Data Set Information
DATA_SET_NAME LP MAGER SPINAVG MAGNETIC FIELD LUNAR COORDS 5SEC V1.0
DATA_SET_ID LP-L-MAG-4-SUMM-LUNARCRDS-5SEC-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Overview:========Magnetometer data records are time-ordered series of magnetic vectormeasurements. Each record consists of a time tag followed by sixscalar values representing the magnetic field vector, measured innanoteslas, in two different coordinate systems: selenocentric solarecliptic (SSE) and body-fixed selenographic (SEL), followed by the rmsdeviation of the field magnitude, which is independent of thecoordinate system. The spacecraft position is given in both of theabove coordinate systems. These data are obtained continuously at 9Hz 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 Hzbefore being placed into telemetry. In order to cover a very largedynamic range with 12-bit values, the full range of the instrument isdivided into 8 sub-ranges. Range changing is performed dynamicallyonboard based on the ambient field strength. The first step in theprocessing is to extract the data from telemetry and form time-taggedmagnetic field vectors. Then, occasional data spikes due to rangechanges or bad telemetry are flagged; these data points are not used inthe offset determination. The instrumental offsets for Bx and By arecalculated simultaneously for 1 minute data windows using a techniquedeveloped by M. Acuna. Time varying offsets are needed because theoffsets drift slightly as the magnetometer temperature changes. (TheMAG temperature is modulated as the spacecraft goes in and out of theMoon's shadow.) A constant offset is used for the Z component, becauselack of spin modulation in that component precludes routine offsetdetermination. Offsets are calculated separately for each data rangeand subtracted from the data. This correction reduces systematic errorsin the X and Y components to less than ~0.1 nT. Since the Z componentcannot be corrected in this way, systematic errors in that axis (due totemperature-induced offset drifts) can be as large as 0.5 nT.Instrumental gains, different for each of the 8 ranges, are thenapplied to convert to nanotesla. Next, the data are corrected for aslight misalignment between the magnetometer sensor axes and thespacecraft axes. The resulting sensor (SEN) coordinate system has itsZ-axis parallel to the spacecraft spin axis, and its X-axis alignedwith the magnetometer boom. The SEN coordinate system rotates as thespacecraft spins. The next step is to flag spurious data values. Thefirst measurement following a range change is flagged, since the finitetime needed to make the change often corrupts the first measurement inthe new range. Other false spikes also appear in the data, most ofwhich are attributable to occasional noise in the telemetry. Acomparison technique is used to remove outliers. In practice, thiseffectively removes most spurious data values without eliminating anyvalid data. The next step is to ''despin'' the data from SEN to''despun spacecraft'' (SCD) coordinates, which are defined such thatthe Z-axis is parallel to the spacecraft spin vector, and the directionof the sun is in the half-plane defined by X > 0, Y = 0. Despinning isperformed using the reconstructed sunpulse data, which are correctedfor spacecraft spin-up in the Moon's shadow. Next, the data areaveraged in 5-second intervals; this reduces the data volume by afactor of 45. Finally, a rotation is performed from SCD coordinates toselenocentric solar ecliptic (SSE) and body-fixed selenocentric (SEL)coordinates using the spacecraft ephemeris data (the latitude andlongitude of the spin axis obtained from files included in the PDSdistribution of the LP Level-1 magnetic field data) and lunar ephemerisdata obtained from the Jet Propulsion Laboratory's Horizons system(). SSE coordinates are definedsuch that the X-axis points from the center of the Moon to the centerof the Sun, the Z-axis is parallel to Earth's ecliptic north, and theY-axis completes the right-handed coordinate system. SEL coordinatesare 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. TheX-axis intersects the lunar equator at 0 degrees longitude, and is thusnearly aligned with the Moon-Earth line. (It is not exactly alignedbecause of the Moon's libration.) The Y-axis intersects the lunarequator at 90 degrees EAST longitude: SEL coordinates are right handed.Media/Format:============Data are archived on CDROMs in level 1 compliance with the ISO 9660standard. Three CDROMs cover the entire mission. The data are providedas ASCII ''tables'' of 1-day duration in Selenocentric Solar Ecliptic(SSE) and Selenographic (SEL) coordinates. Date/time are given in 2formats as described below.MAG Data:Naming convention: MAyymmdd.TABParameters:1) time parameter 1: PDS date-time format of the mid-time of the 5-secaveraging window in spacecraft event time, i.e., Universal Time at thespacecraft. Example: 1998-11-08T05:50:42.52) time parameter 2: decimal day of the mid-time of the 5-sec averagingwindow in spacecraft event time, i.e., Universal Time at the spacecraft.3) mag_field_SEL: Array[3] giving B-field components (nT) in the SELcoordinate system4) mag_field_SSE: Array[3] giving B-field components (nT) in the SSEcoordinate system5) mag_field_RMS: RMS deviation (nT) of the field magnitude. Providesan 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 thespacecraft is in the sun (0), in eclipse (1), or, if the sunpulse filewas not available, the data were processed using the less accuratedetermination of the sunpulse time in the Level-0 data file and ISUN isset to 2. Note that this parameter contains erroneous values (0 <-> 1)from time to time. To reduce the occurrence of bad ISUM values theparameter was median-filtered with a 9-point window, which removes mostof 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, isunAn 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 aformat 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-V1.0Spacecraft Ephemeris data LP-L-6-EPHEMERIS-V1.0Spacecraft Position data LP-L-6-POSITION-V1.0Spacecraft Command logs LP-L-ENG-6-COMMAND-V1.0These data sets provide additional information about the state of thespacecraft and the instrument during data acquisition that may aid inthe 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 northwardnormal to the Earth's ecliptic plane, and Y completes the right-handedset. The SEL coordinate system used here is a Cartesian representationthat places the Z-axis along the rotation axis of the moon, positive inthe direction of angular momentum. The X-axis lies in the lunarequatorial plane at 0 degrees longitude, and Y completes theright-handed set.Software:========There are no software provided with this data archive.
DATA_SET_RELEASE_DATE 2002-07-11T00:00:00.000Z
START_TIME 1998-01-16T12:00:00.000Z
STOP_TIME 1999-07-29T12:00:00.000Z
MISSION_NAME LUNAR PROSPECTOR
MISSION_START_DATE 1995-01-01T12:00:00.000Z
MISSION_STOP_DATE 1999-07-31T12:00:00.000Z
TARGET_NAME MOON
TARGET_TYPE SATELLITE
INSTRUMENT_HOST_ID LP
INSTRUMENT_NAME DUAL TECHNIQUE MAGNETOMETER
TRIAXIAL FLUXGATE MAGNETOMETER
MAGNETOMETER
FLUXGATE MAGNETOMETER
INSTRUMENT_ID MAG
INSTRUMENT_TYPE MAGNETOMETER
Magnetometer
NODE_NAME planetary plasma interactions
ARCHIVE_STATUS ARCHIVED
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). Furtherreview 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 spacecraftephemeris data so that perturbations to the ambient magnetic fieldvector due to crustal sources can be localized in selenographiccoordinates. It is also important to evaluate the plasma environmentusing electron reflectometer data, since the Moon can be in the solarwind, in the Earth's magnetosheath, in a geomagnetic tail lobe, or inthe geotail current sheet. The plasma environment can stronglyinfluence the usefulness of the data for probing lunar crustal magneticfields. By far, the best (steadiest) data are obtained in thegeomagnetic tail lobes.Data Quality:============Magnetometer data are of excellent quality. Systematic errors in themagnetic field component orthogonal to the spacecraft spin vector havebeen reduced to ~0.1 nT by time-variable offset corrections (seeabove). Systematic errors in the magnetic field component parallel tothe spin axis can be as large as ~0.5 nT. The B_RMS value provides anindication of the field variability during the 5-sec window. A single,large value for the B_RMS would likely indicate that bad-telemetry orsome similar problem had caused large variability during a singleaveraging window.Data Coverage:=============Magnetic field data are obtained continuously; however, telemetry gapsdo 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 partof the present Level 1 archive. Other gaps may exist due to datacontamination or processing limitations. In particular, we list inAppendix A, times when we have explicitly removed data from the datasetfor reasons such as corrupted sun pulse data preventing the despinningof the magnetic field data. There are also a number of data gaps thatresult because the MAG/ER instruments were telemetering burst modedata; these intervals are listed in Appendix B.APPENDIX A - Time intervals for which Magnetic field data were deletedfrom this archiveYear Month Day Start decday Stop decday1998 4 8 98.407899 98.4122401998 5 1 121.704774 121.7338831998 5 15 135.739902 135.7437211998 5 16 136.570399 136.5863141998 8 15 227.220689 227.2327261998 8 17 229.684809 229.7124711998 12 3 337.314265 337.3146121999 1 29 29.313513 29.3384551999 2 25 56.501591 56.5219621999 3 3 62.877170 62.9549481999 3 24 83.758767 83.7820891999 4 16 106.511603 106.5154801999 4 17 107.210503 107.2114291999 5 1 121.045168 121.0808741999 5 12 132.137703 132.149334APPENDIX B - Approximate times of data gaps due to MAG/ER burst modetelemetryYear Month Day Day of year: time of day1998 12 03 day 337: 3 intervals from 5:20-10:151999 03 03 day 62: 21:00-24:001999 03 04 day 63: 0:00- 0:351999 03 18 day 77: 3 intervals from 11:30-24:001999 03 19 day 78: 4 intervals from 0:00-24:001999 03 20 day 79: 4 intervals from 0:00-24:001999 03 21 day 80: 4 intervals from 0:00-13:301999 04 14 day 104: 22:30-24:001999 04 15 day 105: 4 intervals from 0:00-24:001999 04 16 day 106: 5 intervals from 0:00-24:001999 04 17 day 107: 5 intervals from 0:00-24:001999 06 08 day 159: 2 intervals from 15:20-24:001999 06 09 day 160: 4 intervals from 0:00-24:001999 06 10 day 161: 5 intervals from 0:00-24:001999 06 11 day 162: 2 intervals from 0:00-17:301999 07 05 day 186: 2 intervals from 16:00-24:001999 07 06 day 187: 4 intervals from 0:00-24:001999 07 07 day 188: 5 intervals from 0:00-24:001999 07 08 day 189: 4 intervals from 0:00-18:00
CITATION_DESCRIPTION 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_TEXT Magnetic field data from the Lunar ProspectorMagnetometer, averaged in 5-second intervals, in SEL and SSE coordinatesin units of nanotesla for dates 1998-01-16 to 1999-07-29, plusspacecraft position data.
PRODUCER_FULL_NAME DR. MARIO ACUNA
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