Make use of microwaves.

Such instruments were invented as early as1950 in South Africa by Dr. T.L Wadley andnamed theam as Tellurometers.

The instruments need only 12 to 24 V batteries.

They are light and highly portable.

Tellurometers can be used in day as well as innight.

The range of these instruments is up to 100km.

It consists of two identical units. One unit isused as master unit and the other as remoteunit.

In these instrument amplitude modulatedinfrared waves are used.

Prism reflectors are used at the end of line to bemeasured.

With these instruments accuracy achieved is +/10mm.

800m1km (singe prism)

The range of these instrument is up to 3km.

These type of instrument was first developed inSweeden and was named as Geodimeter

During night its range is up to 2.5 km while inday its range is up to 3 km.

Accuracy of these instrument varies from 0.5mm to 5mm / km distance.

These instruments are also very useful for civilengineering projects.

operate instrument to measure the distance

an EDM is set over one point and a prism overthe other

at a trial distance, measure a slopedistance.(convey this information to chainmanby hand signal or radio)

then move the prism to a new trial position.(when the prism is within 23m of its requireddposition, compute a horizontal distance)

measure the difference between trial andrequired position with a tape and move theprism to the new position

the distance can be checked and the groundmarkd as required.

proceed to measure the slope distance

with basic EDM the difference in height iscalculated from (slope distance x sine of verticalangle)