Comparison of Co-Located TEC Observations Made By COSMIC Satellite and Mountaintop GPS Receiver

Brian
Breitsch
Colorado State University
Dongyang Xu, Colorado State University
Jade Morton, Colorado State University
Poster
One of the principal observations derived from GNSS (Global Navigation Satellite Systems) signals is ionospheric total electron content (TEC), which is a measure of the density of free electrons integrated along the signal path. TEC is typically computed using the difference of dual-frequency signals from a GNSS satellite, thereby taking advantage of the frequency dispersive effects of ionosphere plasma on microwave-band propagation. In turn, TEC measurements made using GNSS receivers provide valuable observations for ionosphere modeling and imaging applications [1]. It has been noted that TEC measurements made by low-earth-orbiting (LEO) satellites such as COSMIC are especially valuable to these applications since they provide complementary horizontal observations to the slant and vertical observations that ground receivers provide. However, radio occultation measurements are relatively sparse compared to those made by the vast GNSS ground receiver networks. If we can make reliable TEC estimates from ground receiver measurements of signals from very low-elevation satellites, these observations can help provide more horizontal information to ionosphere imaging and modeling applications.

Estimating TEC using low-elevation GNSS observations introduces new challenges such as increased multipath and signal attenuation. These challenges can partially be overcome with improved receiver tracking algorithms, high-gain antennas, and the use of multi-frequency (i.e.\ triple-frequency GPS) signals. In April 2015, a mountaintop dish experiment was performed at Mount Haleakala to collect signals from low-elevation GPS satellites. Observations of the triple-frequency GPS satellite G25 made using the high-gain dish antenna were co-located with observations made by COSMIC satellite C002. In this work, we compare TEC observations made by the COSMIC satellite with those made using the mountaintop dish. Applying the work from [2] and [3], we use G25's triple-frequency signals to optimally estimate TEC. We compare the abilities of COSMIC and the mountaintop receiver to identify the E-layer peak that is present during the time of the observation. E-layer presence can be seen in the electron density profile, which was obtained using the C002 TEC observations and the Abel inversion technique. Ultimately, we aim to use COSMIC observations in order to demonstrate that TEC estimates from ground receivers observing low-elevation satellites can provide another valuable set of horizontal observations.

[1] Bust, Gary S and Mitchell, Cathryn N, ``History, current state, and future directions of ionospheric imaging,'' Reviews of Geophysics, 2008

[2] B. Breitsch, ``Linear combinations of gnss signals and application to precision TEC estimation,'' Master’s thesis, Colorado
State University, 2017.

[3] J. Spits, ``Total electron content reconstruction using triple frequency GNSS signals,'' PhD thesis, Université de Liège, Belgique,
2012.

OSTS session
Regional and Global CAL/VAL for Assembling a Climate Data Record