Pawel Maksym
Lodz, Poland
Nowadays, when we want to get to know what the geographic position
of our house, company etc. is, we only need to take in our hands a GPS
and we will get our position. We know how important it is for the observers
of occultations.
The standard receiver shows us with what exactness it works.
Usually it is signified by the abbreviations “acc” or “EPE”, for example
3.4 means that the position is given with the exactness of 3.4 metres.
However, we do not know if it is true! Perhaps the exactness
is different – smaller or larger. That is why the Department of Positions
and Occultations (DPO) of Polish Association of Amateur Astronomers has
decided to examine what the exactness of the measurements depends on and
if the results are true. To make such an “investigation” we need certain
tools, from the right program, through the equipment, to the information
of the GPS system and the way it works. For this type of research, we will
have to choose the right statistic method. Its choice depends on how much
material and of what type of quality we will have to do with. Nowadays,
three GPS receivers, connected to the computer 24 hours per day, take part
in the project. The computer records the working of the device.
After the right decoding of data, we will be able to calculate
what the real exactness of the measurement has been. Naturally, to confront
all the measurements with the geodesic measurements, all the data will
be calculated into the rectangular positions.
The project is also meant to check the working of many models
of GPS to find which are the most useful for the observers of occultations.
The right program supplied by lieutenant J.C. Kazyc from the NATO Navigation
Centre allows the simultaneous register of working of a GPS and of what
it shows. Next, the specially written for this purpose program for the
Mac computers sorts and analyses statistically the observations material.
The further job is done by a human. It is the interpretation of the results.
The initial results are relatively interesting because they indicate
the general tendency of receivers. The conclusions presented below come
from the analysis of 2983 hours of the material from the receivers Garmin
12, 12 CX and e-map De-lux.
The most frequent exactness shown on the display has been 5,1 metres.
After the analysis, we come to conclusion that the most frequent exactness
should be 4,8. After the accurate grouping of the material, it appears
that 83,7 % of measurements show distortion between 0.3 and 0.4 m and this
border is rather unlikely to lessen. It means that GPS should show 0.3
– 0.4 better exactness of almost 84 % of measurements.
As an interesting fact, it is worth mentioning that 61 times GPS receivers
have shown on the display the exactness 3.0 whereas they should have shown
approximately 2.8.
After more than two months of measurements, we can exclude the
hypothesis that the exactness depends on the generation of the GPS satellite,
which was suspected at the beginning. It was as if some satellites had
been working more efficiently but till today there have not been enough
materials to confirm it. We must admit that civil GPS receivers are very
precise devices, which show initial results of Polish measurements.
The next stages of the project will be: further collecting of
the measurements results and their analysis, comparing them to the geodesic
measurements (x,y) and trying to mathematically describe the devices behaviour.
I will be informing about the further results through the DPO
Materials and my own web site www.astromax.prv.pl.
I am planning to finish the work and to sum it up at the end
of October 2003.
I would like to thank:
M. Tivoli Ph.D. from Garmin Int. company
W. Kalinowski Ph.D. from University of Lodz
Lieutenant J.C. Kazyc
M. Borkowski M.A., director of Planetarium and Observatory of Lodz
Kamila Glinkowska from PAAA
and all those who have got involved in the project, especially members
of DPO
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