CN113702402A - Method for automatically calibrating azimuth and elevation angles of water vapor radiometer - Google Patents

Abstract

The invention discloses a method for automatically calibrating the azimuth and elevation angles of a water vapor radiometer, which comprises the following steps: step 1, horizontally calibrating a base of a water vapor radiometer: step 2, initial north-seeking adjustment: step 3, obtaining the accurate longitude and latitude of the station; step 4, calculating the solar altitude angle and azimuth angle of the calibration day; step 5, calibrating the time of the terminal computer; step 6, searching an azimuth angle and an elevation angle according to the current moment: step 7, adjusting the errors of the azimuth and the angle; and 8, re-performing angle sweeping observation, and 9, calibrating the azimuth angle and the elevation angle of the water vapor radiometer according to the determined calibration values of the azimuth angle and the elevation angle. The calibration method disclosed by the invention has the advantages that the azimuth angle and the elevation angle of the water vapor radiometer are calibrated by using the sun as a radiation source, extra special instruments such as a theodolite and the like are not needed, and compared with the traditional calibration method, the calibration method has accurate result and is simple to operate.

Description

Method for automatically calibrating azimuth and elevation angles of water vapor radiometer

Technical Field

The invention belongs to the technical field of passive atmospheric microwave remote sensing and atmospheric refraction correction, and particularly relates to an automatic calibration method for the azimuth and elevation angle of a water vapor radiometer in the field.

Background

The high-precision atmospheric refraction correction system measures atmospheric microwave radiation signals of a water vapor frequency band and ground meteorological environment parameter elements in real time by using a water vapor radiometer and corrects troposphere atmospheric distance refraction errors. The key of atmospheric refraction error correction is to obtain the electric wave environment parameter of the electric wave signal path. Atmospheric delay can be divided into dry delay and wet delay according to different dependence on atmospheric parameters, wherein the dry delay is caused by atmospheric temperature and pressure, and the wet delay is mainly related to atmospheric relative humidity and atmospheric brightness temperature on a signal propagation path.

A moisture radiometer is a passive remote sensing device used to measure atmospheric microwave radiation. It does not emit electromagnetic waves itself, but detects target characteristics by passively receiving microwave energy radiated by the scene being examined. The water vapor radiometer realizes high-precision real-time calculation of atmospheric delay by utilizing the atmospheric temperature and the atmospheric pressure which are measured in real time and the atmospheric brightness temperature on a signal propagation path; and (3) by constructing a wet delay and bright temperature model and combining with the measurement of the atmospheric bright temperature, acquiring the high-precision correction of the wet delay in real time.

When the water vapor radiometer executes an atmospheric refraction correction task, the antenna needs to point to a specified azimuth and pitch angle according to instructions of the monitoring and data center. During installation and erection, the calibration work of the azimuth and the elevation angle of the steam radiometer is very important and is closely related to the actual pointing accuracy of the azimuth and the elevation angle during subsequent tasks. The azimuth and elevation precision directly influences the microwave radiation signals measured in real time on the measuring path and the inverted wet delay result.

Most documents do not mention how radiometers are used for azimuth and elevation calibration, and the traditional method is to level equipment by adopting a level gauge during erection and then use a compass or an electronic compass and other instruments to find true north. The method has the defects that on one hand, the method is influenced by the precision of a north-pointing tool, the calibration precision is not high, on the other hand, the method is greatly restricted by the appearance of the equipment, when a horizontal and north-pointing calibration instrument is placed on the surface of radiometer equipment at an uneven position, the equipment needs to be disassembled and assembled, the actual operation is complicated, and the calibration precision cannot be guaranteed. The other azimuth angle and elevation angle calibration method is to use a theodolite to calibrate the mechanical axis pointing direction of an antenna of a water vapor radiometer, and the method is limited by station conditions, and many stations do not have the theodolite. The blackbody cover of the water vapor radiometer is mostly of an arc-shaped structure, so that the development of a water vapor radiometer azimuth and elevation angle calibration method suitable for different appearance characteristics is very necessary.

Disclosure of Invention

The invention aims to provide an automatic calibration method for the azimuth and elevation angles of a water vapor radiometer.

The invention adopts the following technical scheme:

the improvement of a method for automatically calibrating the azimuth and elevation angles of a water vapor radiometer is that the method comprises the following steps:

step 1, horizontally calibrating a base of a water vapor radiometer:

adjusting a bottom angle bolt to horizontally calibrate the base;

step 2, initial north-seeking adjustment:

carrying out initial north-pointing adjustment on the water vapor radiometer by using a north-pointing needle or an electronic compass, so that the dial scale of the equipment is aligned to the true north direction at 0 degree, and the deviation is controlled within 10 degrees;

step 3, obtaining the accurate longitude and latitude of the station;

step 4, calculating the solar altitude angle and azimuth angle of the calibration day:

the calculation formula of the solar altitude angle is as follows:

sinφ＝sinα·sinδ+cosα·cosδ·cos t (1)

in the formula, phi is the altitude angle of the sun, alpha is the latitude of the survey station, delta is the solar declination at that time, and t is the time angle;

the declination delta is found from the astronomical calendar, and the time angle t is the local true sun of the measuring station and is calculated by the following formula:

t＝(t_{north China}+Δt_{Time difference}+Δt_{Longitude (G)})*180/12-180° (2)

Wherein, t_{North China}Is the Beijing time, Δ t, at which the calibration operation is performed_{Time difference}Is the time difference of the day, found from the almanac, Δ t_{Longitude (G)}Is the time difference of the longitude of the observation point, and is calculated by the following formula:

Δt_{longitude (G)}＝12×(E-120°)/180 (3)

E is the longitude of the station;

the calculation formula of the solar azimuth angle is as follows:

tanθ＝-tanδ×cos M/sin(M-α) (4)

tan M＝tanδ/cos t

wherein, theta is the azimuth angle of the sun, M is a coefficient, and the correction method of theta is as follows:

when M < a: θ' ═ θ +180 °

When M > a: if t is less than 0, theta is equal to theta;

if t is greater than 0, theta is equal to theta +360 degrees;

where θ' is the azimuth angle of the actual radiometer antenna;

step 5, calibrating the time of the terminal computer;

step 6, searching an azimuth angle A and an elevation angle B according to the current time T1:

manually controlling the position of the azimuth arrival angle A and the pitching arrival angle B, setting the azimuth as [ A-10, A +10] and the stepping angle as 1 degree through 'program control', if the erection debugging time is in the morning, setting the pitching as [ B-0.5, B +0.5], setting the stepping angle as 0.1 degree, and setting the pitching as [ B +0.5, B-0.5] and the stepping angle as-0.1 degree;

preliminarily screening out the azimuth angle C and the elevation angle D of the voltage maximum at the moment T2 from the scanned azimuth data, searching a sun azimuth angle altitude angle file to obtain the real azimuth angle C ' and the elevation angle D ' at the moment T2, calculating an azimuth deviation angle delta C to be C-C ', and adjusting the azimuth angle error in terminal software;

step 7, searching an azimuth angle E and an elevation angle F of the next minute of the current time T3 of the solar altitude file, setting the azimuth as [ E-2, E +3] and the step angle as 1 degree through 'program control', setting the pitch angle as [ F-0.5, F +1] and the step angle as 0.1 degree in the mode of 'only scanning and pitching' if the erection debugging time is the morning, and setting the pitch as [ F +0.5, F-1] and the step angle as-0.1 degree in the mode of 'only scanning and pitching' if the erection debugging time is the afternoon;

after scanning is finished, an elevation angle F1 corresponding to a voltage maximum value moment T4 in each pitching scanning process is obtained through measured voltage data, the elevation angle calculated by a sun altitude angle file corresponding to the moment T4 is F2, an elevation angle deviation angle delta F is calculated to be F2-F1, if the delta F is larger than 0.5 degree, whether the level is adjusted correctly needs to be checked, and when the delta F is smaller than 0.5 degree, an elevation angle error is adjusted in terminal software;

step 8, after the azimuth and angle errors are adjusted, angle sweeping observation is carried out again to obtain the corresponding voltage maximum value moment T5 in azimuth scanning, the sun azimuth angle at the moment is calculated, and if the sun azimuth angle is inconsistent with the azimuth angle at the moment T5 in display control software, the step 6 is repeated; calculating the solar altitude angle at the moment corresponding to the voltage maximum value moment T6 in the pitching scanning result data, if the solar altitude angle at the moment is inconsistent with the elevation angle at the moment T6 in the scanning data, repeating the step 7, adjusting the initial angle and the angle interval of the angle scanning measurement until the error meets the requirement, and determining the calibration values of the azimuth angle and the elevation angle;

and 9, calibrating the azimuth angle and the elevation angle of the water vapor radiometer according to the determined calibration values of the azimuth angle and the elevation angle.

The invention has the beneficial effects that:

the calibration method disclosed by the invention has the advantages that the azimuth angle and the elevation angle of the water vapor radiometer are calibrated by using the sun as a radiation source, additional special instruments such as theodolite and the like are not needed, compared with the traditional calibration method, the calibration method has accurate result and simple operation, is suitable for being used in field erection and daily inspection of the water vapor radiometer, ensures the calibration precision of the azimuth angle and the elevation angle, and further improves the refraction error correction precision of the water vapor radiometer.

The calibration method disclosed by the invention has no special requirement on the appearance of the steam radiometer, overcomes the defect of large azimuth and elevation calibration errors caused by appearance factors of the steam radiometer during field erection, solves the practical difficulty that precise instruments such as a theodolite and the like are lacked under the condition of field erection, further improves the accuracy of signal measurement and refraction error correction of the atmospheric microwave radiometer, and further meets the application requirement of a steam radiometer system.

Drawings

FIG. 1 is a schematic flow chart of the calibration method of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Embodiment 1, in order to solve the problem of azimuth and elevation calibration in the erection of the outfield of the steam radiometer, this embodiment discloses an automatic calibration method for azimuth and elevation of a steam radiometer, which is simple in operation. When the terminal computer comprehensive display control software displays the maximum noise voltage value, the fact that the main lobe axis of the radiometer antenna is aligned with the sun at the moment is shown, the azimuth angle and the altitude angle of the sun at the moment are the actual azimuth angle and the elevation angle of the radiometer antenna, information such as time, the solar azimuth angle, radiometer antenna azimuth angle reading, the solar elevation angle and radiometer antenna elevation angle reading at the moment is automatically recorded according to the comprehensive display control software, and after scanning is finished, an error report is obtained. And the erection personnel adjust the radiometer antenna according to the given error report, wherein the adjustment amplitude is the difference between the actual azimuth angle and elevation angle of the antenna and the azimuth angle and elevation angle reading of the antenna at the moment displayed by the terminal display and control software. For convenience of operation, the elevation angle can be changed for horizontal scanning, the azimuth angle is changed for elevation scanning after the azimuth angle error is determined, and the elevation angle error is determined. And performing azimuth and elevation scanning for multiple times, and determining the final azimuth angle and elevation calibration value according to the error average value.

As shown in fig. 1, the method specifically comprises the following steps:

step 1, horizontally calibrating a base of a water vapor radiometer:

when erecting the external field of the water vapor radiometer, firstly, horizontally calibrating a base by adjusting a bottom angle bolt before calibrating the azimuth angle and the elevation angle;

step 2, initial north-seeking adjustment:

the water vapor radiometer is initially regulated by utilizing tools such as a compass or an electronic compass, so that the dial scale of the device is aligned to the true north direction at 0 degree, and the deviation is controlled within 10 degrees; note that the declination is different from place to place.

Step 3, obtaining the accurate longitude and latitude of the station;

step 4, calculating the solar altitude angle and azimuth angle of the calibration day:

the sun is a source of electromagnetic radiation over a broad spectrum, similar to a noise signal. The sensitivity of the water vapor radiometer is very high, and microwave radiation of the sun can be detected. When the antenna of the water vapor radiometer is not aligned with the sun, the receiver receives atmospheric radiation noise, and when the antenna is aligned with the sun, the receiver indicates the maximum, and the azimuth angle and the elevation angle of the antenna of the water vapor radiometer can be calibrated according to the azimuth angle and the elevation angle of the sun at the moment.

There are two ways to determine the azimuth and elevation of the sun: one is to observe the azimuth and elevation angle of the sun at that moment directly with a theodolite. When the theodolite is used for observing the sun, the color filter needs to be deepened to prevent sunlight from burning eyes, and the theodolite needs to accurately determine the north; secondly, according to the operation rule of the sun in the sky, the azimuth angle and the elevation angle of the sun are determined by the time when the antenna is aligned with the sun. The azimuth angle and the elevation angle of the sun relative to a fixed place in the sky at a certain moment can be accurately calculated according to the longitude and latitude of the measuring station, the visual declination of the day, the time difference, the time angle and other parameters. The calibration method of the embodiment adopts a second mode to determine the azimuth angle and the altitude angle of the sun, and the mode does not depend on a special instrument, is simple and easy to operate and has high precision.

The calculation formula of the solar altitude angle is as follows:

sinφ＝sinα·sinδ+cosα·cosδ·cos t (1)

wherein phi is the altitude angle of the sun, alpha is the latitude (unit: degree) of the measuring station, delta is the declination of the sun at that time, and t is the true sun, which is also called the hour angle (unit: degree);

the declination delta can be found from the astronomical calendar, and the time angle t is the true sun of the local place of the measuring station, which is obtained by correcting according to the time difference of the day when the local place is flat at that time and is expressed by the angle. t can be calculated from the following formula:

t＝(t_{north China}+Δt_{Time difference}+Δt_{Longitude (G)})*180/12-180° (2)

Wherein, t_{North China}Is the Beijing time, Δ t, at which the calibration operation is performed_{Time difference}Is the time difference of the day, which can be looked up according to the astronomical almanac, Δ t_{Longitude (G)}Is the time difference (unit: hour) of the longitude of the observation point, and is calculated by the longitude of the observation station:

Δt_{longitude (G)}＝12×(E-120°)/180 (3)

In the above formula, E is the longitude of the survey station;

the calculation formula of the solar azimuth angle is as follows:

tanθ＝-tanδ×cos M/sin(M-α) (4)

tan M＝tanδ/cos t

wherein, theta is the azimuth angle of the sun, and alpha, delta and t are the same as the calculation formula of the altitude angle of the sun. M is a coefficient introduced for ease of calculation.

The solar azimuth angle calculated according to the formula (4) is used in astronomy, and when used in a moisture radiometer, angle correction is required. Otherwise, when the method is used for calibration, when the actual solar altitude angle is low in the morning and evening, the difference between the calculated solar azimuth angle and the actual solar azimuth angle is 180 degrees. The specific correction method comprises the following steps:

when M < a: θ' ═ θ +180 °

When M > a: if t is less than 0, theta is equal to theta;

if t is greater than 0, theta is equal to theta +360 degrees;

wherein θ is the solar azimuth angle calculated according to equation (4), and θ' is the azimuth angle of the actual radiometer antenna;

step 5, calibrating the time of the terminal computer; because the change of the elevation angle and the elevation angle of the sun is large at different moments, the time of the computer needs to be calibrated before the calibration is carried out so as to ensure the accuracy of the time of the computer.

Step 6, searching the azimuth angle A and the elevation angle B of the sun according to the current time T1:

switching a water vapor radiometer from a terminal computer display control software operation mode to manual control, manually controlling the azimuth to reach an angle A and the pitching to reach the position of an angle B, setting the azimuth to be [ A-10, A +10] and the stepping angle to be 1 degree through 'program control', if the erection debugging time is in the morning, setting the pitch angle to be [ B-0.5, B +0.5], the stepping angle to be 0.1 degree, and the mode to be 'only sweeping azimuth', if the erection debugging time is in the afternoon, setting the pitch angle to be [ B +0.5, B-0.5], the stepping angle to be-0.1 degree and the sun to turn from high to low in the afternoon;

preliminarily screening out the azimuth angle C and the elevation angle D of the voltage maximum at the moment T2 from the scanned azimuth data, searching a sun azimuth angle altitude angle file to obtain the real azimuth angle C ' and the elevation angle D ' at the moment T2, calculating an azimuth deviation angle delta C to be C-C ', and adjusting the azimuth angle error in terminal software;

step 7, after the azimuth angle of the water vapor radiometer is adjusted, searching the azimuth angle E and the elevation angle F of the next minute of the current time T3 of the solar altitude file, setting the azimuth angle to be [ E-2, E +3] and the step angle to be 1 degree through program control, if the erection debugging time is the morning, setting the pitch angle to be [ F-0.5, F +1] and the step angle to be 0.1 degree in a mode of 'only scanning and pitching', and if the erection debugging time is the afternoon, setting the pitch to be [ F +0.5, F-1] and the step angle to be-0.1 degree;

after scanning is finished, an elevation angle F1 corresponding to a voltage maximum value moment T4 in each pitching scanning process is obtained through measured voltage data, the elevation angle calculated by a sun altitude angle file corresponding to the moment T4 is F2, an elevation angle deviation angle delta F is calculated to be F2-F1, if the delta F is larger than 0.5 degree, whether the level is adjusted correctly needs to be checked, and when the delta F is smaller than 0.5 degree, an elevation angle error is adjusted in terminal software;

step 8, after the azimuth and angle errors are adjusted, angle sweeping observation is carried out again to obtain the corresponding voltage maximum value moment T5 in azimuth scanning, the sun azimuth angle at the moment is calculated, and if the sun azimuth angle is inconsistent with the azimuth angle at the moment T5 in display control software, the step 6 is repeated; calculating the solar altitude angle at the moment corresponding to the voltage maximum value moment T6 in the pitching scanning result data, if the solar altitude angle at the moment is inconsistent with the elevation angle at the moment T6 in the scanning data, repeating the step 7, properly adjusting the initial angle and the angle interval of the angle scanning measurement until the error meets the requirement, and determining the calibration values of the azimuth angle and the elevation angle;

and 9, calibrating the azimuth angle and the elevation angle of the water vapor radiometer according to the determined calibration values of the azimuth angle and the elevation angle.

Claims (1)

1. A method for automatically calibrating the azimuth and elevation angles of a water vapor radiometer is characterized by comprising the following steps:

step 1, horizontally calibrating a base of a water vapor radiometer:

adjusting a bottom angle bolt to horizontally calibrate the base;

step 2, initial north-seeking adjustment:

carrying out initial north-pointing adjustment on the water vapor radiometer by using a north-pointing needle or an electronic compass, so that the dial scale of the equipment is aligned to the true north direction at 0 degree, and the deviation is controlled within 10 degrees;

step 3, obtaining the accurate longitude and latitude of the station;

step 4, calculating the solar altitude angle and azimuth angle of the calibration day:

the calculation formula of the solar altitude angle is as follows:

sinφ＝sinα·sinδ+cosα·cosδ·cos t (1)

in the formula, phi is the altitude angle of the sun, alpha is the latitude of the survey station, delta is the solar declination at that time, and t is the time angle;

the declination delta is found from the astronomical calendar, and the time angle t is the local true sun of the measuring station and is calculated by the following formula:

t＝(t_{north China}+Δt_{Time difference}+Δt_{Longitude (G)})*180/12-180° (2)

Wherein, t_{North China}Is the Beijing time, Δ t, at which the calibration operation is performed_{Time difference}Is the time difference of the day, found from the almanac, Δ t_{Longitude (G)}Is the time difference of the longitude of the observation point, and is calculated by the following formula:

Δt_{longitude (G)}＝12×(E-120°)/180 (3)

E is the longitude of the station;

the calculation formula of the solar azimuth angle is as follows:

tanθ＝-tanδ×cos M/sin(M-α) (4)

tan M＝tanδ/cos t

wherein, theta is the azimuth angle of the sun, M is a coefficient, and the correction method of theta is as follows:

when M < a: θ' ═ θ +180 °

When M > α: if t is less than 0, theta is equal to theta;

if t is greater than 0, theta is equal to theta +360 degrees;

where θ' is the azimuth angle of the actual radiometer antenna;

step 5, calibrating the time of the terminal computer;

step 6, searching an azimuth angle A and an elevation angle B according to the current time T1:

manually controlling the position of the azimuth arrival angle A and the pitching arrival angle B, setting the azimuth as [ A-10, A +10] and the stepping angle as 1 degree through 'program control', if the erection debugging time is in the morning, setting the pitching as [ B-0.5, B +0.5], setting the stepping angle as 0.1 degree, and setting the pitching as [ B +0.5, B-0.5] and the stepping angle as-0.1 degree;

preliminarily screening out the azimuth angle C and the elevation angle D of the voltage maximum at the moment T2 from the scanned azimuth data, searching a sun azimuth angle altitude angle file to obtain the real azimuth angle C ' and the elevation angle D ' at the moment T2, calculating an azimuth deviation angle delta C to be C-C ', and adjusting the azimuth angle error in terminal software;

step 7, searching an azimuth angle E and an elevation angle F of the next minute of the current time T3 of the solar altitude file, setting the azimuth as [ E-2, E +3] and the step angle as 1 degree through 'program control', setting the pitch angle as [ F-0.5, F +1] and the step angle as 0.1 degree in the mode of 'only scanning and pitching' if the erection debugging time is the morning, and setting the pitch as [ F +0.5, F-1] and the step angle as-0.1 degree in the mode of 'only scanning and pitching' if the erection debugging time is the afternoon;

after scanning is finished, an elevation angle F1 corresponding to a voltage maximum value moment T4 in each pitching scanning process is obtained through measured voltage data, the elevation angle calculated by a sun altitude angle file corresponding to the moment T4 is F2, an elevation angle deviation angle delta F is calculated to be F2-F1, if the delta F is larger than 0.5 degree, whether the level is adjusted correctly needs to be checked, and when the delta F is smaller than 0.5 degree, an elevation angle error is adjusted in terminal software;

step 8, after the azimuth and angle errors are adjusted, angle sweeping observation is carried out again to obtain the corresponding voltage maximum value moment T5 in azimuth scanning, the sun azimuth angle at the moment is calculated, and if the sun azimuth angle is inconsistent with the azimuth angle at the moment T5 in display control software, the step 6 is repeated; calculating the solar altitude angle at the moment corresponding to the voltage maximum value moment T6 in the pitching scanning result data, if the solar altitude angle at the moment is inconsistent with the elevation angle at the moment T6 in the scanning data, repeating the step 7, adjusting the initial angle and the angle interval of the angle scanning measurement until the error meets the requirement, and determining the calibration values of the azimuth angle and the elevation angle;

and 9, calibrating the azimuth angle and the elevation angle of the water vapor radiometer according to the determined calibration values of the azimuth angle and the elevation angle.

Images