A multiwavelength distance-measuring instrument for geophysical experiments

Abstract

A multiwavelength distance-measuring (MWDM) instrument that utilizes the dispersive nature of the atmosphere has been developed and tested. With this instrument there is no need for the usual meteorological observations and corrections. This MWDM instrument simultaneously measures the optical path length at three wavek/ngths, two in the optical region of the spectrum and one in the microwave region. The instrument calculates correction terms from the optical path length differences and then computes the corrected base line distance, the first-order effects of temperature, pressure, and water vapor fluctuations along the line thus being eliminated. Field testing demonstrated that the instrument was capable of making consecutive distance determinations with a standard deviation from the mean as small as 4 parts in l0 s. The long-term stability of the instrument was investigated from June 1974 to November 1974. The results showed a standard deviation of 1.3 parts in 107 when the data were fit to a sine wave of annual periodicity. The amplitude of this sine wave was 3 parts in 107, which was in good agreement with the predicted results of a two-dimensional t, hermoelastic model. o d c• i I ß ß ß ß ß ß ß 'l ß ß ß ß ß l' ß ß I. ß ß ß e e ß ß ß '.l ß ß ß ß ß .I t (•u •u) 30NV.L$10 SLATER AND HUGGETT: A MWDM INSTRUMENT

Correlated errors in geodetic time series: Implications for time‐dependent deformation

“…The standard deviations of the residuals range from 0.7 mm for a 3-kin-long baseline to 1.5 mm for an 8-km line. These standard deviations are derived from 15 years of observations and are small by geodetic standards, but they are still a factor of 2 greater than the precision of the two-color technique based upon physical and engineering constraints [Slater and Huggett, 1976] and other analyses of the data [Langbein et al, 1987].…”

“…With respect to a time-dependent source in the instrument precision the most likely source is the psychrometer used to measure the partial pressure of water in the atmosphere. For the two-color EDM technique the measurement of the water vapor is the most critical parameter needed to achieve the best precision [Slater and Huggett, 1976;Langbein et al, 1987], and possible drift in the thermometers along with changing the psychrometer over time could contribute to the length-dependent term for the random-walk noise.…”

Monitoring unrest in a large silicic caldera, the long Valley-inyo craters volcanic complex in east-central California

“…Twenty-two of the stations are operated by the U.S. Geological Survey, four by the University of Nevada at Reno, and six by the California Division of Mines and Geology (solid circles, open squares and triangles, respectively in Fig. 2)+ These stations were installed beginning in mid-1982 to supplement the regional seismic network covering western Nevada and east-central California, which has been operated by the University of Nevada, Reno, since 1975(SMITH and RYALL, 1980, 1982. The stations in this dense Long Valley network are of the same type as those used in the central California Seismic Network operated by the U.S. Geological Survey in Menlo Park, California (Eaton, 1977 oscillator (VCO) and pre-amplifier.…”

“…The earliest leveling measurements in the Long Valley region date back to a 1905 survey along Higway 395 (Line 1). Subsequent surveys along this section of Highway 395 were completed in 1914, 1932, 1957, 1975, 1982. Lines 3 and 6 within the caldera were established in 1975 (DENLINGER and RILEY, 1984) and the remaining lines were established in the surnmer of 1982 (see Fig.…”

The Loma Prieta, California, earthquake of October 17, 1989: Aftershocks and postseismic effects

“…The instrument used to measure the baseline lengths is a portable, two-color geodimeter (Slater and Huggett, 1976), with a nominal precision between 0.4 mm and 0.9 mm for lengths between 2 and 7 km (Langbein, 1989). For distances of less than 10 krn, this instrument has at least a factor of three better precision than any other geodetic techniques (Savage and Prescott, 1973;Prescott and others, 1989a).…”