GITR is short for GNU Ionospheric Tomography Receiver, and appropriately it is pronounced as "jitter". This is a software defined radio based set of tools that is intended for measuring relative slant total electron content (TEC) curves based on beacon satellite transmissions measured on ground stations. With enough receivers, these TEC curves can then further be used to perform 2d or 3d reconstructions of the electron density of the ionosphere within the measurement volume of the ground stations.
Ionospheric tomogaphy is a tomographic method of deducing the 2D or 3D electron density function of the ionosphere by measuring the relative propagation delay between two or more interlocked radio channels between a satellite and a ground station. The underlying inverse problem is similar to limited angle X-ray tomography used for dental imaging. This method has been used for some time now, e.g., at the Sodankylä Geophysical Observatory. Recent tomographic reconstructions can be viewed here.
Stay tuned, we will be soon publishing the source code and receiver design for a next generation software defined radio based ionospheric tomography receiver, which is based on hardware from Ettus Research and software based on GNU R, C++ and the gnuradio framework.