11:00 AM - 1:00 PM
[PEM13-P16] A new HF Doppler observation system: addition of FM-CW function for observing reflection height
Keywords:HF Doppler, ionospheric disturbances, FM-CW, radar altimeter, JG2XA
Observations of ionospheric disturbances using the High Frequency Doppler (HF Doppler: HFD) sounding have been carried out in various latitudes since the early 1960s. In Japan, observations have continued for the past ~50 years, and the Doppler shifts imposed at the time of reflection at the ionospheric E, and F regions have been used to study traveling ionospheric disturbances (TIDs), sporadic E (Es), and various ionospheric phenomena caused by energy input from the magnetosphere or lower atmosphere. The University of Electro-Communications (UEC) started HFD observations using the standard radio JJY (Communications Research Laboratory) in 1977, and has conducted multipoint observations by operating a number of receivers at multiple stations in Japan. After the stop of HF JJY transmission, in order to continue ionospheric researches using HFD, the experimental radio transmission station JG2XA was newly established in 2001 which employs radio waves at 5006 kHz and 8006 kHz, which are close to the frequencies used by JJY.
About 20 years after the start of the JG2XA transmission station, the general performance of commonly available equipment constituting the transmitter has been improved as well as the equipment in use are aged. Therefore, now we plan to modify the format of radio wave and renew the transmission system. Addition of the distance measuring (i.e., ranging) function will allow us to distinguish ionospheric reflections from E and F regions. Then, in combination with the multipoint receiving observations, it will be possible to observe a change in the electron density structure in the three dimensional fashion. We have already renewed the receiving system with digital receivers consisting of software defined radio system and are ready for modifications of the radio signal. There are three requirements for this renewal of the system: (1) to be consistent with the existing observation data, (2) to be able to measure the reflection altitude, which was previously only inferred from the Doppler shift data, and (3) to meet the domestic radio regulations and obtain a radio license. To satisfy these requirements, now we plan to newly add a frequency modulated continuous wave (FM-CW) signal while continuing the transmission of the continuous wave (CW).
CW is the simplest radio format suitable for observing Doppler frequency variations. Currently, transmissions with a bandwidth of 1.5 kHz from the center frequency are allowed for each of the two frequencies. Callsign with SSB modulation is additionally transmitted together with CW signal. For new FM-CW transmissions to measure the reflection altitude, a bandwidth of 150 kHz is required to achieve the 1 km distance resolution required from the science side. Currently, it is assumed that the frequency sweep will be performed 20 times per second over the 150 kHz bandwidth. By synchronizing the start timing of the frequency sweep with the GPS-synchronized 1pps signal both at transmitting and receiving site, it will be possible to detect the propagation delay by frequency difference between the received and transmitted signals, and derive the reflection height. In the presentation, we will describe the details of the radio format and the configuration of the transmission system under development.
About 20 years after the start of the JG2XA transmission station, the general performance of commonly available equipment constituting the transmitter has been improved as well as the equipment in use are aged. Therefore, now we plan to modify the format of radio wave and renew the transmission system. Addition of the distance measuring (i.e., ranging) function will allow us to distinguish ionospheric reflections from E and F regions. Then, in combination with the multipoint receiving observations, it will be possible to observe a change in the electron density structure in the three dimensional fashion. We have already renewed the receiving system with digital receivers consisting of software defined radio system and are ready for modifications of the radio signal. There are three requirements for this renewal of the system: (1) to be consistent with the existing observation data, (2) to be able to measure the reflection altitude, which was previously only inferred from the Doppler shift data, and (3) to meet the domestic radio regulations and obtain a radio license. To satisfy these requirements, now we plan to newly add a frequency modulated continuous wave (FM-CW) signal while continuing the transmission of the continuous wave (CW).
CW is the simplest radio format suitable for observing Doppler frequency variations. Currently, transmissions with a bandwidth of 1.5 kHz from the center frequency are allowed for each of the two frequencies. Callsign with SSB modulation is additionally transmitted together with CW signal. For new FM-CW transmissions to measure the reflection altitude, a bandwidth of 150 kHz is required to achieve the 1 km distance resolution required from the science side. Currently, it is assumed that the frequency sweep will be performed 20 times per second over the 150 kHz bandwidth. By synchronizing the start timing of the frequency sweep with the GPS-synchronized 1pps signal both at transmitting and receiving site, it will be possible to detect the propagation delay by frequency difference between the received and transmitted signals, and derive the reflection height. In the presentation, we will describe the details of the radio format and the configuration of the transmission system under development.