LOCAL EVALUATION OF EARTH GRAVITATIONAL MODELS, CASE STUDY: IRAN

Ismael Foroughi,Yosra Afrasteh,Abdolreza Safari,Sabah Ramouz

doi:10.3846/20296991.2017.1299839

Ismael Foroughi, Yosra Afrasteh + Show 2 more

Open Access

https://doi.org/10.3846/20296991.2017.1299839

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Abstract

Global gravity models are being developed according to new data sets available from satellite gravity missions and terrestrial/marine gravity data which are provided by different countries. Some countries do not provide all their available data and the global gravity models have many vague computational methods. Therefore, the models need to be evaluated locally before using. It is generally understood that the accuracy of global gravity models is enough for local (civil, mining, construction, etc.) projects, however, our results in Iran show that the differences between synthesized values and observation data reach up to ∼300 mGal for gravity anomalies and ∼2 m for geoid heights. Even by applying the residual topographical correction to synthetized gravity anomalies, the differences are still notable. The accuracy of global gravity models for predicting marine gravity anomalies is also investigated in Persian Gulf and the results show differences of ∼140 mGal in coastal areas. The results of evaluating selected global gravity models in Iran indicate that the EIGEN-6C4 achieves the lowest RMS for estimating the geoid heights. EGM08 predicts the closest results to terrestrial gravity anomalies. DIR-R5 GOCE satellite-only model estimates the low-frequency part of gravity field more accurately. The best prediction of marine gravity anomalies is also achieved by EGM08.

Highlights

Earth Gravitational Models (EGMs) are divided into two different types: satellite-only models and satellite-combined models
Global gravity models can be used directly to compute the quasigeoid height and they can be converted to geoid by computing topographical correction of geoidto-quasigeoid separation
The effect of high frequency topographic signals was removed by considering the Residual Terrain Model (RTM); this is shown in the color-map of residuals in (Fig. 7) which has smoother trend rather than (Fig. 4); it can be seen by narrower histograms in (Fig. 8)

Summary

Introduction

Earth Gravitational Models (EGMs) are divided into two different types: satellite-only models and satellite-combined models. Satellite-only models are computed using the satellite missions such as GRACE, GOCE, CHAMP and Lageos and provide only the low frequency (maximum degree/order 300) part of gravity field and they are homogenous everywhere as they are independent from any terrestrial data. The height datums are often defined by synthesizing values from EGMs. many researchers within the frame of projects like: mining, geological and extraction etc. Need an estimation of gravity anomalies over study area and synthesized values from EGMs are the only source of data instead of terrestrial gravity anomalies. This is done usually without any error estimation of these models

Results

Discussion

Conclusion