The Potential for Observing African Weather with GNSS Remote Sensing

Abstract

When compared to the wide range of atmospheric sensing techniques, global navigation satellite system (GNSS) offers the advantage of operating under all weather conditions, is continuous, with high temporal and spatial resolution and high accuracy, and has long-term stability. The utilisation of GNSS ground networks of continuous stations for operational weather and climate services is already in place in many nations in Europe, Asia, and America under different initiatives and organisations. In Africa, the situation appears to be different. The focus of this paper is to assess the conditions of the existing and anticipated GNSS reference network in the African region for meteorological applications. The technical issues related to the implementation of near-real-time (NRT) GNSS meteorology are also discussed, including the data and network requirements for meteorological and climate applications. We conclude from this study that the African GNSS network is sparse in the north and central regions of the continent, with a dense network in the south and fairly dense network in the west and east regions of the continent. Most stations lack collocated meteorological sensors and other geodetic observing systems as called for by the GCOS Reference Upper Air Network (GRUAN) GNSS Precipitable Water Task Team and the World Meteorological Organization (WMO). Preliminary results of calculated zenith tropospheric delay (ZTD) from the African GNSS indicate spatial variability and diurnal dependence of ZTD. To improve the density and geometry of the existing network, countries are urged to contribute more stations to the African Geodetic Reference Frame (AFREF) program and a collaborative scheme between different organisations maintaining different GNSS stations on the continent is recommended. The benefit of using spaced based GNSS radio occultation (RO) data for atmospheric sounding is highlighted and filling of geographical gaps from the station-based observation network with GNSS RO is also proposed.

Modelling weighted mean temperature in the West African region: implications for GNSS meteorology

“…The term PWV is used in this report. The relationship between ZWD and water vapour content in the atmosphere expressed by IWV and PWV is reported by Isioye et al () and expressed in Equation : …”

“…The ZTD at each GNSS station was estimated daily within a 24 h window session. Details of the adopted strategy for processing the GNSS data from the NIGNET stations has already been already reported (Isioye et al , ). PWV was estimated from the ZTD values and other constants defined in Equation alongside the different T m models.…”

“…The zenith tropospheric delay (ZTD) represents the total delay through the atmosphere in the direction of the zenith. The ZTD comprises the hydrostatic (ZHD) and wet (ZWD) components of the delay (Bosy et al , ; Isioye et al , , ), as shown in Equation : …”

Design of a web-based GNSS data management system at HartRAO: preliminary results

“…Space Geodesy has proven to have the capabilities to observe these geophysical processes with very high temporal, spatial and spectral resolutions through global networks of diverse equipment (VLBI, SLR, GNSS and DORIS), each making a valuable and unique contribution. The GNSS technology has been used as a multipurpose technique to study planet Earth with high accuracy levels, for example, detecting tectonic plate motion at millimetre accuracy, time transfer applications using GNSS (Defraigne et al, 2007) and studying atmospheric water vapour for applications in meteorological studies (Isioye et al, 2015).…”

Performance Evaluation of Blind Tropospheric Delay correction Models over Africa

“…However, in this contribution, this issue is addressed more comprehensively considering the peculiarities of the African GNSS network. Most GNSS stations on the African continent are characterised by the lack of collocated meteorological sensors, as it is required for such to be collocated with the GNSS antenna if the GNSS data are to be processed for integrated water vapour content determination (Isioye et al, 2015).…”