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.
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.
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.
Raw records and summary records
The following variables are logged in data files. Additional variables may be present, depending on the configuration.
| 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.
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.
| 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 |