Abstract:The focus of this study is the assessment of the main range and geophysical corrections needed to derive accurate sea level time series from satellite altimetry in the Indonesia seas, the ultimate aim being the determination of sea level trend for this region. Due to its island nature, this is an area of large complexity for altimetric studies, a true laboratory for coastal altimetry. For this reason, the selection of the best corrections for sea level anomaly estimation from satellite altimetry is of particular relevance in the Indonesian seas. The same happens with the mean sea surface adopted in the sea level anomaly computation due to the large gradients of the mean sea surface in this part of the ocean. This study has been performed using altimetric data from the three reference missions, TOPEX/Poseidon, Jason-1 and Jason-2, extracted from the Radar Altimeter Database System. Analyses of sea level anomaly variance differences, function of distance from the coast and at altimeter crossovers were used to assess the quality of the various corrections and mean sea surface models. The selected set of corrections and mean sea surface have been used to estimate the sea level anomaly time series. The rate of sea level rise for the Indonesian seas was found to be 4.2 ± 0.2 mm/year over the 23-year period (1993-2015).

Using the ionospheric total electron content (TEC) data from ground-based Global Navigation Satellite System (GNSS) receivers in Japan, we compared ionospheric responses to five explosive volcanic eruptions 2004–2015 of the Asama, Shin-Moe, Sakurajima, and Kuchinoerabu-jima volcanoes. The TEC records show N-shaped disturbances with a period ~ 80 s propagating outward with the acoustic wave speed in the F region of the ionosphere. The amplitudes of these TEC disturbances are a few percent of the background absolute vertical TEC. We propose to use such relative amplitudes as a new index for the intensity of volcanic explosions. Graphical Abstract

Innovations in GNSS technology have been increased rapidly with significant development in geodetic and navigation types due to its low-cost. One of the advantages of low-cost GNSS is in its price tags, which varies from the geodetic type. This study determines GNSS Tersus BX316 and Comnav K706 Oem Board’s equivalent abilities compared to Stonex S800 GNSS geodetic. The post-processing and precise point positioning were used to determine the activities of RTK. In conclusion, the data obtained by BX316 are closer to those from Stonex S800.

Kenaikan muka air laut (sea level rise) merupakan konsekuensi dari perubahan iklim yang memiliki dampak signifikan terhadap kehidupan sosial, ekonomi, dan infrastruktur, serta ancaman tenggelamnya kawasan pesisir Indonesia yang ditinggali oleh 60% penduduknya. Sejak akhir abad ke-19, perubahan kedudukan air laut diamati dari stasiun pasang surut di sepanjang garis pantai. Namun, pengamatan stasiun pasang surut memiliki keterbatasan dalam jumlah, distribusi, dan jangkauannya, serta adanya pengaruh land subsidence. Oleh karena itu, penelitian ini menganalisis tren kenaikan muka air laut Indonesia menggunakan data pengamatan misi referensi satelit altimetri, yaitu Topex/Poseidon, Jason 1, Jason 2, dan Jason 3. Setelah dilakukan least square intercalibrated dan a-seasonal-trend decomposition procedure based on loess diketahui bahwa laju sea level rise di Indonesia +4,5 mm/tahun pada periode tahun 1993-2018. Tren linier bernilai positif ini menunjukkan bahwa ketinggian muka laut di Indonesia akan terus meningkat dengan persamaan y = 4,6x-9133,5 mm, dimana y adalah sea level anomaly dan x adalah waktu. Sehingga berdasarkan hasil tersebut dapat dilakukan perencanaan pra-kejadian terhadap dampak dari sea level rise yang akan mendatang.