CN114332589B - A precise detection method for water or hydroxyl on the surface of non-atmospheric celestial bodies - Google Patents

Abstract

The present invention proposes a precise detection method for water or hydroxyl on the surface of an atmospheric celestial body, including: traversing the hyperspectral image, shielding the pixel spectrum with weak signal, excessive noise or containing abnormal reflectivity, and obtaining the noise shielding area map; calculating the original spectral image The band depth of each pixel spectrum in the unshielded area at the 3 μm band. If the band depth is greater than the set threshold, the corresponding pixel position is marked as containing water/hydroxyl, and the water/hydroxyl distribution area of the original spectrum is obtained; use histogram equalization Methods Smooth each channel of the original hyperspectral image separately, and use the above method to process the smoothed hyperspectral image to obtain the water/hydroxyl distribution area of the smoothed spectrum; the water/hydroxyl distribution area of the original spectrum and the smoothed spectrum The intersection of the water/hydroxyl distribution area of is used as the final accurate water/hydroxyl distribution area. The present invention adopts a coarse-to-fine strategy, and can stably obtain accurate water/hydroxyl detection results.

Description

A precise detection method for water or hydroxyl on the surface of non-atmospheric celestial bodies

technical field

The invention belongs to the field of planetary science and technology, and in particular relates to a precise detection method for water or hydroxyl on the surface of an atmospheric celestial body.

Background technique

Water ice in non-atmospheric bodies such as the moon and asteroids has recorded important information about solar wind injection, impact transfer of volatiles, and incorporation and retention of volatiles during solar nebula accretion and evolution. One of the core considerations in planetary resource mining. At present, many international missions are planning to detect the south pole of the moon and asteroids. Based on data such as visible-infrared spectra, researchers have conducted research on the distribution, timing changes and sources of water ice on the moon, asteroids and other non-atmospheric celestial bodies, and obtained a large number of research results. results.

Pieters et al. used the ^M3 spectral data to study the global distribution of water/hydroxyl on the lunar surface for the first time, and found that there is a latitude effect on the water/hydroxyl on the lunar surface. Li et al. constructed a global quantitative map of water/hydroxyl on the lunar surface based on a new thermal correction model, and found that the content of water/hydroxyl on the lunar surface not only increases with latitude, but also increases with the degree of space weathering. change between. Klima et al. found water/hydroxyl in the central peak of the Bullialdus impact crater through M ³ spectral data, and believed that it might come from the lunar magma ocean. Milliken et al. found water/hydroxyl also present in lunar pyroclastic deposits by employing a new temperature-corrected model of the ^M3 spectrum. Kramer et al. identified lunar vortices using the water/hydroxyl absorption signature of ^M3 spectral data. Based on the ^M3 spectral data, Wang et al. studied the changes of water/hydroxyl on the surface of the moon inside and outside the earth's magnetic field, and then inferred the existence of the earth's wind. In addition, Simon et al. used the visible-infrared spectrometer to map the global distribution of Bennu asteroid hydrated minerals.

Due to the poor lighting conditions, there are generally serious noises in the spectral data of the south pole region of the moon. However, existing studies rarely fully consider various noises in the original spectral image data when detecting lunar water/hydroxyl groups, resulting in uncertainties caused by noise in the detection results. Therefore, it is urgent to propose a coarse-to-fine detection method to further improve the detection accuracy of water/hydroxyl on the surface of the lunar south pole region and other similar non-atmospheric celestial bodies.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a precise detection method for water or hydroxyl on the surface of an atmospheric celestial body, and the adopted technical scheme is as follows:

A method for precise detection of water or hydroxyl on the surface of an atmospheric celestial body, comprising the following steps:

Step 1: traverse each pixel of the hyperspectral image, shield the pixel spectrum with weak signal, excessive noise or abnormal reflectance, and obtain the noise masked area map of the original spectral map;

Step 2: traverse each pixel in the unshielded area of the original hyperspectral image, and calculate the band depth of each pixel spectrum at the 3 μm band. If the band depth is greater than the set threshold, mark the corresponding pixel position as containing water/hydroxyl, thereby obtaining the original spectrum The water/hydroxyl distribution area of the graph;

Step 3: Use the histogram equalization method to smooth each channel of the original hyperspectral image, and sequentially use the methods of steps 1 and 2 to process the spectra of each pixel of the smoothed spectral image to obtain the water/hydroxyl distribution of the smoothed spectral image area;

Step 4: The intersection area of the water/hydroxyl distribution area of the original spectrogram and the water/hydroxyl distribution area of the smoothed spectrogram is used as the final accurate water/hydroxyl distribution area.

Further, said step 1 includes the following steps:

S1.1. Traversing the pixels of the original hyperspectral image, if the reflectance of any band contained in the spectrum of a certain pixel is less than 0 or greater than 1, then mask the pixel to obtain the spectral image img1 with the shielding mark;

S1.2. Traversing the unshielded pixels in the spectrogram img1, calculating the average reflectance of each band after removing the maximum reflectance and minimum reflectance of each pixel spectrum, if the average reflectance is less than the set threshold, the corresponding pixel is shielded , to get the spectral image img2 with masked markers;

S1.3. Traverse the unshielded pixels in the spectral image img2, calculate the difference between the reflectance of each pixel spectrum in each band in the 2.5-3 μm wavelength range and the average reflectance e of the front and rear bands, and further calculate the difference and reflectance The ratio r of the rate mean value e; if the ratio r calculated by any band in the 2.5-3 μm wavelength range is greater than the set threshold, the pixel is shielded to obtain a spectral image img3 with shielding marks;

S1.4. Traversing the unshielded pixels in the spectral image img3, using the cubic spline fitting method to smooth the spectrum of each pixel, and calculating the corresponding spectral signal-to-noise ratio index, if the signal-to-noise ratio index is greater than the set threshold, then the The corresponding pixels are masked to obtain a noise masked area map.

Further, the band depth of the pixel spectrum at the 3 μm band in step 2 is expressed as:

BD=1-R _b /R _c ,

Among them, BD represents the depth of the band, R _b represents the average reflectance of the pixel spectrum at the 2.9 μm band, and R _c represents the average reflectance of the pixel spectrum at the 2.6 μm band.

Further, the calculation formula of the spectral signal-to-noise ratio index is:

Among them, SNRI represents the signal-to-noise ratio index, N is the total number of bands in the spectral image, r _i and r' _i represent the original reflectance and smoothed reflectance of the pixel spectrum in the i-th band, respectively.

Further, the set threshold of the band depth in step 2 is 0.02, the set threshold of the reflectance mean value in S1.2 is 0.05, the set threshold of the ratio r in S1.3 is 0.1, and the signal-to-noise ratio index in S1.4 The set threshold is 0.07.

Compared with existing methods, the present invention has the following beneficial effects:

(1) The coarse-to-fine strategy is adopted to obtain accurate water/hydroxyl detection results robustly.

(2) Considering the interference of band noise in the original image on the water/hydroxyl absorption characteristics in the wavelength region near 3 μm, a large number of suspicious water/hydroxyl pixel spectra in strip distribution are shielded, which improves the reliability of the detection results.

Description of drawings

Fig. 1 is a schematic flow sheet of the inventive method;

Figure 2 is the original hyperspectral image;

Fig. 3 is the noise masking area diagram of original spectrum image;

Fig. 4 is the water/hydroxyl distribution area diagram of original spectrogram;

Fig. 5 is the hyperspectral image after smoothing;

Fig. 6 is the water/hydroxyl distribution region figure of smooth spectrogram;

Figure 7 is a plot of the final water/hydroxyl distribution area.

Detailed ways

The present invention is described in further detail now in conjunction with accompanying drawing.

The present invention provides a kind of precise detection method of water or hydroxyl on the surface of atmospheric celestial body, as shown in Figure 1, mainly comprises the following steps:

Step 1. In order to ensure the robustness of the detection of water/hydroxyl absorption features, the original hyperspectral image is shielded from weak signals, excessive overall noise, and pixel spectra containing abnormal reflectivity. The original hyperspectral image is shown in Figure 2. Specifically include:

Step 1.1, shield the pixel spectrum containing any band reflectance less than 0 or greater than 1, the normal value range of the band reflectance in the hyperspectral image is [0,1], and abnormal values will appear due to noise interference;

Step 1.2, respectively calculate the mean value of the reflectance of each band after removing the maximum reflectance and the minimum reflectance of each pixel spectrum, if the mean value of the band reflectance is less than 0.05, then shield the corresponding pixel spectrum;

Step 1.3, traverse the unshielded pixels in the spectral image img2, calculate the difference between the reflectance of each pixel spectrum in each band in the 2.5-3 μm wavelength range and the average reflectance e of the preceding and following bands, and further calculate the difference and the reflectance The ratio r of the mean e. If the ratio r calculated by any band is greater than 0.1 in the 2.5-3 μm wavelength range, the pixel is blocked;

Step 1.4, use the cubic spline fitting method to smooth each pixel spectrum, and calculate the signal-to-noise ratio index (SNRI) of each pixel spectrum after smoothing, if the signal-to-noise ratio index is greater than 0.07, the corresponding pixel spectrum is masked. The formula for calculating the signal-to-noise ratio index is:

Among them, SNRI represents the signal-to-noise ratio index, N is the total number of bands in the spectral image, r _i and r' _i represent the original reflectance and smoothed reflectance of the pixel spectrum in the i-th band, respectively.

Through the above pre-denoising processing, the noise shielding area diagram shown in Figure 3 is obtained, and the black in Figure 3 represents the noise shielding area.

Step 2. Calculate the band depth of the unshielded pixel spectrum in the 3 μm band. In order to ensure the accuracy of the detection results, mark the spectral pixels with a band depth (BD) greater than 0.02 as the position of potential water/hydroxyl, and obtain the original spectrum The water/hydroxyl distribution area of the diagram. The formula for calculating the band depth (BD) is as follows:

BD=1-R _b /R _c ,

Among them, R _b represents the average reflectance of the pixel spectrum at the 2.9 μm band (2.896 μm band and 2.936 μm band), and R _c represents the pixel spectrum at the 2.6 μm band (2.617 μm band, 2.657 μm band, 2.697 μm band) average reflectance.

The water/hydroxyl distribution area of the original spectrum is shown in Figure 4, and the white area in the figure is the distribution area of water/hydroxyl.

Step 3, identifying and shielding the suspicious water/hydroxyl pixels due to band noise interference in the original spectrum, to obtain a more accurate water/hydroxyl distribution, including:

S3.1, using the histogram equalization method to smooth each channel of the original hyperspectral image (as shown in Figure 2), respectively, to obtain a smoothed spectral image (as shown in Figure 5);

S3.2, traversing the smoothed spectral image, sequentially using the method of steps 1 and 2 to process, to obtain the water/hydroxyl distribution area of the smoothed spectral image (as shown in Figure 6);

S3.3. Take the common area of the water/hydroxyl distribution area of the original spectrum and the water/hydroxyl distribution area of the smoothed spectrum as the final accurate water/hydroxyl distribution area, that is, take the intersection of the two areas, and the final result is shown in Figure 7 shown.

The above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (5)

1. The fine detection method of the atmospheric celestial body surface water or hydroxyl is characterized by comprising the following steps of:

step 1: traversing each pixel of the hyperspectral image, and shielding the pixel spectrum with weak signal, excessive noise or abnormal reflectivity to obtain a noise shielding area diagram of the original spectrogram;

step 2: traversing each pixel in an unshielded area of an original hyperspectral image, calculating the band depth of each pixel spectrum at a 3 mu m band, and if the band depth is larger than a set threshold value, marking the corresponding pixel position as water/hydroxyl, thereby obtaining a water/hydroxyl distribution area of the original spectrogram;

step 3: smoothing each channel of the original hyperspectral image by using a histogram equalization method, and sequentially processing each pixel spectrum of the smoothed hyperspectral image by using the methods of the steps 1 and 2 to obtain a water/hydroxyl distribution area of the smoothed spectrogram;

step 4: the intersection area of the water/hydroxyl distribution area of the original spectrogram and the water/hydroxyl distribution area of the smooth spectrogram is taken as the final accurate water/hydroxyl distribution area.

2. The fine detection method of water or hydroxyl groups on the surface of an atmospheric-free celestial body according to claim 1, wherein the step 1 comprises the steps of:

s1.1, traversing an original hyperspectral image pixel, and shielding the pixel if the reflectivity of any wave band contained in the spectrum of a certain pixel is smaller than 0 or larger than 1, so as to obtain a spectrogram img1 with a shielding mark;

s1.2, traversing the unshielded pixels in the spectrogram img1, calculating the average value of the reflectivities of all the wave bands after the maximum reflectivities and the minimum reflectivities of the spectrums of all the pixels are removed, and shielding the corresponding pixels if the average value of the reflectivities is smaller than a set threshold value to obtain a spectral image img2 with shielding marks;

s1.3, traversing the unshielded pixels in the spectrum image img2, calculating the difference value between the reflectivity of each wavelength band of each pixel spectrum in the wavelength interval of 2.5-3 mu m and the reflectivity mean value e of the front wavelength band and the rear wavelength band of each pixel spectrum, and further calculating the ratio r of the difference value to the reflectivity mean value e; if the ratio r calculated by any wave band exists in the wavelength interval of 2.5-3 mu m is larger than a set threshold value, shielding the pixel to obtain a spectral image img3 with a shielding mark;

s1.4, traversing the unmasked pixels in the spectral image img3, smoothing the spectra of the pixels by using a cubic spline fitting method, calculating corresponding spectral signal-to-noise ratio indexes, and shielding the corresponding pixels if the signal-to-noise ratio indexes are larger than a set threshold value to obtain a noise shielding region diagram.

3. The fine detection method of water or hydroxyl groups on the surface of an atmospheric-free celestial body according to claim 1, wherein the band depth of the pixel spectrum at the 3 μm band in step 2 is expressed as:

BD＝1-R _b /R _c ，

wherein BD represents the band depth, R _b Represents the average value of the reflectivity of the pixel spectrum at the wave band of 2.9 mu m, R _c The average value of the reflectivity of the pixel spectrum at the 2.6 μm band is shown.

4. The fine detection method of water or hydroxyl on the surface of an atmospheric-free celestial body as set forth in claim 2, wherein the calculation formula of the spectral signal-to-noise ratio index is:

wherein SNRI represents signal-to-noise ratio index, N is total band number of spectrum image, r _i And r' _i Representing the original reflectance and the smoothed reflectance of the pixel spectrum in the ith band, respectively.

5. The fine detection method of water or hydroxyl on the surface of an atmospheric celestial body according to claim 2, wherein the set threshold of the band depth in the step 2 is 0.02, the set threshold of the average value of the reflectivity in the step S1.2 is 0.05, the set threshold of the ratio r in the step S1.3 is 0.1, and the set threshold of the signal to noise ratio index in the step S1.4 is 0.07.

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