Question

The Indian Remote Sensing Satellites (IRS)
A. look over a fixed point at the same local time
B. are at a low altitude ($<$ 1000 km)
C. are used for weather forecasting
D. have large agricultural and natural resources applications
E. provide service to telecommunications
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A, B and C only
• C. B, D and E only
• D. A, D and E only

Hint:

Remember the 2 Main Families of Indian Satellites:
IRS = Resource/Land/Agricultural Mapping (Low Polar Orbit).
INSAT = Weather/Communication/TV (High Geostationary Orbit).
Sun-synchronous means "Same Sun Angle" every time.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify the correct operational and functional characteristics of the Indian Remote Sensing (IRS) satellite series.
Detailed Explanation:

• Orbit and Altitude (Statements A and B):
IRS satellites are placed in Sun-Synchronous Polar Orbits (SSPO).
A Sun-synchronous orbit ensures that the satellite passes over any given point of the Earth's surface at the same local solar time. This is crucial for remote sensing because it ensures consistent illumination conditions (sun angle) for comparing images taken over time.
These are "Low Earth Orbit" (LEO) satellites, typically operating at altitudes between $700$ km and $900$ km, which is well below the $1000$ km threshold mentioned.

• Applications (Statement D):
The primary purpose of the IRS series is Earth observation.
They provide high-resolution data for crop acreage and yield estimation, drought monitoring, forest cover mapping, groundwater targeting, and land use planning.

• Incorrect Statements (C and E):
Weather Forecasting: While some polar satellites help, primary weather forecasting and "Continuous" monitoring in India are done by the INSAT (Indian National Satellite System) series in Geostationary orbits ($36,000$ km).
Telecommunications: This is exclusively the domain of Geostationary satellites (INSAT/GSAT) because they stay fixed relative to a point on the ground, allowing for constant signal transmission. IRS satellites move too fast across the sky for TV or phone signals.

Step 2: Final Answer:
Statements A, B, and D correctly describe the IRS system, while C and E describe the INSAT/Communication systems.