Observations of field-aligned irregularities in the ionosphere using multi-frequency range imaging technique

Multi-frequency range imaging (RIM) implemented in the Middle and Upper atmosphere Radar (MUR; 34.85°N, 136.10°E) was utilized for the first time to observe the field-aligned irregularities (FAI) in the mid-latitude ionosphere. Five frequencies equally spaced between 46 MHz and 47 MHz were employed. Two types of RIM data collected with 16-element binary complementary codes and without phase codes were examined, respectively. It is shown that RIM works well and can resolve striation structures of FAI within the pulse length, thereby improving the range resolution of measurement greatly. However, duplicated echoes due to code-sidelobes appeared frequently at altitudes above and below the source regions. A procedure taking advantage of RIM to mitigate the code-sidelobe echoes is progressing.