Patent Description:
Conventionally, an observation device for water vapor as shown in Patent Document <NUM> is known.

"<NPL>) is concerned with a terahertz superconducting radiometric spectrometer that is a dual-band heterodyne receiver system based on high sensitive superconductor-insulator-superconductor mixers which cover the frequency range of <NUM> to <NUM>.

<CIT> discloses a frequency changing part that changes an input signal into an intermediate frequency and a level detecting part that outputs a level detection signal proportionate to the logarithm of a signal level. A gain control part that corrects a frequency characteristic of the frequency changing part according to an instruction of a control part. A corrective means that is inserted in the middle of a gain control signal path for making an appropriate temperature correction.

One method of observing water vapor is to use an intensity of radiated electromagnetic waves (RF signals). In this case, there is a problem that the observation result has an error due to the characteristics of circuit elements constituting the observation device such as a detector.

Accordingly, it is an object of the present invention to provide an observation technique capable of reducing errors in observation results.

This is achieved by the claimed subject-matter, which defines the present invention. Embodiments not covered by the claims do not form part of the present invention.

According to the present invention, the error of the observation result can be reduced.

The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein:.

An observation technique according to a first embodiment of the present invention will be described with reference to the drawings. <FIG> is a block diagram showing a configuration of an observation device <NUM> according to a first embodiment. Note that the observation techniques shown in the following embodiments are used for the observation of water vapor. However, the configuration of the observation device <NUM> according to the present embodiment can be applied to a device for observing a radio frequency (RF) signal such as an electromagnetic wave emitted to an observation object.

As shown in <FIG>, the observation device <NUM> includes a mixer <NUM>, a reference signal generator <NUM>, a local signal generator <NUM>, an intermediate frequency (IF) filter <NUM>, an amplifier <NUM>, a detector <NUM>, a noise suppression filter <NUM>, an operation module <NUM>, and a variable attenuator (variable ATT) <NUM>. The calculation module <NUM> includes a calibration information setting module <NUM> and an observation data generating module <NUM>.

The mixer <NUM>, the local signal generator <NUM>, the IF filter <NUM>, the amplifier <NUM>, the detector <NUM>, the noise suppression filter <NUM>, and the variable attenuator (variable ATT) <NUM> can be realized, for example, by a predetermined analog electronic circuit. The reference signal generator <NUM> and the operation module <NUM> can be realized by, for example, an arithmetic element such as a CPU and a program executed by the arithmetic element.

The observation device <NUM> has an input terminal Pin. The input terminal Pin is connected to an antenna ANT via a first stage low noise amplifier (LNA) (not shown). The input terminal Pin is connected to the mixer <NUM>. In this case, the mixer <NUM> is directly connected to the first stage LNA. The local signal generator <NUM> is connected to the mixer <NUM>. The local signal generator <NUM> is connected to a reference signal generator <NUM>. The reference signal generator <NUM> is connected to the calculation module <NUM>.

The mixer <NUM> is connected to the IF filter <NUM>, and the IF filter <NUM> is connected to the amplifier <NUM>. The amplifier <NUM> is connected to the variable attenuator <NUM>, and the variable attenuator <NUM> is connected to the detector <NUM>. The detector <NUM> is connected to a noise suppression filter <NUM>, and the noise suppression filter <NUM> is connected to the operation module <NUM>.

The antenna ANT receives an electromagnetic wave radiated from a black radiator (blackbody) <NUM> or an electromagnetic wave radiated from water vapor to be observed. The RF signal (electromagnetic wave) received by the antenna ANT is inputted to the input terminal Pin via the first stage LNA.

The RF signal input to the input terminal Pin is input to the mixer <NUM>.

The reference signal generator <NUM> generates, for example, a reference signal composed of sawtooth waves. The reference signal generator <NUM> outputs the reference signal to the local signal generator <NUM> and the operation module <NUM>.

The local signal generator <NUM> generates a local signal of a predetermined frequency based on the reference signal. A frequency of the local signal is set within a frequency range of a frequency spectrum of an observation object. The local signal generator <NUM> individually generates local signals of a plurality of frequencies. In other words, the local signal generator <NUM> generates the local signals of the plurality of frequencies at different timings. The local signal generator <NUM> outputs the local signal to the mixer <NUM>.

The mixer <NUM> mixes the RF signal and the local signal to down-convert them to generate an IF signal. The mixer <NUM> outputs the IF signal to the IF filter <NUM>.

The IF filter <NUM> has filter characteristics including a frequency necessary for generating observation data of the observation object in a pass region and other noise components in an attenuation region. The IF filter <NUM> filters the IF signal and outputs it to the amplifier <NUM>.

The amplifier <NUM> amplifies the IF signal and outputs it to the variable attenuator <NUM>.

The variable attenuator <NUM> has a circuit configuration capable of adjusting an attenuation of the IF signal. An attenuation of the variable attenuator <NUM> can be set, for example, by the calibration information setting module <NUM> of the operation module <NUM>. The IF signal that has passed through the variable attenuator <NUM> is input to the detector <NUM>.

The detector <NUM> detects the IF signal and outputs a detection signal.

The noise suppression filter <NUM> is realized by, for example, a smoothing filter. The noise suppression filter <NUM> suppresses a noise component of the detection signal and outputs it to the operation module <NUM>.

The calibration information setting module <NUM>, which will be described later in detail, sets calibration information for calibrating errors caused by the circuits up to the detector <NUM> including the detector <NUM>. The calibration information setting module <NUM> outputs the calibration information to the observation data generating module <NUM>.

The observation data generating module <NUM> generates the observation data by using a detection signal (reference detection signal) obtained in a state where the blackbody <NUM> covers a reception surface of the antenna ANT and a detection signal (observation object detection signal) obtained in a state where the blackbody <NUM> is removed from the reception surface of the antenna ANT. In this case, the reference detection signal and the observation object detection signal are obtained in a state where the attenuation of the variable attenuator <NUM> is fixed.

More specifically, the observation data generating module <NUM> receives the reference detection signal and the observation object detection signal in a state where the attenuation of the variable attenuator <NUM> is fixed. The observation data generating module <NUM> generates the observation data from a difference (intensity difference) between an intensity of the reference detection signal and an intensity of the observation object detection signal.

The observation data generating module <NUM> calculates an intensity difference for each of a plurality of frequency components of the RF signal. Thus, the observation data generating module <NUM> obtains the frequency spectrum of the radiated electromagnetic wave for the phenomenon to be observed as the observation data.

At this time, the observation data generating module <NUM> performs calibration in advance using the calibration information. Thus, errors due to the detector <NUM> and the like included in the intensity difference are suppressed. Therefore, the observation data becomes a highly accurate value (value with little error) corresponding to the intensity of the radiation electromagnetic wave of the observation object.

The detector <NUM> generally has, for example, a temperature characteristic. Note that, although circuit elements (electronic devices) other than the detector <NUM> also have temperature characteristics, in the present application, the detector <NUM>, which has a large influence on the output due to the temperature characteristics, will be mainly described. Accordingly, the intensity of the detection signal varies depending on a temperature of the detector <NUM>, for example, an environmental temperature of the observation device <NUM>. As described above, when the intensity of the detection signal changes depending on the environmental temperature, an error occurs in the observation data. Therefore, the observation device <NUM> sets the calibration information according to the following concept and uses it for the generation of the observation data.

<FIG> is a graph showing a relationship between the intensity of the detected signal and an attenuation amount, and <FIG> is a graph showing the definition of the intensity difference.

The calibration information is set, for example, in a state where the blackbody <NUM> covers the receiving surface of the antenna ANT. It should be noted that the blackbody <NUM> need not be used as long as the environment in which an RF signal having a constant signal intensity is input to the antenna ANT can be maintained.

The calibration information setting module <NUM> generates a control signal for changing the attenuation to the variable attenuator <NUM>. The variable attenuator <NUM> changes the attenuation amount according to the control signal. Thus, the variable attenuator <NUM> attenuates and outputs the IF signal with the set attenuation amount.

The calibration information setting module <NUM> adjusts the attenuation of the variable attenuator <NUM> and acquires an intensity of the detection signal for the plurality of attenuation amounts. The set attenuation amount is set within a range necessary for generation of the observation data, and the number of set attenuation amount can be appropriately set.

The calibration information setting module <NUM> calculates an amount of change ΔPt of the intensity of the detection signal with respect to an amount of change ΔATT of the attenuation of the variable attenuator <NUM>, as shown in <FIG>, from the relationship between the difference of the plurality of attenuation amounts and the difference of the intensity of the detection signal with respect to each attenuation amount. In this case, the calibration information setting module <NUM> may calculate the amount of change ΔPt by calculating an average value or the like by using a plurality of sets of the difference between the plurality of attenuation amounts and the difference in intensity of the detection signal with respect to each attenuation amount.

As described above, the detector <NUM> and the like have a temperature characteristic. Therefore, as shown in <FIG>, an amount of change ΔPt1 (a rate of change Kt1 of the signal intensity) of the detected signal intensity at a temperature t1 with respect to the amount of change ΔATT of the attenuation of the variable attenuator <NUM> at the temperature t1 is different from an amount of change ΔPt2 (a rate of change Kt2 of the signal intensity) of the detected signal intensity at a temperature t2 with respect to the amount of change ΔATT of the attenuation of the variable attenuator <NUM> at the temperature t2.

The calibration information setting module <NUM> calculates a rate of change Kt of the intensity depending on the temperature. Then, the calibration information setting module <NUM> calculates the calibration information, for example, by using the rate of change Kt as the calibration information or by using the rate of change Kt.

Thus, the calibration information appropriately reflects the temperature characteristic of the detector <NUM> or the like.

The observation data generating module <NUM> generates the observation data from the difference (intensity difference) between the intensity of the reference detection signal and the intensity of the observation object detection signal, as described above. The observation data generating module <NUM> generates the observation data from, for example, an intensity difference ΔP1, an intensity difference ΔP2, and an intensity difference ΔP3 shown in <FIG>. That is, the observation data generating module <NUM> generates the observation data from the intensity difference between the detection signals in the two different states.

Therefore, by using the rate of change Kt of the intensity as the calibration information, the observation data generating module <NUM> can accurately calibrate the intensity difference of the detection signal, and can generate a highly accurate observation data. For example, the observation data generating module <NUM> normalizes the intensity difference between the reference detection signal and the observation object detection signal by using the rate of change Kt. Thus, the observation data generating module <NUM> can suppress an error caused by the temperature characteristic or the like of the detector <NUM> and generate a high-precision observation data.

In the present embodiment, the two different states are a state in which radiated electromagnetic waves are received from the blackbody <NUM> and a state in which radiated electromagnetic waves are received from water vapor. Therefore, the observation device <NUM> can generate the observation data corresponding to the intensity of the radiation electromagnetic wave of water vapor with high accuracy.

As described above, by using the configuration of this embodiment, the observation device <NUM> can generate an observation data of a phenomenon to be observed, such as water vapor, with high accuracy. The observation device <NUM> can set calibration information only by generating a detection signal while adjusting the attenuation using the variable attenuator <NUM>. That is, the observation device <NUM> can set the calibration information with a simple configuration and simple processing, and can generate a highly accurate observation data.

<FIG> is an equivalent circuit diagram showing an example of the circuit configuration of the variable attenuator <NUM>. As shown in <FIG>, the variable attenuator <NUM> includes a variable impedance circuit <NUM>, a fixed resistance circuit <NUM>, and a fixed resistance circuit <NUM>. The fixed resistance circuit <NUM> corresponds to the "first fixed resistance circuit" of the present invention, and the fixed resistance circuit <NUM> corresponds to the "second fixed resistance circuit" of the present invention.

The variable impedance circuit <NUM>, the fixed resistance circuit <NUM>, and the fixed resistance circuit <NUM> are connected in series. At this time, the variable impedance circuit <NUM> is connected between the fixed resistance circuit <NUM> and the fixed resistance circuit <NUM>. The fixed resistance circuit <NUM> is connected to the output terminal of the amplifier <NUM>, and the fixed resistance circuit <NUM> is connected to the detector <NUM>.

The variable impedance circuit <NUM> is a circuit including a resistance element and a semiconductor element, and changes impedance (resistance value) by a control signal flowing in the semiconductor element.

The fixed resistance circuit <NUM> and the fixed resistance circuit <NUM> have, for example, a circuit configuration in which a plurality of resistance elements are connected in a predetermined pattern. The fixed resistance circuit <NUM> functions as an impedance matching circuit between the variable impedance circuit <NUM> and the amplifier <NUM>. The fixed resistance circuit <NUM> functions as an impedance matching circuit between the variable impedance circuit <NUM> and the detector <NUM>. Thus, even if the impedance of the variable impedance circuit <NUM> is changed, the change and mismatch of the impedance between the variable attenuator <NUM> and the amplifier <NUM> can be suppressed, and the change and mismatch of the impedance between the variable attenuator <NUM> and the detector <NUM> can be suppressed. Therefore, the observation device <NUM> can obtain highly accurate calibration information and generate a highly accurate observation data.

In the above description, the setting process of the calibration information and the generation process of the observation data are shown to be realized by the respective functional parts, but each of the above-mentioned processes may be stored as a program, and the above-mentioned functions of the observation device <NUM> may be realized by executing the program by a computing device such as a computer. The specific contents of the respective processes are described above, and the explanation thereof is omitted except for portions where additional explanation is considered necessary.

<FIG> is a flow chart showing a first mode of the main process executed by the observation device <NUM>, and <FIG> is a flow chart showing a second mode of the main process executed by the observation device <NUM>.

In the processing of <FIG>, a computing device constituting the observation device <NUM> sets calibration information (S11). An arithmetic module generates an observation data by using the calibration information (S12). This processing shows a case where the calibration information is set and used at the beginning of observation. This method may be used when the observation time is short.

In the processing of <FIG>, the arithmetic module sets initial calibration information (S101). The arithmetic module generates an observation data by using the initial calibration information (S12). The arithmetic module has a time counting function and repeats the process of generating the observation data by using the initial calibration information (S12) until a calibration time is reached (S13: NO).

When the calibration time is reached (S <NUM>: YES), the arithmetic module sets new calibration information (S102). Then, the arithmetic module performs calibration by using the updated calibration information, and generates the observation data (S12). By using such processing, the arithmetic module can periodically update the calibration information while continuously generating the observation data. The update of the calibration information is not limited to that based on the time, and may be performed, for example, when the level (intensity) of the electromagnetic wave of the blackbody <NUM> exceeds a preset reference value.

Therefore, the arithmetic module can continuously generate a high-precision observation data. In addition, since the temperature change of the detector is generally not rapid, by updating the calibration information at predetermined intervals, the arithmetic module can continuously generate the high-precision observation data while reducing the processing load.

<FIG> is a flow chart showing an example of a specific method of setting calibration information. As shown in <FIG>, the blackbody <NUM> is installed on the receiving surface of the antenna ANT (S21). The arrangement of the blackbody <NUM> may be mechanically controlled by providing a moving mechanism for the blackbody <NUM> on the antenna ANT or manually. The arithmetic module sets the attenuation of the variable attenuator <NUM> (S22). The arithmetic module measures the intensity of the detection signal obtained by the set attenuation amount of the variable attenuator <NUM> (S23).

The arithmetic module preliminarily sets the range of all attenuation amounts for obtaining the intensity difference necessary for generating the observation data. If the intensity of the detection signal is not obtained in all attenuation amounts (S24: NO), the arithmetic module changes the attenuation setting of the variable attenuator <NUM> (S22), and measures the intensity of the detection signal (S23).

When the detection signal is obtained for the whole range of attenuation amounts (S24: YES), the arithmetic module calculates the calibration information from the difference in the intensity of the detection signal in the different attenuation amounts, that is, the rate of change of the intensity (S25). Using the calibration information, the arithmetic module performs calibration for the measurement of the intensity described later (S26).

<FIG> is a flow chart showing an example of a specific method of generating an observation data. As shown in <FIG>, the computing device fixes the attenuation of the variable attenuator <NUM> (S31). In this case, the attenuation amount is preferably as small as possible.

The blackbody <NUM> is installed on the receiving surface of the antenna ANT (S32). The arrangement of the blackbody <NUM> may be mechanically controlled by providing a moving mechanism for the blackbody <NUM> on the antenna ANT or manually.

The arithmetic module measures the intensity of the reference detection signal (S33).

The blackbody <NUM> is removed from the receiving surface of the antenna ANT (S34). The removal of the blackbody <NUM> may be mechanically controlled by providing a moving mechanism for the blackbody <NUM> on the antenna ANT, or may be performed manually.

The arithmetic module measures the intensity of the observation object detection signal (S35).

The arithmetic module calculates an intensity difference between the intensity of the reference detection signal and the intensity of the observation object detection signal (S36). The arithmetic module generates an observation data from the intensity difference, that is, observes water vapor (S37).

An observation technique according to a second embodiment of the present invention will be described with reference to the drawings. <FIG> is a block diagram showing a configuration of an observation device 10A according to a second embodiment.

As shown in <FIG>, the observation device 10A according to the second embodiment differs from the observation device <NUM> according to the first embodiment in that the detection signals are measured in parallel by a plurality of circuits. In other respects, the configuration and processing of the observation device 10A are the same as those of the observation device <NUM>, and the description of the same points is omitted.

As shown in <FIG>, the observation device 10A includes a mixer <NUM>, a mixer <NUM>, the reference signal generator <NUM>, the local signal generator <NUM>, a distributor <NUM>, a distributor <NUM>, an IF filter <NUM>, an IF filter <NUM>, an amplifier <NUM>, an amplifier <NUM>, a detector <NUM>, a detector <NUM>, a noise suppression filter <NUM>, a noise suppression filter <NUM>, a operation module 50A, a variable attenuator (variable ATT) <NUM>, and a variable attenuator (variable ATT) <NUM>. The operation module 50A includes a calibration information setting module 501A and an observation data generating module 502A.

The distributor <NUM> and the distributor <NUM> are implemented by transmission lines of RF signals, such as waveguides.

The distributor <NUM> is connected to the local signal generator <NUM>, the mixer <NUM>, and the mixer <NUM>. The distributor <NUM> is connected to the input terminal Pin, the mixer <NUM>, and the mixer <NUM>.

The mixer <NUM> is connected to the IF filter <NUM>, and the IF filter <NUM> is connected to the amplifier <NUM>. The amplifier <NUM> is connected to the variable attenuator <NUM>, and the variable attenuator <NUM> is connected to the detector <NUM>. The detector <NUM> is connected to the noise suppression filter <NUM>, and the noise suppression filter <NUM> is connected to the operation module 50A.

The mixer <NUM> and the mixer <NUM> have the same configuration as the mixer <NUM> described above.

The IF filter <NUM> and the IF filter <NUM> have the same configuration as the IF filter <NUM> described above except for the filter characteristics. The IF filter <NUM> has filter characteristics including a first intermediate frequency f(IF1) in a pass region and a second intermediate frequency f(IF2) in an attenuation region. The IF filter <NUM> has filter characteristics including the second intermediate frequency f(IF2) in a pass region and the first intermediate frequency f(IF1) in an attenuation region. The first intermediate frequency f(IF1) is set to a frequency obtained by subtracting the frequency of the RF signal from the frequency of the local signal. The second intermediate frequency f(IF2) is set to a frequency obtained by subtracting the frequency of the local signal from the frequency of the RF signal.

The variable attenuator <NUM> and the variable attenuator <NUM> have the same configuration as the variable attenuator <NUM> described above. A control signal is inputted to the variable attenuator <NUM> and the variable attenuator <NUM> from the calibration information setting module 501A.

The detector <NUM> and the detector <NUM> have the same configuration as the detector <NUM> described above. The noise suppression filter <NUM> and the noise suppression filter <NUM> have the same configuration as that of the noise suppression filter <NUM>.

The local signal generator <NUM> generates a local signal of a predetermined frequency set by the reference signal. The frequency of the local signal is set to a frequency within a frequency band of a frequency spectrum used as the observation data.

The distributor <NUM> distributes the local signal and outputs it to the mixer <NUM> and the mixer <NUM>. The distributor <NUM> distributes the RF signal and outputs it to the mixer <NUM> and the mixer <NUM>.

The mixer <NUM> mixes the RF signal and the local signal and outputs a first IF signal. The mixer <NUM> mixes the RF signal and the local signal and outputs a second IF signal. The first IF signal and the second IF signal are the same signal.

The IF filter <NUM> performs filter processing on the first IF signal. The IF filter <NUM> performs filter processing on the second IF signal. As described above, the filter characteristics of the IF filter <NUM> and the filter characteristics of the IF filter <NUM> are different, and the frequency components of the filtered first IF signal and the frequency components of the filtered second IF signal are different.

The amplifier <NUM> amplifies the filtered first IF signal. The amplifier <NUM> amplifies the filtered second IF signal.

The amplified first IF signal is inputted to the detector <NUM> via the variable attenuator <NUM>. The amplified second IF signal is inputted to the detector <NUM> via the variable attenuator <NUM>.

The detector <NUM> detects the amplified first IF signal and outputs a first detection signal. The detector <NUM> detects the amplified second IF signal and outputs a second detection signal. The noise suppression filter <NUM> suppresses a noise component of the first detection signal and outputs it to the operation module 50A. The noise suppression filter <NUM> suppresses a noise component of the second detection signal and outputs it to the operation module 50A.

The calibration information setting module 501A sets calibration information (calibration information) for a first detection signal by using a change of an intensity of the first detection signal acquired by changing the attenuation of the variable attenuator <NUM> in a state that the blackbody <NUM> is arranged on the antenna ANT. The calibration information setting module 501A sets calibration information (second calibration information) for the second detection signal by using a change in the intensity of the second detection signal acquired by changing the attenuation of the variable attenuator <NUM> in a state where the blackbody <NUM> is arranged on the antenna ANT. The calibration information setting module 501A outputs the calibration information to the observation data generating module 502A.

The observation data generating module 502A generates observation data by using a difference in the intensity of the first detection signal acquired in a state where the blackbody <NUM> is arranged on the antenna ANT and a state where the blackbody <NUM> is removed from the antenna ANT, and a difference in the intensity of the second detection signal acquired in a state where the blackbody <NUM> is arranged on the antenna ANT and a state where the blackbody <NUM> is removed from the antenna ANT. In this case, the observation data generating module 502A uses the first calibration information to calibrate the intensity difference of the first detection signal and uses the second calibration information to calibrate the intensity difference of the second detection signal.

As described above, even in a configuration including a plurality of circuits for measuring the detection signal, the observation device 10A can generate a high-precision observation data.

Further, in this configuration, detection signals for RF signals of two frequencies are obtained from local signals of one frequency. Accordingly, the observation device 10A obtains the predetermined number of frequency spectrum components by the half number of local signals. The observation device 10A obtains a frequency spectrum of a predetermined frequency band by a local signal in a frequency band narrower than the predetermined frequency band. Thus, the observation device 10A can generate an observation data composed of a frequency spectrum having the predetermined frequency band with simpler processing while narrowing a frequency band set as a local signal.

An observation technique according to a third embodiment of the present invention will be described with reference to the drawings. <FIG> is a block diagram showing a configuration of an observation device 10B according to a third embodiment.

As shown in <FIG>, the observation device 10B according to the third embodiment differs from the observation device <NUM> according to the first embodiment in the arrangement position of the variable attenuator <NUM>. The other components of the observation device 10B are the same as those of the observation device <NUM>, and the description of the same parts will be omitted.

The variable attenuator <NUM> is connected between the mixer <NUM> and the IF filter <NUM>. In this configuration, the calibration information setting module <NUM> can set calibration information capable of suppressing errors caused by the IF filter <NUM>, errors caused by the amplifier <NUM>, and errors caused by the detector <NUM>.

An observation technique according to a fourth embodiment of the present invention will be described with reference to the drawings. <FIG> is a block diagram showing a configuration of an observation device 10C according to a fourth embodiment.

As shown in <FIG>, the observation device 10C according to the fourth embodiment differs from the observation device <NUM> according to the first embodiment in the arrangement position of the variable attenuator <NUM>. The other components of the observation device 10C are the same as those of the observation device <NUM>, and the description of the same parts will be omitted.

The variable attenuator <NUM> is connected between the IF filter <NUM> and the amplifier <NUM>. In this configuration, the calibration information setting module <NUM> can set calibration information capable of suppressing an error caused by the amplifier <NUM> and an error caused by the detector <NUM>.

Claim 1:
An observation device (<NUM>), comprising:
a reference signal generator (<NUM>) configured to output a reference signal;
a local signal generator (<NUM>) configured to generate a local signal based on the reference signal;
a mixer (<NUM>) configured to mix the local signal and a radio frequency, RF, signal of an observation object to down-convert the RF signal to an intermediate frequency, IF, signal;
a detector (<NUM>) configured to detect the IF signal, and to generate a detection signal;
a variable attenuator (<NUM>), connected between the mixer (<NUM>) and the detector (<NUM>), configured to attenuate the IF signal;
a calibration information setting module (<NUM>) configured to set calibration information from a relationship between a change in an attenuation of the variable attenuator (<NUM>) and a change in an intensity of the detection signal; and
an observation data generator module (<NUM>) configured to generate observation data of the RF signal by using the intensity of the detection signal obtained in a state where the value of the variable attenuator is fixed and the calibration information, wherein:
the RF signal of the observation object is generated by electromagnetic waves radiated from an environment causing a constant signal intensity and from water vapor, and
the observation data is a difference between the intensity of the RF signal due to the electromagnetic wave radiated from the environment causing a constant signal intensity and the intensity of the RF signal due to the electromagnetic wave radiated from the water vapor.