The amplitude of this sound wave is directly proportional to the gas concentration and can be detected using a sensitive microphone if the laser beam is modulated in the audio frequency range.In recent years, the development of new mid infrared laser sources has given a new impulse to infrared laser-based trace gas sensors. In particular, single mode quantum cascade lasers (QCLs) have become very attractive for mid-infrared gas sensing techniques thanks to single-frequency operation, narrow linewidth, high powers at mid-IR wavelengths (3 to 24 ��m), room temperature and continuous wave (CW) operation [12]. They overcom
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�� with respect to nadir for the Fore camera and -5�� 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 Dacomitinib 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).