SHMultiTaperMaskCSE()

Perform a localized multitaper cross-spectral analysis using arbitrary windows derived from a mask.

Usage

mtse, sd = SHMultiTaperMaskCSE (sh1, sh2, tapers, [lmax1, lmax2, lmaxt, k, taper_wt, norm, csphase])

Returns

mtse : float, dimension (lmax-lmaxt+1)

The localized multitaper cross-power spectrum estimate. lmax is the smaller of lmax1 and lmax2.

sd : float, dimension (lmax-lmaxt+1)

The standard error of the localized multitaper cross-power spectral estimates. lmax is the smaller of lmax1 and lmax2.

Parameters

sh1 : float, dimension (2, lmax1in+1, lmax1in+1)

The spherical harmonic coefficients of the first function.

sh2 : float, dimension (2, lmax2in+1, lmax2in+1)

The spherical harmonic coefficients of the second function.

tapers : float, dimension ((lmaxtin+1)**2, kin)

An array of the k windowing functions, arranged in columns, obtained from a call to SHReturnTapersMap. The spherical harmonic coefficients are packed according to the conventions in SHCilmToVector.

lmax1 : optional, integer, default = lmax1in

The spherical harmonic bandwidth of sh1. This must be less than or equal to lmax1in.

lmax2 : optional, integer, default = lmax2in

The spherical harmonic bandwidth of sh2. This must be less than or equal to lmax2in.

lmaxt : optional, integer, default = lmaxtin

The spherical harmonic bandwidth of the windowing functions in the array tapers.

k : optional, integer, default = kin

The number of tapers to be utilized in performing the multitaper spectral analysis.

taper_wt : optional, float, dimension (kin), default = -1

The weights used in calculating the multitaper spectral estimates and standard error. Optimal values of the weights (for a known global power spectrum) can be obtained from the routine SHMTVarOpt. The default value specifies not to use taper_wt.

norm : optional, intger, default = 1

1 (default) = 4-pi (geodesy) normalized harmonics; 2 = Schmidt semi-normalized harmonics; 3 = unnormalized harmonics; 4 = orthonormal harmonics.

csphase : optional, integer, default = 1

1 (default) = do not apply the Condon-Shortley phase factor to the associated Legendre functions; -1 = append the Condon-Shortley phase factor of (-1)^m to the associated Legendre functions.

Description

SHMultiTaperMaskCSE will perform a localized multitaper cross-spectral analysis of two input functions expressed in spherical harmonics, SH1 and SH2, using an arbitrary set of windows derived from a mask. The maximum degree of the localized multitaper power spectrum estimate is lmax-lmaxt, where lmax is the smaller of lmax1 and lmax2. The matrix tapers contains the spherical harmonic coefficients of the windows and can be obtained by a call to SHReturnTapersMap. The coefficients of each window are stored in a single column, ordered according to the conventions used in SHCilmToVector.

If the optional array taper_wt is specified, then these weights will be used in calculating a weighted average of the individual k tapered estimates (mtse) and the corresponding standard error of the estimates (sd). If not present, the weights will all be assumed to be equal. When taper_wt is not specified, the mutltitaper spectral estimate for a given degree is calculated as the average obtained from the k individual tapered estimates. The standard error of the multitaper estimate at degree l is simply the population standard deviation, S = sqrt(sum (Si - mtse)^2 / (k-1)), divided by sqrt(k). See Wieczorek and Simons (2007) for the relevant expressions when weighted estimates are used.

The employed spherical harmonic normalization and Condon-Shortley phase convention can be set by the optional arguments norm and csphase; if not set, the default is to use geodesy 4-pi normalized harmonics that exclude the Condon-Shortley phase of (-1)^m.

References

Wieczorek, M. A. and F. J. Simons, Minimum-variance multitaper spectral estimation on the sphere, J. Fourier Anal. Appl., 13, doi:10.1007/s00041-006-6904-1, 665-692, 2007.