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| Titel |
Averaging and sampling for magnetic-observatory hourly data |
| VerfasserIn |
J. J. Love, V. C. Tsai, J. L. Gannon |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 28, no. 11 ; Nr. 28, no. 11 (2010-11-12), S.2079-2096 |
| Datensatznummer |
250016912
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| Publikation (Nr.) |
 copernicus.org/angeo-28-2079-2010.pdf |
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| Zusammenfassung |
| A time and frequency-domain analysis is made of the effects of averaging and
sampling methods used for constructing magnetic-observatory hourly data
values. Using 1-min data as a proxy for continuous, geomagnetic variation,
we construct synthetic hourly values of two standard types: instantaneous
"spot" measurements and simple 1-h "boxcar" averages. We compare these
average-sample types with others: 2-h average, Gaussian, and "brick-wall"
low-frequency-pass. Hourly spot measurements provide a statistically unbiased
representation of the amplitude range of geomagnetic-field variation, but as
a representation of continuous field variation over time, they are
significantly affected by aliasing, especially at high latitudes. The 1-h,
2-h, and Gaussian average-samples are affected by a combination of amplitude
distortion and aliasing. Brick-wall values are not affected by either
amplitude distortion or aliasing, but constructing them is, in an operational
setting, relatively more difficult than it is for other average-sample types.
It is noteworthy that 1-h average-samples, the present standard for
observatory hourly data, have properties similar to Gaussian average-samples
that have been optimized for a minimum residual sum of amplitude distortion
and aliasing. For 1-h average-samples from medium and low-latitude
observatories, the average of the combination of amplitude distortion and
aliasing is less than the 5.0 nT accuracy standard established by Intermagnet
for modern 1-min data. For medium and low-latitude observatories, average
differences between monthly means constructed from 1-min data and monthly
means constructed from any of the hourly average-sample types considered here
are less than the 1.0 nT resolution of standard databases. We recommend that
observatories and World Data Centers continue the standard practice of
reporting simple 1-h-average hourly values. |
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