Global geopotential models from Satellite Laser Ranging data with geophysical applications: A review

Botai, Christina M.; Combrinck, Ludwig

doi:10.4102/sajs.v108i3/4.662

Cited by 3 publications

(1 citation statement)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This was consistent with the results from an analysis conducted using data from the closest rainfall gauge station at Serere. In a study Botai and Combrinck (2012) indicated 16 th pentad as median onset and planting window 12 th -20 th pentad (6-10 th dekad). These findings are inferred in the NDVI SoS-based information where the mean onset date was the 9 th dekad for the 14 pixels surveyed indicating vegetation development after the onset of the rainy season.…”

Section: Areas At Risk Of a Dry Spell At The Beginning Of The Growing Seasonmentioning

confidence: 98%

Investigating false start of the main growing season: A case of Uganda in East Africa

Ocen

Bie

Onyutha

2021

Heliyon

View full text Add to dashboard Cite

False start of the growing season (Fsos) is a component of the onset variability related to agronomic drought that adversely impact on agricultural production and productivity. In the sub-Saharan Africa (SSA) where agriculture heavily depends on rainfall, the Fsos tends to create confusion among farmers on when to start planting crops thereby affecting seed germination and normal growth after emergence. In this paper, we focus on the Fsos and the occurrence of dry spell especially before the Start of growing Season (SoS). We take advantage of the existing rainfall estimates (CHIRPS) and remotely sensed data for vegetation performance (NDVI) over the period 1999–2017 in combination with local knowledge derived from farmers to map out areas at risk of (i) dry spell at the SoS, and (ii) false timing of SoS or high probability of occurrence of the Fsos. We found that the North Eastern part of Uganda (8.8% of arable area) were at risk of dry spell throughout each year. However, the greater North (58.1% of arable area) was prone to dry spell during the onset of the March–May season. Areas in the South Western (3.7%) region were at risk during the onset of the September–November season. The probability that a location in Uganda experiences an Fsos falls between 0-53%. The findings in this study are vital for planning of predictive adaptation to the impacts of climate variability on agriculture amid struggle aimed at tackling food insecurity challenge in the SSA.

show abstract

Section: Areas At Risk Of a Dry Spell At The Beginning Of The Growing Seasonmentioning

confidence: 98%

Investigating false start of the main growing season: A case of Uganda in East Africa

Ocen

Bie

Onyutha

2021

Heliyon

View full text Add to dashboard Cite

show abstract

A comparative study on the parametrization of a time-variable geopotential model from GRACE monthly solutions

Gschwind,

Seitz,

Dalheimer

et al. 2024

Acta Geod Geophys

View full text Add to dashboard Cite

The gravity field of the Earth is time-dependent due to several types of mass variations which take place on different time scales. Usually, the time-variability of the gravitational potential of the Earth is expressed by the monthly determination of a static geopotential model based on data from gravity field missions. In this paper, the variability of the potential is parameterized by a functional approach which contains a polynomial trend and periodic contributions. The respective parameters are estimated based on the monthly solutions derived from the GRACE and GRACE-FO gravity field mission up to a maximum degree of expansion $$n_\text {max}=96$$ n max = 96 . As a preliminary data analysis, a Fourier analysis is performed on selected potential coefficients from the available monthly solutions of the GFZ. The indicated frequency components are then used to formulate a time-dependent analytical approach to describe each Stokes coefficient’s temporal behaviour. Different approaches are presented that include both polynomial and periodic components. The respective parameters for modelling the temporal variability of the coefficients are estimated in a Gauss-Markov model and tested for significance by statistical methods. Extensive comparative numerical studies are carried out between the newly generated model variants and the existing monthly GRACE, GRACE-FO and the existing time dependent EIGEN-6S4 solutions. The numerical comparisons make it clear that estimated models based on all available monthly solutions describe the essential periods very well, but such monthly events that deviate strongly from the mean behaviour of the signal show less precision in the space domain. Models that are estimated based on fourteen consecutive monthly solutions, covering one selected year, represent the amplitudes much more precise. The statements made apply to four initial data used, which are filtered to varying degrees. In particular, DDK2, DDK5 and DDK8, as well as unfiltered coefficients were used. For all the model approaches used, it can be seen that the potential coefficients contain up to about $$n\approx 40$$ n ≈ 40 in case of DDK5 periodically signals with annual, semi-annual or quarterly, as well as Luna nodal periods and do not vary significantly beyond that degree. Only an offset can be estimated significantly for all Stokes coefficients.

show abstract

Assessments of recent Global Geopotential Models based on GPS/levelling and gravity data along coastal zones of Egypt

et al. 2023

View full text Add to dashboard Cite

The orthometric height has an essential role in a variety of civil engineering projects and it is defined as the length of the curved plumbline from a point (on the earth surface) to its intersection with the geoid surface. Leveling process is considered as the most accurate technique for obtaining these heights. However, regardless of its potentials, it is tedious, costly, and time consuming. Recently many organizations and research centers have developed multi Global Geopotential Models (GGMs) depending on several types of available gravity and height datasets to estimate orthometric heights from GNSS measurements. In this study, we present an evaluation and assessment of the accuracy of five of recent and popular GGMS: XGM2016, XGM2019e, EIGEN-6C4, GO_CONS_GCF_2_TIM_R6e, and EGM2008 using actual 145 GNSS/leveling points and 96 terrestrial gravity points. The goal of this research is to find the best fit model along the study area located along the coastal zones of Egypt with distances of about 1,970 km for further determination of geoid modeling at regional scale. The selection of these areas basically was due to their developmental, urban, and economical importance and their continuous need for protection works to fight against the coastal erosion caused by climate change and global warming. The results indicated that for geoid undulation, GO_CONS_GCF_2_TIM_R6e model is the best fit GGM for the estimation of geoid model along Mediterranean Sea coastal line, while XGM2019e_2159 model is the best suitable for coastal line of the Red Sea. And regarding the gravity anomalies, the most reliable GGMs for this study area are XGM2019e_2159 and EIGEN-6C4 for Bouguer and free-air gravity anomaly, respectively.

show abstract

Global geopotential models from Satellite Laser Ranging data with geophysical applications: A review

Cited by 3 publications

References 52 publications

Investigating false start of the main growing season: A case of Uganda in East Africa

Investigating false start of the main growing season: A case of Uganda in East Africa

A comparative study on the parametrization of a time-variable geopotential model from GRACE monthly solutions

Assessments of recent Global Geopotential Models based on GPS/levelling and gravity data along coastal zones of Egypt

Contact Info

Product

Resources

About