"The Low-latitude Ionospheric Sensor Network (LISN): The First Distributed 
Observatory in South America", by Cesar E. Valladares and Patricia H. Doherty. 
 
This paper describes the characteristics and illustrates the early measurements 
of the first distributed observatory that is being installed in the South 
American region to study the low-latitude ionosphere and upper atmosphere.  The 
LISN distributed observatory will be comprised of nearly 70 GPS receivers with 
the capability to measure Total Electron Content (TEC), amplitude and phase 
scintillation and Traveling Ionospheric Disturbances (TIDs).  In addition, the 
network will include 5 ionosondes and at least 6 magnetometers that will provide 
complementary ionospheric information.  This network of GPS receivers and 
ionospheric sensors span from north to south in the South American continent and 
west of the 55o West meridian.  They will complement each other to provide new, 
time continuous and spatially extended observations of the background 
ionosphere, its motion and the embedded structures over this large dynamic 
region. 
 
This network and the impending data set are important to the Space Based 
Augmentation Systems (SBAS) such as WAAS, EGNOS, MSAS and GAGAN.  Much of the 
ionospheric research and development for WAAS, EGNOS and MSAS focused on 
defining and mitigating ionospheric challenges characteristic of the 
mid-latitude regions, where the ionosphere is nominally quiescent.  WAAS system 
extension into the lower latitudes of Mexico, EGNOS extension into Africa and 
system development in South America, India and China will have to contend with 
much more extreme conditions.  These conditions include strong spatial and 
temporal gradients, plasma depletions and scintillations. 
  
The LISN network is being complemented with an assimilative physics-based model 
that will provide a nowcast of the ionospheric electron density, conductivities, 
E×B plasma drifts, and neutral winds.  This new distributed observatory will 
bring the opportunity to understand the day-to-day variability and the stability 
of the low-latitude ionosphere and to make forecasts on a regional basis.  This 
paper describes the instrumentation, presents the first measurements and 
discusses the scientific benefits of the LISN network.