One of special radiosondes (hereinafter referred to as the Videosonde) focusing on precipitation particles was developed by Takahashi (1990) under the cooperation of Meisei Electric., Japan. The Videosonde can capture precipitation particle images in the air without contact to the particles and can provide information on the size and shape of precipitation particles such as raindrops, snowflakes and graupel. The Videosonde system also has an induction ring to measure the electric charge of the particles. In the previous studies, several hundreds of Videosonde soundings provided valuable results to contribute to the lightning studies (Takahashi et al. 1999; Takahashi and Suzuki 2010; Takahashi et al, 2017, etc.).
On the other hand, another special radiosonde (hereinafter referred to as the HYdrometeor VIdeoSonde, HYVIS) focusing on cloud particles was developed by Murakami and Matsuo (1990), again, under the cooperation of Meisei Electric., Japan. In order to observe cloud particles with sizes down to several micrometers, the HYVIS adopted a method in which a microscope was mounted and the images of the cloud particles deposited on a clear filmstrip were obtained and sent to the ground station in real time. Although there is the NCAR balloon-borne Formvar replicator (e.g., Miloshevich and Heymsfield, 1997) that can obtain ice crystal replica, but only upon recovery of the Formvar instrument; thus, it could not be used, for example, in a place like Japan that is surrounded by seas on all sides. The HYVIS can immediately send the image data to the ground with a 1680 MHz carrier. The HYVIS was mainly used to observe snow clouds and cirrus clouds (Murakami et al. 2003; Orikasa et al. 2005).
The Videosonde and HYVIS have been used as a strong tool for understanding cloud microphysics. In the 2000s, with the progress of remote sensing technology such as radar and with the progress of cloud-resolving models, these instruments were started to be used also as a reference instrument. Nakakita et al. (2009) verified the hydrometeor classification by the latest multi-parameter Doppler radar using the Videosondes and HYVISs. In this research, multipoint, simultaneous sounding capability for these instruments were required, so that a new ground receiving system has been developed aiming at reduction of observation cost and at improvement of usability (Suzuki et al. 2012).
Although the 1680 MHz band radiowave used in the Videosonde and HYVIS has been reserved for meteorological use until now, it is being considered worldwide to be replaced with other communication uses in the future. In the United States, NWS is planning to migrate the frequency for all operational radiosondes from 1680 MHz to 400 MHz. Under these circumstances, we started research and development to change the frequency of the Videosonde and HYVIS from 1680 MHz band to 400 MHz band under the project MIC/SCOPE #195003007. After the change from 1680 MHz for which wide radiowave band width is allowed, to 400 MHz for which narrow band width is only allowed, it is not possible to transmit data of the same size; thus, we need various technical and scientific considerations to meet this limitation while keeping the scientific value as it. Data size compression procedure on the radiosonde board is a must, but we also need to reconsider the temporal resolution of the data acquisition, while not losing scientific information. A positive side is that, by using the 400 MHz band, the ground receiving system would not need a tracking antenna system and thus would be greatly simplified and become much easier to operate. Also, the image data from the new system would be digitized, in contrast to analog signals in the current system, so that the images would become much clearer and post data analysis would be much more efficient.
In this presentation, the past Videosonde and HYVIS studies are reviewed, and the development plan of the new Videosonde and HYVIS system will be introduced and discussed.
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