[P-EM07_30PO1] Lightning and TLEs and their effects on the lower and middle atmosphere

[PEM07-P04] VHF lightning observations by digital interferometry on JEM-GLIMS

*Takeshi MORIMOTO¹, Hiroshi KIKUCHI², Mitsuteru SATO³, Tomoo USHIO², Atsushi YAMAZAKI⁴, Makoto SUZUKI⁴ (1.Kinki University, 2.Osaka University, 3.Hokkaido University, 4.ISAS/JAXA)

Keywords:lightning, VHF radio observations, GLIMS, International Space Station

Global Lightning and sprIte Measurements (GLIMS) mission is now ongoing on Exposed Facility of Japanese Experiment Module (JEM-EF) of the International Space Station (ISS). This paper focuses on an electromagnetic (EM) payload of JEM-GLIMS mission, very high frequency (VHF) broadband digital InTerFerometer (VITF). JEM-GLIMS mission is designed to conduct comprehensive observations with both the EM and the optical payloads for lightning activities and related transient luminous events (TLEs) expecting to give us many scientific impacts to the field.VITF consists of two sets of antennas, band-pass filters, amplifiers, and 2-channel-AD-converter. Impulsive EM radiations received by the antennas are digitized by the AD converter synchronizing with another channel through the filters and the amplifiers. A patch type antenna is developed within the size of 200*200 mm. It is mounted on the antenna base made of aluminum alloy and Teflon block with the total height of 100 mm to gain its bandwidth and to reduce the interference from other structural objects. The same two units of antennas are installed with the separation of 1.6 m. Their bandwidths with the higher return loss than -3 dB are from 70 to 100 MHz. The signals received by the antenna are transmitted along cables with the same lengths to the electronics. The AD converter records 130 waveforms as maximum of one dataset with the duration of 2.5 μs with 200 MS/s. The developments of VITF are based on the heritage of VHF sensor on Maido-1 satellite.JEM-GIMS mission payload was successfully launched at the end of July 2012, and transported and installed to the ISS. After the initial checkout and maintenance, its nominal operation is continued from December 2012. Through the operation period, VITF corrects numerous VHF EM data synchronized with optical signals. About 650 VITF datasets were obtained in January and February 2013, for instance. The estimations of the EM direction-of-arrival (DOA) are attempted using the broadband digital interferometry. Some results agree with the optical observations, even though DOA estimation has difficulties caused by its very short baseline of the antennas and multiple pulses in short time, namely burst-type EM waveforms. VITF is designed expecting to estimate the DOA with about 10 km resolution that is equivalent to the scale of a thundercloud. The results on narrow bipolar pulses (NBPs) and/or transionospheric pulse pairs (TIPPs) are also expected as well as TLEs. The recorded VHF EM signals and the results of their DOA estimations, and the comparisons with optical observations will be introduced in the presentation.