Point and profile measured soil moisture sensors
Our service goal is to choose the right soil sensor equipment for you and make the right decision. We’re digging into the most asked questions. How do soil moisture sensors work, for example, and what are the differences between point and profile measurements?
Soil moisture sensors measure the water content in the soil and can be used to estimate the amount of stored water in the soil horizon. Soil moisture sensors do not measure water in the soil directly. Instead, they measure changes in some other soil property that is related to water content in a predictable way. Each sensor manufacturer uses different technologies to measure soil moisture content; for a detailed explanation of all the different types, we recommend reading about the various technologies here
For a soil sensor to work, no matter the type, it must make contact with the soil. The highest accuracy will be obtained when the soil sensor is entirely surrounded by the soil, with no gaps between the probe and the soil.
Our Soil moisture Sensors utilize Time Domain Transmissometry or TDT technology to measure moisture content. Providing some background, TDT measures the time taken for an electromagnetic wave to propagate (travel) along a given length of a transmission line in the soil. The higher the moisture content surrounding the probe, the slower the signal travels. TDT sensors generally provide greater accuracy and lower power consumption than TDR sensors. The other advantage over the other methods comes down to the bandwidth of the measurement. TDT has a higher bandwidth than other methods like Frequency Domain Reflectance, making it less susceptible to the interference that affects capacitance.
Another critical difference between soil moisture sensor types is the probe geometry and whether it measures a single point, multiple points, or continuously along the entire length of the probe. Point measurements are single-point soil moisture meters, which means they measure a single location and depth.
Soil moisture profiling probes measure moisture content across a vertical soil profile, typically spanning a range of 30cm to 120cm. Most usually consist of multiple single-point sensors housed within an elongated enclosure; this type of geometry allows for several points to be installed quickly and at one time. However, the Profile features modular segments that form a single antenna allowing for continuous measurements across the entire length, giving a true soil moisture profile.
The chief advantage of using a soil moisture profiling probe is the elimination of the cost of multiple single-point sensors and the need to excavate and bury them at the appropriate depths. To install most profiling probes, either plastic or PVC access tubes need to be inserted before the sensor can be. This design imposes uncertainties, and in some cases, there tends to be a preferential flow between the access tube and the sensor.
Depending on whether the soil moisture sensor you choose is a point measurement or a true profiling soil sensor like the Profile, it is essential to know that the readings will be different when placed at the same depth and location. The Point Probe will give measurements at a specific depth, where the Profile averages the moisture content over each segment of the probe, making it less susceptible to inconsistencies in the soil.
If you have any questions, do not hesitate to contact firstname.lastname@example.org at any time, we would be happy to schedule a time to speak directly with you. If you have a question that you would like answered, submit it here.