Die Lichtstrahlkrümmung in Bodennähe

Brocks, Karl

doi:10.1007/bf02026796

Cited by 8 publications

(9 citation statements)

References 2 publications

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“…It vanishes for a temperature gradient of -3. 42°C/l00 m [Brocks, 1950]. For higher values, K becomes negative, that is, the light ray will be bent concavely upward, opposite to the curvature of the surface of the earth.…”

Section: Refraction In a Plane Stratified Mediummentioning

confidence: 99%

Optical scintillation:

Meyer‐Arendt¹

1965

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Section: Refraction In a Plane Stratified Mediummentioning

confidence: 99%

Optical scintillation:

Meyer‐Arendt¹

1965

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“…In order to achieve values of about 200 prad for r, which is roughly ten times the estimated standard error of r, the instrument heights (and thus also 5) were chosen as 1.0 to 1.2 m. This r value was estimated using the tables of Brocks (1950), for which the required input information are the length of sight line, the observation time, and the expected weather conditions at the time of the experiment. The actual average height above the ground h was determined by conventional surveying methods as 1.16 m in the field.…”

Section: Descriptionmentioning

confidence: 99%

Determination of line averages of sensible heat flux using an optical method

Brunner

1982

Boundary-Layer Meteorol

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An optical method is discussed for the determination of the line average of the vertical temperature gradient, which is subsequently used for the calculation of the scaling temperature and of the sensible heat flux. The method requires conventional surveying instrumentation only, and the measurements are carried out easily. The attainable accuracy is estimated as 10% or better. Observations are also possible during night or light-wind conditions. In a field experiment, results from this optical method were compared with measurements taken with a conventional covariance eddy-flux instrument. Excellent agreement between both methods was found.

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“…[3] In geodesy, the coefficient of refraction k represents a common way to quantify terrestrial refraction. It may be defined as the ratio of the radius of the Earth R and the radius of the line of sight r, i.e., the radius of a circular arc used as a mathematical model to approximate a complex curved path of light [e.g., Brocks, 1950a;Kahmen and Faig, 1988]. On the basis of reciprocal vertical angle measurements near Hannover (Germany), Carl Friedrich Gauss found an average value of the refraction coefficient k of approximately +0.…”

Section: Introductionmentioning

confidence: 99%

“…[4] The Gaussian refraction coefficient, though often suitable to describe refraction effects well above the ground, is not representative for the lower atmosphere [e.g., Brocks, 1950aBrocks, , 1950bBomford, 1980]. This region involves the surface layers to a height of about 30 m [Webb, 1984] and, importantly, includes the near-ground domain in which optical geodetic measurements are often carried out (e.g., geometric levelling in general and trigonometrical heighting in flatter regions).…”

Section: Introductionmentioning

confidence: 99%

“…Here, the temperature of the air strata, particularly its vertical temperature gradient, is strongly influenced by daily variations in the surface temperature. This may result in either negative or positive values of the refraction coefficient k near the ground with differences to the Gaussian value as large as two orders of magnitude [e.g., Brocks, 1950aBrocks, , 1950bHübner, 1977;Eschelbach, 2009].…”

Section: Introductionmentioning

confidence: 99%

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Monitoring of the refraction coefficient in the lower atmosphere using a controlled setup of simultaneous reciprocal vertical angle measurements

Hirt¹,

Guillaume²,

Wisbar³

et al. 2010

J. Geophys. Res.

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[1] A great deal of empirical studies have investigated the characteristics of terrestrial refraction. However, only few of these are concerned with short-term fluctuations of refraction influences. The aim of the present work is to analyze the short-term characteristics (amplitudes and variations at scales of minutes to hours) of terrestrial refraction in the lower atmosphere around 1.8 m above the grass surface. We apply the known method of simultaneous reciprocal vertical angle measurements to derive time series of the refraction coefficient k as a measure for refraction. Our study uses a new setup of two pairs of total stations for parallel observations of the refraction coefficient along adjacent lines of sight. Such a controlled experiment not only allows us to determine refraction coefficients independently but also to assess measurement errors from the residuals between refraction coefficient pairs. Over five observation days in the summer of 2008, a total of 33 h of parallel observation data of the refraction coefficient were collected at sampling frequencies of 1 min. On one observation day, unique parallel observations of the refraction coefficient along three lines of sight with a total of six total stations were possible. For mostly sunny days, we found wave-like and sawtooth-like fluctuations of the refraction coefficient with amplitudes of 1-1.5 at time scales of 10-30 min. On cloudy days, the amplitudes of fluctuations were on the order of 0.5. Our refraction experiments show a variation range of k between −4 and +16 near the ground on sunny summer days. This equates to vertical temperature gradients between −0.5 and −0.1 K/m during the day and 1-2 K/m shortly after sunset. Cloud cover reduces the variability of k to a range of −2 to +5. Our results show that the frequently used Gaussian refraction coefficient of +0.13 is not suited for describing refraction effects in the lower atmosphere. As a conclusion, our results may be helpful to better assess the role of refraction in near-ground precision surveys, such as geometric levelling or trigonometric heighting.Citation: Hirt, C., S. Guillaume, A. Wisbar, B. Bürki, and H. Sternberg (2010), Monitoring of the refraction coefficient in the lower atmosphere using a controlled setup of simultaneous reciprocal vertical angle measurements,

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Die Lichtstrahlkrümmung in Bodennähe

Cited by 8 publications

References 2 publications

Optical scintillation:

Optical scintillation:

Determination of line averages of sensible heat flux using an optical method

Monitoring of the refraction coefficient in the lower atmosphere using a controlled setup of simultaneous reciprocal vertical angle measurements

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