A method for improving the absolute calibration accuracy of a ground-based microwave radiometer

Abstract

The present invention discloses a method for improving the absolute calibration accuracy of a ground-based microwave radiometer. Based on the ground-based microwave radiometer used on platforms such as offshore platforms, small islands in the sea, polar edges, and ships, the method proposes to use a movable shielding source body to perform absolute calibration on the system. This method solves the electromagnetic interference, humidity, salinity, temperature and other meteorological factor interferences of the ground-based microwave radiometer in the external field environment, eliminates the influence of the external field test environment on the equipment safety and equipment calibration, and has the characteristics of high efficiency, high precision and wide application range.

Description

Technical Field

[0001] The present invention relates to a method for improving the absolute calibration accuracy of a ground-based microwave radiometer, belonging to the field of space microwave remote sensing technology. Background Art

[0002] Spaceborne microwave radiometers are the main sensors for ocean observation, which can simultaneously provide parameters such as observed sea surface temperature, sea surface wind speed, wind direction, total water vapor, total liquid water, and rainfall.

[0003] The observation accuracy of spaceborne microwave radiometers (including spaceborne salinity meters) depends on their calibration accuracy. However, due to numerous uncertainties or interferences in the laboratory calibration and on-orbit calibration of spaceborne microwave radiometers, it is difficult for their calibration results to directly meet the application requirements. This requires substituting the calibration of spaceborne microwave radiometers based on an external calibration source, and the substitution calibration accuracy depends to a large extent on the external calibration source and the calibration method. The construction of a calibration field for spaceborne microwave radiometers in China can provide a stable and reliable external calibration source for the on-orbit calibration of spaceborne microwave radiometers in China. Combining with the calibration method developed synchronously during the construction of the calibration field, this is of great significance for further improving the accuracy of the observation data of spaceborne microwave radiometers in China and the operational application benefits.

[0004] Currently, the calibration methods for ground-based microwave radiometers in the calibration field network include zenith angle calibration, liquid nitrogen calibration, noise injection calibration, etc. Such methods are greatly affected by environmental temperature and humidity and electromagnetic interference, and liquid nitrogen calibration is not suitable for microwave radiometers in the form of a reflector surface. Summary of the Invention

[0005] The technical problem solved by the present invention is: overcoming the deficiencies of the prior art, providing a method for improving the absolute calibration accuracy of a ground-based microwave radiometer, and performing two-point calibration on the ground-based microwave radiometer using a movable and precisely temperature-measuring shielding source body, effectively improving the calibration accuracy and time efficiency.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for improving the absolute calibration accuracy of a ground-based microwave radiometer, the steps are as follows:

[0008] Step 1: Establish a movable shielding source body to form a shielding chamber;

[0009] Step 2: After the movable shielding source body is fixed, place the ground-based microwave radiometer in the shielding chamber;

[0010] Step 3: The ground-based microwave radiometer is powered on and preheated for 1 hour;

[0011] Step 4: When the ground-based microwave radiometer is powered on, turn on the dehumidifier at the same time, and synchronously detect the humidity in the shielding chamber to ensure that the humidity in the shielding chamber is less than 70%;

[0012] Control the humidity in the shielding chamber with a dehumidifier to prevent the bright temperature measurement error caused by frosting of the liquid nitrogen cold source;

[0013] Step Five: After the humidity in the shielding chamber meets the requirements, operate the turntable to align the antenna port of the microwave radiometer with the normal temperature source and observe for 10 minutes, record the output voltage V of the microwave radiometer h , and synchronously record the body temperature T of the normal temperature source h ;

[0014] Step Six: Add liquid nitrogen to the liquid nitrogen cold source and stabilize for 5 minutes, and monitor the humidity change in the shielding chamber during this period;

[0015] Step Seven: Operate the turntable to align the antenna port of the microwave radiometer with the liquid nitrogen and observe for 10 minutes, record the output voltage V of the microwave radiometer c , and synchronously record the temperature T of the liquid nitrogen cold source c ;

[0016] Step Nine: The dehumidifier continuously operates during the process from Step Four to Step Eight, and calculate the calibration coefficient;

[0017] Step Eight: Operate the turntable to align the antenna port of the microwave radiometer with the scene for observation.

[0018] Further, the calibration coefficient is calculated specifically through the following method:

[0019] When the ground-based microwave radiometer observes the normal temperature source:

[0020] V h = kT h + b

[0021] where k and b are calibration coefficients;

[0022] When the ground-based microwave radiometer observes the cold source:

[0023] V c = kT c + b

[0024] According to the above two equations, the calibration coefficient can be obtained:

[0025]

[0026] Further, the movable shielding source body specifically includes: an aluminum frame, an outer aluminum skin, and a shielding wire mesh; the outer aluminum skin is covered on the outside of the aluminum frame, and the shielding wire mesh is arranged on the outside of the outer aluminum skin to form a shielding chamber for shielding external electromagnetic signals;

[0027] A liquid nitrogen cold source is arranged on the inner bottom surface of the movable shielding source body, and a normal temperature source is arranged on the inner walls of the side and top surfaces. The movable shielding source body is connected to a dehumidifier and a thermometer for controlling the humidity inside the movable shielding source body and measuring the temperature of the normal temperature source.

[0028] The source is placed in a shielded room, which effectively reduces the impact of electromagnetic interference in the field test environment;

[0029] Furthermore, the liquid nitrogen cooling source is a containing device composed of a foam box, in which an absorbing material is placed, and the standard temperature of the liquid nitrogen is 80K.

[0030] Furthermore, the room temperature source is a source body of the tip-batch structure, the tip-batch is coated with absorbing material, a temperature measuring resistor is provided at the installation location of the tip-batch to perform real-time temperature measurement, and the temperature is collected by a thermometer.

[0031] Furthermore, a turntable is provided on the inner bottom surface of the movable shielding source body, and the ground-based microwave radiometer is fixed on the turntable to realize horizontal and elevation rotation. The present invention places the ground-based microwave radiometer as a whole in the shielding room, and can realize full-link calibration of the microwave radiometer in the form of a reflective surface.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] In view of the shortcomings of existing methods that are limited by electromagnetic interference and humidity in the test environment, the present invention provides a method for improving the absolute calibration accuracy of ground-based microwave radiometers. A movable shielding source is used to perform two-point calibration on the microwave radiometer, overcoming the influence of environmental electromagnetic interference and humidity, and realizing full-link calibration of microwave radiometers in the form of reflector antennas. The movable shielding source is not limited by site time, and can solve the absolute calibration problem of microwave radiometers of multiple frequency bands and systems, effectively improving data accuracy and time efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a block diagram of the overall composition of a movable shielding source provided by an embodiment of the present invention;

[0035] Figure 2 It is a schematic diagram of the composition of a movable shielding source body normal temperature source provided by an embodiment of the present invention;

[0036] Figure 3 It is a flowchart of the calibration operation of a ground-based microwave radiometer provided by an embodiment of the present invention;

[0037] Figure 4 This is a schematic diagram of the state of the ground-based microwave radiometer provided by an embodiment of the present invention when observing a source body at a normal temperature;

[0038] Figure 5It is a schematic diagram of the state of the ground-based microwave radiometer provided by an embodiment of the present invention when observing a liquid nitrogen cold source. DETAILED DESCRIPTION

[0039] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0040] Figure 1 1 is a block diagram of a movable shielding source body in a method for improving the absolute calibration accuracy of a ground-based microwave radiometer provided by an embodiment of the present invention. Figure 1 As shown, the movable shielding source body specifically includes: an aluminum frame, an outer aluminum skin and a shielding wire mesh; the outer portion of the aluminum frame is covered with an outer aluminum skin, and a shielding wire mesh is arranged outside the outer aluminum skin to form a shielding room for shielding external electromagnetic signals;

[0041] A liquid nitrogen cold source is arranged on the inner bottom surface of the movable shielding source body, and a normal temperature source is arranged on the inner walls of the side and top surfaces. The movable shielding source body is connected to a dehumidifier and a thermometer for controlling the humidity inside the movable shielding source body and measuring the temperature of the normal temperature source.

[0042] The movable shielding source body includes the following features:

[0043] (1) Main structure: including aluminum frame, outer aluminum skin and shielding wire mesh, with functions such as shielding external electromagnetic signals, wind and rainproof, detachable and movable;

[0044] (2) Liquid nitrogen cold source: a container consisting of a foam box with absorbing materials placed inside. The standard temperature of liquid nitrogen is about 80K.

[0045] (3) Normal temperature source: A source body with a pointed structure is used. The pointed structure is coated with an absorbing material with a known absorption rate. It has the function of using a temperature measuring resistor for real-time temperature measurement. A temperature measuring resistor is installed at the installation point of the pointed structure for real-time temperature measurement. The temperature is collected by a thermometer. Figure 2 As shown;

[0046] (4) Auxiliary equipment: Dehumidifier and thermometer, which can control the humidity in the shielding room within an appropriate range and record and save the calibration source temperature data in real time.

[0047] like Figure 4 and Figure 5As shown in the figure, a turntable is provided on the inner bottom surface of the movable shielding source body, and the ground-based microwave radiometer is fixed on the turntable to achieve rotation in two degrees of freedom, namely horizontal and pitch.

[0048] Figure 3 It is the operation flowchart of a method for improving the absolute calibration accuracy of a ground-based microwave radiometer provided by an embodiment of the present invention. As Figure 3 shown, this process includes the following steps:

[0049] Step 1: Establish a movable shielding source body to form a shielding chamber;

[0050] Step 2: After the movable shielding source body is fixed, place the ground-based microwave radiometer in the shielding chamber;

[0051] Step 3: The ground-based microwave radiometer is powered on and preheated for 1 hour;

[0052] Step 4: When the ground-based microwave radiometer is powered on, turn on the dehumidifier at the same time, and synchronously detect the humidity in the shielding chamber to ensure that the humidity in the shielding chamber is less than 70%;

[0053] Step 5: After the humidity in the shielding chamber meets the requirements, operate the turntable to align the antenna port of the microwave radiometer with the normal temperature source for observation for 10 minutes, record the output voltage V of the microwave radiometer h , and synchronously record the temperature T of the normal temperature source body h ; As Figure 4 shown.

[0054] Step 6: Fill liquid nitrogen into the liquid nitrogen cold source and stabilize for 5 minutes, and monitor the humidity change in the shielding chamber during this period;

[0055] Step 7: Operate the turntable to align the antenna port of the microwave radiometer with the liquid nitrogen for observation for 10 minutes, record the output voltage V of the microwave radiometer c , and synchronously record the temperature T of the liquid nitrogen cold source c ; As Figure 5 shown.

[0056] Step 9: The dehumidifier continuously operates during the process from Step 4 to Step 8, and calculate the calibration coefficient;

[0057] The calibration coefficient is calculated specifically in the following way:

[0058] When the ground-based microwave radiometer observes the normal temperature source:

[0059] V h = kT h + b

[0060] where k and b are calibration coefficients;

[0061] When the ground-based microwave radiometer observes the cold source:

[0062] Vc = kT c + b

[0063] Based on the above two equations, the calibration coefficient can be obtained:

[0064]

[0065] Step 8: Operate the turntable to align the antenna aperture of the microwave radiometer with the scene for observation.

[0066] In this embodiment, aiming at the complex calibration environment of the outfield ground-based microwave radiometer, a method of using a movable shielding chamber source body to improve the absolute calibration accuracy of the system is proposed. This method mainly includes two improvements:

[0067] 1. Eliminate the influence of the outfield test environment on the calibration accuracy;

[0068] 2. Realize the full-link calibration of the reflector-type microwave radiometer. This method can effectively solve the problem of absolute calibration in the outfield test of the ground-based microwave radiometer, provide accurate calibration parameters, and provide a calibration basis for the spaceborne microwave radiometer.

[0069] The above-described embodiments are only relatively preferred specific embodiments of the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the absolute calibration accuracy of a ground-based microwave radiometer, characterized in that Here are the steps: Step 1: Establish a movable shielding source body to form a shielding room; Step 2: After the movable shielding source body is fixed, the ground-based microwave radiometer is placed in the shielding room; Step 3: Turn on the ground-based microwave radiometer and preheat it for 1 hour; Step 4: Turn on the ground-based microwave radiometer and the dehumidifier at the same time, and simultaneously detect the humidity in the shielded room to ensure that the humidity in the shielded room is less than 70%; Step 5. After the indoor humidity meets the requirements, operate the turntable to align the antenna port of the microwave radiometer with the normal temperature source and observe for 10 minutes, and record the output voltage V of the microwave radiometer h , and synchronously record the body temperature T of the normal temperature source h ; Step 6: Add liquid nitrogen to the liquid nitrogen cooling source and stabilize it for 5 minutes, during which the humidity changes in the shielding room are monitored; Step 7: Operate the turntable to align the antenna port of the microwave radiometer with the liquid nitrogen observation for 10 minutes, and record the output voltage V of the microwave radiometer c , and synchronously record the temperature T of the liquid nitrogen cold source c ; Step 9: During step 4 to step 8, the dehumidifier keeps working and the calibration coefficient is calculated; Step 8: operate the turntable to align the microwave radiometer antenna aperture with the scene for observation; The calculation of the calibration coefficient is carried out in the following way: When the ground-based microwave radiometer observes a room temperature source: V h = kT h + b Among them, k and b are calibration coefficients; When ground-based microwave radiometer observes cold sources: V c = kT c + b According to the above two formulas, the calibration coefficient can be obtained: The movable shielding source body specifically includes: an aluminum frame, an outer aluminum skin and a shielding wire mesh; the outer portion of the aluminum frame is covered with an outer aluminum skin, and a shielding wire mesh is arranged outside the outer aluminum skin to form a shielding room for shielding external electromagnetic signals; A liquid nitrogen cold source is arranged on the inner bottom surface of the movable shielding source body, and a normal temperature source is arranged on the inner walls of the side and top surfaces. The movable shielding source body is connected to a dehumidifier and a thermometer for controlling the humidity inside the movable shielding source body and measuring the temperature of the normal temperature source.

2. A method for improving the absolute calibration accuracy of a ground-based microwave radiometer according to claim 1, characterized in that: The liquid nitrogen cold source is a container consisting of a foam box with absorbing materials placed inside. The standard temperature of liquid nitrogen is 80K.

3. A method for improving the absolute calibration accuracy of a ground-based microwave radiometer according to claim 1, characterized in that: The room temperature source is a source body of a tip-batch structure, the tip-batch is coated with absorbing material, a temperature measuring resistor is provided at the installation location of the tip-batch for real-time temperature measurement, and the temperature is collected by a thermometer.

4. A method for improving the absolute calibration accuracy of a ground-based microwave radiometer according to claim 1, characterized in that: A turntable is arranged on the bottom surface of the inner side of the movable shielding source body, and the ground-based microwave radiometer is fixed on the turntable to realize the rotation of two degrees of freedom, horizontal and pitch.

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