This question requires identifying the correct statements about Global Navigation Satellite System (GNSS) errors. Let's analyze each statement:
GNSS Error Statement Analysis
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Statement 1: Tropospheric delay increases with increasing relative humidity.
This statement is CORRECT. The troposphere, the lowest part of Earth's atmosphere, contains water vapor. Higher relative humidity indicates more water vapor, which significantly increases the signal delay experienced by GNSS signals as they pass through.
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Statement 2: Ionospheric error is highly correlated with the position of the Moon.
This statement is INCORRECT. Ionospheric error is primarily caused by the interaction of GNSS signals with charged particles (electrons) in the ionosphere. This error is mainly influenced by solar activity, time of day, and season, not the Moon's position.
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Statement 3: Multipath error is caused by buildings and man-made features and not by vegetation.
This statement is INCORRECT. Multipath error occurs when satellite signals reflect off surfaces before reaching the receiver. While buildings and structures are major contributors, dense vegetation, water bodies, and even aircraft can also cause signal reflections, leading to multipath effects.
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Statement 4: The observed range is called as pseudorange because of its erroneous nature.
This statement is CORRECT. The range calculated directly from the time-of-flight of a GNSS signal is termed 'pseudorange'. It's called 'pseudo' because it includes errors from various sources, such as satellite/receiver clock offsets, atmospheric delays (tropospheric and ionospheric), and ephemeris errors. It is not the true geometric range.
Conclusion on GNSS Errors
Based on the analysis, statements 1 and 4 are correct descriptions of GNSS errors.
Important Questions from Errors in Observations
The carrier phase observation model in GNSS is given as $$ \phi_A^i = f \delta^i - \frac{\rho_A^i}{\lambda} - f \delta_A + N_A^i - f \delta_{\text{iono}} + f \delta_{\text{tropo}} + \epsilon $$ where $\phi_A^i$ is the observed carrier phase in cycles, $f$ is the frequency of the carrier in hertz, and $\lambda$ is the wavelength of the carrier in meters.
What is the unit of the ionospheric ($\delta_{\text{iono}}$) and tropospheric ($\delta_{\text{tropo}}$) delay terms in the given equation?- In GNSS positioning, the cycle slips are the most detrimental for estimating _______.
- According to the first order ionospheric delay term, the time delay experienced by the GNSS signal is directly proportional to the Total Electron Content (TEC) in the ionosphere, and inversely proportional to the square of the frequency of the carrier wave. Based on this, the GPS L2 (1227.60 MHz) carrier is slower than the GPS L1 (1575.42 MHz) carrier by a factor of ________ for a given TEC (Rounded off to the nearest integer).
- In the context of Global Navigation Satellite System positioning, the Saastamoinen model provides a correction for ________.
- In the choke ring antenna there are concentric cylinders placed around the antenna that are of a certain depth to minimize the multipath effect. If the signal wavelength is $\lambda$, then the depth of the cylinders in the choke ring antenna should be
