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National atmospheric research Laboratory (NARL) under Department of Space (ISRO) and RISH, Kyoto University has close interaction in the area of atmospheric research. Both institutes have number of similar kind of instruments and number of scientific campaigns conducted. In joined collaboration with RISH, NARL is developing a Radio Acoustic Sounding System (RASS). NARL has been planning to augment present MST radar system to a fully active phased array system with more transmitted power in multi channel configuration. Similar kind of system - MU radar is already in operation at RISH, Kyoto University. In addition to this ISRO is in the process of building a new wind profiler system for its operational requirement at launch station and India is planning to have wind profiler network for its meteorological application.
During my stay at RISH between 13 - 20 July 2008, experiments were conducted with MU radar in the coherent radar imaging (CRI)/ Image Doppler Interferometry (IDI) mode. The study is expected to bring out result on some of the scientific problem which is other wise unable to address with general radar observations in DBS mode. The proposed study is only possible to conduct with MU radar with multi channel configuration. This demands expert signal processing algorithm development and interpretation of data to its scientific goals. Study has been initiated to carryout the aforesaid objectives. With the experience and expertise obtained with the research programmes at RISH, I will be able to implement same at NARL/ DOS (ISRO) on new system being developed and address number of scientific problems. Being associated with a world class research institution, experts and instruments, I will be able to enrich my knowledge and satisfy the scientific tempo carrying with me. The interaction, I am initiating with host institute will help me in continue the research programmes of common interest in the future. A brief plan of the different objective is given below
1. Study on Convection and precipitation using Coherent Radar Imaging (CRI)/ Image Doppler Interferometry (IDI) : It is understood that the study on convection; generation, mature and decaying process is difficult with normal Doppler Beam Swinging technique due to its instantaneous changes in velocity field over the observation time. It is important to know vertical velocity and horizontal velocity simultaneously to study the evolution of the process and kinematics associated with it. This may be possible if the observation is conducted in imaging /interferometirc mode. IDI technique is a proven tool for observing the horizontal wind vectors with in the radar observation volume using a multi channel receiver configuration. Once the velocity field is known, the study will lead in to possible impact of the process on atmosphere such as wave activity, mass energy transport across tropopause etc. Development of computational tool and signal processing algorithm is part of the study. The study will extend with Frequency Domain Interferometry so that finer vertical resolution will be able derive and there by deriving fine structure of the atmosphere during the event.
2. Investigation of IDI as a tool for optimization of momentum flux computation time: Momentum flux computation uses wind vectors derived from MST radar. Since the standard deviation of error is more than mean vertical wind of observation it is reported that the effective time of integration around 16 hours is essential for computing momentum flux. Here I would like to conduct an experiment with IDI technique in clear air condition. In IDI, it is expected to give number of scattering centers (eddies) with in radar scattering volume moving with different velocities (DBS technique expected to give mean wind velocity with in the volume). By identifying different wind fields and averaging it will reduce the variance. The averaging effect expected to give better accuracy of observation there by reducing the long time integration time reported for momentum flux computation. Development of necessary computation algorithm is part of the study.
3. Array signal processing: The classical problem in array signal processing is to determine the location of an energy radiating planar source relative to the location of the array. We are interested in estimating the direction of arrival (DOA) of a signal in the presence of noise and interfering signals. The array antenna attacks this problem by exploiting the spatial separation in the locations where the desired and interfering signals originate. It is planned to develop algorithm for array processing with different approaches available in literature and compare the results for suitability in atmospheric targets. The will lead in to understanding best method to be adopted in post beam steering method of wind estimation and other atmospheric parameters. With the experience obtained from this study it is proposed to adopt new algorithm which is more efficient and computationally less loaded.