How is atmospheric moisture measured? Explain the principle of operation of the two most widely used instrumen

Question

What factors cause relative humidity to change?

Why is dewpoint temperature a better indicator of atmospheric moisture?

If the weather forecaster at 10:00 PM states that "the relative humidity has increased to 85% from the 65% relative humidity measured at 6pm” discuss what this statement may mean. Hint: The air in the evening usually cools down.

Summarize the processes by which water changes from one state to another. Indicate whether heat energy is absorbed or released.
on a cold winter day, when the temperature is –10°C and the RH is 50 percent, what is the total amount of water vapor in the air (also called the saturation mixing ratio)?
determine the RH and Td if the dry-bulb thermometer reads 16°C and the wet-bulb thermometer reads 12°C. Next, determine what the RH and Td would be if the dry bulb reads 16°C and the wet-bulb thermometer reads 8°C.

write a statement relating temperature and the capacity of the air to hold moisture.

Answer 1

Wow, you want it all.
Taking just your primary question
Sling thermometer and chilled mirror
If a thermometer (thermocouple, thermister, etc.) is provided with a wet cloth cover and exposed to moving air via a fan or by slinging the thermometer around the head, it will produce a temperature reading lower than the still air temp due water evaporation. The less moisture in the air, the lower the temp, giving the dew point. A table can be used to give relative humidity.
A metal mirror is provided with a method of chilling it in a controlled way, today this is done with an electronic thermopile that chills on one side and heats on the other. A sensor observes the light reflected off the metal mirror and when the moisture condensing on the mirror changes the light, the measured temp of the plate is the dew point.
Humidity can also be measured as it has for hundreds of years, by using a hair which changes length with humidity and pulls around a needle and at the other extreme by the modern method of a semiconductor covered with a material that changes resistance or capacitance depending on the moisture in the air, thus allowing direct electronic measurement used in modern instruments.