Devices

The temperature loggers are of the type Hobo H8 Pro. They are digital devices that can measure the air temperature at a given interval. The Hobo’s can be connected to a PC or laptop computer. Using a software called BoxCar Pro it is possible to read the log file and to set the logger’s measuring interval. When setting the interval it is also possible to set the exact time at which the logging starts. The Hobo contains a build in clock that supports this functionality. Furthermore, the loggers can be read with a device called Hobo Shuttle. It cannot be used for changing the configuration of the logger, but for reading log files it’s useful since the device is much smaller and lighter than a laptop. The Hobo H8 Pro loggers were delivered together with white plastic radiation shields that protect the temperature sensors from any direct sunlight.

Picture 1. Hobo H8 Pro temperature logger and cross section of it inside radiation field

The Onset Computer Cooperation promises an accuracy of ±0.2 degrees celsius. During tests carried out before the loggers where placed into the field the results indicated that the loggers met this precision. When carrying out the tests no correction values for the individual loggers were calculated. This should however be possible. Doing so may increase the accuracy of the measurements in the future.

In November 2009 – January 2010 90 new temperature loggers were ordered, delivered and calibrated. The new loggers were installed during the spring 2010. The old Hobo H8 Pro temperature loggers run simultaneously beside the new ones for two years. The logger network was also extended from 60 to 75 observation sites during the years 2010-2012.

The HOBO U23 Pro V2 Temperature/Relative Humidity data logger is a weatherproof data logger with built-in temperature and relative humidity sensors. The Relative Humidity sensor provides superior durability in humid environments and is user replaceable.

•    Weatherproof housing for use in outdoor or condensing environments

•    42,000 Measurements

•    Sampling Rate: 1 Second to 18 Hours

•    Multiple Logging Intervals

•    High accuracy

•    Replaceable Relative Humidity sensor provides fast response and superior recovery from condensing conditions

•    Small-diameter external sensor versions for measurements in tight spaces

•    Optic USB interface for fast and reliable download

Picture 2. Hobo Pro v2 Temperature/Relative Humidity logger. The devices will be installed into a radiation shield like the old ones to protect the logger from the effect of direct sunlight. (source: http://www.onsetcompany.com)

The weather stations are of the type MAWS 201. They are portable and can rather quickly be setup (in several hours). The one currently running in Tuorla is most advanced and measures air temperature, soil temperature, precipitation, humidity, solar radiation, net radiation, air pressure, wind direction and wind speed. The radiation and air pressure sensors are not available in all three stations. Like the temperature loggers, the weather stations can be connected to a PC or laptop. Using a monitor program it is possible to read the stations log files. A software called MAWS Lizard, produced by Vaisala, allows the user to setup a configuration for the weather station. This configuration determines the interval of different measurements, what measurements are logged and what variables are directly calculated from the measurements (e.g. relative humidity and temperature in Fahrenheit). Depending on the configurations the weather stations can store data for a certain period of time.

When the weather station is continuously connected to a computer, the software YourVIEW allows the user to maintain a real time connection with the weather station. In a standard interface it shows the current weather conditions. Furthermore, YourVIEW offers an opportunity to store the data on the computer’s hard drive. The station currently running in Tuorla is connected to a PC and does therefore offer the opportunity to use the software. As an advantage it would not anymore be necessary to read the station every four weeks. However, it is hard to guarantee a continuous connection. In case someone switches off the computer, data would be lost. We therefore decided not to use the YourVIEW program.

Picture 5. Maws 201 weather station

The weather stations can obtain energy from a fixed electricity source as well as a solar panel. The initial plan was to use a solar panel for at least one of the stations, but in winter it turned out to be problematic. Especially when the panel gets covered with snow and ice, the station is not provided with enough energy. For that reason there’s fixed electricity source at both Tuorla and Pääskyvuori stations.

The installation of the temperature loggers started in autumn 2000 and was finished in summer 2001. The main work faces were finding the most proper locations in the field, applying for permissions to install the loggers and the installation itself. Finding proper locations was not always easy. During the planning of the project, the preferred locations of the loggers were defined from maps, but in practice it was not always possible to install the loggers to the selected locations. Either there were no objects to attach the loggers to, or one or more of the defined criteria (see Planning of the project) could not be met. Especially in the urban areas shadowing objects are abundant and grass undergrounds sparse. In such cases the logger was normally installed to a location that represented the best compromise between optimum and possibilities.

Picture 6. Map of the locations of the temperature loggers (black stars) and the weather stations (red dots).

Most of the loggers were attached to lampposts belonging to the city of Turku, low voltage electricity line posts belonging to Turku Energy and poles at school properties. Furthermore, some loggers are put to military properties, private properties etc. A few loggers have their own pole that was placed at installation. For each individual logger an application was made to the owner of the location/pole it was installed to. A list of contact details containing all organizations that provided permissions can be found under the Ilmasto project folder in the sub-folder Contact Info.

In order to be able to install the loggers so that they are not located too close to heat radiating objects, horizontal metal arms were made at the university (about 40cm long). On the one side they are connected to the solar radiation shields and on the other side to the objects that hold the logger. In most cases metal and nylon bands were used to attach the logger arms to the objects in the field. Example of logger placement can be found as an attachment at the bottom of this page.

Picture 7. Example of logger location.

Installation of the weather stations started in summer 2001. Two stations were installed in summer 2001. One at the Tuorla agricultural school (Varsinais-Suomen maaseutuoppilaitos) and one at Pääskyvuori kasarmi. Both of them were put on aluminum poles in order to higher the position of the temperature probe to exactly three meters above ground level. The station in Tuorla was provided with power from the normal electricity network and a computer was connected. The computer is situated in a building of the agricultural school. The station runs well, but there’s some breaks in observations due to the service measures and damages caused by thunder. On the Pääskyvuori station a solar panel was used as a power source, but it did not provide enough energy in winter. Coverage of the panel with snow formed the main problem. The station was taken out of the field in spring 2002, and it was replaced when a connection to the regular electricity network was established. The third station has never been installed since no proper location was found. It should be located in the city centre, but it’s hard to find a safe and representative place.

As described earlier, there is going to be a renewal of the loggers during spring 2010 with the new type of data loggers. There will be information about the installation process here on the web page when the process in finished.