PSP FIELDS Digital Fields Board (DFB), XXX ⨯ YYY cross spectra 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 cross spectra data for a pair of input channels consist of:\n\n 1) Power spectral densities (auto spectra, e.g. FT₁ ⨯ FT₁)\n 2) Real and imaginary parts of the spectral cross term (FT₁ ⨯ FT₂)\n 3) Coherence\n 4) Phase\n\nwhere all as a function of frequency and time. The last two terms are describedcoherence and phase are defined in [3].\n\nThese cross spectra are averaged in both frequency and time as described in [3]. The cross spectra have either 56 or 96 bins (selectable) with the bin central frequencies reported in the metadata. The AC cross spectra are duty-cycled such that spectral averaging takes place over the first 1/8 of any given NYs (assuming a 1 NYs data cadence). Less data are averaged by 2^N for cadences faster than 1 NYs by 2^N. For cadences slower than 1 NYs, the first 1/8 of each NYs of data included are averaged together to form 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. The units for phase are degrees.\n\nThe Level 2 voltage 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 cross spectra data are rotated into a non-intuitive coordinate system with components [d,e,f]. For solar orbits 3 and beyond, the magnetic field cross spectra data are expressed by using search coil magnetometer sensor coordinates with components [u,v,w].\n\nTo rotate from [d,e,f] coordinates to [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\nFor some orbits, sufficient spectral information exists in the auto spectra and cross spectra to determine wave ellipticity, planarity, and wave normal angles. One method for accomplishing this is presented in reference [4].\n\nTime resolution of the DFB AC cross spectral data can vary by multiples of 2^N. During encounter (when PSP is within 0.25 AU of the Sun), cadence for the DFB AC cross spectra is typically 1 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\n 4) Santolik, O., Parrot, M., Lefeuvre, F. Radio Science (2003), 38, 1010. https://doi.org/10.1029/2000RS002523