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Submit DataData ReportingCommentsModulesvnames    November 11, 2019

Variable names (vnames) 

Description

These lines contains the names of the dependent variables. The number will depend on which parameters are analyzed in the sample and must always be the same as specified in line 10. 

Please make sure that component names are spelled correctly and reported in the correct unit. A list of components currently defined in EBAS can be found here.

Tag=value may be used for components having metadata different from the default metadata in the file, for example if the detection limit is different or has a different unit, or if the analytical method is different.


Syntax:

vname(1), unit, Tag_1=value_1, ..., Tag_n=value_n
...                                                                              
vname(n), unit, Tag_1=value_1, ..., Tag_n=value_n

 
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Flag variables

Each data point of a data variable (measurement) in EBAS may be accompanied by one or more EBAS flags (see the ebas flag list). The flags for a data variable are stored into a separate variable in the NASA Ames file, called a flag variable.

A flag variable can apply to one or more data variables. In order to use one flag variable for more than one data variable, the whole sequence of flags in the file must be exactly the same for all variables sharing the flag variable. A flag variable always follows the data variable(s) it applies to. When a flag variable applies to more then one data variables, the data variables must be in sequence, directly followed by the applicable flag variable. With other words: A flag variable applies to all data variables between the previous flag variable and the current one.


Variable name for flag variables

The variable name (VNAME) of a flag variable always starts with the word numflag.

An additional convention is highly recommended in order to state more explicitly which data variables a flag variable applies to (in addition to the rule above):

  • If the flag variable applies to only one data variable, the variable name (VNAME) of the data variable is copied, prepended with the word numflag and the unit is changed to no unit.
    Example for the variable names (VNAMEs) specified in lines 12ff of a NASA Ames file:
     calcium, ug/m3
     numflag calcium, no unit
     chloride, ug/m3
     numflag chloride, no unit
  • If the flag variable applies to more than one data variable, the variable name (VNAME) for the flag variable is only numflag, no unit.
    Example:
     calcium, ug/m3
     chloride, ug/m3
     numflag, no unit

Values used for flag variables

A data variable's value needs to store one or more EBAS flags (each a three digit flag code). Since NASA Ames 1001 does only allow float variables, we use the following algorithm to encode the EBAS flags into one float value:

  • the flag value is always a float number starting with 0.
  • after the comma, groups of three digits are used to express the single EBAS flags
Examples:
0.999 One flag (999), meaning "Missing measurement, unspecified reason". Please keep in mind, that this is not a missing value for the flag variable (it must be applied to a missing value of the corresponding data variable though)
0.999000 The same as above, except that there would be space for a second flag (which is not set)
0.676647392 This is an example of a flag value encoding three different EBAS flags. 676: "station inside cloud (visibility < 1000 m)", 647: "Fire/wood burning nearby" and 392: "Data completeness less than 75%"

Please pay particular attention to the fact that a flag value can never be missing. A data value (measurement) can be missing, but the corresponding flag value will always be valid (e.g. 0.999).


Missing values for flag variables

As mentioned in the previous section, a flag variable's value can never be missing. But the NASA Ames 1001 specification requires a missing value for eacxh depenendent variable. As far as NASA Ames 1001 is concerned, an EBAS flag variable is just a regular dependent variable, thus we need to define a missing value in line 12 (VMISS). The higest possible value for a flag variable is 0.999990980... (EBAS flags 999, 990, 980 and so on), terefore we should use a missing value of 9.999999999... (one order of magnitude higher then the highest possible value and all digits are nines).

The number of digits needed varies from file to file and from variable to variable (three times the maximum number of flags that will be used at the same time). The needed number format (and thus the missing value) can either be calculated according to the actual file contents before writing the file (the python EBAS IO package does this automatically) or can be set to a constant maximum by the data submitter (e.g. maximum 3 flags allowed, which means 9 digits needed, missing value = 0.999999999).

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