Guidelines for the use of GNSS in surveying and mapping

GPS (Global Positioning System)
The United States GNSS system.
GPS-ICD-200
The GPS interface control document is a US
government document that contains the full
technical description of the interface between the
satellites and the user. GPS receivers must comply
with this specification if they are to receive and
process GPS signals properly.
GPS week
GPS time started at Saturday/Sunday midnight on
6 January 1980 and the weeks are numbered from
that date, up to 1024 weeks. The first week
‘rollover’, the start of the next renumbering,
occurred on 21 August 1999.
Gravitational constant
The proportionality constant in Newton’s Law of
Gravitation is G = 6.672 x 10 -11 m 3 kg -1 s -2 .
Half-wave
Measurements made using L2 squared
measurements. The squaring process results in only
half of the original L2 wavelength being available, a
doubling of the original L2 frequency.
HDOP (Horizontal dilution of precision)
See DOP and PDOP.
Height – ellipsoidal
The distance above or below the ellipsoid
measured along the normal to the ellipsoid at that
point. Not the same as elevation above sea level.
GNSS receivers output position-fix height as the
height above the ITRS89 ellipsoid.
HOW (Handover word)
The word is the GNSS message that contains time
synchronisation information for the transfer from the
C/A code to the P-code.
IERS
International Earth Rotation Service.
Initialisation
The moment when a rover GNSS receiver in a high
precision real-time dynamic system (RTK) solves
the integer ambiguity and gains a real-time high
precision fixed baseline solution.
Integer bias search
The biases calculated in the float solution are fixed
to integers. A search is then undertaken to find
closely related sets of integers. These sets are
compared to the initial set by dividing the sum of
the squares of residuals of the trial set by that of
the original set. A strong data set allows only one
set of integers, and produces a ratio factor greater
than 3.0. A weak data set may accept several
different sets of integers with only small changes in
its sum of the squares fit, thus producing a small
ratio factor.
Integer bias terms
The receiver counts the radio waves from the
satellite, as they pass the antenna, to a high degree
of accuracy. However, it has no information on the
number of waves to the satellite at the time it
started counting. This unknown number of
wavelengths between the satellite and the antenna
is the integer bias term.
Integrated Doppler
A measurement of Doppler shift frequency of phase
over time.
Ionospheric delay
The ionosphere is a non homogeneous (both in
space and time) and dispersive medium. A wave
propagating through the ionosphere experiences
variable delay. Phase delay depends on electron
content and affects carrier signals. Group delay
depends on dispersion in the ionosphere as well,
and affects signal modulation. The phase and
group delay are of the same magnitude but
opposite sign.
ITRF (International terrestrial reference frame)
See Reference frame.
JPO
Joint Program Office for GPS located at the USAF
Space Division at El Segundo, California. The JPO
consists of the USAF Program Manager and
Deputy Program Managers representing the Army,
Navy, Marine Corps, Coastguard, National Imagery
and Mapping Agency (NIMA) and NATO.
Kalman filter
A numerical method used to track a time-varying
signal in the presence of noise. If the signal can be
characterised by some number of parameters that
68 | GUIDELINES FOR THE USE OF GNSS IN LAND SURVEYING AND MAPPING