PDS_VERSION_ID = PDS3                                                         
                                                                              
RECORD_TYPE    = "STREAM"                                                     
                                                                              
OBJECT     = TEXT                                                             
  PUBLICATION_DATE = 2011-05-16                                               
  NOTE             = "AAREADME File for re-organized IHW data set"            
END_OBJECT = TEXT                                                             
                                                                              
END                                                                           
                                                                              
Re-organized International Halley Watch (IHW) Data Sets                       
=======================================================                       
The original IHW "LSPN disks" contained ground-based observations from        
various observatories contributing to the Large-Scale Phenomena Net.          
These data, originally consituting the CDROM volumes HAL_0001 to              
HAL_0018, have been combined here in a single, integrated logical             
volume, sorted by date.                                                       
                                                                              
The observational data are in a compressed format that is not supported       
by PDS.  These original files are under the COMPRESSED/ subdirectory          
of the DATA/ directory. The browse data are sub-sampled, raster versions      
of thecompressed images and are stored in a parallel directory structure      
under BROWSE/.  Browse files have names that correspond to their original     
observational image file names.  Calibration observations are also included   
in the CALIB/ directory, and the summary index and errata information         
provided on the final disk in the LSPN series, HAL_0018, has been             
incorporated into the DOCUMENT/ subdirectory here.                            
                                                                              
In the HAL_0019-HAL_0023 "mixed disks", subsampled versions of the            
LSPN observations and calibrations were included that, while apparently       
identical to the browse images in terms of data content, had improved         
labels with at least minimal metadata included (start time, LSPN number,      
and target, for example).  These have been included in the SUBSAMPLED/        
subdirectory of the DATA/ directory.                                          
                                                                              
Some description of the compression/decompression algorithm and source        
code was included on the original disks, and is duplicated here.  It is       
unlikely the source code will compile on any modern system, but it may        
at least provide an example of the algorithmas once used.                     
                                                                              
The data were also archived under a fairly early form of the PDS              
Standards, and formatted to an equally early form of the FITS                 
standard, where appropriate, resulting in some particularly arcane            
formats for the modern user - including PDS labels with deprecated            
terminology and almost no metadata, a FITS headers which refer to an          
extension type of 'COMPRESS' that was never formally adopted into the         
standard and no longer exists even as a conforming extension.                 
                                                                              
The reorganization effort sought to separate the data files constituting      
the unique data sets into a more contemporary, single-data-set-per-volume     
format for ease of access and distribution.                                   
                                                                              
The data files and most supporting files are presented here in their          
original format, problematic though that might be.  Users interested in       
analyzing the data would probably do well to inquire of the PDS or the        
Small Bodies Node for version 2.0 of the observational data set.              
                                                                              
- A.C.Raugh, 2011-05-16