Water vapor observing apparatus

A water vapor observing system for calculating an amount of water vapor contained within atmospheric air, comprising:

• a transmitter circuitry configured to transmit a first transmission wave and a second transmission wave having different frequencies;
• a receiver circuitry positioned at a different position from the transmitter circuitry and configured to receive the transmission waves after passing through the water vapor as reception waves;
• and
• an arithmetic processor configured to calculate an amount of the water vapor in a passing area of the transmission waves based on a first reception information generated from a first reception wave obtained from the first transmission wave, and a second reception information generated from a second reception wave obtained from the second transmission wave, wherein
• the arithmetic processor calculates the water vapor amount in the passing area of the transmission waves based on a level difference between a first reception signal as the first reception information and a second reception signal as the second reception information.