Fig 6 - uploaded by Selassie Mayunga
Content may be subject to copyright.
Source publication
Citations
... The acquisition data are engaged from short, medium or long wavelength frequency. However, data multi discipline sources need proper engage in order to minimal the bias [12]. The acquisitions data engaged are GGM, DEM, terrestrial and airborne gravity data as well as GNSS leveling data. ...
... The KTHKVGM2020Gr av geoid model evaluated by parameter model and correlated surface in order fitted quasi geoid with GNSS leveling denoted as equation (12) [27]. ...
Klang Valley is a fast-growing area and its development shall be equivalent with precise measurements for a precise vertical reference. Thus, existing vertical reference with 3 centimetres (cm) is inadequate and processed with complicated remove-compute-restore (RCR) procedure. Apart from this, areas such as Klang Valley should better than one (1) centimetre level vertical reference. Meanwhile processing method for vertical reference should be simplified and easy tasking. Because of that, methodology for this study is by employing the least squares modification of Stokes formula with additive corrections (KTH). This approach fully uses anomalies rather than residuals which it is more complicated. At the same time, the additive corrections estimator introduced combining the direct and indirect computations method. Datasets used in this study were refined rigorously prior to the gridding scheme in cross validation, free air anomalies, as well as anomaly correction. The KTHKVGM2020 gravimetric and geometric geoid models are evaluated from the reference position using GNSS levelling. It found that KTHKVGM2020 Geoid model is better than one (1) centimetre for Klang Valley area with efficiency processing method. Therefore, the study is an essential in future to develop high-precision geoid model with efficient methods particular for urban and rapidly developing areas.
... As currently in Tanzania there is no comprehensive national geoid model which has been released for the public use, several attempts have been done to develop and validate models that best fit in the Tanzania region. Mayunga (2016( , p. 268, cited in Silyvester, 2013 indicates the developed model which was used to compute point values of a gravimetric geoid using short wavelength which later on were compared with GPS/leveling derived geoid heights. The differences obtained and the biases between the geometric and gravimetric geoid models were recorded. ...
... The validation process should be done by comparing geoid heights obtained from the global models against the GPS/levelling derived geoid heights. However, it is worth mentioning that though many researchers have reviewed the need of National Geoid Model in Tanzania, such as Ulotu (2009) and Mayunga (2016), the validation context has always remained a research area of interest due to lack unified geodetic network. This paper checks the compatibility of the EGM08, EGM96, AGP03 and the TZG13 geoid models against the existing GPS/levelling -derived geoid in Tanzania by using the weighted mean approach. ...
... The Tanzania Primary Levelling Network (TPLN) was designed in the 1960 and implemented between 1961 and 1964 (Mayunga, 2016). ...
This paper compares the geoid heights from the Global Models-EGM2008, and EGM1996 against the GPS/Levelling-derived geoid heights in Tanzania. For the sake of comparison, the existing Preliminary African Geoid Model (AGP03) and the Tanzania Geoid Model (TZG13) are also tested against the GPS/levelling derived geoid heights at 13 benchmarks selected within the Tanzania Primary Levelling Network (TPLN). The comparisons of geoid heights obtained from these geoid models against the GPS/levelling geoid heights have been performed in absolute sense. Due to the fact that the ellipsoidal heights (h) obtained from the GPS do not provide the actual positions of points on the geoid, the orthometric heights (H) are needed. Broadly speaking, the orthometric heights are obtained through traditional sprit levelling which is a labour intensive work. In order to convert the ellipsoidal height (h) determined from GPS applications to orthometric height, the Geoid heights are needed. The spatial positions of these benchmarks have been recently determined at cm-level accuracy (with respect to ITRF2005) through a GPS campaign. The statistics of the differences between GPS/levelling-derived geoid heights (NGPS) and the corresponding geoid heights obtained from the available three geoid models (Nmodel) suggests that, AGP03 model is the most suitable at this moment. The Root Mean Square (RMS) fit of the AGP03 geoid model against the GPS/levelling data is 53.8 cm, which is a 2 times better fit compared to the Global Geopotential Models (EGM08 and EGM96) in the area of interest. On the other hand, the RMS of the height differences between the TZG13 and the GPS/leveling derived heights was 74.7cm. The study suggests that AGP03 geoid model is closer to the GPS/levelling geoid observations in comparison to EGM08 model in Tanzania.
