How's cloud height measured?

Answer 1

Unfortunately the method discussed in the previous answer doesn't offer much usefulness for stationary sensors, and can be difficult because clouds have different shapes.

I believe typical ASOS weather instrument packages use ceilometers. You can read more about them here: http://en.wikipedia.org/wiki/Ceilometer
To sum the idea up: We know the speed of light. So we send up a laser pulse and record the times when the beam is reflected back. Using distance = rate * time, we can then calculate the distance the beam travelled... which is the cloud height/2 (and since not all the beam is reflected, the receiver continues to get beam feedback until the top of the cloud, so we can also determine cloud depths and multiple cloud levels). Typical ceilometers only look straight up... so you may see it report clear outside when it hasn't been, if none of the clouds move directly over the instruments.
The method used by the ceilometer is pretty simliar to how a radar beam works to detect rainfall, we're just looking up instead of sideways.

It's been a while since my instruments class. I'm sure there are a few other methods... but I'm pretty sure this is the primary one used in the daily weather data we see.

Hope I helped!

Answer 2

There are various ways of estimating and measuring the height of the cloud base. All trained meteorological observers are taught to estimate heights using the mark one eyeball and most cloud heights are so estimated.

Aircraft flying through cloud will report the cloud base if asked and you can also track a balloon into cloud measuring the base that way. In Australia, cloud base searchlights are still used at night on some airfields - a spotlight is shone on the cloud and the angle from a fixed observing point to the light spot on the cloud is measured with a clinometer. This angle gives the cloud height.

There are ceilometers which record cloud heights electronically and these are found at major airfields.

Finally, a quick estimate for convective cloud can be made from the dew point depression. Subtract the dewpoint from the dry bulb temperature to get the DP depression. Multiply this figure by 400feet to get the cloud base. Thus temperature 22°C, Dewpoint 15°C, cloud base 7 X 400ft = 2800ft.

Answer 3

I don't know if this method is actually used to measure clouds. But this is a method to measure altitude of any point, from the ground level.

- Locate a specific point/region in the cloud (by shape).
- From your current location measure its angle of elevation. [ a simple hollow cylindrical tube with a protractor and a pendulum attached at its midpoint can be used to measure an elevation ]
Call it A1 degrees.
- Walk a significant distance towards the marked point, on the ground, a measured distance, D meters.
- Measure the elevation again: A2 degrees.

Now use the trigonometric relations and solve for h, height of
the desired point. Denote the distance on the ground, of the cloud's position, from your initial location, as x.

tan(A1) = h/x ; x = h*cot(A1);
tan(A2) = h/(x-D); x = h*cot(A2) + D;
Hence, h = D/[cot(A1) - cot(A2)]

Not only, the cloud, you can measure height of a mountain or a building or anything, provided it doesn't move during the time you walk the distance, D.

Answer 4

Just do it the lazy way, find a high tech radar that scans the storms from the base to th top of it. However, typically, they measure to around 25,000 ft. during all times of the year. So when a top doesn't have pileus clouds sticking out of the top of it, chances are thres no lighting with the cloud.