Li. Fernandez et al., Combination procedure for length-of-day time series according to the noisefrequency behavior, J GEODESY, 75(5-6), 2001, pp. 276-282
Length-of-day (LOD) estimates from seven Global Positioning System (GPS) an
d three satellite laser ranging (SLR) analysis centers were combined into a
n even-spaced time series for a 27-month period (1996-1998). This time seri
es was compared to the multitechnique Earth-orientation-parameter (EOP) com
bined solution (C04) derived at the Central Bureau of the International Ear
th Rotation Service (IERS/CB). Due to inhomogeneities in the different seri
es derived from the various techniques (time, length, quality, and spatial
resolution), the concept of a combined solution is justified. The noise beh
avior in LOD for different techniques varies with frequency, the data serie
s were divided into frequency windows after removing both biases and trends
. Different weight factors were assigned in each window, discriminating by
technique, and produced one-technique combined solutions. Finally, these on
e-technique combined solutions were combined to obtain the final multi-tech
nique solution. The LOD combined time series obtained by the present method
based on the frequency windows combined series (FWCS) is very close to the
IERS C04 solution. It could be useful to generate a new LOD reference time
series to be used in the study of high-frequency variations of Earth rotat
ion.