The Tiny Ionospheric Photometer: An Instrument for Measuring Ionospheric Gradients for the COSMIC Constellation

Kenneth F Dymond,Ronald J Thomas,Jan Bai Nee

doi:10.3319/tao.2000.11.1.273(cosmic)

Abstract

We describe the specifications for an ultraviolet radiometer for measuring the F-region electron density gradients from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). We also present a technique for determining the two-dimensional structure of the ionosphere using the measured ionospheric gradients inferred from observation of the radiative recombination emission at 1356 A in conjunction with occultations of Global Positioning System satellites observed from the COSMIC satellites. Our scheme uses a nadir viewing UV photometer to characterize the F-region gradients while obtaining altitude information about the F-region from the GPS occultation measurements. We present the results of simulations that demonstrate the applicability and accuracy of the technique and observational concept.

Highlights

The use of total electron content measurements acquired during occultation of the Global Positioning Satellites (GPS ) by a receiving platform in low Earth orbit has recently been dem onstrated as a viable technique for determining the ionospheric electron density (Hajj et al, 1994)
The cornerstone of the technique is use of the Abel inversion to convert the total electron content measurements made by the GPS receiver into electron density profiles
We have found that this complication is not important as the 0 density gradients are much smaller than the o+ gradients

Summary

INTRODUCTION

The use of total electron content measurements acquired during occultation of the Global Positioning Satellites (GPS ) by a receiving platform in low Earth orbit has recently been dem onstrated as a viable technique for determining the ionospheric electron density (Hajj et al, 1994). The cornerstone of the technique is use of the Abel inversion to convert the total electron content measurements made by the GPS receiver into electron density profiles. This technique assumes that the ionosphere is spherically symmetric with no horizontal density gradients. The emissions are produced by radiative recombination of o+ ions and electrons to produce atomic oxygen in an excited state that subsequently decays by emitting a photon These emissions have been observed at visible wavelengths (7774 and 8446 A) from the ground (Tinsley et al, 1973; Tinsley and Bittencourt, 1975) and at ultraviolet wavelengths (911, 1304, and 1356 A) from space (Hicks and Chubb, 1970; Barth and Shaffner, 1970; Chakrabarti et al, 1984; Feldman et al, 1992). This algorithm can accurately retrieve the elec tron density distribution over the region where the occultation occurs regardless of the gradi ents

RADIATIVE RECOMBINATION PROCESS

INSTRUMENT

ALGORITHM

3 Algorithm Test Results

CONCLUDING REMARKS