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magnitude of the radid component is the m e from both site. T k is commonly
referred to a~ the baseline instability. Ak, at rangen which are much Larger than the
site separation, the same radial component is sensed h m both sites. Therefore, the
spacing of these stations must be d eMed fmm the single station range and the
required mverage. However, if a two-station setup is logistically difficult to deploy
an alternative appro& may be needed.
1.3.3 One Station Approach
If the surface current field can he estimated using only one station, then the problems
esociated with the *station appmaeh can be avoided. First of dl, the geometric
constraints no longer apply since there are no baseline or range dependent insta-
bilities. Also, hardware casts and manpower demands are minimized. Inter-site
communication m also not necessary. This is especially vsefvl in regioor, where only
one site can be constructed due to geographic constraints.
The surface current vector &mated from the radial data is based on the w
sumptlon of a uniform current about the region where a point estimate is required.
If this is the ease the radial components within this region wiu simply be dierent
projections of this current. By fitting the data in a lesst-~quarer sense we can obtain
the original vector current. The quality of the fit can be determined by analysing the
variance of the errozs from the estimated and actual pmjeetions. For example, if the
standard error is small as compared to the computed current magnitude, then the
vector current is more likely to be d i m in the region. As well, an average current
estimate may also be obtained if detailed current information is not required, for
example in the estimation of the mean current vector over a large area for mescale
-nt studis. H~we~wee~we, this is dependent on the required application.