4.5 Ionospheric electron density measurements using COSMIC (2008

4.5

Ionospheric electron density measurements using COSMIC

Kenneth F. Dymond, NRL, Washington, DC; and S. A. Budzien, P. A. Bernhardt, C. Rocken, and S. Syndergaard

At 0140 UTC on 15 April 2006, the joint Taiwan-U.S. COSMIC/FORMOSAT-3 (Constellation Observing

System for Meteorology, Ionosphere, and Climate and Formosa Satellite mission #3; hereafter COSMIC)

mission, a constellation of six micro-satellites, was launched into a 512-km orbit from Vandenberg Air

Force Base in California. Using on-board propulsion these satellites are being deployed to their final orbits

at 800 km with 30 degrees of separation. This process will take about 17 months following the launch.

There are three instruments aboard each COSMIC satellite: the GPS Occultation Experiment (GOX), the

Tri-Band Beacon (TBB), and the Tiny Ionospheric Photometer (TIP). These three instruments constitute a

unique suite of instruments for studying the Earth's ionosphere. The GOX instrument operates by inferring

the slant total electron content (the integral of the electron density along the line-of-sight) between the

COSMIC satellites and the GPS satellites as a function of tangent height above the Earth's limb. These

data can be inverted to produce electron density profiles in the E and F regions of the ionosphere. The TBB

is a three frequency radio beacon that radiates coherently at 150, 400, and 1067 MHz. When the relative

phases of the signals are measured between the COSMIC satellites and ground-based or space-based

receivers, the total electron content along the line-of-sight can be determined. By making the

measurements from a set of receivers, the two-dimensional distribution of electrons beneath the satellite

can be determined using tomographic techniques. The TIP instrument measures the optical signature of the

natural decay of the ionosphere produced via recombination of the O+ ions and electrons. The TIP

measurements can be used to characterize the morphology and dynamics of the global ionosphere.

Additionally, the TIP measurements can be inverted in conjunction with the GPS occultation

measurements, using tomographic techniques, to produce the two-dimensional distribution of electrons

beneath the satellite. We present an overview of the COSMIC mission, the instruments, and their

application to ionospheric sensing.