Water vapor observation system

Abstract

To easily observe water vapor content at one measuring point without requiring two measuring points and without using a reflector.SOLUTION: A terrestrial digital broadcasting signal received from a broadcasting station BR is transmitted from a gap-filler receiving station GRx to a gap-filler transmitting station GTx via a first optical line 12. The terrestrial digital broadcasting signal is re-transmitted from the GTx and received at a measuring point M disposed at the same position as the GRx. The terrestrial digital broadcasting signal is also transmitted from the GTx to the measuring point M via a second optical line 13. An observation device 20 at the measuring point M observes the water vapor content in the atmosphere between the measuring point M and the GTx based on a complex delay profile of a measurement quantity M1, a measurement quantity M2, and a measurement quantity R2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a water vapor observation system that can easily observe the amount of water vapor. [Background technology]

[0002] In recent years, heavy rain disasters have occurred frequently across the country, and various research is being conducted from the perspectives of disaster prevention, mitigation, safety, and security. The occurrence of heavy rain disasters is largely due to the amount of water vapor in the atmosphere, and it has been demonstrated that measuring this water vapor amount with high precision and assimilating the data into meteorological parameters can significantly improve the accuracy of heavy rain forecasts. Currently, research into water vapor observations over a wide area is being conducted. Incidentally, it is known that the propagation speed of radio waves changes depending on the total amount of air, including water vapor, present in the space through which the waves propagate, and conventional water vapor measurement devices that calculate the amount of water vapor by utilizing the propagation delay time of radio waves received at an observation point are described in Patent Documents 1 and 2. In addition, Non-Patent Documents 1 and 2 describe water vapor observation using terrestrial digital broadcasting waves. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2-212750 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-10460 [Non-patent literature]

[0004] [Non-Patent Document 1] "Successful development of a water vapor estimation method using terrestrial digital broadcasting waves ~ Measuring radio wave propagation delay with picosecond accuracy, improving the accuracy of forecasting sudden heavy rain ~," March 9, 2017 [online], National Institute of Information and Communications Technology, [Retrieved June 16, 2021], Internet <URL: https: / / www.nict.go.jp / press / 2017 / 03 / 09-1.html> [Non-patent document 2] S. KAWAMURA et al., "Water vapor estimation using digital terrestrial broadcasting waves," [online], National Institute of Information and Communications Technology, [Retrieved June 16, 2021], Internet〈URL: https: / / agupubs.onlinelibrary.wiley.com / doi / full / 10.1002 / 2016RS006191〉 Summary of the Invention [Problem to be solved by the invention]

[0005] A conventional method for water vapor observation using terrestrial digital broadcasting waves, described in Non-Patent Document 2, will be described with reference to Figures 14 to 16. Figure 14 is a diagram for explaining a conventional synchronization method for water vapor observation using terrestrial digital broadcasting waves, Figure 15 is a diagram for explaining a conventional reflection method for water vapor observation using terrestrial digital broadcasting waves, and Figure 16 is a diagram showing an example of a complex delay profile in the reflection method shown in Figure 15. The conventional synchronization method for water vapor observation using terrestrial digital broadcasting waves shown in Figure 14 includes measurement point A, which receives terrestrial digital broadcasting waves emitted from broadcasting station 500, and measurement point B, which is located between measurement point A and broadcasting station 500, and observes the amount of water vapor in the atmosphere between measurement point A and measurement point B. This method takes advantage of the fact that radio wave propagation is slightly delayed when the amount of water vapor in the atmosphere increases (a 1% increase in humidity at 1 atmosphere and a temperature of 20°C over a propagation distance of 5 km delays the propagation time by approximately 17 picoseconds). The conventional synchronization method is said to be able to obtain information on the amount of water vapor by measuring the propagation delay with high precision using terrestrial digital broadcasting waves.

[0006] A receiving unit capable of receiving terrestrial digital broadcast waves is provided at each of measurement points A and B. Here, the phase rotation corresponding to the delay time until the terrestrial digital broadcast waves emitted from broadcast station 500 reach measurement point A is denoted as τA, the phase rotation corresponding to the delay time until the terrestrial digital broadcast waves emitted from broadcast station 500 reach measurement point B is denoted as τB, and the phase noise of the transmitting unit in broadcast station 500 is denoted as φ T , the phase noise of the receiver at measurement point A is φ A , the phase noise of the receiver at measurement point B is φ B Then, the measured amount MA of the phase rotation of the terrestrial digital broadcasting wave measured at measurement point A is MA=τA+φ T +φ A (1) The measured amount MB of phase rotation of the terrestrial digital broadcasting wave measured at measurement point B is as follows: MB=τB+φ T +φ B (2) The phase rotation corresponding to the delay time for the terrestrial digital broadcasting wave to reach measurement point A from measurement point B is calculated as (MA-MB). (MA-MB)=(τA-τB)+(φ A -φ B ) (3) (φ A -φ B Since the phase noise term in (φ A -φ B ) = 0. If measurement point A and measurement point B are synchronized, then φ A =φ B That is, in the synchronization method, by synchronizing measurement point A and measurement point B, (φ A -φ B ) = 0 to prevent measurement errors as shown in the following equation (4). (MA-MB)=(τA-τB) (4) The phase rotation (τA-τB) shown in equation (4) and the speed of radio waves in a vacuum (2.99792458×10 8The amount of water vapor in the atmosphere between measurement point A and measurement point B can be observed based on the propagation delay time, which is the difference between the phase rotation corresponding to the delay time it takes for the terrestrial digital broadcasting wave to reach measurement point A from measurement point B based on the propagation delay time (m / s).

[0007] Next, the conventional reflection method for observing water vapor using terrestrial digital broadcasting waves, shown in Figure 15, is equipped with a reflector R that reflects terrestrial digital broadcasting waves emitted from broadcasting station 500, and measurement point C between reflector R and broadcasting station 500, and observes the amount of water vapor in the atmosphere between reflector R and measurement point C. The reflection method also makes use of the fact that radio wave propagation is slightly delayed when the amount of water vapor in the atmosphere increases (a 1% increase in humidity at 1 atmosphere and a temperature of 20°C over a propagation distance of 5 km delays the propagation time by approximately 17 picoseconds). The reflection method obtains information on the amount of water vapor by measuring the propagation delay with high precision using terrestrial digital broadcasting waves.

[0008] A receiving unit capable of receiving terrestrial digital broadcast waves is provided at measurement point C. Here, the phase rotation corresponding to the delay time from when the terrestrial digital broadcast waves radiated from broadcast station 500 are reflected by reflector R to when they reach measurement point C is denoted by τR, the phase rotation corresponding to the delay time from when the terrestrial digital broadcast waves radiated from broadcast station 500 are reflected by reflector R to when they reach measurement point C is denoted by τC, and the phase noise of the transmitting unit in broadcast station 500 is denoted by φ T , the phase noise of the receiver at measurement point C is φ C Then, the measured amount MC1 of the phase rotation of the direct wave from the broadcasting station 500 measured at the measurement point C is expressed as follows: MC1=τC+φ T +φ C (5) The measured phase rotation MC2 of the wave reflected by the reflector R measured at the measurement point C is MC2=τR+φ T +φ C (6) This becomes:

[0009] At measurement point C, a complex delay profile is observed of a measured amount MC1 of the phase rotation of the direct wave from broadcast station 500 and a measured amount MC2 of the phase rotation of the reflected wave reflected by reflector R at measurement point C. An example of this complex delay profile is shown in FIG. 16. As shown in FIG. 16, the complex delay profile has the horizontal axis as the time axis and the vertical axis as the amplitude axis, with the horizontal axis representing the phase rotation as delay time. If the phase rotation corresponding to the delay time from measurement point C where the measured amount MC1 is measured until it reaches reflector R is τM, then the phase rotation corresponding to the delay time until the reflected wave from reflector R reaches measurement point C is also τM. Then, the phase rotation corresponding to the delay time from when the terrestrial digital broadcast wave reaches reflector R from measurement point C until the reflected wave reflected by reflector R returns to measurement point C can be calculated as (MC2-MC1). That is, (MC2-MC1)=(τR-τC) (7) As is clear from FIG. 16, (MC2-MC1) shown in equation (7) is a phase rotation corresponding to the round-trip delay time between reflector R and measurement point C, so (MC2-MC1) is equal to 2τM, τM=(MC2-MC1) / 2=(τR-τC) / 2 (8) As shown in equation (8), the reflection method can cancel out the phase noise between the broadcasting station 500 and the measurement point C without requiring a synchronization means. In the reflection method, the phase rotation τM, which corresponds to the delay time between the reflector R and the measurement point C, and the speed of radio waves in a vacuum (2.99792458×10 8 The amount of water vapor in the atmosphere between reflector R and measurement point C can be observed based on the propagation delay time, which is the difference between the phase rotation corresponding to the delay time it takes for the terrestrial digital broadcasting wave to reach measurement point C from reflector R based on the propagation delay time (m / s).

[0010] Next, the positions of the two measurement points A and B in the conventional synchronization method will be explained with reference to the overhead view shown in Fig. 17. Fig. 17 is an overhead view seen from above. In the conventional synchronization method, as shown in FIG. 17, measurement point B is located on a straight line connecting broadcast station 500 and measurement point A. In the conventional synchronization method, it is possible to obtain information on the amount of water vapor by providing two measurement points, measurement point A and measurement point B. However, there may be cases where broadcast station 500 and the two measurement points are not located on a straight line. Referring to FIG. 17, the case where they are not located on a straight line will be explained. If measurement point B is not located on a straight line connecting broadcast station 500 and measurement point A', as shown in FIG. 17, then equation (4) above will not hold. That is, the difference between distances LA' and LB (LA'-LB) should be equal to the distance between measurement point A and measurement point B (L4+L5). However, LA' = (LB+L4) and (LA'-LB) = L4, and therefore the delay time propagating through distance L5 becomes an error. In this regard, conventional synchronization methods require the establishment of two measurement points, measurement point A and measurement point B, and furthermore, broadcasting station 500 and measurement point A and measurement point B must be positioned on a straight line. Note that the amount of water vapor in the space between measurement point A and measurement point B is usually different from the amount of water vapor in the space between measurement point A' and measurement point B. Therefore, if a measurement point is set at the position of measurement point A', the amount of water vapor in the space between measurement point A and measurement point B cannot be observed.

[0011] Next, the positions of the measurement point C and the reflector R in the conventional reflection method will be described with reference to the overhead view shown in Fig. 18. Fig. 18 is an overhead view seen from above. In the conventional reflection method, as shown in FIG. 18, measurement point C is located on a straight line connecting broadcast station 500 and reflector R. By providing one measurement point C between broadcast station 500 and reflector R, it is possible to obtain information on the amount of water vapor in the conventional reflection method. However, there may be cases where broadcast station 500, measurement point C, and reflector R are not located on a straight line. Referring to FIG. 18, the case where they are not located on a straight line will be explained. If measurement point C is not located on a straight line connecting broadcast station 500 and reflector R' as shown in FIG. 18, the above equations (7) and (8) do not hold. That is, the difference between distance L2 and distance L1 (L2-L1) should be equal to the distance between reflector R and measurement point C (L4'+L5'). However, since L2 = (L1+L4') and (L2-L1) = L4', an error occurs due to the delay time propagating through distance L5'. In this regard, the conventional reflection method assumes the existence of a reflector R, and further requires that measurement point C be placed on a straight line connecting broadcast station 500 and reflector R. In addition, since the amount of water vapor in the space between measurement point C and reflector R is usually different from the amount of water vapor in the space between measurement point C and reflector R', if a reflector is installed at the position of reflector R', the amount of water vapor in the space between measurement point C and reflector R cannot be observed.

[0012] The synchronization method described above has the problem that it requires two measurement points with the location where water vapor is to be observed between them, and also requires a synchronization means to synchronize between the two measurement points. Furthermore, since water vapor observations utilize a slight propagation delay time, a highly accurate synchronization means is required, which results in an expensive synchronization means. Furthermore, the reflection method described above requires a reflector between the measurement point and the location where water vapor is to be observed, but in areas such as low mountainous regions or vast grain-producing areas in the shadows of mountains where radio waves are blocked, there are no structures such as high-rise buildings or apartment buildings, making it difficult to find a usable reflector. Even if there were a power line or other reflector in such areas, there was a problem in that the phase fluctuation was large and it was not suitable for measurement. Furthermore, in the synchronization method, as explained in Figure 17, measurement point B must be set on the straight line connecting broadcasting station 500 to measurement point A, and in the reflection method, as explained in Figure 18, measurement point C must be set on the straight line connecting broadcasting station 500 to reflector R, but there is a problem in mountainous areas, etc., where obstacles make it impossible to set measurement point B or measurement point C so as to satisfy these conditions. Therefore, the present invention aims to provide a water vapor observation system that does not require two measurement points and can easily observe water vapor at a single measurement point without using a reflector. [Means for solving the problem]

[0013] The water vapor observation system of the present invention, which can achieve the above-mentioned object of the present invention, comprises a gap filler receiving station that receives terrestrial digital broadcast waves from a broadcast station and transmits the terrestrial digital broadcast signals to a gap filler transmitting station via a first communication line; a gap filler transmitting station that retransmits the terrestrial digital broadcast signals transmitted from the gap filler receiving station as terrestrial digital broadcast waves; and a measurement point that is installed at a position beyond the gap filler receiving station and the gap filler transmitting station as seen from the broadcast station and is able to receive the terrestrial digital broadcast waves from the broadcast station and the terrestrial digital broadcast waves retransmitted from the gap filler transmitting station, and has the most main feature that the measurement point observes the amount of water vapor in the atmosphere between the gap filler receiving station and the gap filler transmitting station based on a measured amount G1 of phase rotation corresponding to the delay time for the terrestrial digital broadcast waves to reach the measurement point directly from the broadcast station, and a measured amount G2 of phase rotation corresponding to the delay time for the terrestrial digital broadcast waves to reach the measurement point from the broadcast station via the gap filler receiving station, the first communication line, and the gap filler transmitting station.

[0014] Another water vapor observation system of the present invention, which can achieve the above-mentioned object of the present invention, includes a gap filler receiving station that receives terrestrial digital broadcast waves from a broadcast station and transmits the terrestrial digital broadcast signals to a gap filler transmitting station via a first communication line, a gap filler transmitting station that retransmits the terrestrial digital broadcast signals transmitted from the gap filler receiving station as terrestrial digital broadcast waves and transmits the terrestrial digital broadcast signals to a measurement point via a second communication line, and a gap filler transmitting station that is located at the same position as the gap filler receiving station and receives the terrestrial digital broadcast waves from the broadcast station, the terrestrial digital broadcast waves retransmitted from the gap filler transmitting station, and the terrestrial digital broadcast signals transmitted from the gap filler transmitting station to a measurement point via a second communication line. The measurement point is equipped with an observation device capable of receiving a terrestrial digital broadcasting signal transmitted via a second communication line, and the most important feature of the observation device is that it observes the amount of water vapor in the atmosphere between the measurement point and the gap filler transmitting station based on a measured amount of phase rotation M1 corresponding to the delay time until the terrestrial digital broadcasting wave arrives at the measurement point from the broadcasting station, a measured amount of phase rotation M2 corresponding to the delay time until the terrestrial digital broadcasting wave retransmitted from the gap filler transmitting station arrives at the measurement point, and a measured amount of phase rotation R2 corresponding to the delay time until the terrestrial digital broadcasting signal transmitted via the second communication line arrives at the measurement point.

[0015] Furthermore, the main feature of the water vapor observation system of the present invention is that the observation device observes the water vapor amount by calculating a first phase rotation corresponding to the delay time it takes for the terrestrial digital broadcasting wave to reach the measurement point from the gap filler transmitting station based on the complex delay profile of the measurand M1, the measurand M2, and the measurand R2. Furthermore, the water vapor observation system of the present invention is mainly characterized in that it obtains a third phase rotation D1, which is the sum of the first phase rotation and a second phase rotation corresponding to the delay time it takes for the terrestrial digital broadcast signal to reach the gap filler transmitting station from the gap filler receiving station via the first communication line, by calculating the difference between the measurand M2 and the measurand M1, and obtains a fourth phase rotation corresponding to the delay time it takes for the terrestrial digital broadcast signal to reach the gap filler transmitting station from the gap filler receiving station via the first communication line, and then to be returned from the gap filler transmitting station by the second communication line and reach the measurement point by calculating the difference between the measurand R2 and the measurand M1, and calculates the first phase rotation based on the third phase rotation D1 and the fourth phase rotation D2. Furthermore, the water vapor observation system of the present invention has a main feature in that it observes the amount of water vapor in the atmosphere between the measurement point and the gap filler transmitting station based on the propagation delay time, which is the difference between the first phase rotation and a phase rotation corresponding to the delay time it takes for terrestrial digital broadcast waves to reach the measurement point from the gap filler transmitting station based on the speed of radio waves in a vacuum. Furthermore, the water vapor observation system of the present invention has a main feature in that the gap filler receiving station cancels out the phase noise of the gap filler receiving station by applying a local oscillation signal from a single local oscillator to a first mixer that converts the terrestrial digital broadcast signal received from the transmitting station into an intermediate frequency signal, and to a second mixer that converts the intermediate frequency signal back into a terrestrial digital broadcast signal. Furthermore, the main feature of the water vapor observation system of the present invention is that the gap filler transmitting station distributes the terrestrial digital broadcast signal transmitted from the gap filler receiving station using a distribution means, and transmits one of the distributed terrestrial digital broadcast signals to the measurement point via the second communication line. Furthermore, the main feature of the water vapor observation system of the present invention is that, at the measurement point, terrestrial digital broadcast waves from the broadcast station are received by a first receiving means, terrestrial digital broadcast waves from the gap filler transmitting station are received by a second receiving means, and level adjustment is performed between the first received signal received by the first receiving means and the second received signal received by the second receiving means. [Effects of the Invention]

[0016] The water vapor observation system of the present invention can observe the amount of water vapor in the atmosphere between the gap filler receiving station and the gap filler transmitting station at a single measurement point installed beyond the gap filler receiving station and the gap filler transmitting station as viewed from the broadcasting station, by receiving terrestrial digital broadcast waves arriving directly from the broadcasting station and terrestrial digital broadcast waves arriving from the broadcasting station via the gap filler receiving station, a first communication line, and the gap filler transmitting station. Furthermore, the water vapor observation system of the present invention can observe the amount of water vapor in the atmosphere between a measurement point and a gap filler transmitting station by receiving terrestrial digital broadcast waves transmitted from the gap filler transmitting station at a single measurement point. This eliminates the need for two measurement points and makes it easy to observe the amount of water vapor at a single measurement point without using a reflector. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a block diagram showing the configuration of a water vapor observation system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of a complex delay profile at a measurement point of the water vapor observation system according to the first embodiment of the present invention. [Figure 3] FIG. 10 is a block diagram showing the configuration of a water vapor observation system according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing an example of a complex delay profile at a measurement point of the water vapor observation system according to the second embodiment of the present invention. [Figure 5] FIG. 10 is a block diagram showing the configuration of a receiving section of a gap filler receiving station in a water vapor observation system according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a block diagram showing the configuration of a gap filler transmitting station in a water vapor observation system according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a block diagram showing a characteristic configuration of a water vapor observation system according to a second embodiment of the present invention. [Figure 8] FIG. 10 is a graph showing propagation delay time as a function of humidity under conditions of 1 atmospheric pressure and a temperature of 20° C. [Figure 9] FIG. 2 is a diagram showing an example of an actual complex delay profile at a measurement point of a water vapor observation system according to an embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing a configuration for adjusting levels at measurement points in a water vapor observation system according to a second embodiment of the present invention. [Figure 11] FIG. 10 is a diagram showing an example of an actual complex delay profile after level adjustment at a measurement point of the water vapor observation system according to the second embodiment of the present invention. [Figure 12] FIG. 10 is a bird's-eye view showing the positions of gap-filler receiving stations and gap-filler transmitting stations in a water vapor observation system according to a second embodiment of the present invention. [Figure 13] FIG. 1 is a block diagram showing a configuration of a gap filler system. [Figure 14] FIG. 1 is a block diagram showing the configuration of a conventional synchronization method for observing water vapor using terrestrial digital broadcasting waves. [Figure 15] FIG. 1 is a block diagram showing the configuration of a conventional reflection method for observing water vapor using terrestrial digital broadcasting waves. [Figure 16] FIG. 1 is a diagram showing an example of a complex delay profile in a conventional reflection method for observing water vapor using terrestrial digital broadcasting waves. [Figure 17] FIG. 1 is a bird's-eye view showing the positions of two measurement points in a conventional synchronization method. [Figure 18] FIG. 1 is a bird's-eye view showing the arrangement positions of measurement points and reflection points in a conventional reflection method. DETAILED DESCRIPTION OF THE INVENTION

[0018] [First embodiment of the present invention] FIG. 1 shows a block diagram illustrating the configuration of a water vapor observation system according to a first embodiment of the present invention. The water vapor observation system 1 according to the first embodiment of the present invention shown in Fig. 1 utilizes a gap filler system. First, the gap filler system will be described with reference to Fig. 13. Fig. 13 is a block diagram showing the configuration of a general gap filler system 200. The gap filler system 200 shown in FIG. 13 has a broadcast station 500 that transmits television broadcast waves in all directions in a horizontal plane and a residence H that receives the television broadcast waves, and there may be an obstacle S, such as a mountain, between the broadcast station 500 and the residence H that blocks the propagation of the television broadcast waves. In this way, when the residence H cannot receive the television broadcast waves well due to the obstacle S, the system is installed so that the television broadcast waves can be received well at the residence H located beyond the obstacle S. In the gap filler system 200 shown in FIG. 13, there is an obstacle S, such as a mountain, that blocks the propagation of the terrestrial digital broadcast waves between the broadcast station 500 (or relay station) that transmits the terrestrial digital broadcast waves and the residence H that receives the terrestrial digital broadcast waves. Therefore, the gap filler receiving station Rx is installed in a location near the top of the mountain, which is the obstacle S, where it can properly receive the terrestrial digital broadcast waves from the broadcast station 500. The gap filler receiving station Rx receives the terrestrial digital broadcast waves transmitted from the broadcast station 500 using an antenna 411 and a receiving unit 410 to obtain a terrestrial digital broadcast signal. The terrestrial digital broadcast signal is sent from the receiving unit 410 to a communication line T made up of optical fiber or coaxial cable, and transmitted to a transmitting unit 530 of a gap filler transmitting station Tx. The gap filler transmitting station Tx is preferably installed in a location overlooking a plurality of houses H scattered beyond an obstacle S. The transmitting unit 530 of the gap filler transmitting station T distributes the terrestrial digital broadcast signal transmitted from the gap filler receiving station Rx via the communication line T using a distributor 533, amplifies each distributed signal, and transmits it from a first transmitting antenna 531 and a second transmitting antenna 532. As a result, the terrestrial digital broadcast waves are retransmitted from the first transmitting antenna 531 and the second transmitting antenna 532, and the retransmitted terrestrial digital broadcast waves are received by each of the plurality of houses H located beyond the obstacle S as viewed from the broadcasting station 500. In this case, because the gap filler transmitting station Tx is installed beyond the obstacle S, just like the houses H, the houses H can receive the terrestrial digital broadcast waves well.

[0019] The water vapor observation system 1 of the first embodiment of the present invention shown in Fig. 1 utilizes the gap filler system 200 shown in Fig. 13, and is typically configured with a measurement point M installed at a point beyond the existing gap filler system 200 as viewed from the broadcast station BR. The water vapor observation system 1 of the first embodiment of the present invention includes a broadcast station BR that transmits terrestrial digital broadcast waves in all directions in the horizontal plane, a gap filler receiving station Rx that receives the terrestrial digital broadcast waves emitted from the broadcast station BR, a gap filler transmitting station Tx that retransmits the terrestrial digital broadcast signal transmitted from the gap filler receiving station Rx via an optical line 13 as a terrestrial digital broadcast wave, and a measurement point M that is installed on an extension of a straight line connecting the broadcast station BR with the gap filler receiving station Rx and the gap filler transmitting station Tx, and that receives the terrestrial digital broadcast waves emitted from the broadcast station BR and the terrestrial digital broadcast waves retransmitted from the gap filler transmitting station Tx. The water vapor observation system 1 of the first embodiment of the present invention observes the amount of water vapor in the atmosphere between a gap filler receiving station Rx and a gap filler transmitting station Tx by taking advantage of the fact that an increase in the amount of water vapor in the atmosphere causes a slight delay in the propagation of radio waves (a 1% increase in humidity at 1 atmosphere and a temperature of 20°C over a propagation distance of 5 km results in a delay of approximately 17 picoseconds).In this case, the observation system 1 of the present invention obtains information on the amount of water vapor by measuring the propagation delay with high precision using terrestrial digital broadcasting waves retransmitted from the gap filler transmitting station Tx.

[0020] A detailed description of the water vapor observation system 1 according to the first embodiment of the present invention, shown in FIG. 1, is provided. The gap filler receiving station Rx includes a receiving antenna 01, and receives a terrestrial digital broadcast signal of a terrestrial digital broadcast wave transmitted from a broadcast station BR. The terrestrial digital broadcast signal received by the gap filler receiving station Rx is converted into an optical signal and transmitted to a gap filler transmitting station Tx via an optical line 03. The gap filler transmitting station Tx converts the transmitted optical signal into an electrical signal, and the terrestrial digital broadcast signal is retransmitted from a transmitting antenna 02. The transmitting antenna 02 retransmits the terrestrial digital broadcast signal from the broadcast station BR toward areas where reception is poor. At a measurement point M, which is located on an extension of a straight line connecting the broadcast station BR, the gap filler receiving station Rx, and the gap filler transmitting station Tx, a direct wave of the terrestrial digital broadcast signal transmitted from the broadcast station BR is received by a receiving antenna 04, and the terrestrial digital broadcast wave retransmitted from the gap filler transmitting station Tx is also received by the receiving antenna 04. At measurement point M, the direct wave from broadcast station BR and the retransmitted wave from gap filler transmitter station Tx are observed as a complex delay profile, and the phase difference between the direct wave from transmitter station BR and the retransmitted wave from gap filler transmitter station Tx is measured from the observed complex delay profile. Note that measurement point M is installed at a location farther away from broadcast station BR, beyond gap filler receiving station Rx and gap filler transmitter station Tx, but because it is installed in a location with good visibility to broadcast station BR, such as on a mountain or hill, it can receive terrestrial digital broadcasting signals from broadcast station BR well.

[0021] [Observation of water vapor content] The observation of water vapor content in the water vapor content observation system 1 according to the first embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 2 is a diagram showing an example of a complex delay profile observed at measurement point M in the water vapor content observation system 1 according to the first embodiment of the present invention. Here, the phase rotation corresponding to the delay time from when the terrestrial digital broadcasting wave transmitted from the broadcasting station BR propagates through space to when it reaches the gap filler receiving station Rx is defined as τ AThe phase rotation corresponding to the delay time from when the terrestrial digital broadcasting wave transmitted from the broadcasting station BR propagates through space to when it reaches the gap filler receiving station Rx and the gap filler transmitting station Tx is τ B The phase rotation corresponding to the delay time until the terrestrial digital broadcasting wave retransmitted from the gap filler transmitting station Tx propagates through space and arrives at the measurement point M is τ C The phase rotation corresponding to the delay time from when the terrestrial digital broadcasting signal is received by the gap filler receiving station Rx, transmitted from the gap filler receiving station Rx through the optical line 03, reaches the gap filler transmitting station Tx, and is then retransmitted from the gap filler transmitting station Tx is τ GF In addition, the phase noise of the local oscillator of the transmitter in the broadcasting station BR is φ T , the phase noise of the reference signal at measurement point M is φ R In addition, τ B is subjected to a phase rotation depending on the amount of water vapor in the atmosphere between the gap filler receiving station Rx and the gap filler transmitting station Tx.

[0022] In the above notation, the terrestrial digital broadcasting wave transmitted from the broadcasting station BR propagates through space and arrives at the measurement point M as a direct wave, and is observed as a complex delay profile. The measured amount of phase rotation G1, which corresponds to the delay time of the complex delay profile, is G1=φ T +τ A +τ B +τ C +φ R (10) Furthermore, if the measured amount of phase rotation corresponding to the delay time from when the terrestrial digital broadcasting wave transmitted from the broadcasting station BR is received by the gap filler receiving station Rx, transmitted to the gap filler transmitting station Tx via the optical line 03, and when the terrestrial digital broadcasting wave is retransmitted from the gap filler transmitting station Tx and reaches the measurement point M is G2, then G2=φ T +τ A +τ GF +τ C +φ R (11) Here, the measurands G1 and G2 are measured as complex delay profiles at measurement point M, and an example of the measured complex delay profile is shown in FIG.

[0023] In the complex delay profile shown in Figure 2, the horizontal axis is the time axis, the vertical axis is the amplitude axis, and the horizontal axis indicates the phase rotation in terms of delay time. In the water vapor amount observation system 1 of the first embodiment of the present invention, the amount of water vapor in the atmosphere between the gap filler receiving station Rx and the gap filler transmitting station Tx can be observed based on the difference between the measurand G1 and the measurand G2. In this case, τ GF Assume that the delay time can be accurately estimated. Here, the phase rotation H of the difference between the measurand G1 and the measurand G2 is calculated as follows: H=G2-G1=τ GF -τ B (12) In this case, the phase noise φ of the broadcasting station BR that causes the error T and the phase noise φ of the reference signal at measurement point M R It can be seen that the phase rotation H removes the phase rotation τ B When we ask for τ B =τ GF -H (13) The phase rotation H can be calculated as the phase difference (time difference) between two complex delay profiles, as shown in Figure 2. The phase rotation H calculated from the complex delay profile and the time difference τ that can be accurately estimated are then calculated. GF The delay time and the phase rotation τ B Calculate the speed of radio waves in a vacuum (2.99792458×10 8 m / s ), the amount of water vapor in the atmosphere between the gap filler receiving station Rx and the gap filler transmitting station Tx can be observed.

[0024] The humidity can be determined by referring to the graph of propagation delay time as a function of humidity under conditions of 1 atmosphere and 20°C temperature shown in Figure 8, and the amount of water vapor can be calculated from the determined humidity. The horizontal axis of the graph in Figure 8 represents the propagation distance [km], and the vertical axis represents the propagation delay time [sec]. The graph shows the humidity set to 100%, 80%, 60%, 40%, and 20%. In the graph shown in Figure 8, when radio waves propagate over a distance of 5 km, a 1% increase in humidity results in a propagation delay of approximately 17 ps (picoseconds), which corresponds to a length of approximately 5 mm. Because the delay due to the amount of water vapor is very small, effective observation requires highly accurate measurements (at least on the order of several tens of ps). In the water vapor observation system 1 of the first embodiment, the phase noise φ of the broadcasting station BR, which causes errors, is used. T and the phase noise φ of the reference signal at measurement point M R and are removed, and τ GF Since the delay time can be accurately estimated, very accurate observations of water vapor content can be made. At measurement point M, a complex delay profile is measured and phase rotation is observed from the in-phase component I signal and the quadrature component Q signal. However, instead of the complex delay profile, a delay profile may be measured at measurement point M and phase rotation may be observed from amplitude information.

[0025] [Second embodiment of the present invention] FIG. 3 is a block diagram showing the configuration of a water vapor observation system according to a second embodiment of the present invention. The water vapor observation system 2 according to the second embodiment of the present invention shown in Fig. 3 utilizes the gap filler system shown in Fig. 13. The gap filler system 200 shown in Fig. 13 has been described above, so a description of the gap filler system 200 shown in Fig. 13 will be omitted here. The water vapor observation system 2 of the second embodiment of the present invention shown in Fig. 3 utilizes the gap filler system 200 shown in Fig. 13, and is typically configured by installing a measurement point in an existing gap filler system 200. That is, the water vapor observation system 2 of the second embodiment of the present invention includes a broadcasting station BR that transmits terrestrial digital broadcast waves in all directions in the horizontal plane, a gap filler receiving station GRx that receives the terrestrial digital broadcast waves emitted from the broadcasting station BR, a gap filler transmitting station GTx that retransmits the terrestrial digital broadcast signals transmitted from the gap filler receiving station GRx via an optical line as terrestrial digital broadcast waves, and a measurement point M that is installed at the same location as the gap filler receiving station GRx and receives the terrestrial digital broadcast waves emitted from the broadcasting station BR and the terrestrial digital broadcast waves that are retransmitted from the gap filler transmitting station GTx and propagating through space, and also receives the terrestrial digital broadcast signals transmitted from the gap filler transmitting station GTx via a second optical line 13. The water vapor observation system 2 of the second embodiment of the present invention observes the amount of water vapor in the atmosphere between measurement point M and gap filler transmitting station GTx by taking advantage of the fact that an increase in the amount of water vapor in the atmosphere causes a slight delay in the propagation of radio waves (a 1% increase in humidity at 1 atmosphere and a temperature of 20°C over a propagation distance of 5 km results in a delay of approximately 17 picoseconds).In this case, the observation system 1 of the present invention obtains information on the amount of water vapor by measuring the propagation delay with high precision using terrestrial digital broadcasting waves retransmitted from gap filler transmitting station GTx.

[0026] [Gap filler receiving station] FIG. 5 is a block diagram showing the configuration of a gap filler receiving station GRx in an observation system 2 according to a second embodiment of the present invention. The gap filler receiving station GRx shown in FIG. 5 includes at least an antenna 11 and a receiving unit 10 for receiving terrestrial digital broadcast waves transmitted from a broadcast station BR. The receiving unit 10 amplifies the terrestrial digital broadcast signal received by the antenna 11 while adjusting the gain so that the signal is output at a predetermined level in an amplifier AGC unit 110. The terrestrial digital broadcast signal from the amplifier AGC unit 110 is converted to an intermediate frequency by a first mixer 111 to which a local oscillation signal from a local oscillator 114 is supplied, and predetermined signal processing is performed by an intermediate frequency signal processing unit 112. The intermediate frequency signal output from the intermediate frequency signal processing unit 112 is returned to the frequency band of the terrestrial digital broadcast signal by a second mixer 113 to which a local oscillation signal from the local oscillator 114 is supplied. The terrestrial digital broadcast signal output from the second mixer 113 is amplified to a predetermined level in an amplifier unit 115 and then supplied to a laser diode (LD) 116. The terrestrial digital broadcasting signal converted into an optical signal output from the LD 116 is sent to the first optical line 12 and transmitted toward the gap filler transmitting station GTx as shown in FIG. The phase noise φ of the local oscillator 114 L Since the local oscillation signal of the local oscillator 114 is supplied to the first mixer 111 and the second mixer 113, the phase noise φ L Therefore, in the gap filler receiving station GRx, the phase noise φ L This means that the above phenomenon has not occurred.

[0027] [Gap filler transmitter] FIG. 6 is a block diagram showing the configuration of a gap filler transmitting station GTx in an observation system 2 according to a second embodiment of the present invention. The gap filler transmitting station GTx shown in FIG. 6 includes a transmitter 30, a first transmitting antenna 31, and a second transmitting antenna 32. A terrestrial digital broadcast signal transmitted from the gap filler receiving station GRx via a first optical line 12 is input to the transmitter 30. The input terrestrial digital broadcast signal is split into two optical signals by a coupler 130, and one of the split optical signals, the terrestrial digital broadcast signal, is sent to a second optical line 13 and transmitted to a measurement point M. The other optical signal, the terrestrial digital broadcast signal, split by the coupler 130, is converted back into an electrical terrestrial digital broadcast signal by a photodiode (PD) 131 and supplied to a transmitter 132, where it is amplified to a predetermined level and output. The terrestrial digital broadcast signal output from the transmitter 132 is split into two by the splitter 133, one of the split terrestrial digital broadcast signals being supplied to the first transmitting antenna 31 and the other of the split terrestrial digital broadcast signals being supplied to the second transmitting antenna 32. In this case, the directivities of the first transmitting antenna 31 and the second transmitting antenna 32 are directed toward the respective areas where multiple residences H are concentrated, and the terrestrial digital broadcast waves retransmitted from the first transmitting antenna 31 and the second transmitting antenna 32 can be well received by the residences H in the multiple areas. The first optical line 12 and the second optical line 13 are configured by a single optical fiber cable having multiple optical fibers, and each optical fiber of the multiple optical fibers is assigned to the first optical line 12 and the second optical line 13. Therefore, the first optical line 12 and the second optical line 13 have the same length and almost the same transmission characteristics. Furthermore, even if an intermediate frequency signal processing unit is provided in the transmitter 132, phase noise does not occur. This is because the same configuration as that of the gap filler receiving station GRx shown in Fig. 5 is adopted as the configuration for converting the terrestrial digital broadcast signal into an intermediate frequency signal and the configuration for returning the intermediate frequency signal to the frequency band of the terrestrial digital broadcast signal.

[0028] [Characteristic configuration of the water vapor observation system according to the second embodiment of the present invention] Next, a block diagram showing a characteristic configuration of a water vapor observation system 2 according to a second embodiment of the present invention is shown in FIG. As shown in FIG. 7 , the observation device 20 receives a digital terrestrial broadcast signal M1', which is a digital terrestrial broadcast wave transmitted from a broadcast station BR and received by a first antenna 21, and a digital terrestrial broadcast signal M2', which is a digital terrestrial broadcast wave transmitted from a gap filler transmitter station GTx and received by a second antenna 22. The observation device 20 measures a phase measurement quantity M1 of the digital terrestrial broadcast signal M1' and a phase measurement quantity M2 of the digital terrestrial broadcast signal M2'. The observation device 20 also receives a digital terrestrial broadcast signal R2', which is an optical signal transmitted from the gap filler transmitter station GTx via a second optical line 13 and converted into an electrical signal by a PD 24. The observation device 20 also measures a phase measurement quantity R2 of the digital terrestrial broadcast signal R2'. In this case, the digital terrestrial broadcast signal M1', the digital terrestrial broadcast signal M2', and the digital terrestrial broadcast signal R2' are input to a combiner 23, where they are combined and output to a complex delay profile measurement / phase difference measurement unit 25. In the complex delay profile measurement / phase difference measurement unit 25, the terrestrial digital broadcast signals M1', M2', and R2' are displayed as a complex delay profile, and measurands M1, M2, and R2 are measured from this complex delay profile, and the phase difference between the measurands M2 and M1 and the phase difference between the measurands R2 and M1 are measured. An example of a complex delay profile is shown in Fig. 4, which will be described later. It can be seen that the complex delay profile shown in Fig. 4 is a complex delay profile of the measurands M1, M2, and R2. The terrestrial digital broadcast signal received by the receiving unit 10 of the gap filler receiving station GRx is transmitted to the gap filler transmitting station GTx via the first optical line 12, and the terrestrial digital broadcast signal, which is split into an optical signal by the coupler 130 in the gap filler transmitting station GTx, is transmitted to the observation device 20 via the second optical line 13. In this case, one optical fiber of the optical fiber cable with a multi-core structure is assigned to each of the first optical line 12 and the second optical line 13, as described above, and they are made to have the same line length and exhibit the same transmission characteristics.

[0029] [Observation of water vapor content] The observation of water vapor amount in the observation system 2 according to the second embodiment of the present invention will be described with reference to FIGS. The phase rotation corresponding to the delay time until the terrestrial digital broadcasting wave transmitted from the broadcasting station BR reaches the gap filler receiving station GRx installed at the same location and the measurement point M is defined as τ1, the phase rotation corresponding to the delay time until the terrestrial digital broadcasting wave retransmitted from the gap filler transmitting station GTx reaches the measurement point M is defined as τa, the phase rotation corresponding to the delay time until the terrestrial digital broadcasting signal is transmitted on the first optical line 12 and reaches the gap filler receiving station GRx to the gap filler transmitting station GTx is defined as (τb+τc), and the phase rotation corresponding to the delay time until the terrestrial digital broadcasting signal is transmitted on the second optical line 13 and reaches the gap filler transmitting station GTx to the gap filler receiving station GRx is defined as (τb+τc). Also, the phase noise of the local oscillator of the transmitting section in the broadcasting station BR is defined as φ T , the phase noise of the local oscillator in the complex delay profile measurement and phase difference measurement unit 25 of the observation device 20 at the measurement point M is φ MThe first optical line 12 and the second optical line 13 have the same line length and exhibit the same transmission characteristics, so the delay time (phase rotation) is equal, but the phase rotation is defined as (τb + τc) because the optical fiber lines in the first optical line 12 and the second optical line 13 generally use silica-based glass fiber, which has an extremely small expansion coefficient but can cause errors as the length of the optical line increases, so the phase rotation corresponding to the expansion length based on the expansion coefficient is defined as τc. In other words, the delay time (phase rotation) changes depending on the temperature, so the phase rotation of the first optical line 12 and the second optical line 13 is expressed as the sum of the fixed phase rotation τb and the phase rotation τc, which changes depending on the temperature.

[0030] Using the above notation, the measured amount of phase rotation M1, which corresponds to the delay time from when the terrestrial digital broadcasting wave transmitted from broadcasting station BR arrives at measurement point M until the complex delay profile is observed, is M1=τ1+φ T +φ M (14) Furthermore, if the measured amount of phase rotation corresponding to the delay time from when the terrestrial digital broadcasting signal is received by the gap filler receiving station GRx installed at the same point as the measurement point M to when it reaches the gap filler transmitting station GTx via the first optical line 12 is R1, then R1=τ1+τb+τc+φ T (15) However, the measured value R1 is used for the purpose of explanation, and the measured value R1 is not actually measured in the gap filler transmitting station GTx. In the gap filler receiving station GRx, as described above, the phase noise φ L are cancelled out. When the terrestrial digital broadcasting wave is retransmitted from the gap filler transmitting station GTx, the retransmitted terrestrial digital broadcasting wave is received at the measurement point M. The measured amount M2 of phase rotation, which corresponds to the delay time until the terrestrial digital broadcasting wave retransmitted from the gap filler transmitting station GTx reaches the measurement point M, is given by M2=R1+τa+φ M =τ1+τa+τb+τc+φ T +φM (16) Furthermore, the measured value R2 of the phase of the phase rotation, which corresponds to the delay time from when the terrestrial digital broadcasting signal transmitted from the gap filler transmitting station GTx via the second optical line 13 reaches the measurement point M until the complex delay profile is observed, is given by R2=R1+τb+τc+φ M =(τ1+τb+τc+φ T )+τb+τc+φ M =τ1+2(τb+τc)+φ T +φ M (17) Here, the measurands M1, M2, and R2 are measured as a complex delay profile by the complex delay profile measurement and phase difference measurement unit 25 in the observation device 20, and an example of the measured complex delay profile is shown in FIG.

[0031] As shown in Figure 4, the complex delay profile has a time axis on the horizontal axis and an amplitude axis on the vertical axis, with the phase rotation indicated by the delay time on the horizontal axis. The terrestrial digital broadcasting signal received by the gap filler receiving station GRx is transmitted to the gap filler transmitting station GTx via the first optical line 12, and the terrestrial digital broadcasting wave is then retransmitted from the gap filler transmitting station GTx and reaches the measurement point M, whereupon the phase rotation D1, which corresponds to the delay time until the complex delay profile is observed, can be calculated as (M2 - M1). That is, D1=(M2-M1)=(τ1+τa+τb+τc+φ T +φ M )-(τ1+φ T +φ M ) =τa+τb+τc (18) In this case, the phase noise φ of the broadcasting station BR that causes the error T and the phase noise φ of the observation device 20 MIt can be seen that this is removed in the phase rotation D1. Furthermore, the phase rotation D2, which corresponds to the delay time from when the terrestrial digital broadcasting signal transmitted from the broadcasting station BR and received by the gap filler receiving station GRx is transmitted to the gap filler transmitting station GTx via the first optical line 12, returns from the gap filler transmitting station GTx via the second optical line 13, and arrives at the measurement point M where the complex delay profile is observed, can be calculated by (R2-M1). That is, D2=(R2-M1)={τ1+2(τb+τc)+φ T +φ M}-(τ1+φ T +φ M ) =2(τb+τc) (19) In this case, the phase noise φ of the broadcasting station BR that causes the error T and the phase noise φ of the observation device 20 M It can be seen that this is removed in the phase rotation D2. Furthermore, since D2 is a phase rotation equivalent to the delay time travelling back and forth on the optical line between the gap filler receiving station GRx and the gap filler transmitting station GTx, it is clear that the phase rotation equivalent to the one-way delay time on the optical line between the gap filler receiving station GRx and the gap filler transmitting station GTx is (D2 / 2). Then, the phase rotation equivalent to the delay time from when the terrestrial digital broadcasting wave retransmitted from the gap filler transmitting station GTx arrives at the measurement point M until the complex delay profile is observed can be calculated as (D1 - D2 / 2), and so D1-D2 / 2=(τa+τb+τc)-(τb+τc)=τa (20) and the phase rotation τa is calculated as the delay time until the terrestrial digital broadcasting wave retransmitted from the gap filler transmitting station GTx reaches the measurement point M. In this case, it can be seen that the delay times in the first optical line 12 and the second optical line 13 are canceled out, and the influence of the expansion coefficient of the optical fiber is eliminated. By finding the values ​​of the phase rotations D1 and D2 from the complex delay profile shown in Figure 4 in the complex delay profile measurement / phase difference measurement unit 25, the phase rotation τa can be calculated from equation (20).

[0032] As described above, the water vapor observation system 2 according to the present invention utilizes the fact that the terrestrial digital broadcasting waves from the broadcasting station BR and the terrestrial digital broadcasting waves retransmitted from the gap filler transmitting station GTx are phase-synchronized, thereby making it possible to remove phase noise between the broadcasting station BR and the measurement point M without requiring any synchronization means. The water vapor observation system 2 according to the present invention utilizes the phase rotation τa, which corresponds to the delay time until the terrestrial digital broadcasting waves retransmitted from the gap filler transmitting station GTx reach the measurement point M, and the speed of radio waves in a vacuum (2.99792458×10 8 The propagation delay time between measurement point M and gap filler transmitting station GTx can be calculated based on the difference between the phase rotation corresponding to the delay time it takes for the terrestrial digital broadcasting wave to reach measurement point M from gap filler transmitting station GTx (based on the propagation delay time of the gap filler transmitting station GTx and the phase rotation corresponding to the delay time it takes for the terrestrial digital broadcasting wave to reach measurement point M from gap filler transmitting station GTx).The amount of water vapor in the atmosphere between gap filler transmitting station GTx and measurement point M can be observed based on the calculated propagation delay time. In this case, the humidity can be determined by referring to the graph of propagation delay time as a function of humidity under conditions of 1 atmosphere and a temperature of 20°C shown in Figure 8, and the amount of water vapor can be calculated from the determined humidity. The horizontal axis of the graph in Figure 8 represents the propagation distance [km], and the vertical axis represents the propagation delay time [sec]. The graph shows the results for humidity settings of 100%, 80%, 60%, 40%, and 20%. In Figure 8, when radio waves propagate over a distance of 5 km, a 1% increase in humidity results in a propagation delay of approximately 17 ps (picoseconds), which corresponds to a length of approximately 5 mm. Because the delay due to water vapor is so small, effective observation requires highly accurate measurements (at least on the order of tens of ps). At measurement point M, a complex delay profile is measured and phase rotation is observed from the in-phase component I signal and the quadrature component Q signal. However, instead of the complex delay profile, a delay profile may be measured at measurement point M and phase rotation may be observed from amplitude information.

[0033] [Modification of the water vapor observation system according to the present invention] An example of an actually measured complex delay profile is shown in Fig. 9. In the complex delay profile shown in Fig. 9, one reflected wave (multipath) is observed. In this case, when the complex delay profile shown in Fig. 9 is measured by the complex delay profile measurement and phase difference measurement unit 25 of the observation device 20, the reflected wave corresponds to the measured quantity M2 of the terrestrial digital broadcasting wave retransmitted from the gap filler transmitting station GTx. However, in the complex delay profile shown in Fig. 9, the level of the measured quantity M2 is too low, which may make it difficult for the complex delay profile measurement and phase difference measurement unit 25 to measure the propagation delay time with high accuracy. Therefore, a means for measuring the propagation delay time with high accuracy in the complex delay profile measurement and phase difference measurement unit 25 is shown in Figures 10(a) and 10(b). In the means shown in Figure 10(a), the antenna at measurement point M is the observation equipment antenna 26A. The observation equipment antenna 26A is a high-gain Yagi antenna equipped with a reflector having multiple reflecting elements and multiple directors, and is installed so that it has high directivity in the direction in which the retransmitted wave RT arrives and low directivity in the direction in which the direct wave from the broadcast station BR arrives. This increases the reception level of the retransmitted wave RT, and the complex delay profile measured by the complex delay profile measurement and phase difference measurement unit 25 can be made into a complex delay profile with a high level of the retransmitted wave RT, as shown in Figure 11. In other words, the complex delay profile measurement and phase difference measurement unit 25 can measure the propagation delay time with high accuracy.

[0034] In the means shown in FIG. 10(b), the antenna at measurement point M is designated observation device antenna 26B. Observation device antenna 26B includes two Yagi antennas, each of which includes a reflector with multiple reflecting elements and multiple directors. One Yagi antenna is designated first antenna 21 shown in FIGS. 3 and 7 and has high directivity in the direction of the direct wave arriving from broadcast station BR. The other Yagi antenna is designated second antenna 22 shown in FIGS. 3 and 7 and has high directivity in the direction of the retransmitted wave RT. The direct wave DT received by first antenna 21 is amplified by amplifier (AMP) 27, its level adjusted by attenuation resistor Re1, and supplied to combiner 23. The retransmitted wave RT received by second antenna 22 is amplified by amplifier (AMP) 28, its level adjusted by attenuation resistor Re2, and supplied to combiner 23. The outputs from attenuation resistors Re1 and Re2 are combined by combiner 29 and output. This makes it possible to adjust the reception levels of the direct wave DT and the retransmitted wave RT output from the combiner 29, and the complex delay profile measured by the complex delay profile measurement and phase difference measurement unit 25 can be made into a complex delay profile with a high level of the retransmitted wave RT as shown in Fig. 11. In other words, the complex delay profile measurement and phase difference measurement unit 25 can measure the propagation delay time with high accuracy.

[0035] [Arrangement of gap-filler transmitting stations in the water vapor observation system according to the present invention] Next, the positions of the gap filler receiving stations GRx and gap filler transmitting stations GTx in the water vapor observation system 2 according to the present invention will be described with reference to the overhead view shown in Fig. 12. Fig. 12 is an overhead view seen from above. In conclusion, in the water vapor observation system 2 according to the present invention, it is not necessary to place the gap filler transmitter station GTx on a straight line connecting the broadcast station BR with the measurement point M and the gap filler receiving station GRx. The gap filler transmitter station GTx can be placed anywhere as long as it can retransmit terrestrial digital broadcast waves to multiple residences H. The reason why it does not need to be placed on a straight line will be explained with reference to FIG. 12. As shown in FIG. 12, the gap filler transmitter station GTx is not placed on a straight line connecting the broadcast station BR with the measurement point M and the gap filler receiving station GRx. This is because an obstacle S exists on the straight line connecting the broadcast station BR with the gap filler receiving station GRx, making it impossible to place the gap filler transmitter station GTx on the straight line. Even if the gap filler transmitter station GTx is placed as shown in FIG. 12, the terrestrial digital broadcast signal is transmitted via optical lines 12 and 13 laid between the measurement point M and the gap filler receiving station GRx and the gap filler transmitter station GTx. Therefore, the above equations (15) to (20) hold true in the case shown in FIG. 12. That is, even if the gap filler transmitting station GTx is arranged as shown in Fig. 12, the phase rotation corresponding to the delay time propagating the distance N2 between the measurement point M and the gap filler transmitting station GTx is expressed as τa. Therefore, even if the gap filler transmitting station GTx is arranged as shown in Fig. 12, no error occurs in the propagation delay time. [Industrial Applicability]

[0036] In the water vapor observation system according to the present invention described above, the measurement point can be installed on an extension of the straight line connecting the broadcasting station with the gap filler receiving station and the gap filler transmitting station. The gap filler receiving station and the measurement point can also be installed at the same location. In this case, since the gap filler system is generally already installed, if there is room in the gap filler receiving station building, the antenna and observation equipment that make up the measurement point can be installed in the gap filler receiving station building. Furthermore, when a new gap filler system is installed, the gap filler receiving station and the measurement point can be combined into one. The water vapor observation system of the present invention described above utilizes the phase synchronization between terrestrial digital broadcast waves from a broadcast station and terrestrial digital broadcast waves retransmitted from a gap filler transmitting station. Simply installing a measurement point equipped with an antenna and observation equipment enables water vapor observation between a gap filler transmitting station and a gap filler receiving station or measurement point. Therefore, only one measurement point is required, eliminating the need for two measurement points and the need to synchronize the two measurement points. Furthermore, no reflector is required, and if the measurement point is installed at the same location as the gap filler receiving station, there is no need to place all equipment on a straight line connecting the broadcast station and the measurement point. Even if the measurement point is installed on an extension of the line connecting the broadcast station and the gap filler receiving station or gap filler transmitting station, it is not necessary to place measurement point M on that extension if corrections can be made based on not placing measurement point M on that extension. Furthermore, in the water vapor observation system according to the present invention, when the system is installed at the same location as a gap filler receiving station, the gap filler system is already installed, so the multi-core optical fiber cable constituting the first optical line is already installed. Therefore, unused optical fibers in the multi-core optical fiber cable constituting the existing first optical line can be used as the second optical line connecting the gap filler transmitting station and the measurement point. In this way, the work of laying a new optical line can be eliminated. While coaxial lines can be used instead of the first and second optical lines, if the gap filler transmitting station is installed far away from the gap filler receiving station, coaxial lines are not suitable due to the large transmission loss. Therefore, using the first and second optical lines is preferred. Furthermore, the water vapor observation system of the present invention can eliminate phase noise at the transmitting station and measurement point, which can cause measurement errors, and can also offset changes in delay time due to expansion and contraction of the optical path, which can cause measurement errors when installed at the same location as the gap filler receiving station. Furthermore, it has been explained that a complex delay profile is measured at measurement point M and phase rotation is observed from the in-phase component I signal and the quadrature component Q signal, but it is also possible to measure a delay profile instead of a complex delay profile at measurement point M and observe phase rotation from amplitude information. [Explanation of symbols]

[0037] 1,2 Water vapor observation system, 01 receiving antenna, 02 transmitting antenna, 03 optical line, 04 receiving antenna, 10 receiving unit, 11 antenna, 12 first optical line, 13 second optical line, 20 observation equipment, 21 first antenna, 22 second antenna, 23 combiner, 25 complex delay profile measurement / phase difference measurement unit, 26A observation equipment antenna, 26B observation equipment antenna, 27 amplifier, 28 amplifier, 29 combiner, 30 transmitting unit, 31 first transmitting antenna, 32 second transmitting antenna, 110 amplifier AGC unit, 111 first mixer, 112 intermediate frequency signal processing unit, 113 second mixer, 114 local oscillator, 115 amplifier unit, 116 laser diode, 130 coupler, 131 photodiode, 132 transmitter, 133 distributor, 200 Gap filler system, 410 receiving unit, 411 antenna, 500 broadcasting station, 530 transmitting unit, 531 first transmitting antenna, 532 second transmitting antenna, 533 distributor, BR broadcasting station, GRx gap filler receiving station, GTx gap filler transmitting station, H house, M measurement point, Re1 attenuation resistor, Re2 attenuation resistor, Rx gap filler receiving station, S obstacle, T communication line, Tx gap filler transmitting station

Claims

1. a gap filler receiving station that receives a terrestrial digital broadcast wave from a broadcast station and transmits the terrestrial digital broadcast signal to a gap filler transmitting station via a first communication line; a gap filler transmitting station that retransmits the terrestrial digital broadcast signal transmitted from the gap filler receiving station as a terrestrial digital broadcast wave; a measurement point that is installed on an extension of a straight line connecting the broadcast station, the gap filler receiving station, and the gap filler transmitting station, and that is capable of receiving terrestrial digital broadcast waves from the broadcast station and terrestrial digital broadcast waves retransmitted from the gap filler transmitting station; A water vapor observation system characterized in that the measurement point observes the amount of water vapor in the atmosphere between the gap filler receiving station and the gap filler transmitting station based on a measured amount of phase rotation G1 corresponding to the delay time until the terrestrial digital broadcast wave reaches the measurement point directly from the broadcast station, and a measured amount of phase rotation G2 corresponding to the delay time until the terrestrial digital broadcast wave reaches the measurement point from the broadcast station via the gap filler receiving station, the first communication line, and the gap filler transmitting station.

2. a gap filler receiving station that receives a terrestrial digital broadcast wave from a broadcast station and transmits the terrestrial digital broadcast signal to a gap filler transmitting station via a first communication line; a gap filler transmitting station that retransmits the terrestrial digital broadcast signal transmitted from the gap filler receiving station as a terrestrial digital broadcast wave and transmits the terrestrial digital broadcast signal to a measurement point via a second communication line; the measurement point is provided with an observation device that is arranged at the same position as the gap filler receiving station and is capable of receiving terrestrial digital broadcast waves from the broadcast station, terrestrial digital broadcast waves retransmitted from the gap filler transmitting station, and terrestrial digital broadcast signals transmitted from the gap filler transmitting station via the second communication line; A water vapor observation system characterized in that the observation device observes the amount of water vapor in the atmosphere between the measurement point and the gap filler transmitting station based on a measured amount of phase rotation M1 corresponding to the delay time until the terrestrial digital broadcast wave arrives at the measurement point from the broadcast station, a measured amount of phase rotation M2 corresponding to the delay time until the terrestrial digital broadcast wave retransmitted from the gap filler transmitting station arrives at the measurement point, and a measured amount of phase rotation R2 corresponding to the delay time until the terrestrial digital broadcast signal transmitted over the second communication line arrives at the measurement point.

3. The water vapor amount observation system described in claim 2, characterized in that the observation device observes the water vapor amount by calculating a first phase rotation corresponding to the delay time it takes for a terrestrial digital broadcast wave to reach the measurement point from the gap filler transmitting station based on a delay profile of the measurand M1, the measurand M2, and the measurand R2.

4. The water vapor observation system of claim 3, characterized in that a third phase rotation D1, which is the sum of the first phase rotation and a second phase rotation corresponding to the delay time it takes for the terrestrial digital broadcast signal to reach the gap filler transmitting station from the gap filler receiving station via the first communication line, is obtained by calculating the difference between the measurand M2 and the measurand M1, and a fourth phase rotation corresponding to the delay time it takes for the terrestrial digital broadcast signal to reach the gap filler transmitting station from the gap filler receiving station via the first communication line, and then to be folded back from the gap filler transmitting station by the second communication line and reach the measurement point, is obtained by calculating the difference between the measurand R2 and the measurand M1, and the first phase rotation is calculated based on the third phase rotation D1 and the fourth phase rotation D2.

5. The water vapor observation system described in claim 3, characterized in that the amount of water vapor in the atmosphere between the measurement point and the gap filler transmitting station is observed based on a propagation delay time which is the difference between the first phase rotation and a phase rotation corresponding to the delay time it takes for a terrestrial digital broadcast wave to reach the measurement point from the gap filler transmitting station based on the speed of radio waves in a vacuum.

6. A water vapor observation system as described in any one of claims 2 to 5, characterized in that in the gap filler receiving station, a local oscillation signal from one local oscillator is applied to a first mixer that converts the terrestrial digital broadcast signal received from the transmitting station into an intermediate frequency signal, and a second mixer that converts the intermediate frequency signal back into a terrestrial digital broadcast signal, thereby canceling out the phase noise of the gap filler receiving station.

7. A water vapor observation system as described in any one of claims 2 to 6, characterized in that in the gap filler transmitting station, the terrestrial digital broadcasting signal transmitted from the gap filler receiving station is distributed by a distribution means, and one of the distributed terrestrial digital broadcasting signals is transmitted to the measurement point via the second communication line.

8. A water vapor observation system as described in any one of claims 2 to 7, characterized in that at the measurement point, terrestrial digital broadcast waves from the broadcast station are received by a first receiving means, terrestrial digital broadcast waves from the gap filler transmitting station are received by a second receiving means, and level adjustment is performed between the first received signal received by the first receiving means and the second received signal received by the second receiving means.

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