Better weather predictions with a new fleet of European satellites

Fore­cas­ters will be able to iden­ti­fy extreme wea­ther events more qui­ck­ly and effi­cient­ly, thanks to four new ima­ging satel­lites and two soun­der satel­lites, sche­du­led to be laun­ched bet­ween 2022 and 2030. These Third Gene­ra­tion Meteo­sats (or MTGs) will gra­dual­ly replace the second-gene­ra­tion satel­lites cur­rent­ly ope­ra­ting in space. The first of these will be laun­ched at the end of this year, to be ope­ra­tio­nal in 2023, fol­lo­wed by three simi­lar models and two soun­der satellites. 

With them, the images sent to Earth will be twice as accu­rate and reliable : they will be refre­shed eve­ry 10 minutes (com­pa­red with 15 minutes today), in other words, in near real-time. They will also have a new light­ning detec­tion ins­tru­ment (cal­led the Light­ning Ima­ger), never before seen in Europe, which will be able to observe light­ning much more accu­ra­te­ly than cur­rent sys­tems ; and ope­ra­ting from the ground so unable to detect light­ning bet­ween clouds and those about to hit the ground. 

They will also be able to detect severe thun­ders­torms and other extreme wea­ther events at an ear­ly stage. These types of events are like­ly to become more frequent in the future due to glo­bal war­ming. The new obser­va­tions will improve our know­ledge of these events and allow us to warn people when necessary.

The data from these satel­lites – one hun­dred times more than those obtai­ned by the second-gene­ra­tion satel­lites – will be used in new models by the Euro­pean Orga­ni­sa­tion for the Exploi­ta­tion of Meteo­ro­lo­gi­cal Satel­lites (EUMETSAT), the coor­di­na­tor of the Euro­pean wea­ther satel­lite net­work. In France, the Centre de météo­ro­lo­gie spa­tiale in Lan­nion, Brit­ta­ny, is res­pon­sible for pro­ces­sing the data. The advan­tage of this site is that it has good recep­tion, as it is not pol­lu­ted by other satel­lite recei­vers found in lar­ger cities, such as Tou­louse, which is the control centre of Météo-France.

The aim is to make the best pos­sible fore­casts so that we can prevent and secure people and property.

The Second Gene­ra­tion Meteo­sat (SGM) has an ima­ging radio­me­ter that ope­rates in the visible and infra­red parts of the elec­tro­ma­gne­tic spec­trum. This ima­ger observes the Earth in 12 dif­ferent chan­nels with a reso­lu­tion of 1 km for the High-Reso­lu­tion Visible chan­nel and 3 km for the other chan­nels. Com­pa­red to the MSG, we have even more chan­nels with the MTG and more scans, so bet­ter accu­ra­cy. This infor­ma­tion will be use­ful on a dai­ly basis, espe­cial­ly in high-risk phenomena.

After the launch, there will be a test phase fol­lo­wed by an ini­tial use phase where fore­cas­ters will learn to use the new ins­tru­ments. They should have increa­sin­gly rich image and detec­tion qua­li­ty in seve­ral chan­nels, rea­ching a very high reso­lu­tion of about 500 metres for the chan­nel ope­ra­ting in the visible spec­trum. The aim is to make the best pos­sible pre­dic­tions to be able to warn and secure people and property. 

The cur­rent Meteo­sat satel­lites pro­duce com­po­site and colour images, and the third gene­ra­tion will do the same. The goal for the second and third gene­ra­tions is to create mul­ti-spec­trum syn­the­tic images by ‘conden­sing’ obser­va­tions from dif­ferent satel­lite channels. 

There are seve­ral types of satel­lites : first­ly, ‘geo­sta­tio­na­ry’ satel­lites, which always observe the same place on Earth and are loca­ted at an alti­tude of more than 30,000 km. They rotate at the same speed as the Earth and allow us to car­ry out wea­ther ani­ma­tions. In contrast, the so-cal­led ‘non-sta­tio­na­ry’ satel­lites revolve around the Earth and do not see the same band of tra­jec­to­ry. These satel­lites are loca­ted at a much lower alti­tude, only 800 km, which makes it pos­sible to obtain much more pre­cise images, espe­cial­ly of low clouds or fog. 

By using the dif­ferent satel­lite chan­nels, we can make what is cal­led an ini­tial state of the atmos­phere. This will allow us to cor­re­late what we observe with what we fore­cast. To make a good fore­cast, we need to know what is hap­pe­ning now but also what hap­pe­ned a few days ago, for example, a lit­tle fur­ther out in the Atlan­tic. This will allow us to observe the evo­lu­tion of the cloud masses and to make a good repre­sen­ta­tion of them.

The goal is to create mul­ti-spec­trum syn­the­tic images by conden­sing obser­va­tions from dif­ferent satel­lite channels.

The resul­ting images are in black and white gra­da­tions, a kind of pho­to­gra­phic repre­sen­ta­tion of the cloud reflec­ti­vi­ty. The bright white colours represent clouds that are gene­ral­ly very thick, as they stron­gly reflect sun­light. Smal­ler clouds are greyer, even a lit­tle dar­ker, and are often low clouds that are laden with rain and the­re­fore have a low reflec­ti­vi­ty, as they absorb more light.

At night, howe­ver, we use the infra­red chan­nels, which take the tem­pe­ra­ture of the first layer of clouds encoun­te­red. The higher the cloud, the lower the tem­pe­ra­ture. And the lower the tem­pe­ra­ture, the ligh­ter the colour. This is why high clouds appear white in the infra­red. For a short-term fore­cast, an ani­ma­tion of seve­ral images should be consul­ted. Howe­ver, ana­lyses are more dif­fi­cult at cer­tain times of the year – autumn, for example, when we some­times find low clouds that have the same tem­pe­ra­ture as the ground, making them dif­fi­cult to distinguish. 

Interview by Isabelle Dumé

Refe­rences

https://​www​.eumet​sat​.int/​m​t​g​-​l​i​g​h​t​n​i​n​g​-​i​mager

https://​meteo​france​.com