Atmospheric aerosol inversion based on statistical and otsu segmentation

A method for retrieving atmospheric aerosol based on statistical segmentation, the method comprising:

• (S1) acquiring a multi-band high-resolution remote sensing image of an analyzed area using satellites, and performing radiometric calibration to obtain a multi-band remote sensing image comprising an apparent reflectance, wherein the multi-band remote sensing image comprises a mid-infrared 1.6 micrometer band and a mid-infrared 2.1 micrometer band, and selecting a blue/costal band from the multi-band remote sensing image as an retrieval band;
• (S2) inputting the multi-band remote sensing image into an atmospheric radiative transfer model, obtaining a corresponding aerosol optical thickness look-up table according to the retrieval band, wherein the look-up table comprises parameters corresponding to each aerosol optical thickness value AOT for calculating the apparent reflectance;
• (S3) for all pixels in the multi-band remote sensing image, performing categorization using a statistical segmentation method, wherein the segmentation method comprises the steps of:
• (S3.1) partitioning an apparent reflectance range of the mid-infrared 2.1 micrometer band into N segments φn, n=1, 2, . . . , N, according to a predetermined interval λ1;
• (S3.2) based on apparent reflectances of respective pixels in the multi-band remote sensing image in the mid-infrared 2.1 micrometer band, allocating the respective pixels into corresponding segments, to obtain pixel sets xn corresponding to respective segments φn;
• (S3.3) for each pixel set xn obtained in step S3.2, in condition that a number of pixels in the pixel set xn |xn|≥T1, T1 being a predetermined threshold value, retaining the pixel set, otherwise deleting the pixel set;
• marking retained pixel sets as xn′, n=1, 2, . . . , N′, N′ being a number of retained pixel sets;
• (S3.4) partitioning an apparent reflectance range of the mid-infrared 1.6 micrometer band into M segments γm, m=1, 2, . . . , M, according to a predetermined interval λ2;
• (S3.5) based on apparent reflectances of pixels in each pixel set xn′
• γn′,m γm in the pixel sets;
• (3.6) in condition that a number of pixels in the pixel set yn′,m |yn′,m|≥T2, T2 being a predetermined threshold value, retaining the pixel set yn′,m, otherwise deleting it;
• marking retained pixel sets as yk, k=1, 2, . . . , K, K being a number of the retained pixel sets;
• (S3.7) when an apparent reflectance of a pixel in the pixel set yk in the blue/coast band ρy,k,i<T, i=1, 2, . . . , |yk|, |yk| being the number of pixels in the set yk, T being an OTSU threshold of the apparent reflectance of the pixel set yk in the blue/coast band, allocating the pixel into a target set Ys, otherwise allocating the pixel to an error categorization set Yt;
• (S4) for the target set Ys, acquiring the aerosol optical thickness value AOT of each pixel through the steps of:
• (S4.1) marking a p-th pixel set in the set Ys as ys,p, p=1, 2, . . . , |Ys|, |Ys| being a number of pixel sets in the set Ys, for each pixel set ys,p, acquiring a pixel ys,p,min with the minimum apparent reflectance in the blue/coast band, the pixel ys,p,min being a clean pixel;
• (S4.2) setting an aerosol optical thickness value AOT of the clean pixel as ε, ε being a preset minimum value, retrieving a ground surface reflectivity of the clean pixel ys,p,min from the aerosol optical thickness look-up table generated in step S2;
• setting ground surface reflectivities of all pixels in the pixel set ys,p as being equal to the ground surface reflectivity of the clean pixel ys,p,min;
• (S4.3) retrieving aerosol optical thickness values AOTs of all pixels in the target set Ys;
• (S5) performing retrieval on the error categorization set Yt through the steps of:
• (S5.1) traversing all pixels in the set Ys, to search for pixels with no values within a predetermined radius, designating an aerosol thickness value of a pixel with no value as the aerosol thickness value of the pixel, and marking a set comprising all designated pixels as Ps;
• (S5.2) for each pixel in the set Ps, obtaining parameters corresponding to the designated aerosol optical thickness value from the aerosol optical thickness look-up table, and then calculating and obtaining a ground surface reflectivity of the pixel according to the apparent reflectance;
• (S5.3) gridding the multi-band remote sensing image according to a predetermined side length;
• (S5.4) marking a q-th pixel set in the set Yt as yt,q, q=1, 2, . . . , |Yt|, |Yt| being a number of the pixel sets in the set Yt;
• for each pixel set yt,q, finding an intersection with Ps from each grid partitioned in step S5.3, and setting the ground surface reflectivity of all pixels of the pixel set yt,q in a current grid as being equal to an average ground surface reflectivity value of all pixels in the intersection;
• (S5.5) performing aerosol thickness value retrieval on each pixel assigned with the ground surface reflectivity in the step S5.4, to obtain the aerosol thickness value of the pixel.