Finnish Meteorological Institute Vaisala

Frequently asked questions

1. Testbed project

Q: What is Helsinki Testbed?
Helsinki Testbed, often abbreviated as HTB, was initiated in order to promote new observational facilities, research and applications in mesoscale meteorology. Testbed covers four seasons and is located in and around Helsinki, Finland. The initial project run for two years and a half, from January 2005 until September 2007.

After the first phase, the Helsinki Testbed Baseline Network continues to serve as development and research platform at least until the end of Ubicasting follow-on project (Dec 2008). The main financier of the project continues to be Finnish Funding Agency for Technology and Innovation. Many Finnish industry and research institutes have participated to Helsinki Testbed since the beginning of the project.

Broadly speaking, the project goal consists of mesoscale weather research, forecast and dispersion models development and verification, demonstration of integration of modern technologies with complete weather observation systems, end-user product development and demonstration and data distribution for public and research community. The HTB team welcomes and encourages any activity to apply the data for research and development.

The term testbed can be generally defined as: "A testbed is a working relationship in a quasi-operational framework among measurement specialists, forecasters, researchers, private-sector, and government agencies aimed at solving operational and practical regional [insert phenomenon or forecast challenge] problems with a strong connection to the end-users. Outcomes from a testbed are more effective observing systems, better use of data in forecasts, improved services, products, and economic/public safety benefits. Testbeds accelerate the translation of R&D findings into better operations, services, and decision-making. A successful testbed requires physical assets as well as long-term commitments and partnerships."

Q: At what times data is available on the web site?
Real time data products were first planned to be publicly available during the defined measurement campaigns of 08/2005, 11/2005, 01-02/2006, 05/2006 and 08/2006. On the course of the project additional periods of March-April, June-July, September-December 2006, and January-August 2007 were decided to be available as well. In August 2007, availability was further extended until January 2009. Research oriented data will be accessible on the project web site for the foreseeable future, through Researcher's Interface.

Q: Why isn't your service publicly available all the time? It would be understandable if the service would be closed at all times from the public, or if it would be open only during specific events, such as World Championships in Athletics 2005.
According to the original project plan, only selected months were chosen to be made publicly available. There were several reasons for this: 1) Project goals included the technology demonstration in meteorological information production, which had to be realized with publicly available weather products, 2) campaign months were chosen in order to capture typical mesoscale weather phenomena of all the seasons, 3) conflicting interests were encountered with commercial weather service providers, and 4) started as a research project, there was not allocated resources for continuous supervision and maintenance of the measurements. On the course of the project public services gained noticeable popularity so that it was later chosen to extend the service availability.

Q: I am pretty sure you will try to collect money with this technology in the future. I very much wonder why people should pay again for the services, which have been paid already once from tax payers money?
This question includes few assumptions that need clarification. First, it is not the intention of the original Testbed project to collect any additional money except for what was initially raised to get the project running. The questioner also seems to presume that the technology developed in the project has been funded by the government money allocated to Finnish Meteorological Institute. In reality, funding of particular projects may have substantially different funding structures from each other, even within a single organization having driving obligations set by the government.

The initiation of Testbed project gained the critical resource from external research funding source (Tekes), and further support from all the project partners. It is true that a fraction of total funding came from government budget allocated to Finnish Meteorological Institute. Yet the vast majority of project funding came from host organization's external sources. It should be noted that private companies' contribution made an essential factor in the effort. We have the confidence the results of the project will ultimately benefit the whole society as well as the project participants. Aside from the Testbed project, Finnish Meteorological Institute is obligated to fund its operations also with cash-flow financing.

After the initial phase, operation has been made possible with funding by project's interest groups and external research sources.

Q: Would it be possible to extend Testbed observations to the other parts of the country?
Area extension has not been considered. The ideology behind the term testbed implies that substantial amount of data is collected in a restricted domain. Feasible findings and best practices are then better justified in larger areas in a cost-efficient manner.

2. Data and products

Q: Are there other similar data available except for what is provided in Testbed project?
As such, Helsinki Testbed is a unique effort. Some ways comparable data, especially radar observations and other weather services are offered by public and commercial weather service providers such as,, and

Q: Is there other sources of weather data for the same region?
Many of the other data sources for the area have been listed on:

Q: What do the colors mean in radar images?
Colors express the strength of precipitation in various regions. These observations are made with weather radars. Radar transmits short electromagnetic pulses which are then partly scattered back to the radar and measured. On the side of radar image there is a legend expressing the echo strength in radar reflectivity factor scale (dBZ), and also adjectives describing the precipitation (light, moderate, and heavy). Quite common misconception seems to be that color regions indicate the movement of clouds. This is true in the sense that raining clouds move together with rain. However, radar echoes originate almost entirely from rain drops, and not from much smaller cloud droplets. Non-precipitating clouds are therefore not shown at all.

Q: What does dBZ mean? Does it relate to rain rate?
The unit dBZ means radar reflectivity factor, expressed in decibel form. This is a common unit in radar meteorology throughout the world. By using this unit the corresponding rain intensity may be derived empirically. This is done by comparing rain intensity on the ground and radar measured dBZ value. It must be noted that radar reflectivity factor is measured relatively near the ground, but not exactly on the ground. Based on a certain approximation, the following relations can be expressed for liquid precipitation:

  Rain intensity (mm/h) Radar reflectivity factor (dBZ)
Light rain 0.1 - 0.2 8 - 12.9
Light rain 0.2 - 0.5 13 - 17.9
Moderate rain 0.5 - 1.0 18 - 22.9
Moderate rain 1 - 2 23 - 27.9
Moderate rain 2 - 4 28 - 32.9
Heavy rain 4 - 10 33 - 38.9
Heavy rain 10 - 24 39 - 44.9
Heavy rain > 24 > 45

Q: What does "m asl" mean in some of the products?
This expression comes from the words "meters above sea level".

Q: Why don't you put names of places on weather maps?
On the maps there are so many observations that additional texts do not fit in properly. However, by clicking the values on the maps, one finds the name of the observation site.

Q: Why the dates and times are not automatically shown in the "History browser"? The map is changing but I can not see the corresponding date and time unless I use the mouse. In my browser, I have defined black background and white letters. Earlier this problem did not exist.
We have changed animation time stamps from images to text. This is to reduce the size of the animation page. Page loads become this way considerably faster especially in mobile phones and PDAs. Now that you have set black background this is likely to affect to the visibility of time stamps. In your browser, after forcing text to be white also look for the following or similar check box: "Allow pages to choose their own colors, Instead of my selections above." Disable this type of feature.

Q: I don't have enough time to have a decent look at the rain areas and all the numbers on History browser's maps. Could the looping speed be slowed down in the animations?
There is a default speed for the animations, but you may view all the maps separately by moving the mouse pointer over the desired time and date. By doing this, the time value turns to red and animation stops until you move the pointer over another time or over the "PLAY" text.

Q: How can I view Testbed data with Google Earth software?
First you need to download Google Earth program from and install it to your computer. After installation select "Add" in the menu bar and click "Network link". Then choose a name for the new link by filling in the "Name" field, and put in the "Location" field. On the left side of the screen you can select various data layers to be shown with the help of check boxes. You can now use Google Earth to see automatically updating Testbed data on the top of satellite image background.

Q: Which operating systems support Google Earth?
Windows 2000, Windows XP, Mac and starting from Google Earth ver. 4.0 also Linux is supported.

Q: How can I use the Testbed's mobile data products?
To use services tailored for WAP phones with color graphics, please see:

Q: I use currently Nokia N80 phone. When I loop the web site radar animation, the site works well. But if I want to stop the animation by pointing at some time on the right side of the screen, the map does not fit in on the screen anymore. Would specifically designed mobile products work better?
Nowadays mobile interfaces have varying graphical display properties. Indeed, it is possible create tailored products for the different phone models. However, in this project mobile products fulfill the general demonstration of mobile purposes only and have been restricted to WAP phones with color graphics.

Q: What is the Researcher's Interface on the Testbed site?
The Researcher's Interface is an internet service for all interested in data from the Helsinki Testbed. It essentially enables users to make Testbed database queries with numerical or graphical outputs. No knowledge of database or programming languages is required. The Researcher's Interface is administered and maintained by the Finnish Meteorological Institute.

Q: How do I use the Researcher's Interface?
Users must register to the service by logging on to the authentication service and filling in the requested information, including a user-id. The user must also agree with the terms and conditions of the User Agreement and the Appendices. After registration, the user will receive a password via e-mail to use the service.

Q: Is there any special web browser requirements in using Researcher's Interface?
Some features in the Researcher's Interface such as ceilometer and sounding displays require Ajax capable web browser. For more information on Ajax technique, visit: The latest version of Mozilla Firefox is recommended, although Internet Explorer works as well. You may have to manually enable pop-up windows in certain versions of Internet Explorer. Please read also the following question.

Q: I can't access the Researcher's Interface. I only get the following notification: "ERROR The requested URL could not be retrieved -------------------------------------------------------------------------------- While trying to retrieve the URL: The following error was encountered: Access Denied. Access control configuration prevents your request from being al". What's wrong?
The service requires users to be authenticated. Consult your network administrator to make sure data packets are allowed to port 8443 from your local network. Additionally, the service uses cookies in the authentication process, so your web browser must be configured to accept cookies. JavaScript must also be enabled to fully access some of the search forms and help dialog boxes.

Q: I'm experiencing problems after logging in to the Researcher's Interface. Menu on the left or the service otherwise ceases to function. Is there anything I can do?
First, you can try deleting local cookies from your web browser's cache and reloading the page manually. The service uses cookies in the authentication process. If this clean-up does not help, close the browser and log in again.

Also, make sure you are using browser new enough. The latest version of Mozilla Firefox is recommended, although Internet Explorer works as well. Browsers evolve constantly and browser related problems are under investigation. We are sorry for the inconvenience. You are welcome to report any browser related problems.

Q: It would be good to get extended periods of data through the Researcher's Interface with a single query. Can this be done?
At the time of introduction of the service data retrieval latency issues were encountered. Fundamental reason for this is the need for complex on-the-fly XML parsing of the data. Although the response times have been improved, it has been chosen to have limits in retrievals to prevent service overload. As a background, it should be noted that Testbed data retrieval architecture has been planned to serve also machine-to-machine processes. This is an important part of the system and in this case great number of short data requests is preferred method over fewer huge transactions.

3. Testbed variables

Q: What is dew point?
Dew point is the temperature to which given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur. Dew point can be interpreted as a single variable containing information on air temperature and humidity. It is a practical descriptor of the sultriness of air or the likelihood for severe convection, for instance.

Q: What does vertical wind profile mean?
Vertical wind profile describes how wind speed and wind direction change as the observation height increases. From the telecom masts it is usually obtained observations at two different levels while with a wind profiler instrument there may be tens of observation levels.

Q: How do you calculate stability?
For the map products we use simple equation for stability (S): S = (T1 - T0) / (z1 - z0), where T1, z1 are temperature and height at the mast top, and T0, z0 are respective variables at the mast base. Positive values for S indicate surface inversion, i.e. very stable conditions.

Q: I think the shown wind speed values do not really represent the average wind speed. They seem to fluctuate too much. What is the reason?
Supposedly this discovery was made according to only one or few stations. Suspicious behavior is likely due to sensor failure, caused by birds disturbing the ultrasonic measurement for instance. Generally, wind is turbulent by its nature and this is why in meteorological measurements common practice is to use 10 minute averaging for wind speed and direction.

Q: Why do the announced wind forecasts deviate so much from the observations? Observed values are higher than forecasted. I also wonder the variability of wind values in such a limited area.
Forecasted values are expressed at 10 m height, which is much lower than mast top measurements usually at 50-120 m levels. This results obvious differences between the two. The situation is a compromise in selecting the observation sites and optimizing the amount of deployed sensors for obtaining bulk vertical profiles of different variables. Further, many observations especially in the urban area are done only at 2 m level. These latter values absolutely should not be compared to the forecasted. All in all, when having a closer look at wind observations, it is essential to pay attention to sensor height. Neglecting any possible sensor failures, spatial variability of wind is explained by real mesoscale weather effects that can not be correctly described in larger scale numerical weather prediction models.

To discuss the matter a little more, wind observation heights at the new Testbed sites are different from the traditional network. Traditionally, wind measurement is preferred in open terrain at 10 m level. Typically at a single Testbed station, one weather transmitter is close to ground at 2 meters, and the other is in free flow at mast top at about 50-120 meters. Sensor heights are therefore not strictly homogenous across the combined new and old observation network. Wind at 2 meters is not at all comparable for the traditional wind observation; wind detection is integrated to the low level weather transmitter and is not worth being separated from the unit.

Q: Why is wind speed so different between 2 m and the upper measurement height, at a single station?
Two meter wind value is not meteorologically representative and should not be used as an indicator of the prevailing wind. There are nearly always significant obstructions for wind at this height and even if there isn't, 2 m level often severely underestimates the meteorologically representative wind speed. At other heights except for mast tops e.g. trees, telecom mast itself and other structures may distort the measurement depending on the prevailing wind direction. Generally the highest available wind measurement should be preferred when using wind data from the Testbed masts, while recognizing the actual measurement height.

Q: I think you should normalize mast top winds down to 10 meter values. Would you do this? Also, you should not average winds more than 2 minutes in the masts, because longer times eliminate local features of the phenomena. Especially now that observation interval is as short as 5 minutes.
We acknowledge methods like log wind profile and wind profile power law have been developed for normalizing wind values. However, there are limitations in their use which is why we have not thus far incorporated this type of features to the service. In short, normalization methods need site dependent information and/or are best established in neutral atmospheric conditions. The dynamic modeling of wind profile gets more complicated in unstable or stable conditions. Applying some approximation is likely to be considered at later stage.

We also realize that in some applications 2 minute winds are used. However, we have chosen to follow World Meteorological Organization's guideline of 10 minute averaging. In its part, this improves the comparability of the observations to other commonly available wind data. As an exception to 10 minute standard, few urban street level stations register 1 minute winds.

Q: I have particular interest in Kerava Ahjo observations. I follow them quite frequently and I have made comparisons with the nearby sites. Wind speeds seem to be only a half of the expected. What is causing this?
There are some stations in the network with 3 different sensor heights. Kerava Ahjo is one, and the others are Helsinki Harmaja, Helsinki Santahamina, Helsinki Roihupelto, and Hyvinkää Kaukas. The extra middle sensor is at about 20m height. Earlier, the web site's wind maps were created with the highest available wind observation from each site. If mast top observation was not available, wind speed was likely to be underestimated with respect to surrounding stations. This is due to lower height and shadowing effects of the mast. These masts have been excluded from wind maps.

Q: It seems that Vantaa Luhtaanmäki is considerably warmer than other nearby stations. Is this true or are these temperature values erroneous?
The measurement itself is not erroneous. The observed temperatures are occasionally higher because the meteorological representativeness of temperature measurement is not as good as in the nearby stations. The sensor is located near building so that on sunny summer days quickly warming surfaces (ground, building) warm up the air locally which, however, does not get effectively mixed with the air of the surrounding area. Naturally the prevailing wind speed and direction also have an influence on the mixing strength.

Q: Do you use geographic north pole or magnetic north pole as a reference to wind direction values?
Geographic north is used.

Q: Are the pressure values reduced to mean sea level?
In the map products this is the case. In the time series display, values are expressed at the actual sensor height.

4. Observation technology

Q: I couldn't find the description of the method how rain intensity is measured in Helsinki Hietaniemi station. Is it actually 1 minute average? Is it possible to tune WXT510 weather transmitter to give readings for shorter periods (like 10 s)?
Rain intensity is measured as 1 minute average with 10 second sampling interval. With the current Testbed configuration, only the described value is available for rain intensity.

In the following is shown the respective information for all the WXT510 variables. Some of the variables are accessible only through Researcher's Interface. Testbed data is polled by the GPRS communications unit every 5 minutes. WXT responds with a data message containing the current output values, computed as follows:

Pressure, Temperature, Humidity:
- Instantaneous value
- Output value update interval: 30 s

Wind average:
- Basic sampling frequency: 4 Hz
- Averaging time: 10 min
- Output value update interval: 1 min

Wind max & min:
- Absolute max & min values of the 4 Hz samples during the averaging time

Rain accumulation:
- Cumulative sum
- Reset at midnight

Rain intensity:
- Averaging time: 1 min
- Output update interval: 10 s

Q: What is a wind profiler?
In short, wind profiler is an instrument capable of measuring wind speed and direction at different heights in the atmosphere. In Helsinki Testbed, a wind profiler has been situated in Malmi airport with RASS option (radio acoustic sounding system). RASS provides information related to vertical temperature profile. For detailed explanation, see:

Q: Observations seem to drop out every now and then. Why?
The products are served on the internet and the data collection is partly routed through the internet. Therefore the availability of the Testbed web site and data collection performance are subject to network load on the observation network operator's firewall and public web services. Occasionally data packets arrive too late to be included in real time web products. Actually, most of the data is collected as GPRS packet data by using public GSM service network, which is prone to network load, too. Depending on the data it is routed via different paths, practically always involving more than one organization.

The reasons above do not mean the data is lost, but it will be available for later use. Of course, there may be also more severe issues such as physical damage due to lightnings or birds. After all, great portion of the weather stations are placed at telecom mast tops. Physical damage will lead to absence of observations for prolonged times. To reduce maintenance costs repair actions are typically taken at regular intervals, and not immediately after a single flaw has been detected. After the fault has been reported, erroneous observations will be rejected from the web products. Also automatic quality control procedures have been incorporated to the system. Yet other possibilities for completely missing WXT data are the changes in the data collection systems or in the network topology. Various changes are done occasionally in the network functioning as a test platform.

5. Miscellaneous

Q: How can I know where a certain weather station is located?
Locations of the stations are included in the Researcher's Interface section of the web site After self-registratiopn and logging in, select link on the left "Station information" or "Station pictures". You will find images as well as a link to a file describing the station properties. For locating a station and studying its surroundings, one handy tool is Google's satellite images visualization software; see the earlier FAQs on Google Earth.

Q: How do I know how reliable is a local rain, cloudiness or fog forecast?
For numerical weather prediction models there are various mathematical descriptors to estimate model uncertainty. One approach is to run several different models or a single model with slightly varying initial conditions, and to produce uncertainty statistics based on the agreement of such model runs. Another approach to estimate forecast quality and reliability is to apply various verification methods, i.e. to compare the forecasts with the actual observed state of the atmosphere. Typically this requires a large dataset of forecast-observation "pairs" to obtain statistically meaningful results. Yet another method to analyze the quality of a (single) numerical forecast is to use the meteorologists' skill and experience to estimate probabilities for certain types of predicted weather variables to occur. In practice, uncertainty estimates are not often included in the operational weather forecasts. However, some weather service products which are produced for specific professional end-users can contain numerical probability estimates of the expected weather.

Note that the products on the Testbed web site are not actually forecast variables but, rather, observations. One can in certain weather types make very short range predictions based on observations only following, e.g. the past movement (advection) of rain areas.

Q: Is there available rain accumulation maps for a prolonged time period, 3 years for instance? I would be interested to know whether it rains more in Espoo Tapiola than in Helsinki Lauttasaari. Or, somehow it feels that in Kerava rains more, and more often than in Helsinki Kaivopuisto.
For finer scales, such as the questioner asks, most of the traditional observation statistics are not particularly well suited. Also the Testbed data has not accumulated long enough for climatological precipitation analysis. In any case, it is well known that in summer near the coastline rains less than in inland. This results from distribution of cloudiness, and ultimately from faster solar heating of land as compared to water surface.

Especially for larger scale investigations, climatological publications are useful. E.g. Drebs, A., A. Nordlund, P. Karlsson, J. Helminen, and P. Rissanen, 2002: Tilastoja Suomen ilmastosta 1971-2000 - Climatological statistics of Finland 1971-2000. The publication is available at the library of the Finnish Meteorological Institute.