The INDEX directory contains 3 indices for this volume : INDEX.TAB,
BROWSE_INDEX.TAB and GEO_VENUS.TAB

Accompanying each index files is a PDS label (INDEX.LBL, BROWSE_INDEX.LBL and
GEO_VENUS.LBL).

The *.TAB files are ASCII files.  Each line (or record) in the .TAB-files
contains information about a single data file in the data or browse archive 
volume. Each line in a *.TAB file is made up of comma-delimited fixed-length 
fields.

Users of the SOIR archive can make use of the BROWSE directory to have a quick
look into the available data products. The structure and naming conventions 
for the BROWSE directory are completely identical to that of the DATA 
directory. 

The geometry index GEO_VENUS.TAB (with its associated .LBL-file) is generated 
for the whole data set. The .TAB-file is a list of consecutive footprints, 
one footprint for every observation in the data set.  
Each footprint consists of a number of lines in the table, each line 
corresponding to a measurement, i.e. there are as much lines in the 
footprint as there are seconds in the observation. The footprint however is 
limited to measurements that have a tangential height of the SOIR boresight 
between 220 and 40 km (last column in GEO index table). It is possible that 
for certain measurements (highest or lowest tangential heights) no 
measurements were taken. In that case N/A values (999.999 or -999.999) are 
placed in the table for geometric parameters that can not be calculated.
Each line in the GEO index table contains a number of geometric parameters 
describing the exact location of each measurement. The geometric parameters 
are documented in the corresponding DESCRIPTION fields in the .LBL-file.
The 6 parameters describing the footprint are (START_POINT_LATITUDE, 
START_POINT_LONGITUDE), (CENTER_LATITUDE, CENTER_LONGITUDE), 
(END_POINT_LATITUDE, END_POINT_LONGITUDE). The CENTER point is the tangential 
point itself projected on a 60 km altitude shell around Venus. The START point
and END point are points at the left and the right of the CENTER point, so 
that at each measurement (each second) not one point but one line is defined 
as footprint of the measurement. The complete footprint of the observation is 
then a sequence of such traces or the contour described by the extremes of the
traces (the START and the END points).
START and END point are situated in a tangential plain to the planet, 
perpendicular to the boresight, at a distance of 10 km (when the tangential 
height is between 40 and 100 km) and at variable distance (when the tangential
height is between 100 and 220 km). This variable distance is calculated by 
linear regression between the 2 following (tangential height, distance to 
center)-points : (100 km, 10 km), (250 km, 500 km).