This paper will introduce and describe the goals, concept and overall approach of the European 7th Framework Programme's project named CLOSE-SEARCH, which stands for 'Accurate and safe EGNOS-SoL Navigation for UAV-based low-cost SAR operations'. The goal of CLOSE-SEARCH is to integrate in a small Unmanned Aerial Vehicle (UAV) (helicopter type, for reasons of maneuverability), a thermal imaging sensor and a multi-sensor navigation system (based on the use of a Barometric Altimeter (BA), a Magnetometer (MAGN), a Redundant Inertial Navigation System (RINS) and an SBAS-enabled GNSS receiver), to support the search component of Search-And-Rescue (SAR) operations in remote, difficult-to-access areas and/or in time critical situations. In addition, it is also the goal of CLOSE-SEARCH to demonstrate the added value of a future multi-constellation augmented GNSS configuration (Galileo/GPS-EGNOS) providing Safety-of-Life (SoL) service. Among others, one key target attribute of the proposed concept is the ultra-safe navigation concept as necessary (but not sufficient). This concept is twofold: firstly, it embodies the condition of integrating a manifold of navigation sensors in a way that the precision, accuracy and reliability can be estimated and compliant to some [rather demanding] criteria. To this regard, the mechanism to measure and manage the achieved reliability by the proposed multi-sensor approach is the so-called Autonomous Integrity Monitoring (AIM). As a first step in CLOSE-SEARCH, a revision of the actual integrity requirements for SoL navigation is needed, usually holding for manned, large, high flying-altitude, Conventional Take-Off and Landing (CTOL) aircrafts while our application deals with unmanned, small, low flying-altitude, Vertical Take-Off and Landing (VTOL) platform types. In addition, enhanced safety margins (protection levels and alert limits) can be defined tackling not just the position domain but the attitude domain, which we believe is of major importance in remote sensing missions (SAR operations, in particular) and for VTOL platforms. Finally, the second step on the proposed AIM approach is the implementation into multi-sensor navigation of the geodetic reliability concept. Outlined by Baarda in the late 60's and further developed by Foerstner in the 80's, it is based on quality measures which take the geometry of the design and the used estimation and testing procedure into account, and yields a quality description of the navigation solution. We believe that integrity definitions and procedures are strongly related with the proposed reliability concept and its estimation proceduresm, and thus a convergent approach is defined. This paper will identify the technical challenges of the proposed approach, from navigating with a BA/MAGN/RINS/GPS-EGNOS-based integrated system to the interpretation of thermal images for person identification, focusing on the description of the AIM approach together with the proposed integrity requirements. Along the paper, some early results obtained during the first test campaign will be presented and, finally, a list of acronyms is presented at the end of this paper in order to ease its readibility.
