Takuya D. Kawahara

Studies of the MLT region using the MU radar and simultaneous observations with OH spectrometer and other optical instruments

Abstract The MU radar (middle and upper atmosphere radar) has been used since 1984 to study the dynamics of the mesosphere and lower thermosphere (MLT) as well as the dynamics of the lower atmosphere and the ionosphere. Gravity waves in the mesosphere have been studied extensively over various time and vertical scales during the daylight hours using backscatter from turbulent irregularities. Scatter from meteor trails can be used during day or night to study the dynamics of the MLT, and techniques to apply the MU radar for meteor scatter observations have been developed and recently improved. The meteor observation mode of the MU radar can detect about 15,000–20,000 echoes/day and 10,000 echoes/day are from underdense trails with arrival angle determination. This high meteor echo rate enables us to determine the wind velocities and molecular diffusion coefficient with the time/height resolutions of 30 min × 1 km at 80–100 km for 24 hours a day. From the horizontal distribution of the meteor echoes, horizontal gradients of the wind fields can also be detected, as well as vertical shears of horizontal winds. These high resolution meteor echo observations were made simultaneously with OH spectrometer observations. These combined observations yielded information on both the horizontal and vertical structure of the gravity waves. Comparisons were made between the temperature variations determined by OH airglow and determined by the diffusion coefficient of the meteor echoes and excellent agreement was found. Cooperative observations with sodium lidars, FPI, airglow imagers, and an MF radar are also being carried out.

Development and performance characteristics of laser-induced fluorescence imaging lidar for forestry applications.

A laser-induced fluorescence (LIF) imaging lidar was developed to monitor and measure the chemical activities and status of trees and forests. A unique feature of the lidar system was the usage and combination of a nano-second pulse laser and a gated image intensified CCD camera as an imaging detector. The system performance was checked using a ginkgo tree located at a distance of 60 m from the system. By operating the high sensitivity image intensifier with a short time duration of 100 ns, the LIF images of the tree were successfully obtained not only at night but also during the day. The ratio of the LIF image at 740 nm to that at 685 nm could be effective to estimate the chlorophyll concentration inside the leaves. It was shown that the system has the potential for macroscale monitoring of trees remotely and nondestructively.

Range-resolved bistatic imaging lidar for the measurement of the lower atmosphere

A bistatic imaging lidar system using a cooled CCD camera as a detector has been developed for the observation of aerosols, fog, and clouds in the lower atmosphere, especially within several hundred meters of the Earths surface. Theoretical discussion showed that the received signal does not depend on the measured range. The potential of the bistatic imaging lidar was confirmed through results of nighttime observations of atmospheric phenomena up to 300 m. A range-resolved profile was obtained without scanning and with a very short time resolution, within 1 min.

Continuous-wave sodium D2 resonance radiation generated in single-pass sum-frequency generation with periodically poled lithium niobate.

With two cw single-mode Nd:YAG lasers at 1064 and 1319 nm and a periodically poled lithium niobate crystal, 11 mW of 2 kHz/100 ms bandwidth single-mode tunable 589 nm cw radiation has been detected using single-pass sum-frequency generation. The demonstrated conversion efficiency is approximately 3.2%[W(-1) cm(-1)]. This compact solid-state light source has been used in a solid-state-dye laser hybrid sodium fluorescence lidar transmitter to measure temperatures and winds in the upper atmosphere (80-105 km); it is being implemented into the transmitter of a mobile all-solid-state sodium temperature and wind lidar under construction.

Ultraviolet imaging spectrometer (UVS) experiment on board the NOZOMI spacecraft : Instrumentation and initial results

An ultraviolet imaging spectrometer (UVS) on board the PLANET-B (NOZOMI) spacecraft has been developed. The UVS instrument consists of a grating spectrometer (UVS-G), an absorption cell photometer (UVS-P) and an electronics unit (UVS-E). The UVS-G features a flat-field type spectrometer measuring emissions in the FUV and MUV range between 110 nm and 310 nm with a spectral resolution of 2–3 nm. The UVS-P is a photometer separately detecting hydrogen (H) and deuterium (D) Lyman α emissions by the absorption cell technique. They take images using the spin and orbital motion of the spacecraft. The major scientific objectives of the UVS experiment at Mars and the characteristics of the UVS are described. The MUV spectra of geocoronal and interplanetary Lyman α emissions and lunar images taken at wavelength of hydrogen Lyman α and the background at 170 nm are presented as representative examples of the UVS observations during the Earth orbiting phase and the Mars transfer phase.

Observations of mesospheric sporadic sodium layers with the MU radar and sodium lidars

The dynamical structure of the atmosphere around the sporadic sodium layer at mid-latitude (∼35°N) below 100 km was studied by simultaneous observation with the MU radar at Shigaraki (34.9°N, 136.1°E), and two Na lidars at Shigaraki and in Hachioji (35.6°N, 139.4°E). In the lidar data, fifteen Nas (sporadic sodium layer) events were detected. Wind shear, temperature, and stability indices, at around the time and height of Nas were observed with the MU radar. Strong total wind shear correlated well with Nas, especially when sporadic Es did not accompany. However, no other clear correlations, such as correlations with temperature etc., were found. The result is similar to the report of the lidar observations in Hawaii during the ALOHA-93 campaign (Qian et al., 1998), and suggests a similar generation mechanism between 20°N and 35°N.

A thermospheric Na layer event observed up to 140 km over Syowa Station (69.0°S, 39.6°E) in Antarctica

We report a thermospheric Na layer event (up to 140 km) observed by lidar in the night of 23–24 September 2000 at Syowa (69.0°S, 39.6°E), Antarctica. The thermospheric Na number densities were 2–9 cm−3 at 110–140 km, 3 orders of magnitude smaller than the peak density of the normal layer at 80–110 km. The thermospheric Na layers exhibited a wave-like structure with a period of 1–2 h. The colocated ionospheric/auroral observations showed sporadic E layers over Syowa through the night and an enhancement of the ionospheric/auroral activity around south side of Syowa at the event beginning. Adopting the theory by Chu et al. (2011), we hypothesize that the thermospheric Na layers are neutralized from converged Na+ layers. An envelope calculation shows good consistency with the observations.

Sodium temperature lidar based on injection seeded Nd:YAG pulse lasers using a sum-frequency generation technique

We report on a sodium (Na) temperature lidar based on two injection seeded Nd:YAG pulse lasers using single-pass sum-frequency generation. The laser power at 589 nm is 400 mW (40 mJ per pulse at a repetition rate of 10 Hz) and the pulse width is 22 nsec FWHM. The narrowband laser tuned to the Doppler broadened Na D2 spectrum enables us to measure the temperature of the mesopause region (80-115 km). This solid-state transportable system demonstrated high performance and capability at Syowa Station in Antarctica for 3 years and at Uji in Japan for an additional year without any major operational troubles.

Range-resolved Image Detection of Laser-induced Fluorescence of Natural Trees for Vegetation Distribution Monitoring

Fluorescence images of in vivo and natural tree leaves induced by the second harmonic of a Q-switched YAG laser have been remotely and directly detected by a lidar with a gated image-intensified charge-coupled-device (II CCD) camera. Simple spectroscopic measurements using a colored glass filter showed that the fluorescence was caused by the chlorophyll in the leaves. The chlorophyll fluorescence was useful to distinguish trees and other objects. Tree locations up to a distance of around 150 m from the system were also determined with a range resolution of 15 m from the range-resolved fluorescence images. The results showed that this technique has a great potential use as a monitor of vegetation distribution.

Laser-Induced Fluorescence Detection of Plant and Optimal Harvest Time of Agricultural Products (Lettuce)

Growth monitoring of agricultural products and prediction of their harvest time were tried by applying laser–induced fluorescence as a nondestructive and in vivo method. Two kinds of lettuce, “Steady” and “Shinanosummer,” grown outside were used in this experiment. The laser–induced fluorescence measurement system was constructed with a 355–nm pulsed laser and a multi–spectral detection system. The fluorescence spectra showed peaks at 460, 520, 685, and 740 nm. Since variations in the 460– and 520–nm intensities of the head leaves were well represented by an exponential regression curve and those of the outer leaves showed a tendency to have a minimum value around harvest time, they may be possible candidates to predict the harvest time. Especially carotenoids were considered as an origin of the 460– and 520–nm fluorescence together with living status/growth phase of the lettuce.