Paul Geladi (1951–2024) Chemometrician, spectroscopist and pioneer

Prof. Paul Geladi was born the 30^th of June of 1951 in Schoten (Belgium) and passed away peacefully on the 18^th of May of 2024 in Umeå (Sweden).

Paul Geladi was a brilliant chemometrician and professor specialized in multivariate data analysis (especially, partial least squares methods), multivariate image analysis, multiway analysis, and spectroscopy (near-infrared), as well as a kind and emphatic person with colleagues, students, friends and family. His work trajectory includes, among other, a list of more than 190 publications (with >29,000 citations) that shows the extent and vigour of Paul, both in life and work.

Paul's passion for nature and chemistry awoke in his early years in Schoten, when he was still a very young child, while playing outdoors or experimenting in the attic for hours with the “Chemistry for Beginners” kit that his parents gave him. This was likely the start of a life dedicated to science and research.

After attending Sint-Eduardus in the Londenstraat (Belgium), Paul received his B.Sc. in Chemistry (1974) and his Ph.D. (doctoral degree) in Analytical Chemistry from the University of Antwerp (1979). Afterwards, in the early 1980's, Paul worked in Norway at the non-profit foundation Norwegian Computing Centre, specializing in applied statistics, and accepted a position as Associate Professor in Chemometrics at the Department of Chemistry of Umeå University (Sweden), generating his most cited publication, the tutorial Principal Component Analysis (Wold, Esbensen & Geladi, 1987). Paul also worked as a visiting Professor at the Department of Chemistry, University of Washington, Seattle, where he wrote his second most cited publication, Partial least-squares regression: a tutorial (Geladi & Kowalski, 1986). In addition, he also held a position as Associate Professor in Chemometrics and Near Infrared Spectroscopy at the University of Vaasa (Finland) since 2003.

In 2007, Paul was appointed Professor of Chemometrics at the Swedish University of Agricultural Sciences (SLU, Umeå, Sweden), which would be his main institution until his retirement in 2016, when he would become Emeritus Professor at SLU. During the active years, Paul was awarded the title of Honorary Doctor of Technology by the University of Vaasa (Finland, 2011) in recognition of his esteemed scholarship on Near Infrared Spectroscopy and the international impact of his work. Paul was also External Professor at the Department of Food Science of Stellenbosch University (South Africa) between 2011 and 2014. His work and publications on NIR spectroscopy, multivariate data analysis, hyperspectral imaging, chemometric method development, and their applications in a variety of fields, had a tremendous impact in the scientific community, yielding to numerous invitations to present his work in international conferences and meetings.

His outstanding work related to chemometrics, multivariate calibration, variable selection, spectroscopy (especially, NIRS), multiway analysis, and multivariate image analysis, generated a significant number of high-impact publications in international journals and the 2002 Eastern Analytical Symposium Award in Chemometrics. His work with spectral and hyper-spectral images had a substantial world-wide impact; Paul's interest for imaging could be related to the fact that he was also a skilled photographer. This interest led him to co-author several book chapters and three highly recommended and popular books: Multivariate Image Analysis (1997), Multi-way Analysis with Applications in the Chemical Sciences (2005), and Techniques and Applications of Hyperspectral Image Analysis (2007).

Paul Geladi's papers range from tutorials on multivariate statistical methods (e.g., principal components analysis, partial least squares regression, neural networks, or data pre-processing) to data analysis' applications in fields such as analytical chemistry, spectroscopy, environmental sciences, medicine, hyperspectral imaging, and food science, among other. His list of publications reaches almost 200 peer-reviewed publications and numerous conference attendances. His tutorials on principal component analysis (cited more than 14,350 times) and partial least squares (cited more than 9,080 times) published in 1986–1987 are still on top of the most helpful resources for young researchers that want to understand PCA and PLS algorithms and learn how to use them; followed by his article on linearization and scatter-correction for near-infrared reflectance spectra published in 1985. His work related to NIR spectroscopy to analyse complex samples had a massive impact in industry (e.g., food and pharmaceutical industries), medicine (e.g., in skin cancer and diabetes related research), and environmental and exposure sciences (e.g., in agricultural applications and human acute toxicity studies).

During his time as Emeritus (2016–2024), Paul continued helping with his knowledge and experience many researchers and students in several institutions. Paul was a very active traveller (all of us remember his trips and international events across the world, and how skilful he was in languages), leading to a vast number of word-wide collaborations and an extensive international network of researchers in countries such as Sweden, Norway, Finland, USA or South Africa. His collaborations ranged from methodological studies (related to advanced algorithms, spectroscopy, imaging, and multivariate data analysis) to applications in archaeology, medicine, chemistry, biotechnology or artificial intelligence. He had time for all of them, he was a real early bird that could be sending you an email with the perfect solution at 5 am, because for Paul using the time wisely was very important, as he used to remind to his students. Paul knew that time management also was important, for a healthy work-life balance. He mastered this, succeeding in science and, at the same time, having time for friends and travelling to sunny and warmer destinations.

His patience, empathy, and ability to actively listen and advise people (especially when supporting and helping students and early-careers) made him one of the most respected and appreciated professors at university. He had the skill of giving the most efficient solution in just a few words to problems that others could be discussing for hours. His way of thinking was so well structured that he could explain the most complex subject in a totally understandable way on a blackboard without any need for pre-prepared slides.

As many scientists highly talented in mathematics, Paul loved music which was an important part of his life. When he was a teenager, he got fascinated by The Beatles and jazz music; and afterwards, while studying Chemistry at the University of Antwerp (Belgium), he joined a performance and avant-garde music group. His pioneer nature brough him to use this passion to create innovative electronic music experimenting with sounds and using out-of-the-box technics. After retiring, he continued nourishing his love for music taking piano lessons in Umeå. He was also a licenced airplane pilot and for many years active in the Umeå aviation club (Umeå flygklubb, UFK), transporting himself and colleagues to desired destinations.

Paul's open-mind and pioneering mindset brought him to apply chemometrics in a very diverse range of fields and industries, but also to question the field to boost a constructive discussion on the state of the art of chemometrics and the future new challenges, as he did in his editorial letter of 2008 at both the J. Chemometrics and the Chem. Intel. Lab. Syst., where he pointed to the need to bring the chemometrics field more inside omics sciences or nanotechnology, with new (rather than just extrapolated) goals of chemometrics.

Prof. Paul Geladi was not only a brilliant scientist, but also the epitome of humility, with a warm personality, willing to help everybody from students to senior scientists. His modest and gentle way of behaving and acting, and his high-quality research legacy and multitude of publications, will continue being example and inspiration for the new generations of chemometricians and scientists.