Irwan Gumilar

Gedebage district is presently experiencing rapid and mass infrastructure development and becoming one of the developed districts in Bandung, Indonesia. A football stadium, several luxury housing, the grand mosque of West Java province, and a business center have been built in this district. However, it is well known that the Gedebage district has turned into one of the Bandung districts that suffers from land subsidence phenomena. Since 2000, the Gedebage district has suffered land subsidence at an average rate of 10 cm per year and becoming one of the fastest sinking districts in Bandung. This fast land subsidence phenomenon is suspected of affecting the infrastructure in this district. Therefore, this work aims to capture the current subsidence rate in the Gedebage district using the geodetic approach of the combination of the Global Navigation Satellite System (GNSS) with Interferometric Synthetic Aperture Radar (InSAR) and investigate the impact of land subsidence on infrastructures in Gedebage district. We use GNSS campaign datasets from the years 2016 and 2019. Each GNSS campaign was performed at least 10-12 hours of observations. We also utilize a similar period of 2016 to 2019 for the InSAR datasets. Utilizing both GNSS and InSAR datasets, we can capture the subsidence with the rate reaching 4 -15 cm per year between 2016 and 2019, and it occurs uniformly in this district. The impact of land subsidence occurred in almost all urban areas in the Gedebage district. These impacts include cracks in buildings, bridges and roads, and also tilted buildings.

In a global scale, the accuracy of Real Time Precise Point Positioning (RT-PPP) method in Global Navigation Satellite System (GNSS) point positioning is within cm to dm level. Unlike other conventional method in GNSS point positioning which used differential data to minimize the error sources, RT-PPP used additional orbit correction, clock correction and other atmospheric correction to minimize the error since RT-PPP is an absolute point positioning method. Currently, there are several providers who give the orbit correction and clock correction in real-time. Not only in the land area, this service can be also used in sea area. Thus, this research aims to analyse the differences in point determination derived from RT-PPP method by using several service providers in sea area. The RT-PPP data acquisition used three different receivers with unique service correction, namely RTX correction from Trimble Net R9 receiver, ATLAS correction from Hemisphere receiver and Veripos correction from Hemisphere receiver. All these antennas were set up on the ship with a controlled distance and the point coordinates were estimated from Seribu Island to Ancol, Jakarta with a different time interval for each receiver due to the technical limitations. To assess the point positioning stability, the distance between each antenna derived from point positioning then evaluated by comparing to its controlled distance. The results indicate that a time lag is found in Trimble Net R9 compared with the others, and it should be corrected first before applying the further analysis. In general, after removing the outliers, the distance and the precision between each antenna between Veripos-ATLAS is 4.472 ± 0.040 m, RTX-ATLAS is 2.054 ± 0.077 m and RTX-Veripos is 3.947 ± 0.060 m. Therefore, RT-PPP method can be used as an alternative in precise point positioning in sea area.

Kiblat merupakan arah yang dituju umat Muslim ketika melakukan ibadah shalat. Terdapat beberapa dalil baik Al-Quran ataupun As-Sunnah yang mewajibkan ibadah shalat untuk menghadap kiblat. Perkembangan teknologi penentuan posisi dan algoritma pengukuran arah sangat memungkinkan untuk menentukan arah kiblat secara teliti, sekalipun untuk daerah yang tidak memungkinkan untuk melihat Kakbah. Tujuan penelitian ini yaitu menentukan mekanisme perhitungan arah kiblat dan rekonstruksinya menggunakan teknologi GNSS. Metodologi yang dilakukan yaitu dengan menerapkan beberapa metode penentuan posisi menggunakan GNSS untuk menentukan arah kiblat dan perhitungan arah kiblat di atas bidang elipsoid menggunakan metode Vincenty. Rekontruksi arah kiblat dilakukan dengan menerapkan irisan koreksi normal geodesik, koreksi skew normal, dan koreksi defleksi vertikal. Hasil penelitian menunjukkan bahwa metode statik, RTK, dan RTPPP GNSS dapat digunakan untuk menentukan arah kiblat. Penerapan metode Vincenty di atas bidang elipsoid untuk penentuan azimut memperlihatkan arah yang tepat ke arah Kakbah. Untuk keperluan rekonstruksi arah kiblat, pemberian koreksi normal geodesik, koreksi skew normal, dan koreksi defleksi vertikal dapat meningkatkan ketelitian sekitar 2 menit. Khusus untuk pengukuran titik backsight dengan RTK, azimut yang didapatkan berbeda sekitar 2 menit dibandingkan dengan metode statik. Perbedaan 2 menit ini menyebabkan arah Kakbah bergeser sekitar 3,6 km, walaupun masih tetap berada di kota Mekah. Dengan demikian dapat disimpulkan bahwa untuk mendapatkan ketelitian yang tinggi untuk pengukuran tepat ke arah kiblat maka harus digunakan metode penentuan posisi statik, menggunakan metode Vincenty di atas elipsoid untuk pengukuran azimutnya, serta menerapkan koreksi irisan normal geodesik, koreksi skew normal, dan koreksi defleksi vertikal untuk rekonstruksinya.

As the modernized Global Navigation Satellite System (GNSS) method, Real Time Kinematic (RTK) ensures high accuracy of position (within several centimeters). This method uses Ultra High Frequency (UHF) radio to transmit the correction data, however, due to gain and power issues, Networked Transport of RTCM via Internet Protocol (RTCM) is used to transmit the correction data for a longer baseline. This Research aims to investigate the performance of short to long-range single baseline RTK GNSS (Up to 80 KM) by applying modified LAMBDA method to resolve the ambiguity in carrier phase. The RTK solution then compared with the differential GNSS network solution. The results indicate that the differences are within RTK accuracy up to 80 km are several centimeter for horizontal solution and three times higher for vertical solution.

Land subsidence by definition is the lowering of ground level from certain elevation references. The rates of subsidence can commonly vary between 1 and 20 centimeters per year and even more in certain places. Subsidence produces impacts such as infrastructure damage, problems with drainage, wider expansion of flood water, as well as tidal inundation (flooding by sea water at coastal areas experiencing land subsidence). These impacts are quite costly. All this is disastrous. In a number of regions of Indonesia, land subsidence and negative impacts in the shape of flooding and tidal inundation clearly exist. In Jakarta and Bandung we can see that the subsiding areas close to rivers frequently suffer from flooding. Tidal inundation is a regular feature at subsiding coastal areas such as Jakarta, Blanakan, Semarang, and Demak. Since these negative impacts are clearly formed a disaster while mitigation and or adaptation is still a big homework, in this case for better adaptation and mitigation in the future, understanding deeply the correlation of land subsidence and flooding is necessary as discused in this chapter. We conclude that the correlation is quite tremendous and indeed producing a disaster.

The demand for more precise positioning method using GNSS (Global Navigation Satellite System) in Indonesia continue to rise. The accuracy of GNSS positioning depends on the length of baseline and the distribution of observed satellites. BeiDou Navigation Satellite System (BDS) is a positioning system owned by China that operating in Asia-Pacific region, including Indonesia. This research aims to find out the contribution of BDS in increasing the accuracy of long baseline static positioning in Indonesia. The contributions are assessed by comparing the accuracy of measurement using only GPS (Global Positioning System) and measurement using the combination of GPS and BDS. The data used is 5 days of GPS and BDS measurement data for baseline with 120 km in length. The software used is open-source RTKLIB and commercial software Compass Solution. This research will explain in detail the contribution of BDS to the accuracy of position in long baseline static GNSS measurement.

Due to oil and gas exploitation, offshore oil and gas platform may experience subsidence. Continuing subsidence may deform the platform infrastructures, adding the risk for any failure on the platform objects. The failure means disaster. Therefore the subsidence information is mandatory for risk assessment and safety requirement. Repeatedly or continuous monitoring of accurate positions on the platform by using global navigation satellite system global positioning system (GNSS GPS) technology may reveal the changing of even small positions which are representing subsidence on the platform. This chapter will be deeply discussed on the use of GNSS GPS technology for offshore oil and gas platform subsidence monitoring, especially in Indonesia, the archipelago country where long baseline between reference station in the land and monitoring station at the sea slightly exists. The capability and especially the high performance of this technology on deriving subsidence information along with data sample of long baseline will be highlighted.

West Java is one of the provinces in Indonesia which is prone to landslide. Over the past few years, landslides in this area have resulted in a large number of victims. One of the areas in West Java with the highest risk of landslide occurrence is Rancabali Ciwidey. In general, the morphology around the landslide location is steep hills, with the slope > 30° and the altitude between 1550 – 1865 m above sea level. Several indications of ground movements can be seen in the form of slumps and cracks on the village roads and tea plantation, as well as slanting trees and electricity poles. The ground movement monitoring in this area is necessary for disaster mitigation. Several methods that can be used to monitor the landslide are using Terrestrial Laser Scanner (TLS) and robotic total station. This research aims is monitoring the landslide using these methods. The methodology used in this research is by obtaining the scanning data using TLS C-10 and Robotic total station MS05 measurements to obtain the coordinates of monitoring point clouds and prism. The TLS software that we used are Cyclone 8.1 and Maptek I-Site. For robotic total station, the software that we used is MSP software. These method hopefully can be used for early warning system of landslide in Rancabali area.

Talaga Bodas Volcano, located near the border of Garut and Tasikmalaya regencies, West Java, Indonesia, is an active stratovolcano whose apparent shape is mainly dominated by the steep-side-cone type. Hence, monitoring Talaga Bodas Volcano to mitigate its potential hazard is extremely necessary. In this research, potential hazards are studied by observing and monitoring the deformation of the Talaga Bodas Crater using the geodetic Terrestrial Laser Scanner (TLS) tool. TLS is a relatively new positioning method in geodesy. TLS is able to obtain the position of the object points (point clouds) in a huge amount and high precision in a relatively short time. This research aims at identifying the deformation and also rock textures and structure around the Crater of Talaga Bodas. The methodology used in this research is by obtaining the scanning data using TLS in 2012 and 2015 and GPS measurements to obtain the coordinates of the reference points. The data processing methods consist of several steps, namely target to target registration, filtering, georeference, and analysis of the registered point clouds. These steps were done using the cyclone 8 software. Registered point clouds show the 3 dimension of the crater. It was found that the average values for the down-lift and up-lift deformation around the crater are about -6.4 cm and 5.1 cm, respectively. Reflected point clouds show the differences of the intensity color of the surface around the crater. This result indicates the differences of the rocks texture and structure around the crater.

Survey Pemetaan Model Bangunan Tiga Dimensi (3D) Metode Terrestrial Laser Scanning untuk Dokumentasi As-Built Drawing