sentences:  In 1980 he published the 1st edition of the book "Parameter Estimation and Hypothesis Testing in Linear Models", with the 2nd, 3rd and 4th editions being published in 1987, 1997, and 2004 respectively.The first and second editions of the English translations were published in 1988 and 1999 respectively.From 1980-1987 he served as an expert in a radar altimeter group of the ESA.