Jökull - 01.12.1994, Page 23

between the L1 and L2 ambiguities), fixing the point
coordinates to the values calculated earlier. In the final
stage, the coordinates of the points and the L1 and L2
ambiguities were calculated using the L3, ionosphere-
free phase combination and the L5 ambiguities obtain-
ed earlier. These final results are the L3 ambiguity-
fixed solutions, called so because they are calculated
holding the L1 and L2 ambiguities fixed at integer val-
ues. In addition to coordinates, the formal (standard)
errors associated with each point coordinate for each
individual measurement are calculated from the phase
data scatter. In this paper we adopt the traditional,
geodetic definitions of measures of the quality of our
measurements (which may differ to some, more recent
usage of the terms e.g., Larson and Agnew, 1991), and
term these errors the precision of the results.
Since the sessions were often over 8 hours long
they were split into two and each part processed sepa-
rately. A different ionospheric model was used for
each half. The final coordinates were calculated by
performing a network adjustment using the program
NETADJ (Heki, 1992). This program solves for the
set of coordinates that minimises the weighted RMS
difference between them and those calculated for the
individual sessions. The weighted RMS scatter of the
measurements for each coordinate about the mean
value defines the repeatability of the coordinate re-
sults (Larson and Agnew, 1991). The repeatability
can, within one survey, give an idea, though not a pre-
cise evaluation, of the accuracy of that survey, i.e.,
how close the results are to the truth.
Point Núpafjall was held fixed so the errors we
calculate correspond to the positions of each point rel-
ative to Núpafjall. The formal errors in the individual
Observation Date, August 1991
Point 10 11 13 14 15 16 18 20 21 22 23 24 25 26 27
OS-7134 * * * * ******* * * * *
DU01 DU02 * * *
DU03 DU04 * * *
DU06 DU07 DU08 DU13 * * * * *
DU15 *
DU16 DU17 * *
DU18 *
DU20 *
DU21 *
DU22 *
DU25 *
DU26 *
DU27 *
DU28 *
DU30 *
NE-79-037 *
OS-1985-7331 *
S027 *
S001 *
S061 *
S056 *
Table 1 Point occupation schedule for the Hengill survey, 10-27 August 1991.
1. tafla. Dagatal staðsetningarmœlinga í öllum stöðvum á Hengilssvæðinu.
JÖKULL, No. 44
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