Throughout the world extensive use is made of radio sounding systems to remotely probe the Earth's ionosphere. One category of sounder is the High Frequency (HF) oblique ionosonde. This is essentially a radar which emits a chirp (swept frequency) signal, and at a second location measures the group delay of the return signals as they bounce back from the ionosphere. QinetiQ designed and built the high performance oblique ionosonde receiver IRIS – Improved Radio Ionospheric Sounder.

Function

IRIS employs a PC and commercial radio receiver, and makes extensive use of digital signal processing techniques. The system is also fitted with GPS for accurate timing. The principal system output is a series of ionograms. These graphs of relative group delay versus radio frequency are collected systematically during the period of operation. IRIS systems are used by QinetiQ, UK Ministry of Defence, UK universities and other organisations.

The main features of IRIS are:

• high resolution colour coded ionograms
• single or multiple ionogram screen layouts
• tracking of up to four chirp transmitters
• variable radio frequency and group delay ranges
• absolute time of arrival measurements on received signals

On pre-selected frequencies:

• noise level measurements
• extraction of signal-to-noise ratio
• extraction of multipath spread

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Applications

• frequency management on communications links
• communications modem and system development and testing
• improvement of propagation prediction codes
• development and configuration of channel simulators