Patent FR-2865545-A1 (FR)
Title: Lidar (Light detecting and ranging) with an emission module producing a light beam at least part of which is then retrodiffused and a receiving module for the retrodiffused signal
Inventor: SANAK JOSEPH
IPC: G01S7/497
Filed: 2004-01-22
Abstract: The receiving module includes means of collection (21) of the astronomical telescope type with an objective (22) provided with at least one lens (22.1) and an optical system (24) containing at least one lens (24.1, 24.2) and placed downstream of the objective. The emission module (10) produces an optical beam (12) at least part of which is subjected to retrodiffusion. The retrodiffused signal (28) is collected by a receiving module (20). The receiving module has an optical axis (YY'), and the emitted light beam is directed along an axis (XX') which is parallel or the same as the receiving module's optical axis. The emission module includes means (13) of shaping the optical beam emitted using one or more lenses (13.1, 13.2) and/or several mirrors (13.3, 13.4). The means of shaping are means of expanding the beam and include an afocal device. The means of shaping act with means of displacement (14) to adjust the direction of the optical beam emitted. When the axis (XX') of the optical beam is the same as the axis of the receiving module, the lens (22.1) of the objective (22) of the astronomical telescope is used such that the lens converges the means of expanding the beam. The beam passes through a semi-reflective layer (16) which deflects the retrodiffused signal after it has passed through the objective of the astronomical telescope. Alternatively, a reflecting device (18) has a zone (18.1) through which the optical beam passes and non-reflective for the retrodiffused signal. The receiving module contains means (23) of detecting the retrodiffused signal containing one or more photomultipliers or photodiodes. The optical system also includes an optical filter system (26) with one or more filters (26.1). The optical system has two lenses in series, with the filter system between them. The filter system acts with means (29) of polarisation. And the filters after with emans of displacement (26.3). The optical system also includes means (27) of limiting the optical field using one or more diaphragms (27.1) acting with means of displacement (27.3). These means of limiting the optical field are placed in the focal plane of the objective of the astronomical telescope. The means of emission are a laser or laser diode emitting in the ultra-violet. The emission module and receiving module also contain at least one optical fibre each, with the receiving module having one optical fibre between the objective of the astronomical telescope and the optical system. Independent claims are made for a device for atmospheric tomography including a lidar as described above and means of angular displacement of the lidar to sweep the optical beam through the atmosphere, and for a device for detecting particles and/or molecules in the atmosphere using a lidar as described above with means of collecting and treating the retrodiffused signal. These means are designed to extract a ratio of mixture of water vapour in the atmosphere as a function of distance, or the density of air and thus deduce its temperature, or to extract structural properties of the layers diffusing over time, to give the altitude of the top of the planetary limit layer and/or the altitude of the clouds and/or the thickness of semi-transparent clouds, or the vertical profile of extinction of aerosols as a function of time.