Wavelengths round trip distance geodimeter geodetic

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: e light and was capable of accurately observing distances up to 40km at night. • Tellurometer transmitted microwaves and was capable of observing distances up to 80km more, day or night. • Accuracies of ±(1-3)mm can be achieved by today’s instruments. • In the current generation, EDM are combined with digital theodolites and microprocessors to produce total station instruments. Eo Y. D., Department of Technology Fusion, copyright® Electronic Distance Measurement(2) • Principle (Maxwell’s equation) – λ=V/f λ: electromagnetic wavelength, V: velocity of EM energy V=C/n( C= vacuum 299,792,458m/sec, n: refraction index) f : modulated EM frequency(Hz) Correction is necessary since the velocity of electromagnetic waves is necessary since the velocity of electromagnetic waves in air is influenced by air temperature and air pressure 1 (nλ + P ), P = Δφ ° λ 2 360° Δφ ° : 위상차 L= n : 완전한 파장의 총수 λ : 기준 전자파의 단위파장의 길이 P : 파장하나의 완전한 길이가 되지 못하는 소수부분의 파장 Eo Y. D., Department of Technology Fusion, copyright® Electronic Distance Measurement(3) • Electro-Optical instrument – Using infrared rays (relatively short distance) and lasers as medium electromagnetic waves – Mostly for short distances ranging from m to Km – Modulated electromagnetic wave leaving the EDM and being reflected (light electromagnetic wave leaving the EDM and being reflected (light waves) or retransmitted (microwaves) back to the EDM. : reflected on prism or spatial feature – Velocity of light (including infrared) through the atmosphere can be affected of light (including infrared) through the atmosphere can be affected by (1) temperature (2) atmospheric pressure (3) water vapor (4) fog (5) dust etc. – In practice, the corrections for temperature and pressure can be performed manually or automatically on some EDM by the on-board processor/calculator ll EDM th after the values for temperature and pressure have been entered. – Quite a few are fixed to Total station – precision: ±(1mm+1ppm) ~ (10mm+5ppm) Eo Y. D., Department of Technology Fusion, copyright® Electronic Distance Measurement(4) • Total Station Instruments – (also called electronic tacheometers) combine an EDM instrument, an electronic digital theodolite, and a computer in one unit. – Automatically measure horizontal and zenith angles, as well as distances, and transmit the results in real time to a built-in computer. – Tracking mode (stakeout) – Distance range of approximately 3 km (single prism) with an accuracy of ±(2mm+2ppm) – Nowadays, most of surveying methods dependent on TS. – With time-pulsed infrared laser signals, distances up to 100m can be observed in reflectorless mode. (ex, LEICA DISTO) – ※ Reduction of Short Lines by Elevation Differences. Eo Y. D., Department of Technology Fusion, copyright® Errors in EDM • Accuracies of EDM are quoted in two parts : a constant error and a scalar error proportional to the distance measured. • The constant error is most significant on short distances. For a long distance, the constant error becomes negligible and the proportional part more important. • where, Ei is the estimated miscentering error in the instrument; Er is the estimated miscentering error in the reflector; Ec the specified constant error for the EDM; ppm the specified scalar error for the EDM; and D the measured slope distance. Eo Y. D., Department of Technology Fusion, copyright® Errors in EDM • Personal Errors – Inaccurate setups of EDM instruments and reflectors over stations setups of EDM instruments and reflectors over stations – Errors in determining atmospheric pressures and temperatures. – Mistakes in manually reading and recording displayed distances are common and costly. • Instrumental Errors – Reflector constant, system measurement constant • Natural Errors – Primarily from atmospheric variations in temperature, pressure and humidity, from atmospheric variations in temperature pressure and humidity which affect the index of refraction and modify the wavelength of electromagnetic energy. Eo Y. D., Department of Technology Fusion, copyright®...
View Full Document

This note was uploaded on 09/27/2013 for the course AEROSPACE 202 taught by Professor Hsu during the Fall '13 term at ASU.

Ask a homework question - tutors are online