IS32, Nairobi, Kenya

Thumbnail: Nairobi

Nairobi, Kenya

With a population of about three million, Nairobi, Kenya, is one of Africa’s largest cities, but just over a century ago this teeming site was little more than uninhabited swampland. That changed with the coming of the railroad. In 1899, during the construction of the Uganda Railroad for the British East Africa Company, workers converged upon the area now known as Nairobi, setting up a supply depot and basic camp called “Mile 327”. As for the name “Nairobi”, it came from the local Masai, an indigenous African ethnic group found in Kenya and Tanzania, who called this place Ewaso Nyirobi, meaning “cool waters”.

By 1907, Nairobi had become the capital of the British East Africa Protectorate, attracting adventurers, hunters and travelers from the far corners of the world. Flourishing as the region’s administrative and tourist centre, Nairobi became the first port-of-call for many British colonialists. With grand hotels built to accommodate British big game hunters, Nairobi experienced an inflow of investment leading to an expansion of the city and its suburbs.

Nairobi National Park, located just outside the city, is home to large herds of buffalo, giraffe, wildebeest and zebra.

In 1963, Nairobi became the capital of newly independent Kenya. The following decades brought continued growth and expansion to the bustling city, which has become one of Africa’s most prominent political, social and economic cities.

Still, wildlife remains one of Nairobi’s most distinctive attributes. Nairobi National Park, located just outside the city on 113 km² of plains, cliffs and forests, is home to large herds of buffalo, giraffe, wildebeest and zebra. Nairobi also boasts more species of birds than any other capital city in the world. As for big game animals, cheetah, lions and rhino roam freely within 20 minutes of the city … and within proximity of Infrasound Station IS32!

Karura Forest on the northern outskirts of Nairobi had been identified as the preferred location for IS32.

Station Location

A site survey was conducted by Kenya’s National Council for Science and Technology (NCST), in collaboration with the CTBTO's Provisional Technical Secretariat (PTS) from 31 March to 18 April 2000. The NCST’s survey identified the Karura Forest on the northern outskirts of Nairobi as the preferred location for establishment of IMS infrasound station IS32.

At an altitude of approximately 1,700 metres, the Karura Forest consists of both indigenous and exotic trees, some as old as 60 years. Measurements of background micro-pressure and wind noise made during the site survey clearly showed that the densely forested areas provided good wind shelter, which is an important criterion for reducing background noise in infrasound measuring.

IS32 is an unmanned station, but the station operator can access the Central Processing Facility (CPF) to make repairs or upgrades at any times.

Station Profile

The IS32 infrasonic array is a seven-element array, equipped with 18 m wind-noise reducing systems to further minimize background micro-pressure noise.

To access the array elements located in the Karura Forest, a four-wheel drive vehicle is needed at all times to travel from Nairobi to the nearest point of each array. IS32 is unmanned, but the station operator can access the Central Processing Facility (CPF) to make repairs or upgrades at any time.

In order to ensure smooth operations, the station operator, a staff member of the Department of Geology at the University of Nairobi, monitors a wide variety of array element state-of-health data on a daily basis. This allows technical staff to quickly identify and diagnose problems, which are usually remedied within a single day.


Learn more about how the infrasound technology works.

Testing, Evaluation and Certification

Walking towards the station during the certification visit in 2003.

Consistent with the CTBTO’s certification process, IS32 successfully met all minimum requirements for an IMS infrasound station. Continuous transmission of data from IS32 via the Global Communications Infrastructure (GCI) to the IMS Laboratory (where the first testing of the functionality and operability of the station is carried out) began in June 2003. During the testing period, data availability amounted to an excellent 99.99% - well within the required specifications. Therefore, IS32 was certified on 25 June 2003 as the 19th of a planned 60-station network.

In addition to infrasound station IS32, Kenya also hosts primary seismic station PS24, located near the town of Thika, which is around 50km from Nairobi. The town was made famous by  Elspeth Huxley‘s novel “The Flame Trees of Thika”.

Learn more about Kenya and the CTBT.