PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " Received at PPI from David Mitchell, 1999-10-04; revised by Mark Sharlow, 1999-12-02; update received at PPI, 2002-08-22; reformatted and ODL keywords added by Mark Sharlow, 2003; Additional Keywords added by D. Kazden, 2009-04-10; Updated cITATION_DESC, D. Kazden, 2020-02-06;" RECORD_TYPE = STREAM OBJECT = DATA_SET DATA_SET_ID = "LP-L-MAG-4-SUMM-LUNARCRDS-5SEC-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "LP MAGER SPINAVG MAGNETIC FIELD LUNAR COORDS 5SEC V1.0" DATA_SET_COLLECTION_MEMBER_FLG = N START_TIME = 1998-01-16 STOP_TIME = 1999-07-29 DATA_SET_RELEASE_DATE = 2002-07-11 PRODUCER_FULL_NAME = "DR. MARIO ACUNA" DETAILED_CATALOG_FLAG = N DATA_OBJECT_TYPE = "TABLE" ARCHIVE_STATUS = ARCHIVED DATA_SET_TERSE_DESC = "Magnetic field data from the Lunar Prospector Magnetometer, averaged in 5-second intervals, in SEL and SSE coordinates in units of nanotesla for dates 1998-01-16 to 1999-07-29, plus spacecraft position data." CITATION_DESC = "Acuna, M., LP-L-MAG-4-SUMM-LUNARCRDS-5SEC-V1.0, LP MAGER SPINAVG MAGNETIC FIELD LUNAR COORDS 5SEC V1.0, NASA Planetary Data System, 2002." ABSTRACT_DESC = "Magnetic field data from the Lunar Prospector Magnetometer, averaged in 5-second intervals, in SEL and SSE coordinates in units of nanotesla for dates 1998-01-16 to 1999-07-29, plus spacecraft position data." DATA_SET_DESC = " Overview: ======== Magnetometer data records are time-ordered series of magnetic vector measurements. Each record consists of a time tag followed by six scalar values representing the magnetic field vector, measured in nanoteslas, in two different coordinate systems: selenocentric solar ecliptic (SSE) and body-fixed selenographic (SEL), followed by the rms deviation of the field magnitude, which is independent of the coordinate system. The spacecraft position is given in both of the above coordinate systems. These data are obtained continuously at 9 Hz and are averaged in 5-second intervals for this data archive. Parameters: ========== Magnetic field data are provided in units of nanotesla (nT). Processing: ========== Magnetic field data are sampled onboard at 18 Hz and averaged to 9 Hz before being placed into telemetry. In order to cover a very large dynamic range with 12-bit values, the full range of the instrument is divided into 8 sub-ranges. Range changing is performed dynamically onboard based on the ambient field strength. The first step in the processing is to extract the data from telemetry and form time-tagged magnetic field vectors. Then, occasional data spikes due to range changes or bad telemetry are flagged; these data points are not used in the offset determination. The instrumental offsets for Bx and By are calculated simultaneously for 1 minute data windows using a technique developed by M. Acuna. Time varying offsets are needed because the offsets drift slightly as the magnetometer temperature changes. (The MAG temperature is modulated as the spacecraft goes in and out of the Moon's shadow.) A constant offset is used for the Z component, because lack of spin modulation in that component precludes routine offset determination. Offsets are calculated separately for each data range and subtracted from the data. This correction reduces systematic errors in the X and Y components to less than ~0.1 nT. Since the Z component cannot be corrected in this way, systematic errors in that axis (due to temperature-induced offset drifts) can be as large as 0.5 nT. Instrumental gains, different for each of the 8 ranges, are then applied to convert to nanotesla. Next, the data are corrected for a slight misalignment between the magnetometer sensor axes and the spacecraft axes. The resulting sensor (SEN) coordinate system has its Z-axis parallel to the spacecraft spin axis, and its X-axis aligned with the magnetometer boom. The SEN coordinate system rotates as the spacecraft spins. The next step is to flag spurious data values. The first measurement following a range change is flagged, since the finite time needed to make the change often corrupts the first measurement in the new range. Other false spikes also appear in the data, most of which are attributable to occasional noise in the telemetry. A comparison technique is used to remove outliers. In practice, this effectively removes most spurious data values without eliminating any valid data. The next step is to ''despin'' the data from SEN to ''despun spacecraft'' (SCD) coordinates, which are defined such that the Z-axis is parallel to the spacecraft spin vector, and the direction of the sun is in the half-plane defined by X > 0, Y = 0. Despinning is performed using the reconstructed sunpulse data, which are corrected for spacecraft spin-up in the Moon's shadow. Next, the data are averaged in 5-second intervals; this reduces the data volume by a factor of 45. Finally, a rotation is performed from SCD coordinates to selenocentric solar ecliptic (SSE) and body-fixed selenocentric (SEL) coordinates using the spacecraft ephemeris data (the latitude and longitude of the spin axis obtained from files included in the PDS distribution of the LP Level-1 magnetic field data) and lunar ephemeris data obtained from the Jet Propulsion Laboratory's Horizons system (). SSE coordinates are defined such that the X-axis points from the center of the Moon to the center of the Sun, the Z-axis is parallel to Earth's ecliptic north, and the Y-axis completes the right-handed coordinate system. SEL coordinates are defined such that the Z-axis is parallel to the Moon's spin vector (north pole) and the X and Y axes intersect the lunar equator. The X-axis intersects the lunar equator at 0 degrees longitude, and is thus nearly aligned with the Moon-Earth line. (It is not exactly aligned because of the Moon's libration.) The Y-axis intersects the lunar equator at 90 degrees EAST longitude: SEL coordinates are right handed. Media/Format: ============ Data are archived on CDROMs in level 1 compliance with the ISO 9660 standard. Three CDROMs cover the entire mission. The data are provided as ASCII ''tables'' of 1-day duration in Selenocentric Solar Ecliptic (SSE) and Selenographic (SEL) coordinates. Date/time are given in 2 formats as described below. MAG Data: Naming convention: MAyymmdd.TAB Parameters: 1) time parameter 1: PDS date-time format of the mid-time of the 5-sec averaging window in spacecraft event time, i.e., Universal Time at the spacecraft. Example: 1998-11-08T05:50:42.5 2) time parameter 2: decimal day of the mid-time of the 5-sec averaging window in spacecraft event time, i.e., Universal Time at the spacecraft. 3) mag_field_SEL: Array[3] giving B-field components (nT) in the SEL coordinate system 4) mag_field_SSE: Array[3] giving B-field components (nT) in the SSE coordinate system 5) mag_field_RMS: RMS deviation (nT) of the field magnitude. Provides an indication of field variability for the 5-sec window. 6) Spacecraft SEL coordinates: coordinate array[3] (km) 7) Spacecraft SSE coordinates: coordinate array[3] (km) 8) ISUN - a parameter from the sunpulse file indicating whether the spacecraft is in the sun (0), in eclipse (1), or, if the sunpulse file was not available, the data were processed using the less accurate determination of the sunpulse time in the Level-0 data file and ISUN is set to 2. Note that this parameter contains erroneous values (0 <-> 1) from time to time. To reduce the occurrence of bad ISUM values the parameter was median-filtered with a 9-point window, which removes most of the errors. These parameters could be named PDS_time, decimal_day, Bx_sel, By_sel, Bz_sel, Bx_sse, By_sse, Bz_sse, B_rms, x_sel, y_sel, z_sel, x_sse, y_sse, z_sse, isun An appropriate format for reading the data is: format='( A21, f12.6, f9.3, 2(f8.3), f9.3, 2(f8.3), f9.3, f10.2, 2(f9.2), f10.2, 2(f9.2), I3 )' however, the records contain blanks between each parameters so that a format statement will not be required by most languages. Ancillary Data: ============== There are several ancillary data files provided with this archive. These include: Spacecraft Attitude data LP-L-ENG-6-ATTITUDE-V1.0 Spacecraft Ephemeris data LP-L-6-EPHEMERIS-V1.0 Spacecraft Position data LP-L-6-POSITION-V1.0 Spacecraft Command logs LP-L-ENG-6-COMMAND-V1.0 These data sets provide additional information about the state of the spacecraft and the instrument during data acquisition that may aid in the scientific analysis of this data set. Coordinate Systems: ================== The SSE coordinate system has its X-axis along the Moon-Sun line, positive towards the Sun. The Z-axis is parallel to the northward normal to the Earth's ecliptic plane, and Y completes the right-handed set. The SEL coordinate system used here is a Cartesian representation that places the Z-axis along the rotation axis of the moon, positive in the direction of angular momentum. The X-axis lies in the lunar equatorial plane at 0 degrees longitude, and Y completes the right-handed set. Software: ======== There are no software provided with this data archive." CONFIDENCE_LEVEL_NOTE = " Review: ====== Magnetometer data quality was reviewed by D.L. Mitchell (UC-Berkeley), M.H. Acuna (NASA-GSFC), and L.L. Hood (LPL-Univ. Arizona). Further review was conducted by R.J. MacDowall (NASA-GSFC), E. Guandique (NASA-GSFC-Emergent), M. Kaelberer (NASA-GSFC-Emergent), and M.H. Acuna (NASA-GSFC). Limitations: =========== The magnetometer data should be used in conjunction with spacecraft ephemeris data so that perturbations to the ambient magnetic field vector due to crustal sources can be localized in selenographic coordinates. It is also important to evaluate the plasma environment using electron reflectometer data, since the Moon can be in the solar wind, in the Earth's magnetosheath, in a geomagnetic tail lobe, or in the geotail current sheet. The plasma environment can strongly influence the usefulness of the data for probing lunar crustal magnetic fields. By far, the best (steadiest) data are obtained in the geomagnetic tail lobes. Data Quality: ============ Magnetometer data are of excellent quality. Systematic errors in the magnetic field component orthogonal to the spacecraft spin vector have been reduced to ~0.1 nT by time-variable offset corrections (see above). Systematic errors in the magnetic field component parallel to the spin axis can be as large as ~0.5 nT. The B_RMS value provides an indication of the field variability during the 5-sec window. A single, large value for the B_RMS would likely indicate that bad-telemetry or some similar problem had caused large variability during a single averaging window. Data Coverage: ============= Magnetic field data are obtained continuously; however, telemetry gaps do occur. A table of gaps in the raw merged telemetry data OUTAGES.TAB) is available in the Level 0 Lunar Prospector archive, but is not part of the present Level 1 archive. Other gaps may exist due to data contamination or processing limitations. In particular, we list in Appendix A, times when we have explicitly removed data from the dataset for reasons such as corrupted sun pulse data preventing the despinning of the magnetic field data. There are also a number of data gaps that result because the MAG/ER instruments were telemetering burst mode data; these intervals are listed in Appendix B. APPENDIX A - Time intervals for which Magnetic field data were deleted from this archive Year Month Day Start decday Stop decday 1998 4 8 98.407899 98.412240 1998 5 1 121.704774 121.733883 1998 5 15 135.739902 135.743721 1998 5 16 136.570399 136.586314 1998 8 15 227.220689 227.232726 1998 8 17 229.684809 229.712471 1998 12 3 337.314265 337.314612 1999 1 29 29.313513 29.338455 1999 2 25 56.501591 56.521962 1999 3 3 62.877170 62.954948 1999 3 24 83.758767 83.782089 1999 4 16 106.511603 106.515480 1999 4 17 107.210503 107.211429 1999 5 1 121.045168 121.080874 1999 5 12 132.137703 132.149334 APPENDIX B - Approximate times of data gaps due to MAG/ER burst mode telemetry Year Month Day Day of year: time of day 1998 12 03 day 337: 3 intervals from 5:20-10:15 1999 03 03 day 62: 21:00-24:00 1999 03 04 day 63: 0:00- 0:35 1999 03 18 day 77: 3 intervals from 11:30-24:00 1999 03 19 day 78: 4 intervals from 0:00-24:00 1999 03 20 day 79: 4 intervals from 0:00-24:00 1999 03 21 day 80: 4 intervals from 0:00-13:30 1999 04 14 day 104: 22:30-24:00 1999 04 15 day 105: 4 intervals from 0:00-24:00 1999 04 16 day 106: 5 intervals from 0:00-24:00 1999 04 17 day 107: 5 intervals from 0:00-24:00 1999 06 08 day 159: 2 intervals from 15:20-24:00 1999 06 09 day 160: 4 intervals from 0:00-24:00 1999 06 10 day 161: 5 intervals from 0:00-24:00 1999 06 11 day 162: 2 intervals from 0:00-17:30 1999 07 05 day 186: 2 intervals from 16:00-24:00 1999 07 06 day 187: 4 intervals from 0:00-24:00 1999 07 07 day 188: 5 intervals from 0:00-24:00 1999 07 08 day 189: 4 intervals from 0:00-18:00 " END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = MOON END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = LP INSTRUMENT_ID = MAG END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_MISSION MISSION_NAME = "LUNAR PROSPECTOR" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "BINDERETAL1998" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "ACUNAETAL1992" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CARLSONETAL1983" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET END