GSM base stations can also be used to measure rainfall

GSM base stations are susceptible to interference caused by rain. The Hydrology and Quantitative Water Management Group of the Wageningen University wants to exploit this property by using the stations as rainfall meters. This will provide more accurate weather and climate models, also resulting in better water management, which can especially benefit developing countries. In any case, this that is what postdoc researcher Dr Hidde Leijnse and project leader Prof. Remko Uijlenhoet expect. Best of all, the costs are negligible.

According to the initiators, the network of GSM stations offers a perfect opportunity to register detailed rainfall data. This can provide benefits not only in the Netherlands, but especially in countries where there is very little systematic monitoring of rainfall.

In order to transmit mobile phone calls, the GSM base stations maintain a constant connection with their neighbouring stations by means of microwave links. There are about 13 thousand of these links in the Netherlands alone, transmitted through the air, each link being several kilometres long. The links are susceptible to interference caused by raindrops, a property which Leijnse and Uijlenhoet believe could provide useful data. ‘Based on the loss of signal strength between two GSM base stations, it is possible to calculate the amount of rainfall in the path of the signal. Rainfall has a nearly proportional effect on signal distortion; however, we have no experience with hail and snow' says Leijnse, who based the proposal on a pilot study conducted by the group in 2003. If funding is granted, the research will be continued and expanded.

The KNMI (Royal Dutch Meteorological Institute) currently records the rainfall in the Netherlands with about 325 rain gauges that are read once a day; they also use 35 automatic weather stations which collect rainfall data every hour. ‘That is only one rain-gauge per 100 to 1000 square kilometres. That gives a distorted image, especially with heavy rainfall’, says Uijlenhoet. Aside from that, the amount of rainfall is tracked by weather radars at De Bilt and Den Helder. There are also drawbacks to this method, which has little accuracy because it measures at a very high altitude.

Leijnse: ‘However, our system also has a drawback; the GSM base stations aren't spread evenly across the country. For example, the density is higher in the west of the country, than in regions such as the Veluwe.’ However, Uijlenhoet also sees a benefit in this uneven spread: ‘The difference in density works in our favour; there is a big demand in the west for information on rainfall with a higher temporal and spatial resolution. This information could be useful for water management, for example for processing wastewater or keeping the polders dry.’

Leijnse and Uijlenhoet expect that the GSM measuring network will be successful in the Netherlands, but will be especially useful in developing countries. ‘In most countries in the northern half of Africa, rainfall is scarcely measured, even though this baseline data is essential to knowledge about water management and the energy balance, and therefore to knowledge about the climate system as a whole. This also determines the accuracy of the climate models’, says Leijnse. By ‘hitchhiking’ on the advancement of mobile telephony – mobile phones have also become a part of everyday life in Africa – he hopes that the rainfall data will become available in time. ‘You could try to set up weather radar in developing countries, but that is expensive and provides little advantage. As a by-product of an exceptionally lucrative business, the method we propose costs virtually nothing.’ / RN