COLUMN DESC RIPTIONS FOR TABLE I Column (1) The nominal frequency as it is customarily used to identify a radioastronomy band. (2) The centre frequency of the allocated radioastronomy band. (3) The assumed bandwidth. (4) The minimum antenna noise temperature includes contributions from the ionosphere, the Earth’s lower atmosphere and radiation from the Earth. (5) The receiver noise temperature is representative of a good radiometer system intended for use in high sensitivity radioastronomy observations. (6) The total system sensitivity in millikelvins as calculated from equation (4) using the combined antenna and receiver noise temperatures, the allocated bandwidth and an integration time of 2000 s. (7) The same as (6) above, but expressed in noise power density using the equation AP = k\T, where k = 1.38 x 10“23 (J/K) (Boltzmann’s constant). The actual numbers in the Table are the logarithmic expression of AP (8) The power level at the input of the receiver considered harmful to high sensitivity observations (AP„). This is expressed as the interference level which introduces an error of not more than IO"n in the measurement of AP; \PH = 0.1 AP\fA. The numbers in the Table are the logarithmic expression of &PH. (9) The total power flux in the allocated band needed to produce a power level &PH in the receiving system assuming an isotropic receiving antenna. The numbers in the Table are the logarithmic expression of SHAfA. (10) The average power flux-density in the allocated band needed to produce a power level AP„ in the receiving system assuming an isotropic receiving antenna. The numbers in the Table are the logarithmic expression of SH. C OLUMN DESC RIPTIONS FOR TABLE II Column (1) The nominal frequency of the spectral line. (2) The spectral line receiver channel bandwidth. The channel bandwidths used represent typical channel widths used for spectral line observations. (3) The minimum antenna noise temperature includes contributions from the ionosphere, the Earth's atmosphere and radiation from the Earth. (4) The receiver noise temperature is representative of a good radiometer system intended for use in high sensitivity radioastronomy observations. (5) The total system sensitivity in millikelvins as calculated from equation (4) using the combined antenna and receiver noise temperatures, the assumed channel bandwidth and an integration time of 2000 s. (6) The same as (5) above but expressed in noise power density using the equation AP = kAT. where k = 1.38 x 10“ 23 (J/K) (Boltzmann’s constant). The actual numbers in the Table are the logarithmic expression of AP. (7) The power level at the input of the receiver considered harmful to high sensitivity observations (&PH). This is expressed as the interference level which introduces an error of not more than 10% in the measurement of AP; AP„ = 0.1 APAf^.. The numbers in the Table are the logarithmic expression of &PH. (8) The power flux in a spectral line channel needed to produce a power level of AP,, in the receiving system assuming an isotropic receiving antenna. The numbers in the Table are the logarithmic expression of 5„A/;.. (9) The average power flux-density in a spectral line channel needed to produce a power level AP„ in the receiving system assuming an isotropic receiving antenna. The numbers in the Table are the logarithmic expression of SH. 7.2.1 Observed sensitivities The sensitivities in Tables I and II are extremely good, several orders of magnitude better than often considered practical, or even obtainable, in other radio services. It is of interest to examine actual high sensitivity observations which have been made at various radioastronomy observatories, and compare these results with the calculated values in Tables I and II. The following Table gives examples of very sensitive continuum and line observations appearing in published literature.
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