Monitoring precipitation sounds easy – but it isn’t. There is a wide range of assessments that need to be made in order to identify the right sensor for the job. That starts with resolution and accuracy, size and weight, the capacity to monitor intensity, the suitability to withstand frost, and even the ability to measure solid precipitation. Not to forget the budget available.
Precipitation comes in many different forms and intensities, from a light drizzle to torrential rains, from liquid to snow to hail. Selecting the right sensor is not an easy task as some technologies are better suited for one task over the other, technical constraints might prevent some instruments from being deployed, and last not least there is a budget that needs to be considered.<
These are great devices for a majority of applications. Their two major advantages are their extremely low power consumption and their low cost. They usually come in the form of tipping bucket sensors, where a double spoon tips back and forth as it is being filled and emptied, and creates a pulse with every action. However, a trade-off needs to be made between resolution and accuracy, resp. the capacity to determine intensity.
The better the resolution of a tipping bucket sensor (e.g. 0,1mm vs. 0,5mm) the more accurately this sensor can measure very light and/or short rainfall events, which are barely wetting the soil and the plants. But when a sudden downpour occurs, with 50, 100, sometimes even 200mm coming down within a matter of minutes, these sensors are overwhelmed by the large volume of water, their action not being able to catch it all and thus under-reading. If such events are the dominant form of precipitation, coarser resolutions need to be selected, such as 0,2 or 0,5mm.
Maintenance is of important! Leaves, dust, sand, bird droppings all might accumulate in the rain gauge’s funnel and eventually reduce accuracy or even block the gauge.
For the most sophisticated of applications weighing sensors are a great choice. With extremely high accuracy they can monitor both light and heavy rain events, and since they are catching precipitation in a container they can even monitor snow and hail. However, they tend to be more costly than mechanical sensors, due to their size, electronics and calibration efforts involved.
Thanks to the fact that they feature a catch can that measures precipitation in time intervals they are hardly influenced by debris falling into the catch can. Thus a weighing sensor usually requires less maintenance, thus less site visits – an advantage that can offset some of the extra cost.
The World Meteorological Organization WMO stipulates an area of 200cm² to be the acceptable minimum. The larger the area, the better the result and resolution, as precipitation is collected from a larger area, reducing error. But that larger area comes with strings attached – such as larger susceptibility to influences by wind pressure, increased weight, requiring better fixation, higher power consumption if heating is required. If weighing systems with catch containers are deployed, these need to be emptied more often as they fill quicker the larger the orifice.
Optical and electromagnetic sensors
There are other forms of measuring precipitation, such as laser or infrared based optical systems, that scan a predetermined area for precipitation type, size and speed of particles, and calculate from these parameters volume and intensity. Electromagnetic sensors in turn detect precipitation particles by the reflection of electromagnetic radiation, applying the same working principles as a radar system in an airport. Again they can measure liquid as well as solid precipitation, just like weighing sensors do, but there are two considerations to be made. One is cost, as such systems are certainly more expensive than mechanical gauges, and the other is power, since both systems need to be heated, as the optics need to be cleared of moisture, and the radar dome needs to be kept ice free at all times.
And as you have probably expected, ADCON can offer a sensor from each of these categories, for any resolution and accuracy demands, for any application, for any budget!
For each resolution and accuracy, for each application and for every budget, ADCON has the right sensor. With well over 35.000 rain gauges sold (2016) we have collected vast experience with all technologies around for all applications imaginable. Thus we can offer the right product for
- Hydrographical Services
- Flood warning
- Urban Meso-Networks
- Sports and Leisure
ADCON has deployed sensors from the polar circle to the Sahara, from the Canadian plains to Costa Rica’s tropical forests. Ask our experts and our distribution partners for the right solution! The following links will guide you to some of our products:
Mechanical sensors, heated and unheated: