For some purposes, such as for accurate orbit prediction, it seems to be useful to replace the large fields of harmonic coefficients, in the Earth gravity field models by a limited set of the lumped geopotential coefficients, tailored to the individual orbits. The lumped values absorb the orbital information to a high degree for the particular order of the harmonics, and a small set of the lumped coefficients, written for various orders, should be sufficient to describe the orbit as perturbed by the Earth. Some problems and questions concerning the application of this method for orbits similar to those of SEASAT or TOPEX are discussed and answered.
Time and latitude observations, made by the circumzenithal at the Geodetical Observatory Pecný (Ondřejov) in the years 1970-1983, were analysed and some secular and periodical terms were proved. These results are studied from the standpoint of possibilities of their geodynamical interpretation: determination of the secular variation of the station position, detection of the secular, Chandler's and annual polar motion from optical measurements at the single station, and tidal influence on the variation of the local plumb-line.