Weak Echoes from the Ionosphere with Radio Waves of Frequency 1.42 Mc./s.

MF and HF radar techniques for investigating the dynamics and structure of the 50 to 110 km height region: a review

“…They found echoes below the E region (~110 km) and which extended down to heights of about 80 km. Their results were obtained at MF using an ionosonde and were followed by similar results at MF and HF obtained by Dieminger (1952), Dieminger and Hofmann-Heyden (1952), and by Gnanalingham and Weekes (1952).…”

Stratification in the lower ionosphere

“…He also concluded that the results were strongly influenced by meteorological phenomena, and that synoptic data over the world might be necessary to understand them. At about the same time, Gnanalingam and Weekes (1952) reported heights of 75 to 80 km on win ter days of high absorption, but on other winter days heights of 90, 96 , and 112 km were common. They used a sensitive frequency modulation technique to detect the weak signals.…”

Massively parallel coherent laser ranging using soliton microcombs

“…Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser based ranging (LI-DAR) [1] is currently developed for long range 3D distance and velocimetry in autonomous driving [2,3]. Its principle is based on mapping distance to frequency [4,5], and to simultaneously measure the Doppler shift of reflected light using frequency chirped signals, similar to Sonar or Radar [6,7]. Yet, despite these advantages, coherent ranging exhibits lower acquisition speed and requires precisely chirped [8] and highly-coherent [5] laser sources, hindering their widespread use and impeding Parallelization, compared to modern time-of-flight (TOF) ranging that use arrays of individual lasers.…”