CN105352609A - Optical remote-sensing satellite absolute radiation scaling method based on spatial Lambert globe - Google Patents

Abstract

The invention relates to an optical remote-sensing satellite absolute radiation scaling method based on a spatial Lambert globe. The spatial Lambert globe is disposed in a space, and solar radiation which is attenuated to a proper range is directly led into a satellite remote sensor. A deep space background is imaged via satellite attitude maneuvering to determine a background signal; and satellite tool software is used to calculate a time period that satisfies the scaling condition, an imaging time point is selected, satellite attitude maneuvering is used to image the spatial Lambert globe and further to determine a reflection signal of the spatial Lambert globe, the irradiance of an entrance pupil position of the remote controller at the imaging time point is calculated, and the absolute radiation scaling coefficient of the single point is determined according to multiple groups of data. According to the method of the invention, influence of atmospheric condition and ground object characteristics is avoided, a unified spatial optical radiation reference is established, requirements for full-optical-path full-aperture radiation scaling that matches spectral distribution are met, and normalized monitoring for the satellite remote controller can be realized.

Description

A kind of Optical remote satellite absolute radiation calibration method based on space lambert's spheroid

Technical field

The invention belongs to remote sensing satellite radiation calibration field, relate to a kind of method that radiance in-orbit to space optical remote satellite carries out normalization absolute calibration.

Background technology

Along with going deep into of remote sensing application, quantitative remote sensing has become the emphasis of remote sensing application, and the basis of quantitative remote sensing and prerequisite are the radiation calibrations of remote sensor.The radiation calibration of Space Remote Sensors can be divided into the Laboratory Calibration before transmitting and the In-flight calibration after launching.After satellite launch, along with the impact of the various factors such as working environment and long-term work state, the calibration coefficient before transmitting all may be made to launch and change, the In-flight calibration after therefore launching is the key guaranteeing remotely-sensed data fiduciary level and accuracy.

In-flight calibration method after transmitting mainly contains the method such as radiometric calibration site, onboard process.Radiometric calibration site relies on the stable atural object of earth surface Large-Area-Uniform as reference source, realizes the radiation calibration of satellite in orbit, and these class methods are subject to ground object target characteristic and atmospheric condition impact, and its calibration precision is on the low side and cost is higher.Onboard process realizes calibration by onboard process device, according to the difference of scaling light source used, mainly contains the modes such as Built-in light, the moon, fixed star, sun calibration.Built-in light is a kind of mode conventional in early stage calibration scheme, but Built-in light is a kind of artificial light source joined in light path, exist non-fully light path, with the defect such as solar spectrum distributional difference is large.The moon is luminous by the dependence sun, absorption, the reflection characteristic of its spectral characteristic and solar spectrum and the moon itself are relevant, owing to not yet obtaining moon spectral distribution accurately at present, its irradiation model not yet reaches the precision of practical application, the mode of therefore being calibrated by the moon can't be directly used in absolute calibration, only for relative detector calibration.Fixed star, as a kind of Celestial Objects, also has certain brightness, but the brightness except the sun in research at present all cannot reach requirement, cannot be used for spaceborne radiant calibration.An at present conventional scaling light source is the sun, and it is an even and high stability Lambertian source, after solar energy being decayed to suitable scope by the mode of reflection or transmission, can provide stable for Space Remote Sensors and calibrate approach accurately.By spaceborne sun diffusing panel, the sun diffuse reflector being coated with diffuse material all has good homogeneity and Lambertian characteristics, sun diffusing panel can realize after opening calibrating the sun of remote sensor, this method generally has the advantages such as unified, full light path, Spectral matching be good, is one of Main Means of current onboard process.But be subject to technical conditions restriction, this mode needs to install independent sun diffuse reflector at satellite itself, its complex structural designs, easily be subject to the pollution of satellite draw-off, and add the operation burden of whole star system, in this mode, the inefficacy of parts brings tremendous influence by follow-up calibration work in addition.

Summary of the invention

The technical matters that the present invention solves is: overcome the deficiencies in the prior art, provide a kind of Optical remote satellite absolute radiation calibration method based on space lambert's spheroid, can on the basis not increasing extra Image processing equipment, breaking away from the impact of terrain object characteristic and the impact of atmospheric conditions, take the sun as the high precision absolute radiometric calibration that reference source realizes full light path, full aperture, Spectral matching.

Technical solution of the present invention is: a kind of Optical remote satellite absolute radiation calibration method based on space lambert's spheroid, comprises the steps:

(1) in space, launch artificial lambert's spheroid by carrier rocket radiation pattern or satellite release radiation pattern, the diameter of spheroid and orbital position meet satellite and calibrate requirement to signal energy; Described artificial lambert's spheroid is the uniform spherome that surface has close to Lambertian characteristics;

(2) parameter of satellite remote sensor to be calibrated is set, integral time, gain and progression are remained unchanged in whole calibration process;

(3) attitude maneuver is carried out to satellite, make satellite remote sensor to be calibrated point to deep space background, obtain the gray-scale value of satellite remote sensor imaging pixel to be calibrated, carry out n time altogether and measure, obtain the gray-scale value DN of each pixel k measured _k0i, wherein n>=1, k is the position of remote sensor pixel, and the span of k is that i is the number of times measured, i=1,2,3......, n from 1 to the sum of remote sensor pixel; After having measured for n time, calculate the background signal mean value DN of satellite remote sensor pixel k to be calibrated _k0,

${\mathrm{DN}}_{k0}=\frac{1}{n}\underset{i=1}{\overset{i=n}{\Σ}}{\mathrm{DN}}_{k0i};$

(4) set up and comprise the scene of satellite, artificial lambert's spheroid and the sun, the transmission of emulation solar radiation energy, obtain satellite, time period that position relationship between artificial lambert's spheroid and sun three meets calibration condition; Described calibration condition comprises the visible condition of geometry and the visible condition of sensor, the visible condition of geometry is that satellite and artificial lambert's spheroid line therebetween do not block by the earth, the visible condition of sensor is behaved and is made lambert's spheroid and be in outside ground shadow, and artificial lambert's spheroid can reflected solar radiation energy thus realize observation imaging;

(5) from the time period of satisfied calibration condition, a certain imaging moment point is chosen, attitude maneuver is carried out to satellite, the entrance pupil normal of satellite remote sensor to be calibrated is made to point to lambert's spheroid, observed by remote sensor the position angle of artificial lambert's spheroid be designated as φ, obtain the relative distance L of artificial lambert's spheroid and the sun _{1 (j)}, artificial lambert's spheroid with wait the relative distance L calibrating satellite remote sensor entrance pupil place _{2 (j)}, line between the sun and artificial lambert's spheroid and wait the angle theta of the line calibrated between satellite remote sensor and artificial lambert's spheroid _j, obtain the irradiance E that artificial lambert's spheroid reflected solar radiation can arrive satellite remote sensor entrance pupil place thus _kj, the pixel position k that artificial lambert's spheroid picture point is corresponding and gray-scale value DN _kj;

(6) keeping, under the condition that φ is constant, repeating step (5), measuring corresponding gray-scale value DN n time that obtains pixel k _kjwith entrance pupil irradiance E _kj, in conjunction with the background signal value DN of pixel _k0, set up linear response relationship by least square method, obtain the Absolute Radiometric Calibration Coefficients G of pixel k _k,

$G_k=\frac{\underset{j=1}{\overset{n}{\Σ}}\[({\mathrm{DN}}_{kj}-{\mathrm{DN}}_{k0})\·E_{kj}\]}{\underset{j=1}{\overset{n}{\Σ}}{E}_{kj}^2}.$

The calibration of described step (1) Satellite to the requirement of signal energy is: satellite remote sensor can receive the solar energy of artificial lambert's spheroid reflection, and the signal voltage that the detector in satellite remote sensor produces is between 20% ~ 80% of detector saturation signal magnitude of voltage.

Described artificial lambert's spheroid is aluminum spheroid, and surface is coated with blanc fixe by bonding agent.

The present invention's advantage is compared with prior art:

(1) the inventive method adopts lambert's spheroid that solar radiation is introduced remote sensor indirectly as reference source, reference source is positioned at whole system outside, optical element in whole light path can be calibrated, also can be full of remote sensor aperture, meet full light path, full aperture, distribute with solar spectrum the radiation calibration requirement of mating;

(2) the inventive method adopts the direct reflected solar radiation of lambert's spheroid in-orbit, break away from the restriction of atmospheric conditions and terrain object characteristic, avoid the uncertainty that in solar radiation relays link, the environmental factor such as air, terrain object is introduced, improve absolute radiometric calibration precision in-orbit;

(3) the inventive method is by disposing lambert's spheroid in space, establish unified space optics radiation benchmark, normalization monitoring can be realized to satellite remote sensor, revise the radiometric response change of satellite remote sensor in time, improve the response efficiency of radiation calibration in-orbit of satellite remote sensor;

(4) the inventive method just can carry out calibration by using lambert's spheroid in-orbit, being easy to realize, without the need to installing extra calibration instrument and equipment at satellite itself, being conducive to the burden alleviating existing Optical remote satellite On-Star system.

Accompanying drawing explanation

Fig. 1 is the FB(flow block) of the inventive method;

Fig. 2 is solar radiant energy TRANSFER MODEL schematic diagram of the present invention;

Fig. 3 is characteristic parameter schematic diagram of the present invention;

Fig. 4 is the relation of lambert's spheroid reflected signal DN value of the present invention and deep space background signal DN value.

Embodiment

As shown in Figure 1, be the FB(flow block) of the inventive method, key step is as follows:

(1) in space, launch artificial lambert's spheroid by carrier rocket radiation pattern or satellite release radiation pattern, the diameter of spheroid and orbital position meet satellite and calibrate requirement to signal energy;

Satellite calibration is that satellite remote sensor receives spheroid reflected sunlight energy to the requirement of signal energy, and the signal voltage that the detector in remote sensor produces is between 20% ~ 80% of detector saturation signal magnitude of voltage.

Described artificial lambert's spheroid is the uniform spherome that surface has close to Lambertian characteristics, and a kind of embodiment is wherein barium sulphate lambert spheroid, and barium sulphate lambert spheroid adopts the method for spraying to make.First by uniform aluminum spherome surface coated abrasive working, blanc fixe and milky white adhesive are mixed and made into the aluminum spherome surface that half pasty state is sprayed on polishing equably, artificial lambert's spheroid after drying, can be obtained.

(2) parameter of satellite remote sensor to be calibrated is set, integral time, gain and progression are remained unchanged in whole calibration process.

(3) attitude maneuver is carried out to satellite, make satellite remote sensor to be calibrated point to deep space background, obtain the gray-scale value of satellite remote sensor imaging pixel to be calibrated, carry out n (n>=1, number of times is more, and precision is higher) measure, obtain the gray-scale value DN of each pixel measured _k0i, wherein, k is the position (span of k is from 1 to the sum of remote sensor pixel) of remote sensor pixel, and i is the number of times measured, i=1,2,3......, n, after having measured for n time, calculates the background signal mean value DN of satellite remote sensor pixel k to be calibrated _k0

${\mathrm{DN}}_{k0}=\frac{1}{n}\underset{i=1}{\overset{i=n}{\Σ}}{\mathrm{DN}}_{k0i}.$

(4) Satellite Tool Kit STK is utilized to emulate the transmission of solar radiant energy, set up the scene comprising satellite, lambert's spheroid and the sun, draw the time period met when satellite, position relationship between lambert's spheroid and sun three under calibration condition, the TRANSFER MODEL of solar radiant energy as shown in Figure 2, in Fig. 2, lambert's spheroid by after the solar radiant energy that receives to external reflection, remote sensor receives the radiation energy reflected by lambert's spheroid.

Calibration condition comprises the visible condition of geometry and the visible condition of sensor, and two conditions must meet simultaneously.The visible condition of geometry is that satellite and lambert's spheroid line therebetween do not block by the earth.The visible condition of sensor for lambert's spheroid be in ground shadow outside, lambert's spheroid can reflected solar radiation energy thus realize observation imaging.

(5) from the time period of satisfied calibration condition, a certain imaging moment point is chosen arbitrarily, attitude maneuver is carried out to satellite, make the sensing lambert spheroid of satellite remote sensor to be calibrated, the detector in satellite remote sensor can obtain the getable signal of lambert's spheroid reflected solar radiation.Remote sensor is observed the position angle of lambert's spheroid, the angle in the line namely between remote sensor and lambert's spheroid and remote sensor entrance pupil direction is designated as φ.

(6) the imaging moment point moment is obtained, satellite, position relationship between lambert's spheroid and sun three.After lambert's ball-shooting to space certain tracks, need the position in-orbit being estimated lambert's spheroid by ground survey mode, obtain satellite to three characteristic parameters inscribed during lambert's spheroid imaging, comprise the relative distance L of lambert's spheroid and the sun _{1 (j)}, lambert's spheroid with wait the relative distance L calibrating satellite remote sensor entrance pupil place _{2 (j)}, line between the sun and lambert's spheroid and wait the angle theta of the line calibrated between satellite remote sensor and lambert's spheroid _j.The signal of characteristic parameter as shown in Figure 3.

(7) the irradiance E at lambert's spheroid place is arrived by following formulae discovery solar radiation _j.

$E_j={\∫}_{{\mathrm{\λ}}_1}^{{\mathrm{\λ}}_2}E\left(\mathrm{\λ}\right)d\mathrm{\λ}={\∫}_{{\mathrm{\λ}}_1}^{{\mathrm{\λ}}_2}\frac{R^2\·M\left(\mathrm{\λ}\right)}{L_{1\left(j\right)}^2}d\mathrm{\λ}$

Wherein:

E (λ) is the spectral irradiance at solar radiation arrival lambert's spheroid place, and unit is Wm ^-2μm ^-1;

λ ₁, λ ₂be respectively spectral coverage lower limit and the upper limit of remote sensor to be calibrated;

R is solar radius, R=6.9599 × 10 ⁸m;

J is pendulous frequency.

(unit is Wm to the spectral radiant exitance that M (λ) is the sun ^-2μm ^-1), solar source can equivalence become temperature to be the radiation black matrix of 5900K, and according to Planck radiation law, the spectral radiant exitance of the sun can be expressed as in formula, λ is wavelength, c ₁be the first blackbody radiation constant (c ₁=3.741844 × 10 ⁴wm ^-2μm ⁴), c ₂be the second blackbody radiation constant (c ₂=14388 μm of K), T is thermodynamic temperature (T=5900K).

(8) by the irradiance E at following formulae discovery satellite remote sensor entrance pupil place _kj.

$E_{kj}=\frac{\mathrm{\ρ}\·E_j}{{\mathrm{\πL}}_{2\left(j\right)}^2}\·f\left({\mathrm{\θ}}_j\right)\·cos\left(\mathrm{\φ}\right)$

Wherein:

ρ is the surface reflectivity of lambert's spheroid;

F (θ _j) be the angle factor between reflected energy and projectile energy, obtain by carrying out optical modeling to space sphere target:

$f\left({\mathrm{\θ}}_j\right)=\frac{d^2}{6}\·\[(\mathrm{\π}-{\mathrm{\θ}}_j)\·{\mathrm{cos\θ}}_j+{\mathrm{sin\θ}}_j\]$

Wherein, d is lambert's sphere diameter;

(9) lambert's spheroid is Point Target, after lambert's spheroid imaging, obtains its position of formed picture point and gray-scale value size on the detector, is designated as k, DN respectively _kj.The relation of lambert's spheroid reflected signal DN value and deep space background signal DN value as shown in Figure 4, in the situation shown in figure, image point position k=15, picture point gray-scale value DN _kj=B.

(10) keeping, under the condition that φ is constant, repeating step (5) ~ (9), measuring corresponding gray-scale value DN n time that obtains pixel k _kjwith entrance pupil irradiance E _kj.In conjunction with the background signal value DN of pixel _k0, set up linear response relationship by least square method, obtain the Absolute Radiometric Calibration Coefficients G of pixel k _k, concrete formula is as follows:

$G_k=\frac{\underset{j=1}{\overset{n}{\Σ}}\[({\mathrm{DN}}_{kj}-{\mathrm{DN}}_{k0})\·E_{kj}\]}{\underset{j=1}{\overset{n}{\Σ}}{E}_{kj}^2}.$

The content be not described in detail in instructions of the present invention belongs to the known technology of those skilled in the art.

Claims (3)

1., based on an Optical remote satellite absolute radiation calibration method for space lambert's spheroid, it is characterized in that comprising the steps:

(1) in space, launch artificial lambert's spheroid by carrier rocket radiation pattern or satellite release radiation pattern, the diameter of spheroid and orbital position meet satellite and calibrate requirement to signal energy; Described artificial lambert's spheroid is the uniform spherome that surface has close to Lambertian characteristics;

(2) parameter of satellite remote sensor to be calibrated is set, integral time, gain and progression are remained unchanged in whole calibration process;

(3) attitude maneuver is carried out to satellite, make satellite remote sensor to be calibrated point to deep space background, obtain the gray-scale value of satellite remote sensor imaging pixel to be calibrated, carry out n time altogether and measure, obtain the gray-scale value DN of each pixel k measured _k0i, wherein n>=1, k is the position of remote sensor pixel, and the span of k is that i is the number of times measured, i=1,2,3......, n from 1 to the sum of remote sensor pixel; After having measured for n time, calculate the background signal mean value DN of satellite remote sensor pixel k to be calibrated _k0,

${\mathrm{DN}}_{k0}=\frac{1}{n}\underset{i=1}{\overset{i=n}{\Σ}}{\mathrm{DN}}_{k0i};$

(4) set up and comprise the scene of satellite, artificial lambert's spheroid and the sun, the transmission of emulation solar radiation energy, obtain satellite, time period that position relationship between artificial lambert's spheroid and sun three meets calibration condition; Described calibration condition comprises the visible condition of geometry and the visible condition of sensor, the visible condition of geometry is that satellite and artificial lambert's spheroid line therebetween do not block by the earth, the visible condition of sensor is behaved and is made lambert's spheroid and be in outside ground shadow, and artificial lambert's spheroid can reflected solar radiation energy thus realize observation imaging;

(5) from the time period of satisfied calibration condition, a certain imaging moment point is chosen, attitude maneuver is carried out to satellite, the entrance pupil normal of satellite remote sensor to be calibrated is made to point to lambert's spheroid, observed by remote sensor the position angle of artificial lambert's spheroid be designated as φ, obtain the relative distance L of artificial lambert's spheroid and the sun _{1 (j)}, artificial lambert's spheroid with wait the relative distance L calibrating satellite remote sensor entrance pupil place _{2 (j)}, line between the sun and artificial lambert's spheroid and wait the angle theta of the line calibrated between satellite remote sensor and artificial lambert's spheroid _j, obtain the irradiance E that artificial lambert's spheroid reflected solar radiation can arrive satellite remote sensor entrance pupil place thus _kj, the pixel position k that artificial lambert's spheroid picture point is corresponding and gray-scale value DN _kj;

(6) keeping, under the condition that φ is constant, repeating step (5), measuring corresponding gray-scale value DN n time that obtains pixel k _kjwith entrance pupil irradiance E _kj, in conjunction with the background signal value DN of pixel _k0, set up linear response relationship by least square method, obtain the Absolute Radiometric Calibration Coefficients G of pixel k _k,

$G_k=\frac{\underset{j=1}{\overset{n}{\Σ}}\[({\mathrm{DN}}_{kj}-{\mathrm{DN}}_{k0})\·E_{kj}\]}{\underset{j=1}{\overset{n}{\Σ}}{E}_{kj}^2}.$

2. a kind of Optical remote satellite absolute radiation calibration method based on space lambert's spheroid according to claim 1, it is characterized in that: the calibration of described step (1) Satellite to the requirement of signal energy is: satellite remote sensor can receive the solar energy of artificial lambert's spheroid reflection, and the signal voltage that the detector in satellite remote sensor produces is between 20% ~ 80% of detector saturation signal magnitude of voltage.

3. a kind of Optical remote satellite absolute radiation calibration method based on space lambert's spheroid according to claim 1 and 2, is characterized in that: described artificial lambert's spheroid is aluminum spheroid, and surface is coated with blanc fixe by bonding agent.