Averaging and sampling for magnetic-observatory hourly data

Averaging and sampling for magnetic-observatory hourly data

Blog Article

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, oljelampe 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 jumbo glory double wall 2li bardak 250 ml 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.