Metop dual operations: benefits and products
The Metop satellites are Europe’s first operational weather satellites in polar orbit providing data for weather forecasting up to 10 days and for climate monitoring.
InsighT - February 2014
On 17 September 2012, Metop-B, the second of the series of three identical weather satellites, was launched, and joined its predecessor, Metop-A, in the same polar orbit. The following year, in April 2013, Metop-B took over as the primary operational satellite.
Although the ageing Metop-A has now exceeded its design lifetime of five years, it is being kept in orbit as a secondary satellite, for as long as it continues to bring benefits to users and does not need to be de-orbited to avoid generating debris in the precious low earth orbit. The two satellites are flying in the same mid-morning orbital plane, but are separated in time by half an orbit (48 minutes).
Dieter Klaes, EUMETSAT’s EPS Programme Scientist said, “While Metop-A continues to function, it means that the Metop system is more robust to orbit anomalies and failures. It also means that with two satellites in operation there are more data being collected, in particular for Numerical Weather Prediction, the basis of modern weather forecasting.”
"the benefits of dual Metop configuration are significant in both hemispheres"
Data products from instruments onboard the Metop satellites, such as temperature, humidity and wind, provide key information about the initial state of the atmosphere for NWP forecasts.
One of the key users of Metop data, the European Centre for Medium Range Weather Forecasts (ECMWF), recently assessed the impact of having data from single or dual Metop satellites on their NWP forecasting system and concluded that “the combined impact of both satellites is superior to using data from the instruments on Metop-A alone”.
Sean Healy, Senior Scientist in the Satellite Section at ECMWF and member of the Radio Occultation Meteorology SAF said, “The results are very encouraging and show that the benefits of dual Metop configuration are significant in both hemispheres.”
Global AVHHR winds from Metop
The dual Metop operation is also bringing other benefits. One example is in the observation of global winds, or Atmospheric Motion Vectors (AMVs), from the AVHRR (Advanced Very High Resolution Radiometer) instrument onboard the Metop satellites.
AMVs are produced from satellite images by tracking the movement of atmospheric features, mainly cloud patterns, through successive images to estimate wind speed and direction. AMVs are useful as input for numerical weather prediction, especially over ocean areas where other wind observations are sparse.
The AMVs collected by polar-orbiting satellites, such as Metop, are particularly important as they provide coverage of winds in the polar regions, which are not well observed by geostationary satellites.
"To extract wind information ... you need overlapping images "
“To extract wind information from AVHRR images you need overlapping images which are separated in time to track the movement of cloud patterns. With one AVHRR instrument on Metop-A, we had overlapping image regions for orbits only over the Polar Regions, but not for the rest of the globe,” said Klaes.
“With two Metop satellites in operation flying on the same polar orbit we have greater spatial coverage and overlap over the entire globe, which gives us truly global wind coverage and double the polar wind data.”
An additional benefit is that as Metop-B is only 48 minutes behind Metop-A on its orbit, this means that overlapping imagery for AMVs is available more quickly than having to wait for a single Metop satellite to complete a full orbit (102 minutes).
GOME-2 – more detailed data
Having two Metop satellites in orbit also creates an opportunity to collect more detailed data from the onboard GOME-2 (Global Ozone Monitoring Experiment) instrument.
Since 15 July 2013, GOME-2 on Metop-A has been operating in a “reduced swath” mode of 960 km resulting in a ground pixel size of 40 x 40 km, half that of the GOME-2 instrument on Metop-B which still operates in “normal” mode, with a swath width of 1920 km and a ground pixel size of 40 x 80 km resolution.
Rose Munro, EUMETSAT’s Atmospheric Composition Manager said, “This operational configuration has several benefits. The provision of data from two GOME-2 instruments ensures full daily coverage, without the gaps in equatorial regions which occur with only one instrument in operation.
At the same time the smaller ground pixels from GOME-2 on Metop-A, with more cloud-free scenes and improved resolution, are better adapted for monitoring atmospheric composition in the troposphere.”
Into the future
The third in the Metop series, Metop-C is scheduled for launch in 2018 and it will then take over from Metop-B to ensure continuous coverage from the polar orbit beyond 2020.