Concept:
Remote sensing satellites are used to collect information about the earth surface and atmosphere from space.
Step 1: Identify the earliest operational satellite among options.
Among the given options, TRIOS/TIROS is considered the earliest operational remote sensing satellite series.
Step 2: Compare with other satellites.
NOAA, GMS and SPOT were later satellite systems used for weather and earth observation purposes.
Step 3: Final answer.
\[
\therefore \text{Correct Answer is (A)}
\]