Tsunamigenesis Revisited

<p>When modelling tsunamis and assessing tsunami hazard, it is frequently necessary to make simplifying assumptions in order to reduce the problem to one which is computationally tractable within a reasonable period of time. In this paper, we examine the key factors controlling the generation of the initial sea surface wave and present a series of clear and simple guidelines for real-world problems. We also provide number of computational resources (a tsunami loader) which may be utilised with existing tsunami propagation codes (e.g. COMCOT) to modify the initial sea-surface way, where necessary.</p><p> </p><p>Most tsunami modelling codes operate under the assumption that the initial sea surface wave is identical to the seafloor perturbation. Yet this is only true for large tsunami sources (Kajiura 1963). With our tsunami loader we model the tsunamigensis process and the formation of the initial sea-surface wave. Critically, the diffusive effect of the water column above the deforming seafloor is accurately addressed, which can result in a substantial decrease in the energy in the initial sea-surface wave.</p><p> </p><p>For example, let us consider a rectangular uplifting patch on the seafloor, at a depth of 4km. For a 4x4km square patch, the diffusive effect will result in an energy reduction of 90%. Even if one of those dimensions is 100 times larger, such that we have a relatively large 400x4 km uplifting region, the energy reduction is still 70%. We find the shortest dimension of the uplifting patch provides a strong control on the energy of the initial sea-surface wave, and consequential tsunami. If we move to a 40x40 km square patch we find the reduction is now 20%, and 400x40 km patch is now a relatively modest, but non-negligible 12%.</p><p> </p><p>We also include other effects such as the time-dependence of seafloor deformation, which also reduces the potential tsunami energy, and horizontal advection of topography, which conversely increases the potential tsunami energy, in our analysis of the tsunamigenesis process. Currently implemented for fault sources, we are working to include landslide and volcanic sources.</p>

Capabilities of Chinese Gaofen-3 Synthetic Aperture Radar in Selected Topics for Coastal and Ocean Observations

Gaofen-3 (GF-3), the first Chinese spaceborne synthetic aperture radar (SAR) in C-band for civil applications, was launched on August 2016. Some studies have examined the use of GF-3 SAR data for ocean and coastal observations, but these studies generally focus on one particular application. As GF-3 has been in operation over two years, it is essential to evaluate its performance in ocean observation, a primary goal of the GF-3 launch. In this paper, we offer an overview demonstrating the capabilities of GF-3 SAR in ocean and coastal observations by presenting several representative cases, i.e., the monitoring of intertidal flats, offshore tidal turbulent wakes and oceanic internal waves, to highlight the GF-3’s full polarimetry, high spatial resolution and wide-swath imaging advantages. Moreover, we also present a detailed analysis of the use of GF-3 quad-polarization data for sea surface wind retrievals and wave mode data for sea surface wave retrievals. The case studies and statistical analysis suggest that GF-3 has good ocean and coastal monitoring capabilities, though further improvements are possible, particularly in radiometric calibration and stable image quality.

Rancang Bangun, Uji Coba dan Analisis Hasil Pengukuran Instrumen Pengukur Tinggi Gelombang Permukaan Laut (Design, Testing and Results Analysis of Sea Surface Wave Height Instrument Measurement)

Gelombang merupakan salah satu parameter penting yang berpengaruh terhadap dinamika yang terjadi di pantai, namun pengukuran langsung gelombang relative masih jarang dilakukan. Makalah ini menguraikan hasil rancang bangun, uji coba dan analisis hasil pengukuran instrument pengukur tinggi gelombang pemukaan laut. Instrumen dirancang menggunakan sensor accelerometer yang diletakkan pada sebuah pelampung untuk dapat mengikuti pergerakan partikel air di permukaan laut dan sebagai pengendali utama kerja instrument digunakan mikro kontroler ATmega32. Data dari sensor kemudian disimpan pada MMC/SD card dan dilakukan analisis data lapang menggunakan perangkat lunak MATLAB. Analisis data menggunakan zero crossing analysis untuk mendapatkan karakteristik gelombang. Pengukuran dilakukan dengan system penambatan pada satu titik tetap pada dasar perairan, dan uji lapang dilakukan di perairanWakatobi, Sulawesi Tenggara pada Juli 2013 di kedalaman 8 meter. Dari hasil analisis data pada lokasi pengamatan selama 22 jam perekaman menunjukkan karakteristik gelombang, yaitu rata-rata tinggi gelombang sebesar 0.72 meter; tinggi gelombang signifikan (Hsig) 1.32 meter dan tinggi gelombang maksimum (Hmax) 2.58 meter. Sebagai kesimpulan, instrument pengukur tinggi gelombang yang telah dikembangkan dan diuji menunjukkan bahwa instrument telah bekerja dengan baik dalam mengukur tinggi gelombang dan data hasil pengukuran ini dapat dianalisis lebih lanjut. Kata kunci: accelerometer, instrumen, gelombang, wakatobi Ocean wave is one of the important parameter that affects the dynamic of the coastal. Ocean monitoring that provides real-time data are needed to help better understand of the ocean. The objectives of this study are designing and constructing an instrument to measure the wave height. The instrument was designed by using accelerometer sensor and it was placed on a buoy to follow the water particle movement on the sea surface. Electronics system used was ATmega32 microcontroller as the main control of this instrument. Data from the sensors were stored on the MMC/SD card. MATLAB software was used to analyse the data by using zero crossing method to get the wave properties. The instrument measured at one fixed point by mooring system. This instrument had undergone fields test in Wakatobi, Southeast Sulawesi and was moored at 8 meters depth. Data analysis in 22 hours recording in location showed that the average wave height was 0.72 meters; the significant wave height (Hsig) was 1.32 meters and the maximum wave height (Hmax) was 2.58 meters.In conclusion, the wave buoy instrument that we have developed and tested showed that it work well as intended in measuring wave height, and the measured data can be further analyzed. Keywords: accelerometer, instrument, wave, wakatobi