NAME:
  occexpt
 PURPOSE:   (one line only)
  Compute suggested exposure time for occultation conditions
 DESCRIPTION:
 CATEGORY:
  Occultations
 CALLING SEQUENCE:
  occexpt,system,gmag,gtarg,speed,diam,exptime,snr
 INPUTS:
  system - scalar string with name of supported camera/telescope system
  These four inputs can be scalar or vector but if more than one is a vector
   all must agree in length.  This is not gracefully enforced.  The normal
   cases are all scalar, all equal length vectors, and just one quantity
   is a vector and the rest are scalar.
  gmag   - G magnitude of the star to be occulted
  gtarg  - Apparent G magnitude of the occulting body
  speed  - shadow velocity speed (km/sec)
  diam   - Expected diameter of the occulting body (km)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  exptime - resulting suggestion for the input conditions
  snr     - predicted SNR for the suggested exposure time
 KEYWORD OUTPUT PARAMETERS:
 CONFIGURATION:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2024/11/15