A test of a moment technique for vector field calculations
Since last year, we have been using a moments technique to calculate the solar vector magnetic field from measurements of the Stokes profiles from the San Fernando Observatory Video Spectra-Spectroheliograph (SFO VSSHG). As part of our evaluation of the accuracy of this technique, I have carried out simulations using analytic profiles. Let S[sub n] be the nth moment of Stokes profile S([lambda]). That is: S[sub n] = [line integral][lambda][sup n]S([lambda]) d[lambda] where [lambda] = 0 is taken at line center and the integral is done over the line profile. We use the following approximations: [sup Q[sup 2]]/[sub I[sub 0]] = [sup 1]/[sub 2]B[sup 2]sin[sup 2][gamma]cos2[chi]; [sup U[sub 2]]/[sub I[sub 0]] = [sup 1]/[sub 2]B[sup 2]sin[sup 2][gamma]sin2[chi]; [sup V[sub 1]]/[sub I[sub 0]] = Bcos[gamma] where B is the magnitude of the field, [gamma] is its inclination to the line of sight, and [chi] is its azimuth angle. These approximations are exact if the Stokes profiles are given by the Seares formulae. We have applied them to profiles generated in the Unno-Rachkovsky solution to the transfer equation, and show that they are a useful approximation for more realistic line profiles as well. The largest systematic errors are in the azimuth angle [chi], with smaller errors in determination of the longitudinal component of the field and essentially no error in determining the manitude of the transverse component.
- OSTI ID:
- 6653718
- Report Number(s):
- CONF-930189-; CODEN: AASBAR
- Journal Information:
- American Astronomical Society, Bulletin; (United States), Vol. 24:4; Conference: 181. meeting of the American Astronomical Society (AAS), Phoenix, AZ (United States), 3-7 Jan 1993; ISSN 0002-7537
- Country of Publication:
- United States
- Language:
- English
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