge on city coastal, the longest set back should be 300 meters from coast line. The function of the coastal line refers to the Public Works guidance. So the process of setback making is done by buffering with the distance of 300 meters from coast line. The result of Alos image along buffer coastal area in Padang city can be seen in Figure 4. Figure 4. Land cover map from visually ALOS image Geological structure of Padang city as displayed on the geological map of Padang sheet Sumatera (Kastowo et al., 1996), in the stratigraphy of Padang city area are: aluvium deposit (Qal) consisting of silt, sand and gravel, (Qtau) consists of lahar rock, fonglomerat and kolovium deposit and (QTt) consists of the crystall hardness. In the Northern area alluvium deposit (Qal) is spread in the coastal of Koto Tengah regency Southern Padang Regency and (QTt) dominated rocks in Bungus Betung Bay Regency.This type of area is relatively more vulnerable to abrasion. In the Southern part of Padang city there is (Qtau) in the Southern Padang Regency, and (QTt) dominated rocks in Bungus Betung Bay Regency. Based on Meteorological Climatological and Geophysical Agency data, the condition of dominant wave in Padang city is from west with the height 0,1-1 m, but the city also gets high wave with the height between 4-5 m every year. This condition fits with, the standard of maximum setback (300 m) for Padang city area. Table 3. Precentage of total wave process by wind data from Meteorological Climatological and Geophysocal Agency Direction Wave Height (m) >5.0 Total South South West West North West Total Form Aster-GDEM data, we can see the average slope in Padang city in northern area is relatively flat with slope between 0-3 o and on the south of Padang city is relatively steep with slope > 3 o especially in mount range area as seen in figure 5. The stratification of vulnerability coastal index is measured based on modification of the method used by United States Geological Surveys (USGS) as

5 reported by Thieler and Hammar-Klose (2000). The parameter used in this research is mentioned on table 4. Table 4. Parameters and index for coastal vulnerability Ranking Parameter Very Low Low Fair High Very High a) Land cover - Dense Dense Vegetation Open Land settlement Vegetation settlement b) Beach Rock Volcanic Vulkanic Loss - Sediment Loss sediment type rock rock sediment c) Slope ( o ) > <2 d) Dense Population People/km 2 < > Equationtocalculate the coastal vulnerability index are as follows: Where: IVC = Index Vulnerabilty Coastal a = index for coastal land cover b = index for type beach rock c = index for beach slope d = index for dense population (1) IVC maximum value in equation (1) is 12.5, IVC further divided into 5 (five) categories based on the following numbers: 1 0-2,49 : Very Low 2 2,5-4,99 : Low 3 5,0-7,49 : Fair 4 7,5-10,0 : High 5 >10,0 : Very High 3. Result and Discussion Costal vulnerability index map resulted from overlay of all paramaters above can be seen in figure 6. Figure 6. Coastal vulnerability index map of Padang City

6 The result of index mapping shows that the area with vulnerability index in Padang city with index value are very high =1.53 km, high = 1.04 km, fair = 2.39 km, low = 2.95 km, and very low = km. Table 6. Coastal vulnerability index calculation results for the city of Padang No Regency COASTAL AREAS OF VULNERABILITY INDEX AREA (Km 2 ) Very Low Low Fair High Very High 1 Bungus Teluk Kabung Lubuk Begalung Padang Selatan Padang Barat Padang Utara Koto Tangah TOTAL Based on vulnerability index, about 15% of coastal area in Padang city is in the categories of high and very high vulnerabilities. Western Padang regency is the largest coastal area with categories very high (1.2 km 2 ). The data of vulnerability coastal area index for Padang city is resulted from 4 (four) main parameters: land use, type of rocks slope area and population density. Alos Avnir-2 image is used to analize type of land cover in Padang city. Alos image (spatial resolution 10 m) is suitable use in the process of the vulnerable coastal area index mapping with the analysis of spatial and smallest regency. Conclusion The use of Alos Avnir-2 to interpret the land cover in coastal areas make the interpretation of land cover is easier to do. But as an optical sattelite image Alos Avnir-2 has a limitation due to the cloud covering on the study area. Acknowledgements We would like sincerely to thank JAXA (Japanese Aerospace Exploration Agency) and RESTEC (Remote Sensing Technology Center of Japan) for giving us the image ALOS AVNIR2 in this research. References Anonymous, 1996, Pedoman Pemanfaatan Ruang Tepi Pantai di Kawasan Perkotaan, Direktorat Jenderal Penataan Ruang,-PU, Jakarta. Anonymous, 2009, Peta Indeks Kerentanan Pesisir Indonesia, BRKP, Jakarta. Anonymous, 2009, Kota Padang dalam Angka 2008, BPS-Padang. Anonymous, 2010, Laporan kegiatan pengembangan wilayah pesisir Kota Padang, Bappeda Kota Padang. accessed on 01 August accessed on 29 July accessed on 29 July lecturer material from Prof. Stephen A. Nelson, Tulane university, accessed on 30 July Kastowo, Gerhard W. Leo, S. Gafoer & T.C. Amin, 1996, Peta Geologi Lembar Padang, Sumatera, Pusat Penelitian dan Pengembangan Geologi, Bandung.

7 Solihuddin Tb., 2009, Karakteristik Pantai Dan Proses Abrasi Di Pesisir Padang Pariaman, Sumatera Barat, Puslitbang Sumberdaya Laut dan Pesisir, Balitbang-KP, Jakarta. Tampubolon W.et al., 2008, Menghitung Panjang Shoreline &Shared Boundary SecaraSimultan dari Data Sseamless Administrasi Kabupaten, Jurnal Geomatika, Vol. 14 No.1, hal 63:86. Thieler, E.R. and Hammar-Klose, E.S., 2000, National Assessment of Coastal Vulnerability to Future Sea-Level Rise: Preliminary Result for the U.S. Pacific Coast, USGS, Open File Report , 1 sheet. Triutomo S., 2006, Manajemen Resiko Bencana, dokumen presentasi seminar, BNPB, Jakarta. Wikantika K., 2010, ALOS - Satelit Penginderaan Jauh Multiguna, CRS-ITB blog archive, diakses tanggal 28 Agustus 2011.