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://​met​eo​france​.com