Measurement Of Electromagnetic Radiation Research Articles

Absolute intensity measurements in the extreme ultraviolet spectrum of solar radiation

Experimental results and problems of absolute intensity measurements of solar electromagnetic radiation in the extreme ultraviolet (EUV) and soft X-ray region of the spectrum (designated cumulatively as “XUV” for brevity) are reviewed. The numerous practical problems are divided in two major areas, (a) general problems of heterochromatic absolute XUV spectrophotometry in the laboratory and (b) specific problems characteristic of requirements of solar physics, the physics of planetary atmospheres, and existing restrictions of space technology. Within the first area (a) emphasis is placed on recent progress toward justified reliance on ionization detectors without necessary connection to source standards. For the second area (b), emphasis is placed on the immediate need to have existing exploratory observations followed by a new phase of more systematic experiments of increased accuracy.

Experimental determination of absolute intensities in the solar XUV spectrum

Experimental problems of absolute intensity measurements of solar electromagnetic radiation in the extreme ultra-violet (EUV) and soft X-ray region of the spectrum (designated cumulatively as “XUV” for brevity) are reviewed. From an evaluation of existing rocket and satellite data together with existing projects and goals of future observations from space vehicles, it is suggested that the numerous associated practical problems be devided into two major areas, namely (a) the general experimental art of heterochromatic absolute XUV spectrophotometry in the laboratory and (b) specific problems characteristic of the objectives of solar physics as well as existing restrictions of space technology. Within the first area (a) emphasis is placed on recent progress toward justified reliance on ionization detectors without necessary connection to source standards. For the second area (b), emphasis is placed on the immediate need to have existing exploratory observations followed by a new phase of more systematic experiments of increased accuracy.

High-latitude geophysical studies with satellite Injun 3: 5. Very-low-frequency electromagnetic radiation

This is a preliminary report of very-low-frequency (VLF) electromagnetic radiation measurements made by the Injun 3 satellite in the altitude range 250 to about 2000 km over North America from December 1962 to March 1963. The radiation is received by a loop antenna on the magnetically oriented satellite. Amplitude is measured with narrow-band filters at six frequencies, the lowest being 0.7 kc/s and the highest being 8.8 kc/s. A wideband amplitude over the frequency band from 0.5 to 7.0 kc/s is also measured. In addition, the VLF signal modulates the telemetry transmitter so that a detailed spectral analysis can be made on the ground. It is found that the amplitude of naturally occurring VLF signals is commonly tens of decibels stronger at Injun 3 than on the ground, and this is to be understood as due to strong absorption of VLF energy in the ionosphere, as has been found previously in other experiments. The maximum observed signal strength over the band 0.5 to 7.0 kc/s is 5 × 10−2 gamma. The amplitude of VLF chorus, considered for local times between 0800 and 1300, shows a maximum at L = 5 over the three-day period studied. Simultaneous occurrences of VLF electromagnetic emission, auroral optical emissions, and particle precipitation into the atmosphere have been repeatedly observed. Two specific instances are discussed. In the more stable of the two, it is concluded that the auroral hiss was generated in the same magnetic shell in much the same region of the magnetosphere (near the outer boundary of trapping) as were the precipitated particles that caused the aurora. For this event it is estimated that, for the VLF radiation having frequencies less than 10 kc/s, the VLF energy flux at the satellite was about 8 × 10−7 erg cm−2 sec−1, the energy flux of precipitated electrons was about 10 ergs cm−2 sec−1, and that from the auroral light was about 0.6 erg cm−2 sec−1. These measurements suggest that, in this event, the electrons caused both the visible aurora and the VLF hiss emission.

V. On the measurement of electromagnetic radiation

V. <i>On the measurement of electromagnetic radiation</i>