Saugus‐Palmdale, California, field test for refraction error in historical leveling surveys

Abstract

A field test designed to measure atmospheric refraction error in historical and modern leveling was conducted in May–June 1981 on a 50‐km‐long grade from Saugus to Palmdale, California. During 1955–1971, the length of sights made between the level instrument and rods systematically decreased from 60 m to 26 m. The difference in height near Palmdale measured by single‐run long‐sight (42‐m) and short‐sight (22‐m) leveling during the test was 6 times larger than expected random error. Correction for refraction by using either the observed or modeled vertical temperature gradient in Kükkamaki's balanced sight equation reduced the height difference to the level of random error uncertainty. The observed temperature gradient obeyed a power law relation, T = a + bzc, where z is the height and a, b, and c are constants that depended on atmospheric conditions and the ground surface beneath the line of sight. The refraction‐corrected leveling satisfies the specifications and meets all standards of first‐order control surveys. The six historical surveys of the Saugus‐Palmdale grade were corrected for refraction error using the results of the experiment and for rod scale errors and nontectonic subsidence considered in previous investigations. The corrected uplift near Palmdale reached 56 ± 16 mm with respect to Saugus during the period 1955–1965. This amount of uplift is about one third that obtained before removal of refraction error. The corrected displacement profiles also reveal previously unrecognized deformation in the epicentral region of the 1971 San Fernando ML = 6.4 earthquake during the decade before the main shock.

Vertical surface displacements at Yellowstone Caldera, Wyoming, 1976–1986

“…The preferred sequence is backsight low, foresight low, foresight high, backsight high (which provides a closure check for each setup). The first procedure is faster but increases the chance of errors owing to movement of the tripod or rods during setups [Stein et al, 1986]. No such errors were detected by double running 43 sections in 1983 and 1984, but the departure is noted nonetheless.…”

Uplift of the Western Transverse Ranges and Ventura Area of Southern California: A Four‐Technique Geodetic Study Combining GPS, InSAR, Leveling, and Tide Gauges

“…Interferometric synthetic aperture radar (InSAR) data complement GPS, providing blanket coverage, but suffer from errors in long-wavelength deformation owing to uncertainties in orbits, refractivity of the troposphere, topographic effects, and difficulties in unwrapping of phase (Chen & Zebker, 2000;Bürgmann et al, 2000;Massonnet & Feigl, 1998). Terrestrial leveling data also constrain VLM along dense lines usually surveyed along highways but suffer from atmospheric refraction and monument noise (Stein et al, 1986;Strange, 1981). Conversely, tide gauge records are sensitive to VLM and have stable records, in some cases nearly a century long, but they use as a reference the mean surface of the ocean and hence are impacted by uncertainties in global mean sea level rise and oceanographic changes (e.g., Burgette et al, 2009;Wöppelmann & Marcos, 2016).…”

On the Use of Repeat Leveling for the Determination of Vertical Land Motion: Artifacts, Aliasing, and Extrapolation Errors

“…Atmospheric refraction is considered the most complex source of systematic error affecting leveling observations (e.g., Angus-Leppan, 1979;Breznikar & Aksamitauskas, 2012;Holdahl, 1981;Kukkamäki, 1938Kukkamäki, , 1939Shaw & Smietana, 1983;Skeivalas, 2005;Stein et al, 1986;Strange, 1981). The variability of atmospheric conditions within and between each epoch of a repeat leveling campaign has the potential to introduce artifacts into the resulting time series.…”