Motoaki Yasui

2-um Coherent Lidar Technology Developed at NICT: Past, Current, and Future

We present a development and research of the 2-µm coherent lidar with a conductively-cooled laser-diode-pumped single-frequency Q-switched Tm,Ho:YLF pulse laser developed at the NICT.

New automated lidar system and multimedia virtual laboratory

We are developing a new remote-operational lidar system, with multimedia technology. This system reduces the necessity to go to the remote place. The system is located in Rikubetsu (43.3N, 143.5E), in north portion of Japan, which is a famous place for a fair weather all the year round. We use SHG of Nd:YAG laser and receive P, S components of Mie back scatter with photon counter. All necessary controling of instruments such as the roof of the housing, tilt mirror, laser, photon counters, oscilloscope, and so on, are done by personal computers. Operator uses a web browser from a remote site to operate the lidar system, with monitoring the weather and the total state of the system. There is another workstation which runs a newly developed desktop video conference system. With these system, several persons can simultaneously observe and watch the data, discuss with each other. We can now observe the aerosols more frequently than ever. This will let us to get precise information about the aerosols in north regions of Japan.

Atmospheric boundary layer observation by ground-based lidar at KMITL, Thailand 13 deg N, 100 deg E

Tropospheric aerosols effects on climate in directly through various cloud formation, the lidar has been used to study the composition of many particles mixing in the atmosphere including to study the aerosol and cloud. Currently, it has many types of lidar systems depending on the purpose of measurements. In this report, the ground-based lidar system was established at King Mongkuts Institute of Technology Ladkrabang (KMITL), THAILAND to study and measure the aerosol in boundary layer and cirrus clouds in the tropopause region. The aerosol measurement is in the form of scattering ratio whereas the signal depolarization has been applied to identify layers of cirrus clouds. The lidar system consists of laser source (Nd:YAG) with second harmonic wavelength, 28 cm Schmidt-Cassegrain telescope, photomultiplier tube (PMT) and data acquisition system.

Seasonal variation of aerosol over Bandung, Indonesia

Variation of stratospheric aerosol affects atmospheric minor constituents and climate through changes in the radiation field as well as by dynamic and chemical processes. In order to estimate the impact quantitatively, it is very important to observe stratospheric aerosol vertical distribution and their lime variation To obtain stratospheric aerosol especially in equatorial region a lidar was installed in Bandung (6.9° S; 107.7° E) Indonesia under collaboration between National Institute of Aeronautic and Space (LAPAN), Communication Research Laboratory of Japan and Meteorological Research Institute of Japan. The Lidar transmitter system employ fundamental (1064 nm), second harmonic (532 nm) and third harmonic (355 am) wavelengths ofNd: YAG laser are transmitted. The second harmonic backscatter light and its N2 ranian backscatter light (607 am) are collected by a 28 cm and a 35 cm diameter telescope. In 35 cm telescope system, upper troposphere and stratosphere are observed by photon counting. 532 am light component polarized parallel and perpendicular to the laser light are separately observed to get information about shape of aerosol. Bandung is located at around 750 m above mean sea level and it is surrounded by mountains, therefore clouds are easily formed especially between 10 and 17 km height. Stratospheric aerosol over Bandung are spreaded between 18 and 35 km in altitude and form more than 1 sub layer, below 30 km and upper 30 km. The maximum aerosol concentration is obtained around 22.5 km height. To understand the seasonal variation of stratospheric aerosol we integrated the backscattering coefficients for altitude range 18-35 km and it was obtained that the stratospheric aerosol concentration in 1997 was higher than in 1999. The integrated backscattering coefficient in June was higher than in August. But seems the seasonal variation of integrated backscattering coefficient in Bandung does not so clear determined yet.

Dustfall and lidar observation in China's desert

The observation of atmosphere dust in Chinas desert show that there is a continuous dust layer always existed in lower atmosphere under the height of 5 km. The dust concentration in the layer is changed with altitude and season. According to the Lidar data analysis the backscattering ratio value changes in the range of 2.5-5.5 in clear weather. The higher value ofthe ratio can be extended to the height about the height of3.5 km. The dust concentration is reduced sharply over 3.5 km. In the range of 15-20 km height, an aerosol layer is often observed in Shapotou region. The maximum backscattering ratio usually appears in 1 5- 1 8 km. The value is approximately 1.2.

Lidar and Optical Particle Counter (OPC) measurements of polar and tropical stratospheric aerosols

Lidar and Optical Particle Counter (OPC) measurements were performed in the Canadian Arctic and in the Indonesian Tropical region. The observations yielded very interesting and important results about the features of the latitudinal difference in the stratospheric aerosols. Besides the latitudinal difference, the aerosol distributions and their time variation showed unique characteristics in each of the regions. In Arctic winter, the aerosol concentration varies frequently day-to-day. In the Tropical region, the aerosol distribution and the vertical transport is, probably, controlled by the variation of the circulation pattern in the lower stratosphere related to the QBO in the tropical stratosphere. Based on the results of the simultaneous measurements by lidar and OPCs, we estimated surface area density, volume density, S-parameter (extinction to backscatter ratio), backscatter to surface area conversion factor, and backscatter to volume conversion factor of the stratospheric aerosols at 20km-altitude in the Arctic and Tropical regions.

Rayleigh lidar and Rayleigh Doppler lidar for measurement of the Arctic atmosphere

Height profiles of temperatures and winds of the middle atmosphere between 30km to 60km are observable only by Rayleigh lidar and Rayleigh Doppler lidar except for rocket sounding which is expensive and not suitable for continuous measurements. We developed a Rayleigh lidar system and it is now working well for temperature observations of the Arctic middle atmosphere at Poker Flat Research Range near Fairbanks, Alaska (65.1N, 147.5W). A comparison of lidar data and balloon sonde data showed good agreement in overlapped altitudes. A Rayleigh Doppler lidar for wind measurements of the middle atmosphere is under the phase of development. The expected accuracy in measurements of horizontal winds up to an altitude of 60km is smaller than 6m/s in 2hours observation. The system will be also operated at Poker Flat. The combination of these lidars and radars installed at Poker Flat give us chances of simultaneous observations of the structure and dynamics of the atmosphere in broad range of altitudes. Here, we give descriptions of the Rayleigh lidar and the Rayleigh Doppler lidar for the observations of the Arctic middle atmosphere at Poker Flat.

Comparison of lidar measurement with balloonborne OPC measurement over Bandung, Indonesia

For the study of stratospheric aerosol over the Tropics, balloon-borne OPC measurements have been made six times from April 1997 to March 2000 at Bandung, Indonesia (6.9 deg S, 107.6 deg E)where Lidar measurements have also been made since early 1997. Correlative measurements of Lidar and OPC were conducted on March 25, 1998 and August 23, 1999. Results of the latter measurement were compared in this paper. The profile of back scattering ratio measured by Lidar almost represents a vertical distribution of small particles having radii smaller than 0.4 μm. We calculated back scattering coefficients from the results of OPC measurement. The calculated and measured back scattering coefficients were not consistent completely but not so unreasonable.

Lidar observations of the stratospheric aerosols at Bandung, Indonesia

We installed a lidar system for observations of the stratospheric aerosols at Bandung, Indonesia on November 1996. The system employed the second harmonic wavelength (532 nm) of Nd:YAG laser. We can measure scattering ratio and depolarization of 532 nm, and Raman scattering of N2 (607 nm). The system works well and the stratospheric aerosols were detected between 18 km and about 35 km. Cirrus clouds are always observed between 10 km and tropopause and area around tropopause is clear except for cloud-like structures. Integrated backscattering coefficient (IBC) of the stratospheric aerosols in 1997 is about 6 X 10-5sr-1 level and smaller than the value observed in mid-latitude, corresponding to the higher tropopause in the equatorial region. Variation of IBC at Bandung seems to be small. It is yet not clear whether current aerosol load is background level or not. We need more long period observations to discuss about seasonal, QBO, and long term variation of aerosol load.