URAP User Notes - Ulysses

URAP - User Notes

URAP Contact:

Dr. R. Hess
Lab. for Extraterrestrial Physics
Code 690.2
NASA/GSFC
Greenbelt, Md 20771
USA

Phone: (1) 301 286-1394
Telefax:

E-mail: hess@urap.gsfc.nasa.gov

GUIDE TO THE ARCHIVING OF ULYSSES RADIO AND PLASMA WAVE DATA 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 Contents 1 Introduction 3 2 Delivery Schedule 3 3 Description of the Unified Radio and Plasma Wave Instrument 4 3.1 Radio Astronomy Receiver 4 3.2 Plasma Frequency Receiver 5 3.3 Waveform Analyzer 5 3.4 Other URAP Instruments 6 4 World Wide Web Access to URAP Data 7 APPENDICES 8 A UDS data files 8 A.1 Radio Astronomy Receiver 8 A.2 Plasma Frequency Receiver 11 A.3 Waveform Analyzer Electric Field 13 A.4 Waveform Analyzer Magnetic Field 15 B URAP DAILY, 10-DAY, & 26-DAY COLOR DYNAMIC SPECTRA 18 C USER'S GUIDE TO RAR 144 SECOND AVERAGED DATA FILES 22 2 1 Introduction The Unified Radio and Plasma wave instrument (URAP) is designed to detect both remotely-generated electromagnetic waves and in-situ plasma waves. The former are radio waves arising from electron beams in the solar wind (type II and type III radio bursts), planetary radio emissions (from Jupiter, the Earth, etc.), and a cosmic background from the local galactic medium. The in-situ waves include thermal plasma fluctuations, electron plasma oscillations (Langmuir waves), ion-acoustic waves, and whistler-mode waves. Wave electric fields from less than 1 Hz to 940 kHz and magnetic fields from less than 1 Hz to 448 Hz can be measured. An extensive description of the five instruments that make up the URAP investigation can be found in R. G. Stone et. al., Astron. Astrophys. Suppl. Ser., 92, 291-316 (1992). Details relevant to the data archive are contained below. The Astron. Astrophys. Suppl. Ser. issue also contains other articles describing the Ulysses spacecraft as a whole and the other Ulysses instruments. Ulysses is spun for stability with a period of approximately 12 sec. The Z axis of the spacecraft is defined as being along the spin axis. The X and Y axes are perpendicular to the spin axis. URAP measures electric field by means of two antennas. One is a dipole formed by two 35 meter long wires along the +/- X axes and the other is a 7.5 meter long monopole that is on the Z axis Because of the longer length of the X antenna compared to the Z antenna, it is much more sensitive and has a much lower background signal level. For these reasons, only the X antenna data are provided in the UDS data files. Magnetic fields are measured by means of a two axis sensor aligned along the spacecraft Y and Z axes. 2 Delivery Schedule The URAP team will provide the archival data products to the Ulysses Data System no later than 6 months after GSFC has received the raw data. These data will be provided to the NSSDC no later than 1 year after GSFC has received the raw data. 3 3 Description of the Unified Radio and Plasma Wave Instrument The Unified Radio and Plasma Wave instrument on Ulysses is divided into several sub-instruments. Data from three of these sub-instruments, the Radio Astronomy Receiver, the Plasma Frequency Receiver, and the Wave Form Analyzer, are represented in the URAP archival data. 3.1 Radio Astronomy Receiver The Radio Astronomy Receiver is divided into two parts, a low frequency receiver and a high frequency receiver. The low frequency receiver has 64 channels that cover the frequency range from 1.25 to 48.0 kHz in linear steps of 0.75 kHz. The high frequency receiver has 12 channels that cover the range from 52 kHz to 940 kHz in approximately logarithmic steps. The high frequency receiver is usually operated in what is called "measure" mode, which causes the receiver to step repeatedly through a list of frequencies that is determined by a ROM on board the spacecraft. There are 16 different lists and one of them is chosen by telecommand. The different lists emphasize different frequency ranges, so as to maximize the information received depending on the type of phenomena being studied. Some of the lists include all 12 possible frequency channels while other lists skip some of the frequencies. The list that has been used for most of the mission does include all frequecies, but there may be times when other lists have been used. At these times only a subset of the frequencies will be present. The low frequency receiver can be operated in measure mode (with its own set of lists of 8 or 16 frequencies) or in "linear sweep" mode where it steps through a contiguous set of frequencies. In linear mode, all 64 frequencies can be stepped through, or a subset of 32 frequencies can be chosen using the lower half, middle half, or upper half of the frequencies. For most of the mission, the low frequency receiver has been operated in linear mode with all 64 frequencies but there have been periods when it has operated in measure mode or in in linear mode with less than 64 frequencies. During these periods only a subset (8, 16, or 32) of the 64 possible frequencies will appear. Besides the intensity of a signal reaching the spacecraft, the RAR can also, when operated in particular modes, determine additional information about the source of the radiation, 4 including its direction relative to the location of Ulysses, its angular size, and its polarization. This is most efficiently done with the signal from the X and Z axis antennas summed together electronically either with or without a phase shift added between the two signals. Although this additional information cannot be recovered from the averaged data, the mode does have a large effect on the background signal level, so the mode of high and low frequency receivers is given in the data as either summed (X and Z antenna combined) or separate (X antenna alone). 3.2 Plasma Frequency Receiver The Plasma Frequency Receiver (PFR) is intended to monitor a wide spectrum of plasma phenomena with constant frequency coverage, large dynamic range, and good frequency resolution. Two receivers for Ex and Ez are supplied with a frequency range from 0.57 to 35 kHz that is covered in 32 logarithmic frequency steps. The threshold sensitivity is approximately 2 microvolts per channel. There are three modes of operation of the PFR. In "fast scan" mode the receivers are swept through all 32 frequencies twice in each telemetry frame (a frame takes 1 second at the highest telemetry bit rate) and 32 such scans are accumulated. The average values of Ex and Ez and the peak signal on Ex are telemetered. In "slow" scan mode the frequency is stepped only twice per telemetry frame. In each half-frame 32 measurements of the signal at the same frequency are accumulated and the average and peak found and telemetered. There is also a fixed-frequency mode of operation where the receiver remains on a single frequency. The instrument is commonly operated in a manner that places it in fast mode for 23 hours, fixed-frequency mode for 1 hour, slow mode for 23 hours, fixed-frequency for 1 hour, and then the cycle repeats. 3.3 Waveform Analyzer The Waveform Analyzer (WFA) measures electric and magnetic signals in the frequency range from 0.08 to 448 Hz. The WFA divides the spectrum into a low and a high band and the analysis is performed separately for the two bands. The low band consists 5 of the frequencies 5.33 Hz and below and the high band consists of frequencies 9.3 Hz and above. The high band processing is performed on Ex, By, and either Bz or Ez depending on a mode command. The information is digitized at a sample rate of 1.792 kHz. Spectra are produced and summed for 2 formats of spacecraft telemetry (64 seconds at the highest telemetry rate). The amplitudes at 12 frequencies are determined using a modified Walsh transform with a bandwidth of 25%. A spectrum is taken for each octant of spacecraft rotation. There are generally 5 or 10 rotations during the 2 format major cycle (depending on the current telemetry bit rate). One set of data obtained, called the averaged data, is the sum of these 5 or 10 spectra per octant, which are then grouped together by opposite octants, giving 4 spectra per antenna. Another set of data, called peak data, is obtained by taking the largest values recorded for the Ex antenna for each frequency and octant, and the values of By and Bz or Ez taken at the same time. Signals for the low band are obtained from Ex and either By or Bz depending on a mode command. The sample rate of the signals is 256 times per spin of the spacecraft and a spectrum is produced every 16 telemetry frames, representing one spin. The same averaging/peak algorithm as the high band is used for the low band. 3.4 Other URAP Instruments In addition to the three instruments discussed above, URAP includes a resonance sounder and a Fast Envelope sampler, which provides short segments of wave data at time resolutions up to 1 msec. The Sounder spectra cover the frequency range from 1.25 to 48.5 kHz. This instrument was implemented in the URAP instrument package late in the development stage. Consequently, it is designed using elements of and telemetry reserved for the other instruments. Because it impacts the data acquired from the other URAP instruments, it is operated with a low duty cycle (e.g., in early 1995, the duty cycle is such as to acquire approximately, six spectra per day). As such, it's purpose is to provide a calibration source for other methods of determining density. These calibration results will be published in the scientific literature. The Fast Envelope Sampler data provide 1024 samples of a wide-band, rectified wave amplitude with time resolution between 1.1 msec and 74 msec. Due to the low Ulysses telemetry rate, only one event can be telemetered every 49 formats (26 or 52 6 minutes depending on bit rate). A synopsis of the FES data is available in panels plotted at the bottom of the black and white URAP Summary Plots (Postscript files). Other formats of the FES data will be archived at a later date. 4 World Wide Web Access to URAP Data Some of the URAP data are being made available over the World Wide Web (WWW). By this means, the data are made convenient and quick to use by a much larger audience, including anyone with access to the Internet. The URAP home page on the WWW provides more information for those interested. The home page makes available color dynamic spectra of RAR, PFR, and WFA data as well as the location of Ulysses during the mission. Educational material and a bibliography of papers describing Ulysses and URAP are also provided. The home page also gives links to other WWW sites of interest including NASA, Goddard Space Flight Center, the Jet Propulsion Laboratory and the European Space Agency, as well as other investigators using the Ulysses instruments and data. The URAP home page at GSFC my be accessed athttp://urap.gsfc.nasa.gov/
7 APPENDICES A UDS data files Eight files are provided that conform to the Ulysses Data System (UDS) conventions regarding file naming and data format. The eight files are divided into 4 pairs of files with each pair consisting of a file containing data averaged over a 10 minute period and a file containing the maximum data value during the same 10 minute period. The 4 pairs of file contain data for the RAR, the PFR, WFA - magnetic field, and WFA - magnetic field. A.1 Radio Astronomy Receiver To reduce the size of the files produced, the UDS files contain 25 frequency channels for the RAR - the upper 12 frequencies of the high receiver, and 13 lower frequencies which are aggregates of the low frequency channels so that they appear in approximately the same logarithmic steps as the high frequency receiver. Since the low frequency receiver steps are linear, there are different numbers of frequency channels that are combined to produce the UDS data. Following is a table giving the approximate center frequency of each UDS channel and the RAR frequencies that were combined to produce it. UDS center RAR frequency channel frequency channels (kHz) (kHz) ------------------------------------------ 1 1.25 1.25 Low receiver 2 2.00 2.00 3 2.75 2.75 4 3.50 3.50 5 4.25 4.25 6 5.75 5.00 - 6.5 7 8.00 7.25 - 8.75 8 11.0 9.50 - 12.5 9 14.75 13.25 - 16.25 10 19.25 17.00 - 21.50 11 24.50 22.25 - 26.75 12 31.25 27.50 - 35.00 13 42.50 35.75 - 48.50 8 14 52.0 52.0 High receiver 15 63.0 63.0 16 81.0 81.0 17 100.0 100.0 18 120.0 120.0 19 148.0 148.0 20 196.0 196.0 21 272.0 272.0 22 387.0 387.0 23 540.0 540.0 24 740.0 740.0 25 940.0 940.0 Two files are produced for each day: they contain averages and peak values for 10 minute periods that start at 00:00:00 and end at 24:00:00. The time specified in the file is the beginning of each time period. The data are computed as follows: For all RAR data that falls within the 10 minute period being considered the average and peak values are found for each of the 76 channels. Next the channels are combined to produce the 25 UDS channels: the average of the combined channels yields the UDS averages and the peak of the combined channels yields the UDS peak value. The names of the files are (following the UDS convention): UURARARAyyddd.ULY : Average data UURARARPyyddd.ULY : Peak data where: yy = Last two digits of year. ddd = Day of year (001..366). The files are Ascii and contain one line for each time period (even if there are no valid data for a time period) so they contain 144 lines each. The format of the data is indicated by the following Fortran read statement which can be used to read the files: DIMENSION F(25) READ(1,100) IYEAR,IDOY,IHOUR,IMIN,ISEC, +MODE_HI,MODE_LO,IBPS,F 100 FORMAT(I4,I4,3I3,3X,3I1,1P25E10.2) where: 9 IYEAR: year IDOY : day of year (Jan 1 = 001) IHOUR: hour, UT IMIN : minute, UT ISEC : second, UT IYEAR .. ISEC is the beginning of the averaging period. MODE_HI: mode of the high receiver: 1: Receiver in summed mode (X and Z antenna combined). 2: Receiver in separate mode(only X antenna). 3: Receiver switched mode during averaging period. 4: Receiver mode unknown. MODE_LO: mode of the low receiver 1: Receiver in summed mode (X and Z antenna combined). 2: Receiver in separate mode (only X antenna). 3: Receiver switched mode during averaging period. 4: Receiver mode unknown. IBPS: telemetry bits-per-second 1: 128 bps. 2: 256 bps. 3: 512 bps. 4: 1024 bps. 5: Bit rate changed during averaging period. 6: Bit rate unknown. F: frequency data - channels 1..25 as defined above. Invalid or missing data are assigned the value -99.0. Units: Units are microvolt/Hz**.5 measured at the receiver input terminals. To convert to electric field strength the given data must be divided by the effective length of the antenna. This is complicated by the fact that the effective length depends on the antenna impedance which is affected by the plasma conditions local to the Ulysses spacecraft. The impedance will also depend on the frequency. In general, the RAR frequency channels that are well above the local electron plasma frequency are not affected by the plasma conditions and the effective length of 23 meters can be used. When the RAR is in summed, rather than separate, mode the determination of field strengths is even more difficult. Time resolution: 10 minutes. 10 A.2 Plasma Frequency Receiver To reduce the size of the UDS files only 16 frequency channels are given which represent the combination of every 2 adjacent channels. The UDS average data files are computed by averaging the Ex-average data values all data that falls in each 10 minute period for each of the 32 channels. Then adjacent channels are averaged together to yield the 16 channels present in the UDS files. The UDS peak data files are computed by finding the the peak value of the Ex-peak data that falls in the 10 minute period. Then the peak of adjacent channels is found to yield the 16 channels present in the UDS files. Because of the limited usefulness of fixed-frequency data when averaged, it has been ignored when creating the UDS files so these 1 hour intervals of fixed-frequency will be replaced by the "bad data" value of -99. File names (following UDS convention): UURAPFRAyyddd.ULY -> Average data UURAPFRPyyddd.ULY -> Peak data yy: Last two digits of year. ddd: Day of year (001..366). The files are Ascii and contain one line for each time period (even if there are no valid data for a time period) so they contain 144 lines each. The format of the data is indicated by the following Fortran read statement which can be used to read the files: DIMENSION F(16) READ(1,100) IYEAR,IDOY,IHOUR,IMIN,ISEC,MODE,IBPS,F 100 FORMAT(I4,I4,3I3,4X,2I1,1P16E10.2) These variables are defined as follows: IYEAR: year IDOY: day of year IHOUR: hour IMIN: minute ISEC: second MODE: PFR scan mode: 11 1: Fast mode. 2: Slow mode. 3: Fixed frequency mode. This value should not occur as fixed frequency data is removed from the UDS data. 4: The mode switched from fast to slow or slow to fast during the averaging interval. 5: Unknown mode. This value occurs if there was no valid data during the averaging interval. This could be due to a data gap or bad data. Data acquired while the PFR is in fixed tune mode is ignored so this value for the MODE will also occur if the PFR was in fixed tune mode during the entire averaging interval. IBPS: Telemetry bit rate: 1: 128 bps. 2: 256 bps. 3: 512 bps. 4: 1024 bps. 5: Bit rate changed during averaging period. 6: Bit rate unknown. F: Contains the PFR data (either average or peak values, depending on the file) of the 16 frequency channels. The frequencies given below are the average of the two adjacent frequencies that are combined. F(1): 0.61 kHz F(2): 0.80 kHz F(3): 1.04 kHz F(4): 1.35 kHz F(5): 1.77 kHz F(6): 2.30 kHz F(7): 3.01 kHz F(8): 3.92 kHz F(9): 5.11 kHz F(10): 6.67 kHz F(11): 8.70 kHz F(12): 11.34 kHz F(13): 14.79 kHz F(14): 19.30 kHz F(15): 25.16 kHz F(16): 32.82 kHz NOTES: These data are electric field intensities detected by the Plasma Frequency Receiver (PFR) on the X antenna of the URAP instrument. 12 Units: Units are microvolt/Hz**.5 measured at the receiver input terminals. To convert to electric field strength the given data must be divided by the effective length of the antenna. This is complicated by the fact that the effective length depends on the antenna impedance which is affected by the plasma conditions local to the Ulysses spacecraft. The impedance will also depend on the frequency. Although, a single number is not accurate for the effective antenna length, the monopole length of 35 meters is a useful approximation. Time resolution: 10 minutes Fill value for bad or missing data is -99.0 A.3 Waveform Analyzer Electric Field Four UDS files are produced per day for the WFA data. Two of the files contain average and peak data for the Ex signals and two files contain average and peak data for magnetic field data. The high band channels (upper 12 frequencies) always contain By. The low band channels (lower 10 frequencies) contain either By or Bz depending on the mode of the instrument. A flag specifying the mode is provided for each time interval. The lowest two frequencies of the WFA are derived in a different manner so they have been left out of the UDS data. This leaves 10 frequencies from the low band and 12 frequencies from the high band. The frequencies are given below. The peak data provided by the WFA high band frequently do not exceed the threshold background so the average values have been used in all cases. The files of 10 minute averaged data were computed by, for all data falling within the 10 minute periods, finding the average values for each frequency. Similiarly, the files of peak data were computed by, for all data falling within the 10 minute periods, finding the maximum value for each frequency. The WFA data is affected by interference from other instruments. In particular, interference from the PFR occurs and is dependent on the PFR scan mode. For this reason a flag indicating the PFR mode is provided in the WFA files. WFA electric field data: The names of the files are (following the UDS convention): UURAWFEAyyddd.ULY -> Average data 13 UURAWFEPyyddd.ULY -> Peak data yy: Last two digits of year. ddd: Day of year (1..366). The files are Ascii and contain one line for each time period (even if there are no valid data for a time period) so they contain 144 lines each. The format of the data is indicated by the following Fortran read statement (which can be used to read the files): DIMENSION F(22) READ(1,100) IYEAR,IDOY,IHOUR,IMIN,ISEC,IPFRMODE,IBPS,F 100 FORMAT(I4,I4,3I3,2X,2I1,1P22E10.2) The variables are defined as follows: IYEAR: year IDOY: day of year IHOUR: hour IMIN: minute ISEC: second IPFRMODE: Indicates the scan mode of the PFR instrument. 1: Fast scan mode. 2: Slow scan mode. 3: Fixed-frequency mode. 4: The mode switched during the averaging interval. 5: The mode could not be determined. IBPS: Telemetry bit rate: 1: 128 bps. 2: 256 bps. 3: 512 bps. 4: 1024 bps. 5: Bit rate changed during averaging period. 6: Bit rate unknown. F: Contains the data for Ex (either average or peak values, depending on the file) of the 22 frequency channels. The frequencies are: F(1): 0.22 Hz F(2): 0.33 Hz F(3): 0.44 Hz F(4): 0.66 Hz F(5): 0.88 Hz 14 F(6): 1.33 Hz F(7): 1.77 Hz F(8): 2.66 Hz F(9): 3.55 Hz F(10): 5.33 Hz F(11): 9.00 Hz F(12): 14.00 Hz F(13): 19.00 Hz F(14): 28.00 Hz F(15): 37.00 Hz F(16): 56.00 Hz F(17): 75.00 Hz F(18): 112.00 Hz F(19): 149.00 Hz F(20): 224.00 Hz F(21): 299.00 Hz F(22): 448.00 Hz These data are electric field intensities detected by the Waveform Analyzer (WFA) on the X antenna of the URAP instrument. Units: Units are microvolt/Hz**.5 measured at the receiver input terminals. To convert to electric field strength the given data must be divided by the effective length of the antenna. This is complicated by the fact that the effective length depends on the antenna impedance which is affected by the plasma conditions local to the Ulysses spacecraft. The impedance will also depend on the frequency. Although, a single number is not accurate for the effective antenna length, the monopole length of 35 meters is a useful approximation. Time resolution: 10 minutes Fill value for bad or missing data is -99.0 A.4 Waveform Analyzer Magnetic Field The names of the files are (following the UDS convention): UURAWFBAyyddd.ULY -> Averaged data UURAWFBPyyddd.ULY -> Peak data yy: Last two digits of year. ddd: Day of year (1..366). The files are Ascii and contain one line for each time period (even if there are no valid data for a time period) so they 15 contain 144 lines each. The format of the data is indicated by the following Fortran read statement (which can be used to read the files): DIMENSION F(22) READ(1,100) IYEAR,IDOY,IHOUR,IMIN,ISEC, +IPFRMODE,IANTENNA,IBPS,F 100 FORMAT(I4,I4,3I3,2X,3I1,1P22E10.2) The variables are defined as follows IYEAR: year IDOY: day of year IHOUR: hour IMIN: minute ISEC: second IANTENNA: Antenna used for low band (0.22 to 5.33 Hz). The high band (9.8 Hz and above) is always By. 1: By 2: Bz 3: Antenna switched during the averaging interval. 4: Antenna unknown. IPFRMODE: Indicates the scan mode of the PFR instrument. 1: Fast scan mode. 2: Slow scan mode. 3: Fixed-frequency mode. 4: The mode switched during the averaging interval. 5: The mode could not be determined. IBPS: Telemetry bit rate: 1: 128 bps. 2: 256 bps. 3: 512 bps. 4: 1024 bps. 5: Bit rate changed during averaging period. 6: Bit rate unknown. F: Contains the data for By or Bz (either average or peak values, depending on the file) of the 22 frequency channels. The frequencies are: F(1): 0.22 Hz F(2): 0.33 Hz F(3): 0.44 Hz F(4): 0.66 Hz F(5): 0.88 Hz 16 F(6): 1.33 Hz F(7): 1.77 Hz F(8): 2.66 Hz F(9): 3.55 Hz F(10): 5.33 Hz F(11): 9.00 Hz F(12): 14.00 Hz F(13): 19.00 Hz F(14): 28.00 Hz F(15): 37.00 Hz F(16): 56.00 Hz F(17): 75.00 Hz F(18): 112.00 Hz F(19): 149.00 Hz F(20): 224.00 Hz F(21): 299.00 Hz F(22): 448.00 Hz These data are magnetic field intensities detected by the Waveform Analyzer (WFA) on the URAP instrument. Units: 10**-15 Tesla/Hz**0.5 Time resolution: 10 minutes Fill value for bad or missing data is -99.0 17 B Ulysses Unified Radio and Plasma wave (URAP) Investigation Daily, 10-day, and 26-day Color Dynamic Spectra June 8, 1999 - plot version 1.20 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 UDS 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 18 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. 19 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 20 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 ishttp://urap.gsfc.nasa.gov/
21 C USER'S GUIDE TO RAR 144 SECOND AVERAGED DATA FILES This document describes the contents and format of the RAR 144 second averaged data files. The time period of 144 seconds was used for the averaging period because that is the basic cycling time of the instrument. The RAR continually cycles through a list of frequencies. There are 16 lists and the list currently in use is chosen by telecommand. The time period to complete the list is 144 seconds for the high band of the receiver (for telemetry bit rates of 1024 and 512 bps, the cycle time is 64 seconds for bit rates of 256 and 128 bps), after which the instrument begins with the list again. Therefore this period was chosen for the averaging period. The format of the data is indicated by the following Fortran statement which can be used to read the data: DIMENSION F(0:75) READ(1,'(I4,2I2,1X,3I2,1X,5I2,12(/6E12.4),/4E12.4)') + IYEAR, IMONTH, IDAY, IHOUR, IMINUTE, ISECOND, + LO_POL_MODE, LO_SUM_MODE, HI_POL_MODE, HI_SUM_MODE, + IBPS, F The variables are defined as follows: The date and time of the beginning of the averaging period are given in IYEAR, IMONTH, IDAY, IHOUR, IMINUTE, ISECOND. LO_POL_MODE and HI_POL_MODE are the polarization modes of the low and high receiver bands. Their values are defined as: 1: Polarization on. 2: Polarization off. 3: Polarization mode switched during the averaging interval. 4: Polarization mode was unknown (usually due to a data gap). LO_SUM_MODE and HI_SUM_MODE are the polarization modes of the low and high receiver bands. Their values are defined as: 1: Summation on. 2: Summation off. 3: Summation mode switched during the averaging interval. 4: Summation mode was unknown (usually due to a data gap). 22 1: Summation on. 2: Summation off. 3: Summation mode switched during the averaging interval. 4: Summation mode was unknown (usually due to a data gap). IBPS indicates the telemetry bit rate during the averaging interval. Its values are defined as: 1: 128 bps. 2: 256 bps. 3: 512 bps. 4: 1024 bps. 5: Bit rate changed during the averaging period. 6: Bit rate unknown - usually due to a data gap. F is a vector containing the average signal for the 76 frequencies of the low and high bands. Elements 0 through 63 are from the low band receiver and correspond to frequencies of 1.25+0.75*N Khz where N is the element number (0..63). The frequency channels from 64 to 75 correspond to the following frequencies: F(64): 52 KHz F(65): 63 KHz F(66): 71 KHz F(67): 100 KHz F(68): 120 KHz F(69): 148 KHz F(70): 196 KHz F(71): 272 KHz F(72): 387 KHz F(73): 540 KHz F(74): 740 KHz F(75): 940 KHz The units of the data are microvolt/Hz**.5 measured at the receiver input terminals. To convert to electric field strength the given data must be divided by the effective length of the antenna. This is complicated by the fact that the effective length depends on the antenna impedance which is affected by the plasma conditions local to the Ulysses spacecraft. The impedance will also depend on the frequency. In general, the RAR frequency channels that are well above the local electron plasma frequency are not affected by the plasma conditions and the effective length of 23 meters can be used. When the RAR is in summed, rather than separate, mode the determination of field strengths is even more difficult. 23