CN113702402B - Automatic calibration method for azimuth elevation angle of water vapor radiometer - Google Patents

Abstract

The invention discloses an automatic calibration method for azimuth and elevation angles of a water vapor radiometer, which comprises the following steps: step 1, horizontal calibration of a water vapor radiometer base: step 2, initial debugging in north: step 3, obtaining the accurate longitude and latitude of the station; step 4, calculating the solar altitude and azimuth of the calibration day; step 5, calibrating the time of the terminal computer; step 6, searching azimuth and elevation according to the current moment: step 7, azimuth and angle error adjustment; and 8, re-observing the sweep angle, and 9, calibrating the azimuth angle and the elevation angle of the water vapor radiometer according to the determined azimuth angle and elevation angle calibration values. According to the calibration method disclosed by the invention, the azimuth angle and the elevation angle of the vapor radiometer are calibrated by using the sun as a radiation source, and additional special instruments such as theodolites are not needed, so that compared with the traditional calibration method, the calibration method is accurate in result and simple to operate.

Description

Automatic calibration method for azimuth elevation angle 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 azimuth and elevation angles of a water vapor radiometer in the field.

Background

The high-precision atmospheric refraction correction system utilizes the water vapor radiometer to measure the water vapor frequency band atmospheric microwave radiation signal and the ground meteorological environment parameter element in real time to correct the troposphere atmospheric distance refraction error. The key of the atmospheric refraction error correction is to acquire the radio wave environment parameters of the radio wave signal path. The atmospheric delay can be classified into a dry delay and a wet delay according to correlation with an atmospheric parameter, wherein the dry delay is caused by atmospheric temperature and pressure, and the wet delay is mainly related to atmospheric relative humidity, atmospheric bright temperature on a signal propagation path.

A moisture radiometer is a passive remote sensing device for measuring atmospheric microwave radiation. It does not itself emit electromagnetic waves, but detects the target characteristics by passively receiving microwave energy radiated by the scene under test. The vapor radiometer utilizes the atmospheric temperature, the atmospheric pressure and the atmospheric bright temperature on a signal propagation path which are measured in real time to realize the high-precision real-time calculation of the atmospheric delay; and by constructing a wet delay and bright temperature model and combining the measurement of the atmospheric bright temperature, the wet delay high-precision correction is obtained in real time.

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

In most documents, no mention is made of how the radiometer performs azimuth and elevation calibration, and conventionally, a level meter is used for leveling equipment during erection, and instruments such as a compass or an electronic compass are used for finding true north. The method has the defects that on one hand, the accuracy of the north-pointing tool is affected, the calibration accuracy is not high, on the other hand, the restriction of the appearance of the device is large, when the surface of the radiometer device is not level to place and the north-pointing calibration instrument, the device is required to be disassembled and assembled, the actual operation is complicated, and the calibration accuracy cannot be ensured. Another azimuth elevation calibration method is to calibrate the antenna mechanical axis orientation of the vapor radiometer by using a theodolite, which is limited by station conditions, and many stations do not have a theodolite. However, most of blackbody covers of the vapor radiometers are arc-shaped structures, so that development of a method for calibrating azimuth and elevation angles of the vapor radiometers, which is suitable for different appearance characteristics, is very necessary.

Disclosure of Invention

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

The invention adopts the following technical scheme:

in the method for automatically calibrating the azimuth elevation angle of a vapor radiometer, the improvement comprises the following steps:

step 1, horizontal calibration of a water vapor radiometer base:

the base is horizontally calibrated by adjusting the base angle bolt;

step 2, initial debugging in north:

the compass or the electronic compass is utilized to perform initial north-pointing adjustment on the vapor radiometer, so that the 0-degree scale of the equipment is aligned to the true north direction, 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 and azimuth of the calibration day:

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 of the measuring station, delta is the declination of the sun at that time, and t is the time angle;

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

t＝(t _{north China} +Δt _{Time difference} +Δt _{Longitude and latitude} )*180/12-180° (2)

Wherein t is _{North China} Is the Beijing time, deltat of the calibration operation _{Time difference} Is the time difference of the day, is obtained from the astronomical calendar, deltat _{Longitude and latitude} The time difference of the longitude of the observation point is calculated by the following formula:

Δt _{longitude and latitude} ＝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 θ is the azimuth angle of the sun, M is the coefficient, and the correction method of θ is as follows:

when M < a: θ' =θ+180°

When M > a: if t < 0, θ' =θ;

if t > 0, θ' =θ+360°;

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

step 5, calibrating the time of the terminal computer;

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

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

the azimuth angle C and the elevation angle D of the moment T2 where the maximum voltage value is positioned are preliminarily screened out according to the scanning azimuth data, a solar azimuth angle altitude file is searched for, the true azimuth angle C ' and the true elevation angle D ' of the moment T2 are obtained, an azimuth deviation angle delta C=C-C ' is calculated, and an azimuth angle error is adjusted in terminal software;

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

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

step 8, after azimuth and angle error adjustment, angle scanning observation is carried out again to obtain a 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 sun altitude at the moment corresponding to the voltage maximum moment T6 in the pitching scanning result data, if the sun altitude 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 scanning angle 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 azimuth angle and elevation angle calibration values.

The beneficial effects of the invention are as follows:

according to the calibration method disclosed by the invention, the azimuth angle and the elevation angle of the vapor radiation meter are calibrated by using the sun as a radiation source, and additional special instruments such as a theodolite are not needed.

The calibration method disclosed by the invention has no special requirement on the appearance of the vapor radiometer, overcomes the defect of large azimuth elevation angle calibration error caused by the appearance factor of the vapor radiometer during on-site erection, solves the practical difficulty of lacking precise instruments such as theodolites and the like under the condition of external field erection, and further improves the accuracy of signal measurement and refraction error correction of the atmospheric microwave radiometer, thereby meeting the application requirements of the vapor radiometer system.

Drawings

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

Detailed Description

The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

In order to solve the problems of azimuth and elevation calibration in the erection of an external field of a vapor radiator, the embodiment 1 discloses an automatic calibration method for the azimuth and elevation of the vapor radiator, which is simple to operate, wherein the vapor radiator passively receives microwave energy continuously emitted by the sun, automatically controls the vapor radiator to perform fan scanning within a certain spatial range through input control parameters, and displays noise voltage values received by the vapor radiator on comprehensive display and control software of a terminal computer. When the terminal computer comprehensive display control software displays the maximum noise voltage value, the main lobe axis of the radiometer antenna is indicated to be aligned with the sun at the moment, the azimuth angle and the altitude angle of the sun at the moment are the actual azimuth angle and the actual elevation angle of the radiometer antenna, and the error report is obtained after the scanning is finished according to the information of the time, the sun azimuth angle, the radiometer antenna azimuth angle reading, the sun elevation angle, the radiometer antenna elevation angle reading and the like of the moment. The erector adjusts the radiometer antenna according to the error report, and the adjusted amplitude is the difference between the actual azimuth angle and elevation angle of the antenna and the azimuth angle and elevation angle readings of the antenna displayed by the terminal display control software at the moment. In order to facilitate operation, the pitch angle can be changed for horizontal scanning, the azimuth angle can be changed for pitching scanning after the azimuth angle error is determined, and the elevation angle error is determined. Multiple azimuth and elevation scans are performed, and final azimuth and elevation calibration values are determined from the error average.

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

step 1, horizontal calibration of a water vapor radiometer base:

when the water vapor radiometer is erected in the external field, the base is horizontally calibrated by adjusting a base angle bolt before the calibration of azimuth angle and elevation angle;

step 2, initial debugging in north:

the instrument such as a compass or an electronic compass is utilized to perform initial north-pointing adjustment on the vapor radiometer, so that the 0-degree scale of the equipment is aligned to the true north direction, and the deviation is controlled within 10 degrees; note that geomagnetic bias angles are considered to be different from place to place.

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

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

the sun is a very broad spectrum source of electromagnetic radiation, resembling noise signals. The sensitivity of the vapor radiometer is very high, and the microwave radiation of the sun can be detected. When the water vapor radiometer antenna is not aligned with the sun, the receiver receives atmospheric radiation noise, and when the antenna is aligned with the sun, the receiver indicates maximum, and the azimuth angle and the elevation angle of the water vapor radiometer antenna 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 altitude of the sun: one is to observe the azimuth and elevation of the sun at this point directly with a theodolite. When the theodolite is used for observing the sun, a deep color filter lens is needed to prevent the sun from burning eyes, and the theodolite itself needs to be accurately north-stabilized; and secondly, determining the azimuth angle and the elevation angle of the sun by using the time when the antenna is aligned to the sun according to the operation rule of the sun in the sky. The azimuth angle and the altitude angle of the sun in the sky at a certain moment relative to a certain fixed place can be accurately calculated according to the longitude and latitude of the measuring station, the 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 special instruments, 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 solar time, also called as the time angle (unit: degree);

the visual declination delta can be found from an astronomical calendar, the time angle t is the real solar time of the local place of the measuring station, and the real solar time is obtained by correcting the local place at the time according to the time difference of the day, and the time angle is expressed. t can be calculated from the following formula:

t＝(t _{north China} +Δt _{Time difference} +Δt _{Longitude and latitude} )*180/12-180° (2)

Wherein t is _{North China} Is the Beijing time, deltat of the calibration operation _{Time difference} The time difference of the day can be obtained according to the astronomical calendar, and delta t _{Longitude and latitude} The time difference (unit: hours) of the observation point longitude is calculated from the longitude of the observation point:

Δt _{longitude and latitude} ＝12×(E-120°)/180 (3)

In the above formula, E is the longitude of the measuring 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 θ is the azimuth angle of the sun, and the descriptions of α, δ, and t are the same as the calculation formula of the solar altitude. M is a coefficient introduced for ease of calculation.

The solar azimuth calculated according to equation (4) is used astronomically and requires an angular correction when used in a moisture meter. Otherwise, when the method is used for calibration, when the actual altitude angle of the sun is lower in the morning and evening, the phenomenon that the calculated sun azimuth angle is 180 degrees different from the actual sun azimuth angle can occur. The specific correction method is as follows:

when M < a: θ' =θ+180°

When M > a: if t < 0, θ' =θ;

if t > 0, θ' =θ+360°;

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 elevation angle and elevation angle of the sun are greatly changed at different moments, the time of the computer is calibrated before the calibration to ensure the accuracy of the time of the computer.

Step 6, searching for a solar azimuth angle A and an elevation angle B according to the current time T1:

the method comprises the steps of switching a water vapor radiometer from a terminal computer display control software operation mode to manual control, manually controlling the position to reach an angle A and the position to reach an angle B, setting the position to be [ A-10, A+10] and the walking angle to be 1 degree through program control, setting the pitch angle to be [ B-0.5, B+0.5] and the walking angle to be 0.1 degree if the erection and debugging time is am, setting the pitch angle to be [ B+0.5, B-0.5] and the walking angle to be 0.1 degree if the erection and debugging time is pm, and turning the sun afternoon from high to low;

the azimuth angle C and the elevation angle D of the moment T2 where the maximum voltage value is positioned are preliminarily screened out according to the scanning azimuth data, a solar azimuth angle altitude file is searched for, the true azimuth angle C ' and the true elevation angle D ' of the moment T2 are obtained, an azimuth deviation angle delta C=C-C ' is calculated, and an azimuth angle error is adjusted in terminal software;

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

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

step 8, after azimuth and angle error adjustment, angle scanning observation is carried out again to obtain a 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 sun altitude at the moment corresponding to the voltage maximum moment T6 in the pitching scanning result data, if the sun altitude is inconsistent with the elevation angle at the moment T6 in the scanning data, repeating the step 7, and properly adjusting the initial angle and the angle interval of the scanning angle 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 azimuth angle and elevation angle calibration values.

Claims (1)

1. An automatic calibration method for azimuth elevation angle of a vapor radiometer is characterized by comprising the following steps:

step 1, horizontal calibration of a water vapor radiometer base:

the base is horizontally calibrated by adjusting the base angle bolt;

step 2, initial debugging in north:

the compass or the electronic compass is utilized to perform initial north-pointing adjustment on the vapor radiometer, so that the 0-degree scale of the equipment is aligned to the true north direction, 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 and azimuth of the calibration day:

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 of the measuring station, delta is the declination of the sun at that time, and t is the time angle;

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

t＝(t _{north China} +Δt _{Time difference} +Δt _{Longitude and latitude} )*180/12-180° (2)

Wherein t is _{North China} Is the Beijing time, deltat of the calibration operation _{Time difference} Is the time difference of the day, is obtained from the astronomical calendar, deltat _{Longitude and latitude} The time difference of the longitude of the observation point is calculated by the following formula:

Δt _{longitude and latitude} ＝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 θ is the azimuth angle of the sun, M is the coefficient, and the correction method of θ is as follows:

when M < a: θ' =θ+180°

When M > α: if t < 0, θ' =θ;

if t > 0, θ' =θ+360°;

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

step 5, calibrating the time of the terminal computer;

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

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

the azimuth angle C and the elevation angle D of the moment T2 where the maximum voltage value is positioned are preliminarily screened out according to the scanning azimuth data, a solar azimuth angle altitude file is searched for, the true azimuth angle C ' and the true elevation angle D ' of the moment T2 are obtained, an azimuth deviation angle delta C=C-C ' is calculated, and an azimuth angle error is adjusted in terminal software;

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

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

step 8, after azimuth and angle error adjustment, angle scanning observation is carried out again to obtain a 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 sun altitude at the moment corresponding to the voltage maximum moment T6 in the pitching scanning result data, if the sun altitude 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 scanning angle 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 azimuth angle and elevation angle calibration values.