INCOHERENT SCATTER MODE

Since it began operating in 1961, the Jicamarca Incoherent Scatter radar has been an important source of plasma density, temperature, composition, and drift measurements in the equatorial zone. Jicamarca’s radar capabilities and observing modes have evolved over the years and are different from those of other incoherent scatter radars. Its distinction is due partly to its proximity to the dip equator (11.95o S, 76.87o W, 1o N magnetic, 1o dip.) Jicamarca has a modular, phased array antenna with a main lobe that can be directed perpendicular to the geomagnetic field. The narrowness of the incoherent scatter spectrum for perpendicular backscatter permits very accurate measurements of cross-field plasma drifts. When its main beam is steered a few degrees off perpendicular, Jicamarca’s crossed-dipole antenna can be used to measure the Faraday rotation of incoherent scatter, a technique which affords an independent, absolute estimate of electron density and provides means of calibrating conventional power profiles.

The Jicamarca radar is also unique in its operating frequency, 49.92 MHz. The sky noise temperature at this frequency varies between about 3000 and 28,000 K, depending on the sidereal time, limiting the radar sensitivity. A plot of sky noise over Jicamarca for a given day of the year can be obtained at Sky-noise. Furthermore, the autocorrelation time of the incoherent scatter signal when observed a few tenths of a degree or more off perpendicular is of the order of 1 ms, and the autocorrelation function (ACF) must usually be measured to lags of ~2 ms for accurate parameter estimation. This implies that the range resolution of a conventional long-pulse experiment can be no better than ~300 km at Jicamarca for the shortest lags. Finally, coherent scatter from the equatorial electrojet received through the antenna sidelobes is an almost continuous source of clutter. The clutter contaminates signals from long-pulse experiments in range gates up to ~450 km altitude, rendering them impractical for work near and below the F region peak.

Given that the main Jicamarca antenna, used for these modes, points currently only at one position at the time, not all the parameters and ranges are measured with a single operational mode. In the table below we summarize the different modes and the variables they measure.