Exp) Option d is the correct answer.

GAGAN is the acronym for GPS Aided GEO Augmented Navigation. The GAGAN uses a system of ground stations to provide necessary augmentations to the GPS standard positioning service(SPS) navigation signal. GAGAN is jointly developed by the Indian Space Research Organisation (ISRO) and the Airports Authority of India (AAI).

Statement 1 is correct. GAGAN is India’s satellite-based augmentation system (SBAS). The SBAS is a navigation system, which builds on the Global Navigation Satellite Systems (GLONASS), and adds to the accuracy and integrity of these navigation tools. For aircraft operators, both civilian and military, it means that pilots can land aircraft at smaller airports and airstrips using navigation guidance without expensive instrument-based landing systems being installed on the ground.

Statement 2 is correct. The GAGAN is designed to provide the additional accuracy, availability, and integrity necessary to enable users to rely on GPS for all phases of flight, from en route through approach for all qualified airports within the GAGAN service volume. GAGAN also provides the capability for increased accuracy in position reporting, allowing for more uniform and high-quality Air Traffic Management (ATM).

Statement 3 is incorrect. GAGAN provides benefits beyond aviation to all modes of transportation, including maritime, highways, and railroads.

Source: https://www.aai.aero/en/content/what-gagan

https://www.thehindu.com/sci-tech/science/global-positioning-system-relativity-gnss-navic-explained/article67606417.ece

https://indianexpress.com/article/business/aviation/in-a-first-indigo-uses-indian-navigation-system-to-land-aircraft-7892360/