Analysis of frequent trilateration observations from the
two-color EDM networks in California, demonstrate that
the noise power spectra are dominated by white noise at
higher frequencies and power-law behavior at lower
frequencies which contradict prior assumptions that only
white noise is present in a geodetic time-series, After
removing a linear trend from the two-color data, it
becomes evident that there are primarily two recognizable
types of time-correlated noise present in the residuals.
The first type is a seasonal variation in displacement
which is probably a result of measuring to shallow
surface monuments installed in clayey soil which responds
to seasonally occurring rainfall. The second type of
correlated noise becomes evident only after spectral
analysis of line-length changes and shows a functional
relation at long periods between power and frequency of
where f is frequency and
. With
, this type of
correlated noise is termed random-walk noise and its
source is mainly thought to be small random motions of
geodetic monuments with respect to the Earth's crust,
though other sources are possible. Because of problems
associated with spectral analysis of these data, we
assume that there are only two sources of noise (white
noise and random-walk) and use maximum likelihood
estimation to measure the size of each component. We
find that the random-walk noise level averages about
and that our estimates of the white
noise component confirm theoretical limitations of the
measurement technique. Because of the presence of
random-walk noise in these time series, modeling and
interpretation of the geodetic data must account for this
source of error.
AGU Index Terms: 1294 Geodesy; Instruments and Techniques; 1244 Standards and absolute measurements
Keywords/Free Terms: Geodesy, Error analysis, Monument noise
JGR-Solid Earth 96JB02945
Vol. 102
, No. B1
, p. 591