JPH07111448B2 - Microwave radiometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a microwave radiometer mounted on, for example, an artificial satellite.

[Conventional technology]

FIG. 2 is a diagram showing a configuration of a conventional microwave radiometer, in which (1) is a reflecting mirror, (4) is an RF circuit section,
(5) is a receiving unit, (6) is a signal processing unit, (7) is a horn antenna called a sky horn, (8) is a standard noise source, and (9) is a primary radiator.

Next, the operation will be described. The input noise radio wave received from the primary radiator (9) via the reflecting mirror (1) is amplified, frequency-converted and detected by the receiving unit (5) via the RF circuit unit (4), and the input noise is received. A voltage V _M corresponding to the noise temperature T _{M of the} radio wave is obtained. This relationship is shown in equation (1).

V _M = K ・ B ・ G ・ C _d・ T _M (1) where K: proportional constant B: band G: receiver gain C _d : detection sensitivity T _M : input noise temperature Measured in equation (1) by calibrating the voltage V _M giving noise electric wave of known noise temperature instead of the noise temperature T _M that, it is possible to determine the input noise temperature T _M corresponding to an arbitrary V _M. Therefore, as a normal calibration, the sky horn (7) whose noise temperature is known and the standard noise source (8) using a room temperature dummy are switched by the RF circuit section (4).
Doing point calibration. Then, the obtained observation and calibration voltage is A / D converted by the signal processing unit (6) and transmitted to the ground.

By the way, since it is necessary to scan the ground in an actual radiometer, as shown in FIG. 3 as one of the scanning methods, a plurality of different beam directions (in the figure, facing the reflecting mirror (1)) are used. An array (10) of primary radiators (8 elements) is placed and RF is provided by switches (3) connected to each primary radiator.
There is a case where a switching antenna for scanning the ground by changing the beam direction by switching the primary radiator connected to the circuit unit (4).

Further, the temperature resolution ΔT of the microwave radiometer is generally expressed by the equation (2).

Where T _{A is the} input noise temperature T _{R is the} total noise temperature of the radiometer including the antenna feed system B is the frequency band τ is the integration time by the integrator inside the receiver K is the coefficient determined by the receiver method (in the case of the Daisuke type) [Problems to be solved by the invention] The smaller the temperature resolution of the radiometer, the more desirable. However, in the equation (2), T _R has a constraint such as a noise figure of a semiconductor element used for the receiver, and B has a constraint of a guard band determined by the used frequency. Therefore, in order to improve the temperature resolution, it is necessary to lengthen the integration time τ.

However, for example, in a microwave radiometer mounted on an artificial satellite, the ground velocity V _g is constant depending on the orbital conditions, so as shown in Fig. 4, the footprint of the antenna beam on the ground (scanning length x (13) X Direction length y (1
Assuming that the overlap Δy (14) in the traveling direction is taken with respect to 2)), the scanning period T becomes constant when the scanning range l (11) is constant, and is represented by the following equation.

Where A: distance between beam centers in the direction of travel (16) y: length in the direction of travel of the beam spot (12) △ y: weight in the direction of travel of the beam spot (14) V _g : satellite ground speed Also, the integration time at this time τ is expressed by the following equation (4).

Where B: distance between beam centers in scanning direction (17) x: length of beam spot in scanning direction (13) Δx: weight of beam spot in scanning direction (15) l: scanning range (11) T: scanning period Since the scanning range 1 (11) and the scanning period T are constant, if the integration time τ is lengthened, the beam center distance B (17) in the scanning direction becomes longer, and eventually an underlap of the beam spot occurs and the radiometer The distance resolution of is degraded.

Therefore, there is a problem that the temperature resolution and the distance resolution conflict with each other.

The present invention has been made in order to solve the above-mentioned problems, and provides a microwave radiometer capable of improving temperature resolution (integration time) while keeping the distance B (17) between beam centers in the scanning direction constant. To aim for things.

[Means for Solving the Problems]

In the microwave radiometer according to the present invention, an array (2) composed of a plurality of primary radiators is divided into several sets, and an RF circuit section (4), a receiving section (5) and a calibration are provided for each set. It has a source.

[Action]

In the microwave radiometer of the present invention, for example, when the primary radiator array (2) is equally divided into n sets, the ground speed and the like are the same as before the division. The scanning range scanned by one set of arrays is 1 / n of the original scanning range. As a result, the time required for the receiver to integrate the same beam spot is n times, and the temperature resolution ΔT is Only improved.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

As an example, FIG. 1 shows, as an example, the switching antenna type radiometer shown in FIG. 3 in which the primary radiator array (10) (8 elements) is divided into four equal parts.

In FIG. 1, (1) is a reflecting mirror, (2) is a divided primary radiator array, (3) is a switching switch, and (4) is
RF circuit section, (5) receiver section, (6) signal processing section,
(7) is a sky horn, and (8) is a standard noise source.

Other satellite ground speed V _g Antenna beam width, scanning range l
The same conditions apply to the radiometer according to the present invention and the conventional radiometer. At this time, in the microwave radiometer of the present invention, since the primary radiator array (8 elements) is divided into two to form four elements, the beam spot on the ground corresponding to each array is the right 4 in FIG. And left four. Since the satellite ground speed V _g and the beam width are constant, the scanning cycle is the same as before when this radiometer is used. On the other hand, the scanning range is 1/2 of the conventional scanning range l (11) for one divided primary radiator array. In the structure of the radiometer of the present invention, since one receiving unit (integrator) (5) is connected to one divided primary radiator array, the integration time τ of each receiving unit (integrator) (5) is ′ Is expressed by the following equation.

As a result, the integration time for one beam spot when divided is twice as long as the conventional one. From this, the temperature resolution ΔT 'according to the present invention is as follows from the equation (2).

As a result, by using the present invention, the temperature resolution ΔT
Compared to conventional radiometers Only improved.

In the present embodiment, the case where the array is divided into two equal parts is shown. Similarly, when the array is equally divided into n parts and n system receivers (integrators) are used, the temperature resolution is the same as that of the conventional one. Only doubled.

Further, when the array is not divided into equal parts but divided into an appropriate ratio, the effect of improving the temperature resolution corresponding to the total is obtained.

Even if the antenna is not a switching antenna, the same improvement effect can be obtained by connecting a receiving unit (integrator) to each of the disassembled antennas if the scanning range can be divided with the same configuration.

〔The invention's effect〕

As described above, according to the present invention, the primary radiator array of the switching antenna of the microwave radiometer is divided, and the receiving portion (integrator) is provided in each of them, so that a certain range resolution is secured. Above, there is an effect that the temperature resolution can be improved.

[Brief description of drawings]

1 is a block diagram showing a microwave radiometer according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional microwave radiometer, and FIG. 3 is a block diagram of a microwave radiometer of a switching antenna system. , Fig. 4 is an illustration of the ground print of the microwave radiometer. In the figure, (1) is a reflecting mirror, (2) is a divided primary radiator array, (3) is a switching switch, (4) is an RF circuit section,
(5) is a receiving unit, (6) is a signal processing unit, (7) is a sky horn, (8) is a standard noise source, (9) is a primary radiator,
(10) is the primary radiator array, (11) is the scanning range l, (12)
Is the length y in the direction of travel of the beam spot, (13) is the length x in the direction of scan of the beam spot, (14) is the weight in the direction of travel of the beam spot Δy, (15) is the weight in the direction of scan of the beam spot Δ x, (16) is the beam spot center distance A,
(17) shows the distance B between the boom spot centers in the scanning direction. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A reflector, a plurality of primary radiator arrays installed facing the reflector, and a switch connected to the primary radiator for switching the primary radiator to perform antenna beam scanning. , An RF circuit connected to the output terminal of the switch, a receiver for obtaining a voltage value corresponding to the noise temperature of the noise radio wave acquired via the RF circuit, and an output voltage of the receiver for A / In a microwave radiometer equipped with a signal processing unit for D conversion and data processing, the primary radiator array and switches are divided into several sets, and each set is provided with the RF circuit unit and the receiving unit. A microwave radiometer that features things.