CN108362374B - On-site spectral calibration and radiometric calibration method for field hyperspectral irradiance instrument - Google Patents
On-site spectral calibration and radiometric calibration method for field hyperspectral irradiance instrument Download PDFInfo
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Abstract
The invention discloses a field spectrum calibration and radiation calibration method of a field hyperspectral irradiance meter. Under the condition of clear weather, the direct solar light is used as an illumination light source on the operation site of the equipment, and the on-site spectral calibration and the radiometric calibration of the equipment are realized by comparing the actually measured direct solar spectral irradiance. The invention provides a practical technical means for field calibration of field automatic operation high/ultra-spectrum equipment, and has important application value in the fields of meteorology and satellite remote sensor on-orbit radiation calibration.
Description
Technical Field
The invention relates to the technical field of optical radiation measurement, satellite remote sensor calibration and weather, in particular to a field spectrum calibration and radiation calibration method of a field hyperspectral irradiance meter.
Background
The field hyper-spectral irradiance meter is a professional device for measuring global spectral irradiance, sky diffuse spectral irradiance and solar direct spectral irradiance, and the measured irradiance information has important application in the fields of light radiation measurement and weather.
In the in-orbit calibration of the satellite remote sensor, the in-orbit substitution calibration of the satellite remote sensor is realized by performing field measurement on the earth surface reflectivity, the earth surface received irradiance or the earth surface radiance in an external field (generally selecting a special radiation correction field) at the satellite over-top moment and inverting to the satellite entrance pupil radiance through an atmospheric radiation transmission model. At present, methods adopted by the satellite remote sensor in-orbit replacement calibration mainly comprise a reflectivity base method, an irradiance base method and a radiance base method. The radiance base method has the highest precision, but has strict requirements on a calibration site, generally needs to be implemented in areas with high altitude, uniform ground surface, clean atmosphere and stable weather state, and generally needs to be implemented in an airborne load flight test mode, so that the implementation difficulty is high. The reflectivity base method and the irradiance base method are mature, convenient to implement and most widely applied at home and abroad at present. The irradiance base method is mainly applied to the solar reflection wave band, the dependence on the aerosol distribution model assumption in the reflectivity base method is reduced, and the calibration precision is higher than that of the reflectivity base method. In an irradiance base algorithm model, information such as a ratio (diffuse total ratio) of sky diffuse spectral irradiance and global spectral irradiance, atmospheric optical thickness with different wavelengths and the like needs to be measured, and a field hyper-spectral irradiance instrument is special equipment provided by the industry for the application requirement.
The field hyper-spectral irradiance instrument is spectral irradiance measuring equipment, and can realize measurement of sky diffuse spectral irradiance and global spectral irradiance by a sun tracking and light blocking mechanism and by utilizing an internal spectrometer unit, wherein the ratio of the sky diffuse spectral irradiance and the global spectral irradiance obtains spectral diffuse total ratio information, and the difference of the two obtains solar direct spectral irradiance information. The atmospheric optical thickness at each wavelength can be inverted using the direct solar spectral irradiance information. In view of the functional diversity and the important application value of data products, the field hyperspectral irradiance instrument has become one of the core devices in the field replacement calibration of the satellite remote sensor.
At present, the field unattended automatic calibration technology gradually becomes a research hotspot and development trend in the industry, for example, the Chinese remote sensing satellite radiation correction field (Dunhuang) has already resided a batch of automatic observation equipment including a field hyper-spectral irradiance instrument. In the long-term automatic operation process of the automatic equipment, the automatic equipment is influenced by factors such as large-range temperature change (for example, the annual temperature range of Dunhuang area can reach-20 ℃ to 40 ℃), instrument vibration, long-term erosion of outdoor severe environment and the like caused by seasonal change of an outfield, the self responsivity decay and the spectrum drift of the equipment are inevitable, and the accuracy of a measurement result can be ensured only by periodically carrying out spectrum and radiation calibration on the outdoor hyperspectral irradiance instrument. If the equipment is transported back to a laboratory for re-calibration, the route is far, the time period is long, and the cost of the input manpower, material resources and the like cannot be ignored. In addition, even if the instrument is recalibrated in a laboratory, the condition that the equipment is changed again due to factors such as bumpy roads and the like is avoided when the instrument returns to a laboratory site.
Disclosure of Invention
The invention aims to make up for the defects of the prior art and provides a field spectrum calibration and radiation calibration method of a field hyperspectral irradiance meter.
The invention is realized by the following technical scheme:
a field spectrum calibration and radiometric calibration method of a field hyper-spectral irradiance instrument comprises the steps of firstly, mounting a field wavelength transmission etalon on a shading movement mechanism of the field hyper-spectral irradiance instrument to replace an original solar direct shading plate, utilizing solar direct light as an illumination light source, and combining a field actual measurement result of the field hyper-spectral irradiance instrument to calibrate the wavelength of a spectrometer module of the field hyper-spectral irradiance instrument and realize the field spectrum calibration of the field hyper-spectral irradiance instrument; the reference magnitude of the direct solar spectral irradiance is obtained by using the on-site radiation transfer etalon, the spectral irradiance responsivity calibration coefficient is obtained by using the actual measurement result of the field hyper-spectral irradiance, and the on-site radiation calibration of the field hyper-spectral irradiance instrument is realized.
The on-site wavelength transmission etalon comprises a wavelength standard plate, a fixed metal frame, a pressing ring and a metal cover plate, wherein the wavelength standard plate is placed into the fixed metal frame and is pressed and fixed through the pressing ring, and the metal cover plate is detachably arranged in the fixed metal frame and covers the wavelength standard plate.
The wavelength standard plate is made of rare earth oxide-doped quartz or K9 glass sheets, the fixed metal frame is an annular frame body, the center of the fixed metal frame is a through hole, the caliber of one side of the through hole is smaller than the outer diameter of the wavelength standard plate, the wavelength standard plate is limited in a clamping edge fixing mode, the other side of the through hole is provided with threads, and the pressing ring is screwed into the fixed metal frame body to press and fix the wavelength standard plate.
The wavelength standard plate is arranged from one side of the fixed metal frame containing the threads, and after the wavelength standard plate is arranged and fixed in the fixed metal frame, the metal cover plate is arranged from one side of the threads.
The method for realizing the field spectrum calibration of the field hyperspectral irradiance instrument specifically comprises the following steps: firstly, a spectrometer module is arranged in a field hyperspectral irradiance instrument, and the field actual measurement transmittance of a wavelength standard plate is obtained through a ratio method; secondly, comparing the actually measured transmittance with the standard transmittance of the calibrated wavelength standard plate, and confirming the corresponding relation of the pixel numbers of the field hyperspectral irradiance instrument detector corresponding to the standard wavelength at the absorption peak; and finally, referring to the field actual measurement transmittance result of the wavelength standard plate, and realizing the field spectrum calibration of the field hyperspectral irradiance instrument according to the corresponding relation between the standard wavelength of the wavelength standard plate and the pixel number of the field hyperspectral irradiance instrument.
The method for obtaining the field actual measurement transmittance of the wavelength standard plate by the ratio method specifically comprises the following steps: the method comprises the following steps that firstly, a metal cover plate is installed on a fixed metal frame, a shading movement mechanism of a field hyper-spectral irradiance instrument is controlled to move, when the shading movement mechanism is in a horizontal state, the global spectral irradiance is acquired, when the shading movement mechanism is lifted and just shades direct solar light, the sky diffuse spectral irradiance is acquired, and the solar direct spectral irradiance is acquired by subtracting the sky diffuse spectral irradiance from the sky diffuse spectral irradiance; secondly, removing the metal cover plate, controlling a light shielding movement mechanism of the outdoor hyperspectral irradiance meter to move, acquiring new sky diffuse spectral irradiance, and subtracting the new sky diffuse spectral irradiance from the sky diffuse spectral irradiance measured in the first step to obtain new direct solar spectral irradiance containing the transmittance of the wavelength standard plate; and thirdly, the ratio of the direct solar spectral irradiance obtained in the second step to the direct solar spectral irradiance obtained in the first step is a measured value of the wavelength standard plate transmittance on-site ratio method.
The on-site radiation transmission etalon comprises a calibrated reference plate, a calibrated portable spectral radiometer, a measuring rod, an observation lens, a portable computer and a handheld light shading plate, wherein the measuring rod is fixed on a tripod, the observation lens and the portable spectral radiometer are respectively installed on the measuring rod and the tripod, the view field range of the observation lens is totally within the effective working area of the reference plate and is located in the central area of the reference plate, the observation lens is connected with the portable spectral radiometer through an optical fiber, the portable spectral radiometer is connected with the portable computer through a data line and is used for controlling the portable spectral radiometer to collect spectral radiance data, and the handheld light shading plate is located in front of the observation lens and used for shading direct sunlight.
The reference plate is a diffuse reflection white plate made of polytetrafluoroethylene.
The method for realizing the field radiometric calibration of the field hyperspectral irradiance instrument specifically comprises the following steps: (1) controlling a portable spectrum radiometer to collect spectrum radiance data through a portable computer to obtain a spectrum radiance measurement result generated by a hemispherical space global light radiation illumination reference plate, wherein the hemispherical space global light radiation is the sum of direct solar light and sky diffused light;
(2) using a handheld light shielding plate to shield direct sunlight, enabling the shadow to completely cover the reference plate, and controlling a portable spectral radiometer to acquire spectral radiance data through a portable computer to obtain a spectral radiance measurement result generated by the sky diffused light illumination reference plate;
(3) subtracting the spectral radiance measuring result measured in the step (2) from the spectral radiance measuring result measured in the step (1) to obtain a spectral radiance result generated by the solar direct light illuminating reference plate;
(4) calculating to obtain reference direct solar spectral irradiance by using the spectral radiance calculation result generated by the reference plate illuminated by the direct solar light obtained in the step (3) and combining the directional reflectance factor of the reference plate;
(5) and (3) calculating to obtain a spectral irradiance responsivity calibration result of the field hyper-spectral irradiance instrument by using the reference solar direct spectral irradiance obtained in the step (4) and the solar direct spectral irradiance obtained in the second step in the claim 6, and realizing field radiation calibration of the field hyper-spectral irradiance instrument.
The direction reflectance factor of the reference plate is the direction reflectance factor under the angle corresponding to the solar altitude angle at the moment of field actual measurement, and the solar altitude angle is obtained by calculating the longitude and latitude of the field and the test time information.
The reference value transfer method of the wavelength standard is as follows:
replacing a light screen of the field hyperspectral irradiance instrument with a field wavelength transmission etalon, firstly installing a metal cover plate on the field wavelength transmission etalon, wherein the field wavelength transmission etalon has no difference with the light screen of the field hyperspectral irradiance instrument, and controlling the field hyperspectral irradiance instrument to measure the global spectral total illuminance Et(λ), sky diffuse spectral irradiance Ed(lambda), and further obtaining the direct solar spectral irradiance Es(λ)。
Es(λ)＝Et(λ)-Ed(λ) (1)
Removing a metal cover plate on the field wavelength transmission etalon, controlling the field hyperspectral irradiance instrument to measure sky diffuse spectral irradiance E 'according to an inherent acquisition program when the field wavelength transmission etalon is in a light-transmitting state'd
(λ), sky diffuse spectral irradiance E 'at the time when the on-site wavelength transmission etalon is in a light-transmitting state'd
(λ) is the direct solar spectral irradiance and true sky diffuse spectral irradiance E including the in situ wavelength transfer etalon transmittanced(lambda) sum. The direct solar spectral irradiance including the in-situ wavelength transfer etalon transmittance was denoted as E's(lambda). The following relationships apply:
E′s(λ)＝E′d(λ)-Ed(λ) (2)
wherein E isd(λ) is the true diffuse sky spectral irradiance, and the measurement results before removing the metal cover plate are still used due to the short measurement time interval.
Therefore, the transmittance result of the on-site wavelength transfer etalon obtained by the on-site measurement of the field hyperspectral irradiance meter is recorded as t' (λ), and then:
the pixel number corresponding to the absorption peak position can be determined according to the result of the field actual measurement t' (lambda) of the field hyperspectral irradiance instrument, the corresponding relation between the standard absorption peak wavelength and the pixel number of the built-in spectrometer of the field hyperspectral irradiance instrument can be determined according to the standard absorption peak wavelength provided in the standard transmittance result t (lambda) of the field wavelength transmission etalon, and the field spectrum calibration of the field hyperspectral irradiance instrument can be realized.
The portable field radiation transfer etalon comprises a portable spectral radiometer and a reference plate. The spectral radiometer works in the solar reflection wave band, and the working wave band covers or is close to a field hyper-spectral irradiance meter to be calibrated. The reference board is a diffuse reflection white board made of polytetrafluoroethylene, and the surface of the white board is clean and pollution-free.
The portable spectrum radiometer is subjected to spectrum calibration and radiometric calibration in a measurement laboratory with related measurement qualification in advance, the accuracy of the wavelength of the portable spectrum radiometer is ensured through the spectrum calibration, and the absolute spectrum radiance responsivity of the portable spectrum radiometer is obtained through the radiometric calibration.
The directional reflectance factors of the reference plate at each wavelength were previously calibrated in a metrology laboratory with associated metrology qualification.
The reference value transfer method of the total spectral irradiance of the earth surface comprises the following steps:
assuming that the spectral radiance responsivity of the portable spectral radiometer is R (λ), the directional reflectance factor of the reference plate is ρ (θ, λ). When in measurement, the leveling rod is used for ensuring the reference plate to be placed horizontally, and testers face the sun to prevent the shadow from shielding the direct sunlight. And recording the current measurement time by a tester for calculating the solar altitude angle and azimuth angle at the current time. For the reference plate, the directional reflectance factor varies with the solar altitude, but the variation with the solar azimuth angle is almost negligible, so the solar altitude information is a key parameter. And (4) calculating the radiance L (theta, lambda) in the vertical direction of the reference plate when the solar altitude is theta according to the relation shown in the formula (4).
Where ρ (θ, λ) is the directional reflectance factor of the reference plate at the solar elevation angle θ. The solar altitude angle theta value can be calculated by the longitude and latitude of the current position and the time information. Es(theta, lambda) is the direct solar spectral irradiance at a solar elevation angle theta.
The portable spectrum radiometer is vertically aligned with the center of the reference plate and controls the portable spectrum radiometer to measure data, and the data is recorded as DNt(θ, λ) corresponding to a device response value caused after the global spectral irradiance is illuminated to the reference plate. According to the formula (6), the calculation of L (theta, lambda) is preferably performed by using the direct solar spectral irradiance, because the global spectral irradiance illuminates the reference plate from all directions, the directional reflectance factor of the reference plate is closely related to the illumination angle, and the global spectral irradiance is difficult to accurately estimate only according to the radiance data in a certain direction.
Shielding direct sunlight by using a shielding plate, wherein the shadow of the shielding plate just covers the reference plate, and controlling the portable spectral radiometer to collect spectral radiance data, and recording the spectral radiance data as DNd(θ, λ) corresponding to a device response value caused after the reference plate is illuminated by the diffuse sky spectral irradiance. So the response DN of the device caused by the illumination of the reference plate by the direct solar spectral irradiances(θ, λ) can be calculated by the following formula:
DNs(θ，λ)＝DNt(θ，λ)-DNd(θ,λ) (5)
the signal value DN of the portable spectrum radiometer is obtained by calculating the spectral radiance responsivity R (lambda) of the portable spectrum radiometersAnd calculating (theta, lambda) to obtain L (theta, lambda).
L(θ，λ)＝R(λ)·DNs(θ,λ) (6)
The direct solar spectral irradiance E at the current measurement time can be calculated according to the formula (7)s(θ，λ)。
Suppose that the signal of actually measured solar direct spectral irradiance of the field hyper-spectral irradiance instrument at the current measurement moment is DN's(theta, lambda), the responsivity calibration result of the field hyperspectral irradiance meter can be obtained by calculation and is shown in formula (8).
Or, assuming that the direct solar spectral irradiance of the field hyper-spectral irradiance meter at the current measurement moment is Es(theta, lambda), the original/built-in calibration coefficient of the outdoor hyperspectral irradiance meter is R' (lambda), and then the updated responsivity coefficient of the outdoor hyperspectral irradiance meter can be obtained through calculation, see formula (9).
The invention has the advantages that: the invention realizes the spectrum and radiation standard transmission from the laboratory radiation reference to the outfield automation equipment and solves the periodic calibration problem of the outfield automation equipment. The calibration method provided by the invention can directly calibrate the equipment on the working site of the equipment without returning the equipment to a laboratory, has simple calibration flow and convenient operation, can solve the periodic calibration problem of the equipment with least manpower and material resource cost, can ensure that the equipment is permanently watched in the field within the service life of the equipment, and improves the working benefit of the equipment. The method has important practical value in the meteorological field and the business operation of the satellite remote sensor automatic calibration field.
Drawings
Fig. 1 is a schematic diagram of spectral calibration by an in-situ wavelength transfer etalon according to the present invention.
Fig. 2 is an assembly view of the in situ wavelength transfer etalon of the present invention as a mask.
Fig. 3 is an assembly view of the in situ wavelength transfer etalon in light transmission operation of the present invention.
Fig. 4 is a schematic diagram of the global spectral irradiance obtained by an in situ radiation delivery etalon in accordance with the present invention.
FIG. 5 is a schematic of obtaining diffuse sky spectral irradiance with an in-situ radiation delivery etalon in accordance with the present invention.
Fig. 6 is a block diagram of the working principle of the present invention.
Detailed Description
The maintenance personnel use the portable field wavelength transmission etalon 3 and the field radiation transmission etalon calibrated by a metering laboratory in the working field of the field hyper-spectral irradiance to complete the mobile transmission of the laboratory spectrum and the radiation standard through field actual measurement, thereby realizing the field spectral calibration and the radiation calibration of the field hyper-spectral irradiance meter. The specific process is as follows: under the sunny and cloudless weather condition, in a proper time period, field maintenance personnel carry the field radiation transfer etalon, the field wavelength transfer etalon and the auxiliary equipment to an on-duty site of equipment to be calibrated, and the maintenance personnel firstly use the field wavelength transfer etalon to replace a shading device on a field hyperspectral irradiance instrument.
As shown in fig. 1 and 6, a field spectrum calibration and radiation calibration method of a field hyperspectral irradiance instrument, firstly, a field wavelength transmission etalon 3 is installed on a shading movement mechanism 2 of the field hyperspectral irradiance instrument 1 to replace an original solar direct shading plate, solar direct light is used as an illumination light source, the wavelength of a spectrometer module of the field hyperspectral irradiance instrument 1 is calibrated by combining the field actual measurement result of the field hyperspectral irradiance instrument 1, and the field spectrum calibration of the field hyperspectral irradiance instrument 1 is realized; the reference magnitude of the direct solar spectral irradiance is obtained by using the on-site radiation transfer etalon, the spectral irradiance responsivity calibration coefficient is obtained by using the actual measurement result of the field hyper-spectral irradiance, and the on-site radiation calibration of the field hyper-spectral irradiance instrument is realized.
The field wavelength transmission etalon 3 shown in fig. 2 and 3 comprises a wavelength standard plate 4, a fixed metal frame 5, a pressing ring 6 and a metal cover plate 7, wherein the wavelength standard plate 4 is placed in the fixed metal frame 5 and is pressed and fixed through the pressing ring 6, and the metal cover plate 7 is detachably mounted in the fixed metal frame 5 and covers the wavelength standard plate 4.
The wavelength standard plate 4 is made of rare earth oxide-doped quartz or K9 glass sheets, an absorption peak exists at a specific wavelength, the wavelength corresponding to the absorption peak can be obtained by calibration through a reflectivity standard device of a measurement laboratory, the fixed metal frame 5 is an annular frame body, the center of the fixed metal frame 5 is a through hole, the caliber of one side of the through hole is smaller than the outer diameter of the wavelength standard plate, the wavelength standard plate is limited in a clamping edge fixing mode, the other side of the through hole is provided with threads, and the pressing ring 6 is screwed into the fixed metal frame body to tightly press and fix the wavelength standard plate 4. After the wavelength standard plate 4 is installed and fixed in the fixed metal frame 5, the metal cover plate 7 is installed from one side of the screw thread to be used as a lightproof baffle plate, and the function of the baffle plate is the same as that of a direct solar light baffle plate of a field hyperspectral irradiance instrument.
The wavelength standard plate 4 is arranged from one side of the fixed metal frame 5 containing threads, and after the wavelength standard plate 4 is arranged and fixed in the fixed metal frame 5, a metal cover plate is arranged from one side of the threads.
The method for realizing the field spectrum calibration of the field hyperspectral irradiance instrument specifically comprises the following steps: firstly, a spectrometer module is arranged in a field hyper-spectral irradiance instrument 1, and the field actual measurement transmittance of a wavelength standard plate 4 is obtained through a ratio method; secondly, comparing the actually measured transmittance with the standard transmittance of the calibrated wavelength standard plate, and confirming the corresponding relation of the pixel numbers of the field hyperspectral irradiance instrument 1 detector corresponding to the standard wavelength at the absorption peak; and finally, referring to the field actual measurement transmittance result of the wavelength standard plate, and realizing the field spectrum calibration of the field hyperspectral irradiance instrument according to the corresponding relation between the standard wavelength of the wavelength standard plate and the pixel number of the field hyperspectral irradiance instrument.
The method for obtaining the field actual measurement transmittance of the wavelength standard plate by the ratio method specifically comprises the following steps: firstly, a metal cover plate 7 is arranged on a fixed metal frame 5, a shading motion mechanism 2 of a field hyper-spectral irradiance instrument 1 is controlled to move, when the shading motion mechanism 2 is in a horizontal state, the global spectral irradiance is acquired, when the shading motion mechanism 2 is lifted and just shades the direct solar light, the sky diffuse spectral irradiance is acquired, and the sky diffuse spectral irradiance and the direct solar light are subtracted to obtain the direct solar spectral irradiance; secondly, the metal cover plate 7 is removed, the light shielding movement mechanism of the outdoor hyperspectral irradiance meter 1 is controlled to move, new sky diffuse spectral irradiance is acquired, and the new sky diffuse spectral irradiance is subtracted from the sky diffuse spectral irradiance measured in the first step to obtain new solar direct spectral irradiance containing the transmittance of the wavelength standard plate; and thirdly, the ratio of the direct solar spectral irradiance obtained in the second step to the direct solar spectral irradiance obtained in the first step is a measured value of the wavelength standard plate transmittance on-site ratio method.
The on-site radiation transmission etalon comprises a calibrated reference plate 8, a calibrated portable spectral radiometer 9, a measuring rod 10, an observation lens 11, a portable computer 12 and a handheld shading plate 13, the measuring rod 10 is fixed on a tripod 14, the observation lens 11 and the portable spectrum radiometer 9 are respectively arranged on the measuring rod 10 and the tripod 14, the field range of the observation lens 11 is totally within the effective working area of the reference plate 8 and is positioned in the central area of the reference plate 8, the observation lens 11 is connected with the portable spectrum radiometer 9 through an optical fiber, the portable spectrum radiometer 9 is connected with the portable computer 12 through a data line, the portable spectrum radiometer 9 is used for controlling the collection of spectrum radiance data, and the handheld light shielding plate 13 is positioned in front of the observation lens and used for shielding direct sunlight.
The reference plate 8 is a diffuse reflection white plate made of polytetrafluoroethylene.
As shown in fig. 4 and 5, the method for realizing the field radiometric calibration of the field hyperspectral irradiance meter specifically includes the following steps: (1) controlling a portable spectrum radiometer 9 to collect spectrum radiance data through a portable computer 12 to obtain a spectrum radiance measurement result generated by a hemispherical space global light radiation illumination reference plate 8, wherein the hemispherical space global light radiation is the sum of direct solar light and diffused sky light;
(2) using a handheld light shading plate 13 to shade the direct solar light to enable the shadow to completely cover the reference plate 8, and controlling a portable spectrum radiometer 9 to collect spectrum radiance data through a portable computer 12 to obtain a spectrum radiance measurement result generated by the sky diffused light illumination reference plate 8;
(3) subtracting the spectral radiance measuring result measured in the step (2) from the spectral radiance measuring result measured in the step (1) to obtain a spectral radiance result generated by the solar direct light illuminating reference plate;
(4) calculating to obtain reference direct solar spectral irradiance by using the spectral radiance calculation result generated by illuminating the reference plate 8 with the direct solar light obtained in the step (3) and combining the directional reflectance factor of the reference plate;
(5) and (3) calculating to obtain a spectral irradiance responsivity calibration result of the field hyper-spectral irradiance instrument by using the reference solar direct spectral irradiance obtained in the step (4) and the solar direct spectral irradiance obtained in the second step in the claim 6, and realizing field radiation calibration of the field hyper-spectral irradiance instrument.
The direction reflectance factor of the reference plate is the direction reflectance factor under the angle corresponding to the solar altitude angle at the moment of field actual measurement, and the solar altitude angle is obtained by calculating the longitude and latitude of the field and the test time information.
Claims (5)
1. A field spectrum calibration and radiometric calibration method of a field hyperspectral irradiance instrument is characterized in that: firstly, a field wavelength transmission etalon is installed on a shading movement mechanism of a field hyper-spectral irradiance instrument, solar direct light is used as an illumination light source, and the wavelength of a spectrometer module of the field hyper-spectral irradiance instrument is calibrated by combining the field actual measurement result of the field hyper-spectral irradiance instrument, so that the field spectral calibration of the field hyper-spectral irradiance instrument is realized; obtaining a reference quantity value of the direct solar spectral irradiance by using an on-site radiation transfer etalon, obtaining a spectral irradiance responsivity calibration coefficient by using an actual measurement result of the field hyper-spectral irradiance, and realizing on-site radiation calibration of a field hyper-spectral irradiance instrument;
the on-site wavelength transmission etalon comprises a wavelength standard plate, a fixed metal frame, a pressing ring and a metal cover plate, wherein the wavelength standard plate is placed in the fixed metal frame and is pressed and fixed through the pressing ring;
the method for realizing the field spectrum calibration of the field hyperspectral irradiance instrument specifically comprises the following steps: firstly, a spectrometer module is arranged in a field hyperspectral irradiance instrument, and the field actual measurement transmittance of a wavelength standard plate is obtained through a ratio method; secondly, comparing the actually measured transmittance with the standard transmittance of the calibrated wavelength standard plate, and confirming the corresponding relation of the pixel numbers of the field hyperspectral irradiance instrument detector corresponding to the standard wavelength at the absorption peak; finally, referring to the field actual measurement transmittance result of the wavelength standard plate, and realizing the field spectrum calibration of the field hyperspectral irradiance instrument according to the corresponding relation between the standard wavelength of the wavelength standard plate and the pixel number of the field hyperspectral irradiance instrument;
the method for obtaining the field actual measurement transmittance of the wavelength standard plate by the ratio method specifically comprises the following steps: the method comprises the following steps that firstly, a metal cover plate is installed on a fixed metal frame, a shading movement mechanism of a field ultra-spectral irradiance instrument is controlled to move, when the shading movement mechanism is in a horizontal state, the overall spectral irradiance is acquired, when the shading movement mechanism is lifted and just shades direct solar light, the sky diffuse spectral irradiance is acquired, and the direct solar spectral irradiance is acquired by subtracting the sky diffuse spectral irradiance from the sky diffuse spectral irradiance; secondly, removing the metal cover plate, controlling a light shielding movement mechanism of the outdoor hyperspectral irradiance meter to move, acquiring new sky diffuse spectral irradiance, and subtracting the new sky diffuse spectral irradiance from the sky diffuse spectral irradiance measured in the first step to obtain new direct solar spectral irradiance containing the transmittance of the wavelength standard plate; thirdly, the ratio of the direct solar spectral irradiance obtained in the second step to the direct solar spectral irradiance obtained in the first step is a measured value of the wavelength standard plate by a transmittance on-site ratio method;
the field radiation transmission etalon comprises a calibrated reference plate, a calibrated portable spectral radiometer, a measuring rod, an observation lens, a portable computer and a handheld light shading plate, wherein the measuring rod is fixed on a tripod, the observation lens and the portable spectral radiometer are respectively arranged on the measuring rod and the tripod, the field range of the observation lens is completely positioned in the effective working area of the reference plate and is positioned in the central area of the reference plate, the observation lens is connected with the portable spectral radiometer through an optical fiber, the portable spectral radiometer is connected with the portable computer through a data line and is used for controlling the portable spectral radiometer to collect spectral brightness data, and the handheld light shading plate is positioned in front of the observation lens and is used for shading direct solar light;
the method for realizing the field radiometric calibration of the field hyperspectral irradiance instrument specifically comprises the following steps: (1) controlling a portable spectrum radiometer to collect spectrum radiance data through a portable computer to obtain a spectrum radiance measurement result generated by a hemispherical space global light radiation lighting reference plate, wherein the hemispherical space global light radiation is the sum of direct solar light and diffused sky light; (2) using a handheld light shielding plate to shield direct sunlight, enabling the shadow to completely cover the reference plate, and controlling a portable spectrum radiometer to collect spectrum radiance data through a portable computer to obtain a spectrum radiance measurement result generated by the sky diffused light illumination reference plate; (3) subtracting the spectral radiance measuring result measured in the step (2) from the spectral radiance measuring result measured in the step (1) to obtain a spectral radiance result generated by the solar direct light illuminating reference plate; (4) calculating to obtain reference direct solar spectral irradiance by using the spectral radiance calculation result generated by the reference plate illuminated by the direct solar light obtained in the step (3) and combining the directional reflectance factor of the reference plate; (5) and (4) calculating to obtain a spectral irradiance responsivity calibration result of the field hyperspectral irradiance instrument by utilizing the reference solar direct spectral irradiance obtained in the step (4) and the solar direct spectral irradiance obtained in the second step of the method for obtaining the field actual measurement transmittance of the wavelength standard plate by a ratio method, and realizing the field radiometric calibration of the field hyperspectral irradiance instrument.
2. The on-site spectral calibration and radiometric calibration method of the field hyperspectral irradiance meter of claim 1, characterized in that: the wavelength standard plate is made of rare earth oxide-doped quartz or K9 glass sheets, the fixed metal frame is an annular frame body, the center of the fixed metal frame is a through hole, the caliber of one side of the through hole is smaller than the outer diameter of the wavelength standard plate, the wavelength standard plate is limited in a clamping edge fixing mode, the other side of the through hole is provided with threads, and the pressing ring is screwed into the fixed metal frame body to press and fix the wavelength standard plate.
3. The on-site spectral calibration and radiometric calibration method of the field hyperspectral irradiance meter according to claim 2, characterized in that: the wavelength standard plate is arranged from one side of the fixed metal frame containing the threads, and after the wavelength standard plate is arranged and fixed in the fixed metal frame, the metal cover plate is arranged from one side of the threads.
4. The on-site spectral calibration and radiometric calibration method of the field hyperspectral irradiance meter of claim 1, characterized in that: the reference plate is a diffuse reflection white plate made of polytetrafluoroethylene.
5. The on-site spectral calibration and radiometric calibration method of the field hyperspectral irradiance meter of claim 1, characterized in that: the direction reflectance factor of the reference plate is a direction reflectance factor under an angle corresponding to the solar altitude at the moment of field actual measurement, and the solar altitude is calculated by the longitude and latitude of the field and the test time information.
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