ANALISIS SPEKTRAL DALAM PENENTUAN PERIODISITAS SIKLUS CURAH HUJAN DI WILAYAH SELATAN JATILUHUR, KABUPATEN SUBANG, JAWA BARAT

Rainfall data was studied to know how rainfall in the region has a span of time to form a repetitive pattern. The cycle is a change or a wave up and down within a period and repeated at other periods. The cycle has a frequency that can be completed in one period of time. Fourier transform is an algorithm to convert the time domain X to the domain or the frequency spectrum Y, by breaking the signal into a sinusoidal component. This study used the Fast Fourier Transform (FFT) to find the nature of the trend recurrence of rainfall in the southern region of Jatiluhur Subang. Simulation model was done using monthly rainfall data 1975 - 2012. The results showed a trend of rainfall in the study area was repeated every 12 months (1 cycle). Rainfall prediction was done by using a 5-year rainfall data and used the data observation of the next 5 years as a comparison result predicted to see the performance. Performance prediction was resulted using the Mean Square Error (MSE) used to obtain the difference between the standard derivation calculation of observed data and data modeling. The results of the analysis at the time of validation of the model was MSE 14.92 with a 95% confidence level. FFT used to calculate the value of the error (the difference between the values calculated by the ANN model and observed data) resulted in the change cycle of rainfall occurs over a period of months or approximately 71.68 months or 5-6 years.Keywords: Rain!all, prediction, Fast Fourier Trans!orm (FFT), Mean Square Error (MSE), Subang District ABSTRAKData curah hujan dipelajari salah satunya untuk mengetahui bagaimana curah hujan di suatu wilayah mempunyai rentang waktu untuk membentuk suatu pola berulang. Siklus merupakan suatu perubahan atau gelombang naik dan turun dalam suatu periode serta berulang pada periode lain. Siklus mempunyai frekuensi yang dapat diselesaikan dalam 1 periode waktu. Transformasi Fourier merupakan algoritma untuk mengubah domain waktu X menjadi domain atau spectrum frekuensi Y, dengan cara menguraikan sinyal menjadi komponen sinusoidal. Penelitian ini menggunakan metode Fast Fourier Trans!orm (FFT) untuk mencari sifat berulangnya trend curah hujan di wilayah selatan Jatiluhur Kabupaten Subang. Simulasi model menggunakan data curah hujan bulanan tahun 1975 - 2012. Hasilnya menunjukkan trend curah hujan di lokasi penelitian berulang setiap 12 bulan sekali (1 siklus). Prediksi curah hujan dilakukan dengan menggunakan data curah hujan 5 tahun dan menggu