Measurement and Analysis of Ocean Current using High- Frequency (HF) Radar Observation in the Bali Strait

Abstract

High-Frequency (HF) Radar is an instrument using radio waves to measure ocean currents and waves remotely. This technology has many advantages, including has unprecedented spatial and temporal resolution, can operate in any weather condition, and is not dangerous for the environment. However, HF Radar's research is still limited in Indonesia. This research aimed to analyze the tidal and residual current in the Bali Strait in July 2020. Radial velocity from two HF Radar sites is combined to obtain the total currents. Current data from HF Radar were compared with Acoustic Doppler Current Profiler (ADCP) data to investigate its accuracy. Surface current data were analyzed using harmonic analysis to separate tidal and residual currents. Comparison between HF Radar and ADCP data are in good agreement for meridional current with a very high correlation of 0.813 and a small RMSE value of 0.22 m/s. Harmonic analysis shows that the dominant currents are tidal currents. The current direction was northward (southward) at flood (ebb), with maximum northward (southward) velocities are 2.17 m/s (2.97 m/s), respectively. The residual current has a random pattern, slightly faster northward than southward, and has similar spectral with the wind.

Karakteristik Arus Laut Permukaan dari High Frequency Radar pada Musim Timur di Selat Bali

“…Panjang gelombang yang dipancarkan oleh HF Radar ialah sebesar 0-10 m dengan frekuensi 3-30 MHz (Barrick & Snider, 1977). Perbandingan rata -rata selama tiga jam dari kecepatan meridional antara data arus HF Radar dan ADCP di Selat Bali selama 10 hari menunjukkan nilai korelasi tinggi sebesar 0.813 dan RMSE 0.22 m/s (Firdaus et al, 2021). Perbandingan analisis statistik antara kecepatan arus laut permukaan dari HF Radar dan ADCP dengan lowpass filter 36 jam, didapatkan nilai RMSE dan IA 6,4 cm/s dan 0,99.…”

“…Karakteristik arus permukaan laut di perairan sekitar Bali telah dikaji oleh Theoyana et al (2015) dan Tanto et al (2017) di perairan Selat Badung dan Teluk Benoa dengan menggunakan data arus pengukuran ADCP. Di wilayah Selat Bali, penelitian arus permukaan dengan data HF Radar dilakukan oleh Setiawan (2020) pada musim barat yaitu Desember -Februari dan oleh Firdaus et al, (2021) yang hanya dilakukan pada bulan Juli tahun 2020. Supriyadi et al (2021) menyatakan bahwa pada bulan Juni, Juli, Agustus (musim timur) di Selat Bali memiliki kecepatan arus yang lebih tinggi dari bulan -bulan lainnya.…”

Multistatic estimation of high-frequency radar surface currents in the region of Toulon

“…In the case of the Bali Strait, the tidal velocity can reach a maximum of 2.97 m.s −1 and 2.17 m.s −1 during ebb and flood, respectively. Data from two HFRs operating at 26.275 MHz were tested against ADCP (Acoustic Doppler Current Profiler) data from Firdaus et al (2021). Good agreement was found between the two datasets with a correlation coefficient of 0.813 and an RMSE of 0.22 m.s −1 for the meridional velocity.…”