Data Set Overview : The Clementine Bistatic Radar Intermediate and Reduced Data Archive (BSR-IRDA) is a collection of partially and fully reduced products 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 (RCP and LCP, respectively) 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 first analysis of spotlight data was published by [NOZETTEETAL1996]. The authors identified an enhancement in right-circularly polarized echo power near the time when the bistatic angle was zero in permanently shaded regions near the South Pole. A second analysis [SIMPSON&TYLER1999] focused on the data with the reported enhancement but was unable to reproduce the earlier results.  This data set includes intermediate products from the second analysis. These are large files of double precision complex time samples in both RCP and LCP. The data cover the time period 1999-04-09T18:36:45 to 18:52:45 - the time at which the bistatic angle was 0 nearest the South Pole was 18:46:36.5. The intermediate files are processing output after correction for ripples in the receiver filters (equalization), after correction for gain changes in both channels, after digitally centering the carrier in the passband, and after changing the frequency reference so that the South Pole frequency bin would be in the center. These 8 files are in the DATA directory, which is spread over all volumes in the data set.  Also in the data set are more highly processed data, including a subset of power spectra from the final processing stage described above. Measured echo powers in these spectra were sorted to construct empirical scattering functions at 72 locations near the South Pole. The spectra, the sorted power values, and a table containing two versions of the scattering function are in the SORT directory on the final volume.  In order to carry out the sorting, it was necessary to know the mapping of Doppler frequencies onto the Moon's southern hemisphere. Grids of frequency and other parameters were computed at 100 second time steps. These are stored in PDS IMAGE format in the IMG directory, which appears on all volumes.  Users of the Clementine data interested in fully understanding the signal processing might prefer to begin with the raw data, which have been archived separately on 13 CD-R volumes as PDS data set CLEM1-L-RSS-1-BSR-V1.0. Users interested in other orbits necessarily must start with the raw data, since only part of a single orbit is included in this archive.  Users of the partially processed data could pick up the processing at any stage and follow it through to completion. The calibration files which were used during the Stanford processing to equalize the filter response, adjust the gain, and modify the frequency of the data are stored in the CALIB directory. Two versions of the list of target points for constructing the scattering function(s) are included in the GEOMETRY directory.  Users interested only in the two scattering functions derived in the Stanford analysis will find them in the file RATIOFN.TAB in the SORT directory. Note, however, that these are functions giving the RATIO of RCP to LCP power rather than the individual powers themselves, that they were derived in only two of several possible ways, and that the uncertainties (based on noise in the original measurements of echo power) are large.   Parameters : Files in the DATA directory contain double precision complex time samples of receiver output in RCP and LCP between 1994-04-09T18:36:45 and 18:52:45, after corrections and adjustments for various effects.  Files RCP.IMG and LCP.IMG in the SORT directory are calibrated arrays (in PDS IMAGE format) giving echo power in RCP and LCP, respectively.  Files SRTPWRR.TAB and SRTPWRL.TAB contain power measurements from the arrays above, sorted according to proximity to one of 72 surface target points and bistatic angle at that point. File SRTNPWR.TAB gives the number of measured values that have been associated with each target point at each bistatic angle.  File RATIOFN.TAB gives the RCP to LCP ratio as a function of bistatic angle for the 13 target points poleward of 88 S latitude. The ratio is computed in two different ways.  Ephemerides were used to compute the observing geometry for a 700x700 grid. Each grid point was related to a surface point orthographically projected onto a plane tangent to the lunar surface at the South Pole. Various observing parameters were computed at 100 second time steps and stored in PDS IMAGE format. These include:  BET bistatic angle (degrees) DAR area (square meters) DBR offset from boresight at the (DSN) receiving antenna (degrees) DPR incremental received power (watts) from the surface element FQZ Doppler frequency relative to the South Pole (Hz) GAM tilt of the surface element (degrees) GRX receiving antenna gain at the surface element (dB) GTX spacecraft transmitting antenna gain at the surface element (dB) RRX distance from the receiving antenna (meters) RTX distance from the spacecraft transmitting antenna (meters) SBR offset from boresight at the spacecraft antenna (degrees) SG0 assumed specific radar cross section for calculating DPR THI incidence angle at the surface element (degrees) THS scattering angle at the surface element (degrees) VAL validity mask (1 : grid point within lunar disk; 0 : outside) DFQ time derivative of FQZ (Hz/sec)   Processing : Processing is described in more detail in the file PROCSSNG.TXT in the DOCUMENT directory. The DOCUMENT directory also contains other files which may be useful in understanding the processing carried out at Stanford.  The raw 8-bit samples from the analog-to-digital converters were stored on tape during data acquisition. Those samples were separated into two computer files, corresponding to RCP and LCP (also referred to as Channel 1 and Channel 3, respectively, in some contexts). This program (called PREPMO) also padded the samples to 16 bits.  The two files of 16-bit samples were then used as input (separately) to program PREPFND which carried out digital filtering. The output of this stage was a stream of double precision complex time samples at half the original rate for each polarization (channel). The filtering operation in PREPFND was 'equalization', in which signal amplitude in the center 80 percent of the passband was normalized by the filter response with only noise as input.  The output from PREPFND was fed to program GAIN which adjusted the sample amplitude in each channel for changes in attenuator settings during data acquisition, gain drift in the receiving system, and gross differences in levels between the two channels.  The output from GAIN was passed to program POWERFIT, which located the peak signal in the passband and estimated both its amplitude and frequency. The frequency estimates were used to create a file of coefficients for a piecewise continuous linear approximation to the carrier frequency.  Using the file of coefficients, the program STEER adjusted the phase of the complex output samples from GAIN so that the carrier appeared to be at the center of the passband (12500 Hz).  Using ephemerides for the spacecraft and planetary bodies, the expected Doppler offset between the carrier signal and a hypothetical echo from the lunar South Pole was computed. This offset was converted to a second set coefficients for a piecewise linear approximation to the difference frequency.  The second set of coefficients was used in a second application of the STEER program to move the estimated frequency of the South Pole to the center of the passband (12500 Hz). From this point, the South Pole frequency became the reference.  Program FNDLOOK was used to compute 16384-point power spectra from the second-order STEER results. There was no averaging, so spectra were spaced by 0.65536 seconds and frequency resolution was approximately 1.5259 Hz. A subset of the frequency range (bins 7356-8379) was saved for further analysis. This array of 1464 1024-point spectra had the South Pole echo in bin 838. A smoothed version of the bin 838 response (and 21 of its neighbors) appeared in [SIMPSON&TYLER1999] as Figure 10, from which the authors concluded there appeared to be nothing unusual about the response of the South Pole.  The ephemerides were used to locate points in the vicinity of the South Pole where bistatic angle went to 0 during the course of this observation. 72 such points, spaced by 1 second, were identified, forming a track which passed very close to the Pole (Figure 2 in [SIMPSON&TYLER1999]).  The values stored in the 700x700 grids could be used to map Doppler contours onto the lunar surface and to compute expected echo spectra (for an assumed scattering function). As tools for interpreting the measured values, they could be used to determine which of the 72 target points (if any) contributed to a frequency bin at a certain offset from the South Pole frequency. And they could be used to determine the bistatic angle at such a target point when the measurement was made.  Such an inversion was accomplished, through a number of steps, leading to the sorted echo power measurements in files SRTPWRR.TAB and SRTPWRL.TAB in the SORT directory. The arrays of sorted measurements for 72 targets and 101 bistatic angles (with up to 42 values in each bin) were then reduced to scattering functions for each of the 72 targets and for aggregations of those targets. RATIOFN.TAB in the SORT directory contains two such possibilities.   Data : The data set contains two each of the following files (one for each polarization). Each file is accompanied by a detached PDS label which completely describes both the format and content of the file. Each data file has 384002048 bytes and is located in the DATA directory.  A. PREPFND output file after filter equalization. File names: PF1.TAB (RCP) and PF3.TAB (LCP) B. GAIN output file after gain corrections. File names: GN1.TAB (RCP) and GN3.TAB (LCP) C. First-order STEER output file after centering carrier at 12500 Hz. File names: S11.TAB (RCP) and S13.TAB (LCP) D. Second-order STEER output file after centering South Pole echo. File names: S21.TAB (RCP) and S23.TAB (LCP)  The data set contains two each of the following files (one for each polarization). Each file is accompanied by a detached PDS label which completely describes both the format and content of the file. These files are in the SORT directory.  E. FNDLOOK output file converted to PDS IMAGE format. Each is a 1464x1024 array of echo power density with the South Pole at bin 838. File names: RCP.IMG and LCP.IMG  F. Output array from the echo sorting process. Each file is a table but represents data in a three-dimensional array (up to 42 valid power measurements in a 72 target by 101 angle array). File names: SRTPWRR.TAB (RCP) and SRTPWRL.TAB (LCP).  Accompanying the sorted data are two other arrays. Each is accompanied by a detached PDS label which completely describes the format and content of the data file. These files are in the SORT directory.  G. An array giving the number of valid measurements in the two data arrays SRTPWRR.TAB and SRTPWRL.TAB. File name: SRTNPWR.TAB  H. A table containing two empirical scattering functions. File name: RATIOFN.TAB.  The data set contains 59 sets of 15-16 grids. The sets are spaced by 100 seconds in time, starting at 65696 seconds past 0 h on 1994-04-09 and covering the time during which DSS 14 tracked the Clementine spacecraft. Each file occupies 980000 bytes and is accompanied by a PDS detached label. Grids are ordered chronologically on CD-R volumes (but with no more than 256 grids per volume) and are stored in the IMG directory. Because the DFQ grid is formed by differencing the EQZ grids at the immediately adjacent time steps, there is no DFQ grid for the first or last time step. At each of the other steps there are 16 grids.   Ancillary Data :  Files in the CALIB directory include the following. Each is accompanied by a PDS detached label which describes the format and content of the data file.  A. Filter equalization files with names of the form FLssbpnn.SPC where ss is the DSN antenna number (14 or 43) f is the frequency band (S) p is the polarization (R or L) nn is the sequence number (01 or 02) Only data from DSS 14 (ss:14) are included in this archive; only filters with sequence number nn:01 were used in the Stanford processing.  B. Files containing coefficients for gain correction with names of the form G099C14c.TAB where c denotes the channel number (1:RCP, 3:LCP)  C. A file containing coefficients for centering the carrier frequency with name STEERCF1.TAB  D. A file with coefficients describing the difference in frequency between the carrier and South Pole bin with name DF2SCM.TAB  E. A table of noise level measurements for calibrating system gain and determining system noise temperature with name TABLE2.TAB (see Table 2 in [SIMPSON&TYLER1999])  Files in the GEOMETRY directory include the following. Each is accompanied by a PDS detached label which describes the format and content of the data file.  F. A table summarizing geometry and observing conditions with name BSRGEOM.TAB  G. Two tables listing coordinates for 72 target points around which sorting was carried out and scattering functions derived. BETAZER0.TAB lists the coordinates in radians; BETAZER1.TAB lists the coordinates in degrees.   Coordinate System : The radio measurements can be understood without reference to a particular coordinate system. For mapping measurements to the lunar surface, a selenocentric system with positive east longitude was used.   Software : This data set contains no software.   Media/Format : The archival data set is written on CD-WO media using a Yamaha CRW4260tx CD writer and GEAR software running on a Sun Ultra-5 workstation.

Overview : The calibrations, gain corrections, and frequency adjustments were done with considerable care. They have been described by [SIMPSON&TYLER1999] and in several documents in the DOCUMENT directory. The files in the DATA and CALIB directories and the RCP.IMG and LCP.IMG files in the SORT directory fall into this category.  The geometrical calculations were also done carefully and are documented in [SIMPSON&TYLER1999] and in the DOCUMENT directory of this volume. Files in the GEOMETRY and IMG directories fall into this category.  The sorted files (SRTPWRR.TAB, SRTPWRL.TAB, and SRTNPWR.TAB) and the scattering function (RATIOFN.TAB) have been done once. The procedures are documented in the DOCUMENT directory and in in an abstract for Lunar and Planetary Science XXXI (see LPSC_ABS.LBL in the DOCUMENT directory). But resource limitations have prevented the careful scrutiny and double checking that were possible in the earlier analysis. Users should view these files more skeptically.   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.   Data Coverage and Quality : The times covered by this data set are listed in the table below. The depth of coverage is given in the 'Analysis' column at the right, with entries explained below the table.  Revolution Start Time (ERT) Stop Time (ERT) Number DSS Analysis ------------------- ------------------- ---------- --- -------- 1994-04-09T17:48:45 1994-04-09T18:04:44 233 14 2 1994-04-09T18:04:45 1994-04-09T18:20:44 233 14 2 1994-04-09T18:20:45 1994-04-09T18:36:44 233 14 2 1994-04-09T18:36:45 1994-04-09T18:52:44 233 14 1 1994-04-09T18:52:45 1994-04-09T19:08:44 233 14 2 1994-04-09T19:08:45 1994-04-09T19:24:44 233 14 2 1994-04-09T19:24:45 1994-04-09T19:40:44 233 14 2 1994-04-09T19:40:45 1994-04-09T19:56:44 233 14 2 1994-04-09T19:56:45 1994-04-09T20:05:09 233 14 2 1994-04-09T23:00:55 1994-04-09T23:16:54 234 43 3 1994-04-09T23:16:55 1994-04-09T23:32:54 234 43 3 1994-04-09T23:32:55 1994-04-09T23:48:54 234 43 3 1994-04-09T23:48:55 1994-04-10T00:04:54 234 43 3 1994-04-10T00:04:55 1994-04-10T00:20:54 234 43 3 1994-04-10T00:20:55 1994-04-10T00:36:54 234 43 3 1994-04-10T00:36:55 1994-04-10T00:52:54 234 43 3 1994-04-10T00:52:55 1994-04-10T01:08:54 234 43 3 1994-04-10T01:08:55 1994-04-10T01:24:54 235 43 3 1994-04-10T01:24:55 1994-04-10T01:33:55 235 43 3 1994-04-10T04:02:22 1994-04-10T04:18:21 235 43 3 1994-04-10T04:18:22 1994-04-10T04:34:21 235 43 3 1994-04-10T04:34:22 1994-04-10T04:50:21 235 43 3 1994-04-10T04:50:22 1994-04-10T05:06:21 235 43 3 1994-04-10T05:06:22 1994-04-10T05:22:21 235 43 3 1994-04-10T05:22:22 1994-04-10T05:38:21 235 43 3 1994-04-10T05:38:22 1994-04-10T05:54:21 235 43 3 1994-04-10T05:54:22 1994-04-10T06:10:21 235 43 3 1994-04-10T06:10:22 1994-04-10T06:26:21 236 43 3 1994-04-10T06:26:22 1994-04-10T06:42:21 236 43 3 1994-04-10T06:42:22 1994-04-10T06:46:54 236 43 3  Analysis levels represented in the archive: 1 Exhaustive calibration and correction of data; data values sorted into empirical scattering functions 2 Filter functions, gain corrections, and grids provided; no data in the archive, no frequency coefficients available. 3 Notes on gain variations observed are in the archive; no calibration/correction files and no data included.  Only very limited work with DSS 63 data from 1994-04-10 was carried out at Stanford. And virtually nothing was attempted with data from days 1994-04-23 and 1994-04-24.   Limitations : See section Overview and Data Coverage and Quality above.