Guidance to open data observations

How to interpret open data observations? Here we have the summarized some of the most used observations and what should be taken into account when using them.

Weather observations

Parameter name Temporal resolution Interpretation
Total cloudiness Instant Given in numbers out of eight: 0 = clear skies, 8 = overcast, 9 = cloud coverage could not be determined. Takes into account all cloud layers.
Precipitation intensity Instant Equivalent to the precipitation amount if the same intensity prevails for an hour. To get the true 10 minute precipitation amount, divide by 6.
Mean wind speed Instant The average wind speed during the previous 10 minutes.
Wind gust Instant The highest 3-second average wind speed during the previous 10 minutes.
Wind direction Instant In degrees. 0/360 means that the wind is blowing from the north towards the south.
Sea level pressure Instant The air pressure reduced to sea level.
Relative humidity Instant Calculated relative humidity.
Snow depth Instant Snow depth from automated weather stations. Accuracy +- 2 cm.
Visibility Instant Estimated visibility at weather station.
Dew point Instant Dew point temperature.
Mean temperature Daily The average temperature based usually on 4 or 8 observations per day.
Maximum temperature Daily The highest temperature during two 12 hours period, i.e. between 8 p.m. previous evening and 8 p.m. this evening (9 p.m. - 9 p.m during summertime).
Minimum temperature Daily The lowest temperature during two 12 hours period, i.e. between 8 p.m. previous evening and 8 p.m. this evening (9 p.m. - 9 p.m during summertime).
Precipitation Daily The daily precipitation is measured between 8 a.m. (9 a.m. in summertime) and 8 a.m. (9 a.m. in summertime) local time the following day and is given in millimetres (snowfall=water equivalent).
Snow depth Daily Snow depth is measured at 8 a.m. local time (9 a.m. during summertime).
Precipitation Monthly The monthly precipitation sum is the sum of daily precipitation sums.
Mean temperature Monthly The monthly mean temperature is the average of daily mean temperatures.

Sea observations

Parameter nameInterpretation
Significant wave heightWave height is the vertical difference between the wave through and the wave crest. The significant wave height is calculated as the average of one third of the highest waves from the energy spectrum.
Wave direction (from)The wave direction given here is simply the direction along which most of the wave energy is propagated. As with the wind direction, the wave direction is usually given as the direction from where the waves are arriving.
Wave directional spreadingAn irregular wave field always consists of waves traveling in different directions. Their distribution with respect to the mean direction is described by the directional spreading.
Modal periodThe wave period is defined as the time between two wave crests. The modal period describes the dominant wave period of irregular waves.
Water temperatureA buoy measures water temperature once every hour from 20 cm deep.
Water levelWater level is referred to theoretical mean water level.

Air quality observations

Parameter nameInterpretation
Particulate matter (diameter < 10 μm / <2.5 μm)

Mean concentration (μg/m**3) of the previous hour (UTC-time)

Nitrogen dioxideMean concentration (μg/m**3) of the previous hour (UTC-time)
Sulphur dioxideMean concentration (μg/m**3) of the previous hour (UTC-time)
OzoneMean concentration (μg/m**3) of the previous hour (UTC-time)
Odorous sulphur compoundsMean concentration (μg/m**3) of the previous hour (UTC-time)
Carbon monoxideMean concentration (μg/m**3) of the previous hour (UTC-time)