SGD22-P01

Room:Convention Hall

Time:May 27 18:15-19:30

VLBI observation of multi-geostationary satellites in a same antenna beam II
KONDO, Tetsuro1∗ ; ICHIE, Yasuhide2 ; SATO, Eiji2
1

National Institute of Information and Communications Technology, 2 SKY Perfect JSAT Corporation

1. Introduction
On a VLBI observation of multiple geostationary satellites received in the same antenna beam, it is unable to separate eachsatellite independently by using a conventional processing system. In order to get each satellite delay we have improved thecorrelation software and delay search software to get observed delay. Improved software was evaluated by using laboratory
experiment data and true observation data as well. We could confirm that expected results were obtained.
2. Improvement of the software
The software correlator (K5 correlation processing software) was developed for geodetic VLBI system. It is therefore assumed
that white noises from a quasar are received and processed. On the other hand multiple narrow band signals are received in caseof a geostationary satellite observation. In this case a so-called ”delay resolution function” shows a comb-like form unlike thecase of white noises. In case of receiving signals from multiple satellites the delay resolution function becomes a combination offunctions for multiple satellites, and it is impossible to separate to each delay resolution function. However if frequencies differ
among satellites, it becomes possible to get a delay resolution function independently by filtering at either correlation processing
or delay search processing. Hence filtering function was implemented in the correlation software and the delay search software.
In addition, envelope interpolation function is also implemented in the delay search software for processing a comb-like form
delay resolution function.
Two kinds of filtering method are possible for correlation processing; one is filtering on the time domain and the other is on
the frequency domain. We have adopted the frequency domain filtering considering from reasons such as ease of both implementation and change of filtering characteristics. It has also been adopted to the delay search software.
3. Evaluations
In order to evaluate the function and performance of revised software, data processing was carried out by using laboratoryexperiment data and true observation data. A laboratory experiment was carried out using four signal generators (SGs) and a
4-ch sampler as follows. Two pairs of SGs simulate two satellites and signals are mixed each other. They are then fed to two
input channels of the sampler through coaxial cables with different lengths. An extra cable is applied between two pairs of SGs
to simulate the path difference of satellites. Sampled data are processed by revised software. By using a filtering function, delays
for simulated two satellites are successfully separated. Two cases of filtering, one is at correlation processing and the other is atdelay search processing, are compared. Observed delays are well-coincided with each other. The comparison was also carriedout by using true observation data, and it was confirmed that both results are well-coincided. It is also compared between thetwo delay search methods; one is a conventional way and the other is an envelope interpolation. Daily variation can be seen in
the difference between delays obtained by two methods, and peak-to-peak variation reaches a few hundred nanoseconds. Moredetailed evaluation should be made through the determination of satellite orbit.
4. Summary
A filtering function was implemented in the correlation software and the delay search software to get delay for each geostationary satellite independently under the condition that multiple satellite signals are received simultaneously. An envelope
interpolation function is also implemented in the delay search software for processing delay resolution function when it shows
a comb-like form. According to evaluations by using both laboratory experiment data and true observation data, it is confirmedthat improved software shows an expected performance. As for more detailed evaluation, it is necessary to carry out the determination of satellite orbit.

Keywords: VLBI, geostationary satellite

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