JPS6176943A - Water vapor density measuring system in atmospheric air, using dispersion of refractive index - Google Patents

Abstract

PURPOSE:To measure a mean value of water vapor density on a propagation path by transmitting simultaneously two electric waves of each different frequency, and measuring the phase difference between the two frequencies. CONSTITUTION:In a transmitting part 1, an output frequency (f) of an oscillator 4 and a frequency (mf) obtained by multiplying 5 the frequency (f) are transmitted, and the frequencies (f), (mf) are influenced by water vapor while they are propagated in the atmospheric air, and generate phase delays of phi1 and phi2, respectively. In a reception detecting part 2, these two frequencies are received, the frequency (f) and an output frequency f-DELTAf are mixed 11, and also the frequency (mf) and a frequency obtained by multiplying 13 the frequency f-DELTAf by (m) are mixed 14, by which they are converted to intermediate frequencies of DELTAf and mDELTAf, respectively. These frequen cies DELTAf, mDELTAf are subjected to phase delays of phi'1 and phi'2 in the detecting part 2, and outputted to intermediate frequency output terminals 12, 15 by phase relations of phi1+phi'1 and phi2+phi'2, respectively. In a phase detecting part 3, a signal proportional to a difference phi2-mphi1+(phi'2-mphi'1) of those which have multiplied a phase phi2+phi'2 of mDELTAf and a phase phi1+phi'1 of DELTAf is outputted to a phase difference output terminal 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the measurement of water vapor density in the atmosphere.

Various types of direct measurement instruments (so-called hygrometers) have been put into practical use for measuring the water vapor density in the atmosphere, but until now only water vapor radiometers have been put into practical use as remote sensors. It was hot.

A water vapor radiometer estimates the amount of water vapor in the upper atmosphere by measuring the noise temperature of electromagnetic waves emitted from water vapor molecules in the atmosphere. Water vapor radiometers measure not only the integrated amount of water vapor in the line-of-sight direction but also the height distribution of water vapor by changing the elevation angle of the receiving antenna at multiple frequencies. estimation of attenuation using very long baseline radio interferometer (VLB)
■) However, this water vapor radiometer is difficult to measure at low elevation angles close to the horizontal direction; cannot be used to measure the integral amount of water vapor.

The present invention is characterized in that the refractive index dispersion (the frequency-dependent component of the real part of the refractive index) in the atmospheric window region (frequency region with relatively little absorption between absorption lines) in the millimeter wave band By propagating radio waves of two different frequencies in the atmosphere, we find the average value of the dispersion of the refractive index between the two frequencies as a relative receiving phase difference, and It is characterized by measuring the water vapor density of Another object of the present invention is to be able to measure the integrated amount of water vapor in vertical, horizontal, and diagonal directions with high precision by arbitrarily changing the position and angle of the transmitting and receiving antenna.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in which 1 is a transmitter, 2 is a reception detector, 3 is a phase detector, 4 is an oscillator, 5 and 13 are frequency multipliers, 6 and 7 are transmitting antennas, 8 and 9 is a receiving antenna, 10 is a receiving local oscillator, 11 and 14 are mixers, 12 and 15
1 is an intermediate frequency output terminal, and 16 is a phase difference output terminal. In the transmitter l, the output frequency f of the oscillator 4 and its frequency f
The frequency mf obtained by multiplying by the multiplier 5 is transmitted.

Those frequencies f and mf have a coherent phase relationship and are influenced by water vapor while propagating through the atmosphere, and are respectively φ1. This causes a phase delay of φ2.

The reception detection unit 2 receives these two frequencies, and the mixer 11
In the mixer 14, the receiving frequency f and the output frequency "-Δ" (frequency detuned by Δf from the transmitting frequency f) of the local oscillator 10 are mixed, and in the mixer 14, the receiving frequency mf and f-Δf are mixed in the multiplier 13. f) By mixing the frequency multiplied by m, it is converted into intermediate frequencies of Δf and mΔ', respectively. Those intermediate frequencies Δf and mΔf are
In the reception detection section, φ1. After receiving a phase delay of φ2, φ1+φ1 . φ2+φ6
It is output with a phase relationship of The phase detection section 3 inputs these two intermediate frequencies and calculates the difference between the phase φ2+φ2 of mΔ'' and the phase φ1+φ; of Δf multiplied by m, φ2−...φ10(φ, Hmφ;)...・・・・・・
......(1) In equation (1), φ2-mφl is the reception phase difference caused by the difference between the transmission frequency f and mfO propagation delay, and φ6-mφl' is the phase delay generated within the reception phase detector. It's the difference.

Since φ6 mφl' is considered to be constant if a reception detection section with good phase stability is used, the reception phase difference φ2-mφ1 can be measured with high precision by calibrating it in advance. This reception phase (phase delay)
φ1. φ2 is expressed by the following formula.

Below margins However, f, m( are transmission frequencies, n(f), n(mf
) is the mean value of the atmospheric refractive index, L is the propagation distance, and C is the speed of light. From equations (2) and (3), the difference in the average value of the atmospheric refractive index at the transmission frequencies f and mf (refractive index dispersion) n(m
f)-n (f) is calculated as follows.

n (mf)-n(f) = -艷一(φ2-mφ1
) --(4) 2πf - Reception phase difference φ2-ro measured at the phase difference output terminal 16]
φ1 and refractive index dispersion n(mf)−n(f) are (4)
As is clear from the equation, there is a proportional relationship, and the dispersion of the refractive index at the atmospheric window in the millimeter wave band is approximately proportional to the water vapor density in the atmosphere flJ. Therefore, the phase difference between the two frequencies φ2
By measuring -[n-1, the average water vapor density on the propagation path can be estimated.

However, in order to obtain this water vapor density, it is necessary to calibrate the relationship between the output signal of the phase difference output terminal 16 and the water vapor density. In this method, the water vapor density is measured using a standard hygrometer and the output signal of the terminal 16 is measured simultaneously under several conditions with different water vapor densities, and the relationship between these two measured values is calculated in a linear manner. It is calibrated by approximating it with a function.

Figure 2 shows the refractive index dispersion between two frequencies of 245.52 GHz and 81.84 GHz measured using the present invention in a propagation path of 810 m, and the direct -1
1 shows the relationship between constant water vapor density (near the receiving point). It can be seen that the dispersion of the refractive index and the water vapor density are approximately proportional to each other. In addition, the solid line in Figure 2 indicates the temperature range from 5°C to 35°C.
This figure shows the results of theoretically calculating the dispersion of the refractive index for temperatures at intervals of 5 degrees Celsius, and it can be seen that the results agree well with the results measured by applying the present invention.

As described above, by applying the present invention, it is possible to accurately remotely measure the average value of water vapor density on a propagation path, and it is expected to be applied to the design of terrestrial communication lines, environmental monitoring, etc.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the present invention, and Figure 2 is a diagram showing the relationship between the dispersion of refractive index and water vapor density between 245.52 GHz and 81°84 GHz measured by applying the present invention. It is. In the figure, 1... transmitter, 2... reception detector, 36
11 Phase detector, 4... Oscillator, 5.13... Frequency multiplier, 6, 7... Transmitting antenna, 8.9... Receiving antenna, 10...- Receiving local oscillator, 11.14・
...Mixer, 12゜15...Intermediate frequency output terminal, 16
...This is a phase difference output terminal.

Claims (1)

[Claims] In measuring the water vapor density in the atmosphere, radio waves of two different frequencies in the millimeter wave band are simultaneously transmitted, and the difference in phase delay between the two frequencies caused by the difference in the refractive index of water vapor molecules on the propagation path is measured on the receiving side. A method for measuring atmospheric water vapor density using refractive index dispersion, which measures the average water vapor density on the propagation path from the difference in reception phase delay.