Conversion of raw TMS soil moisture values to volumetric water content (VWC)

Function converts the raw TMS soil moisture (scaled TDT signal) to volumetric water content (VWC). Calculated VWC values are added as new virtual logger.

mc_calc_vwc(
  data,
  moist_sensor = mc_const_SENSOR_TMS_moist,
  temp_sensor = mc_const_SENSOR_TMS_T1,
  output_sensor = "VWC_moisture",
  soiltype = "universal",
  localities = NULL,
  ref_t = mc_const_CALIB_MOIST_REF_T,
  acor_t = mc_const_CALIB_MOIST_ACOR_T,
  wcor_t = mc_const_CALIB_MOIST_WCOR_T,
  frozen2NA = TRUE
)

Arguments

data: cleaned myClim object see myClim-package
moist_sensor: name of soil moisture sensor to be converted from TMS moisture values to volumetric water content (default "TMS_moist") see names(mc_data_sensors). Soil moisture sensor must be in moisture_raw physical units see names(mc_data_physical).
temp_sensor: name of soil temperature sensor (default "TMS_T1") see names(mc_data_sensors). Temperature sensor must be in T_C physical units.
output_sensor: name of new virtual sensor with VWC values (default "VWC_moisture")
soiltype: Either character corresponding to one of soiltype from mc_data_vwc_parameters (default "universal"), or a list with parameters a, b and c provided by the user as a list(a=Value_1, b=Value_2, c=Value_3).
localities: list of locality_ids used for calculation; if NULL then all localities are used (default NULL)
ref_t: (default 24)
acor_t: (default 1.91132689118083) correction parameter for temperature drift in the air, see mc_calib_moisture()
wcor_t: (default 0.64108) correction parameter for temperature drift in the water, see mc_calib_moisture()
frozen2NA: if TRUE then VWC values are set to NA when the soil temperature is below 0 °C (default TRUE)

Value

myClim object same as input but with added virtual VWC moisture sensor

Details

This function is designed for TOMST TMS loggers. The raw TMS units represents inverted and numerically rescaled (1-4095) electromagnetic signal from the moisture sensor working on Time Domain Transmission principle (Wild et al. 2019). For TMS3 logger version, the typical raw TMS moisture values ranged from cca 115 units in dry air to cca 3635 units in distilled water. TMS4 version has slightly different range of raw values (typically 250-700 units for air and 3650-3900 in water, depending on production series) and calibration is needed to comply with available calibration curves inferited from Wild et al. 2019 - see mc_calib_moisture.

Raw TMS moisture values can be converted to the soil volumetric water content with calibration curves. The function provides several experimentally derived calibration curves which were developped at reference temperature. To account for the temperature drift, the function uses difference between actual soil temperature measured by TMS_T1 soil and reference temperature (default = 24°C)

The default calibration curve is "universal", which is average of curves derived for different mineral soils (see Kopecký et al. 2021). Specific calibration curves were developed for several soil types (see Wild et al. 2019) and the user can choose one of these or can define its own calibration - see mc_data_vwc_parameters

Currently available calibration curves are: sand, loamy sand A, loamy sand B, sandy loam A, sandy loam B, loam, silt loam, peat, water, universal, sand TMS1, loamy sand TMS1, silt loam TMS1. For details see mc_data_vwc_parameters.

It is also possible to define a new calibarion function with custom parameters a, b and c. These can be derived e.g. from TOMST TMS Calibr utility after entering custom ratio of clay, silt, sand.

Warning: TOMST TMS Calibr utility was calibrated using TMS3 series of TMS loggers, which have different range of raw soil moisture values than TMS4 series. It is necessary to recalibrate TMS4 loggers using mc_calib_moisture function for actual range of raw air and water moisture signal.

The function by default replace the moisture records in frozen soils with NA (param frozen2NA), because the TMS soil moisture sensor was not designed to measure in frozen soils and the returned values are thus not comparable with values from non-frozen soil.

References

Wild, J., Kopecký, M., Macek, M., Šanda, M., Jankovec, J., Haase, T. (2019) Climate at ecologically relevant scales: A new temperature and soil moisture logger for long-term microclimate measurement. Agriculture and Forest Meteorology 268, 40-47. https://doi.org/10.1016/j.agrformet.2018.12.018

Kopecký, M., Macek, M., Wild, J. (2021) Topographic Wetness Index calculation guidelines based on measured soil moisture and plant species composition. Science of the Total Environment 757, 143785. https://doi.org/10.1016/j.scitotenv.2020.143785

Examples