SNiP-SMT for Soil Moisture
The SNiP-SMT is a 'Sensor Node Integrated Package' for LoRaWAN or CAT-M1 communication of real-time soil moisture measurement for continuous soil monitoring. Typical applications taking advantage of IoT SNiPs include irrigation management of orchards, permanent plantings, sporting fields, public gardens and greenhouses.
The SNiP-SMT
The base SNiP-SMT integrates 1x S-NODE and 1x SMT-100 soil moisture sensor to a site’s unique network, communication and power requirements.
The SMT-100 measures the dielectric permittivity of a surrounding medium using a proprietary Time Domain Transmission (TDT) technology, using a ring oscillator to produce a frequency of >100MHz, allowing it to operate well even in clayey soils.
See Further Specifications on the S-NODE
See Further Specifications on the SMT-100 Sensor
Further parameters or additional SMT-100s can be added to the SNiP-SMT, without requiring loggers to match each distinct sensor, substantially reducing the cost of getting a fuller picture on the application. The S-NODE can support an added 5x SMT-100 devices (for a total of 6x SMT-100 sensors).
Time Domain Transmission – SMT-100
The SMT-100 soil moisture probes uses Time Domain Transmission (TDT) technology, combining the advantages of the low-cost FDR sensor system with the accuracy of a TDR system. Like a TDR, it measures the travel time of a signal to determine the relative permittivity εr of the soil, converting εr into an easy to measure frequency.
The SMT-100 utilizes a ring oscillator to transform the signal’s travel time into a frequency. The resulting frequency (>100 MHz) is high enough to operate well even in clayey soils. Consequently, it corrects the VSW% value (volumetric soil water) independent of soil type. Maintenance free and frost resistant, the SMT-100 can be used for long-term observations (8+ years continuous).
| Single-Point TDT SNiPs | SNiP-SMT |
| SNiP Measures | VWC % / EC Temperature |
| Core Sensor/Device (Single-Point) |
SMT-100 |
| UOM | VWC % / °C |
| SNiP Node | S-NODE |
| Sensors SNiP Supports | Up to 4 (STD)* |
| *Custom SNiP can support more | |
S-NODE
The S-NODE (for Environmental Monitoring) has been designed to support the broad suite of SDI-12 based environmental sensors. The S-NODE can support sensors with higher power requirements; a solar panel can charge either the internal lithium-ion battery or both the node and sensor can be powered by an external 12V system (e.g. battery or mains source).
A decoder suitable for TTN will be provided based upon sensor configuration. See more information on the S-NODE.
- LoRaWAN™ low-power long-range connectivity
- Supports the full range of SDI-12 commands, and sensors requiring constant excitation.
- Optional CAT-M1
- Solar rechargeable Lithium-ion, Single use LiSOCl2, or external 12V power options
- Optional Multi-constellation GNSS
- AS923, AU915 and US915 available, with other region plans available upon request.
- Standard IP65 enclosure, optional IP67
SMT-100
The SMT-100 soil moisture probes uses a TDT (Time Domain Transmission) technology. The SMT-100 determines the volumetric water content and the soil temperature. It has a broad measurement range, it is maintenance free and frost resistant. With a short response time robust design and manufacture, hence can be used for long-term observations (8+ years continuous use).
SMT-100 combines the advantages of the low-cost FDR sensor system with the accuracy of a TDR system. Like a TDR, it measures the travel time of a signal to determine the relative permittivity εr of the soil. And like a FDR, it converts εr into an easy to measure frequency. The SMT-100 utilizes a ring oscillator to transform the signal’s travel time into a frequency. The resulting frequency (>100 MHz) is high enough to operate well even in clayey soils. Consequently, it corrects the VSW% value (volumetric soil water) independent of soil type. This is not the case for capacitance sensors.
Higher measurement frequencies are better than lower frequencies. See more details on the SMT-100.
Advantages
- Frost resistant
- Reliable measurement
- Maintenance free
- Long lifetime
- Fast response
- Low influence of salinity and pH
- Cost efficient
| Signal output | – digital (RS485 with UGT-protocol. SDI-12 is available on request) – analog (0-1V, other voltage ranges on request) |
| Cable length | 10 m |
| Power supply | digital 4 to 24 VDC (analog 12 to 24 VDC) |
| Dimensions | 182 x 30 x 12 mm |
| Moisture | |
| Measurement range | 0-60% vol (0 … 100% vol with limited accuracy) |
| Accuracy with generic calibration | ±3% vol in mineral soils with average salinity over 0 … 50% vol |
| Accuracy after specific calibration | ±1% vol |
| Resolution | 0.1% vol |
| Temperature | |
| Range | -40 to +80°C (analog -40 to +60°C)
extended temperature range on request |
| Accuracy | ±0.2°C (analog ±0.8°C) |
| Resolution | 0.01°C (analog 0.2°C) |
Test
Berthelin, R., Rinderer, M., Andreo, B., Baker, A., Kilian, D., Leonhardt, G., Lotz, A., Lichtenwoehrer, K., Mudarra, M., Padilla, I. Y., Pantoja Agreda, F., Rosolem, R., Vale, A., & Hartmann, A. (2020). A soil moisture monitoring network to characterize karstic recharge and evapotranspiration at five representative sites across the globe. Geoscientific Instrumentation, Methods and Data Systems, 9(1), 11–23. https://doi.org/https://doi.org/10.5194/gi-9-11-2020
Bogena, H. R., Huisman, J. A., Schilling, B., Weuthen, A., & Vereecken, H. (2017). Effective Calibration of Low-Cost Soil Water Content Sensors. Sensors, 17(1), 208. https://doi.org/10.3390/s17010208
Pellet, C., & Hauck, C. (2017). Monitoring soil moisture from middle to high elevation in Switzerland: Set-up and first results from the SOMOMOUNT network. Hydrology and Earth System Sciences, 21(6), 3199–3220. https://doi.org/10.5194/hess-21-3199-2017
Pellet, C., Hilbich, C., Marmy, A., & Hauck, C. (2016). Soil Moisture Data for the Validation of Permafrost Models Using Direct and Indirect Measurement Approaches at Three Alpine Sites. Frontiers in Earth Science, 3. https://doi.org/10.3389/feart.2015.00091
Schaffitel, A., Schuetz, T., & Weiler, M. (2019). A distributed soil moisture, temperature and infiltrometer dataset for permeable pavements and green spaces. Earth System Science Data Discussions, 1–27. https://doi.org/https://doi.org/10.5194/essd-2019-97
Schwank, M., & Naderpour, R. (2018). Snow Density and Ground Permittivity Retrieved from L-Band Radiometry: Melting Effects. Remote Sensing, 10(2), 354. https://doi.org/10.3390/rs10020354
Tarnik, A. (2019). Impact of Biochar Reapplication on Physical Soil Properties. IOP Conference Series: Materials Science and Engineering, 603, 022068. https://doi.org/10.1088/1757-899X/603/2/022068
Thom, J. K., Szota, C., Fletcher, T. D., Grey, V., Coutts, A. M., & Livesley, S. J. (2019, July 1). Transpiration and the water balance of tree-based stormwater control measures. Novatech 2019: Urban Water Planning and Technologies for Sustainable Management. Novatech 2019, Lyon, France. www.novatech.graie.org/documents/auteurs/1D24-096THO.pdf
Schaffitel, A., Schuetz, T., & Weiler, M. (2019). A distributed soil moisture, temperature and infiltrometer dataset for permeable pavements and green spaces. Earth System Science Data Discussions, 1–27. https://doi.org/10.5194/essd-2019-97