Urban climate sensors 

Introduction 

In the summer of 2022, to outline to city officials and the public the value of the Pollinator Highway to Tallinn’s climate, SEI Tallinn placed 18 meteorological sensors in western Tallinn to produce visualised data streams. This effort will demonstrate the value of the Pollinator Highway from a city-climatological perspective by comparing green and grey areas and infrastructure, thereby supporting Tallinn’s preparations to become the European Green Capital in 2023. City climate measurements and visualisations provide proof of the importance of green spaces along the Pollinator Highway to the well-being of Tallinn’s citizens, especially during summer heatwaves.

Data generation began in May 2022 and will continue for at least three years after the end of B.Green. Eighteen sensor units were installed on lamp posts along existing and planned trail sections and the surrounding urban areas. The sensors measure temperature, to capture urban heat island intensity; relative humidity (the pollinator highway as a storage of humidity); and precipitation, or the variable distribution of rainfall patterns. The data generated will allow visualisation and analysis of a number of important locally relevant meteorological features that have been hardly explored in Tallinn. In the near future, the results should feed into a range of applications useful for decision making on city planning, climate risk reduction and adaptation planning, among other things. They could also support rain radar calibration and highly localised weather forecasts, and even projections of heat stress and vulnerability.

Description of practice

Process
Preparing the sensor network (incl. time commitment):
● Reconciling methods and expected output (data, visualisation, communication) with the B.Green project team and technical experts (meetings and preparation work, about two days)
● Securing funds from the project budget to buy sensor units and related services and from organisational co-funding for related staff costs (writing applications and reconciliation in project group, about two days)
● Preparing the terms of reference, including project background and vision, required sensor and service package, approximate distribution and location of sensors in western Tallinn, technical specifications, data accessibility, delivery and price offer (writing the document and checking back with technical experts and research of best practice, about two days)
● Public procurement: internet search to find producers of low- to medium-priced climate sensors; obtaining the minimum of three price offers (whole process about two days)
● Preparing a request for permission to install sensor units from the City of Tallinn. To ease the process, sensors were installed only on lamp posts owned by the city council (covering most, but not all, lamp posts) (half a day)
● Careful identification of the exact location of the lamp posts for all 18 sensor units; documentation and requests for permission; choice of locations to obtain coverage of the factors most relevant to Tallinn’s climate (see below) (3 days)
● Preparing the 18 sensors: unpacking, unscrewing and re-screwing to activate battery and prepare rain gauge, and fixing new holders (1 day)
● Preparing metadata on sensor units and locations (half a day)
● Installation of sensors (2 days for most sensors; 1 day for remaining sensors and replacements)

Installing the sensors:
● Installation of each sensor usually took two days and was technically supported by the City of Tallinn with three technical staff, two cars with storage room for technical equipment and the sensor units, and one car with a lifting platform to securely install the sensor units (additional budget needed for this).
● The installation steps outlined above use the Tallinn Harku meteorological station as an example. Here, the sensor was installed at a height of 2.6 m on the post of an automatic snow height detector to be close to the reference sensors of the Estonian Weather Service.

Who was involved  

The project was developed by SEI Tallinn as part of the B.Green project. The sensor units were delivered by Pessl. Meteoblue supports the data and visualisation services and the street lighting service company installed most of the sensor units. 

Promotion and communication

The project was publicised using Facebook posts and on the SEI Tallinn page. It has also been presented on local television in Tallinn. Early results will be presented in a YouTube video (work in progress). A report on spring and summer 2022 results was published in September by the B.Green project.  

Requirements

● Skills: Expertise related to meteorology and data analysis. Organisational skills to manage unexpected issues.
● Resources: Funding to buy and install the sensor units. 

Time commitment

Preparation work began in October 2021 and was completed in May 2022. Most of the sensor units were installed on 19–20 May 2022; some installations/replacements took until mid-June. 

Lessons learned

● The time taken to find a suitable location for each sensor (environment of the lamp post and agreement of the City of Tallinn) and install the sensor was generally underestimated. Procurement of suitable sensors was also a challenge.

● There were also technical difficulties with finding a suitable height to install the sensor. The sensor must be low enough to be reachable with a ladder but high enough to be unreachable by pedestrians, cyclers etc. At 3.5 m, at least four people with ladders will be needed to remove, clean and reinstall the sensors.

● Sensor units are relatively cheap but they require regular cleaning. The batteries may not work in winter. 

Outcomes

● An overall good representation of different urban environments. The temperature measurement is very accurate (~0.15°C < than expected), and relative humidity and precipitation show tangible results. Precipitation measurement, however, seems to be affected by strong winds.

● Hourly accurate data.

Read more

Live weather info in Tallinn https://www.meteoblue.com/en/products/cityclimate/tallinn