Judul: Internal Wave Detection and Quantification Using SIMRAD EK80 Broadband Echosounder Instrument in Padang Bay Waters Bali
Abstrak: Internal wave adalah peristiwa yang terjadi di laut dangkal dan laut dalam, dimana kemunculan internal wave hanya dapat terjadi jika kolom air terstratifikasi akibat adanya perbedaan densitas massa air. Penelitian ini bertujuan mendeteksi peristiwa internal wave, serta mengukur nilai acoustic backscatter dari internal wave terjadi di Selat Lombok. Data yang digunakan adalah hasil pengukuran instrument broadband echosounder SIMRAD EK80 frekuensi 200 kHz tipe pulsa continuous wave (CW) dengan data pendukung elevasi muka air, suhu, salinitas, dan densitas dari Conductivity Temperature Depth (CTD) “yoyo” selama 24 jam. Nilai hambur balik didapatkan dengan analysis menggunakan perangkat lunak Sonar5-Pro. Echogram menunjukkan adanya pembentukan nonlinearinternal wave disertai dengan adanya turbulent terjadi pada saat gelombang pasang membawa massa air dengan densitas berbeda melewati topografi kasar di Selat Lombok. Nilai backscatter hasil segmentasi berentang dari -75 dB sampai -59 dB., Internal waves are events that occur in shallow sea and deep sea, where the appreanced of internal waves can only occurs if the water column is stratified due to differences in water mass density. This study aimed to detect internal wave events, as well as measure the acoustic backscatter value of internal waves occurring in the Lombok Strait. The data used is the measurement result of SIMRAD EK80 broadband echosounder instrument with frequency of 200 kHz continuous wave (CW) pulse type with supporting data for water level elevation, temperature, salinity, and density from Conductivity Temperature Depth (CTD) “yoyo” for 24 hours. The backscatter value was obtained by analysis using the Sonar5-Pro software. Echogram showed the formation of nonlinear internal waves accompanied by the presence of turbulence that occur when high tidal waves carry water masses from different density through rough topography in Lombok Strait. The backscatter value of the segmentation results range from -75 dB to -59 dB.
Keyword: Backscatter, Broadband, Continuous Wave, Internal Wave, Tidal Wave

Judul: Karakteristik Gelombang Internal di Laut Bali dari Data Sentinel-1A dan Pemodelan Laut
Abstrak: Gelombang internal yang merambat ke Laut Bali diduga berasal dari bagian selatan Selat Lombok, dimana terdapat ambang laut (sill) Nusa Penida sebagai area pembangkitan gelombang internal. Pendeteksian rona permukaan gelombang internal dapat menggunakan citra satelit radar Sentinel-1A serta pemodelan sirkulasi laut CROCO. Penelitian ini bertujuan untuk mendeskripsikan rona permukaan dari gelombang internal, serta mendeskripsikan mekanisme pembentukan dan penjalaran gelombang internal di Laut Bali. Citra radar menunjukkan paket gelombang internal di Laut Bali tersebar di dua wilayah, yaitu di wilayah pembangkitan yaitu di dekat Selat Lombok, dan di wilayah propagasi yaitu di bagian barat dan utara Laut Bali. Panjang puncak gelombang internal semakin meningkat seiring pergerakan gelombang ke wilayah propagasi. Laut Bali memiliki tipe pasang surut campuran cenderung ganda, dengan pergerakan ke arah utara dan selatan secara bergantian pada fase pasang dan surut secara berturut-turut. Arus meridional di wilayah sill dominan bergerak ke arah utara pada fase pasang menuju surut dan mengakibatkan peningkatan kedalaman piknoklin pada bagian utara sill hingga kedalaman 400 m. Penelitian ini menunjukkan adanya pergerakan arus ke arah atas dan bawah secara bergantian setelah arus melewati sill dan membuktikan terbentuknya puncak dan lembah dari gelombang internal., Internal waves (IWs) that propagate into Bali Sea are expected to originate from the southern part of Lombok Strait, which has Nusa Penida sill as IWs generating area. IWs detection was carried out using Sentinel-1A radar satellite imagery and CROCO ocean circulation modeling. This study aims to describe the surface hue of the IWs, also describe the mechanism of IWs formation and propagation in Bali Sea. The radar image shows that wave packets are spread over two areas, namely in the generation area near Lombok Strait, and in the propagation area, namely in the western and northern parts of Bali Sea. The IWs crest length will increase as it moves into the propagation region. Bali Sea has a mixed semidiurnal tidal type, with currents in the sill area move north and south alternately during the high and low tide phases. Meridional currents in the sill area move northward during the high to low tide phase, resulting in the subsidence of the pycnocline in the northern part to 400 m. This study shows an alternating upward and downward movement of vertical currents in the northern part of the sill and indicate the occurrence of peaks and valleys of IWs.
Keyword: Bali Sea, CROCO, internal wave, sill, Sentinel-1A

Judul: Approximation of the Median of Poisson Distribution Using the Relation of Poisson-Gamma Distribution
Abstrak: A major drawback of median is that median cannot usually be defined in closed form, even in the cases where their distribution functions are known. This study gives an approximation of the closed form for the median of the Poisson distribution by using the relation of Poisson-Gamma distribution. The approximation uses elementary techniques based on the monotonicity of certain sequences involving tail probabilities of the Poisson distribution and the Central Limit Theorem. Furthermore, a closed form expression for the mean absolute deviation 􀜧|􀜰􀰒 􀵆 􀜯􀝁􀝀􁈺􀜰􀰒􁈻| is also studied. The median is relevant because of the fact that it minimizes the mean absolute deviation of a Poisson random variable (􀜰􀰒􁈻 by considering median as central tendency.
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