Modern agricultural technology has made irrigation more sophisticated, and soil sensors based on the FDR principle help us to better understand soil moisture. However, the soil is different in different places, so when using this sensor, it has to be adjusted to the soil characteristics to make it measure more accurately. Therefore it needs to be not counted as a correction parameter to reduce the error. This requires calibration.

Calibration principle

The FDR soil tube sensor measures soil moisture by detecting the effect of moisture in the soil on the propagation of electromagnetic waves. First, it will give a reading based on the moisture content of the soil. Then, we take some soil samples and dry them in a laboratory method to get the actual moisture content. Finally, we compare the sensor's reading with the lab results and adjust the sensor's settings so that it doesn't have more than a 0.1 measurement error, which gives us a more accurate idea of the soil's moisture content.

After weighing all the soil samples, the data were entered into the "Soil Bulk Weight and Moisture Content Calculation EXCEL Template" to calculate the average bulk weight and volumetric moisture content of each soil sample. Next, when fitting the parameters, the adjusted frequency parameters were entered in order to make the humidity values measured by the sensors match as closely as possible with the humidity values predicted by the computational model. This process allows us to derive new parameter coefficients and power values that will be used to optimize the accuracy of soil moisture measurements.

The latest parameters of the soil tube sensors measured in the laboratory are updated into the sensors, and then the data output of the sensors is checked at the actual monitoring site to ensure that everything is normal. In this way, the calibration process is successfully completed.