Question
For 3D-positioning, Global Navigational Satellite System (GNSS) requires a
minimum of ________ satellites.
The correct answer is
4
GNSS Satellites for 3D Positioning
Global Navigational Satellite Systems (GNSS), such as GPS, enable users to determine their location on Earth. To achieve 3D positioning, which includes latitude, longitude, and altitude, an additional factor must be accounted for: the precise time synchronization between the satellite signals and the receiver.
- Calculating a position in 3D space requires determining four unknown variables: the receiver's coordinates (x, y, z) and the receiver's clock error (t).
- Each GNSS satellite transmits signals that allow a receiver to calculate its distance (pseudorange) from that satellite.
- To solve for four unknowns, a minimum of four independent measurements are necessary.
- Therefore, a minimum of 4 satellites are required for GNSS to perform 3D positioning and accurate time determination. With fewer than four satellites, only 2D positioning (latitude and longitude) can be reliably determined, or 3D positioning with significant timing inaccuracies.
The minimum number of satellites required for 3D positioning using GNSS is 4.
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Important Questions from Principle Used
- The total irradiance on a Lambertian surface is $540 \text{ W m}^{-2}$. The reflectance of the surface is 20%. The path radiance from the atmosphere towards the sensor is $2.5 \text{ W m}^{-2} \text{ sr}^{-1}$. The transmissivity of the atmosphere is 80%. The radiance reaching the sensor is ________ $\text{W m}^{-2} \text{ sr}^{-1}$ (Rounded off to the nearest integer).
- Which one of the following is responsible for attenuation of the incoming solar radiation in the atmosphere?
- Part of the solar radiation incident on the water surface gets refracted as per
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