The smart climate observation network that covers all Africa

Only 300 official weather stations in Africa report to the World Meteorological Organization (WMO). They are spread unevenly; most found in northern and southern Africa, leaving huge data gaps in the central continent. Consequently, national governments, regional planners, insurers, and farmers, do not have data to make critical decisions regarding weather and climate-impacted activities or investments in infrastructure to address climate resilience. Additionally, the few climate data there are held tightly by meteorological offices, generally inaccessible. 

With an increase quality sensors at ever lower costs, and widespread cellular communication infrastructure to take data from weather stations to the internet, Africa can move forward towards the goal of obtaining accurate climate data. This is exactly the idea behind TAHMO (Trans-African Hydro-Meteorological Observatory): to develop a dense network of weather and climate monitoring stations in sub-Saharan Africa with no more than 30 km between stations in areas of significant human activity. This requires the installation of 20,000 stations.

School to School 

By applying innovative sensor technology and ICTs, TAHMO stations are both inexpensive and robust. Stations are mostly placed at schools, where they are integrated in the educational programme, adding richness to the curriculum and helping foster a new generation of climate aware and resilient citizens. Data from the stations are uploaded automatically to an internet server, and schools are provided with software and classroom education tools to view and analyse the local weather data that their station and the stations at other schools are recording. TAHMO partners schools throughout Africa with sister schools in the United States and Europe (see School2School.net). 

At the start of 2018 TAHMO has over 500 stations reporting from 18 African countries, with most having over 20 stations spread across the entire land area. With its data, TAHMO is committed to serving the public by advancing the free and open exchange of weather data and closing the existing hydro-meteorological data gaps in Africa and increasing the communication and application of this information. 

Smart measurement tools

Weather monitoring starts with a set of sensors. Since the development of the smartphone, sensing technology has advanced dramatically in cost, robustness, and precision. TAHMO stations leverage all of these advancements. 

Precipitation drives hydrology, and yet is subject to myriad errors when measured with the standard tipping bucket gauge. Any slight angle in the station installation ruins the calibration. Any dust, pollen, insects, or seeds deposited in the buckets do likewise. A spider web can stop the bucket from operating. TAHMO decided that there would be no moving parts in its stations. Using technology that now has been tested in the field for six years, precipitation is measured by counting the drops that fall off a guide leading from the funnel collector. The size of these drips is dictated by the surface tension of water and the force of gravity – universal constants on earth (no calibration required). 

The TAHMO stations measure wind speed with a rugged, research-grade sonic anemometer. Accuracy far exceeds mechanical devices, reading to zero wind with resolution of 0.01 m/s with a range going from 0 to 60 m/s. No maintenance is required, and since it is based on the speed of sound, it never needs calibration once it leaves the factory. The TAHMO sonic anemometer requires 100 to 1000 times less power than other ultrasonic anemometers, allowing TAHMO stations to run the entire sensor suite for months on the standard five AA batteries, even if the solar panel fails.

Accuracy

The TAHMO stations solve the problem of over-reporting temperature and under-reporting relative humidity that happens normally in enclosed sensors by using an independent thermometer to measure the free-air temperature independently of the temperature measurement taken with the humidity sensor. In fact, temperature is measured three times on the TAHMO station: with sound (the speed of sound is a function of air temperature); with a needle thermometer built into the sonic anemometer opening; and with a high-precision, Swiss-built sensor that measures temperature per relative humidity (T/RH), that is built into the top of the sonic anemometer. The sonic and needle air temperatures are unaffected by heating of the housing, providing exceptional accuracy, and are then used to correct values reported by the T/RH sensor in the protection of the station housing.

All TAHMO stations also include sensors for solar radiation (pyronometer), GPS location, compass heading, and orientation (a digital accelerometer tell us if the station is vertical), lightning detection, along with GSM cell-phone communication.

Repairs

All hardware fails eventually, and the failures can be quite subtle – e.g., diminished solar radiation due to dirt; elevated temperature due to a cracked shield. Therefore, TAHMO plans “local” redundancy on each TAHMO station by including multiple measurements for solar radiation (photo diode and solar panel), temperature (three independent measurements), and rainfall (two measurements). We plan spatial redundancy by placing TAHMO stations close enough together (e.g., 30 km spacing), to achieve high spatial correlation in sensor values. 

Time-series modelling of the joint probability distribution among the local and spatially-redundant sensors allows us to detect when one or more sensors are failing. These models can also predict the value of the target quantity (air temperature, solar radiation, precipitation), which will allow TAHMO to infer these quantities even when some sensors have failed. Furthermore, TAHMO station caretakers are paid according to the data quality, so they are highly motivated to respond to text messages indicating that a station needs attention.

Data collection

The TAHMO weather station uses the solar-powered EM60G data logger from METER. This data logger has been specifically developed with a small solar panel supplying enough energy for the station to function and keep the 5 AA batteries charged. The logger is a 6-port, self-contained data logger especially suited for field research (collaboration welcome!). The TAHMO station occupies only one port, leaving 5 ports open for local studies that might include soil moisture, stream flow, groundwater level, etc. This device is housed in a weather-resistant enclosure, making them suitable for long-term outdoor operation. Measurements from the EM60G are sent wirelessly to TAHMO’s cloud-based data system where the data are processed using advanced quality assurance and control before being delivered to governments, schools, and other clients.

The TAHMO station network averages advancements across the spectrum of electrical engineering, computer science, geodesy, and telecommunications, allowing Africans to make better use of water resources and to produce food for the own population and the rest of the world. Accuracy in observation gives insurance companies the data they need to keep premiums to a minimum and will ensure that farmers who have experienced crop failure get the compensation they deserve.