Sains Malaysiana 51(2)(2022): 369-378

http://doi.org/10.17576/jsm-2022-5102-04

Comparison of Three Water Indices for Tropical Aquaculture Ponds Extraction using Google Earth Engine

(Perbandingan Tiga Indeks Air untuk Pengekstrakan Kolam Akuakultur Tropika menggunakan Google Earth Engine)

YI LIN TEW¹, MOU LEONG TAN¹, NARIMAH SAMAT¹*, NGAI WENG CHAN¹, MOHD AMIRUL MAHAMUD¹, MUHAMMAD AZIZAN SABJAN², LAI KUAN LEE³, KOK FONG SEE⁴ & SEOW TA WEE⁵

¹GeoInformatic Unit, Geography Section, School of Humanities, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia

²Philosophy and Civilization Section, School of Humanities, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia

³School of Industrial Technology, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia

⁴School of Distance Education, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia

⁵Faculty of Management Technology and Business, Universiti Tun Hussein Onn, 86400 Batu Pahat, Johor Darul Takzim, Malaysia

Diserahkan: 26 Mac 2021/Diterima: 12 Jun 2021

ABSTRACT

Information on the spatial distribution of aquaculture ponds, especially the inland brackish aquaculture, is crucial for effective and sustainable aquaculture management. Google Earth Engine (GEE) has been utilized to quickly map aquaculture ponds in different parts of the world, but the application is still limited in tropical regions. Selection of an optimal water index is essential to accurately map the aquaculture ponds from the Landsat 8 satellite images that are available in GEE. This study aims to evaluate the capability of three different water indices, namely Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI) and Automated Water Extraction Index (AWEI), in mapping of the aquaculture ponds in Sungai Udang, Pulau Pinang, Malaysia. The results show that MNDWI is the best index for aquaculture ponds extraction in Sungai Udang, with an accuracy of 81.87% and Kappa coefficient of 0.61. Meanwhile, the accuracy of NDWI and AWEI as compared to the digitized aquaculture ponds are 58.21 and 61.60%, and Kappa coefficient of 0.33 and 0.36, respectively. Then, MNDWI was applied to calculate the spatial changes of aquaculture ponds from 2014 to 2020. The result indicates that the area of aquaculture ponds has expanded by 26.16% since the past seven years.

Keywords: Aquaculture; Google Earth Engine; Landsat; Malaysia; tropical

ABSTRAK

Maklumat ruang kolam akuakultur terutamanya kolam akuakultur air payau pedalaman adalah penting dalam keberkesanan pengurusan akuakultur yang lestari. Google Earth Engine (GEE) telahpun dimanfaatkan dalam pemetaan kolam akuakultur di beberapa negara, namun aplikasinya di kawasan tropika masih kurang. Pemilihan indeks air yang sesuai boleh memetakan kolam akuakultur dengan tepat daripada imej Landsat 8 dengan menggunakan GEE. Kajian ini bertujuan untuk menilai kemampuan tiga jenis indeks air yang bernama Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI) dan Automated Water Extraction Index (AWEI) dalam pemetaan kolam akuakultur di Sungai Udang, Pulau Pinang. Hasil daripada kajian ini, MNDWI menunjukkan ketepatan yang paling tinggi dalam memetakan kolam akuakultur di Sungai Udang, dengan ketepatan sebanyak 81.87% dan nilai pekali Kappa 0.61. Manakala bagi NDWI dan AWEI pula, ketepatan kedua-dua indeks air ini adalah 58.21 dan 61.60%, serta nilai pekali Kappa 0.33 dan 0.36 sahaja. Dengan ini, MNDWI telah digunakan untuk memperoleh perubahan ruang kawasan kolam-kolam akuakultur di Sungai Udang dari tahun 2014 sehingga 2020. Hasilnya menunjukkan kawasan kolam-kolam ini telah berkembang sebanyak 26.16% dalam masa tujuh tahun.

Kata kunci: Akuakultur; Google Earth Engine; Landsat; Malaysia; tropika

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*Pengarang untuk surat-menyurat; email: narimah@usm.my