PSP FIELDS Digital Fields Board, DFB, SCMmf data:\n\nThe DFB is the low frequency, less than 75 kHz, component of the FIELDS experiment on the Parker Solar Probe spacecraft, see reference [1] below. For a full description of the FIELDS experiment, see reference [2]. For a description of the DFB, see reference [3].\n\nDFB AC spectra data consist of power spectral densities as a function of frequency and time. These spectra are averaged over both frequency and time as described in [3]. The spectra have pseudo-logarithmically spaced frequency bins with the bin central frequencies reported in the metadata. The AC spectra are duty-cycled such that spectral averaging takes place over the first 1/8 of any given NYsecond when the data cadence is equal to one NYsecond. Less data are averaged by a factor of 2^N for data cadences that are faster than one NYsecond by 2^N. For cadences slower than one NYsecond, the first 1/8 of each NYsecond of data included are averaged together to construct the reported data.\n\nThe Level 2 data products contained in this data file have been calibrated for:\n\n 1) The Hanning window used in the spectral calculation\n 2) DFB in-band gain\n 3) DFB analog filter gain response\n 4) DFB digital filter gain response\n 5) The search coil preamplifier response, when applicable\n 6) The bandwidth of each spectral bin\n\nNote that compensation for the DFB digital filters will introduce a non-physical positively sloped power trend at high frequencies when the non-corrected signal is dominated by noise. This effect should be examined carefully when determining spectral slopes and features at the highest frequencies. Calibrations for the FIELDS preamplifiers have not been implemented as the preamplifier response is flat and equal to one through the DFB frequency range. Corrections for plasma sheath impedance gain and antenna effective length have not been applied to voltage sensor signals. These corrections will be applied in the Level 3 DFB data products. Therefore, all voltage sensor quantities when present in these Level 2 data products are expressed by using units of Volts squared per Hertz. Likewise, all magnetic field quantities when present in these Level 2 data product are expressed by using units of nanoTesla squared per Hertz.\n\nThe Level 2 data products contained in this data file are expressed in sensor coordinates: e.g. dV12, dV34 for voltage measurements. For solar orbits 1 and 2, the search coil magnetometer spectral data are rotated into a non-intuitive coordinate system with components [d,e,f]. For solar orbits 3 and beyond, the magnetic field spectral data are in expressed in search coil magnetometer sensor coordinates with components [u,v,w].\n\nTo rotate from [d,e,f] coordinates into [u,v,w] search coil sensor coordinates, use the following matrix, written in IDL notation, and the following equation: spectra_uvw_vector = R ## spectra_def_vector.\n\nR = [[ 0.46834856, -0.81336422 , 0.34509170]\n [ -0.66921924, -0.071546954, 0.73961249]\n [ -0.57688408, -0.57733845 , -0.57782790]]\n\nThe time resolution of the DFB AC spectral data can vary by multiples of 2^N. During encounter when PSP is within 0.25 AU of the Sun, the DFB AC spectra data cadence is typically NYsecond NYsecond [2]. Timestamps correspond to the center time of each window.\n\nReferences:\n\n 1) Fox, N.J., Velli, M.C., Bale, S.D. et al., Space Sci Rev (2016) 204:7. https://doi.org/10.1007/s1121401502116\n 2) Bale, S.D., Goetz, K., Harvey, P.R. et al., Space Sci Rev (2016) 204:49. https://doi.org/10.1007/s1121401602445\n* 3) Malaspina, D.M., Ergun, R.E., Bolton, M. et al., JGR Space Physics (2016), 121, 5088-5096. https://doi.org/10.1002/2016JA022344