Institute for Scientific Research
Boston College







AGREES stands for African GPS Receivers for Equatorial Electrodynamics Studies

AGREES (Proposed)

PIs: Endawoke Yizengaw (PI) and Mark Moldwin (Co-PI), University of California at Los Angeles

In looking at a map of the world showing the location of ground-based space physics instru-mentation (radars, magnetometers, ionosondes, GPS dual frequency receivers, and lidars), one quickly recognizes Africa’s relative lack of space physics research infrastructure. This has cre-ated a gap of global understanding of the physics behind the evolution and formation of plasma irregularities in the equatorial region, which imposes severe limitations on ionospheric and plas-maspheric density modeling efforts. Knowledge of ionospheric and plasmaspheric (inner-magnetospheric) density structure is required to create weather dependent density model and mitigate the navigation and communication degradation. Understanding the source and loss processes of plasma during magnetically active and quiet periods also requires knowledge of in-ner-magnetospheric density structure. Knowing the topside ionosphere and plasmasphere density structure is also essential for obtaining the density contributions of these regions to the ground based total electron content (TEC), which is a long standing problem. The question is how do we obtain reliable density structure of the inner-magnetosphere as a function of local time and mag-netic activity? The scientific community has been developing and using different means to gather density information on the ionosphere and plasmasphere. This includes: incoherent scatter radar probing, coherent scatter radar observations of under dense electron density irregularities, obser-vations using topside sounders onboard satellites, just mention few. However, they are sparsely located around the globe and unable to provide the global understanding of the inner-magnetospheric density structure and dynamics.

The ground- and space-based GPS receivers continuously provide the integrated total elec-tron content (TEC) between the satellite and receiver on the ground, which is one of the most important quantitative characteristics of the ionosphere and plasmasphere. However, the uneven distribution of ground-based GPS receivers hinders our ability to obtain a global understanding of the dynamics and structures of the inner magnetosphere. Although ground-based GPS receiv-ers are located in dense regional arrays, they are primarily only in North America and Europe. In regions like Africa, observations of the inner-magnetosphere are not possible due to lack of ground-based instruments. The density structure over this region has been traditionally estimated by using vast areas of model interpolation. Therefore, to have a complete and global understand-ing of the electrodynamics of the inner-magnetosphere in a cost effective way, deployment of small instruments, like ground-based GPS receivers, is essential. Therefore, we propose to de-ploy the AGREES (African GPS Receivers for Equatorial Electrodynamics Studies) GPS receiv-ers network in Africa to study the fundamental governing electrodynamics of equatorial iono-spheric motion. As shown in the Figure (blue dots), AGREES network will contain five GPS re-ceivers which will be deployed at mid- and low-latitudes in the African continent. The AGREES network will be deployed based on two main priorities that are required for this study. These in-clude:

(1) to routinely monitor the strength and evolution of EA region by filling the largest land-based gap of GPS receiver coverage in Africa,, and

(2) to understand the electrodynamics that governs the equatorial ionospheric motion by com-bining data from GPS receivers network with the already available magnetometer (MAGDAS and AMBER) data.

The ground-based GPS receivers, including AGREES, in the African region will be aug-mented by data from GPS receivers on board Low-Earth-Orbit (LEO) satellites that are equipped with dual-band GPS receivers. The two hours coverage of eight LEO satellites (COSMIC, CHAMP, and JASON) in the region is shown in the Figure. Therefore, the simultaneous applica-tion of tomographic reconstruction technique on both ground- and space-based GPS TEC data will allow us to monitor the structure and dynamics of inner-magnetospheric density. This will provide a great opportunity to the scientific community to clearly quantify the dynamics of mag-netosphere-ionosphere (M-I) coupling phenomenon.

The geographic locations of AGREES stations will be 12.73 S, 15.78 E; 12.11 N, 15.05 E; 17.92 N, 19.12 E; 26.00 N, 14.15 E; and 32.90 N, 13.18 E. Three African countries (Angola, Chad, and Libya) will participate in the AGREES project by hosting the GPS receivers. There-fore, AGREES project will have direct impact on space science research and education both in African and in the United States by fostering international scientific cooperation. In addition to providing world-class science data to the scientific community, AGREES infrastructure will also provide a self-sustained training and research opportunities in the African universities where space science research activities are rare. In the United State AGREES project will create oppor-tunities for graduate and undergraduate students to do research that will provide them high qual-ity research experiences. The experience will include expertise in data analysis, remote-sensing, computer modeling, data assimilation, and grid-based computing and data retrieval.

Table 1: The geographic and geomagnetic locations of AMBER magnetometer stations


Name of Stations


Geog. Lat

Geog. Long

Mag. Lat

Mag. Long


Tripoli, Libya


32.90 N

13.18 E

23.00 N

86.00 E


Marzuq, Libya


26.00 N

14.15 E

14.04 N

86.34 E


Faya-Largeau, Chad


17.92 N

19.12 E

06.16 N

90.80 E


N'Djamena, Chad


12.11 N

15.05 E

00.83 N

86.83 E


Huambo, Angola


12.73 S

15.78 E

22.68 S

85.69 E