Density and Temperature Profile in the Lower
Atmosphere at Kmitl, Thailand
Sokkiat Lerkvaranyu, Kobachai Dejhan,
Fusak Cheevasuvit
Faculty of Engineering and Research Center for Communication and Information Technique,
King Mongkut's Institute of Technology Ladkrabang, Ladkrabang,
Bangkok 10520, Thailand
Tel-: 66-2-3269967, 66-2-3269081, Fax : 66-2-3269086.
E-mail: kobchai@telelan.telecom.eng.kmitl.ac.th
Toshikasu Itabe, Kohei Mizutani
Toshikasu Itabe, Kohei Mizutani
Communication Research Laboratory
Nukui-Kitamachi 4-2-1, Koganei, Tokyo 184, Japan
Tel : 81-423-27-7546, Fax : 81-782-7094
Abstract
Continuously, the developed of lidar system at The King Mongkut's Institute of Technology Ladkrabang (KMITL) is ex tended. The ability of laser radar to measure the density and temperature profiles by the method or Rayleigh scattering also called Rayleigh lidar. An 180 mJ Nd: YAG laser at 532 mm wavelength and 28 cm diameter of Schmidt-Cassegrain telescope the density and temperature profiles in the lower atmosphere are installed. The density profile can be indirectly obtained from lidar equation, the temperature profile will be obtained from hydrostatic equation. Finally, the results of density and temperature profiles seldom relate to phenomenon profile that obtained from radiosonde. The paper proposes to measure the density and temperature profile in the lower atmosphere at KMITL, these data will be used for the other purposes.
Introduction
To study the behavior of atmosphere, he various lasers were applied after the laser was invented. The atmospheric is very complicated system so the used of laser to study it has many type such as the measurement of ozone, vapor water, cloud, fox and etc., including the aerosol measurement in boundary layer. Those laser system can be called the atmospheric laser radar or synonym the lidar system and has the various techniques of signal processing depend on the purpose of measurements to attract the specific information that come from with the return signal. For the measurement of the number density or the number of a mixture of gases, the used technique is Rayleigh lidar in which he signal can be obtained mainly from the elastic backscattering of the laser energy by any particles in the atmosphere. Moreover, in the Rayleigh technique, it may be use multiwavelength simultaneous for the comparison the different characteristic that effect from the mixing particle. It should avoid the comparison the different characteristic that effect from the mixing particle. It should avoid the absorption band because this technique only use the backscattering. For a single wavelength the Rayleigh technique can also be used but the accuracy will be decrease for more detail see in reference[3]. Considering the Rayleigh technique for measuring the number density, the number relationship of various gases in atmosphere will be different.
If the considered altitude is troposphere or boundary layer, the mixture of gases is homogeneous and a little different. The number of whole gases in the atmosphere closed to a model with respect to the altitude. Nevertheless, it has many atmospheric model and one well-known is the U.S. standard atmospheric model. To assume the mixture of various gases in lower atmosphere is homogeneous so that the average weight and mean molecule number can be obtained. The return signal occurs from scattered the particle in any altitude can be calculated from cross section value of the average number density. It means that the number density can be derived from observation data. It has several methods that convert the return signal to number density, for more detail as in reference [2,3]. Importance, the number density that obtain from return signal is not only the mixture of various gases but also include the aerosol and any particle in the atmosphere. In the volume is constant, the ideal gas law has the relationship with pressure, temperature and molecular number and the hydrostatic equation shows the relationship between pressure and temperature in the equilibrium assumption. It is possible to determine the temperature profile. However, it should care the limitation of this method because the error occurs from the scattered signal from other particles, especially in the boundary layer which ha many aerosol, thin cloud and so on, it can increase the return signal.
