RELIABILITY OF THE GPS CARRIER-PHASE FIX SOLUTION UNDER HARSH CONDITION

Once the unknown integer ambiguity values are resolved, the GPS carrier phase observation will be transformed into a millimeter-level precision measurement. However, GPS observation are prone to a variety of errors, making it a biased measurement. There are two components in identifying integer ambiguities: estimation and validation. The estimation procedure aims to determine the ambiguity's integer values, and the validation step checks whether the estimated integer value is acceptable. Even though the theory and procedures for ambiguity estimates are well known, the topic of ambiguity validation is still being researched. The dependability of computed coordinates will be reduced if a false fixed solution emerges from an incorrectly estimated ambiguity integer value. In this study, the reliability of the fixed solution obtained by using several base stations in GPS positioning was investigated, and the coordinates received from these bases were compared. In a conclusion, quality control measures such as employing several base stations will improve the carrier phase measurement's accuracy.

Land Subsidence Study Using Geodetic GPS and GAMIT/GLOBK Software (Case Study : Banjarasri Village and Kedungbanteng Village, Tanggulangin District, Sidoarjo Regency)

Floods are one of the natural disasters that always occur in various regions in the Republic of Indonesia. Several flood points were recorded in Banjarasri Village and Kedungbanteng Village, Tanggulangin District, Sidoarjo Regency. There is an allegation that one of the factors causing the flooding in the two villages was caused by land subsidence. Therefore, it is necessary to conduct a study to monitor the magnitude of land subsidence in the area. In this study, the Global Positioning System (GPS) observation method was used. The research was carried out by collecting data from six points which were carried out over three periods of time, namely on 22 - 27 October 2020, 24 - 29 November 2020, and 24 - 29 March 2021. Based on the results of processing and analyzing GPS data, the observed values for shift and motion vectors are obtained. There were five points of land subsidence statistically, which included BM02, BM03, BM04, BM05, and BM06 with values of respectively 3.6 cm, 7.3 cm, 5.9 cm, 4.8 cm, and 5.2 cm. The horizontal position vector moves in various ways, where BM01 and BM04 move to the southwest as far as 2.5 cm and 1.9 cm, BM05 moves to the southeast with a shift of 3.3 cm, and BM06 moves to the northeast with a shift of 4.2 cmFloods are one of the natural disasters that always occur in various regions in the Republic of Indonesia. Several flood points were recorded in Banjarasri Village and Kedungbanteng Village, Tanggulangin District, Sidoarjo Regency. There is an allegation that one of the factors causing the flooding in the two villages was caused by land subsidence. Therefore, it is necessary to conduct a study to monitor the magnitude of land subsidence in the area. In this study, the Global Positioning System (GPS) observation method was used. The research was carried out by collecting data from six points which were carried out over three periods of time, namely on 22 - 27 October 2020, 24 - 29 November 2020, and 24 - 29 March 2021. Based on the results of processing and analyzing GPS data, the observed values for shift and motion vectors are obtained. There were five points of land subsidence statistically, which included BM02, BM03, BM04, BM05, and BM06 with values of respectively 3.6 cm, 7.3 cm, 5.9 cm, 4.8 cm, and 5.2 cm. The horizontal position vector moves in various ways, where BM01 and BM04 move to the southwest as far as 2.5 cm and 1.9 cm, BM05 moves to the southeast with a shift of 3.3 cm, and BM06 moves to the northeast with a shift of 4.2 cm.

Signatures of northeast monsoon activity and passage of tropical cyclones in the integrated precipitable water vapour estimated through GPS technique

Water vapour represents a key variable in the atmospheric processes. The importance of assessing water vapour availability in the atmosphere is indicated by the currently prevalent use of vast number of observing systems, both of in-situ and remote sensing types, designed to measure its distribution accurately over wide ranges of space and time scales. One of the widely used techniques world over is use of ground based GPS receivers for measurement of total precipitable water vapour in the atmosphere over the station. One such system is being operated at Chennai since 2007. An analysis of hourly Integrated Precipitable Water Vapour (IWV) data received from this system during Northeast Monsoon (NEM) season of 2008 shows the signatures of NEM activity and the passage of tropical disturbances like cyclonic storms and depressions in the vicinity of the GPS observation site. The GPS based IWV values are found to agree fairly well with radiosonde based IWV values and a good correlation exists between them. The IWV values obtained from GPS based system are found to be consistent with activity of Northeast monsoon with increase (decrease) of IWV during active (weak) phase of NEM 2008. The general expected trend of increase in IWV with approach of tropical systems in the vicinity of GPS station, reaching maximum during closest approach and again its decrease with increase of distance from the station is noticed. The diurnal variation of GPS based IWV estimates during NEM 2008 does not appear to be significant.

Geodynamics of the Talish region according to earthquake source mechanisms and GPS-stations

В статье представлено описание тектонического строения иссле- дуемого региона, а также проанализирована геодинамика Талышского региона по данным механизмов очагов землетрясений. Целью работы являлось определить скорости современных горизонтальных сме- щений отдельных тектонических блоков Талышского региона и проанализировать влияние их на сильные землетрясения, произошедшие за 2016 и 2019 гг. Методы исследования. На основе метода полярности первых вступлений продольных волн были проанализированы механизмы очагов землетрясений. Анализ показал, что в исследуемом регионе в основном преобладает тип подвижки – взброс и сдвиг. Углы паде- ния для подвижек разных типов превышают 45°, что свидетельствует о достаточно крутом погружении зон разломов. Это согласуется с тем, что в исследуемой зоне большинство поперечных разломов имеет углы падения сместителей 50‑90°, то есть углы, достаточно близкие к вертикали. Основное влияние на сейсмическую активность оказывают Талышский, Предталышский, Ярдымоинский и Астаринские разло- мы. Результаты исследования. На основе полученных результатов была построена схематическая карта ориентации осей сжатия и растяжений исследуемых сильных землетрясений. На основе катакластиче- ского анализа механизмов очагов землетрясений c ml>3,0. Установлено, что большая часть исследуемой территории подвержена сжатию, сдвиги отмечены в районе Лерика и Ярдымлы. Для Талышского региона установлены три основных типа подвижек: взбросы (36 %), сдвиги (34 %) и сбросы (30 %). Анализ ско- ростей горизонтальных движений по данным GPS-наблюдений показал движение поверхности земной коры в С-СВ направлении относительно Евразии. Отмечено уменьшение скорости в пунктах наблюдений PQLG, XNGG, ZKTG, ATGG, IMLG и GBLG, расположенных перпендикулярно к Главному Кавказкому Над- вигу. Пункты GPS-наблюдений, расположенные вдоль ГКН, показывают уменьшение скорости в западном направлении. С-СВ движение земной поверхности интерпретируется как одна из причин накопления на- пряжений на этом надвиге. In addition, the article provides a description of the tectonic structure of the region under study, and also analyzes the geodynamics of the Talish region using data from the mechanisms of earthquake sources. Aim of the work was to determine the velocities of modern horizontal displacements of individual tectonic blocks of the Talish region and to analyze their influence on strong earthquakes that occurred in 2016 and 2019yy. Methods. Based on the method of polarity of the first arrivals of longitudinal waves, the mechanisms of earthquake sources were analyzed. The analysis showed that in the studied region the type of movement predominates – reverse faults and strike-slips. The angles of incidence for motions of various types exceed 45°, which indicates a rather steep immersion of fault zones. This is consistent with the fact that in the studied zone the majority of transverse faults have angles of incidence of 50‑90°, that is, angles quite close to the vertical. The main influence on seismic activity is exerted by the Talish, Predtalish, Yardimli and Astara faults. Results. Based on the results obtained, a schematic map of the orientation of the compression and extension axes of the studied strong earthquakes was constructed. On the basis of a cataclastic analysis of the mechanisms of earthquake sources with ml> 3.0, it was established that most of the study area is subject to compression, strike-slip faults were noted in the Lerik and Yardimla regions. For the Talish region, three main types of shifts are established: reverse faults (36 %), strike-slips (34 %) and normal faults (30 %). An analysis of horizontal velocities according to GPS observations showed the movement of the surface of the earth’s crust in the northwest direction relative to Eurasia. A decrease in speed was noted at the observation points PQLG, XNGG, ZKTG, ATGG, IMLG and GBLG located perpendicular to the Main Caucasian Thrust. GPS observation points located along the Main Caucasian Thrust show a decrease in speed in a westerly direction. C-NE motion of the earth’s surface is interpreted as one of the reasons for the accumulation of stresses on this thrust

The Diurnal Variations of GPS PWV near Poyang Lake in China during Midsummer

With the 1 h-averaged data of atmospheric precipitable water vapor (PWV) for 2015–2018 retrieved from 18 ground-based Global Positioning System (GPS) observation stations near Poyang Lake (PL), China, the diurnal variations of the PWV during midsummer (July-August) are studied by the harmonic method. Results show that significant diurnal variations of PWV are found at the 18 GPS stations. The harmonics with 24 h cycle (diurnal cycle) over PL (i.e., Duchang and Poyang) and Nanchang city only have about 50% (or even smaller than 50%) of variance contribution with the amplitude of about 0.2 mm, while above 70% (or even 80%) of variance contribution occurs elsewhere around PL, with the amplitude of about 0.9 mm. The harmonics with diurnal cycles in most stations peak from afternoon to evening (i.e., 1200-2000 LST), but one exception is Duchang site, where the diurnal cycle peaks in the morning (i.e., 1000 LST). Moreover, the harmonics with 12 h cycle (semidiurnal cycle) have the relatively uniform amplitude of about 0.2 mm, but their variance contributions show uneven distribution, with the contributions of about or above 50% in PL and Nanchang city (the semidiurnal cycles peak about 0000 LST or 1200 LST) and below 30% (or even 10%) in other areas. The preliminary diagnosis analysis shows that the diurnal variation of the low-level (below 850 hPa) air temperature (increasing after the sunrise, decreasing after the sunset, and peaking around 1400-1800 LST) may be responsible for the diurnal cycle. Moreover, in PL (Duchang and Poyang) and Nanchang city, the effects (heating or cooling) of lake and urban, the diurnal variation of the 10 m wind over PL, and the acceleration of PL on overlying air also contributed to the diurnal variation of PWV.