m
Ptó
ta
of the earth. The accuracies of these mean values
range from about 5 to 25 mgal, depending on the
amount of data used in the calculation of each
mean.
The satellite solution was for all harmonics up to
12,12 plus higher degree terms with m 1, 2, 3
(that is those terms giving relatively long period
perturbations) and resonance terms.
The normal equations were constructed from the
surface gravity data on the assumption that all
terms of equal degree were equally well represented
in the data. Comparisons of the surface data with
the satellite data lead us to conclude that the ampli
tudes of the harmonics greater than about degree
16 were of the same order of magnitude as the noise
in the data so that we constructed the normal
equations up to this degree before combining the
results with the satellite data [6].
With the expansion up to 16,16 the resolution of the
features in the geoid is about 1200 km. That is,
anomalies of areal extent smaller than this would
not show up in the field even if they are of a large
magnitude. If there are several small wavelength
features they would probably give a broad feature
on the geoid or gravity maps.
+90'
+80'
+60'
2.3y
+40'
+20'
-40'
-60'
-80'
-90'
-180" -160° -140° -120° -100° -80° -60° -40° -20° 0° +20° +40° +60° +80° +100° +120° +140° +160° +180'
Fig. 1. Free air anomalies (mgal) referred to ellipsoid of
flattening 1/298.255. Based on the Gaposchkin and
Lambeck solution [1], Contour interval is 10 mgal.
Shaded areas correspond to negatieve anomalies.
2000 1000 0 1000 2000
DISTANCE (Km)
Fig. 2. Comparisons of gravity profiles based on the global
solution (solid lines) and on data collected by surface
measurements (broken lines).
North Atlantic, Northwest-Southeast - profile from
Halifax to Dakar.
ngt 72
45
