The production of large components, e. g. in aerospace industries, requires flexible and yet highly precise measurement
techniques to determine absolute lengths of up to one hundred metres. Two different approaches are presented in this
paper. One is based on a time-of-flight measurement, using a femtosecond frequency comb as an advanced modulator.
By the combined phase analysis of lines of different distinct frequencies in the Mega- and Gigahertz frequency range, a
measurement distance of one hundred metres with a relative measurement uncertainty of 1x10-7 was achieved in
laboratory conditions. In a second approach to long distance measurements, two standard interferometric measurement
techniques, i.e. variable synthetic and fixed synthetic wavelength interferometry, were combined. The two interferometry
techniques were realised within a single set-up, using two external cavity diode lasers as sources. Experimentally, lengths
of up to twenty metres could thus be determined with relative uncertainties below 1x10-6, in good agreement with
theoretical analysis. Both techniques, femtosecond fibre laser-based time-of-flight and diode laser-based multiwavelength
interferometry, are therefore capable of absolute, guidance-free long distance measurements and have
achieved demonstrated relative measurement uncertainties below 1x10-6 for distances over ten metres.