Magsat vertical field anomalies above 40°N from spherical cap harmonic analysis

Abstract

A new technique, the method of spherical cap harmonic analysis, has provided the means to construct an analytical model of the vertical field above 40°N from Magsat data. With this technique, proper consideration can be taken of altitude variation and of the source‐free constraint that the vertical field be the vertical derivative of a potential function. Maps can be produced at any altitude. Here they are given at the lower and upper limits of the Magsat satellite, 6700 and 6900 km radial distance or approximately 335 and 535 km geodetic altitude. A novel decimation procedure, applied to NASA “Investigator B” data screened for low disturbance levels, results in an approximately uniform distribution in area, about 1 point per (150 km)2. Each of the 5087 data points represents an average over 5 s of time or 37 km of satellite track. The harmonic model, of maximum index 22, includes only those basis functions that are necessary for fitting a potential which need not be differentiable in colatitude and that are therefore completely orthogonal over the spherical cap. Although there are 276 coefficients in the theoretical model, only 190 were found to be statistically significant. The resulting scatter, or standard error of estimate, was 3.6 nT.

Heterogeneous structure of the lithosphere in the Black Sea from a multidisciplinary analysis of geophysical fields

“…11). The largest high gradient zones of the T-and Z-MAGSAT anomaly fields [Coles et al, 1982;Haines, 1985] and the zones of disturbances of the mantle gravity component that are also shown in this figure. These zones indicate the general strikes of the major faults systems and can be the evidence for deep origin of the large faults related to them.…”

Spherical cap models of Laplacian potentials and general fields

“…the Legendre functions, P;:,). The values of degree nk of the Legendre functions of (1) are chosen in order to satisfy the following boundary conditions (Haines, 1985a):…”

“…A new technique was introduced by Haines (1985a) to derive regional models of the geomagnetic potential which satisfy the physics of the problem, i.e. the Laplace's equation (we show briefly this well-known partial differential equation simply to introduce the symbols we are going to mention):…”

The Canadian Geomagnetic Reference Field 1995

“…Careful selection criteria, as described by Coles et al (1982) and Coles (1985), resulted in a set of quiet data that were then variably decimated to produce a relatively uniform areal distribution north of 40°N, with an approximate density of 1 point per (150 km)2. The latter procedure has been described by Haines (1985b).…”