87-98Y. V. Somayajulu and A. P. Mitra (Scient. Rep. No. 29, Radio Science Division, National Physical Laboratory, New Delhi, 1966) proposed a rocket-borne riometer technique to derive the electron density profile by measuring the changes in cosmic noise absorption in the lower ionosphere. Using this principle a rocket-borne riometer was flown on a Nike-Apache rocket (ISRO 30.01) on 2 January, 1970 at 1212 hrs LT. Two additional experiments have been included in the same payload to measure electron density, viz. a propagation experiment and a Langmuir probe. The principle and feasibility of the new technique are described and the instrumentation and the design considerations are discussed. The flight performance and data analysis are Presented. It is found that the changes in cosmic noise absorption with altitude are consistent with the absorption changes measured by the propagation experiment in the 60-80 km altitude region. Above 85 km altitude the large electron densities cause impedance changes of the riometer antenna. The antenna detuning is utilized to estimate the electron densities in this region. Thus the flight demonstrates the scientific and technical feasibility of riometer experiment for lower ionospheric studies. The measurement accuracy is better when the D-region absorption is high, as during solar flare or PCA, etc
