Infrared Satellite Imagery Product
- “Well-known split window channels (e.g., AVHRR). Essential for measuring sea and land surface and cloud-top temperatures; also for the detection of cirrus cloud (e.g., Inoue 1987) and volcanic ash clouds (Prata 1989). Note that for the infrared thresholding technique, an infrared window channel is used, such as the 10.8 micrometre channel onboard Meteosat. An infrared window is a region of the electromagnetic ultraviolet spectrum where absorption by atmospheric gases is minimal, meaning that views of the cloud-free surface and clouds at various levels are not significantly affected by atmospheric gases such as water vapor.”
Water Vapor Composite Satellite Imagery Product
- “RGB (Red, Green, Blue) composite based upon data from infrared and water vapor channels from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instrument. It is designed and tuned to monitor the distribution of different air masses and evolution of cyclones, in particular, rapid cyclogenesis, jet streaks, and PV (potential vorticity) anomalies. Due to the incorporation of the water vapor and ozone channels, its usage at the highest satellite viewing angles is limited. The Airmass RGB is composed of data from a combination of the SEVIRI water vapor 6.2, water vapor 7.3, infrared 9.7, and infrared 10.8-micrometer channels.”
Infrared Rapid Development Thunderstorms Satellite Product
- “This software tracks clouds, identifies those which are convective in nature, and provides some descriptive attributes for their dynamics. MSG data (over Western Europe, Africa, and the Indian Ocean) is used; but the RDT software can also use GOES-E data for the Caribbean Sea. The main and non-optional satellite channel is Infrared 10.8 micrometer (for detection and tracking of systems). Additionally, water vapor 6.2, water vapor 7.3, infrared 8.7 and infrared 12.0-micrometer channels can be used (for convective discrimination between different types of convective storms).”
Cloud Type Satellite Product
- “The cloud type product mainly aims to support nowcasting (i.e., short-term forecast operations between roughly 30 minutes to 12 hours) applications. The main objective of this product is to provide a detailed cloud analysis. It may be used as input to an objective meso-scale analysis (which in turn may feed a simple nowcasting scheme), as an intermediate product input to other products, or as a final image product for display at a forecaster’s desk. The cloud type product is essential for the generation of the cloud top temperature and height product, cloud microphysics and for the identification of precipitation clouds.”
Pressure Peaks Satellite Product
For high thick clouds: a method called the radiance ratioing method (see the next bullet for further explanation of this method) is first applied to remove any remaining semi-transparency that could have been undetected by the cloud type scheme. In case of failure, the method defined for medium opaque clouds is then applied.
For high semi-transparent clouds: The 10.8 micrometer infrared brightness temperatures are contaminated by the underlying surfaces and cannot be used as for opaque clouds. A correction of semi-transparency is applied, which requires the use of two infrared channels: the 10.8µm window channel and a sounding (6.2 micrometer, 7.3 micrometer, and 13.4 micrometer for METEOSAT Second-Generation) channel. The basis is that clouds have a stronger impact in a window channel than in a sounding channel.”
- “Cloud top pressure or height are derived from their Infrared brightness temperatures by comparison to simulated Infrared brightness temperatures computed from temperature and humidity vertical profiles forecast by numerical weather prediction systems using an infrared radiative transfer model (RTTOV). Exact retrieval method depends on cloud type as semi-transparency correction using window and sounding infrared channels may be needed.
For high thick clouds: a method called the radiance ratioing method (see the next bullet for further explanation of this method) is first applied to remove any remaining semi-transparency that could have been undetected by the cloud type scheme. In case of failure, the method defined for medium opaque clouds is then applied.
For high semi-transparent clouds: The 10.8 micrometer infrared brightness temperatures are contaminated by the underlying surfaces and cannot be used as for opaque clouds. A correction of semi-transparency is applied, which requires the use of two infrared channels: the 10.8µm window channel and a sounding (6.2 micrometer, 7.3 micrometer, and 13.4 micrometer for METEOSAT Second-Generation) channel. The basis is that clouds have a stronger impact in a window channel than in a sounding channel.”
Credit for all above goes to: ©EUMETSAT 2019 and Keraunos.org
Natural Color Satellite Imagery Product
- “The Natural Colour RGB is composed of the visible 0.6, visible 0.8 and the near-infrared 1.6 channel data. In the Natural Colour RGB, the cyan colour of snow and ice on the Earth’s surface results from a strong reflection of shortwave solar radiation (see the green arrows on the left hand image). The more homogenous the snow/ice cover is, the brighter the cyan colour will be. Snow and ice on mountains (see the image below) will therefore be depicted in a stronger cyan colour than snowy surfaces on ground which are often disrupted by vegetation.
High reaching, cold clouds like frontal or Cumulonimbus clouds but also thin Cirrus clouds appear cyan in the Natural Colour RGB. Ice crystals strongly absorb solar radiation at 1.6 micrometer, while it is reflected for a large extent at 0.6 and 0.8 micrometer. With changing sun zenith angles and uneven cloud heights, the illuminated parts of the clouds may cause an inhomogeneous cyan colour pattern. Parts of the cloud which reflect more solar radiation might appear brighter than shadowed regions.
Liquid water strongly absorbs shortwave radiation emitted from the sun. The SEVIRI instrument onboard MSG measures only small amounts of back scattered radiation from the sun in the spectral range between 0.6 and 1.6 microns. Therefore the Natural Colour RGB depicts ocean and lake surfaces in dark (black) colours.
Vegetation cover over land is depicted in green in the Natural Colour RGB. The intense green colour stems from the strong response of the VIS 0.8 micron channel. Vegetated surfaces much stronger reflect solar radiation at 0.8 than at 0.6 microns. This is one of the reasons, this channels combination is called "Natural Colour RGB".
The reflected solar radiation at NIR1.6 from sand and non-vegetated surfaces is stronger than reflected solar radiation in both visible channels (VIS0.6 and VIS0.8) as can be seen in the image below of the Arabian peninsula. Sandy deserts are shown in red colours.
Rocky fields and vegetation-less mountains appear darker (green circles). Reflected solar radiation at 1.6 micrometer has about the same intensity over rocks than radiation measured in both VIS channels.”
Infrared Satellite Imagery Product
- “Well-known split window channels (e.g., AVHRR). Essential for measuring sea and land surface and cloud-top temperatures; also for the detection of cirrus cloud (e.g., Inoue 1987) and volcanic ash clouds (Prata 1989). Note that for the infrared thresholding technique, an infrared window channel is used, such as the 10.8 micrometre channel onboard Meteosat. An infrared window is a region of the electromagnetic ultraviolet spectrum where absorption by atmospheric gases is minimal, meaning that views of the cloud-free surface and clouds at various levels are not significantly affected by atmospheric gases such as water vapor.”
Airmass RGB Composite Satellite Imagery Product
- “RGB (Red, Green, Blue) composite based upon data from infrared and water vapor channels from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instrument. It is designed and tuned to monitor the distribution of different air masses and evolution of cyclones, in particular, rapid cyclogenesis, jet streaks, and PV (potential vorticity) anomalies. Due to the incorporation of the water vapor and ozone channels, its usage at the highest satellite viewing angles is limited. The Airmass RGB is composed of data from a combination of the SEVIRI water vapor 6.2, water vapor 7.3, infrared 9.7, and infrared 10.8-micrometer channels.”
Convection/Severe Storms Satellite Imagery Product
- “Convection RGB combines the brightness temperature difference (BTD) between the water vapor 6.2 and water vapor 7.3 channels (on red), the BTD between the infrared 3.9 and infrared 10.8 channels (on green) and the reflectance difference between the near-infrared 1.6 and the visible 0.6 channels (on blue). Severe convective storms appear bright yellow in this color scheme because of the near zero BTD water vapor 6.2 - water vapor 7.3 of overshooting cumulonimbus (Cb) clouds (high red). The strong updrafts in these clouds produce small ice particles at cloud tops due to homogeneous freezing of cloud drops, resulting with large BTD infrared 3.9 - infrared 10.8 (high green). Finally, large negative values of near-infrared 1.6 - visible 0.6 because of the large absorption at near-infrared 1.6 by ice particles keeps the blue very low. Please note that small ice crystals of cirrus clouds should not be confused with vigorous convection. Inferred small ice crystals that are not associated with anvils of Cb clouds must form by elevated strong updrafts, such as in high altitude orographic wave clouds.”
Cloud Top Height (CTH) Satellite Product
- “Cloud Top Height (CTH) product is an image-based product which indicates the height of the highest cloud. Using pixel-based cloud analysis retrieval, the CTH product is derived for 3 × 3 pixel areas, in which the highest cloud top is assigned to a 320 meter thick cloud height band. If a specified minimum number of cloudy pixels are available within the CTH 3 × 3 pixel pixel processing area, then the pressure level of the highest cloud is extracted for determining the aforementioned cloud height band. The pressure level is taken from a cloud analysis that uses forecast data for the determination of the cloud height in the geophysical unit of “pressure”. Currently, the product may contain up to 51 bands reaching up to approximately 15 kilometers. For the CTH height band determination, the International Civil Aviation Organization (ICAO) standard atmosphere (pressure and height) is used to derive the heights corresponding to the pressure levels determined in the cloud analysis product.
An important user community for the CTH products is the aviation industry. CTH products are typically used to provide aircraft crew with information on the presence of high-level clouds. The latest change to the product increased the frequency of the product generation and distribution. This greatly improved the service for the aviation user community. With dissemination only on the hour, a single missed product immediately resulted in a gap of two hours between consecutive products deliveries. This is no longer the case.“
Multi-sensor Precipitation Estimate (MPE) Satellite Product
- “Multi-Sensor Precipitation Estimate (MPE) product provides estimated instantaneous rain rates in full pixel resolution. The algorithm is based on a combination of Infrared 10.8 channel and passive microwave data from the Special Sensor Microwave Imager (SSM/I) instrument on the US Defense Meteorological Satellite Program (DMSP) polar satellites. The Infrared 10.8 channel data can be taken from Meteosat-8, Meteosat-9, or Meteosat-10 satellites (SEVIRI instrument) or from Meteosat-7 satellite (MVIRI). Processing is done in near-real time mode with a time delay of less than 10 minutes between image acquisition and data dissemination. The product is most suitable for convective precipitation, and is intended mainly for areas with poor radar coverage, especially in Africa and Asia.”
Water Vapor Satellite Product
- “The water vapor 6.2 channel continues the Meteosat water vapor channel to measure upper-troposphere water vapor. In addition, the water vapor 7.3 channel provides information on the humidity conditions in the mid-troposphere. The humidity information from both channels is used for tracking water vapor features and thus provides the local wind field in even cloud-free conditions. These channels also support scene identification and height assignment for semi-transparent clouds. The water vapor channel data are used to infer possible local atmospheric instability which might lead to convection and severe storms.”
Credit for all above goes to: ©EUMETSAT 2019 and sawx.co.za