Meteosat RGB-Dust product for the Middle East
There are many complementary ways of monitoring dust. Satellite products have the advantages of large spatial coverage (regional to global) and regular observations, which can be made available to weather centres and other institutions in Near-Real-Time (NRT). Shortcomings include the highly integrated nature of satellite measurements, not only over the atmospheric column but also over all aerosol components, and the low aerosol detectability over bright surfaces, which affects instruments operating in the visible part of the spectrum. The high-resolution infrared spectrometers and interferometers on polar-orbiting satellite platforms have the potential to provide good quality dust information, but they present it at insufficient time resolution. The latest generation of satellites provide a vital tool for real-time dust monitoring: they combine the specific advantages of geosynchronous orbits (high time resolution over a wide geographic domain) with the geometric, radiometric and spectroscopic capabilities of high resolution radiometers.
Multispectral products are generated from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument on the geostationary Meteosat Second Generation (MSG) satellite and operationally implemented to address a number of forecast challenges for both daytime and nighttime applications. Referred to as “RGB Imagery” or “RGB Products,” brightness temperatures or paired band differences are used to set the red, green, and blue intensities of each pixel in the final image, resulting in a false-color composite (EUMETSAT, 2009). In particular, the EUMETSAT MSG dust product is based upon infrared channels of SEVIRI. It is designed to monitor the evolution of dust storms over deserts during both day and night. The RGB combination exploits the difference in emissivity of dust and desert surfaces. In addition, during daytime, it exploits the temperature difference between the hot desert surface and the cooler dust cloud. The RGB composite is produced using the following MSG IR channels: IR12.0-IR10.8 (on red), IR10.8-IR8.7 (on green); and IR10.8 (on blue). Dust appears pink or magenta in this RGB combination. Dry land looks from pale blue (daytime) to pale green (nighttime). Thick, high-level clouds have red-brown tones and thin high-level clouds appear very dark (nearly black). Emissions and subsequent transport of individual dust events can be very well observed and followed in the RGB composite pictures. The full disc view includes the whole of Europe, all of Africa and Middle East and allows frequent sampling, every 15 minutes, with a spatial resolution of 3 km in the nadir, enabling monitoring of rapidly evolving events. This aids the weather forecaster in the swift recognition and prediction of hazardous dust events.
In 2016, EUMETSAT relocated Meteosat-8, the first unit of MSG satellites, to 41.5°E, for the continuation of the Indian Ocean data coverage. It allows generation of the RGB-Dust product for West Asia, a region where the coverage was deficient through the MSG satellites centered on 0º.