## 1 Introduction  
On 5 May 2005, the Indian Space Research Organization (ISRO) launched Cartosat-1, the eleventh satellite of its IRS constellation, dedicated to the stereo viewing of the Earth's surface [1,2]. Cartosat-1 carries two high-resolution imaging cameras: the afterward looking camera (Aft) and the foreword looking camera (Fore), both able to collect panchromatic images with a spatial resolution of 2.5 m on the ground. The imaging cameras are fixed to the spacecraft to acquire near-simultaneous imaging of the same scene (with a delay of 52 s between the Fore and the Aft acquisitions) from two different angles: +26\({}^{\circ}\) with respect to nadir for the Fore camera and -5\({}^{\circ}\) with respect to nadir for the Aft camera. This configuration is optimized for along-the-track stereo data collection in a 30 km swath and with a base-to-height ratio of 0.62. However, Cartosat-1 is also able to collect 2.5 m mono images with a combined swath of 55 km [3]. The satellite was mainly designed for terrain modeling and large-scale mapping [3,10-16]. Nevertheless, in previous studies Cartosat-1 data have been also used in different fields, such as natural hazards assessment [4,5], archaeological exploration [6], estimation of hydrological parameters [7,8] or estimation of atmospheric aerosols [9].  
In early 2006, ISRO started the Cartosat-1 Scientific Assessment Programme (C-SAP) jointly established with the International Society for Photogrammetry and Remote Sensing (ISPRS). The aim of the C-SAP was to assess the mapping capabilities of the Cartosat-1 satellite for different types of terrain and for different applications, such as photogrammetric stereo triangulation at scene and block level, extraction of terrain features, terrain modeling and topographic mapping. For this purpose, ISRO and ISPRS selected thirty research groups from different countries as C-SAP Investigators (seventeen from Europe, seven from Asia, five from USA and Canada and one from South America) and provided them with Cartosat-1 stereoscopic data collected over eleven test sites (seven in Europe, one in Asia, one in USA and one in Australia), along with metadata, ground control points (GCPs) and reference digital surface models (DSMs).  
Within the C-SAP framework, Politecnico di Milano University (Italy), being one of the European Investigators, evaluated the capabilities of terrain modeling for the French test sites of Mausanne les Alpilles and Salon de Provence. The investigation focused on the generation of multi-resolution DSMs and was addressed to typical remote sensing users (also for non specialists in photogrammetry). Since the study would like to be able to provide some operative hints about the potentialities and limits in the generation of DSMs from Cartosat-1 data for landscapes similar to the C-SAP French test sites, all the data processing was done using standard commercial off-the-shelf software (RSI ENVI\({}^{\text{\textregistered}}\)) rather than homemade or scientific software.  
Results were compared with reference data expressly acquired for C-SAP [15,17] and also with existing standards and products actually used in France (i.e., the French Institut Geographique National's and Spot Image's Reference 3D\({}^{\text{\textregistered}}\), the French DB Alti\({}^{\text{\textregistered}}\) and the French DB ORTHO\({}^{\text{\textregistered}}\)). Finally, the investigation also provided a comparison between the Cartosat-1 DSMs and the global Shuttle Radar Topography Mission (SRTM) DSMs, widely used in the remote sensing community as topographic layer [18].