DOI: 10.48322/9n1r-5q47
title: Ulysses Unified Radio and Plasma wave (URAP) Daily Color Dynamic Spectrogram Plot
title: Ulysses Unified Radio and Plasma wave (URAP) Investigation Daily Color Dynamic Spectrogram Plot

description: from URAP Users Notes: Guide To The Archiving Of Ulysses Radio And Plasma Wave Data by Roger Hess, Robert MacDowall, Denise Lengyel-Frey March 15, 1995 - version 1.0 revised March 24, 1999 - version 1.1 revised June 8, 1999 - version 1.2 These color plots present URAP radio and plasma wave data in a format referred to as dynamic spectra. For the daily plots, the time resolution is 128 seconds, providing high-time resolution across the entire frequency range of the URAP receivers. The 10-day plots use 10-minute resolution data, which permits good detection of bursty wave activity. The 26-day plots use 1-hour resolution data; these plots correspond to the other Ulysses 26-day plot intervals, but the ability to identify wave activity is reduced. The power of the electric or magnetic field is shown in color as a 2-dimensional function of time and frequency. The plots include data from the URAP Radio Astronomy Receivers (RAR), Plasma Frequency Receiver (PFR), and Waveform Analyzer (WFA). Refer to the documentation for the 10-minute average archive data files, as well as Stone et al. (1992), for more general information on these instruments. Here, we describe the choices that were made in generating these plots. 1. Formats - These plots are available in 2 formats: GIF files for viewing with a web browser and Postscript files for high quality printed copies. The resolution of the GIF files is 776 x 600 pixels, a compromise between smaller size for network transfer and larger size for improved resolution. The Postscript files are sized to fit both 8.5x11 inch paper or A4 paper. The daily unzipped (zipped) Postscript files are typically 400-440 kB ( 130-140 KB) in size; the daily GIF files are typically 200-230 kB in size. (The 10-day and 26-day plots are similar in size.) 2. Data units - The data and the associated color bar are plotted in units of decibels, an old radio astronomer unit for describing signal to background ratio on a logarithmic scale. Specifically, Data_in_dB = 10. * log10(total power/background power) The data for electric field observations are in units of microvolts**2 Hz**(-1) as are the calculated background levels. The units for magnetic field observations (the bottom panels on the page) are nT**2 Hz**(-1). The data for the 1-day plots are comparable to the squared values of data in the URAP UFA 10-minute files. Although the ratio (total power-background power)/background power permits one to see weaker events in such plots, it is more sensitive to background determination and enhances the noise seen in the plots. Therefore, it is not used here. 3. Backgrounds - The background levels as a function of frequency for the RAR and WFA are determined from the data for the day, because they vary throughout the mission. The PFR background does not vary significantly with time, so fixed background levels are used. For each of the instruments, the backgrounds vary with the instrument mode, so separate sets of backgrounds are derived for each mode that is present. (Modes are discussed below). The PFR and WFA backgrounds also depend significantly on bit rate. For the RAR the background level selected is the lowest 3% of the data for each frequency; for the PFR and WFA, the background level selected is the lowest 10% of the data for each frequency. The higher number is chosen for the WFA because the data are substantially noisier than the RAR. It should be noted that this type of background subtraction will remove any signal at a given frequency that is constant throughout the day. An example is the quasithermal noise line ("plasma line" in the RAR data, when the density does not vary throughout the day. Note that for 10-day and 26-day plots, in particular, the background determination might result from a few hours of very low intensity data, which will cause all the other data, referenced to that background, to appear enhanced. This is an unfortunate consequence of determining the background levels from intervals of minimum data intensity. 4. Modes and other labels - Each of the instruments has several modes that affect the data display. The telemetry bit rate is also an important parameter. The key modes and the bit rate are shown on the dynamic spectrum as the thickness (or nonexistence) of a line. The RAR Hi and Lo bands are plotted in separate panels because they are commanded separately. For each band, the spin-plane and spin-axis antennas can be either summed or separate. If the RAR Hi or Lo band instrument is in summed mode, then a white line for the appropriate band is present under the RAR plot. Summed mode provides data used for 3-dimensional direction finding at the expense of a higher background level. Because the backgrounds will differ between summed and separate modes, backgrounds are calculated for both modes when they are present. Although the RAR is typically operated in a mode where measurements are made at all 76 frequencies, there are times when only a subset of the frequencies are sampled (called Measure mode). In these cases, the data plotted are interpolated in frequency to give a clearer picture of the events that might be taking place. These intervals are evident from the appearance of the data, which is smoothed in frequency; see Nov. 6, 1990, where the RAR Lo band is in Measure mode for the first 18 hours of the day. This example also shows the RAR hi band in a rarely-used, single frequency mode. If the Measure mode data occupy less than 10% of the day; they are not interpolated, because the events occurring at these times should be clear from the non-Measure mode data, and it is useful to see which frequencies are being sampled. The Jupiter flyby interval (e.g., Feb. 8, 1992) includes examples of short intervals of measure mode. The bit rate significantly affects the PFR and WFA backgrounds. If the science data bit rate is 1024 bps, it is indicated by a thick line, 512 bps is indicated by a thin line, and low ("emergency" bit rates, either 256 or 126 bps, by no line. The PFR operates in one of 3 modes - fast scan, slow scan, or fixed tune (see Stone et al., 1992). These 3 modes have different backgrounds and generate different interferences for the WFA instrument. Fast scan is shown by the white line under the PFR plot, slow scan is in progress if there is no line, and fixed tune is a single frequency mode (evident from the PFR data display), typically used in 1 hour/day intervals. The WFA instruments can sample either the electrical (E) antennas or the (B-field) search coil. For the low band of the WFA B field data (< 8 Hz), either By or Bz data are telemetered. The available parameter is shown by the white line above the B (WFA) plot (present=By, absent=Bz). 5. Interpolation - In addition to the interpolation discussed above for the RAR, the RAR data are interpolated to remove data gaps of 384 seconds or less. We interpolate the RAR data because the events observed in the RAR, such as solar type II and type III radio bursts, are mostly smoothly varying on time scales of a few minutes. Therefore, they are easier to visualize and interpret when data gaps are interpolated. For the events in the PFR and WFA data, predominantly bursty wave events, interpolation is not necessary and not performed. An exception occurs when the data telemetry rate is either 256 or 128 bps; then the WFA data are interpolated in time because they are not sampled every 128 sec. Finally, the RAR Hi band data, for which there are only 12 channels of data, are interpolated to fit a logarithmic frequency scale with 37 equivalent frequencies. 6. Interference and other issues affecting data interpretation - Each of these instruments, like all sensitive wave receivers, is affected by interference from other sources. For the RAR Hi band, an interference signal at 81 kHz is produced by the Ulysses GAS instrument. Depending on the mode in which the GAS instrument is operating, this interference can occur from 0 to 24 hours per day. If an algorithm determines that this interference is present in more than about 10% the RAR data for the day, we remove the 80 kHz data and interpolate from adjacent frequencies. The RAR Hi band also has an enhanced background at 120 kHz (source unknown). Subtraction of this enhanced background can cause artifacts in other events, like type III bursts. See Nov. 30, 1990 as an example. The RAR Lo band has an interference line at 8.75 kHz and odd harmonics caused by the Ulysses traveling wave tube amplifier (TWTA), which is part of the high gain telemetry system. In general, this signal is removed by the background subtraction, sometimes producing artifacts in weak radio events or the thermal noise spectrum at these frequencies The PFR experiences interference from the URAP Sounder; these data are removed from the plots and appear as short data gaps. The background levels of the PFR depend on bit rate, PFR mode, and the cadence of the URAP Fast Envelope Sampler (FES data not presented in these plots); these background variations can affect the appearance of events at the transition from one mode to another. The WFA data are affected by numerous interferences, of which the URAP PFR is the dominant source. WFA "backgrounds" vary significantly depending on whether the PFR is in fast or slow scan mode or fixed tune, so separate backgrounds are calculated for each of these. The URAP Sounder also causes interference; these data are removed from the plots and appear as short data gaps. Spacecraft thruster operations produce a variety of artifacts in the data; since we have no indication of these in our telemetry, they are not flagged on the plots. Examples may be seen on Feb 23, 1995 at 12:00 and on Feb. 25, 1995 at 15:00. An interesting "interference" is seen to disappear on Dec. 17, 1990; this is when the spacecraft nutation was stopped. This is best seen on the 26- day plots. To summarize, there are a variety of artifacts in the wave data that affect interpretation. These can result from corrupted telemetry values (producing bad pixels (most evident in the RAR plots, see March 23, 1993, from 6:00-14:00, or August 16, 1991, a very good example of very bad data quality), interferences (e.g., non-physical, block-like structures sometimes seen in the highest frequencies of the WFA E and B data (see March 14, 1995)), or changes of the instrument mode or the physical medium (e.g., a short interval of data with a very low signal level defines a background for the rest of the day that is not appropriate; see Nov. 4, 1990, when the Ex antenna was deployed). 7. Spacecraft location - At the lower left on the plots, 4 parameters related to the location of Ulysses at the mid-time of the plot are printed: a) the Ulysses-Sun (U-S) distance in AU, b) the heliographic latitude (Hlat_U) of Ulysses in degrees, c) the Ulysses-Sun-Earth (U-S-E) angle in degrees, and d) the Ulysses-Jupiter (U-J) distance in AU. These are among the most relevant parameters for interpreting the URAP data. Additional parameters, as well as a graphic showing the Ulysses location relative to the Sun, Earth, and Jupiter, can be found at the URAP Home Page at Goddard Space Flight Center (see below). 8. For additional information on these plots or on the URAP data, contact the PI of the URAP investigation, Dr. Robert MacDowall, at phone: 1-301-286-2608 fax: 1-301-286-1683 email: robert.macdowall@gsfc.nasa.gov. The URL for the URAP Home Page at Goddard Space Flight Center is http://urap.gsfc.nasa.gov/