PDS_VERSION_ID      = PDS3                                                    
LABEL_REVISION_NOTE = "                                                       
  17 Sep 1998, a.c.raugh: Creation"                                           
                                                                              
OBJECT     = INSTRUMENT                                                       
  INSTRUMENT_HOST_ID = "LOWELL"                                               
  INSTRUMENT_ID      = "PHOT"                                                 
                                                                              
  OBJECT     = INSTRUMENT_INFORMATION                                         
    INSTRUMENT_NAME = "PHOTOMETER"                                            
    INSTRUMENT_TYPE = "PHOTOELECTRIC PHOTOMETER"                              
    INSTRUMENT_DESC = "                                                       
                                                                              
      Instrument Overview                                                     
      ===================                                                     
      This general instrument description is used to reference any of         
      several conventional photoelectric photometers equipped with a          
      variety of photomultiplier tubes and electronic systems of both         
      DC and pulse-counting types.  This description is used when it          
      is not possible to differentiate between instruments used in            
      individual observations underlying the final data product.              
                                                                              
      Calibration                                                             
      ===========                                                             
      The DC amplifiers were calibrated using standard voltages while the     
      results from pulse-counting systems included the first order dead       
      time correction.  Several standard stars were observed each night (in   
      almost all cases at a range of airmass bracketing any comet obser-      
      vations) for both evaluation of extinction coefficients and absolute    
      calibration.  A discussion of standard stars and the zero point of the  
      magnitude system with respect to the International Halley Watch         
      filter set can be found in [OSBORNETAL1990]. Much of the calibration    
      procedure is also fully detailed in the International Halley Watch      
      Archive.                                                                
                                                                              
      Filters                                                                 
      =======                                                                 
      The program began with a set of narrowband filters isolating the        
      emission species CN, C3,and C2 as well as three continuum regions at    
      392, 412, and 524 nanometers (A'Hearn, et al. 1979 [AHEARNETAL1979]).   
      In 1979, filters isolating the emission species OH and NH were added    
      along with an additional continuum filter at 367 nanometers (A'Hearn,   
      et al. 1981 [AHEARNETAL1981]).  By 1984, the standardized filters of    
      the International Halley Watch (IHW) replaced the earlier filters at    
      wavelengths greater than 365 nm.  Full details of the IHW filters can   
      be found in A'Hearn, et al. (1991) [AHEARNETAL1991] and A'Hearn and     
      Vanysel (1992) [AHEARN&VANYSEK1992]."                                   
                                                                              
                                                                              
  END_OBJECT = INSTRUMENT_INFORMATION                                         
                                                                              
  OBJECT     = INSTRUMENT_REFERENCE_INFO                                      
    REFERENCE_KEY_ID = { "OSBORNETAL1990",                                    
                         "AHEARNETAL1979",                                    
                         "AHEARNETAL1981",                                    
                         "AHEARNETAL1991",                                    
                         "AHEARNETAL1995",                                    
                         "AHEARN&VANYSEK1992" }                               
  END_OBJECT = INSTRUMENT_REFERENCE_INFO                                      
END_OBJECT = INSTRUMENT                                                       
END