Validating methods to infer mass changes from satellite gravity measurements using Synthetic Earth Gravity Modelling

Leakage properties of isotropic and anisotropic filters used to recover mass changes from space gravity observations are studied. These are done through the use of gravity induced by simulated mass changes within a closed-loop validation procedure. Results show that the use of filter techniques can introduce significant errors introducing distortions between recovered and simulated mass. Previously not well known, the study revealed that leakage is dependent on the geographic location if the mass change considered

Spatio-temporal analysis of GRACE gravity field variations using the principal component analysis

Gravity Recovery and Climate Experiment (GRACE) mission has amplified the knowledge of both static and time-variable part of the Earth’s gravity field. Currently, GRACE maps the Earth’s gravity field with a near-global coverage and over a five year period, which makes it possible to apply statistical analysis techniques to the data. The objective of this study is to analyse the most dominant spatial and temporal variability of the Earth’s gravity field observed by GRACE using a combination of analytical and statistical methods such as Harmonic Analysis (HA) and Principal Component Analysis (PCA). The HA is used to gain general information of the variability whereas the PCA is used to find the most dominant spatial and temporal variability components without having to introduce any presetting. The latter is an important property that allows for the detection of anomalous or a-periodic behaviour that will be useful for the study of various geophysical processes such as the effect from earthquakes. The analyses are performed for the whole globe as well as for the regional areas of: Sumatra- Andaman, Australia, Africa, Antarctica, South America, Arctic, Greenland, South Asia, North America and Central Europe. On a global scale the most dominant temporal variation is an annual signal followed by a linear trend. Similar results mostly associated to changing land hydrology and/or snow cover are obtained for most regional areas except over the Arctic and Antarctic where the secular trend is the prevailing temporal variability.Apart from these well-known signals, this contribution also demonstrates that the PCA is able to reveal longer periodic and a-periodic signal. A prominent example for the latter is the gravity signal of the Sumatra-Andaman earthquake in late 2004. In an attempt to isolate these signals, linear trend and annual signal are removed from the original data and the PCA is once again applied to the reduced data. For a complete overview of these results the most dominant PCA modes for the global and regional gravity field solutions are presented and discussed

Pemodelan Deformasi Gunung Sinabung Untuk Memprediksi Posisi Pusat Tekanan Magma Dengan Model Yokoyama Menggunakan Data Citra SAR Metode PS-InSAR

Indonesia merupakan negara tektovulkanik dengan terdapat 129 gunung api aktif. Keberadaan gunung api tentunya berdampak positif, seperti daerah sekitar gunung menjadi subur dan berdampak negatif karena sering terjadinya bencana. Salah satu gunung aktif di Indonesia adalah Gunung Sinabung. Adanya aktivitas magma pada gunung api aktif mengakibatkan perubahan bentuk baik akibat pergerakan dan pergeseran tanah pada permukaan gunung api yang disebut deformasi. Deformasi dapat diketahui metode terestrial dengan menggunakan theodolit, Sipat darat dan metode ekstra-tersrial dengan pengamatan GPS dan pengolahan data citra SAR dengan metode pengolahan  InSAR, D-InSAR, MT-InSAR yang meliputi, PS-InSAR dan SBAS. Penelitian ini dilakukan untuk mengetahui deformasi yang terjadi pada gunungapi Sinabung menggunakan metode PS-InSAR dilanjutkan memodekakan posisi sumbertekan magma dengan model Yokoyama. Model Yokoyama mengasumsikan kerak bumi tersusun atas ruangan yang elastis, dan sumber tekanannya adalah sebuah ruang kecil berbentuk spherical dengan tekanan hidrostatik yang bersifat searah dan perluasannya bersifat radial. Data SAR yang digunakan, terdiri dari terdiri dari 7 citra akusisi ascending dan 8 citra akusis descending pada tanggal akuisisi 1 Oktober hingga 31 Desember 2020. Dengan melakukan pengolahan citra secara ascending dan descending, LOS velocity rate dapat ditranformasikan ke nilai pergeseran horizontal dan vertikal.  Hasil pengolahan PS-InSAR menunjukkan LOS velocity rate berkisar 394,1 mm/tahun sampai 320,7 mm/tahun arah  ascending dan  secara descending  menunjukkan LOS velocity rate berkisar -277,5 mm/tahun sampai 31.5,8 mm/tahun. Setelah melakukan decomposition LOS velocity rate, diperoleh nilai displacement titik PS pada arah horizontal dan vertikal pada titik PS1 adalah (0,288; -0,037) meter , titik PS2 adalah (0,004; 0,010) meter dan titik PS3 adalah (0,041, -0,084) meter. Sehingga diperoleh posisi pusat tekanan magma menggunkan nilai  pergeseran horizontal pada gunung sinabung berdasarkan model yokoyama terletak pada koordinat 03°10’02,64”LU dan 98°24’26,64”BT pada kedalaman 11850 meter. Sementara, Posisi pusat tekanan magma menggunkan nilai  pergeseran vertikal terletak pada koordinat 03°09’54,72,64”LU dan 98°24’18,36”BT pada kedalaman 11250 meter

Analisis Deformasi Gunung Raung Menggunakan Teknologi Differential Interferometry Synthetic Aperture Radar (DInSAR)

Gunung Raung merupakan salah satu gunung api aktif Indonesia yang terletak di bagian timur pulau Jawa. Erupsi yang terjadi menyebabkan adanya perubahan (deformasi) pada permukaan gunung Raung. Deformasi yang ada pada permukaan gunung Raung dapat diukur dengan berbagai teknologi, salah satunya yaitu menggunakan teknologi DInSAR. Hasil menunjukkan bahwa metode two-pass dan three-pass teknologi DInSAR dapat di terapkan untuk mengetahui deformasi pemukaan gunung Raung, yang menunjukkan terjadinya deformasi mayoritas ada di kaldera gunung Raung. Dari kedua metode, nilai LOS displacement yang dihasilkan memiliki nilai yang sama pada kaldera bagian utara dan selisih relatif kecil, yakni 1 mm pada kaldera bagian selatan. Sedangkan perbedaan terdapat pada kaldera bagian timur dan barat, yang memiliki selisih hasil cukup besar, yakni ~40 mm. Metode three-pass interferometry dapat menunjukkan hasil deformasi yang signifikan di banding dengan metode two-pass, yang dapat dilihat di kaldera bagian timur dan barat, jika dikaitkan dengan kondisi geologi gunung Raung yang mengalami aktivitas dari bulan Agustus 2015 hingga awal tahun 2016 menurut laporan PVMBG. Meskipun begitu untuk mengetahui besar nilai deformasi yang akurat perlu dilakukan pengukuran secara langsung di lapangan

Analysing Peatland Subsidence in Pelalawan Regency, Riau Using DInSAR Method

Indonesia is known as a country that have the largest peatland in Southeast Asia. Peatland is often used in agricultural, plantation and settlement purposes. Before, peatland must be drained as one procedure of land clearing activity. However, an error during this process often comes and cause some problems such as drought, subsidence and even forest fire. A characteristic of peatland, irrewetable, making peatland is very hard to be wet after getting dry. This research is aiming to observe peatland subsidence in Pelalawan Regency, Riau using SAR data Sentinel 1-A. The method that we use is Differential Interferometry Synthetic Aperture Radar (DInSAR). Beside Sentinel 1-A, DEM STRTM is used to remove topographic effect. Temporal baseline in this research is about one year between two acquisition data. The first pair of data is acquired in June 2015 and June 2016. While the second pair of data is acquired in June 2016 and July 2017. By using two pass DInSAR method, the process will yield two images of Line of Sight (LOS) Displacement during each period. The first DInSAR (June 2015-June 2016) reveals that the highest subsidence that occur in peatland is about 109,113 mm and the highest uplift is about 108,089 mm. The second DInSAR (June 2016-July 2017) reveals that the highest peat subsidence is about 251,842 mm and the highest uplift is about 73,715 mm

POLA MUSIM DI INDONESIA TAHUN 2002 SAMPAI 2016 BERDASARKAN EQUIVALENT WATER HEIGHT (EWH)

Season is the weather that is clearly visible at certain timescales. Based on its geographical location, the most striking seasonal variation in Indonesia is rainfall. Seasonal changes are also called weather changes that result from surface water interactions such as the water cycle. This shows that weather variations are related to changes in water mass on earth. Water availability can be seen from the Equivalent Water Height (EWH) variations obtained from gravity satellite data Gravity Recovery and Climate Experiment (GRACE) then the used of TRMM (Tropical Rainfall Measuring Mission) satellite data can be used to observe rainfall as well as supporting data for GRACE satellites. From the results of GRACE gravity satellite data processing, the largest EWH value was 27.298 cm in January 2015 and the smallest EWH value of -29.816 cm was in June 2004 on Sumatra Island. During the years 2002 to 2016 Changes in seasonal patterns occurred in 2010 and 2015, each of which was caused by extreme changes in rainfall and by the occurrence of El Nino events

GNSS Accuracy Analysis for Efficiency of Ground Control Point (GCP) Measurement

Nowadays, the Global Navigation Satellite System (GNSS) has a significant role in the field of surveying and mapping, especially in determining the coordinates of ground control points for rectifying aerial photography, satellite imagery and airborne lidar. Each of these rectification processes requires a different coordinate accuracy from 5 to 20 cm. This research will conduct GNSS measurement with radial method and observation length to see how far the required accuracy will be fulfilled. This research examined ten Ground Control Points (GCPs) using the GNSS receiver in Surabaya. Each GCP was observed for 2 hours with 15” epoch and then they were processed with an interval of 15 minutes such as 15’, 30’, 45’, 60’, 75’, 90’, 105’ and 120’ with the radial method. In general, the results showed that the longer the GNSS observation the more accurate coordinates from 0.923 m (15 minutes) to 0.011 m (120 minutes) will be achieved. Measurement of GCPs for aerial photogrammetry, High-Resolution Satellite Image (HRSI), and airborne LIDAR needs 15’ observation both of radial and network method for less than or equal 10 km of baseline. For 10 – 20 km, the radial method needs 90’ observation for photogrammetry, 75’ observation for HRSI, 45’ GCPs observation of airborne LIDAR, but for network methods need 45’ observation for photo and HRSI and 30’ observation for Airborne LIDAR.

Evaluating GPS CORS Data for Crustal Deformation Analysis in East Java

The tectonic setting of Indonesia is very complex due to its location on the boundaries of several major tectonic plates. The complexity of the tectonics also makes Indonesia prone to natural disasters such as earthquakes, tsunamis, volcanic eruptions etc. Crustal deformation caused by the tectonics activities can be monitored using geodetic techniques such as Global Positioning System (GPS) survey, Interferometry Synthetic Aperture Radar (InSAR) processing, etc. In this research, we analyze the crustal deformation in the northern part of East Java using ten GPS Continuously Operating Reference Stations (CORS) data provided by the Indonesian Geospatial Information Agency from 2015 to 2018. The results showed the horizontal movement toward southeast for all the stations. The horizontal velocity rates are range between 2.63 cm/yr and 2.96 cm/yr. For the vertical displacements, nine stations are subject to subsidence with the rates range from -0.021cm/yr to -0.4 cm/yr that we suspect related to the geological settings of the study area

Studi Pengamatan Penurunan Permukaan Tanah Menggunakan Metode PS-InSAR di Daerah Blok Cepu

Pengambilan bahan cair dari dalam tanah dapat berupa pengambilan air tanah atau ekstraksi minyak bumi dari dalam tanah. Pengambilan bahan cair dapat menjadi salah satu faktor pemicu terjadinya penurunan tanah. Salah satu wilayah eksploitasi minyak bumi adalah Blok Cepu, yang terletak di Kabupaten Blora, Jawa Tengah dan Kabupaten Bojonegoro, Jawa Timur. Saat ini Blok Cepu diproyeksikan menjadi tulang punggung produksi minyak nasional dengan produksi minyak mencapai 225 ribu barel per hari. Dengan besarnya eksploitasi tersebut, perlu dilakukan pengamatan terkait kemungkinan adanya penurunan tanah di wilayah tersebut. Studi pengamatan dilakukan dengan menggunakan metode PS-InSAR dengan data Sentinel-1A dari akhir tahun 2014 hingga 2019 menggunakan perangkat lunak SARProz. Dari hasil pengolahan data menunjukkan bahwa penurunan tanah terjadi di semua blok dari Blok Cepu, kecuali di Blok D yang tidak terdeteksi titik PS. Penurunan tanah tertinggi terjadi di Blok dengan rata-rata laju mencapai -27,75 mm/tahun. Selama rentang akuisisi citra, jumlah produksi minyak pun berangsur angsur meningkat sehingga dilakukan potongan melintang untuk Blok A dimana terdapat cukup banyak sumur di wilayah tersebut