From a8d889b68e0768f2fb7e1e3fa2ae585fda35deff Mon Sep 17 00:00:00 2001 From: hasimpson-usgs <hasimpson@usgs.gov> Date: Tue, 14 Jul 2015 12:29:30 -0600 Subject: [PATCH] Update deltaf.md --- docs/deltaf.md | 31 +++++++++++-------------------- 1 file changed, 11 insertions(+), 20 deletions(-) diff --git a/docs/deltaf.md b/docs/deltaf.md index c0aa9e910..fb0598043 100644 --- a/docs/deltaf.md +++ b/docs/deltaf.md @@ -17,11 +17,10 @@ Magnetic vector measurements are typically made with fluxgate sensors capable of capturing rapid variations along three orthogonal axes simultaneously. However, the same technology that allows fast and accurate measurements of magnetic field variation is generally more prone to erroneous measurements -than slower, more stable total-field sensors. The difference between the -estimated total field obtained by adding magnetic vector components in -quadrature, and the measured total field, provides a useful time-dependent -diagnostic for magnetic observatory operators and automated software tools. We -call this value “Delta Fâ€. +than slower, more stable total-field sensors. "Delta F" is the difference +between the estimated total field, obtained from vector components, and the +measured total field. Delta F provides a useful time-dependent diagnostic for +magnetic observatory operators. ## Math and Theory @@ -33,23 +32,15 @@ Delta F (∆F) is, conceptually, very simple: field obtained by adding vector components in quadrature (see figure for vector component definitions): -- <a name="eq2"></a>Equation 2: 'Fv = X2 + Y2 + Z2 = H2 + Z2 = h2 + e2 + Z2' +- <a name="eq2"></a>Equation 2: 'Fv = X<sup>2</sup> + Y<sup>2</sup> + Z<sup>2</sup> = H<sup>2</sup> + Z<sup>2</sup> = h<sup>2</sup> + e<sup>2</sup> + Z<sup>2</sup>' Of course, if data are only available in hdZ (where d=(D-D0)) coordinates, as is common with USGS preliminary data, they should be converted into a Cartesian -system used in (2). - - +system used in (2). See  for a discussion on the +cartesian coordinate system used. ## Practical Considerations -### Magnetic Intensity Units - -It is understood that all raw data inputs are provided in units of nanoTesla -(nT). Of course this is not required for the equations to be valid, but it is -incumbent on the programmer to make sure all input data units are the same, -and that output units are defined accurately. - ### Non-synchronous Observations Fluxgates and total-field sensors operate at different frequencies, with the @@ -62,7 +53,7 @@ secondsâ€. That said, this standard clearly allows scalar measurements to be made less frequently than vector measurements. If this is indeed the case, Delta F should correspond to the scalar measurement time steps, however is not clearly stated in any found references which vector measurement should be used -to calculate Delta F. +to calculate Delta F. The library requires all inputs use the same sampling rate. ### Missing Observations @@ -73,14 +64,14 @@ set Delta F equal to -Fs. ## References -IAGA WG V-DAT (2011), Addition to the IAGA2002 Data Exchange Format: Quasi +- IAGA WG V-DAT (2011), Addition to the IAGA2002 Data Exchange Format: Quasi Definitive (q) data type and valid geomagnetic element (G), IAGA WG V-DAT business meeting held during the IUGG-2011 Assembly in Mebourne, Austrailia, 04 July 2011. -St-Louis, B. (Ed.) (2012), INTERMAGNET Technical Reference Manual, Version 4.6, +- St-Louis, B. (Ed.) (2012), INTERMAGNET Technical Reference Manual, Version 4.6, obtained from: http://www.intermagnet.org/publication-software/technicalsoft-eng.php -Turbitt, C.; Matzka, J.; Rasson, J.; St-Louis, B.; and Stewart, D. (2013), An +- Turbitt, C.; Matzka, J.; Rasson, J.; St-Louis, B.; and Stewart, D. (2013), An instrument performance and data quality standard for intermagnet one-second data exchange, IN: XVth IAGA Workshop on Geomagnetic Observatory Instruments and Data Processing, Cadiz, Spain, 4-14 June, 2012, p 186-188. -- GitLab