The Validation of the Transformation Between an Old Geodetic Reference Frame and a Modern Reference Frame, by Using External Space Techniques Sites: The Case Study of the Hellenic Geodetic Reference System of 1987

Abstract

Many of the old geodetic reference frames which realized in the previous decades using classical observations carry biases. These biases are mainly caused due to the problematic observations and/or the tectonic motion. That is the case of the official Greek geodetic reference frame which consists of classical and satellite observations. Herein, we present a rigorous approach of the reconstruction of the Greek official reference frame based on the modern geodetic reference frames and their ability to express the spatial position and the dynamic change of the stations. We applied the rigorous approach to ninety stations located in Greece and we compare it with the officially accepted procedure. We found a consistency at 59.4cm between the rigorous and the officially accepted approaches, respectively. The associated mean bias estimation was estimated at 51.4 cm, indicating the resistance of a rather large amount of systematic effects. In addition, the observed discrepancies between the two approaches show great inhomogeneity all over the country. Keywords: Geodetic Reference System (GRS), GRS Datum, transformation between two GRS, ETRS89Resumo: Muitos dos antigos sistemas geodésicos de referência que foram realizados nas últimas décadas por meio de observações clássicas apresentam erros. Estes erros são principalmente oriundos de problemas nas observações e/ou movimentos tectônicos. Este é o caso do sistema geodésico de referência Grego, que consiste de observações clássicas e por satélites. Neste trabalho apresenta-se uma abordagem rigorosa para a reconstrução deste sistema geodésico de referência baseada nos sistemas de referência modernos e na sua habilidade de expressar a posição espacial e as mudanças dinâmicas das estações de referência. Foi aplicada a abordagem rigorosa a noventa estações localizadas na Grécia e foi realizada uma comparação com o procedimento oficialmente aceito. Encontrou-se uma consistência de 59,4 cm entre os procedimentos rigoroso e oficial. A estimativa de erro associada foi de 51,4 cm, indicando grande efeito sistemático. Além disso, as discrepâncias observadas entre as duas abordagens demonstram falta de homogeneidade ao longo do país.Palavras-chave: Datum Clássico; Transformação; Campo de velocidade; ETRS89; Sistema de referência.

Realization of time-dependent geocentric datum transformation parameters for Nigeria

“…Since the MINNA datum for Nigeria was realized based on classical methods of surveying, it is known to be subjected to biases as a result of poor observations and techniques [8]. Also, Nigerian MINNA datum is faced with biases such as inaccuracies of the scale factor by compression of the Clarke 1880, poor definition of origin, geoidal height model absence and difficulty in datum parameters determination [30].…”

“…Therefore, with these inherent errors, there is the need to move away from the still-in-use MINNA datum and adopt a new datum that is geocentric in nature as done in countries like Australia (GDA2020), China (CTRF2000), Indonesia (DGN1995), Malaysia (GDM2000), New Zealand (NZGD2000), USA (NAD83), amongst others [7,20]. Studies of [5,8,12,18,25] further justify the need for this study, in that coordinates of points anywhere in the world will change with time. Therefore, by integrating velocity, epoch and episodic deformation information, locations of points can be kept on track.…”

Expressing the NOANET GNSS network to the Hellenic Geodetic Reference System of 1987 (HGRS1987): A synergy between Geodesy and Geodynamics

“…We should notice that the ETRF2005 is a defunct reference frame. The transformation scheme relies on the transformation from the ITRF2005 to the ETRF2005 (see e.g Doukas et al 2017…”