Subject: [IGSMAIL-2614] GLONASS/GPS publication
From: H. Habrich
Date: Wed, 8 Dec 1999 1:14:55 PST

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IGS Electronic Mail      Wed Dec  8  1:14:55 PST 1999      Message Number 2614
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Author: H. Habrich
Subject: GLONASS/GPS publication

Dear Colleagues,

please note that a pdf-file (Adobe Acrobat format, use Acrobat Redaer 4.0) of
my dissertation (supervised by Gerhard Beutler and Markus Rothacher) entitled

   "Geodetic Applications of the Global Navigation Satellite System
    (GLONASS) and of GLONASS/GPS Combinations"

is available at BKG's ftp-server from

   ftp://igs.ifag.de/dist/habrich_glonass.pdf .

Attached is an Introduction to this work.

Kind regards,

Heinz Habrich

--------------

The GLObal NAvigation Satellite System or GLObal'naya NAvigatsionnaya
Sputnikovaya Sistema (GLONASS) is a satellite-based radionavigation system
which enables the user to obtain three dimensional position and velocity
vectors and timing information anywhere on or near the Earth's surface. It is
operated by the Ministry of Defence (Russian Space Forces) of the Russian
Federation. There are several other global positioning systems like TRANSIT,
DORIS or PRARE, but the concept of GLONASS may be best compared with the
NAVSTAR Global Positioning System (GPS) developed by the U.S. Department of
Defence. GLONASS was developed for military navigation purposes and timing
needs. But by decree of March 7, 1995, the government of the Russian
Federation confirmed to put the system at the disposal of military and civil
users. GLONASS is used for navigation and geodetic applications by civil
users.

In this work we deal with geodetic applications of GLONASS and also with the
combined processing of GLONASS and GPS data. The combination of both, GLONASS
and GPS observations, leads to an improved reliability of the resulting
products due to the usage of two autonomous systems. Furthermore the
additional satellites contribute to shorter observation sessions for, e.g.,
ambiguity resolution in real-time kinematic (RTK) applications. RTK
applications are not addressed here.

The first Chapter reviews the components of  the GLONASS, in particular the
space, control, and user segments. The satellite signal structure transmitted
on the L1 and L2 frequencies are described and compared to that of GPS. The
most important difference is the use of satellite-specific frequencies by
GLONASS satellites. The definition of the GLONASS reference frame PZ-90 and
the system time as defined in the interface control document [ICD, 1995] are
discussed. The satellite positions, velocities, and accelerations for every
30 minutes are included in the navigation message and may be used to
calculate the satellite position for a current epoch using formulas given in
[ICD, 1995].

The observation equations for GLONASS observables are introduced in
Chapter 2. They are similarly to those of GPS except for the satellite-
specific GLONASS frequencies. A "new" single difference bias term remains in
the double difference phase observable. Its size depends on the wavelength
difference of the two satellites and is not present in case of GPS. Chapter 3
deals with the pre-processing of GLONASS phase observations. Cycle slips have
to be detected on the single difference level and assigned to the correct
satellites because of the single difference bias term.

An ambiguity resolution approach for processing GLONASS double difference
phase observations is described in Chapter 4. The single difference bias term
destroys the integer nature of the ambiguities for observations referring to
satellite pairs with large differences in the carrier wavelengths, whereas
the ambiguities for satellite pairs with small wavelength differences may be
resolved easily. Our ambiguity resolution algorithm successively resolves
the ambiguities for all satellite pairs starting with satellite pairs with
small wavelength differences. This approach is appropriate for long
observation sessions and long baselines. In order to combine GLONASS and GPS
a unique time scale for the observations and a unique reference frame for
the satellite and receiver positions are required. Chapter 5 shows
explicitly how the two requirements can be met. The new ambiguity resolution
algorithm may also be used for GPS and combined GLONASS/GPS observations.

Results for short baselines are discussed in Chapter 6. In this case detected
cycle slips and real-valued estimates for the ambiguities are close to
integer numbers. Observations stemming from the International GLONASS
Experiment (IGEX-98) were processed following our routine processing scheme
which is explicitly shown in Chapter 7. Our analysis results include
improved orbits for GLONASS satellites, system time differences between the
GLONASS and the GPS, and transformation parameters between the PZ-90 and the
ITRF terrestrial reference frames.

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