Sea ice thickness measurement method based on solar microwave radiation enhancement

Abstract

The invention relates to the field of sea ice remote sensing, and discloses a sea ice thickness measuring method based on solar microwave radiation enhancement, which comprises the following specific steps of: calculating a solar altitude angle and an azimuth angle at a current position and moment; setting a microwave radiometer overlook sea ice area based on the solar altitude angle and the azimuth angle, and receiving a reflection signal of solar microwave heat radiation; extracting the relative propagation delay inequality of the reflected signal; and calculating the thickness of the sea ice according to the relative propagation delay inequality. The ice thickness is measured by using the characteristics of strong solar microwave radiation and related reception, the problem that the sun is regarded as a harmful factor in the existing remote sensing technology is solved, and the method has the characteristic of being capable of reducing data acquisition and processing pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sea ice remote sensing, and particularly relates to a sea ice thickness measurement method based on solar microwave radiation enhancement. BACKGROUND

[0002] Sea ice has characteristics such as high albedo and low thermal conductivity, and plays an indispensable role in the climate and ecological system of the polar region and even the whole world. As a key parameter of sea ice, sea ice thickness is one of the most sensitive indicators reflecting global climate change, so sea ice thickness remote sensing measurement is crucial to understanding and verifying the accuracy of climate models. In addition, in recent years, the trend of decreasing sea ice area and thinning sea ice thickness in the Arctic has become increasingly obvious, and the potential of the Arctic shipping route as the "Silk Road on Ice" is increasing, so high-precision sea ice thickness information is needed to support safe navigation and route planning of ships.

[0003] Currently, sea ice thickness measurement mainly includes radar altimeter, infrared remote sensing and passive microwave remote sensing. Passive microwave remote sensing has unique advantages in sea ice thickness remote sensing, such as wide swath, all-weather and all-day. However, the existing mainstream passive microwave remote sensing method of sea ice thickness requires very high accuracy of sea ice absolute brightness temperature. If the sun appears in the field of view of the microwave radiometer, the solar microwave radiation will become a very serious interference source, greatly deteriorating the accuracy of the brightness temperature measurement. Moreover, the solar microwave radiation varies with frequency, observation geometry and solar activity state, so it is difficult to correct accurately. Another sea ice thickness microwave radiation measurement method based on wideband autocorrelation requires a wide system bandwidth and a high-speed ADC, which has high requirements for hardware design, data transmission and signal processing. In addition, due to the large attenuation of sea ice and the weak microwave radiation signal of sea ice itself, both methods have the problem of limited thickness measurement.

[0004] In the existing passive microwave remote sensing technology of sea ice thickness, the sun is regarded as a serious harmful factor, and the ice thickness measurement is limited. Therefore, how to invent a method that is not affected by the sun and can improve the upper limit of passive microwave remote sensing sea ice thickness is a technical problem to be solved in the technical field. SUMMARY

[0005] The present application provides a sea ice thickness measurement method based on solar microwave radiation enhancement to solve the problem that the existing remote sensing technology regards the sun as a harmful factor, which has the characteristics of reducing the data acquisition and processing pressure.

[0006] To achieve the above-mentioned purpose of the present application, the technical scheme adopted is as follows: A sea ice thickness measurement method based on solar microwave radiation enhancement, comprising the following specific steps: Calculate the solar elevation angle and azimuth angle of the current position and time; Based on the solar elevation angle and the azimuth angle, a microwave radiometer is set to overwatch the sea ice area to receive the reflected signal of the solar microwave thermal radiation; The relative propagation time delay difference of the reflected signal is extracted; The thickness of the sea ice is calculated according to the relative propagation time delay difference.

[0007] Preferably, the solar elevation angle and the azimuth angle at the current position and time are calculated, and the specific steps are as follows: The accumulated day of the current time is obtained N， The solar declination angle at the current time of the place is calculated :

[0008] The current position longitude and latitude , the current time T , the solar hour angle at the place is calculated :

[0009]

[0010]

[0011]

[0012] Wherein, ; The solar elevation angle at the current time of the place is calculated ;

[0013] The solar azimuth angle is calculated ; .

[0014] Further, the microwave radiometer is set to overwatch the sea ice area, specifically: the azimuth angle of the microwave radiometer is set to the solar azimuth angle, and the incident angle of the microwave radiometer is set to , and the sea ice area is overwatched.

[0015] Further, the reflected signal includes two parts: the ice-atmosphere interface reflected wave signal of the solar microwave radiation reaching the antenna after being reflected at the sea ice-atmosphere interface, and the ice-sea interface reflected wave signal of the solar microwave radiation penetrating the sea ice and reaching the antenna again after being reflected at the sea ice-sea interface.

[0016] Further, the microwave radiometer is a broadband microwave radiometer, and its core components include a cascade of ultra-wideband antennas, ultra-wideband receivers, and broadband high-speed ADCs.

[0017] Furthermore, after receiving the reflected signal of solar microwave thermal radiation, the reflected signal received by the antenna is amplified and filtered by the receiver, and then acquired by the ADC to obtain a digital signal. .

[0018] Furthermore, it also... Spectral analysis is performed, and for each sample point to be detected, the average of the data on its left and right sides is used to estimate the background noise level. If the power at a certain point in the spectrum exceeds a preset threshold K times the background noise level, the signal at that point is considered a spurious signal and is filtered out, resulting in the signal after interference removal. .

[0019] Furthermore, the relative propagation delay difference of the reflected signal is extracted, specifically by constructing an autocorrelation processing formula:

[0020] in, To filter out the reflected wave signal from the ice-air interface after interference, The signal of reflected waves from the ice-sea interface after filtering out interference; The non-zero delay corresponding to local peaks in the autocorrelation function curve is extracted using a peak extraction method. .

[0021] Furthermore, based on the relative propagation delay difference, the thickness of the sea ice is calculated. Specifically, this involves acquiring sea ice salinity data and air temperature data (which serves as the sea ice temperature), and then calculating the complex permittivity of the sea ice using the Vant sea ice dielectric constant model. Then the refractive index of the sea ice was calculated. :

[0022] in Indicates taking the real part; The thickness of the sea ice is calculated based on the relative propagation time delay difference. :

[0023] in It is the speed of light.

[0024] A sea ice thickness measurement system based on solar microwave radiation enhancement includes a solar angle calculation module, a signal receiving module, a time delay extraction module, and a thickness measurement module. The solar angle calculation module is used to calculate the solar altitude angle and azimuth angle at the current location and time; The signal receiving module is used to set up a microwave radiometer to look down at the sea ice area based on the solar altitude angle and azimuth angle, and to receive the reflected signal of solar microwave thermal radiation. The delay extraction module is used to extract the relative propagation delay difference of the reflected signal; The thickness measurement module is used to calculate the thickness of the sea ice based on the relative propagation time delay difference.

[0025] The beneficial effects of this invention are as follows: This invention uses a microwave radiometer as the measurement system and measures sea ice thickness by utilizing the relationship between the relative propagation delay difference of the reflected signal of solar microwave thermal radiation and ice thickness. Unlike traditional microwave radiometers that require strict avoidance of solar microwave radiation interference to quantitatively measure the absolute brightness temperature of sea ice, this method actively utilizes the strong solar microwave radiation and measures the relative delay difference instead of the absolute brightness temperature, thus avoiding the problem of difficulty in correcting for variations in solar brightness temperature. Compared with broadband autocorrelation-based microwave radiometric methods for measuring sea ice thickness using seawater thermal radiation, this method utilizes the fact that solar radiation is more than 20 times higher than seawater thermal radiation. On the one hand, it can penetrate thicker sea ice, increasing the upper limit of measurement; on the other hand, it can appropriately reduce the bandwidth of the correlation radiometer, reducing the burden of data acquisition and processing. Attached Figure Description

[0026] Figure 1 This is a flowchart of the sea ice thickness measurement method based on enhanced solar microwave radiation in this invention; Figure 2 This is a schematic diagram of the measurement scenario in this invention; Figure 3 This is a schematic diagram of the structure of the microwave radiometer of the present invention; Figure 4 This is a schematic diagram of the overall system in the example of the present invention; Figure 5 This is a comparison diagram of spurious signal processing before and after in an example of the present invention; Figure 6 The time delay difference is extracted when the incident angle of the radiometer in the invention example is 59°. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1 like Figure 1 As shown, a method for measuring sea ice thickness based on enhanced solar microwave radiation includes the following specific steps: Calculate the solar altitude angle and azimuth angle at the current location and time; Based on the aforementioned solar altitude angle and azimuth angle, a microwave radiometer is set up to look down at the sea ice area and receive the reflected signals of solar microwave thermal radiation. extracting a relative propagation time difference of the reflected signals; calculating a thickness of sea ice according to the relative propagation time difference.

[0029] Embodiment 2 More specifically, in one specific embodiment, the solar altitude angle and azimuth angle at the current location and time are calculated, and the specific steps are as follows: acquiring the current time and the accumulated day of the year N， calculating the solar declination angle at the current time of the place :

[0030] In this embodiment, the date is June 4, 2025, the accumulated day of the year is 155, and the calculated solar declination angle is 22.42°. N acquiring the current location longitude and latitude , the current time , calculating the solar hour angle of the place : T

[0031]

[0032]

[0033]

[0034] wherein, ; In this embodiment, the longitude and latitude are 150°E and 80°N respectively, the Beijing time T is 12, L and the calculated solar hour angle is 30°. calculating the solar altitude angle at the current time of the place ;

[0035] In this embodiment, the calculated solar altitude angle is 31°. calculating the solar azimuth angle ; .

[0036] ​​In one embodiment, the microwave radiometer is set to view the sea ice region, specifically, the azimuth angle of the microwave radiometer is set to the sun azimuth angle, and the incidence angle of the microwave radiometer is set to , to view the sea ice region.

[0037] In this embodiment, the azimuth angle of the microwave radiometer is set to , and the incidence angle is set to .

[0038] In one embodiment, the reflected signal includes two parts: the ice-atmosphere interface reflected wave signal of the solar microwave radiation reaching the antenna after being reflected at the sea ice-atmosphere interface, and the ice-sea interface reflected wave signal of the solar microwave radiation penetrating the sea ice and then penetrating the sea ice-atmosphere interface again after being reflected at the sea ice-sea interface.

[0039] In this embodiment, the observation scene is as shown in Figure 2 . The sea ice salinity is 8 PSU, the temperature is -5°C, and the thickness is 30 cm; the microwave radiometer operates in the frequency range of 1-3 GHz, and the radiometer system is as shown in Figure 3 . The overall system structure is as shown in Figure 4 .

[0040] In one embodiment, the microwave radiometer is a broadband microwave radiometer, and the core components thereof include a cascade of an ultra-wideband antenna, an ultra-wideband receiver, and a broadband high-speed ADC.

[0041] In one embodiment, after receiving the reflected signal of the solar microwave thermal radiation, the reflected signal of the solar microwave thermal radiation received by the antenna is amplified and filtered by the receiver, and then a digital signal is obtained by the ADC. In this embodiment, the signal acquisition time is 0.1 s, and the step is 0.1 ns.

[0042] In one embodiment, the is also subjected to spectrum analysis, and for each sample point to be detected, the average value of the data on the left and right sides is used to estimate the background noise level. If the power of a certain point on the spectrum exceeds the preset threshold K times of the background noise level, it is considered that the signal of the point is a spurious signal and is filtered out to obtain the signal after filtering out the interference . In this embodiment, the number of one side of the data on the left and right sides is M, M , which is set to 1000 ， . The value of K is between 3 and 5, and the comparison before and after signal processing is as shown in Figure 5 .

[0043] In one embodiment, the relative propagation time delay difference of the reflected signal is extracted, specifically, a self-correlation processing formula is constructed:

[0044] wherein, is the ice-ocean interface reflected wave signal after interference filtering, is the ice-ocean interface reflected wave signal after interference filtering; In this embodiment, the time delay is obtained The curve of , wherein the maximum value of is the integral time of the signal, and the minimum value is 0; The non-zero time delay corresponding to the local peak value is extracted from the autocorrelation function curve by the peak extraction method; In this embodiment, the autocorrelation curve obtained is analyzed and processed, M The value is 15, if the autocorrelation amplitude of the point exceeds the threshold value 6 times, it is considered that the point is the autocorrelation response peak value. The time delay corresponding to the autocorrelation response peak value is extracted, and the time delay extraction result is as follows Figure 6 .

[0045] In one specific embodiment, the thickness of sea ice is calculated according to the relative propagation time delay difference, specifically: the sea ice salinity data and the air temperature data as the sea ice temperature are obtained, and the complex permittivity of sea ice is calculated by combining the Vant sea ice permittivity model , and then the refractive index of sea ice is calculated :

[0046] wherein represents taking the real part; In this embodiment, the sea ice salinity data can be obtained from the ESA or EarthData website, and the 2m air temperature obtained from the European Centre for Medium-Range Weather Forecasts is taken as the sea ice temperature, and the sea ice permittivity is calculated according to the sea ice temperature and the sea ice salinity combined with the Vant sea ice permittivity model In the example, the sea ice salinity is obtained by auxiliary data as 8 PSU, the temperature is-5℃, and the calculated sea ice permittivity is , and the calculated sea ice refractive index is 1.90.

[0047] The thickness of sea ice is calculated according to the relative propagation time delay difference :

[0048] wherein is the speed of light.

[0049] The sea ice thickness is calculated in this example ， Very close to the actual value 30cm, the results show that the above method performs well in measuring sea ice thickness.

[0050] Embodiment 3 A sea ice thickness measurement system based on solar microwave radiation enhancement, comprising a solar angle acquisition module, a signal receiving module, a time delay extraction module, and a thickness measurement module; The solar angle acquisition module is used to calculate the solar elevation angle and azimuth angle at the current location and time; The signal receiving module is used to set the microwave radiometer to look down on the sea ice area based on the solar elevation angle and azimuth angle, and receive the reflected signal of solar microwave thermal radiation; The time delay extraction module is used to extract the relative propagation time delay difference of the reflected signal; The thickness measurement module is used to calculate the thickness of the sea ice according to the relative propagation time delay difference.

[0051] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Any modification, equivalent replacement, and improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for measuring the thickness of sea ice based on the enhancement of solar microwave radiation, characterized in that: The method comprises the following specific steps: Calculate the sun elevation angle and azimuth angle at the current position and time; Based on the sun elevation angle and azimuth angle, set the microwave radiometer to view the sea ice area to receive the reflected signal of the solar microwave thermal radiation; Extract the relative propagation time delay difference of the reflected signal; Calculate the thickness of the sea ice according to the relative propagation time delay difference.

2. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 1, characterized in that: The specific steps of calculating the sun elevation angle and azimuth angle at the current position and time are as follows: obtaining a current time N， calculating a solar declination angle for the current time at the location : Obtain current location longitude and latitude , current time T , calculate the local solar time angle : wherein ; calculating the solar elevation angle for the current time at the location ; Computing the solar azimuth ; 。 3. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 1, characterized in that: The microwave radiometer is arranged to view the sea ice region, specifically, the azimuth angle of the microwave radiometer is arranged as the sun azimuth angle, and the incident angle of the microwave radiometer is arranged as , the sea ice region is viewed.

4. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 1, characterized in that: The reflected signal comprises two parts: the ice-air interface reflected wave signal of the solar microwave radiation reaching the antenna after being reflected at the sea ice-atmosphere interface, and the ice-sea interface reflected wave signal of the solar microwave radiation penetrating the sea ice, being reflected at the sea ice-seawater interface, and then penetrating the sea ice-atmosphere interface to reach the antenna again.

5. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 4, characterized in that: The microwave radiometer is a broadband microwave radiometer, and the core components thereof comprise a super-wideband antenna, a super-wideband receiver, and a broadband high-speed ADC connected in cascade.

6. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 5, characterized in that: After receiving the reflected signal of the solar microwave thermal radiation, the reflected signal of the solar microwave thermal radiation received by the antenna is amplified and filtered by the receiver, and then a digital signal is obtained by the ADC .

7. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 6, characterized in that: Also on The spectrum is analyzed, and for each sample point to be detected, the average of the data on the left and right is used to estimate the background noise level. If the power of a certain point on the spectrum exceeds the preset threshold K times of the background noise level, it is considered that the signal of the point is a spurious signal and is filtered out to obtain the signal after filtering out the interference .

8. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 7, characterized in that: The specific steps of extracting the relative propagation time delay difference of the reflected signal are as follows: construct an autocorrelation processing formula: wherein, is the ice-ocean interface reflected wave signal after interference filtering, is the ice-ocean interface reflected wave signal after interference filtering, extracting the non-zero time delay corresponding to the local peak from the autocorrelation function curve by a peak extraction method .

9. The solar microwave radiation enhancement based sea ice thickness measurement method according to claim 8, characterized in that: According to the relative propagation time delay difference, the thickness of the sea ice is calculated, specifically: obtaining sea ice salinity data and air temperature data as sea ice temperature, combining the Vant sea ice dielectric constant model to calculate the complex dielectric constant of the sea ice , and then calculating the refractive index of the sea ice : wherein represents the real part; The thickness of the sea ice is calculated from the relative difference in propagation time : wherein is the speed of light.

10. A sea ice thickness measurement system based on solar microwave radiation enhancement, characterized by: The system comprises a sun angle calculation module, a signal receiving module, a time delay extraction module, and a thickness measurement module. The sun angle calculation module is used to calculate the sun elevation angle and azimuth angle at the current position and time. The signal receiving module is used to set the microwave radiometer to view the sea ice area to receive the reflected signal of the solar microwave thermal radiation based on the sun elevation angle and azimuth angle. The time delay extraction module is used to extract the relative propagation time delay difference of the reflected signal. The thickness measurement module is used to calculate the thickness of the sea ice according to the relative propagation time delay difference.

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