ЛЕК Устр и действ / Устройство и действие Л-15

All the main MLC’s channels provide equal sounding distance – 15 km.

In the short wave – visible and near - infrared range the considerable atmosphere backward scattering coefficient allows receiving lidar signals at distances of about 15 kilometers with standard direct detection methods.

In regard to the far-infrared range the only solution providing atmospheric sounding at such a distance is a heterodyne lidar with a large receiving aperture. Such integrated solution is implemented in the optical scheme of the MLC.

MLC structure

Equipment of each of the multi-wave lidar complexes is mounted in a special container of regular shipping dimensions.

The container in working position is leveled with the automated hydraulic supports, providing optical axes constant position during the whole measurement session. All the MLC’s power and information communication is completely independent, that is why the complex can be installed both stationary and on any other suitable type of carrier

Interior space & operator’s workplaces

 The container’s interior space is divided into the laser optical section, operator section and power section.

 Laser sources, relay optics, sensors and special electronic equipment are located in the laser optical section.

 The operator section incorporates working places for two operators, computers, and communication racks.

 The power section includes equipment for lasers’ power supply, cooling, gas supply and the complex’s climate control, which provides operators and equipment with comfortable work conditions within the ambient temperature range of -40 to +50 С.

Multi-wave Receiving/Transmitting Telescope

and Scanner

The telescope includes an aspheric 500 mm main reflector (aperture ratio 1:2). Magnification is M=7. The parabolic secondary reflector is equipped with a highprecision driving unit allowing focusing of the telescope within the range of 500 m to infinity. The telescope is utilized in the longwave range both to transmit and receive radiation. Aperture area is divided to transmitting and receiving zones. Shortwave channels, which operate according to the direct detection method, utilize the entire telescope aperture area to receive backscattered radiation, while the sounding radiation is transmitted through independent input mirrors.

The telescope is installed rigidly on a common optical plate as well as all the lasers, relay mirrors and receivers.

Space scanning is performed by single-mirror or two-mirror scanner. All large-scale mirrors have been made from sitall/zerodur (light-weight design is used) and equipped with multi-layer metal-dielectric coating operating from 266 nm to 11 mkm. Reflectance is not less than 0.95 from 355 nm to 11 mkm and about 0.87 for 266 nm.

The single-mirror scanner automatically disposes inside the MLC container for

transportation and between sounding sessions. Scanning range is from -7 to +20 (elevation),180 (azimuth). Kinematics of the two-mirror scanner allows scanning of the whole upper hemisphere.

Scanning drives are designed on the basis of torque direct-drive motors. Video-observation performs simultaneously with the lidar sounding in visible range as well as in far-infrared range (8- 14 mkm).

Space scanning is performed by single-mirror or two-mirror scanner. All large-scale mirrors have been made from sitall/zerodur (lightweight design is used) and equipped with multi-layer metal-dielectric coating operating from 266 nm to 11 mkm. Reflectance is not less than 0.95 from 355 nm to 11 mkm and about 0.87 for 266 nm.

The single-mirror scanner automatically disposes inside the MLC container for transportation and

between sounding sessions. Scanning range is from -7 to +20 (elevation), 180 (azimuth). Kinematics of the two-mirror scanner allows scanning of the whole upper hemisphere.

Scanning drives are designed on the basis of torque direct-drive motors. Video-observation performs simultaneously with the lidar sounding in visible range as well as in far-infrared range (8-14 mkm).

The MLC integrated optical layout includes the following subsystems:

Aerosol lidar of visible and near-infrared range developed upon the basis of the Nd:YAG laser. The laser operates at any of the four harmonics (266 nm – 1064 nm) with the pulse repetition rate 10 to 25 Hz;

Differential absorption short-wave lidar (SW-DIAL)

developed on the basis of a two-channel tunable TiSph laser: 700 960 nm, 350 480 nm, 230 310 nm;

Differential absorption long-wave heterodyne lidar (LW-DIAL) developed on the basis of single-frequency

tunable two-channel СО2 laser system and a broadband matrix MCT sensor;

Coherent Doppler wind СО2 lidar;

Turbulent lidar operating on the wavelength of 532 nm and allowing measuring the altitude profile of the atmospheric refraction index structural constant;

Fluorescent lidar operating on the excitation

wavelength of 266 nm and measuring a fluorescence spectrum within the range of 300 500 m;

Polarization lidar where the Nd:YAG-laser’s second harmonics is utilized as the sounding radiation.

Heterodyne receiving-transmitting system

Each channel includes a pulsed ТЕА-СО2 laser and two continuous singlefrequency waveguide СО2 lasers – an injector and a local oscillator (heterodyne). Each of the lasers encloses rotating diffraction grating serving as a back mirror; the grating’s angular position determines a VR-spectrum operational line; and a piezoelectric drive controlling resonator’s length.

Pulse-repetition rate in each channel is 10 Hz; time delay between the channels is 10 ms. A heterodyne two-channel tunable lidar system of this kind has been implemented on a mobile carrier for the first time. An optical layout of the heterodyne receiving-transmitting system is presented in Fig.5. Continuous injector radiation (waveguide laser8) has a line width about 1MHz. The spectrum checking is provided by a broad-band cooled MCT sensor (5). The injector (2) and local oscillator (1) are mounted in a common box. The portion of the injector radiation is directed to the TEA laser resonator (3). Radiation reflected back by the resonator is directed to the low-frequency sensor (5) for the operation of the AFC system. Remaining injector radiation is mixed with the heterodyne radiation and is directed to the broad-band cooled MCT sensor, which is used in order to provide 20 MHz injector-heterodyne frequency shift. Heterodyne’s beam, expanded by the Galilean telescope (9), is mixed with the scattered radiation and is directed to the matrix MCT sensor (7). A portion of the TEA laser’s pulse gets to the strobe sensor (8) for synchronization. The optical chopper (6) is meant for the entire system synchronization and sensors protection.