Filters

Filter specification

• Number: Characteristic frequency of the filter [1/yr]
  
  
• Letter 1: Type of spectrum
  (formulas: see TechRep p. 35)
  

  g	Gaussian
  t	Triangular
  T	Triangular (truncated)
  ....

  
  
• Letter 2 (if any): Treatment of seasonal cycle
  

  d	Deseasonalized
  m	Mean seasonal cycle
  r	Running yearly average - removes seasonal cycle
  a	Anomaly around running yearly average
  A	Seasonal cycle amplitude
  x	(no special treatment)

  
  
• Letter 3 (if any): Treatment of long-term mean
  

  a	Anomalies around long-term mean (= subtract average)
  l	Long-term mean (constant)
  z	Subtract filtered value at beginning of restricted period
  Z	Subtract filtered value at beginning of restricted period, and set to zero before restricted period
  x	(no special treatment)

  
  
• Letter 4 (if any): Treatment of linear trend
  

  a	Anomalies around linear trend (= detrend)
  s	Special: apply filter to detrended part only (= detrend, filter, and re-add trend)
  z	Subtract value of linear fit at beginning of restricted period
  x	(no special treatment)

  
  

Further filter specification options in specific circumstances

• Reading in 2D files:
  Add "~" in front of the filter specification to first read in the file 'as is' and then filter it. This allows the full standard filter syntax to be used. It does not allow, however, to calculate mean flux properties (average, mean seasonal cycle) from any input records outside the inversion period.