CN104406686B - Sun shortwave incident radiation evaluation method under MODEL OVER COMPLEX TOPOGRAPHY - Google Patents

Sun shortwave incident radiation evaluation method under MODEL OVER COMPLEX TOPOGRAPHY Download PDF

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CN104406686B
CN104406686B CN201410750687.0A CN201410750687A CN104406686B CN 104406686 B CN104406686 B CN 104406686B CN 201410750687 A CN201410750687 A CN 201410750687A CN 104406686 B CN104406686 B CN 104406686B
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transmitance
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张彦丽
李新
阳坤
赵军
摆玉龙
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Northwest Normal University
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Abstract

Sun shortwave incident radiation evaluation method under a kind of MODEL OVER COMPLEX TOPOGRAPHY, by the broadband atmospheric transmittance of the estimation of broadband water vapor absorption transmitance, broadband aerosol scattering transmitance estimation MODIS Atmosphere Product, according to the aerosol optical depth of 0.55 μm and actual <i> α </i> value derivation <i> β </i> again; Estimate other three kinds of broadband transmitance components; Based on ATCOR3 model inversion surface albedo; Sun shortwave incident radiation from direct solar radiation, anisotropic scattering radiation, isotropic scatterning radiation and surrounding terrain reflected radiation four aspect estimation MODEL OVER COMPLEX TOPOGRAPHY.This evaluation method carries out quick landform standardization to study area based on TM image based on ATCOR3 model, obtains the true albedo in earth's surface, substitutes into mountain area radiative transfer model as priori value, calculates surrounding terrain reflected radiation; Using DEM and MODIS steam and gasoloid Atmosphere Product as mode input parameter, need not ground station observational data.

Description

Sun shortwave incident radiation evaluation method under MODEL OVER COMPLEX TOPOGRAPHY
Technical field
The invention belongs to technical field of solar, relate to sun shortwave incident radiation evaluation method under a kind of MODEL OVER COMPLEX TOPOGRAPHY.
Background technology
The short incident wave radiation of the sun (DownwardSurfaceShortwaveRadiation, DSSR) be physics on epigeosphere, biological and chemical process (as snow melt, transpiration, crop photosynthesis etc.) main energy sources, be also the call parameter in ecosystem process model, hydrological model and Biophysical model.The factors such as air, earth's surface characteristic and process determine the incident shortwave radiation of the sun that earth's surface receives, and are therefore necessary to determine that surface shortwave is local, change in time and space on region and Global Scale.The classic method obtaining DSSR change in time and space is that earth's surface is measured.When earth's surface is smooth, under the supposition that atmospheric level is homogeneous, the measurement of ground station can be extrapolated to two-dimensional space.But when earth's surface heterogeneity or rugged and rough time, sun shortwave incident radiation special heterogeneity is very strong, just can not extrapolate.Utilize Value of Remote Sensing Data, digital elevation model (DigitalElevationModel, DEM) and in conjunction with atmospheric radiation transmission estimation MODEL OVER COMPLEX TOPOGRAPHY under the incident radiation of sun shortwave, be the new method developed nearly ten years.
The DSSR that earth's surface, mountain area receives is from three aspects: direct solar radiation, atmospheric scattering radiation and surrounding terrain reflected radiation.Three kinds of components affect by air and topographic condition to some extent.Under MODEL OVER COMPLEX TOPOGRAPHY, the incident radiation of broadband sun shortwave is mainly by the impact of four factors, i.e. the sun-earth's surface geometrical factor, atmospheric attenuation, orographic factor and ground mulching type.Wherein, geometrical factor determines latitude effect and the Seasonal variation of the incident radiation of sun shortwave, controls the solar space distribution characteristics of Global Scale and mesoscale; Solar shortwave radiation was subject to atmospheric attenuation through air before arrival earth's surface, and complex topographic area atmospheric transmittance is with change in time and space, and especially steam and gasoloid transmitance change more violent; Orographic factor describes the sun shortwave incident radiant energy uneven distribution because different gradient, slope aspect and surrounding terrain impact etc. cause, and determines the variation characteristic in landform small scale sun shortwave incident radiation amount.In above four influence factors, what the difficulty of sun shortwave incident radiation estimation was that atmospheric effect acts on orographic effect and both superposes.
Summary of the invention
The object of this invention is to provide sun shortwave incident radiation evaluation method under a kind of MODEL OVER COMPLEX TOPOGRAPHY, take air and orographic effect simultaneously into account, improve estimation precision.
For achieving the above object, the technical solution adopted in the present invention is: sun shortwave incident radiation evaluation method under a kind of MODEL OVER COMPLEX TOPOGRAPHY, and it is characterized in that, this evaluation method specifically carries out according to the following steps:
Step 1: the broadband atmospheric transmittance based on MODIS Atmosphere Product is estimated:
Broadband atmospheric transmittance is divided into two classes: direct solar radiation transmitance and scattered radiation transmitance, the female atmospheric transmittance model of design parameter Scheme Choice sun;
Direct solar radiation transmitance formula is:
In formula: t r ( θ s ), t a ( θ s ), t g ( θ s ), t σ 3 ( θ s ) and t w ( θ s ) represent that Rayleigh scattering transmitance, aerosol scattering transmitance, stabilizing gas absorb transmitance, Ozone Absorption transmitance and water vapor absorption transmitance respectively.
Scattered radiation transmitance t d ( θ s ) computing formula is:
Direct solar radiation decay size is in an atmosphere determined by direct solar radiation transmitance, and the damping capacity of scattered radiation is determined by scattered radiation transmitance; The reflected radiation of surrounding terrain is the direct radiation of atural object reception around and the function of scattered radiation;
1, broadband water vapor absorption transmitance estimation:
Air quality in formula m( θ s ) see World Meteorological Organization's suggestion computing formula; wbe precipitable water thickness, unit is centimetre, replaces with MODIS steam product P W;
2, broadband aerosol scattering transmitance estimation:
In formula: βfor turbidity; MODIS steam product directly inputs water vapor transmittance formula, and in positive female atmospheric transmittance pattern, it is assumed to be Wavelength Indices and is assumed to be 1.3, and βderived by 0.50 μm of aerosol optical depth, that is:
β=τ 0.500.5 1.3（6）
In formula, τrepresent aerosol optical depth, τ 0.50represent 0.50 μm of aerosol optical depth;
But MODIS aerosol product does not record the AOD at 0.50 mum wavelength place, need the aerosol optical depth according to 0.55 μm and actual wavelength index αit is right to be worth βre-start derivation:
β=τ 0.55 (0.5/0.55) - α 0.5 1.3(7)
3, other three kinds of broadband transmitance component estimations
Rayleigh scattering transmitance, ozone transmitance and stabilizing gas absorb transmitance three kinds of transmitance formula and still utilize positive female model, that is:
Wherein, lfor ozone thickness total amount, unit cm or many cloth is gloomy, changes with geographic latitude and season; 24 annual mean interpolations of Satellite Product are utilized to obtain m c = m( θ s ) p s / p 0, represent the air quality that air pressure corrects; p s be work as surface pressure, in order to avoid atmospheric transmittance calculates the dependence to ground measured data, utilize experimental formula directly to be estimated by earth's surface elevation, that is:
p s = p 0exp(- z/ H T )(11)
In formula, zfor ground elevation, unit, rice; p 0for standard atmospheric pressure; h t be atmospheric scale height, highly often raise an absolute altitude h t , then atmospheric pressure reduces 1/e=0.37;
Step 2: based on ATCOR3 model inversion surface albedo:
For high-resolution satellite sensors such as the Landsat of observed ray near zenith, ground, mountain area apparent bearing Reflective regulation factor G-function:
G=cos i s /cos i T (12)
Wherein, i t for angle threshold, show to only have the actual irradiating angle of slope unit place's sun i s g-function is just used to carry out earth's surface two to reflection correction when being more than or equal to this threshold value; That is, if solar illumination angle is less than threshold value, then thinks that earth's surface is lambert's body, do not distinguish hillside fields reflectivity reflectivity pacifically; According to this topographic correction principle, by hillside fields reflectivity ρ t be converted to level land reflectivity ρ h , realize the object of topographic correction, obtain the true albedo in earth's surface, its formula is:
ρ H= ρ T G(13)
Step 3: sun shortwave incident radiation estimation under MODEL OVER COMPLEX TOPOGRAPHY
1) direct solar radiation
The direct radiation of sun shortwave incident radiation is from the direct irradiation of the sun, and computing formula is:
Direct solar radiation is by the incident radiation of TOA sun shortwave e 0 , solar zenith angle θ s , local solar illumination angle i s , the terrain masking factor v s with air direct projection transmitance t b ( θ) s joint effect; Surface slope and slope aspect will cause the actual illumination angle of the sun to change with landform; Under dem data is auxiliary, all accurately can be obtained by geometric relationship between the sun and earth's surface; The terrain masking factor judges that whether atural object blocked by surrounding terrain and can not get shining upon, and shows when local illumination angle is greater than 90 ° that earth's surface is in shade equally owing to self covering; Both of these case makes direct solar radiation be zero;
2) anisotropic scattering radiation
Wherein, ring day the factor , be that the direct solar radiation that horizontal earth's surface receives accounts for the proportion of TOA sun shortwave incident radiation, its essence is the direct transmitance of air, show the proportion of total scattering radiation shared by anisotropy solar radiation;
Horizontal earth's surface scattered radiation can by following formulae discovery:
3) isotropic scatterning radiation
Isotropic scatterning radiation is from each to uniform the vault of heaven, and its scattering strength depends on the visual factor of earth's surface each pixel sky v iso , that is:
4) surrounding terrain reflected radiation
In formula, f ij for the shape of mountain factor of i-th pixel in n pixel around goal pels j, show, from the emittance of i-th pixel, the part of a jth pixel can be arrived.
Evaluation method of the present invention utilizes high resolution DEM and Moderate Imaging Spectroradiomete (ModerateResolutionImagingSpectroradiometer, MODIS) Atmosphere Product, take air and orographic effect into account simultaneously, describing atmospheric parameter, DEM and terrain factor estimates all extremely important to mountain area solar radiation, improve estimation precision.
1) first derive how using MODIS steam and aerosol product as atmospheric transmittance Parameterization Scheme input parameter, obtain atmospheric transmittance.Directly using the MODIS near infrared steam product of 1km spatial resolution as precipitable water thickness input parameter, avoid earth's surface observed readings such as utilizing surface pressure, surface temperature, relative humidity and substitute into empirical model and calculate; The aerosol optical depth locate MODIS aerosol product 0.55 micron and Wavelength Indices are as mode input parameter.Utilize 56 clear sky ground observation data verification sun shortwave incident radiation precision, result shows, 56 clear sky condition atmospheric environments have larger fluctuation change, and MODIS steam and aerosol product truly feature satellite at that time and to pass by moment atmospheric condition, thus improve solar radiation estimation precision.
2) by above broadband atmospheric transmittance, it introduces mountain area radiative transfer model, synchronous removal orographic effect and atmospheric effect, mountain area sun shortwave incident radiation under estimation clear sky condition.
3) based on ATCOR3 model, based on TM image, quick landform standardization has been carried out to study area, obtained the true albedo in earth's surface, substituted into mountain area radiative transfer model as priori value, calculated surrounding terrain reflected radiation.
Sun shortwave incident radiation algorithm using DEM and MODIS steam and gasoloid Atmosphere Product as mode input parameter, need not ground station observational data, and ground observation value is only verified for arithmetic accuracy.
Accompanying drawing explanation
Fig. 1 is that solar shortwave radiation arrives earth's surface rear-inclined earth's surface built-up radiation schematic diagram.
Fig. 2 is that solar shortwave radiation arrives atmospheric attenuation schematic diagram before earth's surface.
Fig. 3 is sun shortwave incident radiation observed reading and estimated value scatter diagram and the result figure.
Fig. 4 is sun shortwave incident radiation earth's surface observed reading and four kinds of model assessment result scatter diagrams.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.
Remote sensing appraising sun shortwave incident radiation method is divided into two classes: one is empirical statistics method.Set up the recurrence empirical relationship between earth's surface observation and remote sensing radiance observed reading; Two is the Parameterization Scheme utilizing radiative transfer model or simplified by radiative transfer model, in acquisition TOA solar radiation, atmospheric optical properties, earth surface reflection characteristic, earth's surface net short-wave radiation is estimated on isoparametric basis.Orographic factor controls the time and space distribution of the solar shortwave radiation that complex topographic area earth's surface receives, atmospheric environment weakens and arrives earth's surface intensity of solar radiation and space distribution, earth's surface elevation also affects surface pressure, moisture content etc. simultaneously, thus changes the atmospheric transmittance such as Rayleigh scattering, stabilizing gas.And global energy and water cycle test-Surface Energy Budget balancing item GEWEX-SRB(GlobalEnergyandWaterCycleExperiment(GEWEX)-SurfaceRadiationBudget (SRB), cloud and Earth radiant energy system CERES-EBAF(CloudandEarth ' sRadiantEnergySystems(CERES)-EnergyBalanceandFilled(EBAF)) etc. global radiation revenue and expenditure product space resolution very low, be not suitable for region or less Watershed Scale research.When the rare and skewness of solar radiation ground observation point, there is larger uncertainty in ground observation and the empirical statistics method analog result set up thus.
The incident radiation of sun shortwave arrives in surficial process, inevitably with the sun-air-Biao system interaction, as shown in Figure 1, in figure, (1) is direct radiation, and (2) are anisotropic scatterings, (3) be isotropic scatterning, (4) are surrounding terrain scatterings.Therefore, the calculating of broadband solar irradiance is determined by following four factors: the sun-earth's surface geometric relationship, atmospheric attenuation, orographic factor and ground mulching type.The sun-earth's surface geometric relationship determines the incident radiation of TOA sun shortwave, by astronomical formula accurate Calculation.Solar shortwave radiation was subject to atmospheric attenuation through air before arrival earth's surface, the atmospheric transmittance component that general definition 5 kinds is separate: Rayleigh scattering, aerosol scattering, Ozone Absorption, moisture sorption and stable trace gas absorb, and the total transmitance of air is five kinds of component transmitance summations, as Fig. 2.In figure, T is atmospheric transmittance, is the incident radiation of TOA sun shortwave.Atmospheric transmittance is with change in time and space, and especially water vapor transmittance and gasoloid transmitance change more violent.Meanwhile, the incident radiation of mountain area sun shortwave changes by the local influence of topography consumingly.Ground mulching type or surface albedo (Albedo) are the 4th class factors affecting the incident radiation of sun shortwave, and high albedo ground surface type will provide more reflected radiation to contribute, as the naked rock of ice and snow etc. for the visible pixel of target.Therefore, radiation flux calculate in often desirably Table A lbedo as priori calculate surrounding terrain contribution.
Mountain area sun shortwave incident radiation is broken down into three parts: direct solar radiation, atmospheric scattering radiation and surrounding terrain reflected radiation.Direct solar radiation accounts for the largest portion of built-up radiation, and secondly, surrounding terrain reflecting radiation energy is minimum for scattered radiation, but when peripheral ground is covered by high reflectance atural objects such as ice and snow, its value is very important.Scattered radiation according to whether with solar direction about being divided into again the isotropic scatterning radiation that has nothing to do with solar direction and the anisotropic scattering radiation from solar direction.That is:
In formula, represent the incident radiation of sun shortwave, direct solar radiation, atmospheric scattering radiation, isotropic scatterning radiation, anisotropic scattering radiation and surrounding terrain reflected radiation respectively.Although the incident radiation of sun shortwave in radiation transmission by the impact of four factors, different solar radiation component to affect principle different from rule.
Although the various atmospheric radiation transmission such as MODTRAN is usually used in estimating atmospheric transmittance, atmospheric parameter often needs station-observed data as input, and the atmospheric transmittance exported is also One-Point-Value, is difficult to meeting spatial distribution calculation requirement.Compared with sparse earth's surface observation data, MODIS sensor provides the Atmosphere Product of spatial and temporal distributions, provides a large amount of necessary input parameter, as atmospheric precipitation thickness, aerosol optical depth etc. for calculating Land surface energy budget model.For this reason, it can be used as input parameter, utilize experimental formula derivation water vapor transmittance and gasoloid transmitance.
In addition, in mountain area with a varied topography, the reflected radiation of surrounding terrain is very important.Especially, when around high reflectance atural object covers, albedo is at this moment needed to calculate from around to the earth surface reflection radiation contributions of Target scalar.Surface albedo and the incident radiation of sun shortwave are all the parameters of earth's surface net short-wave radiation, and in order to ensure earth's surface net short-wave radiation estimation precision, usually limiting two parameters is independently.Therefore, usually surrounding terrain reflected radiation is calculated by surface albedo priori.The randomness chosen in order to avoid this albedo priori and surface albedo special heterogeneity, evaluation method of the present invention utilizes TM image, has the Albedo of space distribution by topographic correction software module ATCOR3 fast inversion.The topographic correction software module that ATCOR3 is developed by German Wessling photoelectricity research institute Richter etc., can remove remote sensing image air and orographic effect simultaneously, and reduction mountain area atural object detailed information, obtains the true Albedo in earth's surface.
The invention provides sun shortwave incident radiation evaluation method under a kind of MODEL OVER COMPLEX TOPOGRAPHY, specifically carry out according to the following steps:
Step 1: the broadband atmospheric transmittance based on MODIS Atmosphere Product is estimated
Broadband atmospheric transmittance is divided into two classes: direct solar radiation transmitance and scattered radiation transmitance, design parameter Scheme Choice sun female atmospheric transmittance model (Yangetal., Ahybridmodelforestimatingglobalsolarradiation. solarEnergy).
Direct solar radiation transmitance formula is:
In formula: t r ( θ s ), t a ( θ s ), t g ( θ s ), t σ 3 ( θ s ) and t w ( θ s ) represent that Rayleigh scattering transmitance, aerosol scattering transmitance, stabilizing gas absorb transmitance, Ozone Absorption transmitance and water vapor absorption transmitance respectively.
Scattered radiation transmitance t d ( θ s ) computing formula is:
Direct solar radiation decay size is in an atmosphere determined by direct solar radiation transmitance, and the damping capacity of scattered radiation is determined by scattered radiation transmitance.The reflected radiation of surrounding terrain is the direct radiation of atural object reception around and the function of scattered radiation.Five class broadband air component transmitance computation processes will be introduced respectively below, introduce how using MODIS steam and aerosol product as input parameter.
1, broadband water vapor absorption transmitance estimation:
Two parameters are related to, air quality in formula m( θ s ) see World Meteorological Organization's suggestion computing formula; wbe precipitable water thickness, unit is centimetre, generally can calculate according to Sounding Data, and sometimes in order to easy, the conventional parameter such as ground water vapor pressure, humidity is estimated, can directly replace with MODIS steam product P W in this evaluation method.
2, broadband aerosol scattering transmitance estimation:
In formula: βfor turbidity; MODIS steam product can directly input water vapor transmittance formula, and in positive female atmospheric transmittance pattern, it is assumed to be Wavelength Indices and is assumed to be 1.3, and βderived by 0.50 μm of aerosol optical depth (AOD), that is:
β=τ 0.500.5 1.3（6）
In formula, τrepresent aerosol optical depth, τ 0.50represent 0.50 μm of aerosol optical depth.
But MODIS aerosol product does not record the AOD at 0.50 mum wavelength place, therefore need the aerosol optical depth according to 0.55 μm and actual wavelength index αit is right to be worth βre-start derivation:
β=τ 0.55 (0.5/0.55) - α 0.5 1.3(7)
3, other three kinds of broadband transmitance component estimations
Rayleigh scattering transmitance, ozone transmitance and stabilizing gas absorb transmitance three kinds of transmitance formula and still utilize positive female model, that is:
Wherein, lfor ozone thickness total amount (centimetre, cm or many cloth is gloomy, 1000DobsonUnits) changes with geographic latitude and season.Generalized case, except the South Pole, Ozone depth increases along with latitude and increases, and spring is high, and autumn is low, and 24 annual mean interpolations of the Satellite Product that this method utilizes NASAGSFC ozone treatment team to provide obtain m c = m( θ s ) p s / p 0, represent the air quality that air pressure corrects. p s be work as surface pressure, in order to avoid atmospheric transmittance calculates the dependence to ground measured data, experimental formula can be utilized directly to be estimated by earth's surface elevation, that is:
p s = p 0exp(- z/ H T )(11)
In formula, zfor ground elevation (rice), p 0for standard atmospheric pressure (1.013 × 10 5pa). h t =8430 ( m) be atmospheric scale height, show highly often to raise an absolute altitude h t , then atmospheric pressure reduces 1/e=0.37;
Step 2: based on ATCOR3 model inversion surface albedo
For the high-resolution satellite sensors such as the Landsat of observed ray near zenith, ground, mountain area apparent bearing Reflective regulation factor G-function is often selected:
G=cos i s /cos i T (12)
Wherein, i t for angle threshold, show to only have the actual irradiating angle of slope unit place's sun i s g-function is just used to carry out earth's surface two to reflection correction when being more than or equal to this threshold value.That is, if solar illumination angle is less than threshold value, then thinks that earth's surface is lambert's body, do not distinguish hillside fields reflectivity reflectivity pacifically; According to this topographic correction principle, by hillside fields reflectivity ρ t be converted to level land reflectivity ρ h , realize the object of topographic correction, thus obtain the true albedo in earth's surface, its formula is:
ρ H= ρ T G(13)
Step 3: sun shortwave incident radiation estimation under MODEL OVER COMPLEX TOPOGRAPHY
1) direct solar radiation
The direct radiation of sun shortwave incident radiation is from the direct irradiation of the sun, and computing formula is:
Direct solar radiation is by the incident radiation of TOA sun shortwave e 0 , solar zenith angle θ s , local solar illumination angle i s , the terrain masking factor v s with air direct projection transmitance t b ( θ) s joint effect.The terrain masking factor judges that whether atural object blocked by surrounding terrain and can not get shining upon, and when local illumination angle is greater than 90 °, shows that earth's surface is in shade equally owing to self covering.Except these two kinds of special circumstances make direct solar radiation be except zero, surface slope and slope aspect will cause the actual illumination angle of the sun to change with landform.This several factor, under dem data is auxiliary, all accurately can be obtained by geometric relationship between the sun and earth's surface.
2) anisotropic scattering radiation
Wherein, ring day the factor , be that the direct solar radiation that horizontal earth's surface receives accounts for the proportion of TOA sun shortwave incident radiation, its essence is the direct transmitance of air, show the proportion of total scattering radiation shared by anisotropy solar radiation.
Horizontal earth's surface scattered radiation can by following formulae discovery:
3) isotropic scatterning radiation
Isotropic scatterning radiation is from each to uniform the vault of heaven, and its scattering strength depends on the visual factor of earth's surface each pixel sky v iso , that is:
4) surrounding terrain reflected radiation
In formula, f ij for the shape of mountain factor of i-th pixel in n pixel around goal pels j, show, from the emittance of i-th pixel, the part of a jth pixel can be arrived.
Various terrain factor is related to, as the right terrain masking factor in mountain area sun shortwave incident radiation estimation v s , local solar illumination angle cosine cos i s , the shape of mountain factor f ij , the visual factor of sky v iso deng, its detailed computing formula is shown in Lee's recent studies on (Lietal., Modificationofsolarradiationmodeloverruggedterrain. chineseScienceBulletin, 1999).
the model that the present invention sets up is verified:
For the clear sky sun shortwave incident radiation data of modelling verification from large Noguchi small watershed Nei Malian beach, Heihe River basin upstream with close two, beach ground observation website.Generally, three kinds of method determination Cloudless atmosphere conditions are had.1) whether be smooth varies with sinusoidal function according to website observed reading; 2) by checking whether MODIS aerosol product has value, if shortage of data shows have cloud to cover; 3) MODIS cloud mask product is utilized.Utilize first two method choice 56 clear sky data, in table 1.
The clear sky data that 56 MODIS that table 1 is selected pass by
In order to utilize station-observed data quantitative description and evaluate sun shortwave incident radiation and net short-wave radiation estimation precision, need to calculate several empirical statistics value, as mean deviation (themeanbiaserror, MBE), root-mean-square error (therootmeansquareerror, and the statistical model such as linearly dependent coefficient (thelinearcorrectioncoefficient, R2) RMSD).Its computing formula is described below shown in table 2.
Several model definition of table 2
Two website Surface radiation observation data every ten minutes records once, are selected to pass by moment immediate twice ground observation mean value for ground result verification with MODIS.Fig. 3 is 56 clear sky ground observed readings and model assessment result scatter diagram and verifies statistics.Result shows, the instantaneous sun shortwave incident radiation of model assessment exists generally underestimates phenomenon, its mean deviation MBE and mean deviation number percent MBE% is respectively-61.9Wm-2 and-6.2%, and root-mean-square error RMSD and root-mean-square error number percent RMSD% is respectively 74.4Wm-2 and 7.5%.
Be not difficult to find from Fig. 3, the solar shortwave radiation that same Target scalar receives at different time changes greatly.Be so, that what factor causes so large difference? by showing 56 the clear sky data analyses of 2 websites, the solar shortwave radiation amount that earth's surface receives is the most responsive to solar zenith angle, its R 2=0.528, be secondly aerosol optical depth AOD, its R 2=0.237.Therefore, the incident radiation of sun shortwave not only with the sun-earth's surface geometric relationship change, is also subject to the impact of different atmospheric conditions simultaneously.
Evaluation method (improvedalgorithm, IA) of the present invention increases in two: one is that solar radiation evaluation method considers complicated terrain factor; Two is that MODIS steam and aerosol product are as the input parameter of air through computation model.In order to prove this evaluation method superiority both ways, increasing by three kinds of sun shortwave incident radiation evaluation methods especially at this and comparing.Four kinds of DSSR evaluation method input parameter details are in table 3.First method is called BMFA(MODIS-basedflatalgorithm), atmospheric parameter based on MODIS Atmosphere Product, but does not consider terrain factor.Second algorithm is called GBMA(GADS-basedmountainalgorithm), consider terrain factor, but precipitable water thickness is obtained by the empirical model method under the meteorological measuring support of earth's surface, AOD data are then by global aerosol data collection GADS(GlobalAerosolDataSet2.3b, http://wdc.dlr.de/data_products/SPECTRA/gads/) interpolation obtains, circular refers to document (Yangetal., 2006).The third method is called GBFA(GADS-basedflatalgorithm), atmospheric parameter acquisition methods is identical with second method, but does not consider landform.Below four kinds of sun shortwave incident radiation estimation results are compared.
Table 3 four kinds of sun shortwave incident radiation evaluation methods compare
Table 4 provides four kinds of method air input parameters and earth's surface observed reading thereof and model assessment statistics.Do not consider that MBFA and the GBFA sun shortwave incident radiation appraising model of terrain factor is not owing to considering terrain factor, sun shortwave incident radiation space, study area is situated between does not have special heterogeneity, and two kinds of method mean deviation number percent MBE% are all lower.But table 4 also shows, this method sun shortwave incident radiation estimation precision is on the contrary lower than the MBFA not considering landform.Find by analysis, the reason producing this phenomenon is two aspects: one is that two observation websites are all positioned at Schattenseite, does not consider that the estimation algorithm of landform will over-evaluate the incident radiation of sun shortwave; Two is that MODIS gasoloid and steam product all exist in test block and over-evaluate phenomenon, it can be used as model parameter, then the incident radiation of sun shortwave can be made to underestimate.So at these two experiment websites, the incident radiation of sun shortwave is over-evaluated and is cancelled out each other with underestimating, thus improves MBFA estimation precision.
Table 4 four kinds of method air input parameters and earth's surface observed reading thereof and model assessment statistics
Fig. 4 shows evaluation method of the present invention and has good correlativity between MBFA two kinds of method estimated values and earth's surface observed reading, illustrate and observe empirical statistics method compare with global aerosol data collection and earth's surface, MODIS Atmosphere Product is than more reflecting that satellite passes by moment atmospheric condition exactly.
Above result shows, mountain area sun shortwave incident radiation to landform and atmospheric parameter all responsive, and these two kinds effect reciprocal effects.Therefore, evaluation method of the present invention has larger application potential and practical value, particularly for the mountain area that mountain area observed reading is more sparse.
The solar shortwave radiation source of error that hillside fields receives is in three aspects: one is the error of calculation of DEM spatial resolution and terrain factor; Two is estimations of air principal ingredient transmitance, as AOD and PW; Three is surface albedos.
Evaluation method of the present invention has developed sun shortwave incident radiation estimating algorithm by MODIS Atmosphere Product and high resolution DEM data.Statistics shows, the method accurately can estimate the incident radiation of complex topographic area sun shortwave.In addition, this evaluation method does not rely on ground station observational data, therefore has very strong practicality, especially in mountain area.Broadband atmospheric transmittance computation model in the inventive method make use of positive female model for transmittance, but improve from two aspects: one is, directly using the MODIS steam product of 1km spatial resolution as precipitable water thickness input parameter, avoid earth's surface observed readings such as utilizing surface pressure, surface temperature, relative humidity and substitute into empirical model and calculate; Two is as mode input parameter using micron aerosol optical depth of 0.55 in MODIS aerosol product and Wavelength Indices.56 clear sky condition atmospheric environments have larger fluctuation change, and MODIS Atmosphere Product truly features satellite at that time and to pass by moment atmospheric condition, thus improve solar radiation estimation precision.Based on ATCOR3 model, based on TM image, quick landform standardization is carried out to study area, obtained surface albedo, substituted into mountain area radiative transfer model as priori value, calculated surrounding terrain reflected radiation.
Compared with other three kinds of empirical method results, describe atmospheric parameter, DEM and terrain factor and mountain area solar radiation is estimated all extremely important.MODIS atmospheric parameter, than global standards atmosphere data accurate description atmospheric condition more, therefore can improve estimation precision.
The maximum advantage of this evaluation method is that mountain area solar radiation estimation with only DEM with Remote Sensing Products as mode input parameter, need not ground station observational data, and ground observation value is verified for arithmetic accuracy.

Claims (1)

1. a sun shortwave incident radiation evaluation method under MODEL OVER COMPLEX TOPOGRAPHY, first carries out according to the following steps:
Step 1: the broadband atmospheric transmittance based on MODIS Atmosphere Product is estimated:
Broadband atmospheric transmittance is divided into two classes: direct solar radiation transmitance and scattered radiation transmitance, the female atmospheric transmittance model of design parameter Scheme Choice sun;
Direct solar radiation transmitance formula is:
In formula: t r ( θ s ), t a ( θ s ), t g ( θ s ), t σ 3 ( θ s ) and t w ( θ s ) represent that Rayleigh scattering transmitance, aerosol scattering transmitance, stabilizing gas absorb transmitance, Ozone Absorption transmitance and water vapor absorption transmitance respectively;
Scattered radiation transmitance t d ( θ s ) computing formula is:
Direct solar radiation decay size is in an atmosphere determined by direct solar radiation transmitance, and the damping capacity of scattered radiation is determined by scattered radiation transmitance; The reflected radiation of surrounding terrain is the direct radiation of atural object reception around and the function of scattered radiation;
1, broadband water vapor absorption transmitance estimation:
Air quality in formula m( θ s ) see World Meteorological Organization's suggestion computing formula; wbe precipitable water thickness, unit is centimetre, replaces with MODIS steam product P W;
2, broadband aerosol scattering transmitance estimation:
In formula: βfor turbidity; MODIS steam product directly inputs water vapor transmittance formula, and in positive female atmospheric transmittance pattern, it is assumed to be Wavelength Indices and is assumed to be 1.3, and βderived by 0.50 μm of aerosol optical depth, that is:
β=τ 0.500.5 1.3（6）
In formula, τrepresent aerosol optical depth, τ 0.50represent 0.50 μm of aerosol optical depth;
But MODIS aerosol product does not record the AOD at 0.50 mum wavelength place, need the aerosol optical depth according to 0.55 μm and actual wavelength index αit is right to be worth βre-start derivation:
β=τ 0.55 (0.5/0.55) - α 0.5 1.3(7)
3, other three kinds of broadband transmitance component estimations
Rayleigh scattering transmitance, ozone transmitance and stabilizing gas absorb transmitance three kinds of transmitance formula and still utilize positive female model, that is:
Wherein, lfor ozone thickness total amount, unit cm or many cloth is gloomy, changes with geographic latitude and season; 24 annual mean interpolations of Satellite Product are utilized to obtain m c = m( θ s ) p s / p 0, represent the air quality that air pressure corrects; p s be work as surface pressure, in order to avoid atmospheric transmittance calculates the dependence to ground measured data, utilize experimental formula directly to be estimated by earth's surface elevation, that is:
p s = p 0exp(- z/ H T )(11)
In formula, zfor ground elevation, unit, rice; p 0for standard atmospheric pressure; h t be atmospheric scale height, highly often raise an absolute altitude h t , then atmospheric pressure reduces 1/e=0.37;
Step 2: based on ATCOR3 model inversion surface albedo:
For high-resolution satellite sensors such as the Landsat of observed ray near zenith, ground, mountain area apparent bearing Reflective regulation factor G-function:
G=cos i s /cos i T (12)
Wherein, i t for angle threshold, show to only have the actual irradiating angle of slope unit place's sun i s g-function is just used to carry out earth's surface two to reflection correction when being more than or equal to this threshold value; That is, if solar illumination angle is less than threshold value, then thinks that earth's surface is lambert's body, do not distinguish hillside fields reflectivity reflectivity pacifically; According to this topographic correction principle, by hillside fields reflectivity ρ t be converted to level land reflectivity ρ h , realize the object of topographic correction, obtain the true albedo in earth's surface, its formula is:
ρ H= ρ T G(13)
It is characterized in that, this evaluation method also carries out according to the following steps:
Step 3: sun shortwave incident radiation estimation under MODEL OVER COMPLEX TOPOGRAPHY
1) direct solar radiation
The direct radiation of sun shortwave incident radiation is from the direct irradiation of the sun, and computing formula is:
Direct solar radiation is by the incident radiation of TOA sun shortwave e 0 , solar zenith angle θ s , local solar illumination angle i s , the terrain masking factor v s with air direct projection transmitance t b ( θ) s joint effect; Surface slope and slope aspect will cause the actual illumination angle of the sun to change with landform; Under dem data is auxiliary, all accurately can be obtained by geometric relationship between the sun and earth's surface; The terrain masking factor judges that whether atural object blocked by surrounding terrain and can not get shining upon, and shows when local illumination angle is greater than 90 ° that earth's surface is in shade equally owing to self covering; Both of these case makes direct solar radiation be zero;
2) anisotropic scattering radiation
Wherein, ring day the factor , be that the direct solar radiation that horizontal earth's surface receives accounts for the proportion of TOA sun shortwave incident radiation, its essence is the direct transmitance of air, show the proportion of total scattering radiation shared by anisotropy solar radiation;
Horizontal earth's surface scattered radiation can by following formulae discovery:
Isotropic scatterning radiation is from each to uniform the vault of heaven, and its scattering strength depends on the visual factor of earth's surface each pixel sky v iso , that is:
4) surrounding terrain reflected radiation
In formula, f ij for the shape of mountain factor of i-th pixel in n pixel around goal pels j, show, from the emittance of i-th pixel, the part of a jth pixel can be arrived.
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