Meet Meteosat
There are many types of tools available for use in remote sensing. Sensors are mounted to satellites or drones and perform scans at regular intervals depending on the rotation schedule of the module to which they are attached. Geostationary satellites are fixed to a point on the earth above the equator at an altitude that allows them to seem as though they hover above that point while in orbit. Meteosat Second Generation (MSG) is the current geostationary satellite spacecraft orbiting 36,000 km above Europe and Africa. It is owned and operated by Europe’s Meteorological Satellite Organization (EUMETSAT) and sends an image to Earth every 5–15 hours.
One of the radiometers on the MSG is the Spinning Enhanced Visible and Infrared Imager (SEVIRI). This is a spectral radiometer which provides infrared and high resolution visible (HVR)images of the Earth at a ground resolution of 1km in 12 spectral channels. SEVIRI spins with the satellite at 100rpm and and builds full disk views through a series of swaths to transmit back to Earth every 15 minutes. These images provide accurate meteorological data by measuring cloud, land and ocean temperatures in near-real time, providing predictive power of oncoming storm events.
The Geostationary Earth Radiation Budget (GERB) is a visible infrared radiometer which measures thermal radiation from the upper atmosphere for Earth Radiation Budget studies. The radiation budget is the balance between incoming energy from the sun and outgoing thermal (long-wave) and reflected (short-wave) energy from the Earth which is important for climate monitoring studies. Together these two sensors cover an electromagnetic spectrum from 4.0 to 30 µm, well beyond the visible spectrum.
The Normalized Difference Vegetation Index (NDVI) is an indicator of photosynthetic activity in vegetation on the ground. The equation to determine the NDVI is a calculation of the R(VIS), which is the reflectance of the 0.6 µm channel and the R(NIR), which is the reflectance in the 0.8 µm channel. Reflectance is the measurement of the electromagnetic waves effectively bouncing off solid objects back into the radiometer. This calculation is adjusted to account for changing zenith angles (sensor’s angle between the sun and the ground point) and aggregated over a number of days to account for cloud cover, which skews or blocks the reflectance. The adjusted calculation is as follows:
Results from NDVI calculations are represented from 0, deserts to 5, dense vegetation. The results look something like this when mapped out:
This map clearly shows the densely vegetated jungle areas in greens and deep blues and the less vegetated or drought afflicted areas in yellows and oranges. This imagery is important for drought management as it indicates active vs inactive photosynthesis or plant growth. Stressors, such as drought and climate change, affect plant health and that is in turn measured with the radiometer.
The main strength of the MSG is its sensing frequency. A study evaluating the results of the first NDVI from the SEVRI sensor on the MSG determined that the capacity to produce a composite cloud free image at the continent scale is about 5 days, with 82 potential cloud free days of the growing season for NDVI observation, as compared to 47 from available polar-orbiting satellites.
Meteosat images can be disseminated via internet access, as on the EUMETSAT and NOAA websites, which update as they come in as both visible spectrum and infrared images. The NDVI can be processed through a geoprocessing software such as ArcGIS and transformed into the above map.
These maps are the essential climate change and drought mitigation communication link between the satellites and the farmers and pastoralists on the ground.. a discussion for another day.
