A Low-Cost Sensor Network for Monitoring Peatland
Abstract
:1. Introduction
2. Materials and Methods
2.1. System Objectives
- Collect useful and meaningful data for monitoring peatland health.
- Be compatible with the peatland environment.
- Be easy for those unfamiliar with IoT to use.
- Reduce long-term peatland monitoring costs.
2.2. Design Requirements
- Each sensor node should be capable of detecting carbon dioxide, methane, air temperature, humidity, soil moisture and soil temperature levels.
- Each sensor node should take measurements at least hourly.
- The system must be able to operate in the conditions expected for the site—i.e., wet ground, rain, frost−10 to 35 °C, and variable sunlight.
- The system may not rely on any external power supply, such as mains electricity.
- The system should minimise the risk of disturbance or harm to wildlife.
- The system should operate without human interaction for a minimum of 1 month.
- Collected data should be transmitted wirelessly and at least daily.
- The system should be portable and easy to deploy and retrieve.
- The system cost should be comparable to or cheaper than a similar month-long manual study.
2.3. System Architecture
2.4. Gateway Node
2.5. Sensor Node
2.5.1. Sensor Selection
2.5.2. Sensor Calibration
2.5.3. Node Operations
2.5.4. Data Format
- Retrieve the value from a sensor (Reading).
- Round the data to the accuracy of the sensor (Rounded).
- Subtract the minimum possible reading of the sensor from the current value (Vs min).
- Scale up the current value to an integer (Decimal to send).
- Convert the value to hexadecimal nibbles (Hex to send).
- Concatenate the resulting hexadecimal values into a single string for submission.
2.5.5. Error Filtering
- Humidity exceeding 100%
- Temperature exceeding 100 °C
- Temperature below −30 °C
- Battery charge value exceeding 100%
- Extreme outliers for CO2 (outside the range 100 to 3000 ppm)
- Extreme outliers for methane (raw sensor voltage outside the range from 0.4 to 1.6 V)
- Extreme outliers for soil moisture (outside the raw sensor data range of 200 to 1200)
2.6. Site Selection
3. Results
3.1. Overall System Specifications
3.2. Recorded Data
3.3. System Performance
3.3.1. Gateway Performance
3.3.2. Sensor Issues
- Null values—created when a sensor fails to return a reading. The recorded value will be either zero or the minimum value the sensor can return;
- Saturated values—often caused by sensor faults or disconnection, leading to the maximum possible sensor output being recorded;
- Random values—multiple potential causes, often difficult to diagnose or prevent but usually short-lived and easy to filter out as they often affect multiple sensors in a given node at the same time. Causes may include moisture ingress, unstable wireless communication, or malfunctioning components;
- EEPROM data corruption—errors created when writing to the EEPROM. This issue occurred most commonly when the battery charge fell below 16% and was caused by a bitwise shift in the stored data. This was reversed in post-processing to repair the data.
3.3.3. Limits on Deployment Duration
4. Discussion
4.1. Performance against System Objectives
4.1.1. Objective 1: Useful and Meaningful Data
4.1.2. Objective 2: Compatible with the Peatland Environment
4.1.3. Objective 3: Ease of Use
4.1.4. Objective 4: Long-Term Cost Reduction
4.2. Datastring Encoder
4.3. Limitations and Future Work
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
CH4 | Methane |
CO2 | Carbon Dioxide |
GHG | Greenhouse Gas |
PPM | Parts Per Million |
RH | Relative Humidity |
RMSE | Root Mean Squared Error |
SD | Secure Digital |
WSN | Wireless Sensor Network |
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Reading | Rounded | Vs min | Decimal to Send | Hex to Send | |
---|---|---|---|---|---|
Min. temperature | −40 | −40 | 0 | 0 | 0 |
Max. temperature | 70 | 70 | 110 | 1100 | 44C |
Example temperature | 32.62 | 32.6 | 72.6 | 726 | 2D6 |
Parameter | Value |
---|---|
Sensor node mass | 1 kg |
Gateway node mass | 5.6 kg |
Total system mass | 9.6 kg |
Materials cost | £1350 1 |
Monthly running costs | £8 1 |
Sampling interval | 30 min |
Maximum theoretical deployment | 121 days 2 |
Tested continuous deployment | 28 days |
Measured variables | Air temperature, relative humidity, CO2 concentration, methane concentration, soil moisture, surface soil temperature, battery charge level |
Without Encoder | With Encoder | Units | |
---|---|---|---|
System voltage | 5 | V | |
Measurements per day | 48 | ||
Measurement current | 0.5 | A | |
Measurement power | 2.5 | W | |
Measurement duration | 60 | s | |
Total measurement duration | 2880 | s/day | |
Total measurement energy | 2 | Wh/day | |
Transmit current | 0.13 | A | |
Transmit power | 0.65 | W | |
Transmit duration | 60 | 46.2 | s |
Total transmit duration | 2880 | 2217.6 | s/day |
Total transmit energy | 0.52 | 0.4004 | Wh/day |
Sleep current | 0.0008 | A | |
Sleep power | 0.004 | W | |
Total sleep duration | 80640 | 81302.4 | s/day |
Total sleep energy | 0.0896 | 0.090336 | Wh/day |
Total energy | 2.6096 | 2.490736 | Wh/day |
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Mitchell, H.L.; Cox, S.J.; Lewis, H.G. A Low-Cost Sensor Network for Monitoring Peatland. Sensors 2024, 24, 6019. https://doi.org/10.3390/s24186019
Mitchell HL, Cox SJ, Lewis HG. A Low-Cost Sensor Network for Monitoring Peatland. Sensors. 2024; 24(18):6019. https://doi.org/10.3390/s24186019
Chicago/Turabian StyleMitchell, Hazel Louise, Simon J. Cox, and Hugh G. Lewis. 2024. "A Low-Cost Sensor Network for Monitoring Peatland" Sensors 24, no. 18: 6019. https://doi.org/10.3390/s24186019
APA StyleMitchell, H. L., Cox, S. J., & Lewis, H. G. (2024). A Low-Cost Sensor Network for Monitoring Peatland. Sensors, 24(18), 6019. https://doi.org/10.3390/s24186019