The US/F A-TRAIN Concept

Observing and analyzing the Earth as an integrated system at various scales paved the way to dramatic advances in Global Change understanding, mitigation and adaptation, which in turn evidenced needs for innovative observation systems. Such an integrative concept is the guideline of the Earth System Science Partnership (ESSP). Space programmes developers understood for long that fulfilling such needs required a wide range of quite different simultaneous observations systems from space and ground. They implemented relevant cooperation. This widens the scope of ‘Remote Sensing’ to a contribution to a system approach of the Earth System at various scales, and not only to Earth surface observation, as often understood.
In terms of space systems, two quite different concepts can be developed. First, implementing different instruments on the same large satellite: this is the ESA/ENVISAT concept – by far the largest environment satellite ever built and operated. This is well known by the EARSeL community. The other solution is much poorly known. The basic concept is to implement several mini or micro-satellites close to one another on the same orbit, thus crossing the equator within a few minutes interval.

This has led to so-called “A-Train” French/US satellites formation, which includes 7 mini or micro-satellites: AQUA, AURA, CLOUDSAT, CALIPSO, PARASOL,OCO (which failed to be launched) and GLORY. It is quite interesting first to analyze each of these satellites as a single dedicated observatory, then to understand how their synergy within the A-Train concept allows better answering some basic Earth system questions, such as:

- better understanding and quantifying some Earth surface properties,
- better characterizing the aerosols types and how do observation match global emission and transport models,
- better understanding and quantifying the vertical distribution of cloud water/ice in cloud systems,
- better understanding the role of polar stratospheric clouds in ozone loss and their linkages with the Arctic vortex.
- In a more global way, better understanding the Earth system major cycles (especially the role of aerosols and cloud layering in radiation budget and forcing).

Answering such basic questions are critical paths to better characterize, understand and predict global Earth system changes and the related impacts at global and regional scales such as for instance Europe or the Mediterranean basin, as well as their coupling and teleconnections.
This shows the European capacity to develop international cooperation and bring relevant innovative observation systems to contribute to the objectives of the ESSP scientific community.

European Earth remote sensing research, science and technology has always been on the forefront, such giving Europe a great and respected scientific capacity, making it a reliable partner for scientific and high-tech cooperation, and giving European Union sound capacities to build up in-house and international policies about global change issues.

The A-Train capacities contribute to these worldwide efforts. They have to be developed, widely advertised and exploited at their full capacity.