Satellite data for Europe from the Meteosat MSG satellites is usually available every 15 minutes. Depending on the available sensors, the satellite data was recorded over the period of 5 or 15 minutes. Our fog and visible images are typically taken over 5 minutes, whereas products like the cloud type index are 15 minute scans.
Please note that the queried time refers to the end of the scan (e.g. a fog image for 14:00 was usually taken from 13:55 to 14:00), and that times will be rounded down to the last full 15 minute step. This means that a query for a satellite image for 13:59 will return the image dated for 13:45, taken from 13:30/13:40 to 13:45 depending on the type.
Please note that only cloud_type(_transparent):idx and sat_hrv:idx parameters below can be useful if queried as non-image data. The other parameters are intended for visualization purposes and are only meaningful if queried as a png image with the correct colormap (using png_default does that for you), as the values correspond to a specific color.
A near true color satellite image based on multiple channels in the visible spectrum can be queried with the parameter
The high resolution visible (HRV) image goes by the name
where the detected wavelengths range from 600 to 900 nm with a peak at 750 nm. The image is gamma-transformed for better visibility.
By combining data from sensors at various wavelengths, it is possible to distinguish cloud types due to their differing temperature and constituents. Such an image can be queried with the two parameters
sat_cloud_type:idx also includes indices for sea and land, you can query the cloud-related indices (the rest being set to -666 for missing clouds) through
sat_cloud_type_transparent:idx. The values are related to the cloud types according to the following table:
|2||Snow covered land|
|3||Snow/ice covered sea|
|4||Very low stratus|
|6||Mid level clouds|
|7||High opaque clouds|
|8||Very high opaque clouds|
|9||Very thin cirrus|
|12||Thin cirrus above mid/low clouds|
|13||Fractional/broken low clouds|
For visualization purposes, these indices are mapped onto colors according to the following legend:
If you wish to query an image that is transparent wherever there are no clouds and emplaces the HRV image data wherever there are clouds, you can do so by means of the parameter
Please note that since the image data stems from HRV, the clouds will be black wherever there is no sunlight, e.g. during the night.
A clever combination of satellite images at certain wavelengths into an RGB can highlight low clouds and fog as well as distinguish them from one another. Two such RGB composite images queried by the following parameters:
For the interpretation of
sat_day_fog:idx images please refer to the PDF SEVIRI Dust RGB Quick Guide. As indicated by the title of the PDF, this is also helpful with tracking dust clouds.
A brief guide to reading the
sat_night_fog:idx images can be found in the PDF Night Microphysics RGB Quick Guide, with a more detailed presentation containing a lot of examples located here. Please note that the composite is tuned for night time and the presence of sunlight has a significant impact on both the contrast and interpretation of the colors.