CN106596355A - Correction method of extinction coefficient below low clouds in laser radar retrieval - Google Patents

Abstract

The invention discloses a correction method of an extinction coefficient below low clouds in laser radar retrieval. The method comprises the following steps: afresh assigning data of the height area of the clouds through a spline interpolation technology according to a signal above the clouds and a signal below the clouds to obtain a new fitting signal free of the clouds, and carrying out retrieval to obtain a near ground extinction coefficient which is not affected by the clouds and is used for replacing an extinction coefficient of a corresponding height in an original extinction coefficient in order to effectively correct a retrieval result deviation caused by the clouds.

Description

Method for correcting extinction coefficient below middle-low cloud layer in laser radar inversion

Technical Field

The invention relates to the field of environmental science and laser radar, in particular to a method for correcting an extinction coefficient below a middle-low cloud layer in the inversion of the laser radar.

Background

The laser radar is an important technical means in the research field of detecting atmospheric space-time distribution. The laser radar has high spatial and temporal resolution, allows atmospheric observation under various conditions, and can cover the range from near ground to 100km high altitude. Laser radiation interacts with atmospheric components in a variety of ways, and can detect atmospheric fundamental parameters such as temperature, pressure, humidity, wind, in addition to trace gases, aerosols, clouds. Lidar can monitor atmospheric changes of several cubic meters, seconds, and even global and years. Lidar has been applied to turbulent processes, diurnal variation of boundary layers, moisture and ozone flux detection. Lidar can monitor emission rates and trace gas concentration levels. Stratospheric ozone depletion is detected by global lidar. Lidar may be used to distinguish water droplets from ice crystals in the cloud. Lidar has been helpful in understanding the climatic effects of aerosols. The laser radar monitors stratosphere disturbance, air pollution intercontinental transmission, sand dust, forest fire and smoke dust caused by large-scale volcanic eruption. In the middle layer, the lidar demonstrates the presence of metal atoms, ionic layers, gravitational waves.

In the current particulate matter monitoring, the most mature and widely applied method is the Mie scattering laser radar. And (3) utilizing the American standard atmosphere to invert the laser radar millimeter scattering echo signal, so that the height profile of the local and current extinction coefficient can be obtained for relevant research. When a medium-low cloud layer exists and an echo signal below the cloud layer is strong, when the extinction coefficient containing the medium-low cloud layer is inverted by a traditional inversion method (Fernald method and the like), the extinction coefficient below the cloud layer is slightly small.

Disclosure of Invention

The invention aims to provide a method for correcting an extinction coefficient below a medium-low cloud layer in the inversion of a laser radar based on spline interpolation, which is used for correcting the extinction coefficient below the medium-low cloud layer in the inversion of a Mie scattering laser radar, and adopts the following technical scheme in order to achieve the purposes: the method comprises the steps of fitting in a height interval where a laser radar PRR (range square correction signal) cloud layer is located through a spline interpolation method to obtain a pseudo signal without the cloud layer, obtaining an extinction coefficient which is not affected by the cloud layer through a Fernald inversion method, and further correcting an extinction coefficient below the cloud layer in an original extinction signal, wherein the spline interpolation method mainly comprises the following steps:

(1) the laser radar equation corresponding to the backscattering echo signal of the Mi-Scattering laser radar is as follows:

wherein: p (R) is a backscattering echo signal (W) received by the laser radar at the distance R;

c is the laser radar system constant (W.km)³·sr)，

β (R) is the total backscattering coefficient (km) at distance R^-1·sr^-1)，

Wherein,β(R)＝β_a(R)+β_m(R)，β_a(R) and β_m(R) are the backscattering coefficients of aerosol and atmospheric molecules respectively at a distance R,

α (R) is the total extinction coefficient (km-1) at distance R, α (R) α_a(R)+α_m(R),α_a(R) and α_m(R) are the extinction coefficients of aerosol and atmospheric molecules, respectively, at a distance R;

(2) background baseline signals at the far end of the laser radar signals are used as background noise, background noise deduction operation is carried out on the laser radar signals, and effective signals P are obtained_effect(R) and corrected for distance squared, with PRR ═ P_effect(R)·R²；

(3) The original extinction coefficient α can be obtained by inverting the extinction coefficient of the PRR by using a Fernald inversion method_a(R)；

(4) Performing cloud layer judgment by using the PRR data, and ending if no middle or low cloud layer exists; if the medium-low cloud layer exists, the following steps (5) to (7) are carried out;

(5) cloud layer filtering is carried out on the PRR containing the middle and low cloud layers, namely the numerical value of the height interval where the cloud layer is located is deleted, and fitting is carried out by utilizing a spline interpolation method to obtain fitting data of the height interval corresponding to the original cloud layer, and the fitting data is marked as PRR';

(6) utilizing a Fernald method to perform extinction coefficient inversion on the PRR', and obtaining an extinction coefficient corresponding to the pseudo-cloudless data, which is recorded as α_a'(R)；

(7) By α_a' (R) vs. original α_a(R) modifying the cloud lower part, namely directly replacing the numerical value of the cloud lower part to finally obtain a modified aerosol extinction coefficient α_{α_fixed}(R)。

Compared with the prior art, the invention has the beneficial effects that:

through a spline interpolation method, the data of the height area of the cloud layer are reassigned according to the signals above and below the cloud layer to obtain a new fitting signal without the cloud layer, and then inversion is carried out, so that the near-ground extinction coefficient which is not influenced by the cloud layer can be obtained and is used for replacing the extinction value of the original extinction coefficient with the corresponding height, and the deviation of the cloud layer to the inversion result is effectively corrected.

Drawings

FIG. 1 is a flow chart of a method implementation of the present invention;

FIG. 2 shows PRR signal and fitted cloudless PRR'

FIG. 3 shows an original extinction coefficient profile α_a(R) and modified extinction coefficient Profile α_{α_fixed}(R)。

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the following detailed description is further provided with specific data. The illustrative examples of the present invention are provided herein for the purpose of explanation, but not limitation.

The correction method provided by the invention obtains a pseudo signal without a cloud layer by fitting in a height interval where a laser radar PRR (distance square correction signal) cloud layer is located through a spline interpolation method, obtains an extinction coefficient which is not influenced by the cloud layer by using a Fernald inversion method, and further corrects the extinction coefficient below the cloud layer in the original extinction signal, and the method mainly comprises the following steps:

(1) the laser radar equation corresponding to the backscattering echo signal of the Mi-Scattering laser radar is as follows:

wherein: p (R) is a backscattering echo signal (W) received by the laser radar at the distance R;

c is the laser radar system constant (W.km)³·sr)，

β (R) is the total backscattering coefficient (km) at distance R^-1·sr^-1)，

Wherein β (R) is β_a(R)+β_m(R)，β_a(R) and β_m(R) are the backscattering coefficients of aerosol and atmospheric molecules respectively at a distance R,

α (R) is the total extinction coefficient (km-1) at distance R, α (R) α_a(R)+α_m(R),α_a(R) and α_m(R) are the extinction coefficients of aerosol and atmospheric molecules, respectively, at a distance R;

(2) background baseline signals at the far end of the laser radar signals are used as background noise, background noise deduction operation is carried out on the laser radar signals, and effective signals P are obtained_effect(R) and corrected for distance squared, with PRR ═ P_effect(R)·R²；

(3) The original extinction coefficient α can be obtained by inverting the extinction coefficient of the PRR by using a Fernald inversion method_a(R)；

(4) Performing cloud layer judgment by using the PRR data, and ending if no middle or low cloud layer exists; if the medium-low cloud layer exists, the following steps (5) to (7) are carried out;

(5) cloud layer filtering is carried out on the PRR containing the middle and low cloud layers, namely the numerical value of the height interval where the cloud layer is located is deleted, and fitting is carried out by utilizing a spline interpolation method to obtain fitting data of the height interval corresponding to the original cloud layer, and the fitting data is marked as PRR';

(6) utilizing a Fernald method to perform extinction coefficient inversion on the PRR', and obtaining an extinction coefficient corresponding to the pseudo-cloudless data, which is recorded as α_a'(R)；

(7) By α_a' (R) vs. original α_a(R) modifying the cloud lower part, namely directly replacing the numerical value of the cloud lower part to finally obtain a modified aerosol extinction coefficient α_{α_fixed}(R)。

Claims (1)

1. A method for correcting extinction coefficients below middle and low cloud layers in laser radar inversion mainly comprises the following steps:

(1) the laser radar equation corresponding to the backscattering echo signal of the Mi-Scattering laser radar is as follows:

$P\left(R\right)=\frac{C\mathrm{\β}\left(R\right)}{R^2}\exp \[-2{\∫}_0^R\mathrm{\α}\left(r\right)dr\]$

wherein: p (R) is a backscattering echo signal (W) received by the laser radar at the distance R;

c is the laser radar system constant (W.km)³·sr)，

β (R) is the total backscattering coefficient (km) at distance R^-1·sr^-1)，

Wherein β (R) is β_a(R)+β_m(R)，β_a(R) and β_m(R) are the backscattering coefficients of aerosol and atmospheric molecules respectively at a distance R,

α (R) is the total extinction coefficient (km-1) at distance R, α (R) α_a(R)+α_m(R),α_a(R) and α_m(R) are the extinction coefficients of aerosol and atmospheric molecules, respectively, at a distance R;

(2) background baseline signals at the far end of the laser radar signals are used as background noise, background noise deduction operation is carried out on the laser radar signals, and effective signals P are obtained_effect(R) and corrected for distance squared, with PRR ═ P_effect(R)·R²；

(3) The original extinction coefficient α can be obtained by inverting the extinction coefficient of the PRR by using a Fernald inversion method_a(R)；

(4) Performing cloud layer judgment by using the PRR data, and ending if no middle or low cloud layer exists; if the medium-low cloud layer exists, the following steps (5) to (7) are carried out;

(5) cloud layer filtering is carried out on the PRR containing the middle and low cloud layers, namely the numerical value of the height interval where the cloud layer is located is deleted, and fitting is carried out by utilizing a spline interpolation method to obtain fitting data of the height interval corresponding to the original cloud layer, and the fitting data is marked as PRR';

(6) PRR' Using Fernald methodInverting the extinction coefficient to obtain the extinction coefficient corresponding to the pseudo-cloudless data, which is recorded as α_a'(R)；

(7) By α_a' (R) vs. original α_a(R) modifying the cloud lower part, namely directly replacing the numerical value of the cloud lower part to finally obtain a modified aerosol extinction coefficient α_{α_fixed}(R)。