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Snow cover from optical sensors
Development of these products has been supported by Norsk romsenter.
Optical sensors are sensitive to electromagnetic radiation in the visible, near-infrered and infrared parts of the electromagnetic spectrum. Radiation at these wavelengths are strongly affected by the atmosphere, either through clouds or through water vapor etc. The main challenge is to differentiate between clouds and sea ice/snow as these surfaces have similar radiometric signatures.
The products shown below are updated on a daily basis although production is continous. Processing is done in a test system which may be unavailable in periods.
Passage products as well as time integrated products are made available.
Product samples
Show AVHRR RGB for a single satellite pass
Show NWCSAF PPS cloud mask information for the satellite pass
Show the probability for snow for the satellite pass
Show the time integrated probability for snow
Show the time integrated snow classification of probabilities
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Chose an image above.
Evaluation
Qualitative evaluation was done in 2009, 2010 and 2011. These revealed that single satellite passages have some noise in the coastal zone and over large lakes.Depending on observation geometry, layered clouds may also be misclassified. Some of the problems encountered were caused by degrading satellites in the evaluation period. A sample of this is shown by NOAA-17 data from 2010-04-29 09:31 UTC. The left panel shows the probability product and the right panel the RGB product.
| Probability of snow | RGB-composite of AVHRR channels 1, 2 and 4. |
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Snow cover from AVHRR GAC
The movie below shows snow cover extracted from AVHRR GAC data using the same algorithm as above.