About data files

An LI-8100A data file consists of lines of tab-delimited text with one or more Observations. An Observation is preceded by Header information, and also contains Raw Records, Summary Records, and Footer information as shown below.

Header - The lines from "LI-8100A:" through "Labels_01:". See Header variables.

Type - The first item in each record is called the Type, and it identifies the type of record. The types are -1, 1, 2, 3, and 4.

Table 6‑1. Record types and their definitions.
Type Description
-1 Warning record
1 Raw record
2 Initial value (regressed from first 10 seconds of data)
3 Mean value of raw records
4 Range value of raw records

Raw Records - A record of Type 1. These records represent measured data from the time the chamber starts to close, to the time when it starts to open. See Raw records and summary records.

Summary Records - A record of Type 2, 3, or 4. An Observation always has one of each, for a total of three. See Raw records and summary records.

  • Type 2 records for measured columns represent initial values based on a linear regression with Etime of the first 10 seconds of data.
  • Type 3 records for measured columns are the mean values of all the data.
  • Type 4 records for measured columns are the ranges (max - min) of all the data.

Footer – The results of the analysis, including flux values. The footer won’t be present for files logged with the “Compute Flux” option turned off. For these data, a footer can be generated by recomputing the data in SoilFluxPro Software. See Footer variables.

Observation – The Header + n Raw Records + 3 Summary Records + the Footer.

The Summary Records consist of a number of Measured Variables, some of which appear in all Observations, (such as Date, Pressure, CO2, H2O) and some of which are optional, and a number of Final Variables of Type 2, 3, or 4, as shown below. Summary statistics of Measured Variables are identified by the column label, and a prefix of “IV”, “Mean”, or “Range”. Thus, for example, “IV Cdry” means the Type 2 value of the Cdry column, and “Range Etime” means the Type 4 value of the Etime column.

Header variables

lists the LI-8100A variables, including the Label that appears in the Header information, and a description of the variable. A summary of the method and equations used to compute the Measured Variables, including the appropriate slope of Cdry, is given in Theory of operation.

Table 6‑2. Header variables.
Label Description – Header Variables
LI-8100A 5 hexadecimal values giving the size of the header, label, raw data, summary data, and footer
File Name File name stored on LI-8100A
Instrument Name User-entered instrument name
Serial Number Instrument serial number
Software Version of embedded software in the instrument
Comment User-entered at time of data collection
Obs# Observation number
Port# Multiplexer port number (0 if not using multiplexer)
Label User-entered at time of data collection, same value in all records
Type The type of record
Pre-purge Wait time between observations
Observation Length Original observation length
Flow8100 Reads zero at all times
FlowMux Pump setting in the LI-8150 Multiplexer
Tmux Multiplexer temperature at start of observation
Virga IRGA volume, in cm3
Vmux Volume of the multiplexer (if present), in cm3
Vext Volume of extension tubing, in cm3
Vcham Chamber and tubing volume, in cm3
Offset Collar offset dimension (cm)
Area Exposed soil area (cm2)
Vtotal Total system volume, in cm3
V1 Info Information on how the voltage channel is configured; multiplexer channel, slope, offset, etc.
V2 Info “
V3 Info “
V4 Info “
Labels_01 Number of columns in the raw data section

Raw records and summary records

The following variables are logged in data files. Additional variables may be present, depending on the configuration.

Table 6‑3. Variables logged by the LI-8100A.
Label Description Units
Type Type or record (see Table 6‑1) n/a
Etime Elapsed time of the measurement seconds
Date Full instrument time stamp, including date and time n/a
Tcham Air temperature inside the soil chamber during an active measurement (if no measurement is active, displays Multiplexer case temperature) °C
Pressure Atmospheric pressure in the optical bench kPa
H2O Chamber water vapor concentration, in mmol/mol mmol/mol
CO2 Chamber CO2 concentration in μmol/mol μmol/mol
CO2dry Chamber CO2 concentration, corrected for water vapor dilution μmol/mol
Tbench Temperature of the optical bench °C
T1 Temperature measurement °C
T2 Temperature measurement °C
T3 Temperature measurement °C
T4 Temperature measurement °C
V1 Voltage at auxiliary channel 1 (multiplexer flow to LI-8100A when attached)  
V2 Voltage at auxiliary channel 2  
V3 Voltage at auxiliary channel 3  
V4 Voltage at auxiliary channel 4  
LATITUDE Decimal Degrees, + for the northern hemisphere, - for the southern hemisphere  
LONGITUDE Decimal Degrees, + for the eastern hemisphere - for the western hemisphere  
STATUS A indicates valid position; V indicates receiver warning  
SPEED Speed over the ground; (0.0 to 1851.8 km/h) km/h
COURSE True course over ground; (0.0° to 359.9°) °
RH Relative humidity inside the soil chamber %
Tboard Temperature of the analyzer control unit board °C
Vin Input (battery) voltage volts
CO2abs Absorption of photons in the optical bench due to the presence of CO2  
H2Oabs Absorption of photons in the optical bench due to the presence of water vapor  
Hour Hour of the day  
Day of Year Day of the year DOY
RAWCO2 CO2 raw signal  
RAWCO2REF A measure of the optical amplitude of the CO2 channel, primarily for diagnostic purposes  
RAWH2O H2O raw signal  
RAWH2OREF A measure of the optical amplitude of the H2O channel, primarily for diagnostic purposes  
Annotation    

System variables

The following variables are used in calculations. The corresponding variables measured by the LI-8100A system are indicated in the column called Name.

Table 6‑4. Definitions of the variables used in the derivations and implemented in the LI-8100A.
Variable Description Units Name
v Total Volume m3  
V Total Volume cm3 "Vtotal"
s Total Surface Area m2  
S Total Surface Area cm2 "Area"
fw Water Evaporation Rate mol m-2 s-1  
p Pressure Pa  
P Pressure kPa Type 1 "Pressure"
P0 Initial value of P kPa Type 2 "Pressure"
TK Absolute temperature K  
T Temperature °C Type 1 "Tcham"
T0 Initial value of temperature °C Type 2 "Tcham"
R Gas Constant 8.314 Pa m3 K-1 mol-1  
fc CO2 Flux mol m-2 s-1  
Fc CO2 Flux μmol m-2 s-1 Exp_Flux
Lin_Flux
dC'/dt Rate of change in water corrected CO2 μmol mol‑1 s‑1 Exp_dCdry/dt
Lin_dCdry/dt
RH Relative Humidity % "RH"
wc Water Vapor Mole Fraction mol mol-1  
W Water Vapor Mole Fraction mmol mol-1 Type 1 "H2O"
W0 Initial value of W   Type 2 "H2O"
k Rate constant s-1  
u Air flow rate out of the chamber mol s-1  
ca CO2 mole fraction of air outside the chamber mol mol-1  
cs' Dilution-corrected CO2 mole fraction of air in the soil mol mol-1  
cc' Dilution-corrected CO2 mole fraction of air inside the chamber mol mol-1  
ca' Dilution-corrected ambient CO2 concentration    
ρcc The number density of CO2 in the chamber mol m-3  
ρcw The number density of water vapor in the chamber mol m-3  
ρc The total number density of air in the chamber mol m-3  
ρca The number density of dry air in the chamber mol m-3  
g Conductance to CO2 m s-1  
a Rate Constant Exponential Coefficient s-1 Exp_a
t0 Time Zero   Exp_t0
C'(t) Dilution-corrected CO2 μmol mol-1 "Cdry"
Cx' Asymptote parameter from exponential fit μmol mol-1 Exp_cx
C'0 Initial dilution-corrected CO2 μmol mol-1 Exp_Co

NOTE: Additional details on computations are provided in the SoilFluxPro user's guide. Refer to that document for more information on final computations.

Footer variables

There may be several footers organized into columns in some files that have been post processed. The GasColumnID variable specifies the variable that all the following footer variables were computed for. By default from the LI-8100A, the GasColumnID will be Cdry. We added a dilution variable to define the source variable for the dilution correction if one is needed. By default, this is none.

Table 6‑5. Footer variables.
Label Description – Footer Variables
GasColumnID Specifies the variable that all the following footer variables were computed from.
Dilution Specifies the source for the dilution correction.
CrvFitStatus Curve fit solution. “Exp” means the exponential fit was better than the linear fit (Exp_SSN<Lin_SSN). “Lin” means the linear fit was still better after the maximum number of iterations, and the non-linear coefficients have therefore been derived from the linear fit
Exp Flux Flux computed from Exponential Fit
Exp_FluxCV Coefficient of variation (%) of Exp Flux
Exp_dCdry/dt Slope of the Exponential Fit at time t0 (Equation 1‑20)
Exp_R2 Correlation coefficient for Exponential Fit
Exp_SSN Normalized sum of squares of residuals for Exponential Fit
Exp_SE Standard error (%) of the Exponential Fit
Exp_a The a term in the Exponential Fit
Exp_Cx The C term in the Exponential Fit
Exp_Co The C0 term in the Exponential Fit. Usually the IV value of Cdry, but if followed by *, indicates it has been manually set.
Exp_t0 The t0 term in the Exponential Fit
Exp_Iter Number of iterations used in the Exponential Fit
Exp_MaxIter Maximum number of iterations allowed for the Exponential Fit. This is fixed to 10 in the LI-8100A (but can be adjusted in the SoilFluxPro software)
Lin Flux Flux computed from Linear Fit
Lin_FluxCV Coefficient of variation (%) of Lin Flux
Lin dCdry/dt Slope of the Linear Fit
Lin_R2 Correlation coefficient for the Linear Fit
Lin_SSN Normalized sum of squares of residuals for Linear Fit
Lin_SE Standard error (%) of the Linear Fit
Crv_Domain Time span (s) used in the curve fit
Crv_#Smp Number of data points used for curve fitting
Dead Band Time (s) after the chamber closes that are skipped by the analysis, in the latest (re-)computation
TimeClosing Time, in seconds, it took the chamber to close