Covariance Function Modelling in Local Geodetic Applications Using the Simplex Method

Gaetani, Carlo Iapige De; Cazzaniga, N. E.; Barzaghi, Riccardo; Reguzzoni, Mirko; Betti, B.

doi:10.1590/s1982-21702016000200019

Cited by 2 publications

(2 citation statements)

References 6 publications

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“…Least Squares Collocation (LSC) has been widely applied in geodesy for estimating the gravity field of the Earth both locally and globally (Gaetani, 2016). The main aspect of this method is the statistical interpretation of proper covariance functions of the gravity data, which describe the spatial correlation of the observations, as a kernel function.…”

Section: Least Squares Collocationmentioning

confidence: 99%

Regional geoid for Nepal using Least-Squares Collocation

Timilsina¹,

Willberg²,

Rol³

2021

Terr. Atmos. Ocean. Sci.

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An airborne gravity survey for Nepal was carried out in December 2010 with the primary goal to provide data for a new national geoid model, which will in turn provide gravity information for the future global gravity field EGM2020. This gravity data is used again to determine the regional geoid model (NPG20) for Nepal using Least-Squares Collocation (LSC) with Remove-Compute-Restore approach.In comparison to the previously computed geoid model, Nepal Geoid 2011 (NPG11) using EGM2008, this study applies XGM2019e as the global model. The comparative study shows, XGM2019e fits the airborne gravity observations much better than EGM2008 in the study area. The computation of geoid heights is done using LSC with the determination of proper covariance function for the gravity data, while the previous study includes a combination of LSC for downward continuation and spherical FFT for the calculation of the geoid. This contribution evaluates the benefit of our two main adaptions.The comparative study of geoids, NPG11 and NPG20 showed that there exist significant differences between these models especially in the area where the elevation is higher than 7000 m. The data analysis of the study showed that the currently available airborne gravity data was not sufficient to provide high frequency gravity signals and the significant differences in these geoid models was solely related to the different handling of the high-frequency gravity field component of the background model, i.e. EGM2008 and XGM2019e.

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Section: Least Squares Collocationmentioning

confidence: 99%

Regional geoid for Nepal using Least-Squares Collocation

Timilsina¹,

Willberg²,

Rol³

2021

Terr. Atmos. Ocean. Sci.

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“…This figure highlights the area where sediments were removed. In order to compute the accuracy of volume determination, the field of residual between the total station point cloud and the DSM was used also to model empirically the covariance of the error of DSM (Papoulis 1977;De Gaetani et al 2015), assuming that the error is spatially isotropic and homogeneous at each epoch. Thus, two covariance matrices C 1 and C 2 can be computed for the DSM at each time and the variance of the volume difference can be computed as…”

Section: Fusino Dam Case Studymentioning

confidence: 99%

Measuring the volume of flushed sediments in a reservoir using multi-temporal images acquired with UAS

Pagliari

Rossi

Passoni

et al. 2016

Geomatics, Natural Hazards and Risk

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We compute the volume of flushed sediments in a dam using photogrammetry-based multi-temporal surveys with an unmanned aerial system (UAS). Coping with sediments accumulation and erosion in reservoir is a living topic in modern hydraulics of dams, since the increase of sediment may reduce the reservoir capacity, endanger dam's stability, and represent an economical loss. As a result, a number of remedies can be considered, such as flushing or mechanical removal. To evaluate the performance of these operations, measuring the volume of removed sediments and their spatial distribution is important. Here, we show that photogrammetry from UASs represents a suitable solution to reckon the volume of removed sediments. The case study is the Fusino dam (Lombardia region, Northern Italy). Two surveys were performed, before and after sediment removal. In both cases, the flight has been planned with an average flight height equal to 65 m, leading to a mean ground sample distance (GSD) equal to 0.013 m. The 22 ground control points (GCP) used to adjust the photogrammetric block were measured with both global navigation satellite system (GNSS) and a total station. Each survey produced a cloud of about 40 million of points. Moreover, the digital surface model (DSM) produced by each photogrammetric flight has been validated with sample points measured with a robotic total station. Results show high consistency between computed DSMs and validation dataset, with a mean height difference equal, respectively, to 0.003 and ¡0.004 m considering the two different surveys, with a standard deviation around 0.05 m in both the cases. The volume of sediments flushed was estimated to be about 26,000 m 3 , which represents about 2%À3% of the total reservoir capacity. We estimated also a 6% difference in terms of reservoir capacity between the present condition and the no-sediments condition.

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Covariance Function Modelling in Local Geodetic Applications Using the Simplex Method

Cited by 2 publications

References 6 publications

Regional geoid for Nepal using Least-Squares Collocation

Regional geoid for Nepal using Least-Squares Collocation

Measuring the volume of flushed sediments in a reservoir using multi-temporal images acquired with UAS

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