Data Set Overview
    =================
      The Clementine Bistatic Radar Raw Data Archive (BSR-RDA) is
      a time-ordered collection of raw and partially processed data
      from bistatic radar scattering experiments conducted using
      the Clementine spacecraft while it orbited the Moon.
 
      The spacecraft radio system was used as a signal source,
      and the spacecraft high-gain antenna beamed those signals
      toward surface targets on the Moon.  The transmit polarization
      along the boresight of the spacecraft antenna was right-
      circular; the nominal wavelength was 13 cm (S-band).  Echo
      signals were received coherently in both right- and left-
      circular polarizations using 70-m antennas at stations of
      the NASA Deep Space Network (DSN) on Earth.
 
      The scattering experiments were conducted in two
      configurations.  For 'spotlight' experiments a single
      target was identified on the Moon; the spacecraft attitude
      was controlled during the experiment so that the HGA always
      pointed toward that target location.
 
      Spotlight experiments, conducted on polar targets were
      designed to detect and measure enhanced backscatter from
      possible ice deposits in areas permanently shaded from
      solar illumination.  Such enhancements have been seen in
      Earth-based radar studies of the Galilean satellites
      [CAMPBELLETAL1978], Mars [MUHLEMANETAL1991], and Mercury
      [HARMONETAL1994].  Although Earth-based radar studies of
      the Moon [STACY1993] have had considerably better
      sensitivity and surface resolution than this experiment,
      the Clementine geometry uniquely allowed measurements as a
      function of the bistatic angle -- the separation angle
      between transmitter and receiver when viewed from the target
      [SIMPSON1993].  The angular variation of any enhancement may
      be related to the distance the radar signal travels through
      the ice and, hence, to the thickness and/or clarity of the
      ice at 13 cm wavelength.
 
      For 'quasi-specular' observations, the HGA was aimed toward
      the point on the lunar surface where mirror-like (specular)
      reflections were expected.  Signals transmitted by the
      spacecraft would carom from the lunar surface and be received
      at the DSN stations.  Because the (specular) image of
      Earth moved as Clementine orbited the Moon, the HGA
      illuminated a swath across the surface as the spacecraft
      advanced in its orbit.  A single quasi-specular track was
      obtained -- in the southern hemisphere during the last set
      of bistatic radar observations.
 
      The data set includes Original Data Records (ODRs),
      digitized recordings of baseband receiver output; Archival
      Tracking Data Files (ATDFs), edited records of closed-loop
      receiver output and related parameters; Link Monitor and
      Control log files (LMC logs), the automatic diary of
      station operator activities; trajectory and attitude data;
      and relevant documentation.
 
      Typical users of the data set would spectrally analyze the
      echo signals in the ODRs; with trajectory and attitude data,
      the measured signals could be calibrated and mapped to
      reflectivity of specific surface areas.  Unusual
      reflectivities in geometries near backscatter [HARMONETAL1994;
      MUHLEMANETAL1991] might suggest the presence of ice deposits.
      More general scattering properties of the surface can be
      investigated; this is the first planetary data set for which
      scattering from a single target region has been observed over
      a wide range of bistatic angles.
 
 
    Parameters
    ==========
      Open loop data records contain 8-bit samples of receiver
      output as noted above.  Each block of 4000 data samples
      is accompanied a 166 byte header.  The ODR is described
      by a Software Interface Specification (SIS), included as
      RSC11_11.TXT in the DOCUMENT directory of the data set
      archival volume.
 
      For these experiments two S-band (13 cm wavelength)
      open-loop receivers were used, one capturing right-
      circularly polarized signal and the other capturing
      left-circularly polarized signals.  These are identified in
      the data stream as Channels 1 and 3 respectively.  Channel
      1 was sampled alternately by analog-to-digital converters
      (ADCs) #1 and #3; Channel 3 was sampled alternately by ADCs
      #2 and #4.  Each ADC operated at 25000 8-bit samples per
      second giving an effective sampling rate of 50000 on each
      channel.  The effective bandwidth of the filtered output
      on each channel was about 20 kHz.
 
      Each ATDF data record contains 117 parameters, stored in
      records of 288 bytes at rates up to 10 per second.  The
      parameters include estimates of received signal strength
      and frequency as well as status information on components
      of the DSN system.  The ATDF is described by a Software
      Interface Specification (SIS), included as TRK_2_25.TXT
      in the DOCUMENT directory of each BSR-RDA volume.
 
      LMC files are real-time command logs for operators at DSN
      stations.  Although they contain information on a wide
      variety of equipment, their primary value for these experiments
      is their record of configuration changes (ambient load
      calibrations) and attenuator settings.  These are either
      not available or not nearly as well recorded in other files.
      LMC files were not available for all observations.  LMC
      file formats are described by file LMC.TXT in the DOCUMENT
      directory of each BSR-RDA volume.
 
 
    Processing
    ==========
      Open loop data (ODRs) are not edited or otherwise processed
      before being incorporated in the BSR-RDA.  A 32-byte label at
      the beginning of each ODR tape is not included in the data
      file; it gives the software version of the data taking
      equipment and is saved instead as the value of the keyword
      SOFTWARE_NAME in the PDS label that accompanies the data file.
 
      DSN NAV performs editing on data during conversion from the
      Intermediate Data Record (IDR) to ATDF formats; this function
      serves mostly to remove anomalous (out of nominal range)
      values.
 
      LMC files are ASCII files and are not processed before being
      included in the BSR-RDA.
 
 
    Data
    ====
      During the observations on 1994-04-09 and 1994-04-10 the
      Earth was nearly in the Clementine orbit plane; the spacecraft
      appeared to move from north to south across the lunar disk,
      as viewed from Earth.  Spotlight experiments were conducted
      on revolutions 233-236 using target points near the lunar south
      pole, where a large shaded region [SHOEMAKERETAL1994]
      potentially containing permanent deposits of water ice may
      exist [NOZETTEETAL1994].  These experiments were conducted
      at new moon; periselene was on the far side of the Moon at
      approximately 30 degrees S latitude.
 
        NB:  The revolution number refers to an observational pass
        over the Moon.  The revolution number was incremented by one
        each time the spacecraft passed over the south pole prior to
        the beginning of data acquisition.  REVOLUTION_NUMBER was
        used in lieu of orbit number because of the way the orbit
        number was defined by the mission.  The orbit number was
        incremented each time the spacecraft passed through the
        equatorial plane on the sunlit side of the Moon.  Thus, the
        orbit number generally changed in the middle of an
        observational pass.  This proved to be awkward in defining
        the data acquired by a single pass over the Moon.
 
      During the observations of 1994-04-23 and 1994-04-24 Earth
      was also nearly in the spacecraft orbit plane.  The spacecraft
      appeared to move from south to north across the lunar disk,
      as viewed from Earth.  Spotlight experiments were conducted
      on revolutions 299, 301, and 302 using targets near the lunar
      north pole.  A single track of quasi-specular data was
      obtained in the southern hemisphere during one revolution, and
      at least three ingress and one egress occultations were
      recorded.  These experiments were conducted at full Moon;
      periselene was on the near side of the Moon at
      approximately 30 degrees N latitude.
 
      The primary data are Original Data Records (ODRs) -- the
      sampled output from open-loop receivers at stations of the
      NASA Deep Space Network (DSN).  Calibrations preceded and
      followed most bistatic radar observations and were recorded
      on the same ODRs.  Bistatic radar data collection included
      the science events shown in the table below.  The column
      labeled DSS contains the value of the PDS label keyword
      DSN_STATION_NUMBER (the primary ground antenna).
 
                  Revolution
          Date      Number    DSS      UTC          Observation
      ----------  ----------  ---  -----------  -------------------
      1994-04-09      233      14  18:13-19:50  Spotlight (90S, 0W)
                      234      43  23:28-01:17  Spotlight (90S, 0W)
      1994-04-10      235      43  04:33-06:16  Spotlight (90S, 0W)
                      236      63  09:16-10:02  Spotlight (90S, 0W)
      1994-04-23      299      43  08:42-09:46  Spotlight (90N, 0W)
                      299      43  09:56        Occultation Ingress
                      301      63  18:35-19:45  Spotlight (90N, 0W)
                      301      63  19:52        Occultation Ingress
                      301      63  21:04        Occultation Egress
                      301      63  21:22-22:33  Specular Point
                      302      63  22:33-23:23  Specular Point (cont)
                      302      63  23:26-00:42  Spotlight (90N, 0W)
      1994-04-24      302      63  00:52        Occultation Ingress
 
      ATDFs are files of radiometric data produced by the Network
      Operations Control Center (NOCC) Navigation Subsystem (NAV).
      They are derived from Intermediate Data Records by NAV and
      contain all radiometric measurements received from the DSN
      station including signal levels, antenna pointing angles,
      Doppler, range, and residuals.  Doppler data are often used
      to infer spacecraft radial motion relative to the tracking
      antenna.  Data values in ATDFs are reported at rates no
      higher than 10 per second.  A single ATDF covers all but the
      last 90 minutes of the Clementine bistatic radar observations.
 
      Link Monitor and Control log files provide accurate diaries
      of station activities, including changes in configuration and
      changes in attenuator settings.  Hand-written logs also provide
      records of configuration changes, and attenuator settings are
      checked periodically and saved in ODR headers; but the LMC
      log files are by far the most accurate for times at which
      changes were made.  LMC logs have been obtained for the
      DSS 63 coverage on 1994-04-10 and 1994-04-23.
 
      SPICE CK files allow reconstruction of spacecraft attitude;
      SPICE SPK files give the spacecraft trajectory as well as
      planetary positions and velocities.  The SPICE system is
      described in files TK_FTP.TXT, TK_DESCR.TXT, and TK_INSTL.TXT
      in the DOCUMENT directory of each BSR-RDA volume.
 
      Documentation includes real-time notes, stored as text files
      in the CALIB directory.
 
 
    Coordinate System
    =================
      SPK ephemeris files and CK attitude files are produced for the
      J2000 inertial reference frame.  SPICE reader routines may be
      used to convert these to other coordinate systems.
 
      Other data types are not dependent on definition of a
      coordinate system.
 
 
    Software
    ========
      Software for parsing, reducing, and analyzing data such as
      these has been developed at Stanford University and elsewhere.
      The Stanford software has not been prepared for general
      distribution and is not included with the archival data set.
 
 
    Media/Format
    ============
      The archival data set is written on CD-WO media using the
      Young Minds CD Studio authoring system.  The CD-WO volumes
      conform to ISO 9660 standards.

Overview
    ========
      At the time the raw data were archived relatively little
      analysis had been performed, though all ODRs had been
      checked and some 'quick-look' results had been reported.
 
      The primary weakness in the data set is likely to be in
      the calibration of signal amplitudes for absolute echo
      powers.
 
      The experiment involved signals which were both
      very strong and very dynamic.  Calibration measurements
      are included in the ODR collection; but it is not clear
      as of this writing whether the calibrations were performed
      at the remote sites as the experimenters had intended or
      whether the results captured on tape can be interpreted.
 
      During some portions of the experiment, signals propagating
      directly from the spacecraft to the ground station were
      strong enough that the response of the maser was suppressed.
      The quantitative effect on the signals being measured has
      not been estimated.  Since the interfering signal was not
      always within the recorded passband, the times at which
      maser performance was degraded cannot necessarily be
      determined from simple examinations of the data.
 
      Secondarily, the frequency of the spacecraft transmitter
      was controlled by a simple crystal oscillator.  Its frequency
      is known only approximately (and confirmed through these
      observations); its drift characteristics both as a function
      of operating time and as a function of temperature are not
      known.
 
      After these raw data were originally archived, a group of
      Clementine investigators published results of their analysis
      [NOZETTEETAL1996], concluding that there was evidence for
      enhanced backscatter (and, thus, ice) at the South Pole.
      A subsequent reanalysis of the South Pole data at Stanford
      University was unable to reproduce those results.  A Stanford
      paper by R.A. Simpson and G.L. Tyler was expected to appear
      in Journal of Geophysical Research in early 1999.
 
 
    Review
    ======
      This archival data set was distributed to a peer review
      panel prior to its acceptance by the Planetary Data System
      (PDS).  The review panel was appointed by the Manager
      of the PDS Geosciences (GEO) Discipline Node (DN); the
      review was conducted in accordance with PDS GEO
      procedures.
 
      Prior to creation of the final version of the archival data
      set, key elements of the archive were distributed for
      preliminary review.  These included electronic versions
      of example PDS labels, CATALOG files, and Software Interface
      Specifications.  These materials were distributed to PDS
      personnel, the experiment Principal Investigator, and others,
      as appropriate.
 
      Data on the CD-WO volumes was checked using Stanford
      parsing and reduction software to ensure that it was both
      complete and an accurate replica of the data contained
      in the original tape files.
 
 
    Data Coverage and Quality
    =========================
      The times covered by ODR tapes are given below:
 
                                              Revolution
        Start Time (ERT)    Stop Time (ERT)     Number   DSS   Obsn
      ------------------- ------------------- ---------- --- --------
      1994-04-09T17:48:45 1994-04-09T18:04:44     233     14
      1994-04-09T18:04:45 1994-04-09T18:20:44     233     14  S Pole
      1994-04-09T18:20:45 1994-04-09T18:36:44     233     14  S Pole
      1994-04-09T18:36:45 1994-04-09T18:52:44     233     14  S Pole
      1994-04-09T18:52:45 1994-04-09T19:08:44     233     14  S Pole
      1994-04-09T19:08:45 1994-04-09T19:24:44     233     14  S Pole
      1994-04-09T19:24:45 1994-04-09T19:40:44     233     14  S Pole
      1994-04-09T19:40:45 1994-04-09T19:56:44     233     14  S Pole
      1994-04-09T19:56:45 1994-04-09T20:05:09     233     14
      1994-04-09T23:00:55 1994-04-09T23:16:54     234     43
      1994-04-09T23:16:55 1994-04-09T23:32:54     234     43  S Pole
      1994-04-09T23:32:55 1994-04-09T23:48:54     234     43  S Pole
      1994-04-09T23:48:55 1994-04-10T00:04:54     234     43  S Pole
      1994-04-10T00:04:55 1994-04-10T00:20:54     234     43  S Pole
      1994-04-10T00:20:55 1994-04-10T00:36:54     234     43  S Pole
      1994-04-10T00:36:55 1994-04-10T00:52:54     234     43  S Pole
      1994-04-10T00:52:55 1994-04-10T01:08:54     234     43  S Pole
      1994-04-10T01:08:55 1994-04-10T01:24:54     235     43  S Pole
      1994-04-10T01:24:55 1994-04-10T01:33:55     235     43
      1994-04-10T04:02:22 1994-04-10T04:18:21     235     43
      1994-04-10T04:18:22 1994-04-10T04:34:21     235     43  S Pole
      1994-04-10T04:34:22 1994-04-10T04:50:21     235     43  S Pole
      1994-04-10T04:50:22 1994-04-10T05:06:21     235     43  S Pole
      1994-04-10T05:06:22 1994-04-10T05:22:21     235     43  S Pole
      1994-04-10T05:22:22 1994-04-10T05:38:21     235     43  S Pole
      1994-04-10T05:38:22 1994-04-10T05:54:21     235     43  S Pole
      1994-04-10T05:54:22 1994-04-10T06:10:21     235     43  S Pole
      1994-04-10T06:10:22 1994-04-10T06:26:21     236     43  S Pole
      1994-04-10T06:26:22 1994-04-10T06:42:21     236     43
      1994-04-10T06:42:22 1994-04-10T06:46:54     236     43
      1994-04-10T08:52:22 1994-04-10T09:08:21     236     63
      1994-04-10T09:08:22 1994-04-10T09:24:21     236     63  S Pole
      1994-04-10T09:24:22 1994-04-10T09:40:23     236     63  S Pole
      1994-04-10T09:40:24 1994-04-10T09:56:23     236     63  S Pole
      1994-04-10T09:56:24 1994-04-10T10:12:23     236     63  S Pole
      1994-04-10T10:12:24 1994-04-10T10:28:23     236     63
      1994-04-10T10:28:24 1994-04-10T10:44:23     236     63
      1994-04-10T10:44:24 1994-04-10T10:53:05     236     63
      1994-04-23T08:19:08 1994-04-23T08:35:07     299     43
      1994-04-23T08:35:08 1994-04-23T08:51:07     299     43  N Pole
      1994-04-23T08:51:08 1994-04-23T09:07:07     299     43  N Pole
      1994-04-23T09:07:08 1994-04-23T09:23:07     299     43  N Pole
      1994-04-23T09:23:08 1994-04-23T09:39:07     299     43  N Pole
      1994-04-23T09:39:08 1994-04-23T09:55:07     299     43  N Pole
      1994-04-23T09:55:08 1994-04-23T10:11:07     299     43  Occ In
      1994-04-23T10:11:08 1994-04-23T10:27:07     299     43
      1994-04-23T10:27:08 1994-04-23T10:43:07     299     43
      1994-04-23T10:43:08 1994-04-23T10:46:01     299     43
      1994-04-23T18:15:14 1994-04-23T18:31:13     301     63
      1994-04-23T18:31:14 1994-04-23T18:32:23     301     63
      1994-04-23T18:35:32 1994-04-23T18:51:31     301     63  N Pole
      1994-04-23T18:51:32 1994-04-23T19:07:31     301     63  N Pole
      1994-04-23T19:07:32 1994-04-23T19:23:31     301     63  N Pole
      1994-04-23T19:23:32 1994-04-23T19:39:31     301     63  N Pole
      1994-04-23T19:39:32 1994-04-23T19:55:31     301     63  Occ In
      1994-04-23T19:55:32 1994-04-23T20:11:31     301     63
      1994-04-23T20:11:32 1994-04-23T20:27:31     301     63
      1994-04-23T20:27:32 1994-04-23T20:43:31     301     63
      1994-04-23T20:43:32 1994-04-23T20:59:31     301     63
      1994-04-23T20:59:32 1994-04-23T21:15:31     301     63  Occ Eg
      1994-04-23T21:15:32 1994-04-23T21:31:31     301     63  Q-Spec
      1994-04-23T21:31:32 1994-04-23T21:47:31     301     63  Q-Spec
      1994-04-23T21:47:32 1994-04-23T22:03:31     301     63  Q-Spec
      1994-04-23T22:03:32 1994-04-23T22:19:31     301     63  Q-Spec
      1994-04-23T22:19:32 1994-04-23T22:35:31     302     63  Q-Spec
      1994-04-23T22:35:32 1994-04-23T22:51:31     302     63  Q-Spec
      1994-04-23T22:51:32 1994-04-23T23:07:31     302     63  Q-Spec
      1994-04-23T23:07:32 1994-04-23T23:23:31     302     63  Q-Spec
      1994-04-23T23:23:32 1994-04-23T23:39:31     302     63  N Pole
      1994-04-23T23:39:32 1994-04-23T23:55:31     302     63  N Pole
      1994-04-23T23:55:32 1994-04-24T00:11:31     302     63  N Pole
      1994-04-24T00:11:32 1994-04-24T00:27:31     302     63  N Pole
      1994-04-24T00:27:32 1994-04-24T00:43:31     302     63  N Pole
      1994-04-24T00:43:32 1994-04-24T00:59:31     302     63  Occ In
      1994-04-24T00:59:32 1994-04-24T01:15:31     302     63
      1994-04-24T01:15:32 1994-04-24T01:31:31     302     63
      1994-04-24T01:31:32 1994-04-24T01:47:31     302     63
      1994-04-24T01:47:32 1994-04-24T01:54:40     302     63
 
      Both before and after observations of the echo signal,
      calibrations were scheduled.  These typically included a few
      minutes' observation of the zenith sky to obtain a baseline
      characterization of the receiving system with no spacecraft
      signal present.  Ambient loads were then switched in and the
      receiver attenuators were adjusted for approximately the
      same rms output noise level.  From the actual change in the
      noise power, the attenuator differential, and the physical
      temperature of the ambient load, it should be possible to
      calculate the system temperature.  It was not clear during
      the calibrations that the ambient loads were being switched
      in and out as requested -- on both channels -- and it was
      not always possible to obtain the physical temperatures of
      these devices from the remote sites.
 
      After the ambient load tests at zenith, the 70-m antenna was
      slewed to track the spacecraft briefly.  As the spacecraft
      began its maneuver to point toward the target on the
      surface of the Moon, the ground antenna was moved to the
      center of the lunar disk.  This yielded a measurement of the
      thermal microwave emission of the Moon, which was recorded on
      the ODR tapes.  In some cases, however, the signal from the
      spacecraft may have corrupted these measurements.
 
      Finally, the ground antenna was moved to point at the target
      region on the lunar surface.  Again, there were instances in
      which a strong signal propagating directly from the spacecraft
      to the ground may have overloaded the front end of the
      receiving system and corrupted the recording.
 
      After observing the echo signal for typically one hour, the
      procedure was reversed (another calibration at the center of
      the Moon, an ambient load test, and a clear sky measurement).
 
 
    Limitations
    ===========
      See section Data Coverage and Quality above.
 
      Although spotlight coverage on revolution 236 (1994-04-10) was
      nominally the South Pole, negative quaternions were generated
      and the high-gain antenna commanding was in error.  The times
      during which the error occurred were approximately 09:23-09:50;
      the 'target' location under those conditions was approximately
      (-70.73, 274.38).  During revolution 235 a shorter period of
      negative quaternions occurred during approximately 04:38-04:41.
 
      It appears from subsequent analysis that a single antenna feed
      was connected to both receivers during data collection at DSS 43
      on 1994-04-23.  Although attenuators on each channel were
      operated independently, the RCP signal was recorded on both.
      Thus there is no polarization in formation in the DSS 43 data
      from this date.