The international community agrees that the new technology based on the use of Unmanned Air Vehicles High Altitude Very long Endurance (UAV-HAVE) could play an important role for the development of remote sensing and telecommunication applications. A UAV-HAVE vehicle can be described as a low- cost flying infrastructure (compared with satellites) optimized for long endurance operations at an altitude of about 20 km. Due to such features, its role is similar to satellites, with the major advantages of being less expensive, more flexible, movable on demand, and suitable for a larger class of applications. According to this background, Politecnico di Torino is involved as coordinator in an important project named HeliNet, that represent one of the main activities in Europe in the field of stratospheric platforms, and is concerned with the development of a network of UAV-HAVE aircraft. A key point of this project is the feasibility study for the provision of several services, namely traffic monitoring, environmental surveillance, broadband communications and navigation. This paper reports preliminary results on the HeliNet imaging system and its remote sensing applications. In fact, many environmental surveillance services (e.g. regional public services for agriculture, hydrology, fire protection, and more) require very high-resolution imaging, and can be offered at a lower cost if operated by a shared platform. The philosophy behind the HeliNet project seems to be particularly suitable to manage such missions. In particular, we present a system- level study of possible imaging payloads to be mounted on- board of a stratospheric platform to collect Earth observation data. Firstly, we address optical payloads such as multispectral and/or hyperspectral ones, which are a very short-term objective of the project. Secondly, as an example of mid-term on-board payload, we examine the possibility to carry on the platform a light-SAR system. For both types of payload, we show how intelligent processing algorithms for environmental data can be run on-board in real-time, in order to make data analysis and transmission more effective, and designed to match the constrains imposed by a UAV-HAVE platform. The results of the study lead to the conclusion that the stratospheric technology seems to be a competitive infrastructure (with respect to the satellites) in the remote sensing scenarios described above.