In a new measurement, China and Nepal have announced Mount Everest is 86 cm taller than the 8,848 m accepted globally so far.
How the height of a mountain is measured?
The basic principle that was used earlier uses only trigonometry.
This principle can be applied for measuring the height of any object that does not offer the convenience of dropping a measuring tape from top to bottom, or if you can’t climb to the top to use sophisticated instruments.
So, if the distance from the point of observation to the building is d and the angle of elevation is E, then the height of the building would be d × tan(E).
Starting in 1952, the Survey of India undertook an exercise to measure the height of Mount Everest.
That exercise measures the height at 8,848 m (29,028 feet), which remained the globally accepted standard, until now.
What are the problems with this method of measurement?
The main problem is that though you know the top, the base of the mountain is not known. The question is from which surface you are measuring the height. Generally, for practical purposes the heights are measured above mean sea level (MSL).
Moreover, we need to find the distance to the mountain. Now, it is possible with the help of satellite.
One of the problems is whether the point of observation and the base of the mountain are at the same horizontal level.
There is one additional problem is gravity. Gravity is different at different places. In the case of Mount Everest, for example, the concentration of such a huge mass would mean that the sea level would get pulled upwards due to gravity. So, the local gravity is also measured to calculate the local sea level.
The variation in air density causes the bending of light rays, a phenomenon known as refraction. Due to the difference in heights of the observation point and the mountain peak, refraction results in an error in measuring the vertical angle. This needs to be corrected. Estimating the refraction correction is a challenge in itself.
What are the present technological solutions?
These days GPS is widely used to determine coordinates and heights.
Overhead flying planes equipped with laser beams (LiDAR) can also be used to get the coordinates.
What are the problems with the newer technologies?
GPS do not take gravity into consideration. So, the information obtained through GPS or laser beams is then fed into another model that account for gravity to make the calculation complete.
What could be the reasons behind the increment?
The techniques used to measure the height.
It is believed that the height of Mount Everest is increasing at a very slow rate. This is because of the northward movement of the Indian tectonic plate that is pushing the surface up.
