In my role as a caretaker for a large facility with car park and pavements I need to detect hazards and mitigate the dangers. The particular hazard I wish to know is when my footpaths and pavements are covered in ground ice so that I can apply grit. My paths get icy and it is barely visible – the image below has ground ice on a resin bound surface and even wearing boots I could skate the entire length of path.
Ground ice detection systems are expensive – they are used to detect conditions where warning signs are illuminated, deicing is initiated, or other remedial actions taken such as applying deicing solutions to airport runways. My needs are humbler than these; I simply want to be informed by text when ice may be present and arrive early to sweep some salt and grit over the footpaths so people don’t fall over. And I’d be more happy with false positives than false negatives – arriving to find that there is no ice is better than missing a day and someone is injured.
I intend to use LoraWAN to transmit the data as this is cheap and simple, and I have experience in coding and running such systems. Finding a detector that is simple, cheap, and reliable is a challenge. The components will be:
- LoraWAN ice sensor
- LoraWAN gateway through The Things Network (TTN)
- NodeRED process to combine weather conditions including temperature, humidity, cloud cover, and wind. The latter two will likely come from a weather service.
- SMS node in NodeRED to send warning texts
In my searching I found a number of systems that are either too expensive, too elaborate, or I don’t have the technology to produce. I can work with wires, wireless, embedded systems, 3D printed plastics, wood, and some metals such as steel in simple assemblies. Exotic plastics and sensors that require electrical potential are probably beyond my simple facilities, although the electric ones may be possible depending on my battery budget.
There are some good references on the Internet that describe the conditions that lead to ground ice. These are likely to be the same conditions monitored by local council maintenance crews that go out and spread rock salt (called ‘gritting’ here in the UK) on the major trunk roads before a freeze. Mostly, to form ice needs:
- little or no wind
- water vapour in the air, or water on the ground from rainfall
- clear skies without cloud cover
- low temperatures, below freezing point
One way to monitor these things is to use weather sensors and meteorology reports. I could take feeds from something like Weather Underground and combine them, however standard measuring instruments are normally sited well above the ground surface so do not accurately measure the temperature on the ground.
Ice sensors come in a variety of implementations from mechanical to electrical through to optical using thermistors or other IR sensors at a distance. Some are well known in the aircraft runway industry while others are more suited to road surfaces. All the commercial ones cost in the hundreds or thousands of currency, and generally come as part of an integrated system with controller, reporting mechanism and loggers.
I need something under 50 $/£/€ so that I can afford at least a couple of them – one locally for reference, one on site to alert me. That rules out most commercial options. In addition even the most well tested commercial sensors only achieved rates of 86% in university tests, therefore I expect less accuracy in my cheap sensors and will tolerate more false positives.
I will likely go down the route of using a LoraWAN embedded item with temperature and humidity, and using a 3D printed case attach this to a tree or light pole near the main affected pathway. I’ll then combine this with cloud cover and wind sensor data – from locally if possible but if not from a weather service.