Hamaki Inokuchi

Development of an Onboard Doppler Lidar for Flight Safety

Air turbulence has become a major cause of significant injuries and aircraft damages. Timely advanced warning of turbulence ahead of an aircraft may allow pilots to take appropriate action to minimize potential damage, such as reducing speed and securing passengers and unsecured objects, or to avoid the turbulence altogether. The aim of our research is to develop a practical, onboard, Lidar-based proactive sensor that will detect air turbulence in clear air at a range of 5 n miles (9.3 km) at cruising altitudes. In February 2007 we successfully measured wind speeds approximately 3 n miles (5.6 km) ahead of an aircraft in low-altitude flight experiments, and in a subsequent experiment in July of the same year, we succeeded in detecting air turbulence before encountering it. An upgraded 5-n-mile Lidar for low altitudes was developed in fiscal year 2007, and has successfully measured wind speeds at ranges up to 5 n miles in ground tests. This paper describes the master development plan of our Lidar turbulence sensor and the results of basic flight and ground experiments.

All Fiber Coherent Doppler LIDAR for Wind Sensing

An 1.5 micron pulsed Coherent Doppler LIDAR system using all fiber optical components has attracted attention for remote wind sensing application because of its eye-safety, reliability and easy deployment. We report on our key technologies such as fiber based MOPA (Master Oscillator Power Amplification) transmitter, high peak power optical amplification and a real-time signal processing. Some performance results and applications are also provided.

Development of an airborne wind measurement system

Accidents to airliners caused by air turbulence have been increasing in recent years. At present there is no sure way of avoiding encounters with clear air turbulence (CAT) because conventional airborne weather radars cannot detect turbulence in clear conditions. The Japan Aerospace Exploration Agency (JAXA) is therefore developing a Doppler LIDAR (Light Detection and Ranging) which can measure wind speeds ahead of an aircraft even in clear air. Turbulence prediction in flight has already been demonstrated using experimental Doppler LIDARs, and the latest prototype aims at turbulence detection up to 5 nautical miles (9 km) ahead at jet airliner cruising altitudes. Wind velocity measurement by LIDAR is difficult at high altitude because of low aerosol particle density. Regular atmospheric observation flights are therefore being made to establish the basic specifications of a practical device. Furthermore, since air turbulence information should be displayed on the flight deck, a graphical turbulence display is also being studied. This paper describes the development of the airborne wind measurement system and presents examples of flight experiment results.

Wind sensing demonstration of more than 30km measurable range with a 1.5μm coherent Doppler lidar which has the laser amplifier using Er,Yb:glass planar waveguide

Recently, we have developed the high output power laser amplifier using Er,Yb:glass planar waveguide in order to increase the measurable range of our 1.5 μm coherent Doppler LIDAR (CDL). In this paper, we introduce this development and demonstration of a long range wind sensing using the developed system. The transmitted pulse has a peak power of 2.4 kW and a width of 580 ns (i.e. pulse energy of 1.4 mJ) with a pulse repetition frequency of 4 kHz, in addition to a nearly diffraction limited beam quality. With this laser amplifier, we demonstrate the measurable range of more than 30 km. According to our own research, this is the longest measurable range demonstration for wind sensing CDLs.

Numerical Analysis of Clear Air Turbulence by Using Large Eddy Simulation Coupled with a Meteorological Model

5Computational fluid dynamics (CFD) simulation of clear air turbulence (CAT) is conducted by coupling numerical weather simulation and large eddy simulation (LES). Initial and boundary conditions of the LES are defined base on Japan Meteorological Agency’s Non-Hydrostatic Model (JMA-NHM) with three levels of downscaling. The target location and time of JMA-NHM are determined by 40 cases of the flight data that encountered CAT. With a goal of identifying the important turbulence indices, selforganizing map (SOM) is applied to the results of CFD simulation. The results of the SOM showed that CAT can be categorized into two types. One is CAT associated with Richardson number (Ri) and Scorer parameter (SP), which indicate atmospheric stability, and vertical wind shear (VWS), vertical gradient of horizontal wind (dVdz), energy dissipation rate (EDR) and wind direction (WD). Another is CAT cannot be detected by existing indices. Therefore, visualization of flow and turbulence index fields as well as information visualization were conducted for the latter type of CAT. In the result, we found that the unpredictable CAT is associated with the inflection point of vertical profiles concerning wind speed and direction.

1.5-μm high-average power laser amplifier using a Er,Yb:glass planar waveguide for coherent Doppler lidar

We have developed a 1.5-μm eye-safe wavelength high average power laser amplifier using an Er,Yb:glass planar waveguide for coherent Doppler LIDAR. Large cooling surface of the planar waveguide enabled high average power pumping for Er,Yb:glass which has low thermal fracture limit. Nonlinear effects are suppressed by the large beam size which is designed by the waveguide thickness and the beam width of the planar direction. Multi-bounce optical path configuration and high-intensity pumping provide high-gain and high-efficient operation using three-level laser material. With pulsed operation, the maximum pulse energy of 1.9 mJ was achieved at the repetition rate of 4 kHz. Output average power of the amplified signal was 7.6W with the amplified gain of more than 20dB. This amplifier is suitable for coherent Doppler LIDAR to enhance the measurable range.