Session B3: Precise GNSS Positioning Applications

Recent Updates of Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA)
Kento Ichinomiya, Yo Kawashima, Musashi Kato, Nobuhiro Kajiwara, Kuniharu Endo, LHTC; Kyohei Akiyama, Kaori Kawate, Yuki Igarashi, and Toshitaka Sasaki, JAXA
Location: Beacon B

Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA) is a software package,
which has the capability of estimating the orbit and clock offset of GNSS satellites including QZSS, GPS, GLONASS, Galileo and BeiDou, developed by Japan Aerospace Exploration Agency (JAXA).
The joint team named JGX consisting of the Geospatial Information Authority of Japan (GSI) and JAXA has joined the International GNSS Service (IGS) analysis centers on December 2023 and
has continually been providing precise orbit and clock offset products generated with MADOCA.
As a development partner of MADOCA, Lighthouse Technology and Consulting Co., Ltd. (LHTC) has enhanced the software mainly for improvement of its estimation accuracy.
In this presentation, we introduce three recent developments; minimum constraint conditions, an accurate yaw-steering model for Galileo satellites and the output of actual attitude information
according to the Orbit Exchange (ORBEX) format.
First, we evaluate the effect of the so-called “minimum constraint conditions” on the estimated orbit and clock offset with MADOCA.
The minimum constraint conditions ensure the Helmert parameters between the reference coordinate system and the one realized by the estimated station positions are zero.
By incorporating these conditions into the estimation instead of fixing the station positions,
it is possible to align the positions to the reference frame without distorting the geometric relationship of satellites and stations.
In the orbit and clock offset estimation, each IGS analysis center constrains the position of monitoring stations
with the minimum constraint conditions to align the estimated satellite and station positions to the International Terrestrial Reference Frame (ITRF), while the conventional MADOCA fixes the station positions directly to the values defined on the ITRF. Since each IGS analysis center is required to provide the products estimated with the minimum constraint conditions, we have also adopted them to MADOCA.
In this part, we compare the estimated results of orbit and clock offset on the minimum constraint conditions to the ones with fixing station positions.
Second, we evaluate the effect of the attitude model for Galileo satellites published by European GNSS Service Centre (GSC) using MADOCA.
The conventional MADOCA calculates the attitude of Galileo satellites based on the nominal yaw-steering model in which the yaw angle of each satellite is determined
so that the solar array panels are perpendicular to the Sun while the L-band antennas point to the Earth center.
But the actual attitude can differ significantly from this model when the satellite goes across the orbit noon or midnight and the elevation angle of the Sun respect to the orbital plane is low.
It is because the actual yaw-rate in that situation is lower than the one based on the nominal model.
To consider the actual attitude motion of Galileo satellites, we have introduced the model published by GSC into MADOCA.
In this part, we compare the estimated orbit of Galileo satellites with the GSC model to the one with the nominal model.
Third, we evaluate the effects of the precise attitude information generated by MADOCA on precise point positioning.
Following other IGS analysis centers, the JGX is planning to start releasing the estimated attitude data in the ORBEX format.
Conventionally, positioning users are required to calculate the attitude of satellites with various models depending on the systems and the satellite blocks.
With the integrated ORBEX format data, users can apply the precise attitude data without switching those attitude models.
In this part, we compare the precision of precise point positioning with the ORBEX format data generated by MADOCA to the one with the attitude models.