Construction of the Long-Term Global Surface Water Extent Dataset Based on Water-NDVI Spatio-Temporal Parameter Set

Inland surface water is highly dynamic, seasonally and inter-annually, limiting the representativity of the water coverage information that is usually obtained at any single date. The long-term dynamic water extent products with high spatial and temporal resolution are particularly important to analyze the surface water change but unavailable up to now. In this paper, we construct a global water Normalized Difference Vegetation Index (NDVI) spatio-temporal parameter set based on the Moderate-resolution Imaging Spectroradiometer (MODIS) NDVI. Employing the Google Earth Engine, we construct a new Global Surface Water Extent Dataset (GSWED) with coverage from 2000 to 2018, having an eight-day temporal resolution and a spatial resolution of 250 m. The results show that: (1) the MODIS NDVI-based surface water mapping has better performance compared to other water extraction methods, such as the normalized difference water index, the modified normalized difference water index, and the OTSU (maximal between-cluster variance method). In addition, the water-NDVI spatio-temporal parameter set can be used to update surface water extent datasets after 2018 as soon as the MODIS data are updated. (2) We validated the GSWED using random water samples from the Global Surface Water (GSW) dataset and achieved an overall accuracy of 96% with a kappa coefficient of 0.9. The producer’s accuracy and user’s accuracy were 97% and 90%, respectively. The validated comparisons in four regions (Qinghai Lake, Selin Co Lake, Utah Lake, and Dead Sea) show a good consistency with a correlation value of above 0.9. (3) The maximum global water area reached 2.41 million km2 between 2000 and 2018, and the global water showed a decreasing trend with a significance of P = 0.0898. (4) Analysis of different types of water area change regions (Selin Co Lake, Urmia Lake, Aral Sea, Chiquita Lake, and Dongting Lake) showed that the GSWED can not only identify the seasonal changes of the surface water area and abrupt changes of hydrological events but also reflect the long-term trend of the water changes. In addition, GSWED has better performance in wetland areas and shallow areas. The GSWED can be used for regional studies and global studies of hydrology, biogeochemistry, and climate models.

VARIABILITAS SPASIAL DAN TEMPORAL PARAMETER OSEANOGRAFI TERHADAP TANGKAPAN IKAN DI PERAIRAN LAUT BENGKULU

Perairan laut Bengkulu memiliki potensi perikanan cukup melimpah. Potensi tersebut dipengaruhi oleh beberapa parameter oseanografi. Penelitian ini bertujuan untuk menentukan variabilitas spasial dan temporal parameter oseanografi serta mengetahui hubungannya terhadap hasil tangkapan ikan selama lima tahun di perairan laut Bengkulu. Metode yang digunakan adalah analisis deskriptif berdasarkan visualisasi data kecepatan angin, suhu permukaan laut dan salinitas pada tahun 2011 – 2015. Analisis data dilakukan dengan menggunakan software GrADS, Panoply dan ArcGIS. Hasil penelitian menunjukan tangkapan ikan terbanyak 16.514 ton terjadi pada musim barat tahun 2015 dengan kecepatan angin 1,211 m/s, SPL 29,094 oC dan salinitas 33,623 psu. Sedangkan hasil tangkapan ikan terendah terjadi pada musim barat tahun 2012, yaitu sebesar 7.576,60 ton. Kondisi oseanografi perairan pada musim tersebut untuk parameter kecepatan angin 4,624 m/s, suhu permukaan laut 28,765 oC, dan salinitas rata-rata 33,987 psu. Hubungan kondisi oseanografi terhadap hasil tangkapan ikan secara umum yaitu hasil tangkapaan ikan cendrung rendah pada kondisi kecepatan angin dan salinitas yang tinggi, SPL rendah. Sebaliknya jika kecepatan angin dan salinitas rendah, SPL tinggi maka akan didapatkan hasil tangkapan ikan yang banyak.