Overview of the Solution

The solution to this problem is to allow the observer to control the configuration of ISOCAM at the beginning and end of an AOT. This is done by setting the DRK parameter in PGA to special values which are used as flags. Briefly, in most cases, the observer will need to add dummy off-source pointings before and after his target, and will need to use special values of the DRK parameter in all 3 of the observations (both dummies and the target).
The DRK field in PGA is normally used to specify procedures for dark measurements. New values for DRKs have been created, which act as flags to allow control of the instrument mode at the beginning and end of an AOT, instead of performing a dark measurement. PLEASE NOTE: It is the observer's responsibility to insure that ISOCAM does not saturate during the course of his or her observation and that ISOCAM is left in parallel mode at the end of the observation.
The three most commonly used DRK flags are:

1. DRK = 19 Exit the current AOT without changing ISOCAM's configuration
   
2. DRK = 20 Begin the current AOT in the configuration ISOCAM was last left in. Exit the AOT in normal parallel mode.
   
3. DRK = 29 Begin the current AOT in the configuration ISOCAM was last left in and exit without changing mode.
   

• If you have a concatenated chain in which both LW and SW are used, you should not use DRK=20 or 29 in an AOT where the the channel is changed because the startup sequence must be executed.
  
• Since solar system observations cannot be concatenated to off-source pointings, this mechanism can't be used for SSOs.