Data processing method based on carbon dioxide column concentration from spaceborne lidar

Abstract

This invention discloses a data processing method for carbon dioxide column concentration based on a spaceborne lidar, comprising: performing nonlinear correction on the spaceborne integral path differential absorption (IPDA) lidar detection signal; calculating the differential optical thickness based on the IPDA lidar signal; calculating the echo height above sea level and geographic coordinates based on the echo signal location; establishing an absorption cross-section lookup table using differential absorption cross-section data from the High Resolution Transmission Molecular Absorption (HITRAN) database; calculating the pressure at the echo location using the European Centre for Medium-Range Weather Forecasts Reanalysis Dataset (ERA5) and the echo signal height above sea level; calculating the Doppler frequency shift; calculating a weighting function based on pressure profiles, humidity profiles, temperature profiles, and Doppler frequency shift data; and calculating the carbon dioxide column concentration. The key features of this invention are the nonlinear correction of the spaceborne IPDA lidar echo signal, the establishment of a differential absorption cross-section lookup table for carbon dioxide molecules, and the accurate and efficient calculation of the carbon dioxide column concentration using spaceborne IPDA lidar detection data and ERA5 meteorological dataset data.

Description

Technical Field

[0001] This invention belongs to the field of satellite remote sensing inversion of gas concentration technology, and relates to active lidar remote sensing technology, especially for inverting carbon dioxide column concentration using spaceborne lidar. Background Technology

[0002] Following the Industrial Revolution, the burning of fossil fuels has led to a significant increase in global emissions of greenhouse gases such as carbon dioxide and methane, considered a major factor in climate change. Accurate detection of atmospheric carbon dioxide concentration is crucial for studying the impacts of global climate change and predicting future climate trends. Currently, methods for measuring atmospheric carbon dioxide can be categorized as follows: ground-based single-point measurements, airborne trajectory measurements, and global satellite observation. Ground-based single-point measurements include passive measurements using the solar spectrum and gas sampling measurements based on high-resolution direct absorption spectroscopy. Airborne trajectory measurements utilize aircraft platforms equipped with carbon dioxide measuring devices to measure carbon dioxide concentration along the flight path. Compared to the low sample density and small scale of ground-based single-point measurements and airborne trajectory measurements, scientists have proposed using satellite remote sensing technology for global carbon dioxide measurement. However, current passive remote sensing techniques suffer from limitations such as the inability to measure carbon dioxide column concentrations at night, data gaps in the North and South Poles, and significant cloud cover affecting data quality.

[0003] Spaceborne IPDA lidar is based on the difference in absorption by the trace gas being measured through two laser pulses of different wavelengths throughout the entire path. These two wavelengths are referred to as on-line and off-line, respectively. By comparing the ratio of emitted energy to echo energy and integrating the weighting function, the carbon dioxide column concentration along the entire integration path can be obtained. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a data processing method for carbon dioxide column concentration based on spaceborne lidar. This method involves: nonlinear correction of the detection signal from a spaceborne integral path differential absorption (IPDA) lidar; calculation of differential optical thickness based on the IPDA lidar signal; calculation of the echo distance from sea level and geographical coordinates based on the echo signal location; establishment of an absorption cross-section lookup table using differential absorption cross-section data from the high-resolution transmission molecular absorption (HITRAN) database; calculation of the pressure at the echo location using the European Centre for Medium-Range Weather Forecasts (ERA5) reanalysis dataset and the echo signal distance from sea level; calculation of the Doppler frequency shift; calculation of a weighting function based on the pressure profile, humidity profile, temperature profile, and Doppler frequency shift data; and finally, obtaining the carbon dioxide column concentration.

[0005] Data detected by spaceborne IPDA lidar is processed to efficiently acquire high-precision global carbon dioxide column concentration data. The data processing method based on spaceborne lidar carbon dioxide column concentration includes the following steps:

[0006] (1) The lidar system has a transmitter and a receiver. The transmitter emits two laser pulses with similar wavelengths. The laser energy is monitored at the transmitter to obtain the monitoring signal of the spaceborne lidar. At the receiver, the telescope receives the hard target return signal to obtain the echo signal of the spaceborne lidar.

[0007] (2) Correct the monitoring signal and echo signal detected by the spaceborne lidar to obtain the corrected monitoring signal and echo signal power P, as shown in the following formula:

[0008] P = p1 × V 4 +p2×V 3 +p3×V 2 +p4×V+p 5 (2)

[0009] Where V is the echo signal amplitude, and p1, p2, p3, p4, and p5 are the coefficients of the fitted curve obtained by performing a fourth-order fitting on the calibration data after calibrating the detector responsivity in the laboratory.

[0010] (3) Calculate the differential optical thickness of carbon dioxide based on the power of the monitoring signal and the echo signal after correction by the spaceborne lidar.

[0011] (4) Determine the distance of the echo location from the horizontal plane and the latitude and longitude of the echo location.

[0012] (5) Establish a lookup table for the differential absorption cross section of carbon dioxide molecules. The establishment of the lookup table for the differential absorption cross section of carbon dioxide molecules utilizes the absorption cross section data in the HITRAN database. The corresponding absorption cross section data is indexed by temperature, humidity, pressure and laser wavelength data. After convolution calculation with the laser linewidth, the differential absorption cross section data is obtained and filled into the table.

[0013] (6) Surface pressure is calculated using echo geolocation information and ERA5 meteorological dataset.

[0014] (7) Solve for Doppler shift based on satellite attitude, position and velocity data.

[0015] (8) Calculate the weighting function based on the pressure profile, temperature profile, humidity profile and Doppler frequency shift of the ERA5 meteorological dataset.

[0016] (9) Calculate the carbon dioxide column concentration based on differential optical thickness and weighting function.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] (1) The accuracy of detecting carbon dioxide column concentration was improved by using the data from the calibration of the detector in the laboratory to correct the monitoring signal and weak echo signal.

[0019] (2) Using HITRAN database data, an absorption cross-section lookup table for different temperatures, pressures and laser wavelengths was established, which improved the efficiency of satellite data processing.

[0020] (3) The temperature, humidity and pressure profiles at the corresponding locations are accurately solved using the onboard IPDA lidar detection data and ERA5 meteorological dataset data.

[0021] (4) Using the collected lidar data and the data processing method based on the carbon dioxide column concentration of the spaceborne lidar, a high coverage distribution map of the global all-day carbon dioxide column concentration was obtained for the first time. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the specific process of the present invention.

[0023] Figure 2 Defines the orientation of the satellite's body coordinate system. Detailed Implementation

[0024] To more clearly illustrate the data processing method based on the carbon dioxide column concentration of a spaceborne lidar, the present invention will be further described below with reference to examples and accompanying drawings. Figure 1 A schematic diagram illustrating the specific process of the algorithm of this invention is provided.

[0025] The specific implementation scheme of the present invention is as follows:

[0026] (1) The lidar system has a transmitter and a receiver. The transmitter emits two laser pulses with similar wavelengths. The laser energy is monitored at the transmitter to obtain the monitoring signal of the spaceborne lidar. At the receiver, the telescope receives the hard target return signal to obtain the echo signal of the spaceborne lidar.

[0027] (2) Perform nonlinear correction on the signal

[0028] The echo signal detected by the IPDA lidar was nonlinearly corrected using the power-response curve of the detector, which was calibrated in the laboratory. The formula is as follows:

[0029] P = p1 × V 4 +p2×V 2 +p3×V 2 +p4×V+p 5 (3)

[0030] Where V is the echo signal amplitude, P is the echo signal power, and p1, p2, p3, p4, p5 are the coefficients of the fitted curve.

[0031] (3) Solving for differential optical thickness

[0032] The differential optical thickness is calculated using the ratio of the monitoring signal detected by the IPDA lidar to the echo signal, as shown in the following formula:

[0033]

[0034] Where σ is the absorption cross section of a carbon dioxide molecule at a distance r corresponding to a wavelength λ. Let P be the carbon dioxide number concentration at a distance r, where R is the distance from the surface target to the lidar, and P is the power of the on-line and off-line monitoring signals. on0 ,P off0 The power of the echo signal is defined as P. on ,P off .

[0035] (4) Echo geolocation solution

[0036] Obtaining the geographic coordinates of the echo location requires satellite position coordinates, attitude data, velocity, and laser ranging data transmitted from the satellite. The laser ranging formula is as follows:

[0037]

[0038] Where T1 is the delay time of the echo acquisition segment, T2 is the acquisition time of the on-line high-altitude acquisition segment, N is the number of positions where the on-line echo peak is located in the T2 acquisition segment, and C is the speed of light.

[0039] After obtaining the ranging value, the ranging information needs to be transformed to obtain the coordinates of the echo position in the WGS84 coordinate system. The formula is as follows:

[0040]

[0041] Where ρ is the ranging value, α, β, γ are the angles between the laser radar beam pointing and the X, Y, Z axes of the laser radar body coordinate system, as shown in Figure (2). Point O is the origin of the star coordinate system. X, Y and Z are the satellite flight direction, backlight direction and ground direction, respectively. The three are perpendicular to each other. OL is the laser radar beam pointing. This is the transformation matrix between the satellite body coordinate system and the J2000 coordinate system. Let X be the transformation matrix between the J2000 coordinate system and the WGS84 coordinate system. gps ,Y gps Zgps Given the X, Y, Z coordinates of the satellite in WGS84, after obtaining the coordinates of the echo location in the WGS84 coordinate system, the longitude, latitude, and altitude of the echo location can be calculated.

[0042] (5) Establishment of the differential absorption cross section lookup table

[0043] To improve the efficiency of processing spaceborne IPDA lidar, a differential absorption cross section lookup table was established. This table utilizes absorption cross section data from the HITRAN database. The corresponding absorption cross section data is indexed by temperature, humidity, pressure, and laser wavelength data. After convolution with the laser linewidth, the differential absorption cross section data is obtained and entered into the table.

[0044] (6) Solving for surface pressure

[0045] The surface pressure was obtained using ranging values ​​from the IPDA lidar and the ERA5 meteorological surface dataset. The surface pressure was then calculated using a formula:

[0046]

[0047] Among them, P e d represents the pressure and altitude provided by ERA5 meteorological surface data, and H represents the altitude of the echo location. After obtaining the pressure at the echo location, the pressure profile, temperature profile, and humidity profile are obtained based on the ERA5 meteorological profile data.

[0048] (7) Solving for Doppler frequency shift

[0049] Theoretically, the laser beam emitted by the satellite platform should be perfectly perpendicular to the ground. However, in reality, the laser beam has a relatively small angle with the ground normal. As the satellite platform moves at high speed relative to the ground, this angle generates a velocity component in the direction perpendicular to the ground, causing the Doppler effect in the echo signal. The formula for calculating the Doppler frequency shift is:

[0050]

[0051] Where v is the velocity of the satellite relative to the echo position, v0 is the emitted laser frequency, α and γ are the angles between the laser radar beam direction and the X and Z axes of the laser radar body coordinate system, respectively, θ is the deflection angle of the satellite attitude, and c is the speed of light.

[0052] (8) Solving for the weight function

[0053] After obtaining the pressure profile, temperature profile, humidity profile, and laser wavelength data corresponding to the laser pulse, the weighting function is obtained using the differential absorption cross-section data indexed in the differential absorption cross-section lookup table, and then calculated using the following formula:

[0054]

[0055] (9) Solve for the carbon dioxide column concentration

[0056] After obtaining the differential optical thickness and the weighting function, the ratio of the two can be used to calculate the carbon dioxide column concentration, as shown in the following formula:

[0057]

[0058] After obtaining the carbon dioxide column concentration, the carbon dioxide column concentration data obtained from the ground station was compared with the obtained carbon dioxide column concentration to verify the reliability of the treatment method.

Claims

1. A method for processing data on carbon dioxide column concentration based on a spaceborne lidar, characterized in that, Comprising the following steps: (1) The laser radar system includes a transmitting end and a receiving end. The transmitting end transmits two laser pulses with similar wavelengths and monitors the laser energy to obtain a monitoring signal of the spaceborne laser radar. The receiving end receives a target return signal to obtain an echo signal of the spaceborne laser radar. (2) The monitoring signal and the echo signal detected by the spaceborne laser radar are corrected to obtain corrected monitoring signal and echo signal power P, as follows: P = pi x V 4 + p2 x V 3 + p3 x V 2 + p4 x V + p5 (1) Where V is the echo signal amplitude, p1, p2, p3, p4, and p5 are fitting curve coefficients obtained by fitting the four-order term of the detector responsivity calibration data in the laboratory. (3) The differential optical thickness of carbon dioxide is calculated according to the corrected monitoring signal power and echo signal power of the spaceborne laser radar. (4) The distance of the echo position from the horizontal plane and the latitude and longitude of the echo position are solved. (5) A lookup table of carbon dioxide molecular differential absorption cross section is established. The lookup table of carbon dioxide molecular differential absorption cross section utilizes the absorption cross section data in the HITRAN database. Through temperature, humidity, pressure, and laser wavelength data indexing corresponding absorption cross section data, after convolution calculation with the laser linewidth, the differential absorption cross section data is filled into the table. (6) The surface pressure is solved using the echo geographic position information and ERA5 meteorological data set data. (7) The Doppler shift is solved according to the satellite attitude, position, and speed data. (8) The weight function is calculated according to the ERA5 meteorological data set pressure profile, temperature profile, humidity profile, and Doppler shift. (9) The carbon dioxide column concentration is calculated according to the differential optical thickness and the weight function.

2. The method of processing data based on spaceborne lidar carbon dioxide column concentration of claim 1, wherein, The data obtained by calibrating the linearity of the detector in the laboratory is used to correct the echo signal detected by the IPDA laser radar.

3. The method of processing carbon dioxide column concentration data based on spaceborne lidar according to claim 1, characterized in that, The lookup table of carbon dioxide differential absorption cross section is established by convolving the actual outgoing laser linewidth of the IPDA laser radar with the molecular absorption cross section data in the HITRAN database.

4. The method of processing carbon dioxide column concentration data based on spaceborne lidar according to claim 1, characterized in that, The surface pressure is accurately solved using ERA5 ground meteorological data, satellite height measurement data, and conversion formulas. The solved pressure is matched with the ERA5 profile data set to obtain the temperature, humidity, and temperature profile from the echo position to the top of the atmosphere.

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