Decimation

Decimation is a system used to keep the SSR at a resonable fill level. It is set up so that in each segment of the instrument (front and rear) photon counts are deleted. This deletion only applies to a certain fraction of the counts below a specific energy threshold. There are four basic modes that determine these fractions and thresholds: normal-normal, normal-active, active-normal, and active-active. The first word refers to the mode of the front segment and the second refers to the mode of the rear.

Active mode for the front segment can be used to bring down the SSR fill level when the sun is active, and is described by this table. The normal mode of the front segment is described by this table. Active mode for the rear segment can be used to bring down the SSR fill level when there is a lot of high-energy particle precipitation. This mode will delete 3/4 of all counts below an approximate 400 keV threshold. The normal mode for the rear segment will delete 3/4 of all counts below an approximate 200 keV threshold.

Front segment decimation table 4: ("Active Sun")

Values are top decimated energy level/decimation depth

              ____________Shutters____________

SSR level open thin thick both

0-20 none none none none 20-30 4/1 none none none 30-50 5/2 none none none 50-60 6/3 7/3 8/3 9/3 60-70 6/4 7/4 8/4 9/4 70-80 8/5 9/5 10/5 11/5 80-95 12/7 13/7 14/7 15/7 95-99 15/15 15/15 15/15 15/15 99+ events off.

Decimation depth N means N out of (N+1) events are deleted. The top decimation energy levels are APPROXIMATELY:

 Energy     Top       Top
 Level     Channel   Energy
                     (keV)
      0       0      [<0, no decimation]    
      1      15      [<0, no decimation]    
      2      31      [<0, no decimation]
      3      47      2.98000
      4      63      8.42000
      5      79      13.8600
      6      95      19.3000
      7     111      24.7400
      8     127      30.1800
      9     143      35.6200
     10     159      41.0600
     11     175      46.5000
     12     191      51.9400
     13     207      57.3800
     14     223      62.8200
     15     239      68.2600

Front segment decimation table 3: ("Quiet Sun")

Values are top decimated energy level/decimation depth

              ____________Shutters____________

SSR level open thin thick both

0-30 none none none none 30-50 4/1 none none none 50-60 6/1 7/1 8/1 9/1 60-70 6/2 7/2 8/2 9/2 70-80 8/3 9/3 10/3 11/3 80-90 10/5 11/5 12/5 13/5 90-95 12/7 13/7 14/7 15/7 95-99 15/15 15/15 15/15 15/15 99+ events off.

Decimation depth N means N out of (N+1) events are deleted. The top decimation energy levels are APPROXIMATELY:

 Energy     Top       Top
 Level     Channel   Energy
                     (keV)
      0       0      [<0, no decimation]    
      1      15      [<0, no decimation]    
      2      31      [<0, no decimation]
      3      47      2.98000
      4      63      8.42000
      5      79      13.8600
      6      95      19.3000
      7     111      24.7400
      8     127      30.1800
      9     143      35.6200
     10     159      41.0600
     11     175      46.5000
     12     191      51.9400
     13     207      57.3800
     14     223      62.8200
     15     239      68.2600