New Method For Absolute Calibration Research Articles

Absolute calibration of a wideband antenna and spectrometer for accurate sky noise temperature measurements

A new method of absolute calibration of sky noise temperature using a three‐position switched spectrometer, measurements of antenna and low noise amplifier impedance with a vector network analyzer, and ancillary measurements of the amplifier noise waves is described and compared with other methods of calibration. An initial test of the method has been made using brief observations from 55 to 110 MHz at West Forks, Maine, to estimate the sky noise spectral index. Estimates are made of the accuracy that might ultimately be achieved with observations to detect or set limits on the red‐shifted 21 cm line at a radio quiet site. It is concluded that an antenna reflection coefficient better than about −20 dB is required to avoid being limited by the accuracy of the antenna reflection coefficient measurements using a vector network analyzer.

AIRFLY: Measurement of the uorescence yield in atmospheric gases

The goal of the AIRFLY (AIR FLuorescence Yield) experiment is to measure the fluorescence yield (FLY) induced by electrons in air to better than 10% precision. A detailed knowledge of the fluorescence emission characteristics is crucial for UHECR (Ultra High Energy Cosmic Ray) air shower energy reconstruction using the fluorescence technique. AIRFLY has been taking data at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati, Italy. The dependence of FLY on the atmospheric gas pressure and temperature has been studied. The dependence on electron energy has been measured in the range 50–420 MeV. A new method of absolute calibration by comparison with Cerenkov emission has been investigated. The status of the experiment and the results achieved so far are presented.

Comparisons of 93 GHz radiometer predicted attenuationwith integrated precipitable water vapour measured using GPS

Comparisons are presented of integrated precipitable water vapour (IPWV) measured using phase delay measurements from GPS satellites and predicted attenuation from a zenith-pointing 93 GHz ground-based radiometer. These results illustrate the possibility of achieving high accuracy of measurement of IPWV using GPS and also open up a new method of absolute calibration for radiometers. In addition, the results demonstrate the availability of a significant new tool for millimetre-wave radio propagation prediction and event diagnosis.

A new method for absolute calibration of high-sensitivity accelerometers and other graviinertial devices

Abstract To investigate the dynamic characteristics of high-sensitivity graviinertial devices (accelerometers, seismometers, and others) it seems advantageous to use for the input signal the gravitational acceleration produced by bodies with a known mass distribution. This eliminates the need for moving the transducer under investigation. Such motion is needed in the inertial acceleration reproduction as well as for inclining a measuring instrument in the Earth's gravity field. Error in measuring the parameters of the transducer motion is determined by the uncertainties of the length- and angle-measuring instruments being used. Particularly, it concerns the angle measurement errors when the gravity field effects have been taken into account. The existing methods for reproducing gravitational acceleration are based on the use of nonuniform fields of simple shape bodies (sphere, cylinder, and the like). These methods require calculation of the corresponding acceleration, taking into account the spatial mass distribution of the instrument sensing element. The commonly employed approximation results in a procedural error of the order of 10% and over. It is proposed to calibrate a measuring instrument using a uniform, flat gravity field of varying direction. The set-up designed to realize this method reproduces varying accelerations over the frequency range 0.01 to 0.3 Hz with amplitude less than 1.3 × 10−7 m/sec2. This enables calibration of seismometers of various types with a higher accuracy.

Absolute standardless calibration of photodetectors based on quantum two-photon fields

A new method of absolute calibration of photodetectors based on a nonclassical effect in nonlinear optics is discussed. The combined influence of a monochromatic flux of pump photons and quantum vacuum noise on a nonlinear crystal with no center of symmetry results in the appearance of rigorously correlated pairs of photons with continuous spectral distribution in the spontaneous parametric scattering of light (spontaneous parametric downconversion) process. The presence of an optical field in a broad spectral range created by the two-photon states (biphotons) makes it possible to develop a new method of measuring the spectral distribution of the absolute value of the quantum efficiency of photodetectors, both in photon counting and in analog regimes, that does not use any calibrated standard light sources (étalons). The feasibility of the method is demonstrated on different types of photomultiplier tube.

Design of a Wien Filter Type Heavy Ion Beam Probe System for the Measurement of Plasma Potential

This paper describes the design of a Heavy Ion Beam Probe (HIBP) system to measure the two-dimensional plasma potential profile in the central mirror region of an open ended plasma confinement device (RFC-XX-M). This HIBP system incorporates three novel features. The first is a Wien filter-type guide field that reduces the required beam acceleraltion voltage. The second is a set of deflecting electrodes located at the exit position of the secondary ion beam that steers all secondary ions into the analyzer at the same angle. And the third is a new method of absolute calibration.

Absolute calibration of a fluorescence collection system by Raman scattering in H_2

A new method for absolute calibration of the detection efficiency of fluorescence collection systems is described for wavelengths covering the 180–2000-nm range. The radiation source for the technique is spontaneous Raman scattering in H2. An analytic expression is derived for the scattering cross section averaged over the solid angle of the fluorescence collection system. From this result, an optical system is calibrated at 845 nm, demonstrating that the technique is easy to use, is quick to implement, and gives accurate results.

Reciprocity calibration in a compliant cylindrical tube

A new method for absolute calibration of electroacoustic transducers is described which permits low‐frequency reciprocity calibration in a test apparatus of small dimensions. The method takes advantage of the reduced wave speed in a cylindrical water column bounded by a compliant PVC tube to reduce the length of the standing wave to dimensions which can be easily handled in the laboratory. Results of a limited series of experiments show a mean reproducibility of ± 0.8 dB in a 1‐m‐long tube at frequencies between 750 and 1100 Hz and sound speeds from 330–365 m/s. The hydrophone voltage sensitivities obtained by the method, however, systematically differ by 1.5 dB from those measured by comparison with a standard hydrophone. Additional research will be required to resolve this discrepancy. [Work supported by ONR.]

Excitation of low-energy H atoms in H+Ne collisions.

Excitation of 0.05--2.5-keV H atoms in H+Ne collisions has been examined by measuring the absolute emission cross sections for Balmer-..cap alpha.., Balmer-..beta.., and Lyman-..cap alpha.. radiations resulting from the collisions. Lyman-..cap alpha.. emission was also observed when an electric field was applied in the interaction region to investigate excitation of H atoms to the (metastable) 2s state. The radiation polarization for each of the above emissions was measured. A new method for absolute calibration of the Lyman-..cap alpha.. detector is described, and Lyman-..cap alpha.. emission cross sections for H/sup +/+Ar and e/sup -/+H/sub 2/ collisions are compared with previous results, the latter reaction giving a significantly smaller cross section than generally accepted. The peculiar behavior of the H+Ne interaction indicated by the measurements is discussed.

Study of the June 30, 1973 trans-polar coronal hole

Radially and tangentially polarized pictures of the solar corona obtained near 4500 A during the 30 June, 1973 solar total eclipse have been used to derive a model of a trans-polar coronal hole. The hole is identified by using OSO-7 EUV spectroheliograms. The line of sight coincides with the privileged plan of the hole over the N-polar region. A new method of absolute calibration is used. The Saito (1970) method is applied to determine the electron densities. Extrapolated values of densities down to the surface are lower than have ever been observed although derived hydrostatic temperatures are certainly not: Ne × 107 cm−3 and T = 2 × 106 K. The morphological peculiarities of polar regions are considered.

A New Method for Absolute Calibration of Electro-Optic Modulators

A New Method for Absolute Calibration of Electro-Optic Modulators