ANALISIS PERIODISITAS CURAH HUJAN DENGAN PENDEKATAN DERET FOURIER

Studi Kasus, Di Daerah, Aliran Sungai, Kali Hulu
unpublished
The aim of this research is to determine harmonics which contribute the variance of the mean annual rainfall at two rainfall stations of Pujon and Ngan-tang in the upper Kali Konto Watershed, East java. Fourier Series which is based on the theory of harmonic analysis was used. This method used a composite sine and cosine Junction to approximate the variance. Mean annual rainfall at Pujon during 26 years (1951 • 1988) and at Ngantang during 29 years (1960-1988) were used as prima"Y data. The
more » ... ima"Y data. The steps of data analysis include normality test, homogenity test, moving average, and finally the harmonic analysis. The result of this research concludes that normality and homogenity test of the rainfall series showed as normal and homogen, while when using a moving average with smoothing of order 9 is to be the fittest line with original data. At Pujon station there was three harmonics. The largest variance was 61% found in the third harmonic, and in the first and the second harmonics give 4% and 2% respectively. harmonic curve at Ngantang station was nearly the same which contribute the variances 7%, 4%, and 3% respectively. Finally, It can be formulated two. Fourier Series which are usefull to predict the maximum and the minimum annual fainfall during these periods. INTI SARI Tujuan penelitian ini ialah untuk mendapatkan harmonik-harmonik yang memberi sumbangan terhadap ragam data hujan tahunan rata-rata pada Stasiun Pujon dan Ngantang di DAS Kali Konto Hulu, ]awa Timur, sehingga dapat disusun persamaan Deret Fourier. Data utama ialah data hujan tahunan rata-rata di Pujon selama 26 tahun (1951 • 1988) dan Ngantang selama 29 tahun (1960 • 1988). tahap analisis data adalah uji normalitas, uji homogenitas, rata-rata bergerak, dan analisis harmo-nik. Hasil uji normalitas dan homogenitas menunjukkan bahwa data dt kedua, stasiun menyebar normal dan homogen, sedangkan rata-rata bergerak poli-nomial menggunakan orde-9 adalah paling sesuai dengan data asli. Ana/isis har-monik data hujan stasiun Pujon menunjukkan tiga harmonik. Sumbangan ra-gam terjadi pada harmonik III sebesar 61% dan diikuti oleh Harmonik I dan II masing-masing mempunyai ragam 4% dan 2%. Kurva Harmonik pada stasiun Ngantang relatif hampir sama antara harmonik I, II dan III dengan sumbangan ragam bet#turut-turut sebesar 7%, 4% dan 3%. Dengan demtktan dapat disusun dua persamaan deret Fourier untuk kedua stasiun tersebut.
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