- 2081 Baisakh · 4 marks
EDM classification; electromagnetic energy
Short answer
EDM is classified by carrier: microwave (Tellurometer), visible light (Geodimeter), infrared (total stations), and laser (reflectorless). Electromagnetic energy propagates at known speed, can be modulated, reflected by prisms, and its velocity varies with the atmosphere, so temperature, pressure and humidity corrections are needed.
Write the classification of EDM and the significance of electromagnetic energy.
Classification of EDM
EDM instruments are classified according to the type of carrier wave used.
| Type | Carrier | Range | Example/use |
|---|---|---|---|
| Microwave | Radio waves (3 to 30 GHz) | 30 to 100 km | Tellurometer (large control surveys). Needs a master and a remote unit; works in any weather |
| Light-wave (visible) | Modulated visible light | 2 to 5 km (day), more at night | Geodimeter. Needs a reflector prism |
| Infrared wave | Modulated infrared | 1 to 5 km | Distomat, most total stations; used with prisms |
| Laser (reflectorless) | Laser beam | Up to about 1 km without a prism (several km with a prism) | Measures directly to walls, rock faces and other surfaces without a prism |
By measuring principle: pulse method and phase-comparison method. By range: short (up to 5 km), medium (5 to 100 km), long (more than 100 km).
Significance of electromagnetic energy
- EM waves travel at a very high, known velocity ( m/s in vacuum, in air), so measuring the time or phase gives the distance: .
- They travel in a straight line and can be reflected by a prism, which allows round-trip measurements.
- A carrier can be modulated (in amplitude or frequency) so that the wavelength and phase can be measured precisely.
- The velocity changes with the atmosphere (temperature, pressure, humidity), so these are measured and used for correction.
- Different parts of the spectrum give different ranges and weather behaviour, e.g. microwaves pass through haze and rain while light needs clear visibility.
✓ Answer checked by Claude Opus 5.5 (high effort)
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