Dual-frequency GNSS positioning technology

In 2010-2012 there was developed and verified a new effective technology and the appropriate program modules of static and kinematic centimeter accuracy positioning by dual-frequency GPS observations. One of the main peculiarities of this technology is achievement of high reliability (90-100%) of carrier-phase ambiguity resolution in conditions of short samples of kinematic observations (15-60 sec) on long baselines (up to ~100 km) in OTF mode (On-The-Fly, i.e. without static initialization). The characteristics of the developed technology of dual-frequency differential positioning are adequate to the characteristics of the well-known foreign software of the similar purpose.

At present there is a great number of practical applications requiring for high precision positioning of mobile objects with centimeter accuracy. The existing technologies that allow providing kinematic positioning with the given accuracy in real time conditions are called RTK (Real Time Kinematic).

One of the most important criteria of the solution quality of high precision positioning (RTK) is criterion of the achievement of the minimal length (duration) of kinematic observations sample which is necessary for reliable carrier-phase ambiguity resolution (and for obtaining of so-called fixed-solution). The carrier-phase ambiguity resolution (CPAR) solution, i.e. correct estimation of integer carrier-phase ambiguities is a principle condition for obtaining of centimeter accuracy positioning since in case of wrong integer solution the errors of positioning may attain several decimeters.

With the purpose of increasing the reliability of CPAR the developed technology implies a three-stage procedure of processing [1]. At the first stage it is carried out smoothing/filtering of code observations by use of carrier-phase ones for obtaining the current estimations of coordinates of the mobile object with decimeter accuracy level that allows (according to the researches) to limit the area of the integer searching and to «improve» the minimized objective function in the CPAR processes. At the second stage it is carried out CPAR for the linear carrier-phase combination «Wide-Lane». Then in the equations of observations there are entered the corrections to the initial carrier-phase ambiguities of «Wide-Lane» combination. At the third stage there are determined the initial ambiguities on L1 and L2 carrier-phase observations after obtaining «Ionosphere-Free» CPAR solution. One may get acquainted in detail with the developed CPAR procedure in works [1,2].

For determining of the minimal length of observation sample necessary for the reliable carrier-phase ambiguity resolution there were carried out the appropriate tests by use of real pedestrian kinematic surveys, observations on-board the aircraft and helicopter during aerophotography at distance ~60-95 km (flying heights ~1-3 km). The results of the experimental researches (carrier-phase ambiguity resolution reliability dependence on observation sample length) are given in the table (see [1,2]).

Результаты экспериментальных исследований (зависимость надёжности РФН от размера выборки наблюдений) представлены в таблице (см. [1,2].).


Minimal sample length 60 sec 45 sec 30 sec 15 sec
Pedestrian 100% 96% 95% 89%
Aircraft 100% 100% 100% 99%
Helicopter *97% 95,5% 94% 92%

* - 100 % at sample of 90 sec length.


If CPAR is carried out correctly the errors of coordinate determinations do not exceed 1,5-3 cm in the horizontal plane and 3,5-5 cm in vertical direction [1-3].

The comparison of the obtained results with the results of estimations of the Ukrainian users using the foreign dual-frequency receivers of different manufacturers shows that the users on medium baselines (~100 km and more) achieve, as a rule, the reliable CPAR (fixed-solution) only by static initialization (OTF mode is not performed, as a rule) in the intervals from 1-2 min up to 5-7 min.

The obtained results exceed the foreign analogs and allow recommending the use of the created processing algorithms to realize them in the new developments for RTK positioning in the territories with sparse GNSS networks.


References


  1. Жалило А.А., Дицкий И.В. Усовершенствованный метод разрешения фазовой неоднозначности двухчастотных дифференциальных фазовых ГНСС наблюдений // Всеукраинский межведомственный научно-технический сборник «Радиотехника». – 2012, №169. – С. 277-301.
  2. Дицкий И.В, Бессонов Е.А., Жалило А.А., Желанов А.А. О возможности использования отечественных разработок для реализации технологий точного спутникового RTK-позиционирования на длинных базовых линиях // 8-а Міжнародна науково-практична конференція «Новітні досягнення геодезії, геоінформатики та землевпорядкування – Європейський досвід» – Випуск 8 – 2012, С. 64-66.
  3. Жалило А.А., Желанов А.А., Шелковенков Д.А., Дицкий И.В, Бессонов Е.А. Основные результаты разработок исследовательской группы ХНУРЭ/ГАО НАНУ в области высокоточного ГНСС-позиционирования в период с 2002-2011 гг. // Научно-технический и производственный журнал "Геодезия и картография". – 2012, №12, Москва, Россия. – С. 38-50.