Ionosphere Modeling

According to an NSSDC site, the ionosphere is "the region from about 60 km to 2000 km altitude, where the solar irradiance produces a partially ionized plasma of mostly H+ and He+ above 1000 km, O+ from 300 to 500 km and molecular ion (NO+, O2+, N2+) below 200 km. Total ion densities (= electron density) range from 10^8 to 10^13 m-3. Driven by neutral winds and electric fields the ionospheric electrons and ions move along geomagnetic field lines. Knowledge of the ionospheric electron density is essential for a wide range of applications, e.g., radio and telecommunications, satellite tracking, and Earth observation from space. Considerable efforts have, therefore, been concentrated on modeling this ionospheric parameter."

ODTK implements the IRI2016 model or the DSNMedia model.

DSNMedia Model

Models ionosphere delays along the spacecraft line of sight using the JPL DSN media correction data files and as described in 820-013 Deep Space Network External Interface Specification JPL D-16765 TRK-2-23 Media Calibration Interface. Delays are computed based on power or trigonometric series representations of ionospheric delay corrections in the direction of the satellite. Series representations are input via files as specified in the Scenario.EarthDefinition.DSNMediaCalibration file list. A separate series representation is used for each tracking pass. The computed value represents the one way delay in meters at the nominal S-band frequency of 2295 Mhz.

Note: If a facility is configured to use DSN Media Calibration Data for ionosphere modeling and a requested time (during a tracking interval) is not covered by the data specified in the scenario properties, ODTK will stop processing.

IRI2016 Model

The International Reference Ionosphere 2016: Improvements and new parameters is "an international project sponsored by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI). These organizations formed a Working Group . . . in the late sixties to produce an empirical standard model of the ionosphere, based on all available data sources. . . . Several steadily improved editions of the model have been released. For given location, time and date, IRI describes the electron density, electron temperature, ion temperature, and ion composition in the altitude range from about 50 km to about 2000 km; and also the electron content. It provides monthly averages in the non-auroral ionosphere for magnetically quiet conditions. The major data sources are the worldwide network of ionosondes, the powerful incoherent scatter radars (Jicamarca, Arecibo, Millstone Hill, Malvern, St. Santin), the ISIS and Alouette topside sounders, and in situ instruments on several satellites and rockets. IRI is updated yearly during special IRI Workshops (e.g., during COSPAR general assembly)."

According to the International Reference Ionosphere 2016: Improvements and new parameters document, the following are the most important changes introduced with IRI2016:

1. There are two new model options for the F2 peak height hmF2, one based on digisonde data [Altadill et al., 2013] and one based on radio occultation data [Shubin, 2015]. Most signficantly, these new options are now modeling hmF2 directly and no longer through its relationship to the propagation factor M(3000) F2. The digisonde-based model is the recommended choice in IRI-2016. Our comparisons of these models highlight areas and time periods where significant differences exist that warrant further study and a call for more direct measurements of hmF2.
2. There is a more accurate and reliable description of the topside ion composition at low solar activities based on C/NOFS-CINDI data.
3. IRI-2016 accounts for the newly revised sunspot number index in the IRI model parts that depend on this parameter.

Ionosphere Model Options

The following options are provided:

NOTE: The magnitude of the ionosphere range delay is inversely proportional to the square of the frequency. Thus, a higher frequency yields a lower ionospheric delay.