The Paul Melchior Medal

With this Medal the outstanding scientists with a huge experience and influence in the Tidal Community are awarded. The previous Awardees are:

1. Paul Melchior (1997, Bruxelles, Belgium).
2. Hans-Georg Wenzel (2000, Mizusawa, Japan).
3. John Goodkind (2004, Ottawa, Canada).
4. Bernard Ducarme and Tadahiro Sato (2008, Jena, Germany).
5. Houtse Hsu (2013, Warsaw, Poland).

After 2-step procedure we are pleased to inform that 2016 Paul Melchior Medal goes to prof. Trevor F. Baker.

Paul Melchior Medal 2016 Awarded to Trevor F. Baker

Scientific Achievements of Trevor F. Baker (prepared by B. Ducarme).

After a PhD in nuclear physics Trevor F. Baker joined the Proudman Oceanographic Laboratory in Bidston (Liverpool) in 1969. His career was devoted to the interaction between oceanic tides, ocean tide loading (OTL) and Earth tides, using ground based measurements as well as space techniques. He is certainly one of the few scientists who developed an expertise in both techniques. He performed a lot of tidal observations with a reduced number of collaborators. In the 1970s Farrell had already published precise numerical evaluation methods for OTL computations but there was still a lack of global ocean tides models. However, models for the seas around Great Britain were already available. OTL in tidal tilt measurements is very sensitive to the structure of the crust and lithosphere. As a rule of the thumb there is a direct correspondence between distance to the load mass and depth of the most sensitive layer. As ocean tides amplitudes are very large around British Islands, it was a perfect location to study crustal and subcrustal structures using tiltmeters records. Trevor F. Baker worked a lot on that subject in the 1970s with G.W. Lennon. They installed different types of clinometers at Bidston and Llanrwst (Tomaschek and Verbaandert-Melchior horizontal pendulums, Askania vertical pendulums). At the end of the 1970’s Trevor F. Baker launched, in collaboration with R.J. Edge and G. Jeffries, a project at Bassenthwaite in Lake District with the installation of tiltmeters in boreholes (Askania and Hughes bubble tiltmeters). Tidal tilt measurements have excellent signal/noise ratios i.e. precisions, but they have significant systematic errors which decrease the actual accuracies below that required for geophysical interpretation, the more serious one being the strain-tilt coupling in cavities. Careful measurements at a small number of sites were used to show these problems. Trevor F. Baker already spotted these problems in his contributions to the seventh International. Symposium on Earth Tides (Sopron, Hungary, 1973). Confirmation at the Bonn symposium in 1977 eventually resulted in the complete abandonment of tidal tilt (and strain) measurements in the beginning of the 1980’s. A successful determination of the free core nutation (FCN) using tidal gravity records was delayed by the poor calibration of the gravimeters on one side and the lack of precise OTL computations for the world ocean on the other. Trevor F. Baker brought a significant contribution to both subjects. As soon as the first global ocean tides model became available (Schwiderski, 1980), Trevor F. Baker started tidal gravity observations using the best available instruments at that time i.e. the LaCoste&Romberg (LCR) ET meters. A first network was established in the United Kingdom (UK) with stations at Bidston, Llanrwst, Newtown, London, Taunton, Redruth, Newlyn and Edinburgh. In continental Europe tidal observations with the LCR’s ET meters were made at Valle de los Caidos, Brussels, Bad Homburg, Zurich and Chur. Baker stressed the importance of the electrostatic feedback system for LCR meters (Baker et al., 1989, 1991). Of course, the main breakthrough in accuracy was obtained by re-calibrating ET13, ET 15 and ET 10 on Torge's vertical calibration line in the tall building in Hannover (Baker et al., 1989, Wenzel et al., 1991). The ET meters were effectively calibrated with an accuracy of 0.1%. Tidal gravity observations have been also performed in Wuhan (China) and Curitiba (Brazil) to establish reference stations. Having reached the goal of performing tidal gravity observations with an accuracy of 0.1%, which allowed the determination of the FCN, the program was interrupted in 1989, in order to concentrate the efforts on the new FG5 absolute gravimeter. This instrument was used for measuring vertical crustal movements at tide gauges, alongside GPS, for mean sea level research. However he continued to work on OTL evaluation (Baker et al., 1996; Bos and Baker, 2005; Penna et al., 2008). Trevor F. Baker applied OTL corrections to the GGP stations (Baker and Bos, 2003), stressing the importance of a more homogeneous calibration of the superconducting gravimeters (SGs). He detected calibration errors of about 0.3% at that time. Calibration of SGs were then improved so that a general intercomparison of SGs and spring gravimeters results in Western Europe showed a global agreement at the 0.1% level (Ducarme et al., 2009), confirming the excellent work of Trevor and his collaborators. In the 1990’s Trevor F. Baker started to work actively in space Geodesy with V. Ashkenazi, using absolute gravity measurements in parallel. He paid special attention to mean sea level variations. He did not forget the interactions between Earth, Oceans and tides (Curtis et al., 1994). In 1995 Trevor F. Baker started to investigate the potential of GPS observations for vertical land motion and tide gauge stability. Ocean loading was also investigated with papers on ocean tide loading and GPS. Baker et al., 1995 used GPS measurements at Newlyn in south-west England to show that GPS could be used to study OTL. Penna and Baker discussed the importance of correcting GPS observations for OTL in the context of Australia. Allinson et al. (2004) took a preliminary look at OTL from continuous GPS in the UK and compared the observations to 7 recent ocean tide models. It was the beginning of a fruitful collaboration with the GPS research group at the University of Newcastle, UK. Penna et al., 2008 compared the OTL displacement computations given by 3 different algorithms and looked at the M2 observed displacements and model computations at many worldwide GPS sites. The major advance is given in the 2 very recent JGR papers (September, 2015). The GPS analysis methods are described in the Part 1 paper (Penna et al. 2015). In the Part 2 (Bos, et al., 2015) Figure 1 shows the high quality, high spatial density and spatial coherence of M2 OTL vertical displacements at 259 continuous GPS stations in Western Europe. The paper goes on to show that there is clear evidence for anelasticity in the asthenosphere i.e. a reduction of 8-10% in the shear modulus in the asthenosphere at tidal periods. This is the first time that OTL observations have been used to find new information on solid Earth geophysics. The previous work based on tidal gravity and GPS used the earlier available ocean tide models, many of which had significant errors in several parts of the world. All previous attempts using tiltmeters in the 1970s failed, because of the problems of strain-tilt coupling.

Trevor F. Baker was an active member of the Working Group on “Data Processing in Tidal Research” set up by the Permanent Commission on Earth Tides at the Bonn Symposium in 1977. He suggested the now classical representation of the tidal analysis results under the form of a tidal rotating vector associated with an OTL vector, a body tides vector and their derivatives (modelled and corrected tidal vectors on one side and residual vectors on the other). From 1989 to 1997 Trevor F. Baker served as Vice-President of the Earth Tide Commission. From 1995 to 2005 he was in the directing board of the WEGENER project and stayed in the Directing Board of ICET from 1992 to 2008.

Trevor F. Baker has always been a reference in ocean tide loading (OTL) studies. He always tried to get the best possible results with the instrumentation and techniques available. He was very successful with precise gravity tides observations and was one of the first scientists to reach with tidal spring gravimeters the 0.1% accuracy, required for the determination of the FCN. When reaching the physical limit of a technique, he did not hesitate to stop the observations but he never forgot his scientific goals and always tried to reach them with more performing methods. This fact is illustrated by his study of crustal structures through OTL investigation using tiltmeters, which aborted at the end of the 1970’s but was successfully reactivated through space techniques.

Trevor F. Baker’s scientific achievements include more than 160 high-quality scientific papers in peer-reviewed journals, including Nature.