During the Guara campaign, conducted from Alcantara in Brazil, a Black Brant X sounding rocket was launched on 14-th October 1994 at 1955hrs (LT) to investigate into the phenomenon of high-altitude equatorial spread-F events. The rocket, as expected passed through an active topside spread-F event, monitored simultaneously by several ground-based instruments. The electron density height profile and the amplitude of the electron density fluctuations were measured simultaneously by three different plasm density probes; a High Frequency Capacitance (HFC) probe, a conventional Langmuir Probe (LP) and a Plasma Frequency Probe (PFP). While the PFP provided the absolute electron density, the LP gave the relative variation in the electron density. The electron density profile obtained from the HFC probe measurements is practically absolute except for a plasma sheath factor. But this technique does not provide the small-scale electron density fluctuation amplitude. Thus, the three experiments provided data, which could be used not only to obtain reliable electron density data, but also could be used to arrive at some of the inherent difficulties associated with each of these techniques. For example the electron density profiles estimated from the HFC and PFP experiments are almost identical except for a small factor varying with altitude. The amplitude of large-scale fluctuations provided by the LP measurements is considerably less than that provided by HFC and PFP. Characteristic features of the high-altitude spread-F as observed by these experiments are presented here.


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