CN115165786A - Equivalent clear sky radiation correction method for infrared hyperspectral atmosphere detector based on imager - Google Patents
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Abstract
The invention discloses an equivalent clear sky radiation correction method for an infrared hyperspectral atmosphere detector based on a geostationary satellite imager, which comprises the steps of establishing a cross matching model of the infrared hyperspectral atmosphere detector and the imager; using an imager to make clear sky correction on the detector part with a cloud view field; in particular to the equivalent clear sky radiance of each spectrum channel of the detecting instrument view field
Determination of (1); for equivalent clear sky radiance
Performing quality control and radiation verification; generating an equivalent clear sky radiation correction product data set; by adopting the equivalent clear sky radiation correction method for the infrared hyperspectral atmosphere detector based on the geostationary satellite imager, the clear sky correction is carried out on the part of the detector with a cloud view field, so that the influence of cloud radiation is removed, and the infrared hyperspectral atmosphere detector can still be effectively applied in a cloud environment; and performing quality control and radiation check on the equivalent clear sky radiation rate to generate an equivalent clear sky radiation correction product data set, so that the utilization efficiency and the application effect of the detector data entering an assimilation system are improved.
Description
Technical Field
The invention relates to the technical field of quantitative satellite remote sensing products, in particular to an equivalent clear sky radiation correction method for an infrared hyperspectral atmosphere detector based on an imager.
Background
Up to now, china has successfully launched 19 wind cloud meteorological satellites, and at present, runs 7 meteorological satellites on orbit, forms comprehensive earth observation capability which gives consideration to imaging detection and covers visible, infrared, microwave and other spectral bands, and becomes one of a few countries which have two series of service meteorological satellites of polar orbit and static state simultaneously in the world. The new generation of geostationary orbit meteorological satellite, namely the Fengyun IV satellite, realizes the update of the geostationary orbit meteorological satellite observation system in China, and the comprehensive capability partially reaches the international leading level. An interference type atmosphere vertical detector (GIIRS) carried on a Fengyun No. four satellite A star (FY-4A) is a first hyperspectral atmosphere vertical detector carried on a geostationary orbit satellite and is arranged at a long wave (700-1130 cm) -1 ) And medium wave (1650-2250 cm) -1 ) The wave band has 1650 actual measurement channels, and the spectral resolution is up to 0.625cm -1 The method can acquire the atmospheric temperature and humidity profile information with high time resolution, provides large-range, continuous, quick and accurate atmospheric remote sensing information for numerical weather forecast, and has breakthrough. Another important load carried on an FY-4A satellite, namely a multi-channel scanning imaging radiometer (AGRI), is provided with 14 channels covering visible to long-wave infrared bands, the spatial resolution of the infrared channels reaches 4 kilometers, and 5-minute regional quick scanning can be realized; the AGRI of the imager utilizes the black body on the satellite to carry out high-frequency sub-infrared calibration, ensures high precision and high stability of observation data, and can better quantitatively monitor elements such as cloud, aerosol, vegetation, accumulated snow, fire point, water body and the like.
The atmospheric detection instrument GIIRS of the geostationary satellite has the characteristics of high spectral resolution and wide spectral coverage range, has good vertical depiction capacity for the earth atmosphere, but is limited by the radiation detection capacity of the instrument, such as the signal-to-noise ratio of the instrument, so that the spatial resolution of a visual field of the atmospheric infrared vertical detection instrument is usually 10-20km, the atmospheric infrared vertical detection instrument is easily polluted by cloud, and only less than 10 percent of the visual field of the detection instrument is a completely clear visual field. Meanwhile, as the infrared radiation transmission mode (observation operator) in the cloud area has complexity and uncertainty, the influence of cloud on infrared observation needs to be eliminated in atmospheric parameter inversion and business assimilation. In a global business assimilation and forecasting system (GRAPES) of the China Meteorological Bureau, the infrared radiation data of a clear space area has a good application effect, the inversion accuracy of the atmospheric temperature and humidity profile is greatly improved, but the effective application of the infrared hyperspectral atmosphere detector data in a cloud environment is still a difficult problem to be solved urgently.
The combined monitoring and application is carried out based on the fusion matching data of different infrared loads of the same platform, and due to the characteristics of observation time and view field consistency, a large number of data samples can be provided, so that the method is more convenient and economic. Diagnosing and analyzing whether the field of view of the satellite-borne instrument is covered by cloud, and detecting the field of view of the satellite-borne instrument as cloud; the radiation correction is carried out on the visual field of the infrared hyperspectral atmosphere detector with part of clouds to eliminate the influence of cloud radiation, and the method is called cloud elimination. Susskind et al (1984, 1998, 2003) have developed, on the basis of Chahine (1974, 1977), a cloud atmospheric parameters inversion method based on the microwave detector AMSU-A and the infrared hyperspectral atmospheric detector AIRS, using microwave detection to reduce the spatial resolution of the inversion results (from a single field of view to 3 × 3 fields of view). Li et al (2005) adopt an optimal estimation method to perform cloud clearing processing on the AIRS based on 9 infrared channels of an imager MODIS, so that the accuracy of the algorithm is improved without losing the resolution of a field of view.
The GIIRS is a first hyperspectral atmospheric vertical detector carried on a geostationary orbit satellite, carries out cloud judgment on the field of view of the GIIRS based on an imager AGRI carried on an FY-4A geostationary satellite, and carries out cloud clearing on part of the field of view with clouds, thereby being beneficial to improving the utilization efficiency and application effect of GIIRS data in a service synchronization system. Only polar orbit satellites have the capability of simultaneously carrying a detector and an imager, the imager on the polar orbit satellites usually has higher spatial resolution and more channel configurations, and taking the aires and the MODIS as examples, the spatial resolution of the subsatellite point of the MODIS is 1km, and 9 infrared channels completely overlapped with an aires spectrum are arranged. Since the imager AGRI on the FY-4A geostationary satellite has only a limited infrared channel (11.0 μm,12.0 μm and 13.3 μm) overlapping the spectrum of the detector GIIRS, and the undersea point resolution of the infrared channels GIIRS and AGRI is 16km and 4km, respectively, the field of view of the GIIRS is more susceptible to the cloud. Meanwhile, field of view cloud detection and cloud clearing based on the AGRI for the GIIRS are not effective in correcting or have invalid results violating physical assumption conditions. The method for correcting the equivalent clear sky radiation of the atmospheric vertical detector GIIRS by the imager AGRI carried by the Fengyun geostationary satellite in China is urgently needed.
Therefore, those skilled in the art have been devoted to develop an equivalent clear sky radiation correction method for an infrared hyperspectral atmosphere detection instrument based on a geostationary satellite imager to solve the above-mentioned deficiencies of the prior art.
Disclosure of Invention
In view of the above defects of the prior art, the technical problem to be solved by the invention is that the imager (AGRI) and the detector GIIRS on the wind-cloud static satellite in China only have limited spectral overlap (two window regions and one ozone absorption channel) and spatial resolution, and the visual field cloud detection and cloud removal effect of the imager (AGRI) on the atmospheric vertical detector (GIIRS) is poor.
In order to achieve the purpose, the invention discloses an equivalent clear sky radiation correction method for an infrared hyperspectral atmosphere detecting instrument based on a geostationary satellite imager, which comprises the following steps:
further, the step 1 includes the following steps:
step 1-1, according to the observation time of the infrared hyperspectral atmosphere detection instrument and the load of the imager, determining an observation data file with the time difference within a threshold range, and reading information such as the observation time, the geographic position coordinate, the observation angle and the like of the visual field of the infrared hyperspectral atmosphere detection instrument and the pixel of the imager;
step 1-2, calculating the view field of the infrared hyperspectral atmosphere detection instrument and the ground projection shape of the imager pixel according to the geographical position coordinate and observation angle information read in the step 1-1, performing spatial matching, and selecting the imager pixel positioned in the view field of the infrared hyperspectral atmosphere detection instrument as a matched sample;
step 1-3, accurately matching time and observation angles of the matched samples screened in the step 1-2, and selecting the imager pixels meeting the time difference threshold value and the observation angle difference threshold value as accurately matched samples;
step 1-4, for the exact match samples in step 1-3,
i. if the data product of the detector has a default or invalid value, or the pixel proportion of the data products (including radiation data, cloud detection products and the like) of the imager matched with the detector, which are all valid values, is lower than 25%, the field of view of the detector is an invalid field of view, and flag = -1 is defined;
ii, if the data product of the detector is effective value and the pixel proportion of the data product (including radiation data, cloud detection product and the like) of the imager matched with the detector is effective value is more than 25%, the field of view of the detector is effective field of view, and flag =1 is defined;
further, in the step 2,
step 2-1, aiming at the effective visual field (flag = 1) of the detecting instrument in the step 1-4,
1) Calculating apodized radiance R of each channel of detector effective visual field υ Based on the spectral response function SRF of the ith infrared channel of the imager completely overlapping the spectral range of the detector i Performing spectrum convolution to calculate convolution radiance f of detector on ith infrared channel of imager i (R υ )，
Formula 1:
in the above-mentioned formula, the compound has the following structure,
R υ for the apodization radiance of each channel of the detector's effective field of view,
SRF i is the spectral response function of the ith infrared channel of the imager;
2) Calculating the infrared channel radiance Rad of all imager pixels matched with the view field of the detector i (ipix) calculating the spatial mean radiance of the imager on the i-th infrared channel of the imager by spatial convolution based on the spatial weighting function w (ipix) of the detector field of view
Formula 2:
in the above formula, the first and second carbon atoms are,
Rad i (ipix) is the third imager pixel matched to the detectorThe radiance of the i infrared channels,
w (ipix) is a spatial weight function of the pixel of the third ipix imager matched with the detector;
3) Calculating the weight percentage of cloud pixels in all the pixels of the imager matched with the field of view of the detector, recording as effective cloud amount Ncld,
formula 3:
in the above formula, the first and second carbon atoms are,
w (ipix) is the spatial weight function of the image element of the first ipix imager matched to the detector,
w _ clr (ipix) is cloud detection of the image element of the third ipix imager matched with the detector, and if the image element of the third ipix is absolutely clear space or possibly clear space, w _ clr (ipix) =1; otherwise w _ clr (ipix) =0;
step 2-2, classifying the field of view of the detecting instrument according to the effective cloud amount Ncld in the step 2-1,
i. if Ncld =100%, marking the visual field of the detector as a completely cloud visual field, and defining CC _ flag =0;
ii, if Ncld =0%, identifying the visual field of the detector as an absolute clear sky visual field, and defining CC _ flag =5;
if 0% < Ncld <100%, marking the view field of the detector as a part with a cloud view field, and then carrying out clear sky correction processing;
step 2-3, for the absolute clear sky view field ii and the cloud view field iii in the step 2-2, at least one clear sky pixel exists in the imager pixels matched with the detector,
calculating the average radiance of clear sky pixel of imager matched with the view field of detector
Formula 4:
in the above formula, the first and second carbon atoms are,
Rad i (ipix) is the i-th infrared channel radiance of the image element of the first ipix imager matched to the detector,
w (ipix) is the spatial weight function of the pixel of the third imager matched to the detector,
w _ clr (ipix) is cloud detection of the image element of the third ipix imager matched with the detector, and if the image element of the third ipix is absolutely clear space or possibly clear space, w _ clr (ipix) =1; otherwise w _ clr (ipix) =0;
step 2-4, regarding the iii part with the cloud field in step 2-2 as a Main Field (MFOV) corrected by clear sky, assuming that the main field and the adjacent auxiliary field of view of the detecting instrument have the same cloud and radiation characteristic conditions,
for the j (0 < -j < = 8) secondary fields of view (SFOV) around the primary field of view,
i. if the j-th secondary view field is an absolute clear sky view field (Ncld = 0%) or an invalid view field (flag = -1), if the physical assumption condition is not met, defining NGOOD (j) =0;
if the jth sub-field is cloudy or partially cloudy (Ncld > 0%), and the assumed condition that the main field and the adjacent sub-field have identical cloud and radiation characteristics is satisfied, defining NGOOD (j) =1;
step 2-5, if NGOOD (j) =1 for j (0 < -j < = 8) secondary fields in step 2-4,
1) In order to make the convolution radiance of the main view field after being corrected in clear sky close to the average radiance of the imager in clear sky, a cost function J (N) is constructed, because the main view field and the auxiliary view field of the detector have the same cloud and radiation characteristic conditions, the J (N) is only determined by the ratio N of the effective cloud radiance of the main view field and the auxiliary view field,
calculating a correction coefficient N (j) of the jth sub-field by adopting a method of minimizing a cost function,
formula 5:
in the above formula, the first and second carbon atoms are,
NEdR i the observation error of the ith infrared channel of the imager is obtained;
2) Calculating the equivalent clear sky radiance of the jth auxiliary view field
Formula 6:
in the above formula, the first and second carbon atoms are,
n (j) is the correction coefficient of the jth sub-field;
step 2-6, apodizing radiance of each channel of main and auxiliary visual fields of the detector in step 2-5
Equivalent clear sky radiance
Based on the planck function to a luminance temperature (BT) representation,
calculating the average value of the brightness and temperature of all channels, and respectively recording the average value of the brightness and temperature BT1 of the main view field, the average value of the brightness and temperature BT2 (j) of the jth auxiliary view field and the average value of the equivalent clear sky brightness and temperature BTcc (j) of the jth auxiliary view field;
step 2-7, for BT1, BT2 (j), BTcc (j) in step 2-6, since the main and sub fields have identical cloud and radiation characteristic conditions, the field with less effective cloud cover and higher average value of brightness temperature; and because the equivalent clear sky radiance is the reconstructed radiance after eliminating the influence of cloud radiance, the equivalent clear sky radiance can be regarded as a clear sky view field, compared with a main view field and an auxiliary view field, the cloud cover is less, the average value of the brightness and the temperature is higher,
setting a threshold parameter Nstar (Nstar < 1), preliminary quality control conditions,
i. if Nstar < N (j) <1/Nstar, discarding the error due to the larger N (j), defining NGOOD (j) =0;
NGOOD (j) =1 if N x (j) < Nstar, the primary field is less effective clouds than the secondary field, the primary field is warmer, i.e. BT2 (j) < BT1< BTcc (j) is satisfied; otherwise, the physical assumption condition is not met, and NGOOD (j) =0 is defined;
NGOOD (j) =1 if 1/Nstar < N (j), the primary field is more effective cloud than the secondary field, the primary field is colder, i.e. BT1< BT2 (j) < BTcc (j) is met; otherwise, the physical assumption condition is not met, defining NGOOD (j) =0;
steps 2-8, NGOOD (j) for all secondary fields in steps 2-7 (0 < -j < = 8),
i. if NGOOD (j) =1 does not exist, identifying that clear air correction fails, and defining CC _ flag =1;
if NGOOD (j) =1 (0) is present<j<= 8), the clear sky correction is successful, and an optimal main view field is further determined according to the radiation check and the quality control conditionEquivalent clear sky radiance
Further, in the step 3,
the method comprises the following steps:
step 3-1, secondary fields of view for all NGOOD (j) =1 (0 < -j < = 8) in step 2-8,
1) Calculating the equivalent clear sky radiance of the jth auxiliary view field
Clear sky pixel average radiance of imager
Radiation deviation on the ith infrared channel of the imager,
formula 7:
in the above-mentioned formula, the compound has the following structure,
2) The radiation deviation squared sum over the individual infrared channels is calculated,
formula 8:
Δ j ＝∑ i |Δ i，j | 2 ，
in the above-mentioned formula, the compound has the following structure,
Δ i，j equivalent clear sky radiance for jth sub-field
Clear sky pixel average radiance of imager
Radiation bias on the ith infrared channel of the imager;
step 3-2, deviation Δ of all radiation in step 3-1 j And Δ i，j Radiance is converted to luminance temperature (BT) based on the Planck function, denoted DBT (j) and dBT (i, j), respectively,
sorting the radiation deviation square sum DBT (j) on each infrared channel to obtain the minimum value, and recording the minimum value as DBT (jmin);
step 3-3, setting a threshold parameter delta for the radiation deviation square sum minimum DBT (jmin) and dBT (i, jmin) in the step 3-2 thold (Δ thold ＜4×∑ i NEdT i 2 ) Further, the quality control conditions are as follows:
1)QC1：DBT(jmin)<Δ thold ；
in the above formula, the first and second carbon atoms are,
DBT (jmin) is the sum of the squares of the radiation deviations on the individual infrared channels,
Δ thold is a threshold parameter and is not more than 4 times of the observation error NEdT of the infrared channel of the imager i The sum of squares of;
2)QC2：dBT(i,jmin)<2×NEdT i ；
in the above formula, the first and second carbon atoms are,
dBT (i, jmin) is the radiation deviation on the ith infrared channel of the imager;
NEdT i the observation error of the ith infrared channel of the imager is obtained;
step 3-4, controlling the quality control conditions QC1 and QC2 in the step 3-3,
equivalent clear sky radiance of jmin auxiliary view field
And a correction coefficient N (jmin) recorded as the equivalent clear sky radiance of the main view field
And a correction coefficient N x is set for each of the correction coefficients,
the main field of view of the detector is identified,
i. if QC1 and QC2 are met at the same time, it indicates that clear sky correction passes strict quality control, and CC _ flag =4 is defined;
if QC1 is met and QC2 is not met, indicating that clear sky correction passes general quality control, and defining CC _ flag =3;
if the QC1 is not met, indicating that the clear sky correction fails to pass quality control, and defining CC _ flag =2;
further, in the step 4,
the equivalent clear sky radiation correction product data set specifically comprises:
for the observation field of view of the detector, clear sky correction is carried out on part of the cloud field of view based on infrared channel radiation and cloud detection of the imager, and the equivalent clear sky radiance of each spectrum channel of the field of view of the infrared hyperspectral detector is determined
After quality control and radiation verification, an effective field mark flag, an effective cloud amount Ncld, a correction mark CC _ flag, a correction coefficient N and the like of a detection field are determined, and the utilization efficiency and the application effect of the infrared hyperspectral detector data entering an assimilation system are improved;
i. if flag = -1, the detector visual field is an invalid visual field, a default or invalid value exists in a detector data product, or the pixel proportion matched with imager data (including radiation, cloud detection and the like) which are valid values is lower than 25%;
if flag =1, the field of view of the detecting instrument is an effective field of view, the data product of the detecting instrument is effective, and the proportion of pixels matched with the data (including radiation, cloud detection and the like) of the imager, which are all effective values, exceeds 25%;
a) If CC _ flag =0, the cloud field of view is completely available;
b) If CC _ flag =1, the part has a cloud view field, and clear sky correction fails;
c) If CC _ flag =2, the part has a cloud view field, and the quality control condition is not passed in clear sky correction;
d) If CC _ flag =3, the part is indicated to have a cloud view field, and the clear sky correction successfully passes general quality control;
e) If CC _ flag =4, the cloud view field exists in part, and clear sky correction successfully passes strict quality control;
f) If CC _ flag =5, the absolute clear sky view field is indicated;
the detector has a cloud field of view (flag =1, CC_flag =3, 4) equivalent clear sky radiance
Can be directly used as clear sky radiance by a business assimilation system, so that the infrared hyperspectral atmosphere detector can still be effectively applied in a cloud environment, and the utilization efficiency and the application effect of assimilating data of the infrared hyperspectral detector are improved
By adopting the scheme, the equivalent clear sky radiation correction method for the infrared hyperspectral atmosphere detecting instrument based on the imager disclosed by the invention has the following advantages:
by adopting the equivalent clear sky radiation correction method for the infrared hyperspectral atmosphere detector based on the geostationary satellite imager, the clear sky correction is carried out on the part of the detector with a cloud view field, so that the influence of cloud radiation is removed, and the infrared hyperspectral atmosphere detector can still be effectively applied in a cloud environment; and performing quality control and radiation verification on the equivalent clear sky radiance, removing invalid results which do not conform to physical assumed conditions, determining the optimal equivalent clear sky radiance, correction marks and correction coefficients of the detector view field, and improving the utilization efficiency and application effect of the detector data entering an assimilation system.
Drawings
FIG. 1 is a flow chart of an equivalent clear sky radiation correction process for an infrared hyperspectral atmosphere detector based on an imager in an embodiment of the invention;
fig. 2 is a schematic diagram of spatial matching between a field of view of an atmospheric vertical detector (GIIRS) and an imager (AGRI) pixel mounted on an FY4A according to an embodiment of the present invention;
FIG. 3 is a graph showing the Bright Temperature (BT) of the long-wavelength spectrum of an atmospheric vertical detector (GIIRS) in which the Spectral Response Functions (SRF) of three infrared channels (11.0 μm,12.0 μm and 13.3 μm) of an imager (AGRI) mounted on an FY4A according to an embodiment of the present invention are superimposed on the visual field of a GIIRS;
wherein the content of the first and second substances,
in FIG. 2, 1-1 is the field of view of an atmospheric vertical detector GIIRS; 2-1 is the pixel of the imager AGRI;
in FIG. 3, 1 is the Spectral Response Function (SRF) of the three infrared channels (11.0 μm,12.0 μm and 13.3 μm) of the AGRI; 2, the brightness temperature of a long wave spectrum of the field of view of the atmosphere vertical detector GIIRS before clear sky correction; and 3, the brightness temperature of the long-wave spectrum of the field of view of the atmosphere vertical detector GIIRS after being corrected in clear sky.
The conception, the specific technical solutions and the technical effects produced by the present invention will be further described with reference to the following detailed description so as to fully understand the objects, the features and the effects of the present invention.
Detailed Description
The following describes preferred embodiments of the present invention to make the technical contents thereof clearer and easier to understand. The invention may be embodied in many different forms of embodiments, which are intended to be illustrative only, and the scope of the invention is not intended to be limited to the embodiments shown herein.
Taking an imaging apparatus AGRI carried on a wind and cloud satellite a star (FY-4A) to perform clear sky radiation correction on a field of view of an interference type atmosphere vertical detector (GIIRS) as an example, a specific implementation is described;
as shown in fig. 1, fig. 1 is a flowchart of an equivalent clear sky radiation correction process of an infrared hyperspectral atmosphere detector based on an imager in an embodiment of the present invention, and the following is a detailed description:
(1) Calculating L1 data of a visual field of an infrared hyperspectral atmosphere detector and file name information of L1 and L2 CLM data of an imager, determining an observation data file with consistent observation starting time and observation time difference within 15 minutes, reading longitude and latitude and observation angle information of a geographic position of the visual field of the detector, reading a coordinate of the geographic position of the imager and converting the coordinate into the longitude and latitude information;
(2) And (2) calculating the spherical distances between all the imager pixels in the step (1) and the center position of the view field of any infrared hyperspectral atmosphere detector, and then sequencing to obtain the coordinates (ix, iy) of the imager pixel closest to the infrared hyperspectral atmosphere detector. As shown in fig. 2, the observation field of view of the detector GIIRS carried by FY-4A is rectangular, and 5 gamma 5 imager pixels around are selected with coordinates (ix, iy) as the center, and used as a matching sample of the imager pixels matched in the infrared hyperspectral atmospheric detector field of view;
(3) Calculating matching samples of all AGRI pixels matched with the field of view of the detecting instrument GIIRS in the step (2), and selecting the imager pixels meeting the threshold values of time difference and observation angle difference as accurate matching samples;
(4) For each GIIRS field of view, it is determined whether it is an effective field of view,
i. if the L1 data of the GIIRS has a default or invalid value, or the ratio of the matched AGRI effective pixels (AGRI L1 and L2 CLM are both effective values and have no default value) is lower than 25%, the field is an invalid field, and flag = -1 is defined;
if the L1 data of the GIIRS are both effective values and the ratio matched with the AGRI effective pixel (AGRI L1 and L2 CLM are both effective values and have no default value) exceeds 25%, defining flag =1 for effective visual field;
(5) Calculating effective fields (flag = 1) of all the GIIRS in the step (4), performing Hamming apodization transformation (namely three-point moving average filtering, the Hamming coefficient is 0.23,0.54 and 0.23) on the radiance of each spectral channel of the GIIRS, and calculating the convolution radiance f of the hyperspectral channel of the detector according to the formula 1 i (R υ ) (ii) a g, calculating the space average radiance of the imager pixel matched with the field of view of the detector according to the formula 2-3
And an effective cloud amount, ncld;
(6) The GIIRS effective field of view is classified according to the effective cloud number Ncld,
i. if Ncld =100%, the GIIRS field is completely cloudy, defining CC _ flag =0;
if Ncld =0%, the GIIRS visual field is absolutely clear sky, and CC _ flag =5 is defined;
if 0% < Ncld <100%, the GIIRS field of view is partly cloudy, and further performing clear sky correction processing;
(7) Calculating the absolute clear sky and the cloud view field of part of the GIIRS in the step (6), and calculating the average radiance of the clear sky image element of the imager matched with the view field of the detector according to the formula 4
(8) Calculating iii of the GIIRS in the step (6), wherein the part of the GIIRS has a cloud view field as a main view field, performing clear sky correction processing based on j (0-to-j < = 8) th auxiliary view fields adjacent to the main view field,
i. if j (0 < -j < = 8) th secondary view field is absolute clear sky (Ncld = 0%) or invalid view field (flag = -1), defining NGOOD (j) =0;
if j (0)<j<= 8) sub-fields of view are cloudy fields of view (Ncld)>0%), calculating the correction coefficient N (j) of the jth sub-field according to the formula 5 and the formula 6, and calculating the equivalent clear sky radiance of the jth sub-field
Defining NGOOD (j) =1;
(9) Apodizing radiance of main visual field and jth auxiliary visual field of detector in step (8)
And equivalent clear sky radiance
Converting into luminance temperature (BT) representation based on Planck's function, calculating average value of all channel luminance temperatures, and recording as BT1, BT2 (j), and BTcc (j);
(10) A threshold parameter Nstar (Nstar < 1), preliminary quality control conditions,
i. if Nstar < N (j) <1/Nstar, discarding the error due to the larger N (j), defining NGOOD (j) =0;
ii, if N × (j) < Nstar, BT2 (j) < BT1< BTcc (j) is to be satisfied, NGOOD (j) =1;
otherwise, the physical assumption condition is not met, and NGOOD (j) =0 is defined;
if 1/Nstar < N × j, BT1< BT2 (j) < BTcc (j) is to be satisfied, NGOOD (j) =1;
otherwise, the physical assumption condition is not met, and NGOOD (j) =0 is defined;
(11) Calculating the main field of view of the GIIRS of step (6), based on all adjacent sub-fields of view,
i. if NGOOD (j) =1 does not exist, identifying that clear air correction fails, and defining CC _ flag =1;
if NGOOD (j) =1 (0) is present<j<= 8), the clear sky correction is identified, and the optimal main view field equivalent clear sky radiance is further determined according to the radiation check and quality control conditions
(12) For all NGOOD (j) =1 (0) in step (11)<j<= 8), calculating a cross radiation deviation Δ of the equivalent clear sky radiance from the clear sky mean radiance of the imager according to equations 7 and 8 j And Δ i，j And converting the radiance into a luminance temperature (BT) based on a Planck function, and recording the luminance temperature (BT) as DBT (j) and dBT (i, j);
(13) Sequencing the radiation deviation square sum DBT (j) on each channel in the step (12) to obtain the minimum value, wherein the sequence number is jmin and is recorded as DBT (jmin) and dBT (i, jmin);
setting a threshold parameter Δ thold Further, the quality control conditions are as follows:
QC1：DBT(jmin)<Δ thold (Δ thold not more than 4 times of observation error NEdT i Sum of squares);
QC2：dBT(i,jmin)<2×NEdT i ；
(14) For QC1 and QC2 in the step (13), the jmin equivalent clear air radiance is calculated
And a correction coefficient N (jmin) which is recorded as the equivalent clear sky radiance of the main view field
And correction coefficientN*，
The main field of view of the detector is identified,
i. if QC1 and QC2 are met at the same time, it indicates that clear sky correction passes strict quality control, and CC _ flag =4 is defined;
if QC1 and QC2 are met, indicating that clear sky booking passes general quality control, and defining CC _ flag =3;
if the QC1 is not met, indicating that the clear air correction fails to pass quality control, and defining CC _ flag =2;
(15) The equivalent clear sky radiation correction product data set for the GIIRS based on the AGRI specifically comprises:
for the observation field of view of the detector GIIRS, clear sky correction processing is carried out on part of cloud field of view based on infrared channel radiation and cloud detection of the imager, the equivalent clear sky radiance of each spectrum channel of the field of view of the infrared hyperspectral detector is determined, after quality control and radiation verification, an effective field of view mark flag, an effective cloud amount Ncld, a correction mark CC _ flag, a correction coefficient N and the like of the detection field of view are determined, and the available efficiency and the application effect of the infrared hyperspectral detector data entering an assimilation system are improved;
i. if flag = -1, the detector visual field is an invalid visual field, a default or invalid value exists in a detector data product, or the pixel proportion matched with imager data (including radiation, cloud detection and the like) which are valid values is lower than 25%;
if flag =1, the field of view of the detector is an effective field of view, the data products of the detector are all effective values, and the pixel occupancy matched with the data (including radiation, cloud detection and the like) of the imager, which are all effective values, exceeds 25%;
a) If CC _ flag =0, it means that there is a complete cloud field of view;
b) If CC _ flag =1, the part is indicated to have a cloud view field, and clear sky correction fails;
c) If CC _ flag =2, the cloud view field exists in part, and the clear sky is not passed the quality control condition;
d) If CC _ flag =3, the part is indicated to have a cloud view field, and the clear sky correction successfully passes general quality control;
e) If CC _ flag =4, the part is indicated to have a cloud view field, and the clear sky correction successfully passes strict quality control;
f) If CC _ flag =5, the field of view is absolutely clear sky;
after the cloud field of view of the part of the detector GIIRS is corrected in clear sky (flag =1, CC_flag =3, 4), the equivalent clear sky radiance is adopted to replace the observed radiance in L1, and the part of the detector GIIRS can be directly assimilated and utilized as the clear sky radiance in a service assimilation system, so that the infrared hyperspectral atmospheric detector can still be effectively applied in a cloud environment, and the utilization efficiency and the application effect of assimilating the data of the infrared hyperspectral detector are greatly improved.
With the above operations based on the clear sky correction of the atmospheric vertical detector GIIRS by the imager AGRI, as shown in fig. 3, the Spectral Response Functions (SRF) of the three infrared channels (11.0 μm,12.0 μm and 13.3 μm) of the imager (AGRI) are superimposed on a Bright Temperature (BT) diagram of the long wave spectrum of the atmospheric vertical detector (GIIRS) in the field of view before and after the clear sky correction; in fig. 3, 1 is the Spectral Response Function (SRF) of the three infrared channels of AGRI; 2 and 3 are bright temperature profiles of the long-wave spectrum of the visual field of the atmosphere vertical detector GIIRS before (a solid line 2) and after (a dotted line 3) clear sky correction;
as can be seen from fig. 3, the bright temperature (dotted line 3) of the GIIRS long-wave band after clear sky correction is higher than the bright temperature (solid line 2) before clear sky correction, and is closer to the average radiance of the clear sky pixel of the imager matched with the field of view of the detecting instrument, which indicates that, in practical application, the clear sky correction based on the imager AGRI on the field of view of the detecting instrument GIIRS effectively eliminates the influence of cloud radiation, so that the equivalent clear sky radiance of the GIIRS can be used as clear sky radiation, and the application effect of the infrared radiance of the detecting instrument is improved.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (5)
1. An equivalent clear sky radiation correction method for an infrared hyperspectral atmosphere detector based on a geostationary satellite imager is characterized by comprising the following steps:
step 1, establishing a cross matching model of a stationary satellite imager and an infrared hyperspectral atmosphere detector;
step 2, performing clear sky correction processing on a cloud view field of the detector part by using infrared channel radiation and cloud detection of the static satellite imager; in particular to the equivalent clear sky radiance of each spectrum channel of the visual field of the infrared hyperspectral detector
Determining;
step 3, the equivalent clear sky radiance of the step 2
Performing quality control and radiation verification; in particular to the equivalent clear sky radiance meeting the quality control condition
Determining a correction mark CC _ flag and a correction coefficient N;
and 4, generating an equivalent clear sky radiation correction product data set.
2. The method of claim 1, wherein in step 1,
the method comprises the following steps:
step 1-1, according to the observation time of the infrared hyperspectral atmosphere detection instrument and the load of the imager, determining an observation data file with the time difference within a threshold range, and reading information such as the observation time, the geographic position coordinate, the observation angle and the like of the visual field of the infrared hyperspectral atmosphere detection instrument and the pixel of the imager;
step 1-2, calculating the view field of the infrared hyperspectral atmosphere detection instrument and the ground projection shape of the imager pixel according to the geographical position coordinate and observation angle information read in the step 1-1, performing spatial matching, and selecting the imager pixel positioned in the view field of the infrared hyperspectral atmosphere detection instrument as a matched sample;
step 1-3, accurately matching time and observation angles of the matched samples screened in the step 1-2, and selecting the imager pixels meeting the time difference threshold value and the observation angle difference threshold value as accurately matched samples;
step 1-4, for the exact matching samples in step 1-3,
i. if the data product of the detector has a default or invalid value, or the pixel proportion of the data products (including radiation data, cloud detection products and the like) of the imager matched with the detector, which are all valid values, is lower than 25%, the field of view of the detector is an invalid field of view, and flag = -1 is defined;
and ii, if the data products of the detecting instrument are all effective values, and the proportion of pixels of the data products (including radiation data, cloud detection products and the like) of the imager matched with the detecting instrument is more than 25%, the field of view of the detecting instrument is an effective field of view, and flag =1 is defined.
3. The method of claim 1, wherein said step 2,
the method comprises the following steps:
step 2-1, aiming at the effective visual field (flag = 1) of the detecting instrument in the step 1-4,
1) Calculating apodized radiance R of each channel of detector effective visual field υ Based on the spectral response function SRF of the ith infrared channel of the imager completely overlapping the spectral range of the detector i Performing a spectral convolution to calculate the convolution radiance f of the detector on the ith infrared channel of the imager i (R υ )，
Formula 1:
in the above formula, the first and second carbon atoms are,
R υ the apodized radiance for each channel of the detector's effective field of view,
SRF i is the spectral response function of the ith infrared channel of the imager;
2) Calculating the infrared channel radiance Rad of all imager pixels matched with the view field of the detector i (ipix) calculating the spatial mean radiance of the imager on the i-th infrared channel of the imager by spatial convolution based on the spatial weighting function w (ipix) of the detector field of view
Formula 2:
in the above formula, the first and second carbon atoms are,
Rad i (ipix) is the i-th infrared channel radiance of the image element of the first ipix imager matched to the detector,
w (ipix) is a spatial weight function of the pixel of the first ipix imager matched with the detector;
3) Calculating the weight percentage of cloud pixels in all the pixels of the imager matched with the field of view of the detector, recording as effective cloud amount Ncld,
formula 3:
in the above formula, the first and second carbon atoms are,
w (ipix) is the spatial weight function of the pixel of the third imager matched to the detector,
w _ clr (ipix) is cloud detection of the image element of the third ipix imager matched with the detector, and if the image element of the third ipix is absolutely clear space or possibly clear space, w _ clr (ipix) =1; otherwise w _ clr (ipix) =0;
step 2-2, classifying the field of view of the detecting instrument according to the effective cloud amount Ncld in the step 2-1,
i. if Ncld =100%, marking the visual field of the detector as a completely cloud visual field, and defining CC _ flag =0;
if Ncld =0%, identifying the field of view of the detector as an absolute clear sky field, and defining CC _ flag =5;
if 0% < Ncld <100%, marking the view field of the detector as a part with a cloud view field, and then carrying out clear sky correction processing;
step 2-3, for the absolute clear sky view field ii and the cloud view field iii in the step 2-2, at least one clear sky pixel exists in the imager pixels matched with the detector,
calculating the average radiance of clear sky pixel of imager matched with the view field of detector
Formula 4:
in the above-mentioned formula, the compound has the following structure,
Rad i (ipix) is the i-th infrared channel radiance of the image element of the first ipix imager matched to the detector,
w (ipix) is the spatial weight function of the image element of the first ipix imager matched to the detector,
w _ clr (ipix) is cloud detection of an ipix imaging instrument pixel matched with the detecting instrument, and if the ipix pixel is in absolute clear sky or possibly clear sky, w _ clr (ipix) =1; otherwise w _ clr (ipix) =0;
step 2-4, regarding the part of the field of view with clouds in step 2-2 as a main field of view (MFOV) corrected in clear sky, assuming that the main field of view and the adjacent auxiliary field of view of the detector have identical conditions of cloud and radiation characteristics,
for the j (0-and-j < = 8) number of sub-fields (SFOV) around the main field,
i. if the j-th secondary view field is an absolute clear empty view field (Ncld = 0%) or an invalid view field (flag = -1), if the physical assumption condition is not met, defining NGOOD (j) =0;
if the jth sub-field is cloudy or partially cloudy (Ncld > 0%), and the assumed condition that the main field and the adjacent sub-field have identical cloud and radiation characteristics is satisfied, defining NGOOD (j) =1;
step 2-5, for j (0 and less than or equal to j < = 8) sub-fields in step 2-4, if NGOOD (j) =1,
1) In order to make the convolution radiance of the main view field after being corrected in clear sky close to the average radiance of the imager in clear sky, a cost function J (N) is constructed, because the main view field and the auxiliary view field of the detector have the same cloud and radiation characteristic conditions, the J (N) is only determined by the ratio N of the effective cloud radiance of the main view field and the auxiliary view field,
calculating a correction coefficient N (j) of the jth sub-field by adopting a method of minimizing a cost function,
formula 5:
in the above-mentioned formula, the compound has the following structure,
NEdR i the observation error of the ith infrared channel of the imager;
2) Calculating the equivalent clear sky radiance of the jth auxiliary view field
Formula 6:
in the above formula, the first and second carbon atoms are,
n (j) is the correction coefficient of the jth sub-field;
step 2-6, apodizing radiance of each channel of main view field and auxiliary view field of detector in step 2-5
And equivalent clear sky radiance
Based on the planck function to a luminance temperature (BT) representation,
calculating the average value of the brightness and temperature of all channels, and respectively recording the average value of the brightness and temperature BT1 of the main view field, the average value of the brightness and temperature BT2 (j) of the jth auxiliary view field and the average value of the equivalent clear sky brightness and temperature BTcc (j) of the jth auxiliary view field;
step 2-7, for BT1, BT2 (j), BTcc (j) in step 2-6, because the main and auxiliary fields have identical cloud and radiation characteristic conditions, the field with less effective cloud amount has higher average value of brightness temperature; and because the equivalent clear sky radiance is the reconstructed radiance after eliminating the influence of cloud radiance, the equivalent clear sky radiance can be regarded as a clear sky view field, compared with a main view field and an auxiliary view field, the cloud cover is less, the average value of the brightness and the temperature is higher,
setting a threshold parameter Nstar (Nstar < 1), preliminary quality control conditions,
i. if Nstar < N (j) <1/Nstar, discarding the error due to the larger N (j), defining NGOOD (j) =0;
NGOOD (j) =1 if N x (j) < Nstar, the primary field is less effective clouds than the secondary field, the primary field is warmer, i.e. BT2 (j) < BT1< BTcc (j) is satisfied; otherwise, the physical assumption condition is not met, defining NGOOD (j) =0;
NGOOD (j) =1 if 1/Nstar < N (j), the primary field is more effective cloud than the secondary field, the primary field is colder, i.e. BT1< BT2 (j) < BTcc (j) is met; otherwise, the physical assumption condition is not met, defining NGOOD (j) =0;
step 2-8, NGOOD (j) for all sub-fields in step 2-7 (0-j < = 8),
i. if NGOOD (j) =1 does not exist, identifying that clear air correction fails, and defining CC _ flag =1;
ii if NGOOD (j) =1 (0) is present<j<= 8), the clear sky correction is identified, and the optimal main view field equivalent clear sky radiance is further determined according to the radiation check and quality control conditions
4. The method of claim 1, wherein said step 3,
the method comprises the following steps:
step 3-1, for all the sub-fields of NGOOD (j) =1 (0-j < = 8) in step 2-8,
1) Calculating the equivalent clear sky radiance of the jth auxiliary view field
Clear sky pixel average radiance of imager
Radiation deviation on the ith infrared channel of the imager,
formula 7:
in the above formula, the first and second carbon atoms are,
2) The sum of the squares of the radiation deviations over the individual infrared channels is calculated,
formula 8:
Δ j ＝∑ i |Δ i，j | 2 ，
in the above formula, the first and second carbon atoms are,
Δ i，j equivalent clear sky radiance for jth sub-field
Clear sky pixel average radiance of imager
Radiation bias on the ith infrared channel of the imager;
step 3-2, deviation Δ of all radiation in step 3-1 j And Δ i，j Radiance is converted to luminance temperature (BT) based on the Planck function, denoted DBT (j) and dBT (i, j), respectively,
sorting the radiation deviation square sum DBT (j) on each infrared channel to obtain the minimum value, and recording the minimum value as DBT (jmin);
step 3-3, for the radiation deviation sum of squares minimum value DBT (jmin) in step 3-2, and dBT (i, jmin),
setting a threshold parameter Δ thold (Δ thold ＜4×∑ i NEdT i 2 ) Go forward and go forwardOne-step quality control conditions:
1)QC1：DBT(jmin)<Δ thold ；
in the above-mentioned formula, the compound has the following structure,
DBT (jmin) is the sum of the squares of the radiation deviations on the individual infrared channels,
Δ thold is a threshold parameter and is not more than 4 times of the infrared channel observation error NEdT of the imager i The sum of the squares of;
2)QC2：dBT(i,jmin)<2×HEdT i ；
in the above-mentioned formula, the compound has the following structure,
dBT (i, jmin) is the radiation deviation on the ith infrared channel of the imager;
NEdT i the observation error of the ith infrared channel of the imager is obtained;
step 3-4, controlling the quality control conditions QC1 and QC2 in the step 3-3,
equivalent clear sky radiance of jmin auxiliary view field
And a correction coefficient N (jmin) recorded as the equivalent clear sky radiance of the main view field
And a correction coefficient N, and a correction coefficient,
the main field of view of the detector is identified,
i. if QC1 and QC2 are met at the same time, it indicates that clear sky correction passes strict quality control, and CC _ flag =4 is defined;
if QC1 and QC2 are met, indicating that clear sky booking passes general quality control, and defining CC _ flag =3;
and iii, if the QC1 is not met, indicating that the clear sky booking fails quality control, and defining CC _ flag =2.
5. The method of claim 1, wherein said step 4,
the equivalent clear sky radiation correction product data set specifically comprises:
imager-based infrared channel for the observation field of view of a detectorThe radiation and cloud detection processes clear sky correction to part of the cloud field of view, and determines the equivalent clear sky radiance of each spectrum channel of the infrared hyperspectral detector field of view
After quality control and radiation verification, an effective field identification flag, an effective cloud amount Ncld, a correction identification CC _ flag, a correction coefficient N and the like of a detection field are determined, and the utilization efficiency and the application effect of the infrared hyperspectral detector data entering an assimilation system are improved;
i. if flag = -1, the detector visual field is an invalid visual field, a default or invalid value exists in a detector data product, or the pixel proportion matched with imager data (including radiation, cloud detection and the like) which are valid values is lower than 25%;
if flag =1, the field of view of the detector is an effective field of view, the data products of the detector are all effective values, and the pixel occupancy matched with the data (including radiation, cloud detection and the like) of the imager, which are all effective values, exceeds 25%;
a) If CC _ flag =0, the cloud field of view is completely available;
b) If CC _ flag =1, the part is indicated to have a cloud view field, and clear sky correction fails;
c) If CC _ flag =2, the part has a cloud view field, and the quality control condition is not passed in clear sky correction;
d) If CC _ flag =3, the part is indicated to have a cloud view field, and the clear sky correction successfully passes general quality control;
e) If CC _ flag =4, the cloud view field exists in part, and clear sky correction successfully passes strict quality control;
f) If CC _ flag =5, the field of view is absolutely clear sky;
the detector has a cloud field of view (flag =1, CC_flag =3, 4) equivalent clear sky radiance
Can be directly used as clear sky radiance by a business assimilation system, so that the infrared hyperspectral atmosphere detector can still be effectively applied in a cloud environment, and the data of the infrared hyperspectral detector is improvedThe utilization efficiency and application effect of the assimilation are improved.
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