Unmanned Aerial Systems (UAS) are slowing becoming e cient platforms that can be applied in scienti c/commercial remote sensing applications. UAS may o er interesting bene ts in terms of cost, exibility, endurance, etc. On the other side, the complexity of developing a full UAS-system is currently limiting its practical application. Currently, only large organizations like NASA or NOAA have enough budget and infrastructure to develop such applications. Nowadays, UAS technology o ers feasible technical solutions for airframes, ight control, communications, and a wide set of multi-spectrum sensors. However, the generalized development of remote sensing applications are still limited by the absence of systems that support the development of the actual UAS sensing mission. This paper introduces a exible and reusable hardware/software architecture designed to facilitate the development of UAS-based remote sensing applications. This exibility is organized into an user-parameterizable UAS Service Abstraction Layer (USAL). The USAL de nes a collection of standard services are their interrelations as a basic starting point for further development by users. Functionalities like enhanced ight-plans, a mission control engine, data storage, communications management, etc. are o ered. Additional services can be included according to requirements but all existing services and inter-service communication infrastructure can be exploited and tailored to speci c needs. The overall USAL architecture is demonstrated by means of a wild land re remote sensing application currently being developed to support re ghters in the Mediterranean area.