create new script for GC-PGA comparison (MR !2)

create new script for GC-PGA comparison (MR !2 (merged))

• create the new DF simGCsamplesDF with gas-concentration samples per measurement period (mp) that may simulate GC sampling
  • this DF may be used to simulate flux calculation from GC sampling data
• the new option simulateGCdata <- "F" # [F,T] en-/disables the sampling
• the new file sample_gas_concentrations_for_gc_simulation_per_mp.R and function f_sample_gas_concentrations_for_gc_simulation_per_mp is added to actually take the samples per mp and store them in a new DF
  • this new DF has identical columns as the "gas concentration DF" measPeriodN2oCorr and, hence, may be readily used with the flux calculation
  • the new section 6. "Sample gas concentration data for GC simulation" calls this function
  • samples are taken at specific times after the start of the mp, and are calculated from multiple values right before and after the particular time
• options for this sampling are set in the new file additional_info/simulate_gc_n2o_data.txt including
  • the set of filter/correction function to run
  • points in time for sampling
  • min length of mp
• the f_sample_gas_concentrations_for_gc_simulation_per_mp writes a logfile that is formated as table with column header
  • it is ready to anaöyse and get an overview of the sampling of all mp
  • it includes the information about whether sampling was done for data that are "short flatlines"
  • columns are: "measID sample_time_sec median_value median_value_sd sample_time_is_flatline any_meas_of_median_calc_is_flatline"
• a new column is added to the gas concentration DF measPeriodN2o, before data filtering/correcting in the main_script, that marks the measurement data that was identified as "short flatline"
  • column name detected_flatline, with default value 0
  • the data_filter_function_05 in correct_filter_n2o_conc_by_meas_period.R now adds a 1 for each measurement data point that is detected as "short flatline"
• testing:
  • the new DF simGCsamplesDF contains the data as expected
  • the main script runs fine with simulateGCdata set to T & F
  • ... TODO test flux calculation with goFlux

Closes #6 (closed)