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: Pendekatan matematis pada pembangkitan gelombang internal di Selat Makassar
Abstrak: In Makassar strait, which is located between the islands of Kalimantan and Sulawesi, the fascinating phenomena of internal waves can be observed. Internal waves are gravity waves that oscillate within, rather than on the surface of, a fluid medium. Internal waves occur in the interior of water in seas, which exist due to a difference in density of the lower and upper layer of the fluid. Typical characteristics of internal waves are their large wavelength and amplitude. This research aims to derive a dispersion relation based on the basic equations of two-layers fluid, to determine the internal waves in the Makassar Strait, and to create a simulation of generation of the internal waves using the software Mathematica. The results show that the generation mechanism of these internal waves can be formulated based on the Kelvin-Helmholtz dispersion relation for a two-layers fluid. This dispersion relation can also be used as classification criteria of instability of internal waves. Emphasis is given to the types of instability, i.e. temporal and spatial instability. Temporal stability occurs if current velocity in the upper part of fluid is less than its critical velocity. For the spatial instability, internal waves in Makassar strait can be approximated for both layers as deep water waves. The spatially stable region is reached when the frequency of the lower part of fluid is smaller than the critical frequency, or when the frequency of the upper part of fluid is larger than the critical frequency.
Keyword: Sea current, Generation of internal waves, Pycnocline

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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