(4) the geographic location (electron density levels are minimum in mid latitude regions
and highly irregular in polar, auroral, and equatorial regions).
8. Tropospheric Delay

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Tropospheric delays are primarily a factor of atmospheric pressure ,temperature and
humidity.

The troposphere is the electrically neutral atmospheric region that extends up to
about 50 km from the surface of the earth.

The troposphere is a non- dispersive medium for radio frequencies below 15 GHz.
it delays the GPS carriers and codes identically.

the measured satellite-to-receiver range will be longer than the actual geometric
range, which means that a distance between two receivers will be longer

Most receivers employ algorithms which reduce the tropospheric errors to less than
3 metres.

Tropospheric delay may be broken into two components, dry and wet.

Dry component represents about 90% of the delay and can be predicted to a high
degree of accuracy using mathematical models.

Wet component depends on the water vapor along the GPS signal path and is
difficult to measure.

The tropospheric delay is frequency independent

9.Satellite Geometry Measures
ഹ്‌ The overall positioning accuracy of GPS is measured by the combined effect of the

unmodeled measurement errors and the effect of the satellite geometry.

v In general, the more spread out the satellites are in the sky the better the satellite

geometry, and vice versa.

5. a) Name three segments — 1 mark, Explanation of three- 3x3=9)
GPS consists of three segments: the space segment, the control segment, and the user

segment.

Space segment:

٠ The space segment consists of the 24-satellite constellation.

Each GPS satellite transmits a signal, which has a number of components: two sine
waves (also known as carrier frequencies), two digital codes, and a navigation
message.

The codes and the navigation message are added to the carriers as binary biphase
modulations.