RPI passive wave measurement capturing voltage spectral density of the radio emissions in space as a function of frequency, typically between 3 and 1009 kHz. This operating frequency range was selected by the RPI team to provide optimal temporal resolution of the wave observations. Commonly used in the analysis of noise generators, spectral density is a frequency-dependent characteristic that describes how much power is generated by the emission source in a 1 Hz bandwidth. The original description of emissions was done in terms of thermal noise measurements, though the same approach also applies to non-thermal emissions such as AKR. CDF_DS_PT5M stores calibrated data from all three RPI antennas X, Y, and Z individually and a combined X+Y antenna channel. The data are presented as the Voltage Spectral Density (VSD), which is the root of power spectral density, measured in [V/root-Hz] units. Note that conversion of antenna voltage to electric field strength depends on the effective length of the receive antenna, and such conversion is not performed here. (See spase://SMWG/Instrument/IMAGE/RPI for a time history of the lengths of the three mutually orthogonal RPI dipole antennas.) RPI is capable of detecting input radio emissions above its noise floor of 5 nV/root-Hz, which is determined by the internal white noise of the RPI antenna pre-amplifiers. The VSD in RPI spectrogram data is presented in dB relative to 1 V/root-Hz (logarithmic scale), units of dB(V/root-Hz). The RPI instrument noise floor is 5 nV/root-Hz = -166 dB(V/root-Hz) at the receiver input. Software suggested by the science team for CDF file visualization: (1) Plotting tool at the CDAWeb portal, (2) For analysis beyond static image inspection, including color scale optimization, zooming, text export, alternative data representations in physical units, detailed frequency and time information, overlaid model fpe and fce graphs, and EPS quality figures, use BinBrowser software at UML, http://ulcar.uml.edu/rpi.html

Commonly used in circuit analysis, Power Spectral Density (PSD) describes how much noise power is generated by the emission source in a 1 Hz bandwidth. Dynamic Specrtograms use Voltage Spectral Density (VSD), which is root of PSD, measured in V/root-Hz units. The VSD in RPI spectrograms is presented in dB relative to 1 V/root-Hz (logarithmic scale), units of dB(V/root-Hz). On average, the RPI instrument noise floor is 5 nV/root-Hz = -166 dB(V/root-Hz) at the receiver input.

List of operating frequencies at which sample data were collected to obtain VSD values. Actual frequency values vary from measurement to measurement depending on the choice of frequency sweep. Early in the mission, a variety of frequency sweeps were tested until March 27, 2001 when they were streamlined to three basic types: PROGRAM-23: linear sweep from 3 to 20 kHz with 400 Hz step (13 sec running time), PROGRAM-26: logarithmic sweep from 20 to 1009 kHz with 2% stepping (59 sec running time), and PROGRAM-25: logarithmic sweep from 20 to 300 kHz with 2% stepping (37 sec running time). Most commonly used since April 2001, PROGRAM-23 and PROGRAM-26 combination takes 72 sec to complete one sweep from 3 to 1009 kHz. Other frequency sweeps were also exercised, in addition to the three basic types, during experiments on detection of signals from the ground VLF transmitters. For a greater detail on the RPI measurement programming cases in the dynamic spectrogram mode, please refer to RPI operational logs available as part of the RPIAnywhere software package at http://ulcar.uml.edu/rpi.html.

Number of frequencies in the sweep, see "List of Frequencies

Epoch timestamp of the beginning of the spectrogram measurement. Use Measurement Duration to obtain time of measurement stop.

Duration of one spectrogram measurement.

Number of looks at each of the spectrogram frequencies, encoded. Encoding: stored number N is used as power of 2 (i.e., 2**N is actual number of repetitions)

Instrument setting describing receiver gains in X/Y and Z channels, encoded. See data model description at http://ulcar.uml.edu/rpi.html for additional details on base gain decoding procedure.

List of 25 parameter values that specify RPI instrument configuration during the measurement. For further detail on parameter value interpretation see data model description document at http://ulcar.uml.edu/rpi.html.