Data Set Overview
  =================
 
  The HAYABUSA spacecraft included a LIght Detection and Ranging (LIDAR)
  altimeter. The primary objective of LIDAR was to establish the range between
  the HAYABUSA spacecraft and the asteroid Itokawa for navigation purposes
  during the surveying and collection phases of the mission. It provided
  excellent estimates of the location of the spacecraft relative to the
  asteroid.
 
  The secondary scientific objective of the LIDAR included determining the
  mass of the asteroid, and measuring its global surface elevation and
  roughness.
 
  The Calibrated Data Record (CDR) contains LIDAR science and telemetry data
  that has been converted to engineering and physical units. The Experiment
  Data Record (EDR) is the source for the science data, while the House
  Keeping Experiment Data Record (HKEDR) and telemetry provides the data
  needed to determine the position of the HAYABUSA spacecraft relative to the
  asteroid. Resulting orbit, geometric, and calibration data have been
  incorporated, to determine the location of the LIDAR boresight on the
  surface of the asteroid provided in the CDR. With an appropriate shape model
  and density estimates for Itokawa, these can be used to obtain topographic
  profiles of the surface [e.g., CHENGETAL2002] of Itokawa.
 
  Further information about the Hayabusa LIDAR data set may be found in
  [BHARNOUIN-JHAETAL2008].
 
  Data
  ====
 
  All the HAYABUSA LIDAR data records are ascii tables. Each EDR contains
  three columns of data. The first column is the the Mission Elapsed Time in
  units of spacecraft ticks when the LIDAR range was measured. One spacecraft
  tick equals 1/32 of a one second. The second column is equal to this same
  time but translated into units of Universal Coordinated Time UTC. The third
  column equals the range measured by the LIDAR at the time indicated. The
  LIDAR collected data at 1 Hz (1 return per second) for the entire duration
  of the encounter with Itokawa (~3 months).
 
  The EDR is composed of three files: EDR20050911_20050929.TAB which
  corresponds to data acquired during the GATE Position Phase when the
  HAYABUSA spacecraft was at ~20km distance from the surface of the asteroid;
  EDR20050930_20051028.TAB which corresponds to data acquired during the HOME
  Position Phase when the HAYABUSA spacecraft was at 3-7km distance from the
  surface of the asteroid; EDR20051029_20051125.TAB which corresponds to the
  TOUCH DOWN phase when the HAYABUSA spacecraft attempted to sample the
  surface of Itokawa.
 
  The housekeeping (HKEDR) file has not been included in the archive because
  the mission has not yet given permission for it to be archived in PDS.  When
  permission is given to archive it, it will be added.  The first three
  columns of this HKEDR are identical to those in the EDR file. The next two
  columns provide the illuminated centroid of Itokawa within the reference
  frame of the wide angle camera, ONC-W1. This camera is part of the AMICA
  instrument package and more information is given in the description for that
  instrument. In brief, it is a 512 by 512 pixel imager with a field of view
  of 60 degrees.
 
  The software aboard the HAYABUSA spacecraft imager found the centroid of the
  largest illuminated object in the field of view of this ONC-W1, with DN
  values greater than a threshold of 5DN. This happened at 2 min intervals,
  and was accompanied by a LIDAR range and time listed in the first three
  columns of the HKEDR file already discussed. The first of the two pixel
  values gives the x or sample location of the centroid. The second one gives
  the y or line location of the centroid. The one HKEDR file includes data for
  the entire mission.  A pixel value for x and y of zero implies the asteroid
  filled the entire field of view of the ONC-W1.
 
  The CDR data files are of two kinds. The first is an unfiltered (UF) version
  of the data after the processing described in the next section was
  undertaken. The second is composed of the same set but was filtered (F) to
  remove any estimated surface point which was located more that 10m from the
  predicted intersection of the vector defining the pointing of the LIDAR
  boresight and the shape model of the asteroid. The filenames include F and
  UF respectively.  The CDR files include information on both the HAYABUSA
  LIDAR and the boresight of the Near Infra-Red Spectrometer aboard HAYABUSA.
  The NIRS data is provided as a courtesy to others HAYABUSA related efforts
  because it is exactly aligned with the LIDAR.
 
  Both filtered and unfiltered CDR files provide: the spacecraft mission
  elapsed time (MET); the time in UTC; the X,Y and Z LIDAR estimates of the
  spacecraft location after processing; the estimated X,Y,Z position of the
  LIDAR and Near Infra-Red Spectrometer (NIRS; Co-aligned with the LIDAR)
  footprint; the predicted X,Y,Z position of the LIDAR footprint at the
  intersection of the LIDAR boresight vector with the asteroid shape model;
  incidence, emission and phase angle of the center of the LIDAR/NIRS field of
  view (FOV); size of the LIDAR FOV; size of the NIRS (FOV); longitude and
  latitude of the LIDAR/NIRS (FOV); predicted longitude and latitude of the
  LIDAR/NIRS (FOV) at the intersection of the LIDAR boresight vector with the
  asteroid shape model; mean incidence, emission and phase angle of the FOV of
  NIRS which lies on the asteroid; mean longitude and latitude of the NIRS FOV
  which lies on the asteroid; predicted minimum and maximum longitude and
  latitude of the NIRS FOV from the intersection of the NIRS boresight vector
  with the asteroid shape model; number of points 3x3 grid within the NIRS FOV
  that falls on asteroid used to estimate the previous mean, minimum and
  maximum longitude and latitude values.
 
  Processing
  ==========
 
  The CDR incorporates the best orbital solutions and LIDAR boresight
  locations derived by the HAYABUSA LIDAR team. As a first step, a new
  algorithm was developed to better locate the Hayabusa spacecraft relative to
  the asteroid. The most important data initially used was the housekeeping
  (HKEDR) data of the x-y pixel of the illuminated centroid obtained by the
  ONC-W1 (WAC) camera of AMICA. Additional data included the project supplied
  information on the pointing of the WAC (SPICE C-kernels), as well as a good
  shape model of Itokawa (generated by B. Gaskell and part of the HAYABUSA PDS
  delivery).  Our algorithm assumes that the spacecraft attitude (i.e., its
  pointing) provided by the SPICE C-kernels as determined by the on board star
  cameras remained correct throughout the mission.
 
  The algorithm consists of first using a preliminary spacecraft location, the
  spacecraft attitude data and the shape model to create simulated images of
  Itokawa as seen by the WAC at the time the actual HKEDR was acquired. A
  predicted x-y pixel location for the illuminated centroid was computed from
  these simulated images simultaneously with a predicted range to where the
  LIDAR was pointing at the surface of the Itokawa. These predicted HK-data
  were then compared to the actual HKEDR in order to correct the spacecraft
  position. This comparison was repeated iteratively until the predicted and
  actual x-y pixel locations were within 0.1 pixel, and the predicted and
  measured ranges were within 0.5 to 3 m of each other, depending on the range
  of the spacecraft relative to the surface of the asteroid.
 
  The algorithm used to reproduce the HK data provides at 2 min intervals
  excellent estimates of the spacecraft position relative to Itokawa for most
  of the time that Hayabusa observed Itokawa. The data acquired by the LIDAR,
  however, was taken at 1 s intervals. Therefore, good estimates of the
  spacecraft position were still required for those periods between when HK
  data was acquired. After some trial and error, good estimates were obtained
  by initially using linear interpolation to first guess the locations of the
  spacecraft between those estimates provided by the HK data. We then fit all
  the positions using least squares to a second order polynomial or parabolic
  function between spacecraft maneuvers. Such a function should have a form
  that compares favorably with solutions to the semi-orbital equation of
  motion for the Hayabusa spacecraft that include the solar pressure acting on
  the spacecraft, because major maneuvers occurred fairly frequently (between
  a few hour to a few day intervals). Analysis of the resulting data indicate
  significant improvements on how well the new trajectory estimate for
  Hayabusa relative to what was initially provided by the project in the form
  of SPICE SP-Kernels.
 
  In this delivery, we provide two CDR files for each time range. The first
  includes boresight locations that have not been further filtered after the
  above processing was undertaken. The second set is filtered to remove bad
  data: any estimated surface point which was located more that 10m from the
  predicted intersection of the vector defining the pointing of the LIDAR
  boresight and the shape model of the asteroid were removed. This difference
  of 10m was chosen because most small scale variations in surface topography
  on Itokawa are less than this amount. After all these efforts, ~87% of the
  LIDAR points were found useful. This is equal to ~1.3 million LIDAR shots.
 
  Ancillary Data
  ==============
 
    As part of analysis, we found that the AMICA SPICE image kernel  needed
  further modification. A new version (amica_v202.ti) was prepared by Olivier
  Barnouin-Jha. In order to generate the CDR dataset, we used several project
  provided SPICE kernels including the planetary ephemeris kernel
  pck00008.tpc, the Itokawa Ephmeris and rotation kernel sb_25143_140.bsp and
  the HAYABUSA clock kernel hayabusa.tsc (the version of 2005-09-06).  These
  and the other SPICE kernels used to prepare the data files are being
  archived in the PDS SPICE archives.
 
 
  Coordinate System
  =================
 
  A planetocentric coordinate system is employed, which is body-centered,
  using the center-of-figure as the origin. The actual vector from the center
  of Itokawa to the surface should be primarily employed for scientific
  purposes becuase of the important curvature of Itokawa where some locations
  can possess more than one latitude and longitude. However, latitude and
  longitude data are also provided, but should be used with caution. The
  latitude is defined by the angle between the equatorial plane and a vector
  extending from the origin of the coordinate system to the relevant point on
  the surface.  Latitude is measured from -90 degrees at the south pole to +90
  degrees at the north pole.  Longitude extends from 0 to 360 degrees, with
  values increasing eastward (i.e., it is a right-handed coordinate system)
  from the prime meridian. This coordinate system is preferred for use in
  navigation and geophysical studies in which, for example, estimates of
  elevation or gravitational potential are generated mathematically.
 
 
  References
  ----------
 
  Barnouin-Jha, O., A. Cheng, T. Mukai, S. Abe, H. Naru, R. Nakamura, R.W.
  Gaskell, J. Saito, and B.E. Clark 2008.  Small-scale topography of 25143
  Itokawa from the Hayabusa laser altimeter.  Icarus 198, 108-124.
 
  Cheng, A.F., O. Barnouin-Jha, L. Prockter, M. T. Zuber, G. Neumann, D. E.
  Smith, J. Garvin, M. Robinson, J. Veverka, and P. Thomas, Small-scale
  topography of 433 Eros from laser altimetry and imaging. Icarus 155, 51?74,
  2002.

Confidence Level Overview
  =========================
    The resolution of the data is about 50 cm vertically. Along track spacing
    is variable. Small errors in the HAYABUSA emphemeris solutions and
    pointing knowledge yield uncertainties in absolute ground spot location to
    within 10m, but is often better.
 
    Timing Uncertainty
    ==================
    The clock aboard Hayabusa possesses an estimated uncertainty of +/- 12
    seconds due to a periodicity in the control and operation of the analog
    signal processing unit.  This effect was somewhat remedied by the analysis
    used by the LIDAR science team. The relative pointing between the ONC-W2
    camera and AMICA were statiscally adjusted so that a simulated image using
    the Hayabusa shape model would match the location of Itokawa observed by
    AMICA. Both data sets suffer from the same timing problem and our approach
    would thus have minimized their effect over the lifetime of the mission.
    Additional errors due to this timing uncertainty are captured by the 10m
    uncertainty clearly established to be the accuracy of the LIDAR CDR
    filtered data.  Examples of the excellent match between the topography
    observed, the estimated location of the boresight using the LIDAR CDR
    dataset and observations of where this boresight should be in AMICA all
    indicate that this problem has a minor impact on the quality of the
    Hayabusa LIDAR data set (see Barnouin-Jha et al. [2008] for additional
    details.)
 
    Data Coverage/Quality
    =====================
 
    After processing, a total of 87% of the mission's data was found useful.
 
    Limitations
    ===========
 
    The HAYABUSA LIDAR data has met many of its design expectations. It has
    demonstrated a measurement precision of ~50 centimeters over flat terrain.
    After processing, more than 87% of the data was found useful for
    topographic analyses.