Satellite beacon studies have contributed mainly in two areas of resea
rch, namely, total electron content (TEC) and small scale structures o
r irregularities, and both of these have important practical implicati
ons in trans-ionospheric radio propagation. The current status of thes
e two fields of research is summarized, and recent developments in the
study of equatorial anomaly using US NNSS satellite signals, geomagne
tic storm effects, travelling ionospheric disturbances, nighttime enha
ncements, and slab thickness, which are of particular relevance to the
equatorial and low latitudes, are reviewed. Recent initiatives on TEC
modelling and comparison of existing models with observations are hig
hlighted. New concepts like computerized ionospheric tomography are br
iefly outlined. Recent advances in the understanding of scintillation
morphology, particularly its longitude dependence and the variation of
the width of the equatorial scintillation belt are summarized. Future
directions in respect of multitechnique investigation of the low lati
tude ionosphere and the mosphere, measurement of GHz scintillations, a
nd spectral studies are pointed out. Important application areas of th
is field are also included.