Measuring sap flow allows tree and plant water use to be calculated on a daily or seasonal basis, and subsequently informing irrigation choices or species selection. Realtime monitoring of these measurements has not been possible until ICT International developed the SFM1x range of Sap Flow Meters using Internet of Things (IoT).
With IoT connectivity, the SFM1x is ideal for scenarios where trees are being monitored off site. The continuous connectivity via IoT allows for simplified data retrieval for analysis.
For decision makers, enabling the regular collection of data on the water use of the tree is crucial to ensure that an appropriate watering and water management strategy can be developed. Furthermore, this will ensure an efficient allocation of water and other resources in the management of the trees.
Addressing the needs of the researcher, the SFM1x is a scientifically robust instrument. The underpinning method, the Heat Ratio Method, has a proven track record in research publications. This acceptance is due to the designed functionality such as the internal SD card that records all the measurements taken, and the ability to store raw temperature data for off-line analysis.
Since 2013, ICT International has worked with wireless communication networks for the transmission of data from their instruments. In 2021 the SFM1x was launched with CAT-M1 or LoRaWAN capabilities for IoT connectivity.
The SFM1x Sap Flow Meter uses the Heat Ratio Method, developed by Burgess, Adams, Turner, Beverly, Ong, Khan and Bleby (2001). A pulse of heat is provided by a heater needle located in the sapwood area, with a downstream and upstream needle that are accurately spaced to measure the heat difference over time. This measurement, combined with data on the sapwood area allows for the calculation of the sap flow. Uniquely the SFM1x can measure reverse sap flow as well, through the upstream needle.
This data is available to users in both a calculated water use form, as well as raw temperature data for scientific researchers. With the raw temperature data stored in a JSON format, the data can be imported into analysis packages such as R or Python.
With the ability to provide data in common file types, the SFM1x can support researchers or web developers to work with data in a form that is suitable for many varied applications:
For those using R and Python, scripts are available upon request for the processing of data from the SFM1x
The SFM1x is an IoT enabled Sap Flow Meter is available in the following versions:
The use of these communication technologies enables the SFM1x to be deployed wherever there is cellular network coverage, or if there is no cellular coverage, a network using LoRaWAN and subsequent internet connection via 4G or satellite backhaul.
All SFM1x versions contain a Bluetooth module with an internal antenna for wireless data access and configuration of the unit. The SFM1B has a dedicated external Bluetooth antenna allowing long range connection.
The Sap Flow Meter (HRM30 and SFM1) has over 400 listings in Google Scholar, highlighting the wide acceptance by the research community. ICT International has an active library of over 150 leading publications that can be accessed here.
The principles behind the SFM1x – the Heat Ratio Method – have been used to measure plant and tree water use in many applications. Example applications of the SFM1 and HRM30 can be found in:
The heat ratio method can measure reverse flow, low flow and high flow. Supported by widespread use in the research community, the calculations that enable these calculations are well established and verified.
Sap flow measurement provides a measurement of the transpiration of the plant. This indicates the plant water status, and subsequently the daily water requirements can be calculated.
Data from the SFM1x is stored as CSV or JSON for easy access and analysis. The data from the SFM1x can be viewed online or downloaded for analysis using a number of common tools, as well as direct integration into customer dashboards.
Data from the SFM1x can be downloaded to be analysed in many statistical packages or sent via an API to a data visualisation (dashboard) of choice. Data can be downloaded directly from the SFM1x, or from the cloud when using the SFM1C or SFM1L.
When data is downloaded from the cloud, subsequent analysis can be performed using statistical packages. Advanced cloud integration solutions, which provide programming and modelling environments for further scientific analysis, machine learning and management decision making applications are available. Please consult ICT International for more details.
ICT International have integration solutions for the analysis of SFM1x data (CSV or JSON) using:
Advanced cloud integration programming and modelling environments include:
These provide the ability to undertake all analysis in a cloud environment, removing the need for static processing with downloaded data.
For the static processing of data, data from the SFM1x can be downloaded and analysed using the proven ICT International Dataview and Sap Flow Tool software. This is ideal for those who are upgrading their SFM1 to an SFM1x.
Providing real time information of the tree condition and water use, SFM1x data can be integrated into specific tools. These tools can be web based or dedicated apps using the API and JSON feeds. The results are suitable for arborists and the public when visiting an arboretum or tree canopy walk.
Visualisation solutions include:
Data from the SFM1x can also be downloaded and processed using ICT International Sap Flow Tool software. The software also allows for instant visualising of sap flow in 2- and 3- dimensions.
Using the Heat Ratio Method, the SFM1x can measure plant water use when the stem or root diameter is greater than 10mm, including:
Advanced users may choose to use JSON files containing the raw temperature data for subsequent processing and analysis.
The dynamic reference list maintained by ICT International can be found here.
|Output Options||Raw Temperatures: °C
Heat Pulse Velocity: cm hr-1
Sap Velocity: cm hr-1
Sap Flow: cm3 hr-1 (Litres hr-1)
|Range||-100 to +100 cm hr-1|
|Resolution||0.01 cm hr-1|
|Accuracy||0.5 cm hr-1|
|Measurement Duration||120 seconds|
|User Adjustable Heat Pulse||20 Joules (default) approx. Maximum 40 Joules. 20 Joule pulse is equivalent to a 2.5 second heat pulse duration, auto scaling.|
|User Adjustable Logging Interval||Minimum interval 3 minutes, recommended minimum 10 minutes.|
|Needle Diameter||1.3 mm|
|Needle Length||35 mm|
|Measurement Positions||2 per measurement needle|
|Measurement Spacings||7.5 mm and 22.5 mm from the needle tip|
|Dimensions L x W X D||170 x 80 x 35 mm|
|Temperature Range||-10 to 50°C|
INTERNAL POWER AND POWER MANAGEMENT
|Battery Specifications||3300mAh Lithium Ion, 4.20 Volts fully charged|
|Fully Charged Battery||4.20 Volts|
|Low Power Mode||3.60 Volts – Instrument ceases to take measurements. Resumes measurement at 3.70 Volts|
|Discharged Battery||2.90 Volts – Instrument automatically switches off at and below this voltage when no external power connected. Reconnects when battery returns to 3.1 Volts.|
|Battery Life||At the recommended configuration of 20 Joules at 10-minute intervals, upto 40 hours battery life has been observed without additional power supply. With a recommended power source connected, operation can be continuous.|
|Bus Power Source||60mA – 200mA Variable internal charge rate, maximum charge rate of 200mA active when the external voltage rises above 16 Volts DC|
|USB Power Source||100mA fixed charge rate|
|External Power Requirements|
|Bus Power||8-30 Volts DC, non-polarised, current draw is 100mA at 20 volts per SFM|
|USB Power||5 Volts DC|
|Communications||Short Range Bluetooth||Yes||Yes||Yes|
|Long Range Bluetooth||Yes||–||–|
|LoRaWAN||–||–||Yes (L1 = Global, L2 = China)|
|Data||Output File Types||BIN, CSV||CSV, JSON||BIN, CSV|
|Data Storage||MicroSD Card|
|Memory Capacity||Up to 16GB, 8GB MicroSD card included.|
|Manufacturer’s Product Codes||SFM1x-UB||SFM1x-C||SFM1x-L1 or -L2|
The SFM1 Sap Flow Meter is widely used in research; below is a selected list of over 150 publications that have used the Sap Flow Meter in their research.